The Dimensions of Colour - a colour theory discussion thread

[briggsy@ashtons]

The Dimensions of Colour
www.huevaluechroma.com (http://www.huevaluechroma.com)

This started out well over a year ago as a tutorial intended for CA, but it just refused to stop growing. Eventually I took up an offer to have it made into a website as a second year student project at Billy Blue, a graphic design school where I teach drawing. But it's still meant for the community here, and I hope a bunch of you get a chance to work through it and maybe give me some feedback here. Huge thanks also to sciboy for generously hosting it on his server, where it's been sitting for the last week while I tinker with it. Still tinkering, but I think I can finally bear the thought of you guys seeing it now....


EDIT (Dec 11): I'd love for this thread to develop into a place where people come to discuss questions about colour theory. So please add any comments or questions you have, whether in connection with something on the site, or in relation to your own work, or about colour theory in general.

[darkwolfb87]

Thank you, this looks wonderful. I'll get you some feedback as soon as I can.

[Elwell]

David, I'm only about a quarter in, but this is fantastic. Have you posted it at Rational Painting?

[Farvus]

Looks like tons of helpful knowledge. It's really hard to find this kind of websites on the net so thanks a lot. I'll try to read it soon.

[Elwell]

OK, just got through the whole thing, it's great. You'll want to give it another copyediting pass, there are a few typos and coding problems still, but it's a fantastic resource.

[Sonaj]

That is very helpful and a great read, thank you

sticky?

[Elwell]

Oh, and I made this a sticky.

[thinairart]

Awesome, some really great info you've put together! The points you bring up regarding diffuse and specular reflection are well written and on target.

[briggsy@ashtons]

Thanks Tristan - very proud of my first sticky! I've just finished adding the corrections to the text for Part 10, which I didn't quite get onto last night. (Didn't imagine anyone would get through the whole thing in one sitting!) I'll do another pass through the whole thing soon, but at the moment I'd probably add more typos than I fixed. I did post it on Rational Painting just before turning in, but it looks like they're still thinking about it.

Thanks everyone for your comments so far. reidaj - I'm not sure but you may have the impression that there's more 3d rendering on the site than there is. The only image that used a 3d programme is the flash animation Ray made to show a light source moving around a red ball, for which he used Maya. It looks pretty right to me when you allow for the fact that he has used a fairly close light source. All of the other spheres were painted from scratch in Photoshop.

If anyone sees any problems caused by the code please post or PM me telling me where they are and what browser you're using - I 'll see if I can get someone who knows what they're doing to help.

[thinairart]

sorry about that Briggsy, my post turned out to be more confusing then I meant it to be :)

I was reminded of 3d rendering by the appearence of the spheres with specular highlights, and mistaking those illustrations for 3d images, that lead me to make an unrelated comment about the use of 3d rendering as a guide to the modeling of light. I edited my original comments to keep my post on topic.

Excellent guide, glad it has been made sticky.

[romance]

Cheers for this! Brilliant!

[Flynt]

Fantastic---I am so pleased to see someone put this together including citations.

Great!

[briggsy@ashtons]

Thanks for the comments, guys. Flynt, it would be great one day to see Dimensions of Colour among the links on that gorgeous site of yours.

[seth1]

Thanks so much for taking your time to donate this to us. I will be reading through it. Cant wait to get started.

[talbot]

Thank you for this wonderful resource! There looks to be a wealth of information here. Can't wait to get started. Thanks again!



P.S. You spelled "color" wrong.
:P

[Jack the R]

Thanks to Briggsy, this has helped correct a few things I was told wrong, and has got me thinking of painting more of as an act of construction.

Regarding Principle 1, the shading series, shouldn't the hue of the shadow shift some in regard to the light? Is there a way to calculate the shift in hue?

Also -

Also note that, contrary to a widespread myth among painters (e.g. Loomis, 1947), the richest colour is not on the edges of the lighted area.

I think this term "richest" is new, are you referring to brightness or chroma? Either way, if the "richest" area isn't on the edge of the lighted area, would it be the full light area?

[briggsy@ashtons]

Thanks for the responses guys, and especially for the questions, Jack the R. I'd love for this thread to develop into a place where people discuss questions arising from the site, or any questions about colour really.


shouldn't the hue of the shadow shift some in regard to the light?

Colours in the shadow zone very often do shift in hue compared to the light, but not necessarily, and certainly not because they are shadows. If the colours do shift in hue, it is because the hue of the dominant light source in the shadow zone is different to the hue of the primary light source. In addition, if the primary light source is distinctly coloured, the light source in the shadow region appears to shift towards the additive complimentary of that colour, by an instance of simultaneous contrast. This effect is rather inadequately summed up by the artists' rule of warm lights giving cool shadows and vice versa. In the discussion of "Principle One" I am just taking the simplest case first, where the primary and secondary lights are both the same colour, and perceived as white. For the more complex, and common, situation of lights of different hue, you need to take this in conjunction with the principles dealing with coloured light sources and the effects of multiple light sources.

I think this term "richest" is new, are you referring to brightness or chroma? Either way, if the "richest" area isn't on the edge of the lighted area, would it be the full light area?

Thanks. I think I got "richest" from the way I have heard it expressed verbally many times, in a context that implies highest chroma. Actually Loomis (1947, pp.152-3) variously refers to "brighter", "the most brilliant and pure", and the "most intense" colour being located at the edge of the lighted area, but it is clear from his diagram that he also means higher chroma but not higher lightness in the terminology I have been using.

In answer to your second question, the chroma of the diffuse reflection keeps increasing up to the full light (as shown in Figure 10.1), but this colour may be desaturated (1) by the addition of white or different coloured light at the highlight (which may be quite broad and "fuzzy"), and (2) by specular reflection of the environment, especially on the receding planes. So the actual situation is quite variable.

If you look through either of Idiot Apathy's Peer Project threads you will clearly see the difference between the spheres done by guys who used shading sequences based on the uniform saturation principle, as I recommended here (http://www.conceptart.org/forums/showpost.php?p=699669&postcount=175), and others who worked on the theory of putting the highest chroma in the halflight (directly or indirectly following the recommendation of Loomis, I believe).

[Farvus]

In answer to your second question, the chroma of the diffuse reflection keeps increasing up to the full light (as shown in Figure 10.1), but this colour may be desaturated (1) by the addition of white or different coloured light at the highlight (which may be quite broad and "fuzzy"), and (2) by specular reflection of the environment, especially on the receding planes. So the actual situation is quite variable.

I have read more interesting parts from your website but one thing is still confusing to me. Sorry if this was already answered but I'm still not entirely sure. I read everywhere that shadow side is usually less saturated but when I look at different paintings, it's actually the opposite. (especially when it comes to pale skin).

Is it beacause this broad and weak part of highlight extends and dominates almost whole part of light side? Where it doesn't get pale there is real color of object and sometimes it can be only found at the edge of shadow. If it's true then this color close to higlight's white must be even less saturated than shadow side which creates the the opposite result?

At the same time maybe it could be lots of bounce light that saturates the shadow. Propably beacause there is bright surface around like in this painting. Shadow on her cheek gets some light from chest -http://artrenewal.org/images/artists/s/SARGENT_John_Singer/large/Portrait_of_Mrs_Harry_Vane_Milbank.jpg

Basicly I don't see any mounting point when I want to know what closer to object's natural color - it could be shadow or light.

[Jack the R]

Thanks for the reply Briggsy. I'm going back through your site again so I can understand it. Give me another day . . .

What struck me most is the implication of principle 1 for glazing tonal paintings in a way that is technically accurate and realistic looking - and if you can do that, wouldn't it, by virtue of speed, be the superior painting technique? It caught my fancy anyway - I'd like to paint comics, and I need as much speed as I can get. I haven't managed to pull off the glazing process in a way that looks good yet, but I'm working on it.

[briggsy@ashtons]

Thanks for the question Farvus. Certainly the shadow colours in the portrait image you tried to link to are much higher in chroma than the uniform saturation relationship would predict, but do they actually look realistic to you? Apparently even ARC-approved artists are not obliged to copy colours precisely as they appear.

Below I've modelled what I think is a reasonably realistic-looking sphere out of Mrs Milbank's skin. Most of the shadow zone is represented with a low-chroma colour that I think does look like our heroine's skin in a less bright light. However, as you discuss, where the shadow zone receives light from other areas of skin we do get colours more saturated than the main series, because Mrs Milbank has coloured this light twice.

The dreary looking lass on the left of the same ARC page (http://www.artrenewal.org/asp/database/image.asp?id=6032) on the other hand is very obedient to the uniform saturation rule. I'm not for a microsecond suggesting that that makes it a better painting, but I think you'll agree that it does present a more realistic visual appearance.

[Farvus]

Thanks a lot. I think I showed bad example beacause it does look a bit unrealistic. Also talking about skin can be hard beacause it's not consistent "material". There are parts on a face tinted by blood vessels and so on.

I looked at this girl on the left. There are parts that look like it's obvious - for example on the neck and on her right arm. However some parts like on her shoulder blade or face get more pale and beacause of that the saturation drops down. These parts are close to the bone so maybe the skin gets more shiny and there is stronger highlight ? :P.

255287

[briggsy@ashtons]

These parts are close to the bone so maybe the skin gets more shiny and there is stronger highlight ? :P.


Not so much because it is on the bone, I think, but because the surface in those two places is at the critical angle needed to bounce the specular reflection to our eye. Of course, the bone does in each case create the plane break that causes the surface to pass through that critical angle.


In the diagram below, you can see that colours from the girl's back and neck, excluding the highlight on the shoulder blade and the shadow area on the arm, lie along a line of uniform saturation (blue line). The highlight is less saturated because it approaches the colour of the light source. The shadow on the arm lies on a line of lower saturation than the colours in the light because of a difference in hue between the main light and the secondary light (showing up in the shift from creamy light to bluish shadow in the dress).

[Farvus]

Fantastic diagram. Now I see that. It's sometimes hard too see the same occurrence in everything beacause every object has different material properties. I think I'll need to play more with 3d studio max to see these things more clearly. :)

Thanks for taking your time to prepare and explain these things. I still don't have much knowledge about color but I'll try to join discussion if anything interesting comes out.

[fotojb]

Thank you!

[briggsy@ashtons]

I posted the image below on a thread (http://www.conceptart.org/forums/showthread.php?t=112823) started by andymania, but am reposting it here with a quote of his original question because the latter is such a CLASSIC example of how trying to follow an artists' rule of thumb can be far more confusing than a little rational analysis. It's also a great example of the confusion caused by the use of the terms "warm" and "cool" in the popular vague sense that could refer either to a difference of hue or or a difference of chroma. The lighting shown is actually the simplest lighting of all, where the main light and the secondary light are both white. The underlying diffuse reflection (i.e. skin colour) therefore follows a single line of uniform saturation and steadily increasing chroma from shadow into light, as shown by the blue line in the attachment. (If the last sentence makes no sense to you, read this page (http://www.huevaluechroma.com/012.php)). As long the desaturated lighter colours are saved for the specular highlights they shouldn't look chalky.

OK Help me out on this one. Look at photo first.

Here is a photo of my friend in my living room that has a neutral cloudy day light source (I think this light source is cool rather than warm). What temperature is the light area and what temperature is the shadow? It is very hard for me to establish this.

What I do know:

Value: Light area is an average of 15-20% gray and shadow area is around 40%

Chroma: I realize that these colors are in a middle chroma range. That means not much intensity in the colors.

Light source temp: It is (I think) on the cool side but just a bit.

Local color: His flesh is slightly on the warmer side and the hues are not very saturated however I have a cool light on it so Im a little confused as to how I should interpret this temperature wise.

Overall Temperature: Light: warm???
Shadow cool??? But the degree of coolness is very little.

Now, what friggin colors should I use to block this out??? I am afraid of using too much white in the light area, since I am afraid of chalkiness and too much desturation.

Any advice greatly appreciated.

-Andy

Now my biggest problem

[briggsy@ashtons]

What struck me most is the implication of principle 1 for glazing tonal paintings in a way that is technically accurate and realistic looking - and if you can do that, wouldn't it, by virtue of speed, be the superior painting technique? It caught my fancy anyway - I'd like to paint comics, and I need as much speed as I can get. I haven't managed to pull off the glazing process in a way that looks good yet, but I'm working on it.

It appears to me that the difficulty is that, while glazing in theory produces colours in the right relationships, when you create these colours using a greyscale layer under a coloured layer, our visual system tends to recognize this and (unfortunately) to see it just that way. This tendency is very hard to avoid completely in traditional paints. Taking great care to keep the glazes to the exact areas where they are needed, and perhaps introducing a bit of hue and thickness variation into them, may help. Perhaps someone who uses glazes more extensively than I do can add some advice here.

[HunterKiller_]

Exceptional wealth of information. Much thanks to you, sir.
I better take it slowly or my brains gonna melt.

[Earendil]

I'm going to have a lot to process in the next days/months/years. This site is fantastic, I'm so glad you put it in your signature! Excellent, excellent, EXCELLENT!

[PelleTM]

Fantastic site, it will take some time to digest. If you want some feedback and are interested in improving upon the site, all I can say is try to add as many pictures and explainatory "animations" as you can - these help tremendously! Also perhaps add a glossary? (Couldn't find one). Again, thanks a lot. I also appreciate your other links.

[Giorge]

Waw this s&^% is fascinating , i bookmarked this page. Need to study it bather

[briggsy@ashtons]

Thanks for the feedback guys - so glad you like the site. PelleTm, the idea of a glossary is great, I've started work on one, and I'm also planning some additional diagrams. I'll post an alert here as I add them.

If any of you come across anything that seems confusing on the site, or needing more explanation, or just plain wrong, PLEASE feel free to post your questions here.

[Farvus]

There is something I observed today and you may found this completely obvious but I got intrigued for a while. It was late afternoon, really dark and wet from the rain. There were some red lights from the cars that were reflected by the sidewalk. However the edges of these reflections were affected by dark blue light and went into purple while the core of the red light didn't "sink" into the sidewalk. I found photo which shows very similar thing.

312875

So to me the centre light rays that straight into the eye are more dense, but on the edge there is more diffused light and lack of red is complimented with blue. Those two colours then mix in the eye and as a result I see purple :). Is it good thinking?

[Chris Bennett]

So to me the centre light rays that straight into the eye are more dense, but on the edge there is more diffused light and lack of red is complimented with blue. Those two colours then mix in the eye and as a result I see purple :). Is it good thinking?

This is 'mixing paint thinking' not 'physics of light thinking' Farvus.....I think.
My guess is that the longer wavelengths are not absorbed as much at these angles from your eye and are therefore the ones you see 'haloing' the edges. But this is just a guess and probably just as wrong. The fact we see it in the photo means it is not a subjective physical effect produced by the retina at least.

[dose]

Hi Briggsy

I have a question about Photoshop & light, but first- thanks a million for putting the site together. A truly huge undertaking both in the research for and the creation of the site. It's an amazing resource that I'm already referencing constantly to answer questions.

My question is maybe slightly off-topic, but I thought I'd post it anyway. I noticed on the page "Effects of Colored Illumination" that the "Multiply" blend mode in Photoshop suggests the effect of colored illumination. Do any of the other blend modes have similar suggestions of the physics of light?

Specifically- for me a sort of Photoshop holy grail would be a way to have a base layer with the local colors for a given object, with a layer on top with a single color for shadows, and another layer with a single color for diffuse light, such that the local colors on the base layer could be changed and the "shading" (light & dark) would remain consistent visually. In other words, you could change the local colors on the base layer, and the relative shift in dark & light produced by the two upper layers would remain the same regardless of the chroma and value of the colors on the base level. I understand this is somewhat dubious in terms of the physics, and might be impossible given what Photoshop has to offer, but it would be very useful for me in a lot of situations.

I've done a fair bit of experimenting to no avail. "Multiply" works acceptably well for the shadow layer as long as the shadow color is almost totally neutral- something I find undesirable as in some situations I like to shift the color of the shadows slightly (towards blue or brown usually). I've yet to find anything that works well for the light layer across a wide range of base local colors. "Screen" seems to come closest, but the relative shift in lightness is much greater for darker base colors, so that the base color can't be changed freely.

In general though, I'm also just curious how blending modes relate to the physics of light...

Tim

[briggsy@ashtons]

Without being there I can really only guess too, but if you had an uneven wet surface, then each reflection would be centred on the point where a smooth surface would be at just the right angle to bounce light from the light source to your eye. At that point, most microfacets on your uneven surface might reflect light from some point within the area of light source, but moving out from that point, fewer and fewer microfacets would do so, and more and more would reflect the dimmer light from the sky around the light source.

Wherever these two components were not visibly distinguishable, the resulting stimulus would be the result of additive mixing. I'm not quite sure from your description whether the sky was actually bluish, or was a dull grey that appeared bluish by contrast with the red lights. Mixing with bluish light could easily make a purple, but mixing with dim white light could also account for a more subtle shift towards pink.

The term "mixing in the eye" is widely used for situations like this, but may give the impression that the process is more subjective than it really is. What we are really talking about is mixing of physical stimuli that for one reason or another can not be distinguished separately. Many if not all of these effects can be photographed.

P.S. Tim

Your question came up as I was about to post this answer. Could you post an example of your best attempt so far, and maybe email me the psd file (djcbriggs at the dreaded gmail.com)? Glad you like the site!

David

[briggsy@ashtons]

Tim, I'm not totally sure if this is what you were after, but you can use Adjustments on the colour layers to vary both the colour of the object and the colour of the ambient illumination in any way you want.


The psd file is here:

http://djcbriggs.googlepages.com/dose-3.psd

[Farvus]

briggsy@ashtons - Thanks for reply. I just wasn't entirely sure it it was something about light or that it didn't loose it's hue but mixed with surrounding colors in the eye. You explained it more thoroughly than me. The sky was rather cool gray but everything around appeared a blue like in late afternoon. I couldn't say right now if it was contrast to red lights or more general phenomenon.

Today I realised that color brilliance mentioned in Loomis book is something a bit different than saturation and it all suddenly makes sense with all these colors in the shadow. Going back to basics definately helps :P.

[briggsy@ashtons]

Blending modes in Photoshop

To answer dose's main question (as best I can at the moment), the three blending modes that I've found to more or less emulate effects of light are multiply, screen and normal.

In multiply mode the relative brightnesses of the R,G and B components of the two layers are multiplied together, e.g. if the relative brightnesses of the two components are both 0.5 (normalized to 1.0), the resulting brightness will be 0.25. Multiply mode accurately emulates the effects of subtractive mixing, including the effect of coloured illumination. The only proviso here is that if you employ fully saturated colours, you will be emulating light of greater colour purity than comes from most light sources, or is reflected/transmitted from ANY actual coloured surfaces or filters respectively, so you may get some unrealistic results.

In screen mode, the differences between each component and one are multiplied together and then subtracted from one, e.g. if the relative brightnesses of the two components are both 0.5, the resulting brightness will be 0.75. The results of mixing in screen mode often resemble those of additive mixing qualitatively, though generally not quantitatively. Because of the nonlinear response of our visual system to light energy, a light that has twice the energy of another light will look brighter by a factor of, not two, but between the cube root and the square root of two, i.e. around 1.37. However, adding two identical lights together in screen mode results in a light that is brighter by a factor of nearly two for dim lights, reducing progressively to one (i.e. no increase) for bright lights. I assume that some sort of flattening of response of this sort is inevitable, given that brightness has a finite range in RGB space, unlike its open-ended range in the real world. In any case, mixing of bright lights in screen mode can give quite different results to additive mixing. For example, yellow and magenta at maximum brightness mix to give pure white, not the reddish white that would result from additive mixing (and which you in fact get if you mix them at 50% brightness).

I used layers in screen mode to emulate additive mixing in many of the diagrams and interactive animations on the Dimensions of Colour site. For this animation demonstrating additive mixing, you can see the individual layers that I used to make it (against a black background) if you slide any two of the three sliders to the left:

http://www.huevaluechroma.com/pics/4-5.swf

Finally, layers in normal mode (at low opacity) can be used to emulate the effects of atmospheric fog or turbid water.

I should add that I make no claims to be any sort of Photoshop expert - the little I know I've picked up by having to make the illustrations for the site. If anyone with some real experience has anything to add, please jump in and help out.

When I was first trying to find out about the various blending modes I found that a lot of what I read was not very specific on exactly (i.e. mathematically) what each blending mode does. I found this link to be helpful:
http://www.simpelfilter.de/en/grundlagen/mixmods.html

[briggsy@ashtons]

I grabbed a bit of time over the Easter break to reorganize a few pages (although the re- part could be a euphemism), fix some typos (and add others), and add a few more diagrams (on CMY and CMYK (http://www.huevaluechroma.com/092.php), and demonstrating advancing and receding colours, below).

By the way, dose says the stuff I just posted was a big help but he's a bit too busy to drop by and say thank you. :(

[briggsy@ashtons]

Here's another new diagram explaining an efficient way of painting a complex multicoloured surface turning out of a light source. Explanation here (http://www.huevaluechroma.com/107.php).

[dose]

Just stopping in to say that I think Briggsy should win a prize for all his work...

[briggsy@ashtons]

Hey Dose, glad you made it back! I'm not looking for a prize, but it would be great to get a bit more in the way of specific feedback, especially on my stuff about digital painting/Photoshop. Otherwise, since I'm entirely self-trained and relatively inexperienced at the latter, it's hard for me to know if what I'm posting on those subjects is actually helpful, or just common knowledge.

[Graydon]

David solved some issues of chroma for me. The chart of chroma reduction is an excellent concept. Thank you.

[briggsy@ashtons]

O...M...G... I'm guessing there aren't too many people walking around who can claim to have solved some issues of chroma for Graydon Parrish. Thank you! (Looks like I won my prize after all...)

[dose]

I'm not looking for a prize...

That's probably why you deserve one!

Did you get my PM in response to yours? I wrote a bit of feedback in there. I can post it here if you think it would be valuable to the discussion.

I've been giving some thought lately to the placement of the specular highlight. I was taught correctly that the highlight is not at the point of the form closest to the light (which, as you say, is often taught incorrectly). However, I was also taught to largely ignore specular highlights, as for the most part they undermine the illusion of form on a 2D surface. There are, however, times when it useful to put them in when it enhances the feeling of form or conveys critical info about a surface's material. Any thoughts on this?

Tim

[briggsy@ashtons]

Thanks Tim

On the question of whether or not to show the highlight, I think it all depends on whether we're talking about drawing or painting, and if the former, what kind of drawing. A specular highlight won't confuse the form as long as it reads clearly as a highlight. The thing is, though, if you are drawing in pencil or pen on white paper, it takes a lot of rendering to satisfy this condition. This effort may be superfluous if the drawing is what we call a form drawing - one in which the focus is more on showing the 3D form of the subject than its appearance in a particular lighting and atmosphere. If on the other hand we are talking about either a tonal painting or a highly rendered tonal drawing, in which the focus is on the visual appearance of our subject, then I think we would normally want highlights. Not only are they a major component of the visual appearance but, as you say, they convey information about the different surface characteristics of the materials represented (By the way, I think that this distinction also applies in general to the question of whether to show or to suppress other complications like variations in local colour, multiple shadows, or multiple secondary light directions within the shadow zone).

In your PM you talked about how you had been establishing local colour with an underlying layer and shading this with an overlying dark layer in multiply mode, whereas I had represented the pattern of light generated by each light source by a layer in screen mode, and then applied the local colour using an overlying layer in multiply mode. I think the latter method makes it at least easier to represent the additive combination of multiple light sources (in fact I would really have to sit down and think to see if that is even possible the other way). But I think that the real trouble you were having, if I understand you correctly, is that you were trying to change the colour of the darkness, instead of the colour of the light, in the shadow zone.

[dose]

re: specular highlights

Ah, good. That's kind of what I was leaning towards- that there's sort of two "modes" of drawing- one to build/convey form and one to convey surface information, and that in the latter the highlight needs enough context to make sense. I hadn't had the chance to test it out for myself- especially because these days I rarely have time for any detailed rendering. I'll still have to do that to get the ins and outs of it, but your response leads me to believe I'm on the right track.

This also helps me better explain a big difference between the French impressionist technique and the Russian impressionist technique I was taught. For the most part, French impressionists seemed to be mostly concerned with the tonal effects of the light, while the Russians borrowed some of the French impressionist techniques but retained more of an emphasis on form. I had understood this difference before, but it gives me better insight as to why it may have happened.

re: Photoshop layers

Yes, I had been going about it backwards. The method you presented is much more flexible- and honestly one that I had heard & used before and is more common. It's closer to the idea of a grisaille plus glazing. Somehow I'd gotten turned around...

Thanks again!

Tim

[mentler]

All of your color work
is very impressive

Would be great
to pop down
for a visit and
do a workshop
at your digs.

[b1_]

David, thanks for the site. A wealth of knowledge.

I would just like to give some feedback if I may, after reading through the entire site over a few days. I am a beginner to colour theory, so even terms like 'hue' are new to me.

I found, particularly at the beginning, some of the language to be inaccessible. I tried to unravel what you were saying a few times but eventually learned to just read on hoping it would become clearer, and it did. For example, despite the excellent Hue-Chroma-Lightness diagram fig 1.5, I did not fully understand what hue was until the Hue-Chroma-Lightness section and this sentence: 'A colour wheel represents chroma on a radial axis from the centre, and hue by position around the wheel...'. For my own understanding I translated the hue definition to 'On Fig 1.5 a single hue is the sliver of colour under the chroma line, and the level of chroma in that hue is a point on that line. The single line hue circle as depicted in fig 1.5 represents a range of hues having the same chroma.'

I can't say I understood much of the scientific stuff in the trichromacy and opponency section but more than likely I just need to read over it again.

I think you did a good job adding as many visual aids as possible, but I still would liked to have seen less text and more painting or photographic examples (more than one wouldn't hurt) to describe the phenomenon you were discussing, you are dealing with predominantly visual thinkers afterall. In particular I was disappointed by your explanation of your principles. Principles 1 and 2 I understood, and even did some experiments in photoshop to confirm, but I thought 5 to 8 were too briefly explained.

Additionally I found myself many times wishing there were some photoshop exercises I could follow along with to confirm each section of the site. Perhaps a simple sphere painting exercise in Photoshop or Painter for a lot of the sections could be devised where the reader had to translate what is learnt into a correct colour selection for any given situation?

There is certainly more to praise than criticize however. I did get a lot out of the site. As a beginner I don't think I could have a better start in my understanding of colour theory. I feel I now I have a rock solid foundation of understanding that will serve me well for ever more, so thanks again.

With regard to warm and cool colours, interior decorators use warm colours to make a large room seem smaller (make it more cosy), and they use cool colours to make small rooms seem bigger. In effect putting to use in a practical way the advancing tendency of warm colours and the receding tendency of cool colours. I find thinking of colours in this context helps me to classify whether a colour is warm or cool. For example, I once mistakenly thought a dark brown coloured rock with a blueish tinge that was sitting by a flowing river, all slicked over with water, was a cool colour, but it is not despite its context. All I had to do was imagine this colour painted on the wall of a room to realize it would make the room seem more 'cosy'. The same thinking can be used to clarify purple as a warm colour. Yellow is the colour that doesn't quite work when thinking like this however - paint a wall yellow in a room does it make the room more cosy? Perhaps its lightness and closeness to white makes it difficult to judge? There is no doubt warm and cool associations can be ambiguous.

Lastly, I submit the typos I noticed:
051 - In programs such as Painter that cleverly [simulate] the appearance and physical behaviour...
063 - Figure 6.11. Effect of adding white to opaque pigments. Unlike transparent pigments, addition of white to an opaque pigment like Cadmium Red Deep does not increase the chroma, but steadily [reduces] it.
074 - In digital painting programmes, the usual conceptual fr[a]mework for hue is the...
075 - Quinacridone Magenta, Pthalocyanine Blue (Green Shade), and any bright Lemon Yellow mix [is] about the greatest gamut...
077 - Since "warm" and "cool" are psychological associations, it is not [surprising] there is a great deal of inconsistency in usage.
082 - Figure 8.4. Chroma and colorfulness. A surface of a given chroma is more "colorful" in higher illumination (B,D) than in low illumination (A,C). [Tonal] painters would observe this difference in...
083 - Screen (RGB[)] colours have a more complex...
083 - Screen (RGB colours have a more complex geometry for a largely different reason. Among the full-chroma RGB (screen) colours... [You interchange 'screen (RGB)' and 'RGB (screen) - not consistent.]
083 - These differences [can] be accounted for by the fact that in the secondary colours, pixels of both the adjacent primaries are glowing.
083 - These differences be accounted for [because] in the secondary colours, pixels of both the adjacent primaries are glowing. [Pet hate, the use of 'the fact that' - up to you, just thought I'd highlight. Refer Strunk&White The Elements of Style pg24 :)]
101 - My advice is that anyone who doesn't understand colour should not use black, but now that you've got this far you're certainly ready [to] join the black-using party...

[briggsy@ashtons]

mentler

That's a huge compliment, bone doctor!!!! It sure would be great to cross paths with you sometime soon.

b1_

Thank you very much, that's exactly the sort of specific feedback I've been hoping for.

I completely agree that the section on principles needs more content - I've already said on a few occasions elsewhere that that section is still very much a work in progress. I've recently been making various additions and corrections in the earlier sections, and I hope to get onto that section over the next few months when I have time.

I hadn't really thought of the site as an introduction to colour theory for complete beginners, so it's really good to know that with some improvements it might serve well as such. Some accompanying exercises in Photoshop is a great idea! The site in its present state is very much a reaction to the predominant confusion and disinformation about colour circulating in print and on the internet. I guess I had in mind a target audience of somewhat more advanced students, practitioners, and teachers who were already familiar with these myths and legends. I structured things to try to get everything straight for that audience from the ground up, but it looks as if this layout is giving the impression that the site is pitched at a more introductory level than it really is at present. You've done extremely well to go from learning the meaning of the word "hue" to finishing reading the site in a few days!

Thanks very much also for the help with the typos, I'll deal with them in the morning. (Glad you didn't see the site a month ago, though!)

David

[Rares Halmagean]

You sir are an asset to this community. Although I haven't read through the whole writeup yet, You're Dimensions of Color is a wealth of information. Thanks You!

[Jussi Tarvainen]

Hi Brigsy@ashtons,

I've been reading through your site and there's so much information. Most of it is out of my league and I have no idea what you are talking about mainly because I am a beginner at color theory, english isn't my first language and there are so many words which are very particular to color theory(case sensitive) and are new to me. So I have more reading to do and going through the vocabulary.

But I think what would help like some people have said is adding more demonstrative pictures. The more the better. It's easier to understand hard case sensitive words if I can see it in a picture with the context if you know what I mean.

Also one feedback about the site design. I would very much encourage you to change the brown background texture behind the text into a single color non pattern background. The current background really entires ones eyes and especially since there is so much to read. This would be my biggest concern.

I can't express how thankful I am that you've seen the effort and time used to create the site and share it with everyone. Hope my feedback helps and keep at it.

Thank you,

[SoufMeng]

Havent read it all yet but i just wanted to stop by and say: Woow!

Big massive Thank you!!

Gorgeous, really!

Thanx again.

[dose]

Hey David

Just downloaded the Colorspace program after seeing you mention it on an old thread. Seems like a really useful program and I look forward to playing around with it.

I was wondering if you could explain why you use the YCbCr space to plot the color space diagrams here and on your color site...

Thanks!

Tim

[Swampdigger]

briggsy@ashtons,

First off, you've put together a really nice resource. I'm sure a lot of hard work went into it and it shows. The presentation/color scheme of the site is simple and effective.

You stated earlier that the site wasn't necessarily meant to be a resource for beginners. As a beginner, I think I understand why. :) A lot of my problem is even if I understand the concepts, I don't have anything to apply them to. I have so little knowledge of basic color theory. Which brings me to my question: What are some good resources for beginners to color?

I've searched around some on the internet and CA for anything, and it looks like there are one hundred and one different ways to approach color. The sheer size of the subject and opinions on it have in many ways baffled me. I have no idea where to start, so I decided to bring the question to you, someone who's opinion and knowledge of color I respect.

Any advice would be appreciated greatly. Thanks for making such a valuable resource available to everyone. (hey, I may not be able to apply it to my art yet, but I know value when I see it. ;) )

[neo_23]

Thanks a million...Gr8 help for beginners like me.

[slimydoom]

I dont understand but noooothing at all... thought I saved it on the computer knowing it GOT potential not yet discovered by my totally confused brain, I think a lil theory (written) could accompany this graphic since I'm asking so much questions about color theory!
Great work!

[briggsy@ashtons]

Thanks for the comments everyone and sorry I haven't been back to this thread for a while!

Dose, that's a very good question and one that I'm going to have to explain better on the site. For now the short answer is that YCbCr is quite good as a representation of hue-value-chroma: distances outwards from the Y axis correspond very closely with Munsell chroma for a given hue, while Y corresponds fairly closely though not exactly with lightness. I'll add some diagrams on the site to show this more clearly.

To everyone who is finding it hard to know where to start, the really essential thing is that you get used to thinking of colours in terms of three-dimensional spaces. That means hue, value and chroma when thinking of colours of surfaces, but also hue, brightness and saturation when thinking in terms of colours of light. The former dimensions and their importance are relatively widely known among painters, but currently even the best available resources generally miss the significance and even the existence of the different set of dimensions for colours of light. The site is really an attempt to clear this and a few other matters up for people who, like many here, are already familiar with these available resources. I'm still planning additions to make some things easier to understand, but a resouce written for complete beginners would be a quite different site.

In my courses I do take colour from absolute basics for complete beginners, and one day I might put this stuff together, perhaps as a book. But in the meantime, to get a grasp of hue, value and chroma I very highly recommend the exercises and text in the The New Munsell Student Color Set (http://www.amazon.com/New-Munsell-Student-Color-Set/dp/1563672006). Once you've worked your way through that, I doubt if my site will still hold any terrors for you.

Having said all that though, I'd be happy to try setting and commenting on some exercises in thinking about colour on this thread if anyone is interested.

[dose]

For now the short answer is that YCbCr is quite good as a representation of hue-value-chroma

I figured it was something like that. I'll keep an eye out for those diagrams on the site- would love to see more specifics. In the meantime I'll read up on YCbCr.

the really essential thing is that you get used to thinking of colours in terms of three-dimensional spaces.

This is something I've sort of intuitively started doing over the years as I've learned about color, but reading that sentence really crystallized something for me.

Thanks again!

Tim

[briggsy@ashtons]

... reading that sentence really crystallized something for me.

Ah, yes ... I know those crystals ... they're my favorite drug!

[curtmantle]

David - just a thanks for all the effort and hard work put into this site.

I have to admit that for someone who knows absolutely nothing about the concepts (and was rubbish at physics at school), it's extremely hard-going but that isn't your fault at all... it's a complex subject. Ever thought of doing a "Complete Idiot's Guide"...

... you're going to tell me that this IS the complete idiot's guide aren't you?

I will persevere - I'm sure it'll all start to click in place eventually and I have already learnt much from it. Well done.

[senany11]

Thank you, this looks wonderful
some really great info you've put together!

__________________
makepolo (http://www.makepolo.com)

[briggsy@ashtons]

Thanks again for the replies! Here's a colour exercise that I thought some people here might like to try.

I've just finished teaching a short course on colour and light at Billy Blue in Sydney, which was the first one I have given specifically focused on the digital environment. (The workshops I give at Ashton's cater more for traditional media). Towards the end of the course I introduced a variation on the old sphere painting exercise, where I got the students to analyze photographs (ripped off from Flickr) for lighting and atmosphere, and then paint in a sphere so that it looked compatible. You need to decide on the directions, sizes, colours, and relative brightnesses of the main and secondary light sources, and then paint the modeling, highlights, form shadows and cast shadows accordingly. I asked the students to colour the spheres so that they looked bright coloured, that is, neither glowing nor greyed, but you could go on to make them look luminous as a variation. I also worked out an OK way of faking spherical reflections based on the content of the photos. Later we did some misty scenes that required addition of atmospheric perspective. You might also want to look at the image characteristics of the photo and perhaps add some grain and/or blur
to really get the spheres to blend in, though this was not really the focus of my course.

I found this exercise to be really good for drawing together the stuff we had covered on light and colour, as well as all the ways of choosing and adjusting colour in Photoshop.

Anyone care to give it a try?

[Form]

wow briggsy, what a cool exercise! i wish we had such a cool teacher when I was there at billy blue. it warms my heart to see that you are still teaching there and that you have such responsive students!

i have a lot of news to share, i will have to come see you sometime and give you the lowdown!! would be good to catch up. are you around during any of the drop in sessions at ashtons?

[briggsy@ashtons]

Hi Adam, it'd be great to catch up! This week I should be at Ashton's on Wednesday night and all day Saturday and Sunday, if any of those times suit. After that there's a break over Christmas until my first workshop there on the 29th.

Unfortunately this year may have been my last undergraduate class at BB, at least for a while. The new course has a lot less drawing in it, and with Debby, Edwina and a couple of others they have more drawing teachers than they need. Hopefully something will turn up there eventually as I really love the place, and the students have been great. I'm still down to teach my colour "masterclasses" for the general public there next year, so at least I'll have some involvement.

[GDonaldson]

woah I had no idea colour could be so complicated! very well documented resource you have here briggsy. Honestly I dont get it, I just draw what seems right to me, no identifiable method or theory...so when I read this stuff I have no clue how to apply it in a practical manner. I did art at school and have an honours degree in design for interactive media but no one has taught us anything like this about colour.

I assume that I have got some theorys or methods working in my head but I just havent really identified what they are myself. I do alot of 3D so I suppose some of my ideas come from trying to be a human 3D rendering device haha.

[briggsy@ashtons]

For something so important it's amazing how badly colour is taught - almost universally - which is why I put the site together. Of course, how much you need to know depends on how awesome you want to get at it, and what you're satisfied with. I think an exercise like the one I just described is a good test of what someone really knows about colour and light. I'm sure anyone who tries to get a really realistic fit will see where most of the stuff I talk about comes in.

[dose]

Oh- great exercise. I'm going to try to do it on my breaks between work...

[briggsy@ashtons]

Great, Tim - please post what you come up with!

Anyone else - don't be afraid to give it a shot. Happy to help if I can.

[dose]

Work has been crazy lately, but I've been chipping away at the exercise. Will hopefully have something to post soon.

On an unrelated note, I have two rather technical questions. First, what is the function to convert from linear radiance to nonlinear brightness? I saw the charts on the "Effect of Inclination to Light" and "Effect of Distance from Light" pages, but I'd like to play around with some values other than what you have listed (and it's clearly not a simple function). I tried googling it, but it mostly left my head spinning...

Second, how would one apply those brightness values in Photoshop? I understand that in the absence of any ambient or reflected light (i.e. space) the brightness for any surface would drop to zero. But how does the scale shift in the presence of ambient light? Does it just shift up proportionally? And how do you account for the local value of the surface?

(I guess that's more than two questions...)

[briggsy@ashtons]

On an unrelated note, I have two rather technical questions. First, what is the function to convert from linear radiance to nonlinear brightness? I saw the charts on the "Effect of Inclination to Light" and "Effect of Distance from Light" pages, but I'd like to play around with some values other than what you have listed (and it's clearly not a simple function). I tried googling it, but it mostly left my head spinning...

Technically, radiance is the raw amount of light energy, so to convert to perceived brightness this first needs to be weighted, wavelength by wavelength, to the sensitivity of human vision, giving CIE luminance or Y.

The conversion from luminance to perceived brightness has been modeled using power functions ranging from a cube root (i.e. an exponent or gamma of 0.33) to a square root (an exponent of 0.5). Measurements on one of the original Munsell atlases (1915) and on the first Munsell Book of Colour (1929) have shown that their greyscales quite closely fit exponents of 0.43 and 0.40 respectively. For the 1940's renotations, greyscales were experimentally judged against white, grey and black backgrounds, and the (very varied) results were smoothed into a complex polynomial that someone later noticed was very close to a cube root relationship. This cube root relationship was incorporated into the formula for CIE lightness (L*) and presumably in its equivalent (L) in Lab space in Photoshop.

On the other hand the conversion from linear to nonlinear RGB brightnesses, I gather from Charles Poynton's excellent Color FAQ, is based on a simple power function with an exponent of 0.45. Consequently, a series of greys that are evenly spaced in brightness (B) in Photoshop are not exactly evenly spaced in L.

I've taken you to or perhaps beyond the outer fringes of my current knowledge of the subject, so if anyone understands this stuff better than I do please chip in. In any case, as I say on the site, you only need to think about this conversion if you want to exactly calculate the fall-off of light with distance and inclination. For most purposes, including this exercise, you can just eyeball.


Second, how would one apply those brightness values in Photoshop? I understand that in the absence of any ambient or reflected light (i.e. space) the brightness for any surface would drop to zero. But how does the scale shift in the presence of ambient light? Does it just shift up proportionally?
(I guess that's more than two questions...)

You can emulate the effects of multiple light sources in Photoshop by superimposing layers showing the effects of each source in either screen mode or linear dodge mode. Linear dodge is more accurate, but screen is less inclined to reach the limit of the RGB gamut and "clip".


And how do you account for the local value of the surface?
(I guess that's more than two questions...)

(As I suggested to what must have been another dose about a page back) you can apply this with a top layer in multiply mode. :)

[dose]

Awesome- thanks David! That gives me a bunch to experiment with.


For most purposes, including this exercise, you can just eyeball.


Yeah, I totally agree that I don't need to know this stuff for practical painting purposes. But I suffer from a terrible need to understand things, so I just couldn't leave this alone!

I also think the model I have in my head for shading series is incorrect- in my head I think the steps are much more even than they really are. For example, you mention that the full light area can be rather large, but in my head it's pretty small. I think a couple very precise renderings could really clear up the flawed model in my head, and after that I probably wouldn't ever need to be so accurate again.

Further, I've been experimenting with some scripts for Photoshop that will generate strings of swatches to color pick from. It's pretty trivial to do evenly stepped swatches, but I might like to experiment with generating strings based on the inclination to light- so each swatch corresponds to a certain inclination to the light. I'm not sure what will come of it, but I'm curious.

I don't imagine I'll be using much of this for the photo exercise, but like I said, I can't leave it alone...

[dose]

Here's my first attempt. I made a green sphere for variety, and to be able to see the effects of the yellowish/orangish light better...

[briggsy@ashtons]

Great work on the colours, Tim, but looking at the shadows of the trees I'd make the cast shadow on the wall wider. The alignment of the terminator and highlight also look just a little out.

[dose]

Yeah, I'll admit I was a bit sloppy on the drawing side of things- I just eyeballed pretty much everything. That's a really interesting method to find the placement of things, though- never would have thought to apply something like that here. It would have been probably been much less effort than eyeballing.

My high school technical drafting teacher would be disappointed!

[briggsy@ashtons]

I've already written to them.

Now for some aerial perspective:

[Ian Miles]

Just found this Thread!

Here´s one of my first trys at painting!! ^^
Made with painter. I know is not the best for photorealism, but is what I have and the painter look is my fav!

[Elwell]

Ian, I'd pick another photo to work with. That one's been highly manipulated, the sky doesn't match the lighting of the ground.

[Idiot Apathy]

Hey Briggsy, hope you are well!
I still have a hard time lighting warm local colors with cool light, if you ever had the time to demonstrate with a sphere or two I'd be in your debt (again). Understandably in many situations the local color of the sphere wouldn't be apparent in the slightest, but I suppose I am looking more for the situations where there is an obvious transition - perhaps multiple lightsource situations? Tricky business...

[briggsy@ashtons]

Sure, Tom. Just tell me the colour of the main light, secondary light and local colour that you want, and I'll give it a go! My own personal Peer Project exercise, yay!

[Idiot Apathy]

Haha, yayyyyy!

Hmm, let's see. Cyan main light, red secondary and an orange local colour. If that gets too ugly due to the complements maybe the secondary should be white or orange?

Thank you!

[briggsy@ashtons]

How's this look? I've left out the complexities of the reflected light since we're mainly looking at the colours. Here's the PSD file so you can see my logic, and tweak the hues to your heart's content:

http://djcbriggs.googlepages.com/fortom.psd

[Delmar]

This is absolutely amazing!!! I wanna thank you so much for this site and your effort and knowledge you've put in.

I'm also one of that guys who tries to get along with that little bit of color theory knowledge hoarded along the time....wondering why my colored stuff isn't quite working......

I should be working right now, so I'm not able to get through the whole stuff...but i'm really looking forward to read it!!!.

Thanks a lot, i guess i will be back with some questions soon.

Cheers

Andi

[theTooninator]

You're a big man for trying to help us shmucks along. Thanks briggsy.

I've recently been hit with the colour bug. It's all I see anymore. Trying to observe light and colour closer than I ever have before, in hopes to apply it to my work. This thread will serve nicely in helping me along. I'll try to follow along.


-Matt

[germ-X]

awesome color works. impressed. love to see more of your work.

[Idiot Apathy]

Briggsy Sir, thanks so much for that sphere. It's opened my eyes to a lot of things. A bit of a renaissance going over here in my head lately :)

[George Abraham]

Thanks MR Briggs.

Your site is a really good resource that saves alot of time.

I had some raytracing stuff I did yonks ago and played around with words that didn't make sense to me at the time. Now they do.

Just one question. On a dull ball without a specular hilight but with a diffuse effect of saturation change(Closer to the color of the light source).
Does the degree of change have to match the half light and full light direction of the sphere or does it follow the direction of reflecton the specular would have had? In otherwords to simply see the effect as a large dull specular?

[EDIT]
I looked at my hand and the answer came to me. Because the texture is distributed (little bums on the back of the hand's skin texture) each bump has it's own specular almost like a bazillion little spheres stacked together, distributed across the surface of the hand. So the direction of the specular on each bump would confirm to reflection or specular rule but because they are distributed each of them would give a little specular over a wide area but thus only the planes with texture (little balls) in range will display the mixed or combined effect of saturation change:A little bit of light color blended with the object color and illumination of that color resulting in saturation change. Depending on the texture of the surface then the effect would be limited only to certain planes that has it's texture in range and that might not be the fully lit plane, and this effect could diminish down the length of a flat or constant plane as the relationship to the light and eye changes. Therefore the saturation painted on a lit side of a ball and the brightness change would not share the same relationship of degree into the same direction.

[briggsy@ashtons]

Very glad if the site has been of help, everyone - just keep the questions/discussion/crits coming!

zaorr I not sure if I quite follow all of that but it sounds to me like you're on the right track. I'd expect to see an additive combination of the fuzzy specular reflection (the colour of the light source, and centred on the point where the specular on a polished sphere would be) and the diffuse reflection (the colour of the object, and reaching its maximum at the full light plane).

[George Abraham]

Thanx.

[Dile_]

very cool thread.. i had no clue that you could translate so much to the digital medium... very cool , thank you so much!

[George Abraham]

http://i219.photobucket.com/albums/cc256/wenresep/scans/ball.jpg


Couldn't resist.
It's the real deal.
Good ref though.

[briggsy@ashtons]

Thanks, zaorr. Good on you for taking on the challenge of a dappled light source! The main problem for me is that the direction of the light source on the ball doesn't seem to agree with the direction in the scene (assuming that those shadows are cast by more or less vertical trees). Also, the highlight looks very bright for the context - I would expect a fuzzy highlight to get dimmer when it spreads to that extent (and it must be spreading because the sharp-edged cast shadow implies a near point-source light such as the sun). It gives the ball a somewhat unearthly look, which of could be very useful when you want it.

[George Abraham]

Yes Briggsy

I took a real picture and tried to fool you but you spot the over exposure really well. You just reminded me how bad a camera can be compared to real vision. I agree, it looks a bit out, even for a real picture. Didn't notice the direction problem at first but I see now how the overexposed blob makes the direction kinda off looking.

:)

[briggsy@ashtons]

Good one, zaorr! I take it those shadows must actually be cast by something a long way from vertical (fronds?), which would explain the direction thing.

[George Abraham]

OK, now I get it, I don't understand the shadows either looking at them now. The cast shadows are from a palm tree with low hanging branches. The other shadows makes it a little confusing. I will have to check the scene agian to figure out what that's all about.

Something new everyday, so if this was a painting the shadows would have been to complicated to read. But with knowledge of it being a photo the mind just accepts it as fact without question.

[Aaron Death]

I have read through the tutorial several times but I simply don't understand the rule of uniform saturation. From my experience with digi painting and PS color pickering on photos, low brightness almost always goes with high saturation on skin tones and many other things. How is it possible otherwise? Just pick any photo and it's always like this. Oops!

Great tutorial anyway, shockingly amazing, changed almost everything I know about color. It makes color so difficult.

[briggsy@ashtons]

Well, for a start the rule only applies to the underlying diffuse reflection; in various parts of the lit areas this colour will be modified by specular reflections of the light source (the highlight) and of the environment; for strongly coloured objects in most natural lighting situations the effect of these additions will mostly be to locally desaturate the colour. (Another complicating factor is multiple reflection, which can boost the saturation locally both in the shadows and in the lights).

Secondly, there are a couple of good reasons why just picking colours from photos can give the wrong impression of what is actually happening:
1. Colour noise tends to be greater in the darker areas of an image - try sampling from a larger set of pixels or blurring the image to get a more realistic measure of shadow saturation.
2. Any overexposure of the lights will result in artificially low saturation. Once one of the R,G or B components of a colour reaches 255 there is nowhere higher for it to go, and further exposure just adds more of the other two components, resulting in desaturation. Even in an apparently well exposed photograph some individual colours can easily reach this limit and so be "clipped" and artificially desaturated. This is true of any colours in the photo with brightness (B) = 100.

A uniform saturation series is just as series of colours in which the R/G/B ratio stays the same and only the brightness changes. It's hard to argue with the idea that this is basically going to work as a series of image colours representing a surface of one colour reflecting different amounts of light.

http://www.huevaluechroma.com/pics/9-9.png

Anyway, I'm really glad you like the site. As far as making colour difficult goes, whenever a student tells me I'm doing this I take out my copy of Colour Science by Wyszecki and Styles to show them what some real writing on colour looks like!

[Aaron Death]

Thanks David. You're really a expert on colors.

So do you recommend studying colors from photos? What should I keep in mind except over-exposure.

[Dementist]

The information presented in this thread is an amazing resource for the technical applications of color theory. However, I'm currently TAing an introductory design class at an architecture school, and am curious if anyone has any good resources to share for other applications of color in design. Not how to make color, or what it is, or something so banal as "what this color symbolizes," but an in-depth resource on how artists and designers can use color to enhance their creations.

[Jason Ross]

Thank you Briggsy for this wonderful thread. Color is always an interesting topic among artist who care about why they see "what they see". I'm on my 3rd book on Color Theory and I've concluded that there is no "right" answer, but there is good advice out there.

From what I understand, you are a proponent of the uniform saturation principle. Even though I looked at the example you provided, the Loomis recommendation sits much better with me. It really just looks more natural to me. In the "Spheres from Peer Project shaded on principle of highest chroma in half light" the lower 6 on the right look the most real to me (looks like the same person did those, looks like Easter m+m's). The "uniform saturation" ones below look...Photoshoppy to me. ("digital" is probably the appropriate term). I looked at the red ball you created in Photoshop in Idiot Apathy's thread and painted over it with some minor changes (I hope you don't mind). On your ball example it also seems like the change from half light to full light was only a change in "Brightness" and not value, so my full light does look more pink. I also added the background blue as the adjusted HUE of the shadow side of the ball. In my opinion that would be the color of the light that would be illuminating the shadow side. So would you mine explaining your thoughts on why this is incorrect?

[briggsy@ashtons]

Hi Jason, really great to see you on this thread. I'm in the process of switching to a new ISP contract at home, so I'll give you a proper answer as soon as I'm connected again.

Dementist, someone else might be better at answering that one - most of the books I've seen along those lines seem much of a muchness to me. The New Munsell Student Color Set has a concise introduction to the basic concepts, but if you want to look at the subject in more depth I'd be looking at some writing on colour in art history such as John Gage's books (Colour and Culture, etc).

[George Abraham]

The way I understand it now is that we have been studying a highly polished cue ball.

In theory the object will have a constant saturation as it moves into becoming brighter, I like fully lit better as it avoids confusion and implies working with the diffuse effect alone. In Photoshop this will be a movement parallel with the line between black and white in the Photoshop color screen (Bottom right black and top left white).

The movement will be kind of parallel and not straight towards white implying constant saturation. Some colors will hit the roof or top edge or the color square screen so they are forced to move directly towards white getting more saturated, the same with shadow, they will hit the right edge and will have to move down towards black directly. Are these examples existent in reality, is there some exceptions or are these colors too bright or not possible at such a purity for example?

I have named or identified a movement in our examples directly towards white as moving directly towards the color of the light source without changing the energy/diffuse of the surface, thus this movement can only be specular effect. So you cant do a movement like that on the white side without adding the effect as specular. I don’t know about shadow though, I guess shadow should only add a constant drop in value but then to look at the new darker environment as a lit area and shade that accordingly, but what if the drop has hit the side or the color screen. Should that be possible?

The red ball above displays a specular dot and specular effect arround it(Saturation change) making it look pinkish. But if you look closely that could be seen as a faint specular light impression of the room’s roof area around the light source or the sky. Was this intentional or accidental specular effect?

It’s just that I when I heard specular in the beginning I was thinking bright dot and perhaps some have stuck to the same idea. I think studying a shiny ball and a textured ball would have cleared certain things up faster. Anything not polished is textured, skin looks smooth but it's textured and the more common surface type you will encounter.

[George Abraham]

Sorry,

Regarding shadows I have been a moron, I keep trying to render around an object, I think I picked that up from loomis, not that it's what he taught, I just assumed that movement around the ball even for the shadow.

Something I only recently started to grasp and perhaps now solidify is that there is no shadow only change in lighting environments.

So to correct my own shadow behavior on the color picker, The shadow will have a once off drop(Indicating the absence of the main light). The drop on the color picker would be a move directly towards black in a straight line as the point of zero light will be the point of zero diffuse(Assuming the ambient is also white)

This drop should then be treated as a new environment where the ambient or room bounce light source should render the shading and appearance of that part of the ball.

I think a few exercises is in order, Shading a ball in an environment where the rays of the main light source is blocked from it, and once I have convincingly rendered the ball, remove the block and then render the lit side according to the new lighting environment. I should also try to get the idea of the terminater and drop shadow hardness as being an indicator of the light strength. I noticed this effect thankfully on a day standing outside for a smoke, where light clouds would move infront of the sun, Then I noticed how edges and terminators harden and soften.

[briggsy@ashtons]

Hi Jason, sorry it's taken a while to get back to you.

The very first step in understanding the appearance of objects (which Loomis does not take) is to make the distinction between specular and diffuse reflection. The uniform saturation principle applies to the diffuse reflection, but it's important to remember that the latter is almost always modified by specular reflections of the light source(s) and of the environment. These specular reflections are not changed in colour by the object, and so they tend to desaturate the diffuse reflection coming from coloured objects in the areas where they are present. For example, if a small main light source is surrounded by a bright diffuse cloud or surface, then the specular reflection of that cloud or surface will desaturate the colour of the sphere over a relatively large area. This in fact is the way your version of the red sphere reads to me, and apparently also to zaorr.

I'm afraid I can't think of any reason why the six spheres you mention should look right to you - to me they are all great examples of what goes wrong when people follow Loomis' advice! Some of the other spheres (including my 2006 sphere) may look "photoshopped" because they have been painted using a very high saturation series, which gives them an excessive chroma for a real sphere.

On my 2006 sphere I was thinking of the blue as a background rather than a completely encircling environment, and I envisioned that otherwise the shadow area was lit by white light. The hue of the light from the background is very close to being the exact complement of the local colour of the sphere, and so very little of it would be reflected in a diffuse manner from the sphere (actually none from my perfectly red sphere), and thus it would have no real effect on the (diffuse-reflection) hue of the shadow area.

Jason, it would be really great to see you what you could do with the exercise I described on the preceding page here, of painting a sphere into the specific lighting situation judged from a photograph. Personally I think you would soon discover for yourself the limitations of the Loomis advice for realistically representing appearances. Of course if you still prefer the Loomis "look" for aesthetic reasons, that's a different matter.

Zaorr, I'm not sure I follow everything you say in your first post, but the attachment shows what I think is happening in terms of the colour picker in Photoshop.

On the subject of shadow hardness, the tonal contrast depends on the relative strength of the main and secondary light sources, while the softness of the terminator and penumbra vary with the size of the main light source (small light source > sharper edges).


Aaron, sure I think you can study all sorts of questions about colour using photos - after all, a digital camera is really a sort of cheap and portable colourimeter that is intended to have a response closely comparable to human vision. Of course there are limitations but it's hard to comment on what factors to keep in mind unless you tell me what specific kind of question you want to investigate. But obviously the more you learn about how digital cameras work (as well as about light and colour), the more confidently you can use them.

[George Abraham]

Thank you Mr Briggsy for the gem.

I just had to see it on "the squre". :)

[Jason Ross]

Hi Briggsy and Zaorr,
I haven't ditched the thread I just wanted to reply well. But there were some things that did not add up to me when I think about some of the information. And this just shows that no matter if you think you got it right, listen to what others have to say...cause I've been learning quite a bit here. What really made me think is why did you draw the area in full light just brighter and not lighter in value? I then realized that "maybe" it is backwards...that maybe loomis is considering diffused light and yours is specular light. The reason I say this is that "matte" objects are considered as having a diffused quality and the areas in full light, as the planes reach perpendicular to the light source, get lighter in value...Generally. When rendering matte objects...Form change = Value change. Well what gave me that "aha" moment is that I did a search of "red balls" on the internet and I noticed something. Almost all of the balls that I found, the "full light" areas to the "Half lit" areas were close to the same value...they looked pretty flat. And they were all specular...very shiny... and it makes sense that the half lit and full lit areas would be of similar value because the environment is being reflected to the viewer. Zaorr said this about my red ball and I agree that he is correct. So the values of the sky or room make up a somewhat "flat" plane and thus making the reflected half lit and full lit areas appear flat as well. Here are some photographic examples of what I am talking about. I also believe the the "lines" of the color picker for a "diffused" object would be curved towards the top and then head to white...given the earlier scenerio...Now that I look at the top "diffused" ball I think that the irregular shape of the half lit area is actually reflections of surrounding trees. I'll try the exercise on the earlier page and see what I come up with. Thanks guys!

[briggsy@ashtons]

Jason. you're quite correct that the red colour does not change much in brightness within the full light area, but this is just what we expect of a diffuse reflection. If a plane facing the light source catches x amount of light energy, the same plane turned say 45 degrees from the light source will catch cosine 45 degrees or 0.7071 times x. You may also know that our perception of brightness is related in a nonlinear way to light energy, so that a surface that looks middle grey reflects only about 18% of the light reflected by a white surface. By the same relationship, our surface reflecting 0.7071 of the amount of light energy will look about seven-eighths as bright as a fully lit plane. So in turning halfway (45 degrees) from facing the light source, the perceived brightness of the light hitting and being reflected from the surface will drop by only one eighth. For a red or mid grey object this amounts to a change of only a little over half a point on the ten-point Munsell scale.

So - form change creates value change, but only very slowly until we reach the half lights.

On top of that, because our visual system pays less attention to gradual changes than abrupt changes, we tend not to notice even the small amount of change in lightness that does occur in the full light. (? which may be why you thought I had made the full light brighter but not lighter ??)

I would describe what you've illustrated as the difference between a small/medium-sized light source and a very large light source, but it's true that the latter creates a saturation pattern like that described by Loomis in the full light and half light (although as you can see this tends to come with an indistinct terminator and shadow shape).

[George Abraham]

This thread has taught me not to look at specular as a surface condition but to look at the surface as it it's a mirror when dealing with specular regardless how dull it is.

Those are nice balls Jason. Try looking at each as if they are mirrors and feel the light source and blue skies reflected in them. This will help you seperate surface diffuse from the blending reflection.

I did another rendering study the other night and found myself placing the specular and some of the roof lit around the light source, I do believe now that this is the correct way to render speculars, for your mind to shift looking at form as if it's a mirror and then rendering the "source scene" as it may appear on the surface. No more turning a piece of the object into a bright spot mechanically like loomis would have.

I baught some blue scrap books a while back and a nice white color pencil not knowing exactly what I should be doing with it. I guess now is a good time to take those out of the drawer.

[Raceme]

Thank you for this valuable reference. How generous of you to make this available to us.
Thank you!

[dose]

Briggsy (and others)- you might be interested in a Photoshop script I wrote that generates a digital approximation of HVC strings in the swatch palette:

http://www.conceptart.org/forums/showpost.php?p=2260111&postcount=11

[briggsy@ashtons]

Great work Tim! It actually generates hue-value-saturation strings, but they are at least as useful as HVC strings, in their own way, for physical paint as well as digital.

Quite apart from its practical use, the swatches should have a great educational use in helping people to learn to think in terms of an absolute tonal scale of Munsell values.

I look forward to giving it a try!

[dose]

I'm glad you like them David! I'd love to hear any feedback you might have on the script.

I'm contemplating a version which would let you specify saturations on a per-hue basis (rather than applying the same saturations to every hue). It would require the user to learn a special syntax to enter the desired values, but it could be a little more useful & flexible for those willing to brave it (I'd probably choose something close to the HVC slash notation). I'm also contemplating a really fancy version that would only work in CS4, but would allow you to "mix" between swatches on the fly- so that if you wanted to knock the saturation of the current color down a bit you could click on the corresponding gray a couple times, which influence the current color but not replace it. This would be pretty complicated, but a great simulation of painting with strings in oil. But that won't happen for a while- I've been tinkering with the tools too much lately and not painting enough with them!

[dorian]

Excellent info!!
But where did the site go?! www.huevaluechroma.com - it worked a few days ago, will it come back?

[briggsy@ashtons]

It looks like it's been down for most of the weekend our time. I've just sent off an email to ibiblio, so hopefully I'll know something soon. Glad to know it's missed!

[briggsy@ashtons]

OK, it was just a small glitch at ibiblio, which they fixed straight away. If you're still getting the redirect page, just empty your cache.

[Idiot Apathy]

Mr. Briggs sirrrrrr, I have opened pandora's box again and have become rather confused. I've been going over some of the old Peer Project exercises recently for CA's mentoring and got stumped by one of my own questions! Well, it's not that I don't know the answer I wanted at the time; it's that I think I was wrong!

It's an hypothetical exercise with an object of a pure hue in an environment with a single pure and direct lightsource.


The question is as follows; The lightsource is pure red and pure yellow. Our object is green. What do you see?

In my old train of thought I would have said you would see as the end result a yellow sphere. But now I can't help but shake the feeling that you would see a green sphere though perhaps a bit dark...

Can you help untwist my brain as you always have?

The exercise for reference if necessary.
http://www.conceptart.org/forums/showpost.php?p=1016345&postcount=5

[briggsy@ashtons]

Hi Tom

I think the crucial question is what we mean by a green object "of a pure hue". Probably not an object that reflected only monochromatic green light - such an object would appear very dark or black under any other light source. There is a theoretical concept of "optimal" colours that reflect all wavelengths in a given band of wavelengths, and none outside that band. Optimal green surfaces range in theory from darker more saturated greens (reflecting a relatively narrow band of wavelengths) to brighter but less saturated greens (reflecting a broader band). So the answer really depends on which of these it is - the former would reflect neither red nor yellow monochromatic light, but the latter might well reflect yellow. How does that sound?

[Crass]

This is an excellent resource. I am glad that something like this can still be offered for free in this day and age, and it seems that you are very devoted to your subject. Even though it's difficult for a relative beginner like me to take it all in in one setting I still feel I learned something while reading through it the first time, and I'll be sure to keep coming back to it as I learn more.

The chapter on colour constancy I find especially interesting, it's quite amazing how your perception of things needs to change in order to faithfully reproduce reality on canvas, the problems faced when trying to copy what is perceived rather than what is actually there is something I'm sure we've all had to struggle with.

The only thing I could say I would've liked to see that isn't on the site are some analyzes of real-world conditions and how the principles learned can be practically applied in painting, as well as how they have been utilized by others before. This may be something that I'm alone in finding useful, but I think it would have been valuable to see both photographs and master painter's works deconstructed, with the colour dimensions individually analyzed and interpreted, and then (partly) reassembled in paint, revealing not only the information itself but also how it can be used. I know it's too much to ask of a website like this, but it could be an idea if you ever make the site into a book or a DVD.

Anyway, I just wanted to extend a big thanks for the work you've put in, the site is incredible.

[Harriet]

Hey David,

Just saying that I'm finally trying to intergrate with all this computer stuff.. he he you'll see :P

Hope you're well

H

[briggsy@ashtons]

Yay Harriet! :geekg:

Your very first CA post - I'll treasure it always!

But don't forget to link to your blog in your sig!

[briggsy@ashtons]

Whoa! I've just had a massive spike in the visitor stats and it's all from deviantART. Did somebody there make me site of the day or something?

[dragonfury]

So I read through the dimensions of color web page and my little mind had difficulty handling it. So many terms I didn't know! But I muscled through it as I know I have been especially weak on color and I need to figure it out if I am ever going to get better, even if it took me the better part of a week to get through it. Thanks for the resource! I wish I were in Australia so I could do one of your classes and really get a handle on the subject. If you ever put up videos of your classes or instruction I'd definitely watch them even if they were filmed by a 6 year old with a web cam.

Since I am so weak on my color theory I have been attempting little (frustrating) exercises by myself. One I have tried is using the color picker to watch what the color sliders do when I sample across different parts of a photograph. I was quite pleased to discover that the saturation (chroma?) really does pretty much stay the same as value changes across a uniform surface like a red ball as long as its not reflecting too much. Though I am still boggled as can be about trying to replicate skin which moves hue saturation and value all over the place. Is it because skin is translucent and has blood vessels below it or is it subsurface scattering of light or how skin is also oily and a bit reflective or is it because skin is not all the same color/texture/thickness, or maybe because I am looking at photos with multiple light sources ...?:donk:

I attempted the ball exercise and this is what I came up with. I definitely still have a long way to go. But if I squint really really hard... and take off my glasses...

http://i209.photobucket.com/albums/bb81/chibamonster/redball_italy-1.jpg

If anyone knows some really good resources or a really solid and simple way to think about and approach color, I'd love to hear it. I'd especially love it if someone had a blood oath guarded life or death super secret about color torn from the hands of an ancient and mysterious conspiracy of history's phenomenal artists. There have to be secrets about this... right?

[Virg]

Amazing thread, I spend the last week reading all the information on your website, going over it again and again.. I must thank you endlessly for all this free information, im glad the web was invented because a lot of artist would not benefit from all this information since we dont all go to art school :)
The uniform saturation principle really opened my eyes , i used to think like a lot of people that the saturation would vary all the way on a lit sphere ( even with a white light ) The fact that most photos i was studying had a colored ambient + a color light source would always deform that fact and i could never figure how much the hue and saturation should change while the planes receed. If I understand everything right, the only changes in hue and saturation on a surface ( lit by white light only in this case ) would be cause by specular reflection ? Like Zaorr pointed, I think Loomis was probably confusing the 2 in his observation, he would saw diffuse specular reflection as a part of the diffuse reflection since it was probably the lightest part of the lit area, and only considering the light source as the only thing that can be reflected in a specular reflection. Im still unsure of where to place the drastical point of change in temperature from light side to shadow side in the case of ; lets say a warm light vs a cold ambient, it seems the be a bit before the terminator on the light side of the sphere but im probably wrong..
The last part of your webpage where you help artist apply those principle with paint was really helpful, thanks again Mr.Briggsy :)

[briggsy@ashtons]

I wish I were in Australia so I could do one of your classes and really get a handle on the subject. If you ever put up videos of your classes or instruction I'd definitely watch them even if they were filmed by a 6 year old with a web cam.

Come on, airfares are cheap right now and my next digital colour course starts at the end of this month. See you there? :) Anyway, I'm more than happy to comment on anything you post here.

Though I am still boggled as can be about trying to replicate skin which moves hue saturation and value all over the place. Is it because skin is translucent and has blood vessels below it or is it subsurface scattering of light or how skin is also oily and a bit reflective or is it because skin is not all the same color/texture/thickness, or maybe because I am looking at photos with multiple light sources ...?:donk:

All of the above! Skin really looks wrong if it is painted in one colour all over. Look for all those variations and paint them in without overdoing them.

I attempted the ball exercise and this is what I came up with. I definitely still have a long way to go. But if I squint really really hard... and take off my glasses...

I can't put a precise figure on it (for lack of exactly comparable objects) but I think I would have put in the cast shadow a tad lighter (apart from the crevice shadow). Otherwise it looks great to me.

I'd especially love it if someone had a blood oath guarded life or death super secret about color torn from the hands of an ancient and mysterious conspiracy of history's phenomenal artists. There have to be secrets about this... right?

Actually I think that many of history's phenomenal artists would have killed to know what we know about colour today. In most cases their secret is ... hard work, continuous immersion and long experience. Having said that, there is a lot of useful information on painting techniques in various historical documents - what period are you most interested in?

[briggsy@ashtons]

Amazing thread, I spend the last week reading all the information on your website, going over it again and again.. I must thank you endlessly for all this free information, im glad the web was invented because a lot of artist would not benefit from all this information since we dont all go to art school :)

Actually it's because of what you most likely would and wouldn't have been told about colour if you did go to art school that I wrote the thing!

Whatever people think about it, the web is inevitably creating a "loaves and fishes" situation. If everyone, or even a substantial minority, provides one valuable thing for free, we all end up far richer than we would ever get by trying to flog off our own private tutorial/ebook/album etc.

Im still unsure of where to place the drastical point of change in temperature from light side to shadow side in the case of ; lets say a warm light vs a cold ambient, it seems the be a bit before the terminator on the light side of the sphere but im probably wrong..

As you approach the terminator the main light drops off rapidly, and so the ambient light increasingly influences the colour. Beyond the terminator, glare from the main light source may influence the colour for some distance (think of the effect of the sun on the blue sky just beside it). So you often see a transition on both sides of the terminator.

thanks again Mr.Briggsy :)

Ahem, it's Dr Briggsy, thank you :confident

[Virg]

just checked if anyone had replied before i went to bed, thanks a lot for your answer.

Just to be sure, by glare you mean some kind of blur ???

Also , if you allow me , since i forgot to post in my previous post ; your talking somewhere in this thread that you only use screen, multipy and normal modes in photoshop for your demonstration, i understand how you use multiply and screen but about normal mode, do you use it only for specular reflection and atmospheric perspective ?? ( like in the case of that red sphere on a blue background )

anyway thanks doctor ;) thats definitely clarifying a lot of things, I hope this thread will live on for a long tim

Cheers,

[dragonfury]

Thanks for the response! The shadow was something I really couldn't figure out that well since most the other ones seemed to drop straight down to the ground with a bit of ambient light softening their edges, though with your observation I am thinking that I was looking at the crevice shadow instead of the drop shadow. I'm glad the colors worked though for the ball though because that is what I really focused on.

If I could use color like anyone it would be Joaquín Sorolla for how he communicates light's behavior so well, Thomas Moran for landscapes and atmosphere (though that might have been the location of where he was painting more than his own creativity), and probably William Bouguereau for people who more so than a photograph look ALIVE. That is an odd mix, but each of those aspects of their work really floors me. Though my favorite artist at the moment is Alphons Mucha, his colors don't attract me nearly as much as his line work and design, though in some of his pieces the color is phenomenal as well. So if you could tell me their secrets that would be grand. I am noticing that some of them used a lot less color than I thought they did, so that is interesting (well, except sorolla, it looks like his paintings are exploding with light).

I lightened the shadow up a bit.

http://i209.photobucket.com/albums/bb81/chibamonster/redball_italy_2.jpg

As for airfare to the sister colony, I think the trip would cost more than my university tuition when all was said and done :D.

[briggsy@ashtons]

WhiteC

Glad if I helped. In mentioning glare I was thinking that if there is even the slightest atmospheric haze, then adjacent to a strong light source like the sun you will get some white sunlight added to the blue skylight. (Indoors, light reflected off the ceiling adjacent to a light bulb will similarly cause a gradational rather than a completely sharp fall-off of the influence of the light).

dragonfury

The shadow looks good now - congratulations and thanks so much for contributing!

Regarding painting techniques, do you know about the Rational Painting forum? You'll find threads on the techniques of many of the painters that you like (a heated 30+ page thread debating the technique of Bouguereau, for instance).
http://rationalpainting.org

If you like Mucha for composition, have you seen his Lectures on Art?
http://www.amazon.com/gp/product/085670296X

[OmenSpirits]

broken image.

http://www.huevaluechroma.com/pics/5-2.png

http://www.huevaluechroma.com/051.php

[SoufMeng]

Hi David.
Here's the questions i mentioned the other day. : )

Ok, here (http://www.huevaluechroma.com/082.php) in your site you say:T_onal painters would observe this difference in brightness and "colorfulness" of light, and represent it with paint areas of different lightness and chroma, in order to create the illusion of a surface of uniform chroma under varying light I was wondering, what is a "tonal painter" exactly? I couldn't find a proper definition.
Also, several times you wrote about how its better to use uniform saturation for realism (than higher saturation in the half light e.g), ok but when do you recommend not using uniform saturation? I find it doesnt always give pleasing results even after adding specular and bounce light. Also more often than not in photos, saturation is more or less higher in the shadows and although i hear colors are not accurate in photos i'd appreciate your thoughts on all this.

Just for confirmation now: specular light is additive right? So, to reuse the example of a red ball, if there were a bright green wall behind the ball, its receding "planes", affected by the specular light from the wall should get a little... yellowish?

Another thing; according to you, are there some significant advantages for photoshop users to work in lab mode rather than rgb? Then again i heard various things but would like an informed opinion.

Finally, i always wondered why, often under sunlight, there's a saturated reddish rim of color at the shadow edge on human skin, somewhat like in this photo (http://itchstudios.com/psg/tuts/hand2.jpg) (im aware it's completely blown out but couldn't find any better).
Oh and more for the sake of curiosity than anyhthing i'd like to know the formula used to calculate the lowest row of the chart here (http://www.huevaluechroma.com/106.php) (brightness).

I guess that's all. :)

Thanks a lot for your time and any infos on these questions.

[bkkm]

Hi David,

I've recently begun trying to study color on my own, and your tutorial is one of the best sources I have found so far. Thanks!

I have a question, though... in the chapter on Hue (on the section on the traditional artist's wheel) you make a brief reference to Johannes Itten's contribution and mentions "the inexplicable popularity of Itten's books". Would you mind elaborating a bit on this?

In addition to your tutorial (and Ron Lemen's brief tutorial posted here on CA.org), I've been working with Parramon's Color Theory book and have recently borrowed a copy of Itten's The Art of Color from the library. However, since self-studying such a complex topic is already hard enough, I want to make sure I keep on the right track... so any comments regarding the potential or fundamental problems with Itten's book would be much welcome. Thanks a lot in advance!

[briggsy@ashtons]

S.M.

Sorry for the long delay S.M., but (take note everyone) asking seven questions at once is just asking to be put on hold!

1. "Tonal painting" or "tonal realist painting" refers to painting with the aim of evoking the visual appearance of the subject. I found a concise online definition here:
http://www.chadwooters.com/ARTIST_Phases.html

2. The uniform saturation principle simply means keeping the same kind of light from dark to light and merely increasing its brightness. It's always the underlying relationship when the eye is adapted to the general lighting levels, but it's also always modified by specular reflection of environmental light. In addition to the bounce light that you mention, specular reflection of a bright background on the receding planes would also significantly modify the colour relationships. In addition, by appropriately increasing the brightness and decreasing saturation of the lights you may be able to create the effect of very bright lighting beyond the level of adaptation of the eye.

3. Two factors that can affect saturation relationships in photos are overexposure and consequent "clipping" of colour in the lights, and colour "noise" in shadows.

4. Regarding the red ball, yes I think the situation you describe may result in some sort of yellowish image colour (depending on the relative strength of the components), although the perception would probably still be of a green specular reflection on a red ball.

5. Lab vs RGB modes: Adjustment controls such as "saturation"", "brightness", and "contrast", and the various commands like "desaturate" work on different colour dimensions in the different modes. For example, the "Desaturate" command in Lab mode give you a genuine greyscale version of your image, whereas the same command in RGB mode gives you artificially distorted tonal relationships. In this particular case the Lab version is clearly preferable, but in general it's good to learn how the commands work in all the modes to equip yourself with the full range of capabilities.

6. Human skin is translucent and allows significant subsurface light transport. I think that the saturated colour you are seeing in your photo of your hand results from light being transmitted through the skin instead of being just reflected from it.

7. In Table 10.1 the middle row is obtained by reducing the starting value of 100 according to the inverse square law, and the bottom row is obtained by applying a 0.45 power function (see Poynton Color FAQ (http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html): 4. What is lightness?) to convert these to relative values of HSB "brightness".

If you have any more questions I'll try to get on to them a bit quicker!

[briggsy@ashtons]

bkkm

The real problem with Itten is not so much what is in the book as what isn't. Itten's conception of the scope of colour theory was strongly influenced by the Farbenlehre of Goethe (1810), which was a vitriolic and spectacularly misguided attack on the scientific approach to colour vision pioneered by Newton. Itten did at least admit that Newton was right about the spectrum, but otherwise, like Goethe, he ignored almost every development in our scientific understanding of colour after Newton. For example, like Goethe, he explained afterimages in terms of eye animism (the eye "requires" the complementary and "spontaneously generates" it if it isn't already present), not mentioning the fact that these phenomena had already been (at least partly) explained in terms of changing relative sensitivities of three receptors by Thomas Young in 1807 (and even earlier by Palmer).

A bit like Betty Edwards is for drawing, Itten might arguably be ok as a very first introduction to colour if you know nothing about the subject, but you'll want to get beyond that level as soon as possible. His simplistic eighteenth century colour wheel is ok to communicate the basic idea of the circular dimension of hue, but you'll find that it doesn't actually work for mixing colours on your computer or with your paints, and you'll need different hue circles for each of these situations. The colour sphere he adopts (originally published by Goethe's friend Runge in 1810) is a good introduction to the basic conception of three dimensions of colour forming a space, but again you'll want to go beyond it to the more sophisticated conceptions of Munsell or Arthur Pope to put the conception into practice.

It isn't really Itten's fault, but the continued widespread use of his book as the be all and end all of colour theory, nearly fifty years after it was written, and nearer a hundred after his ideas were formulated, is connected with a widespread and powerful tradition of ignorance in art teaching that refuses to engage with any scientific understanding of colour whatsoever. The scale of this great leap backwards is emphasized when you reflect that in the early twentieth century it was an art teacher, Albert Munsell, who invented the most widely used colour order system in the world.

[Alex Chow]

I keep forgetting this thread exists!

Hey, Briggs and other lurkers. Thanks for this thread. I never got to reading this but when I had a chance, it was truly a land of information.

If you do not mind, I have a few questions.

a) How do you ultimately determine the value relationship between light and shadow in a given environment? I was quite intrigued with the "ball in photo" exercises because I wouldn't know where to start with those. In fact, often my struggle comes from finding the correct contrast in a situation. Things just look out of place...

Does it relate to "Consistency in Relative Brightness" (http://www.huevaluechroma.com/102.php)? My current guess is that all objects in an environment (the relationship between main light and secondary light hitting the shadows) will reduce brightness by a percentage when going light to shadow, and each environment will have a different percentage.

b) Sort of similar to question a), but relate it to saturation. It's not so much a problem in a theoretical white main light-white secondary light situation (since that retains saturation between light and shadow), but what happens in coloured illumination? Often times, I find that I overexaggerate the saturation and hue shifts in coloured illuminated environments. Are there ways to actively make sure this doesn't happen? Are there ways to make sure coloured illumination looks consistent between objects?

c) In this post (http://www.conceptart.org/forums/showpost.php?p=2540227&postcount=132), you've stated that "In addition, by appropriately increasing the brightness and decreasing saturation of the lights you may be able to create the effect of very bright lighting beyond the level of adaptation of the eye".

What is "appropriately"? Often when I decrease the saturation, temperature shifts along with it and, depending on the saturation of the shadows, it will also muddy up the object. Are there methods to retain temperature relationships (warm/cool, cool/warm) when decreasing saturation for this purpose?

Thanks in advance.

[theechoinside]

Whoa... just took a quick look at the site, and damn. Definitely thank you, very useful.

[The Pariano]

Dr. Briggs, This has made me realize that I know absolutely nothing about color( in terms of realistically representing an object).
Firstly, the uniform saturation principle boggles my mind because they images with the half lights having a higher chroma do indeed look more " realistic" to me than the spheres having uniform chroma throughout. I may even be using the wrong word- from what I can decipher from your text, chroma is the extent to which a hue is farthest from grey, correct? and saturation is the purity of the hue? I have a hard time finding the difference between those definitions and I have read that page about 4 times over. Also the image you have of a painting where you attempted to create a more " realistic" sphere of her skin tone seems infinitely less realistic than what I see in the painted image.

Also, related to this, I have always been told that the shadow will be of a complimentary color to that of the light, which you say is not true. Reading your text almost leaves me to question that I see color right at all. This may perhaps make sense, as random internet color tests have told me that I may be partially color blind. I don't really know how trust worthy these are because they diagnose that I am partially red/green color blind and I have never noticed seeing something grey, or of a different color that someone has told me it is actually different.

If you have read all that and still don't know what I'm asking, which I would completely understand- I would like a more simple description of how light , and how progressively less light, affects the perception of a color of an object.

The sight is very informative- if only I could wrap my head around it!

[briggsy@ashtons]

Thanks for the input, The Pariano

The whole site is in need of an update, which I'm going to start posting soon. It won't make it any simpler, but hopefully parts of it will at least be clearer. In particular I'll make it as clear as I can that, while the uniform saturation principle describes the underlying pattern, the final effect is modified by reflections of the environment, and also by the adaptation state of the eye.

The flesh coloured sphere may not be one of my finest efforts, but even so I find it hard to see the portrait as being, say, more easily mistaken for a photograph.

Regarding saturation vs chroma, I'm told that Figure 9.8 on this page helps:
http://www.huevaluechroma.com/093.php

The light in shadow zones typically does appear the complementary color to that of the main light - I'm not sure what I said that made you think I thought otherwise.

Finally, colourblindness exists in all degrees. If the classic Isihara tests indicate a problem that otherwise goes unnoticed, then you probably have only very slightly anomalous vision. They are widely available on the internet, e.g.:
http://colorvisiontesting.com/ishihara.htm
http://www.premlobo.com/eyetest.swf
More sophisticated tests have been developed more recently that pick up some deficiencies that Isihara misses, but I don't have any links offhand.


David

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To anyone in Sydney - I'm giving a public lecture at the Art Gallery of New South Wales this Friday 1-2 pm on "Colour and light in the work of Rupert Bunny", in connection with the Rupert Bunny exhibition. Free, all welcome - please say hi if you come along!

[prufrock27]

This is so helpful! Thanks so much!

[Sharkcellar]

I'm desperately trying to banish the amateurish "chalky" look of my paintings and your website is a boon...inasmuch as I can decipher. I haven't yet been able to posit any rational questions yet about what is perplexing me. I think I will try your spheres in photo environments exercise, I imagine that will help me see what it is that I truly don't understand. Thank you so much for the invaluable resource that is 'The Dimensions of Colour'.

[D.C.]

Although a tough read, the site is the best resource on colour I could find as a beginner. After re-reading things and making notes, things are starting to sink in. I don't know if you still reply to questions, but I would appreciate it if you could point out any errors in my understanding of specular/diffuse reflections:

1. Every surface can be considered as reflecting diffuse and specular light, where the relative amount of each is dependent on the material of the surface.
Diffuse reflection of light gives the object its form/colour, specular reflection of light is an image of a light source.

2. Diffuse reflection of light by the environment (or any object) is a light source for another object (where that object again reflects that light both as diffuse and specular).

3. Specular reflection results from light that is unchanged by the object and is an ADDITIVE mixture of the colour of the reflected light source and the colour of the reflected diffuse light from the specular's location (following the angle rule).

Considering the picture below (numbers correspond to brightness levels gathered using color picker).
The highlight is very bright, thus drowning the diffuse reflection at that location and keeping the colour of the light source.
However the diffuse reflection of light by the white paper is a weaker light source, so the colour of its specular reflection is an additive mix of diffuse reflection of light from main light source (light side) + diffuse reflection of light from white paper + specular reflection of light from white paper.
The diffuse reflection of light from the white paper will be strongest close to the paper and diminish as the surface moves away from it in an upward direction. Thus depending on the relative contributions of these three components, the colour of the specular reflection of light from the white paper will vary across the surface of the sphere and will not be same as the colour of its source (the white paper).

957685
Image source:www.huevaluechroma.com

QUESTION 1: Why is the brightness of the paper lower at the back of the sphere compared to the front (80+ vs 65)?
(front = sunlight through a window, back = ambient light in the room perhaps?)

QUESTION 2: Specular reflection of light from the cast shadow is the same colour as the cast shadow? (as diffuse reflection of light from the cast shadow should be quite weak?(originating as diffuse reflection of light from ambient light))

QUESTION 3: You stated that the location of the highlight "is always seen somewhere on the line between the point facing the light source and the visual center of the sphere". With the visual centre do you you mean the actual center of the sphere (see picture)?

957709

[revenebo]

briggsy@ashtons Your website was incredibily helpful to me, quite difficult actually but it made me realize the complexity of the subject and it gave me some technical parameters to evaluate and choose colors.
I'm now trying to merge informations from your site with those from Jason Manley's color theory lesson, who has a less technical and more emotional approach.
Any opinion about if and how the two sources can complement each other?


dragonfury where did you take that picture? That place looks familiar to me... Is it Ferrara??

[briggsy@ashtons]

Although a tough read, the site is the best resource on colour I could find as a beginner. After re-reading things and making notes, things are starting to sink in. I don't know if you still reply to questions, but I would appreciate it if you could point out any errors in my understanding of specular/diffuse reflections:

1. Every surface can be considered as reflecting diffuse and specular light, where the relative amount of each is dependent on the material of the surface.
Diffuse reflection of light gives the object its form/colour, specular reflection of light is an image of a light source.

2. Diffuse reflection of light by the environment (or any object) is a light source for another object (where that object again reflects that light both as diffuse and specular).

3. Specular reflection results from light that is unchanged by the object and is an ADDITIVE mixture of the colour of the reflected light source and the colour of the reflected diffuse light from the specular's location (following the angle rule).

Considering the picture below (numbers correspond to brightness levels gathered using color picker).
The highlight is very bright, thus drowning the diffuse reflection at that location and keeping the colour of the light source.
However the diffuse reflection of light by the white paper is a weaker light source, so the colour of its specular reflection is an additive mix of diffuse reflection of light from main light source (light side) + diffuse reflection of light from white paper + specular reflection of light from white paper.
The diffuse reflection of light from the white paper will be strongest close to the paper and diminish as the surface moves away from it in an upward direction. Thus depending on the relative contributions of these three components, the colour of the specular reflection of light from the white paper will vary across the surface of the sphere and will not be same as the colour of its source (the white paper).

Hi D.C.

You are a bit of a master of the tough read yourself, but that all sounds like you're on the right track, as long as you keep in mind that the phrase "the colour of the specular reflection" has two possible meanings that you need to stay clear about: it might mean either (A) the overall colour of an area where the specular reflection is the most conspicuous component (as in that last sentence), or (B) the colour of the specular reflection seen as a component of the appearance at that point.


QUESTION 1: Why is the brightness of the paper lower at the back of the sphere compared to the front (80+ vs 65)?
(front = sunlight through a window, back = ambient light in the room perhaps?)

QUESTION 2: Specular reflection of light from the cast shadow is the same colour as the cast shadow? (as diffuse reflection of light from the cast shadow should be quite weak?(originating as diffuse reflection of light from ambient light))

QUESTION 3: You stated that the location of the highlight "is always seen somewhere on the line between the point facing the light source and the visual center of the sphere". With the visual centre do you you mean the actual center of the sphere (see picture)?




1. It's just that the surface to the left of the sphere is further from the main light source.

2. Yes, if you mean the colour of the specular reflection in sense B above; no, if you mean it in sense A (if it was a red ball, for example, there would be enough light reflected from the tabletop alone to show the local colour in this area)

3. I was thinking of the centre of the (circular) visual shape of the sphere in the picture plane, though of course this lines up with the physical centre of the sphere.

Hope that helps!

[briggsy@ashtons]

Hi revenebo

Very glad you like the site! I'm afraid I didn't see Jason's colour theory lesson, which by all accounts was excellent, but if there any particular issue that is confusing you I'm happy to try to help.

[D.C.]

Thanks briggsy@ashtons for your reply. You're right that the wording of my post was quite confusing, I had trouble understanding it after re-reading it again :p, sorry about that.

1. It's just that the surface to the left of the sphere is further from the main light source.

Is this because the rays of the main light source are not parallel to each other (light source is not a point light source)? As I understand it, the brightness of a surface facing a light source with parallel rays (like the sun) should be uniform across that surface and vary depending at what angle that surface is facing the light source.
Of course if the surface is big and its farthest point facing the light source is much farther than its closest point to the light source a noticeable difference would occur?

2. Yes, if you mean the colour of the specular reflection in sense B above; no, if you mean it in sense A (if it was a red ball, for example, there would be enough light reflected from the tabletop alone to show the local colour in this area)

Sorry, yeah I meant B. I was actually thinking about how the brightness varied in that region and what influenced it.

Generally, how does the total light reflected of other objects behave as a light source? For example, in your picture, will the diffuse reflection from white paper (tabletop) illuminate the sphere uniformly, will it decrease as the surface turns away from the paper (like with a regular light source), is it strongest closest to the paper? Also does specular light reflected from an object contribute to illumination of other objects (with specular light I mean the part of light reflected at any point on a surface that follows the angle rule).

These questions arose when I tried painting a simple red cube in photoshop. I couldn't figure out how the ground (white canvas, e.g. white paper) would influence the lighting of the cube and how a potential specular reflection of the ground (white canvas) would look like: uniform in brightness across the surface of the cube or decreasing in brightness from bottom towards the top of the cube.

[Elwell]

Of course if the surface is big and its farthest point facing the light source is much farther than its closest point to the light source a noticeable difference would occur?

That's it. The intensity of light falls off predictably, according to the inverse square law (http://en.wikipedia.org/wiki/Inverse-square_law). With a small light source close to an object, this gradation is very evident.

[briggsy@ashtons]

Yes, the main effect is the roughly inverse square fall-off of light flux with distance; but the decreasing angle of incidence of the light rays to the surface, which I think D.C. was suggesting as the explanation, is a distinct though secondary factor.

D.C., to answer the second part of your question you need to understand that the inverse square law applies precisely only to a point source of light; with larger light sources the fall-off is slower, and at the theoretical extreme of a wall of light extending infinitely in all directions, it turns out that there isn't any fall-off of light with distance. (You can demonstrate this by bringing up a white page on your monitor in a darkened room, and observing the minimal fall-off of light on objects up to a few cm from the screen). So you would expect little fall-off of light with distance from the table top on the vertical faces of your cube, whereas you do see it on objects like the sphere that curve away from facing the table top.

[revenebo]

briggsy@ashtons no issue in particular, it's more about a general sense of disorientation between a "mathematical" approach and an emotional approach based on eyeballing, taste and experience given by exercise.
I've seen many great artworks, both traditional and digital, that are quite off if compared to the mechanics of light and color you explained and yet they look awesome. In particular it looks like saturation of colors is subject to personal taste and choices.
I usually try to stick to your instruction when painting (digitally) but, assuming I apply them correctly, I feel that sometimes the result is a little bit boring, in particular in works from imagination. Can the technical parameters be stretched or overlooked in order to convey mood and emotions without screwing up a painting? To what extent?

PS I know it's a vague question but as I said I'm a bit puzzled by all the info about color theory I'm assimilating...

[briggsy@ashtons]

I think its's a valid question. To me, theory is not there to tell you what to do, but to help you to do what you want to do. Take anatomy for example - just because you understand anatomy, it doesn't mean you can only draw "boring" accurately-proportioned humans. Artists who understand anatomy can draw better monsters, aliens or even spaceships than those who don't, because they can use their knowledge in the service of their imagination and emotion.

That's how it should be with light and colour. Certainly if you are trying to get a vivid sense of lighting and atmosphere, whether from life or from the imagination, then there are some relationships that you need to get right. But you are free to play with these relationships creatively as well as to report them objectively. To give two examples that are only just a beginning, you can obtain very beautiful effects by accurately transposing those relationships to a very limited tonal and/or colour range, or by transposing the shadow colours to suggest the effect of simultaneous contrast. Obviously this is a step beyond the basic theory, not a step short of it.

By the way, I'm not at all opposed to eyeballing. As I say somewhere on the site, I think eyeballing rather than mathematical precision is generally sufficient for painting if you understand the relationships involved. All of the spheres in my diagrams for the site were painted by eyeballing the fall-off of light rather than mathematically calculating it.

[melviso]

Hi,

I just wanna say I have read the colour theory stuff on your website.It is a little confusing to assimilate all those stuff but I am slowly getting it and it has improved my knowledge on colour.But I am a little confused cause I am normally into 3d stuff.All I do is model stuff,add the texture and set up my light,hit the render button and voila!!!I get my artwork.
Let me see if I am getting this right:
Lets say I have a sphere and I decided to give it say a red colour,towards the light,you will probably have 4 tones:shaded part(desaturated)dark red----half light(lighter dark red slightly desaturated)---full light(saturated red)----highlight(white).

Right?I understand some people do grayscale but that ain't working for me.I would have drawn a sphere but I am too busy to do so.Wonderful thread,keep it up,briggsy@ashtons.

[millerlandscapes]

First post on this wonderful site! I just read thru the above color theory principles and added more insight to my rudimentary understanding. Thanks for all the input!

[Virg]

Hey Doc,
I've previously asked you questions, and you always been a source of enlightement :)
Though I understand the presence of diffuse and specular reflection on an object, im still trying to understand how light is physically reacting in some cases. Lights is either bounced or absorbed as I understand, however i still dont understand why I see some of the things i see.

The main exemple i could give you, is a black, polished, bowling ball, with bright white specular on it.
So the black comes from most of the light being absorbed by the ball and thus not a lot of light bounce back to the eye.. but you got that specular reflection that does contain white, or any color the environement could have. I think I understand why different surface have different speculars ( Prometheus tutorials explains it very weel, and makes a lot of sense )

But the question here is why can we see a bright specular reflection on a dark object, if photons are supposed to be absorbed almost competely, and not bounced back on dark objects?

If specular reflections is created by the object having a coating making everything shiny, shouldnt it completely override the underlying diffuse reflection ?

I Hope these questions make some sense :)
Thanks for taking time to read this.

[briggsy@ashtons]

Excellent question Virg.

The thing that Prometheus' tutorial doesn't explain is that specular and diffuse reflection are two distinct processes that occur simultaneously on most objects. The specular (or "interface") reflection, which generally remains the colour of the light source, is thought to consist of light that bounces at the surface. The diffuse (or "body") reflection is light that penetrates the surface and re-emerges more or less equally in all directions, often coloured by the object. For example if you look at an orange you will see the light-source coloured specular reflection as well as the orange-coloured diffuse reflection. An uneven surface makes the specular reflection fuzzy, but this fuzzy specular is an entirely different thing to the diffuse or body reflection.

So in your polished black ball, the part of the light that penetrates the surface is largely absorbed, but the part of the light that doesn't penetrate the surface is not affected, and produces the usual interface reflection that you see whatever the colour of the ball.

[Virg]

That makes a lot of sense, thank you very much for the answer !

[Virg]

Hello again Mr.briggsy
I'm still seeking some answers or thoughts on a specific aspect of colors, and again, im asking for your precious help. I hope im not getting annoying ,im thinking others could read this and wanting to ask similars questions, so why not ask :)

This question concern mostly , color harmony , not color harmony in sense of emotion or psychological effect that specific colors are supposed to create to the viewer, but color harmony, as a ''rule'' that defines the amount of temperature shift that occur between light and shadow in a specific light situation.

Your probably seeing my question coming but here it is.
How do you make sure, all the colors in your picture obey to the same color harmony?

Im painting mostly digitally, and use the HSB color picker in photoshop, and your 3d space color system made a lot of sense to me, be cause it is something logical to me, where i can define extremes, a point A and a point B ( A=light B=shadow ) and can imply concious decision of colors and not just random color guessing.

So, as I understand, and tried to applied so far, different hues, either desaturate or get more saturated depending of the location of the color of the light source on the color wheel.

So how do you make sure all your colors have the same diagonal 3d color space , in a specific light situation. And properly place A and B for all colors?

I have know idea how traditional painter manage to do this, my guess is they use the same amount of pigment in each color equally to change their temperature equally.

Thanks so much for sharing all your expertise ! And sorry for my amateur english.

[Elwell]

I have know idea how traditional painter manage to do this, my guess is they use the same amount of pigment in each color equally to change their temperature equally.
Actually, because of the complexities of pigment, that won't work. Most traditional painters do it the same way most digital painters do it: by eye.

[briggsy@ashtons]

Virg

Paint the (coloured) light and shade pattern that would be caused by each light source alone as a separate layer, then overlay these layers in LINEAR DODGE mode over a black background. Vary the strength of each light source by varying the opacity of its layer, and try to keep the total brightness down so that nothing "clips" against maximum brightness (B=100). You can apply the local colours of objects using a MULTIPLY layer on the top. If that all makes sense I'd love to see what you come up with!

There's no equivalent procedure for traditional paints, so if anyone is not satisfied with eyeballing with those I'd suggest working from a digital colour study that you make first, using this method.

[Virg]

hello, thanks for your replies Elwell And Briggsy.

Briggsy: I started to explore various light situation using the technique you mentionned in your last post. Its really quite interesting. Im trying to get an easier understanding and see if theres reoccuring patterns as the result of the mixing of the local hue of the object in relationship with the hue of the lightsource. At which point of the wheel will a color start decreasing more in S than in H.
I just had a couple of questions, maybe you can help me.
I noticed a difference between the blending modes in photoshop CS vs Photoshop CS4
in CS4 the Linear Dodge is also named ( additive ) and seems to do proper additive mixing.
But the Linear Dodge in Photoshop CS seems to gives different result depending of which layer is on top. I tried the Screen blending mode and it seems to do proper additice blending ??

I'll show you what I come up with, ill probably post some stuff in my sketchbook and share you the link so you can give me some feedback :) I dont want to spam your thread with pictures.

Thanks !

[briggsy@ashtons]

Thanks Virg. One tip for your experiments: avoid fully saturated colours (S = 100) for your objects and lightsources, as these don't exist in nature, and can give you some strange results.

I don't know why CS would behave differently to CS4. You're not in a different Image Mode in CS are you? Linear Dodge is exactly additive while Screen Mode is quasi-additive in a way that is less prone to clipping against the limits of the RGB gamut.

I'll keep an eye on your sketchbook but please feel free to post anything you want here.

[briggsy@ashtons]

If you've looked at The Dimensions of Colour, it won't surprise you that I'm very pleased that James Gurney's new book "doesn't contain recipes for mixing colours or step by step painting procedures" (Color and Light, p. 9). Much much better, it shows how an artist of his calibre thinks about colour and light.

Any single book on this subject can only be an introduction, but what an introduction this is! The book is very generously illustrated with his own works, plus those of many of his favourite past masters. These images fully justify their place by showing us what it is possible to achieve, especially from the imagination, by those who are willing to go beyond a simplistic approach to "colour theory".

Gurney admits that when he set out to write the book, he himself at first underestimated the complexity of the subject (p. 222), and that he had to research aspects of physics and visual perception more deeply than he had previously. I suspect it's no coincidence that some of his most perfectly realized imaginative paintings, including the sleeping dinosaur on the cover and Titanoboa on p. 165, are from 2009.

The modern books and websites recommended by Gurney for further reading (pp. 220-1) will probably be the most accessible resources for the next steps in your explorations, but it may be worth mentioning that many of the older texts he lists are available for free download or reading online:

Chevreul, Michel Eugène, 1839. The principles of harmony and contrast of colours ... (1860 Eng. tr. by Charles Martel).
http://books.google.com/books?id=LIMOAAAAQAAJ

Goethe, Johann Wolfgang, 1810. Goethe's Theory of Colours (partial English tr. of Zur Farbenlehre by Eastlake, 1840).
http://www.archive.org/details/goethestheoryco00goetgoog
http://edoc.hu-berlin.de/ebind/hdok/H71_GoetheFarb/XML/index.xml?part=thumb (German edn plates)

Guptill, Arthur L., 1935. Color in sketching and rendering.
http://hdl.handle.net/2027/mdp.39015009248579 (read online)

Hatt, J.Arthur H., 1908. The colorist.
http://books.google.com.au/books?id=3f_VAAAAMAAJ (US access only)

Hawthorne, Charles Webster, 1938. Hawthorne on painting.
http://www.archive.org/details/hawthorneonpaint00hawt (Daisy/borrow)
http://www.archive.org/details/collectionofnote00hawt (NEW LINK WITH PDF)

Minnaert, Arcel G.J., 1954. The nature of light and colour in the open air.
http://hdl.handle.net/2027/mdp.39015065972997 (read online)

Munsell, Albert H. 1905. A color notation. An illustrated system defining all colors and their relations by measured scales of hue, value, and chroma.
http://www.archive.org/details/acolornotation00munsgoog (1st edn)
http://www.archive.org/details/colornotation00muns (5th edn, 1919)

Munsell, Albert H. 1913. Color balance illustrated.
http://www.archive.org/details/colorbalanceillustrated00munsiala

Pollock, Montagu, 1903. Light and water, a study of reflexion and colour in river, lake, and sea.
http://www.archive.org/details/lightwaterstudyo00polluoft

Rood, Ogden, 1879. Modern chromatics, with applications to art and industry.
http://www.archive.org/details/cu31924031167889

Ross, Deman Waldo, 1912. On painting and drawing.
http://www.archive.org/details/ondrawingandpai04rossgoog

Ruskin, John, 1843. Modern painters, Volume 1.
http://www.archive.org/details/modernpainters01rusk (1888 edn)

Ruskin, John, 1857. The elements of drawing. With 8 illustrations drawn by the author.
http://www.archive.org/details/elementsofdraw00ruskuoft (1920? edn)

I'm quite certain that Color and Light will mark the beginning of the end for the simplistic approach to color that still predominates in art teaching. If you are an art or design student, get this book, study it, and then pester your teachers ceaselessly until THEY study it.

At the moment you can buy Color and Light from Better World Books for only US$15.98, with free shipping in the US and only US$3.97 worldwide.
http://www.betterworldbooks.com/color-and-light-id-0740797719.aspx

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Edit: James Gurney's comment on Dimensions of Colour!

"David Briggs is none other than the mastermind behind the website "Dimensions of Color". It’s one of the best resources on light and color on the Internet. I owe much of what I’ve learned on the topic to Mr. Briggs. ..."

- James Gurney
http://gurneyjourney.blogspot.com/2010/12/pester-your-teachers.html

[jams]

I won't be posting any art here for awhile, because I have nothing worth showing yet, but I just joined the forum to give briggsy a huge "thank you!"
I've never seen color explained so well or so in-depth. Seriously, it seems like nobody knows what the hell they're talking about when it comes to color, so finding this here is awesome. Looking forward to finally learning how color actually works over the next few days. This is gonna change the way I paint forever!

Thanks again, briggsy! =)

[guidosalimbeni]

Hi,
i'm new to the forum as a registered member but it has been a while that i'm following the forum and this thread specially. Thankyou very much for all the info and the superb website Brigg!!

I thought i was in the right track of learning the color theory you so well explained and i came into this page on the book called "painting light - the hidden techniques of the impressionists" that i attch..

My question is that : under 2 sources of illumination which one is red and the other is pale yellow (as in the last ill of the image) the cast shadow "of" the red source light thend toward green... I thought this was created by the princeple of simultaneous contrast and that can be seen only by the human eye and not by a camera.. now i'm a bit confused.. i tried to figure out why the shadow looks greenish in this shadow but i could not find a solution.. can you give some advise? thanks

[draw]

I think the Gurney works look like paintings of photographs whereas something like a claude lorraine although not as 'coloured' looks like a painting of 'life'.

IMO All the colour theory in the world will not produce a 'life'like atmospheric relationship if its not painted without a sound gestalt tonal conception and for me ends up with that well entrenched copying photographic look. For me that is the difference between illustration and art.

If there are some examples to the contrary I would love to see the contrast.

[briggsy@ashtons]

Well guidosalimbeni, you're looking at the image with a human eye (I assume), so why would'nt you expect to see "simultaneous contrast"? The image colours of the shadows on the right are much the same in all three pictures - they're all a very low-chroma orange grey (check for yourself in Photoshop!). The greenish hue we see in the bottom right one could be said to be the result of "simultaneous contrast", although I think that term is used for more than one kind of effect. In cases like this I think it's the automatic color correction filter in our brains coming up with a slightly wrong answer. (The shadow is less red than everything else, so our brains "assign" a slightly greenish colour to it).

Welcome aboard, by the way, to you and jams - Hope to hear from you guys here often!

[briggsy@ashtons]

I'm scratching my head over a few things in that, draw, but I guess the main point is that I would have thought that the ultimate aim of undestanding colour (for some painters anyway) would be to obtain a "sound gestalt tonal conception". I'm wondering what you think of Tim Miller (http://www.rockleystudio.com.au/gallery/recentthumbs.html), for example, who we both know has an intense interest in understanding colour and light.

[guidosalimbeni]

i checked in photoshop!! thankyou very much.. guido

[briggsy@ashtons]

I posted this little tutorial yesterday in another thread for someone who was having trouble with making up the effect of coloured lighting, and thought I'd post it here as well, so it won't sink out of sight.

With Linear Dodge you can easily "clip" the upper limit of your RGB gamut and start getting strange results; if that happens you just need to keep your colours a bit darker.

Bear in mind that the procedure applies directly only to this simple situation, and will lead you into trouble if you apply it blindly to more complex situations. Try instead to understand the reasons for each step.

Also bear in mind always that these tips are meant as aids to getting physically correct colour relationships when that is what you are after, not orders to get those relationships. Plenty of lovely painting styles do not use "correct" colour and lighting, or correct perspective or anatomy, for that matter.

[draw]

Thanks for this David... a very effective tutorial :)

[spinor]

Dear Dr. Briggs,

Thank you so much for your invaluable website! have been reading it the whole days and i feel like i just had a new birth! I've been painting digitally for a while but always confused by how to pick up colors. Now you made everything so clear to me. Thousand thanks!!!

Xi

[bbshrmn]

hi and thank you again for taking the time to answer these questions. as per your suggestion in the email, i will post them here so everyone can benefit. these were the major points of confusion that i forgot to ask.

in faber birren's book 'creative color' he mentions, "the most beautiful of all formal color gradations that is known" as the "uniform chroma scale-which have the same apparent color content but which differ in lightness and darkness." is that in fact, the same thing as your described "uniform saturation shading series?" (if its not, how are they related as to what happens in nature?)

if so, he also suggests an "easy" method of making one of these scales by mixing a tint, a tone, and a shade of the same hue and then intermixing them for in-between steps. if this is the case it raises questions.

1. doesn't much care still need to be taken with the tint, tone and shade to ensure they are constant in color saturation amongst themselves? this doesnt just happen naturally, right?
2. assuming you have step 1(question 1) done correct, is he implying that all in-between steps will then be balanced, saturation wise, inherently? if so, by that logic, couldnt i do away with mixing the tone all together and just use the tint and the shade to make the tone? and if not then it would seem this whole approach falls apart a bit.
3. lastly, if i use red, add black and then a bit more red again to bring it back on the saturation line, couldnt i have just used less black to begin with or is it not the same thing? how does this affect step one?

ok, sorry, i guess there is one other thing as well. so what is the proof/evidence that this is actually true and that saturation doesnt decrease or increase in the shadows? im guessing the shoddy results of just color sampling images isnt enough.

thank you thank you, very much appreciated.

[briggsy@ashtons]

You're welcome, draw and spinor!

Thanks for taking the trouble, Bob. They're all very good questions.

Birren's "uniform chroma scales"

in faber birren's book 'creative color' he mentions, "the most beautiful of all formal color gradations that is known" as the "uniform chroma scale-which have the same apparent color content but which differ in lightness and darkness." is that in fact, the same thing as your described "uniform saturation shading series?" (if its not, how are they related as to what happens in nature?)

What Birren calls "uniform chroma scales" are the perceptual (or logarithmic) "isochromes" of the Ostwald system, which is not really used any more. Ostwald's perceptual isochromes were in theory lines of uniform saturation in my terminology, though in practice (in the Ostwald colour atlas) they seem to me to be somewhere between lines of uniform saturation and lines of uniform chroma.


Mixing a shading series


1. doesn't much care still need to be taken with the tint, tone and shade to ensure they are constant in color saturation amongst themselves? this doesnt just happen naturally, right?
2. assuming you have step 1(question 1) done correct, is he implying that all in-between steps will then be balanced, saturation wise, inherently? if so, by that logic, couldnt i do away with mixing the tone all together and just use the tint and the shade to make the tone? and if not then it would seem this whole approach falls apart a bit.
3. lastly, if i use red, add black and then a bit more red again to bring it back on the saturation line, couldnt i have just used less black to begin with or is it not the same thing? how does this affect step one?

1. Of course, and of course.
2. Mixtures between successive steps tend to drift off the uniform saturation line, so the steps should be kept close together.
3. if you are shading red+black+white by adding black, you correct the saturation with red (not red+black+white). If you are shading a pure opaque red with black, there is less of a tendency for the saturation to drop, but if it does you could boost the saturation with a transparent red. Adding some of the opaque red would of course just take you back in the direction you came from).


Uniform-saturation series and illumination

ok, sorry, i guess there is one other thing as well. so what is the proof/evidence that this is actually true and that saturation doesnt decrease or increase in the shadows? im guessing the shoddy results of just color sampling images isnt enough.

I'll answer that by showing you some uniform saturation series and asking what you see. The main rectangle of the attached jpg simply shows seven uniform saturation series (one achromatic). We automatically see it as an image of uniform object colours under varying illumination. To me this simple demonstration neatly proves that
(1) our visual system recognizes relationships of uniform saturation in the visual field, and
(2) it uses these relationships in its amazing capacity to separate effects of illumination from effects of object colour (object-colour constancy).

[bbshrmn]

I'll answer that by showing you some uniform saturation series and asking what you see. The main rectangle of the attached jpg simply shows seven uniform saturation series (one achromatic). We automatically see it as an image of uniform object colours under varying illumination. To me this simple demonstration neatly proves that
(1) our visual system recognizes relationships of uniform saturation in the visual field, and
(2) it uses these relationships in its amazing capacity to separate effects of illumination from effects of object colour (object-colour constancy).

thanks for the quick reply.

... but does this example, starting out with some colors that arent so crisp and saturated to begin with, not work just as well? this reads very natural and as uniform object colors also, no?

[Elwell]

What Birren calls "uniform chroma scales" are the perceptual (or logarithmic) "isochromes" of the Ostwald system, which is not really used any more.

And thank goodness for that! Creative Color is overall a good book, but Birren's big flaw was his attachment to Ostwald.

[briggsy@ashtons]

... but does this example, starting out with some colors that arent so crisp and saturated to begin with, not work just as well? this reads very natural and as uniform object colors also, no?

Not as natural as when you shade the same colours keeping the saturation uniform:

[bbshrmn]

Not as natural as when you shade the same colours keeping the saturation uniform:

yeah, it appears so. given that its the same illumination range, your colors definitely appear to be passing into the darkness, where mine feel to be coming out of it a bit. thank you thats helpful.

i was also trying to color sample some HDR images (http://www.cis.rit.edu/fairchild/HDRPS/HDRthumbs.html) to see what kind of results i would get since they are supposed to be closer to how we perceive reality and i did find mostly uniform saturation throughout them. that said, the saturation was often at 100%. if you will accept the loose terms, why the 'blow out' and are these HDR images better for us to study, from a 'reality standpoint'? are they just constantly pushing the outer limits of the technologies involved, how does this relate to paint?

thank you.

[briggsy@ashtons]

Sorry, Bob, I'm a bit vague on the details of HDR image processing at the moment, so I'll have to pass on those four(!) new questions for now. A digital camera is in a way a kind of inexpensive spectrophotometer, and you can very usefully investigate some things using digital photos, but I'd be much more inclined to use a straightforward image, aware of its limitations, than one that is higly manipulated in a way I don't fully understand.

[bbshrmn]

ok, thank you and sorry for the bombardment. so much to know and so little time. :)

[alvinalbert60]

It's really hard to find this kind of websites on the net so thanks a lot for useful information...

[Jie Kageshinzo]

I decided to go back to the basics and learn as much as I can about value, saturation and hue, and I would just like to say that, as much as how your site gave me a headache trying to understand it on my own, thanks so much for such an invaluable resource Briggsy.

As of the moment, I'm alternating between Gnomon Workshop's Light and Color and your website for studying, and already, my brain is trying to understand the difference between chroma and saturation, and I feel my brain bleeding. I'll continue my reading and studying and hopefully, once I get familiar with the technical aspects of the subject, everything will be that much clearer for me.

Thanks!

[briggsy@ashtons]

Everything about colour is more complicated than many people assume, so a little bit of bleeding is probably a good sign! Saturation especially is a word that requires caution, because it has several different meanings, which people using the word are often not conscious of.

Some people use the word "saturation" for the purity of colours of surfaces, with these colours being considered as mixtures of white, "pure colour", and black, and saturation as the proportion of the "pure colour" component in the mix. People who say that chroma is "very similar" to saturation may simply be confused, but they may also be using saturation in this sense, which in effect means relative chroma - i.e. chroma as a percentage of the chroma of the "pure colour". This concept of "pure colour" is very problematic in relation to surfaces, however, so the open ended scale of chroma is much better.

In Photoshop, saturation is the colour purity of the light that is emitted from the screen. Any light can be considered to be a mixture of a certain percentage of white light, plus coloured light: saturation in this sense is simply one minus the proportion of white light. I use saturation in this second sense, as explained on this page:
http://www.huevaluechroma.com/093.php

Colours like B and C in Figure 9.8 on that page have low chroma, and low saturation in the first sense, because as surface colours they contain a lot of black, but they have high saturation in the second sense, because the light given off is pure red (only the red phosphors are glowing).

Not sure if that will help or not, but anyway a close study of the figure I just mentioned usually seems to get the idea across.

[Valentino]

I'd like to pose a technical question. I am quite familiar with the color theory in general (we had that class back at Academy), and rules and guidelines in particular, yet there are some instances in which I am not 100% certain about the correct procedure.

For instance, one of those guidelines is that the lightest dark is darker than the darkest light. (It is not always valid. I mean - it only applies to certain kinds of light under certain conditions. In overcast light, such rules do not apply. Even in sunlight, a very light ground surface can significantly raise shadow values.)

What I'd like to know is how one shoud draw an area in light which local hue is equally dark or darker than the shadow? Take an apple for instance (or people with really ruddy cheeks). Apple may be yellow/green in hue, appearing rather high value in light, but there is large dark red spot which is partially in light and partially in shadow. That intense, dark red is of equal value as adjacent shadow. If one draws it as he sees it, the drawing may look somewhat odd; the apple will appear flat with oddly looking shadow. I mean - form shadow will go nicely around the form, creating the illusion of roundness, but the shape of adjacent red spot of equal value will confuse the viewer. What one should do in that case?

Should one neglect what he sees in order to create a convincing illusion of form? Should he draw the mentioned dark spot (or say, ruddy cheeks) lighter than it appears, in order to prevent merging it with the shape of the shadow ?

[briggsy@ashtons]

I'm really glad you brought this up Valentino, because this particular piece of advice is doled out far too often on these forums. It's not just that it's wrong factually, it's also very bad teaching to hand out simplistic "rules" instead of encouraging analysis and understanding.

You're perfectly correct that the rule only applies under certain conditions. The brightness of any point is the brightness of the illumination multiplied by the reflectance of the surface. It should be clear from this diagram that the rule can not possibly hold if there are dark and light local colours involved, unless the contrast between the illumination in the light and in the shadow is very high. If the rule has any validity it is as a statement of aesthetic preference, not physical fact.

http://www.huevaluechroma.com/pics/10-4a.jpg

It would be better to say "Always make your lighting so contrasty that the lightest shadow is darker than the darkest light". At least that would make the limitations of the "rule" more obvious.

I don't agree that painting your subject as it appears, ignoring the rule, will make it "appear flat" or create an "oddly looking shadow". All it will do is cause the pattern of lights and darks in your picture to differ a little from the pattern of light and shadow. That's it!

[Valentino]

Thanks for the reply. I'd be grateful if you or someone else could address the second question I posed:
What should one do if he/she has to draw or paint the area (say - ruddy cheeks or dark spots on an apple) that has equal local value (in light) as adjacent shadow. Should one keep its value (in light) equal as the value of shadow?

[briggsy@ashtons]

Sorry if I wasn't clear, my answer was: ignore the rule and paint it as it is - it shouldn't confuse anyone.

[Pavel Sokov]

I just discovered this thread now! I am going to read the shit out of this website!

[briggsy@ashtons]

Infrastructure Migration

The Dimensions of Colour website will go offline sometime very soon because of an infrastructure migration at ibiblio, so if you find you can't get on, just give it 24 hours and it should be back.

@Pavel. Great, mate, and drop by again if you have any questions or comments.

[briggsy@ashtons]

In case anyone reading is from Brisbane, just thought I should mention that Atelier Art Classes (http://atelierartclasses.squarespace.com) is flying me up in April for an intensive weekend colour theory workshop on the 16th-17th - details are on their website (http://atelierartclasses.squarespace.com). In any case I strongly recommend that you check out the classes at their new studio. The teachers, including Ashtons wunderkind Ryan Daffurn, are all excellent, and they regularly conduct workshops with visiting artists. It's really great to see a school specializing in serious art instruction is now established in my home town.

[grapholic]

i have read the dimension of color by brigg, and i say that is the most superb color theory i ever know.
and so sadly, i'm chinese indonesian, and my english is very bad... so i hav to read it several time just for one page. maybe now i'm lost nowhere.
the one that bothering me is the addictive and subtractive complimentary.... i just confuse when we used that... is the addictive for digital media, and subtractive is for traditional media? coz i find it hard to apply for my painting.

the other was the R/G vs Y/B formula... i know how the formula goes by looking in the attached SWF file, and to be honest that was incredible. but somehow i lost why and when to apply the formula.

would you please explain in more simply way for me? sorry of being annoying. but i really2 admire your color theory.

[grapholic]

i always wanna paint a pale skin and low saturation skin, coz i saw the other artist can paint success of pale skin and low saturation environment and the painting doesnt strange and flat. but somehow i ended with very flat tone... what could be my problem?

maybe a link to my portfolio can explain what i mean
grapholic.deviantart.com.
rokai.

really looking forward to hear the solution from you briggs. the website of yours is really2 make my day.

[Saurabhinator]

Colour selection has been something which really bothered me, this site is exactly what I have been looking for.
Much thanks for creating it.

For a newbie like me, it is rather intimidating but im going to read through! :)

[AirCoaster]

Totally amazing Mr Briggs, and I say that after reading only a particle of the whole of your research article. The key thing for me is that you have not only answered some very relative questions about color I have had since childhood, I am now 61 years of age, and I am learning some new aspects of color that make very good sense in my mind. I continue to read, a slow reader I am..... : )).

Thank you very much for the research and the article, amazing stuff for sure.

John

[PS Zant]

hello brigssy you invited me to post some points of trouble I have with color. I never worked alot with color always afraid to use it.

First of all I just have problems with color choice in general.
I think I have the biggest problem with which color to choose when it goes in to the shadow or light. I used to pick just a darker or lighter tone.

here is an example of a painting I made and post in the wip thread. I applied the suggestions and comments I got but I dont understand the why.

http://www.conceptart.org/forums/showthread.php?t=224677

For example I would never make up on my own to use purple and violet colors for the shadow of the red dress. I want to understand why to choose that color.

I loved to have some exercises that can help me with this and color choice/harmony in general.

Hope this was what you suggest to post here. thanks again for the invite.

[briggsy@ashtons]

PS Zant, the only valid reason to make the dress a little bluer in the shadow is if the light influencing the shadow area is bluer, in which case you would need to make everything else bluer in the shadow by just the right amount to get a consistent visual effect. Another problem in your later versions is that you made the shadow colour less saturated, which makes it hard to see the material as being the same red object colour as it is in the light. There was nothing inherently wrong with your idea of just making the shadow colour darker (keeping the saturation the same), though you may have gone too dark in your first attempt (see below).

The most important component of colour is value, and that was your biggest problem. If you compare each of your shadow colours with the colour of the same material in the light, sometimes they are much darker, sometimes only a little darker, even comparing shadow surfaces facing exactly the same direction. You need to make these contrasts more consistent to create the effect of a consistent illumination.

I'll have a think about some practical exercises but in the meantime start working through The Dimensions of Colour if you haven't already. You may find the website easier going after you've read the James Gurney book you just ordered, as it's a very good first introduction to an informed approach to colour.


grapholic - very sorry I missed your questions when they came in. If you're still around I'll work on some answers as soon as I have some time.

[XxMikaruxX]

Hi Everyone! This is pretty much a copy paste from an Art Discussion post I made, but I was directed here by a kind user so here's to hoping someone can help me out!

As of late I've been feeling that everything I do in color turns out Bland and boring, and doesn't have the right sensitivity to color that I need as an artist. Are there any exercises I could do to improve my color selecting/usage abilities? Or does this just come with a LOT of practice.

On the same token, while using color I find I have a lot of issues with pushing Value also.

I just finished my first year of Art school, and I know basic principles of color, as well as the different types of Palettes. And I can look at a piece and discern the way they used the colors. But even still I have a really hard time with it. I've been reading a LOT of color books (Color and Light: Guide for the Realist Painter by James Gurney) and while they've really helped me understand certain lighting types and situation, Understanding and doing are two different things lol. Also, things from Observation I can get the colors fairly spot on, it's only when applying color to things from imagination where things get muddled.

I'll go ahead and post an example of where I'm at with Color, and the sensitivity I hope to achieve.

A quick Doodle I did mostly to practice with color, I realize there are Anatomical issues as well as brush problems and some color issues with the hair:
http://a8.sphotos.ak.fbcdn.net/hphotos-ak-snc6/267910_242315375792300_100000415196081_895864_3793 250_n.jpg

The sensitivity I hope to achieve someday:
http://lucasgraciano.deviantart.com/art/Absinthe-Fairy-193544653

Thank you ahead of time for any responses!

[grapholic]

hi mr briggs, i'm still around. still wait for ur help. ^^

[briggsy@ashtons]

the one that bothering me is the addictive and subtractive complimentary.... i just confuse when we used that... is the addictive for digital media, and subtractive is for traditional media? coz i find it hard to apply for my painting.


The idea is to use the paint-mixing complementary for paint mixing, and the additive complementary for all questions having to do with vision. For example, to find the hue that is the most contrasting visually, use the additive complementary. Also, to know what colour an area will appear to move towards because of simultaneous contrast - > additive complementary. Apparent colour of the shadow of a coloured light source - > additive complementary. Colour to move towards to correct a colour cast in a photograph - > additive complementary.


the other was the R/G vs Y/B formula... i know how the formula goes by looking in the attached SWF file, and to be honest that was incredible. but somehow i lost why and when to apply the formula.


It's really just a better framework to have as your basic conception of colour, instead of the old idea that the basic colours are red, yellow and blue.
---------------------------------------------------------

Looking at your head studies on DA, I think you need to put in some variation in hue (redder and yellower parts) and chroma into your flesh colours. Take a look at this post:

http://www.conceptart.org/forums/showpost.php?p=3204778&postcount=26

You'll see that pale-skinned people have quite prominent colour variation.
------------------------------------------------------------------

Please ask again if I haven't explained anything enough!

[grapholic]

thanks a lot mr. briggs!

i want to ask what if a blue light cast on a magenta surface?
what is the color of the surface become?
is that an addictive mixing or subtractive mixing?
how's the progress?

thanks.. and sorry for my lagging english.

[briggsy@ashtons]

If you think of the blue light as having lost some wavelengths, and the magenta paint as removing more, then it's really a kind of subtractive mixing. Subtractive mixing is not as predictable as additive mixing, because it depends on the exact distribution of wavelengths reflected by the paint as well as in the light. But you could definitely say that the paint would appear more bluish, or even blue if the colour of the light was saturated (pure) enough. But you would also expect that the perceived colour of the paint would not change as much as the actual wavelengths change, because our visual system would partially discount the colour of the light (colour constancy).

It's Doctor Briggs, by the way, but please call me David (or briggsy!).

[ClassicalGIRL]

Oh Dr David , Your THAT DUDE , THE Color and Light dude....I have always had you in my favorites : ).... Brilliant Methodical writing dude ....Thankyou from a Oil painter who sees Color for all its worth ....... Thumping!!!!

[grapholic]

thank you very much Doctor Briggs! ^^
i think now i'm more understand now Doctor Briggs

so when the color of light is losing wavelength or let say "not blue enough" then it subtractive with the surface isn't it?
and if the light wavelength is 100% blue... then it's addictive with magenta?

so the second row is subtractive... then the third row is addictive? (if i'm not wrong)

sorry doctor... if my bad english is lost you somewhere... T^T

(in fact i'm reading your answer about ten times and open google translate for the meaning, i've trying hardest to totally understand what u said, though my english is very bad but i'm severely dying enough to learn it from you Doctor ^^)

[briggsy@ashtons]

Not quite, it's all subtractive mixing. The blue lights have some of the red and green parts of the spectrum missing, and the magenta paint then absorbs some more wavelengths, so the process can be classed as subtractive mixing.

The bottom row just shows squares copied out of the magenta row, against a grey background. These areas do not look as blue in the picture because of colour constancy.

By the way, it's called additive mixing, not addictive mixing!

[Beeston]

Awwww Briggsy, you were in Brisbane earlier this year only a few blocks from where I live? Damn, wish I'd known. I have only just discovered the Atelier in Salisbury and they've still got your April workshop advertised for some reason. But yes, that's looking rather scrumptious. Are you going to come back for another round any time soon? And how long will it be until HuevalueChroma is back up?

[Goog]

Is the website down?

[briggsy@ashtons]

Thanks for alerting me guys - looks like the site was intermittently down for three days or so due to an issue with EveryDNS. All fixed now, thanks once again to help from Ben Green (scibotic).

Sorry you missed the workshop Beeston! At least you've found the guys at Atelier - they're all awesome in different ways so make the most of them. Hopefully there'll be another two-day workshop in Brisbane at some stage; otherwise I run the full five-day workshop fairly regularly in Sydney, including one scheduled for the last week of this month if it gets a couple more students (anyone interested should let me know ASAP) and then again in January.

[fawnha]

Hi, thank you so much for the awesome site. Its amazing such valuable information is free. So much better than any of the books out there.

Just a question about the principle of uniform saturation. I noticed in a lot of photos where a white wall is lit by a light source that when you sample the colour of the wall in photoshop near the light it has a lower saturation than further away.

http://s2.postimage.org/4oa1s6pzl/wall2.jpg

In the above the light source is on the left. The wall near the light has saturation of 18% and on the right the wall has saturation 27%. It's a bit hard to see in the image but the wall is white. Why has the saturation increased? Would this be because of ambient light? The light on the left is the only light source in the room. Wouldn't the ambient light be the same colour as the light source in this case? I assume the light is largely bouncing off other walls so wouldn't change much in hue.

The saturation of the subject's skin also increases on the right (away from the light). Because the light colour is determined using subtractive blending doesn't this suggests that the ambient light is warmer than the direct light on the left? (Because a warmer ambient light has relatively more R than B and G it would tend to make the skin redder thus more saturated).

Thanks very much for any help.

[briggsy@ashtons]

You're not giving me much to go on, fawnha(!), but we need to consider the objects in the room as well as the walls. If the objects are mostly blue, the ambient light would be bluer than the main light; if they are mostly brown, the ambient light would be more yellow/orange, which is what we seem to see.

[Mister Janchichan]

hi,

what would you recommend me to get basics to advanced in color theory, the book "the New Munsell Student Color Set" or "Art of Color" by Johannes Itten?

The munsell book is not as expesinve than Art of Color, but Art of Color is available in my mother tongue.. :xpld:

i really would appreciate a bit of freedom in my head with alle the unanswered questions and vice versa..

@briggsy, i admire your engagement! somehow, it seems to be too advanced for me, but wow..

[Elwell]

I'll save briggsy the trouble of repeating himself:

The real problem with Itten is not so much what is in the book as what isn't. Itten's conception of the scope of colour theory was strongly influenced by the Farbenlehre of Goethe (1810), which was a vitriolic and spectacularly misguided attack on the scientific approach to colour vision pioneered by Newton. Itten did at least admit that Newton was right about the spectrum, but otherwise, like Goethe, he ignored almost every development in our scientific understanding of colour after Newton. For example, like Goethe, he explained afterimages in terms of eye animism (the eye "requires" the complementary and "spontaneously generates" it if it isn't already present), not mentioning the fact that these phenomena had already been (at least partly) explained in terms of changing relative sensitivities of three receptors by Thomas Young in 1807 (and even earlier by Palmer).

A bit like Betty Edwards is for drawing, Itten might arguably be ok as a very first introduction to colour if you know nothing about the subject, but you'll want to get beyond that level as soon as possible. His simplistic eighteenth century colour wheel is ok to communicate the basic idea of the circular dimension of hue, but you'll find that it doesn't actually work for mixing colours on your computer or with your paints, and you'll need different hue circles for each of these situations. The colour sphere he adopts (originally published by Goethe's friend Runge in 1810) is a good introduction to the basic conception of three dimensions of colour forming a space, but again you'll want to go beyond it to the more sophisticated conceptions of Munsell or Arthur Pope to put the conception into practice.

It isn't really Itten's fault, but the continued widespread use of his book as the be all and end all of colour theory, nearly fifty years after it was written, and nearer a hundred after his ideas were formulated, is connected with a widespread and powerful tradition of ignorance in art teaching that refuses to engage with any scientific understanding of colour whatsoever. The scale of this great leap backwards is emphasized when you reflect that in the early twentieth century it was an art teacher, Albert Munsell, who invented the most widely used colour order system in the world.

[Mister Janchichan]

I'll save briggsy the trouble of repeating himself:

thanks, ill go with munsell!

[Shindoh]

Dear Briggsy,

As of now I still can't quiet understand one thing: The Conversion You did in Your two tables (for inclination angle and point source distance) from radiance to non-linear brightness.

How did You convert them?

But first let me see if I understood the meanings right now.

Brightness is a human perceptual value and non-linear, compared to and being the "percieved equivalent" of Luminance, which stands for the physical value of radiance. Two different words are used, to clearify that we see slightly different from what we would expect to see from the physical values. A grey surface with 18% radiance for example, appears mid-tone grey to us, although logic would tell us it should be darker according to a value from 0% - 100%. So Brightness is non-linear in relation to Luminance and it's physical radiance values.

Then You said Photoshop works with non-linear Brightness, in other words, the values from dark to light, dim to bright are graded according to human perception.

Then I found one formula You mention on Your site for converting from non-linear Brightness to linear Brightness (non-linear Brightness = linear Brightness * 0.45).
Does that mean linear Brightness = Luminance?
If not, could You please clarify the difference between these three terms?
And how to convert from Radiance to non-linear Brightness?

I'm a little bit confused now about Lightness too. I thought Lightness was the one perceptual equivalent of Brightness in the beginning. Since it's comparing to a white surface. Now I notice You say they are both perceptual values.

Luminance is the physical value of radiance, which can be physically, scientifically measured. (Okay, the others can to, but all basically in relation to this.)
So, Brightness is the perceptual value of light going from dim to bright. The perceptual value of luminance.
And Lightness is the perceptual value (the perception) of how bright any color seems to appear in relation to each other, including grey; generally compared to the "Lightness" of a white surface.

[briggsy@ashtons]

Hi Shindoh, I'd sum it up like this:

Linear = scaled proportional to light energy
Nonlinear = scaled proportional to human perception
Radiance = light energy, scaled linearly
Luminance = light energy, scaled linearly, but with the visual effectiveness of the spectral components factored in (i.e. green wavelengths count for more than blue, because they look brighter to us at the same amount of energy)
Brightness = luminance, scaled nonlinearly
Lightness = brightness of an object relative to the perceived brightness of a white object in the same setting.

However Charles Poynton, whom I cite on the page where you got that formula, noted that so-called R, G and B "brightnesses" are sometimes given in linear units, and sometimes in nonlinear units, usually with no indication of which of the two is being used. "Linear brightness" of R,G or B would be the radiance (OR luminance) of each relative to their maximum radiance (OR luminance).

Today RGB brightness values seem to be dominantly of the nonlinear kind, though I have encountered the linear kind occasionally. In the two tables I used the inverse square law and cosine relationship respectively to get the fall off of light energy, and then converted this to nonlinear brightness (like the B in HSB) using the *0.45 formula.

[Shindoh]

Today RGB brightness values seem to be dominantly of the nonlinear kind, though I have encountered the linear kind occasionally. In the two tables I used the inverse square law and cosine relationship respectively to get the fall off of light energy, and then converted this to nonlinear brightness (like the B in HSB) using the *0.45 formula.

This is where I feel like I am missing something.
In Your table we have for example 25% Radiance becoming 54% Brightness. (?)
However 25*0.45 = 11.25; and for the next one 11.11*0.45 = 4.9995.

I can't understand how You got to those numbers.

[briggsy@ashtons]

OK. It's not mutiplied by 0.45, it's to the power 0.45:

http://www.huevaluechroma.com/092.php

0.25 to the power of 0.45 is 0.5358867.

[Shindoh]

Thank You man, I really think You are the best.
I am sorry I am getting all easy now, but I would just like to express how fortunate I feel I am to know You; to have found out about Your knowledge and thinking, and even be able to speak to You.
You are like a lexicon, an encyclopedia of the history, the present, and the future on artists' understanding and use of color in regards to understanding light.
A pioneer for catapulting painting- and drawing artists' understanding of colors and light to a new level, a deeper level.

The more You know, the more You don't just paint and draw from experience, but paint from actually knowing why You use the colors You use, how they make sense with the environment, or how to realistically and believably give a desired effect, while making everything else in the painting look consistent in the context of it. And You feel more and more safe doing what You are doing. Eliminating moments of frustration, where You don't know how to achieve a desired effect, or why, where and how to put a certain color at a certain area.
And if You paint from life, You will be able to observe the laws You learned about at work.
You won't just see different colors next to each other and their relationships, but You start to see a system in it all. A system from which You draw the most important necessary values, like basic colors of surfaces, all possible lightsources, all areas of reflected or bounced light, position of lightsources, level of specular reflection, layering of specular reflection on diffuse reflection, angles of surfaces, effects on color the light has (wavelengths present in the lightsource, and their peaks, wavelength absorbance and reflectance in the surfaces and their peaks), intensity of light with inclination angle, intensity of point light sources with distance, fresnel reflection ... . It's a beautiful thing.

You have given me so much I always wanted to know, and I am sure many others too. And not just that, but You sparked my interest in a lot of other areas again too. Making me go out and research and read on a lot of things I never even thought of before. I really feel my life has been enriched and made more colorful.

Thank YOU, briggsy. :) From the bottom of my heart.

[stevejjd]

David Briggs is the best art teacher of all time. - I expect a 50% discount off next term for that comment.

[Shindoh]

But Briggsy, there is still one thing I don't quite understand yet.
I asked the question about light shining through a transparent colored cover, like plastic or glass, before; so I know what happens is substractive mixing of the colors of the light and those of the transparent surface.

What I now don't understand, is how in a lot of colored lamps the inside, the center of the light source, or rather, the lightsource itself, can often still be seen in bright white, although behind the colored transparent cover.

What's happening here? Is it so, that our eyes can only see each color to a certain maximum level, and beyond that, the color can't get any brighter? So that, let's say, in the case of a red cover, the spectral reflectance curve is highest on the red value, and becomes lower and lower to the blue side of the spectrum. Now a strong bright light source easily reaches that maximum red level. Now if compared to red it would only reflect let's say 8% of the blue wavelengths the light source emits (if the curve meant relative reflectance in relation to the other colors and there is a maximum possible level of recognition for a colors in our eyes), then at some point we'd have the brightest for our eyes recognizable red, and at some point we would eventually have the brightest possible version of every color, effectively making it appear white, although the actual relation of the colors in the reflectance curve hasn't changed, we just can't recognize them beyond a certain point of amount?

I don't know, that's the only way I could explain it to myself.
Which would mean, that any surface with exposure to a strong enough light would appear white. Unless it's black. The same way of thinking also explained to myself, that specular reflection of light sources is usually always 100% the 'lightness' of the light source. Although most surfaces (unless metals) have a generally low level of specular reflection at 0 degrees incident angle (I think about 8 percent, for glass for example). As in: 8 % of the brightness of the sun still looks completely white to us. 8% of other surfaces however, which are not illuminants, is much dimmer.

The second thing I was thinking about, was where the glow around light sources comes from. You know, not the glow created by particles, or gases in the air, of the actual light. This glow around the light disappears, if You for example stand away from the light source, and in Your view to the light, cover the light with Your finger. Just hold a finger in front of You to cover the light source in the distance (not actually covering it, just in Your view).
I thought this probably had to do with the adaptation of the eye between levels of illumination. The light source being in the middle of dimmer areas, and the dimmer area being around the brighter light source, creating this gradient of sensitivity originating in the lightsource and steadily becoming weaker outwards.

Related to that, I was wondering where the sparkle appearance of light sources sometimes comes from. Is it really because of light somehow interacting with the eyelashes?

Thank You :)

EDIT: It's not easy to find out about something, when You don't know the correct name for it to begin with. lol But through some deeper research and reading between the lines of articles about other related things, I found what I was seeing is called a "glare" (http://en.wikipedia.org/wiki/Glare_(vision)).

And I was partly right with what I was thinking.

[Lulie]

bbshrmn, in reply to the question on post #174 about using HDR images as colour references: I wouldn't recommend it. First, there are a dozen different ways of creating HDRs; there isn't a standardised way that's "closer to reality". Second, people often over-do them (http://ihateyourhdr.tumblr.com/), leading to artefacts like halos, lack of shadow depth/contrast, and over-saturation.


Shindoh -

Is your question "How come a white light will sometimes shine through as white when behind a coloured translucent barrier, instead of taking on the barrier's colour?"?

If so, as I understand it, it can't be about our eye's exposure range maxing out (like it would be a camera, blowing out the highlights), because even if we look at the sun we can still see colour in it, and that's millions of times brighter than an indoor light. Heck, the sun is so bright that it damages our eyes if we look at it, and we can still see it being yellow.

So, we're imagining a white light source behind a transparent but coloured barrier. The barrier will absorb some of the coloured light. Let's say it's a wall of red jello. Why is it the case that sometimes, the light source looks white (when it's strong), and sometimes it looks red (when it's weak)?

My wild guess -- which might be wrong -- is that this is to do with the fact there's a non-linear relationship between perceived brightness and radiance. (See here (http://www.huevaluechroma.com/105.php).) If you remove 10% of the non-red light photons (radiance) from a dim white light, it will look slightly red, whereas if you remove 10% of non-red light from a bright white light, the result will look more white than the dim one.

For a bright source, losing 10% makes less difference visually than losing 10% when it's dimmer.

Another wild guess is that it's simply colour-correction. We see it as white because it's the whitest thing in our field of view.


The "sparkle appearance of light" you mention in your second question does seem to be from the eyelashes (at least, if I squint and then move my eyelashes out of the way, the effect seems to go away -- hardly scientific but not sure what else it would be).


Briggsy -

I had to go through the whole site a couple of times and make notes to get it, but boy was it worth it. Thank you so much for opening my eyes to this fascinating subject.

My main criticism is that it doesn't always define technical words before using them (or sometimes, at all), so I'd find myself having to guess what you mean. I'll try to write my own simplified take on it, to check understanding and hopefully make some parts more accessible. (And try the sphere exercise, of course.)

Couple questions:

1. What is the origin of the mapping from hues to different greyscale lightnesses?
Some hues, like yellow, are lighter than other hues, like violet-blue. Even the camera exposure meter picks this up (one meters a middle-grey tone for correct exposure, but red and grass-green works too, and yellow would make the image under-exposed). What makes some hues lighter/brighter than others? Do cameras only pick this up because they're made to emulate how we perceive things? (I assume this can't be something objective to do with frequencies, because we don't see frequencies -- metamerism and all that. So.. it's about our eyes? What about them?)

2. How does one learn to bypass one's interpretation of colour constancy? Learn the Munsell system? Learn the situations where colour constancy problems come up? Other tricks like imagining the shadows are actually paint rather than different lighting? All of the above? (I found this to be one of the most amazing ideas mentioned in the site. That's friggin' awesome.)

And, optionally:
3. Does this bypassing of colour constancy affect the qualia ('what it is like' to see a colour), or is it an intellectual thing (i.e. you know the colour is one thing, but it still feels like what colour constancy has it as)?

[Jarlix]

The second graph, the black and white one in the original post. I don't know if anyone'll answer this... Oh whatever, at the risk of sounding clinically retarded I want to know, what does the graph itself mean or what format is it in? I do not comprehend the notation.

Everything else is gratuitiously helpful and appreciated it's just I can't understand that one graph.

[briggsy@ashtons]

The second graph, the black and white one in the original post. I don't know if anyone'll answer this... Oh whatever, at the risk of sounding clinically retarded I want to know, what does the graph itself mean or what format is it in? I do not comprehend the notation.

Everything else is gratuitiously helpful and appreciated it's just I can't understand that one graph.

I'm sure you're not the only one, Jarlix. It's all explained here:
http://www.huevaluechroma.com/012.php

[briggsy@ashtons]

David Briggs is the best art teacher of all time. - I expect a 50% discount off next term for that comment.

I've organized your discount, but they're bringing in a 100% surcharge for smartarses this year, so it'll work out the same. See you next week!

[briggsy@ashtons]

Thanks very much for the praise, Shindoh. Very nice to be appreciated!


What I now don't understand, is how in a lot of colored lamps the inside, the center of the light source, or rather, the lightsource itself, can often still be seen in bright white, although behind the colored transparent cover.


It seems to me that with a strongly coloured filter the colour is still visible even using the strongest artificial light I have handy (I haven't tried it with the sun, and neither should you!). But I agree that there is some reduction in apparent saturation, or in other words, some approach to the appearance of white light. I think your explanation applies exactly to why the light could appear white in a photograph, and is kind of right for the eye as well, except that here it is not just the instantaneous response to the light that is involved. You are looking at the light with a desensitized patch of retina, caused by localized bleaching of the photopigment, which also causes the persistent afterimage that you see when you look away (dark against a light background, light against a dark background).


The second thing I was thinking about, was where the glow around light sources comes from. You know, not the glow created by particles, or gases in the air, of the actual light.
.....
EDIT: It's not easy to find out about something, when You don't know the correct name for it to begin with. lol But through some deeper research and reading between the lines of articles about other related things, I found what I was seeing is called a "glare" (http://en.wikipedia.org/wiki/Glare_(vision)).

And I was partly right with what I was thinking.

As I understand it the main factors are scattering within the media of the eye, and at their interfaces, plus scattering within the retinal epithelium, and stray light bouncing around within the eye. Plus the effect of your eyelashes if your eye are half shut. I think twinkling is caused by turbulent movement of air masses in the atmosphere, though.

[briggsy@ashtons]

1. What is the origin of the mapping from hues to different greyscale lightnesses?
Some hues, like yellow, are lighter than other hues, like violet-blue. Even the camera exposure meter picks this up (one meters a middle-grey tone for correct exposure, but red and grass-green works too, and yellow would make the image under-exposed). What makes some hues lighter/brighter than others? Do cameras only pick this up because they're made to emulate how we perceive things? (I assume this can't be something objective to do with frequencies, because we don't see frequencies -- metamerism and all that. So.. it's about our eyes? What about them?)

The maximum chroma version of yellow is lighter than that of all other hues partly because to be bright yellow an object needs to strongly reflect a particularly large band of the spectrum (ROYG), partly because many yellow materials approach this ideal quite closely (more than cyan and magenta materials do), and partly because the ROYG band of the spectrum spans the part of the spectrum that looks brightest to us (i.e. that our cone cells respond most strongly to), which peaks in yellow-green. Cameras pick this up because they measure luminance, which is light energy weighted according to the effect of each spectral band on the human visual system (no sense in responding to ultraviolet or infrared radiation, right?)


2. How does one learn to bypass one's interpretation of colour constancy? Learn the Munsell system? Learn the situations where colour constancy problems come up? Other tricks like imagining the shadows are actually paint rather than different lighting? All of the above?

Yes, excellent summary! I'd especially stress the second one for people who worry that they will never learn to see through these illusions. Even if you can't avoid making a mistake initially, if you know about these effects you can get it right on the second or third attempt, instead of going around in circles.


And, optionally:
3. Does this bypassing of colour constancy affect the qualia ('what it is like' to see a colour), or is it an intellectual thing (i.e. you know the colour is one thing, but it still feels like what colour constancy has it as)?

Very, very good question. Without doubt some of the tricks for bypassing colour constancy affect the qualia, but unsurprisingly, since they involve a substantial change in the visual stimulus (e.g squinting, or using a reduction screen with two apertures). Certainly it can be a purely intellectual recognition, involving a conscious switch between seeing the colour of an object in an image, and judging the image colour. Most interestingly, a dramatic change in the qualia can sometimes be effected simply by changing between global and attentive viewing, which can bring about the latter switch without us necessarily knowing consciously that this is what we are doing.

[Lulie]

The maximum chroma version of yellow is lighter than that of all other hues partly because to be bright yellow an object needs to strongly reflect a particularly large band of the spectrum (ROYG)

Not sure how this could contribute, because: What about a yellow laser? It would only emit one frequency, but we still see it as yellow and still see it as lighter than other hues.

Surely whether a hue looks light or not can't be different for the pure spectral hue and non-pure spectral frequency version of the hue, because metamerism says they look the same?

[briggsy@ashtons]

Not sure how this could contribute, because: What about a yellow laser? It would only emit one frequency, but we still see it as yellow and still see it as lighter than other hues.


The third part of my explanation still applies to a yellow laser, which indeed is seen as brighter at a given energy level than all other monochromatic hues except yellow green (see attachment). The lightest high chroma object colour is a different question, to which the first two parts of my explanation become relevant.

[Lulie]

The third part of my explanation still applies to a yellow laser, which indeed is seen as brighter at a given energy level than all other monochromatic hues except yellow green (see attachment). The lightest high chroma object colour is a different question, to which the first two parts of my explanation become relevant.
So does the brightest hue of light (at given energy level) happen at a different hue from the lightest hue of a surface?

Also, why doesn't a yellow-green laser look even brighter at a given energy than a yellow one?

To go back to a thing you mentioned earlier:

to be bright yellow an object needs to strongly reflect a particularly large band of the spectrum (ROYG)
Why must this be the case? Couldn't an object reflect a single frequency of yellow, in principle? (I realise real objects may not, but I'm curious about the 'ideal'.)


On the previous topic of bypassing colour constancy: the whole idea of seeing past illusions blows my mind. If anyone has any links or book recommendations for how to learn this skill, please do post them.

[briggsy@ashtons]

What I said was that yellow-green is the brightest hue for monochromatic light. For broadband light, yellow is the lightest hue, as for object colours. For both of the latter, the range of wavelengths that contribute to the hue sensation is critical.

Many, many people assume that we see colour by detecting wavelengths, and consequently that if a yellow object reflects a lot of red and green light, then these red and green components are "impurities" in the yellow. We don't, and they aren't: the red and green reflectances combine additively to make most of the yellow stimulus. An object that just reflected a "single frequency of yellow" would only reflect a tiny proportion of the light falling on it, and so would be black or very dark olive! You can see from the fact that a bright yellow object is close to white in value that it must be reflecting most of the light falling on it.

[sinefinehabitarevolo]

Your website is just amazing and full of information!

I'm a complete idiot on color theory and painting, and all this time, I've thought Saturation/Chroma of color shifts a lot in shadows. Those tutorials from Deviantart.....

I've read your website thoroughly three times but I'm still confused haha. I think I need to read it a hundred times more.

So are my understandings 'basically' correct?

-- Chroma of colors don't shift much throughout the full light-shadows except the rapid transition from highlight to full light?

-- Skins generally have higher chroma in the shadows, little more reddish?

Some questions I have though:

-- On the section that talks about Relative Brightness, you have said that in a painting with B=50 gray representing white, any color with Brightness greater than 50 will be bright and lower will be dark, so is it important to first decide the white value of a painting, then choose highlight/shadow colors based on that Grayscale value?

-- If above is the case, then would it be important to set the white balance value pretty high, say B=70ish, so that your painting will have wide range of colors available, without making the colors look like light sources?

-- On the Figure 10.17 on http://www.huevaluechroma.com/109.php, the top colors with max Brightness look very bright, real world colors are not like them right?

-- On your website, you have said, "The series of colours we use to represent such a surface, here called a shading series, should therefore lie along a line of uniform saturation; such lines radiate from the black point of the colour solid (Figure10.1). Along such a line, chroma decreases steadily as lightness decreases, at the precise rate necessary to keep the saturation of light from the surface constant."

What do you mean by ''chroma decreases steadily as lightness decreases"? I thought the saturation doesn't change along the shading series?

[Lulie]

sinefinehabitarevolo -

This was actually one of the main things I struggled with at first too. The thing that made it click for me was the realisation that there's a difference between describing surfaces (e.g. paint on a canvas) and describing light (e.g. a computer monitor or a light source). You can see this in the diagram on this page (http://www.huevaluechroma.com/012.php) of briggsy's site.

There is often a chroma shift in shadows (if you're already at the max chroma, for example, it's not possible to stay at that chroma at lower values because they are by definition not as pure). But there is not a saturation shift (assuming the ambient light is the same hue as the main light).


Saturation is about purity of light. A colour is desaturated when it's mixed with other light and makes it look greyer to the eye. If an object is just in shadow, there isn't other light being mixed in, it's just dimmer. It's the same photons, there are just less of them.

Chroma is about intensity of colour, but refers to surfaces. Most hues have a peak chroma at a particular value -- so getting darker would lower its chroma.



So to answer your first two questions:

1. If I understand correctly, chroma of colours do shift slightly in full-light. But saturation does not. (Yes, except when it's a specular highlight -- this is because specular highlights are a reflection of the light source, so they take on its colour.)

2. My initial guess based on the above would be no, skin doesn't generally have higher chroma in shadows, but then skin is translucent and has sub-surface scattering which might do that, I'm not sure. Another thing is skin next to skin might influence the ambient light hitting it and make it more saturated/chromatic.
If I were you I'd just colour-pick a few photos, or pay attention to your reference or just look out for it in real life. Keep in mind that the colour of ambient light in real life may well be different from the main light (e.g. the blue sky might reflect blue ambient light, or a sitter on an orange sofa will have light reflected from it which saturate skin tones).


As for the brightness thing, everything you said sounds good to me but I'm curious what the more knowledgable people on this forum have to say.


(And in answer to your last question: chroma decreases, saturation stays constant -- see above explanation.)

[sinefinehabitarevolo]

Thank you for the detailed explanation!

Ooh chroma is different from saturation? My reading comprehension obviously fails. I thought chroma and saturation were basically the same thing. I will read that part again. So chroma is changing when you change the value of a color with saturation staying the same. Now it makes perfect sense.

So how would ambient light affect the main saturation of an object?

If it's in the same hue, saturation stays the same

If the hue of an object is red and the ambient light is blue, then it would turn purplish because of subtractive mixing, (am i right?) but would it lose saturation or stay about the same?

If the hue of an object is red and the ambient light is yellow, would it.... um.... be orange-ish.... um.... I've been thinking about it but I don't know what I'm thinking about.

I was testing out with Multiply layer as the website instructed, but is that really the case? seems like Soft Light layer mode or Screen mode is what it's supposed to be.... How do you simulate colored light on dark surface (Real world surface and not full saturation RGB colors) in photoshop?

I've attached a sample photoshop file. http://www.mediafire.com/i/?o232oxpb8og99b8

[Jason Ross]

I'm gong to go against the grain a little bit and say that chroma does not decrease by default in areas of shadow or blocked light. The color of shadow is entirely dependent on the properties of the light source illuminating the shadow side. That could be a secondary light source, bounced light, or ambient background light. For example, a red ball with one light source placed in a gray box will have a chroma shift in the core shadow since gray bounced light will be illuminating the core shadow. However if you place that same red ball in highly saturated yellow room the core shadow will be very saturated in color with bright yellow illuminating the core shadow. Our eyes depict gray when there is an equal level of Red, Blue, and Green light reaching our eyes at the same time. When the levels of RGB light shift away from equal then colors become more saturated. Play with the RGB sliders in Photoshop to see what RGB colors make color.

[briggsy@ashtons]

sinefinehabitarevolo

Lulie seems to have cleared up your confusion of saturation and chroma, but I'd just add that Figure 9.8 on this page also seems to help people struggling with this.
http://www.huevaluechroma.com/093.php

If you read through the site at least one more time knowing this, thigs should make a lot more sense!

As for brightness, in any natural scene, a white object will be represented by different greyscale values in different parts of the scene, though the highest such value needs to a step or two under 100 if you want to be able to show specular reflections.

Real coloured paints never reflect 100% of any part of the spectrum, or (quite) 0% of other parts, so you're completely right that those digital colours look too bright (and saturated) for actual paints.

[briggsy@ashtons]

So how would ambient light affect the main saturation of an object?

If it's in the same hue, saturation stays the same

If the hue of an object is red and the ambient light is blue, then it would turn purplish because of subtractive mixing, (am i right?) but would it lose saturation or stay about the same?

If the hue of an object is red and the ambient light is yellow, would it.... um.... be orange-ish.... um.... I've been thinking about it but I don't know what I'm thinking about.

I was testing out with Multiply layer as the website instructed, but is that really the case? seems like Soft Light layer mode is what it's supposed to be.... How do you simulate colored light on dark surface (Real world surface and not full saturation RGB colors) in photoshop?

I've attached a sample photoshop file. http://www.mediafire.com/i/?o232oxpb8og99b8

It's impossible to give a precise answer to these questions because this is a subtractive mixing process, and as a subtractive processe it depends on the actual, wavelength-by wavelength spectral distribution of the light source and the reflectance of the object. A yelow laser, a yellow filtered fluorescent lamp, and yellow filtered daylight for example could give all give quite different results.

Using multiply mode gives a mathematically accurate calculation of what you would get using a light source and object with very simple spectral power distributions, but it should only be taken as giving an indication of the general kind of result that might be expected.

[sinefinehabitarevolo]

Hello

I'm really understanding all these color theory concepts. This is great!

But is it true that using multiply layer is what is happening to the objects with colored lights on them?

Shouldn't screen mode with lowered opacity be used to depict this? I really don't know, though.

http://i.imgur.com/tv8wx.png
http://i.imgur.com/TlirJ.png

[briggsy@ashtons]

I'm gong to go against the grain a little bit and say that chroma does not decrease by default in areas of shadow or blocked light. The color of shadow is entirely dependent on the properties of the light source illuminating the shadow side. That could be a secondary light source, bounced light, or ambient background light. For example, a red ball with one light source placed in a gray box will have a chroma shift in the core shadow since gray bounced light will be illuminating the core shadow. However if you place that same red ball in highly saturated yellow room the core shadow will be very saturated in color with bright yellow illuminating the core shadow. Our eyes depict gray when there is an equal level of Red, Blue, and Green light reaching our eyes at the same time. When the levels of RGB light shift away from equal then colors become more saturated. Play with the RGB sliders in Photoshop to see what RGB colors make color.

Jason, all of this may agree perfectly with what I've said (if you fix up the bit about "gray" light!), depending on what you mean by "by default". Chroma does not automatically or invariably decrease in the shadow areas; as you say, if there is a change in spectral composition between the main light and secondary lights dominating in the shadow, it's likely to cause a departure from the path of uniform saturation/chromaticity that would otherwise apply.

[briggsy@ashtons]

Hello
But is it true that using multiply layer is what is happening to the objects with colored lights on them?


It does, but you get some strange-looking results if you use digital colours at full brightness and saturation, i.e. colours that have R, G and B values of 0 and 100%, because these are much more saturated than natural lights and the reflectance of natural objects. Try again using light and object colours no greater than 90 in brightness and saturation and you should get more natural looking results. (In retrospect I should have done this on my own diagrams on the site!).

[Lulie]

The below responses are an attempt at help with understanding the concepts of what's going on, but keep in mind that in real life the results of subtractive mixing depends on the spectral distribution (which we can't see directly) like briggsy said.

So chroma is changing when you change the value of a color with saturation staying the same.
Almost but not quite: Saturation does decrease if you make the value lighter. It just stays the same if you make it darker. Think about what's happening to the light: If you make it lighter, you need to add more photons, and if you're already at max saturation (say only your computer mointor's red phosphors are glowing), you'll need to add photons of other frequencies (blue and green parts of the pixel activate -- in other words you're adding more white light).

If it's in the same hue, saturation stays the same
Assuming it's not already at max saturation, it wouldn't stay the same but increase in saturation. It would stay the same saturation if the ambient light was white.

If the hue of an object is red and the ambient light is blue, then it would turn purplish because of subtractive mixing, (am i right?) but would it lose saturation or stay about the same?
If I understand correctly, that's right, and it would stay the same saturation unless the ambient light is the opposite colour (because as in all colour mixing, combining opposites go to neutral).

[briggsy@ashtons]

Almost but not quite: Saturation does decrease if you make the value lighter. It just stays the same if you make it darker. Think about what's happening to the light: If you make it lighter, you need to add more photons, and if you're already at max saturation (say only your computer mointor's red phosphors are glowing), you'll need to add photons of other frequencies (blue and green parts of the pixel activate -- in other words you're adding more white light).


Actually sinefinehabitarevolo was right. Perceived saturation will stay the same while the value gets higher as long as the eye is adapted to the general level of lighting. With a camera, however, saturation will begin to decrease once the brightness of a colour reaches the limit of the RGB gamut. We can't paint with colours brighter than the adaptation level of the eye, but one way to "fake" their effect is to desaturate the lightest lights in the manner of an overexposed photograph.

[briggsy@ashtons]

Assuming it's not already at max saturation, it wouldn't stay the same but increase in saturation.


Correct in terms of physical "saturation", i.e. spectral purity (though not necessarily in terms of perceptual saturation, because of the phenomenon of colour constancy: in a room lit only by a red light, red objects look surprisingly pale).

[briggsy@ashtons]

If I understand correctly, that's right, and it would stay the same saturation unless the ambient light is the opposite colour (because as in all colour mixing, combining opposites go to neutral).

No, the question about saturation can't be answered because it depends entirely on the spectral distributions of the two colours. If the red and the blue were both saturated enough to have no wavelengths in common, the red object would appear black.

[Lulie]

Actually sinefinehabitarevolo was right. Perceived saturation will stay the same while the value gets higher as long as the eye is adapted to the general level of lighting. With a camera, however, saturation will begin to decrease once the brightness of a colour reaches the limit of the RGB gamut. We can't paint with colours brighter than the adaptation level of the eye, but one way to "fake" their effect is to desaturate the lightest lights in the manner of an overexposed photograph.
Ah, yes, I was thinking about this in terms of digital screens rather than physical objects.

I've heard it's impossible to paint a red rose in bright sunlight accurately (as in both realistic values and realistic 'colours' - i.e. chroma/hues - at the same time). So is this the reason for it? As in, to achieve the effect of both high saturation and high brightness, you would have to dull everything else.

Also, I recall you mentioning on your site that value had a specific meaning and you mostly used lightness or brightness (depending on whether you were talking about light or surfaces), but I couldn't find it. What is the technical definition of value? Is it just a shorthand for lightness/brightness and can mean either?

No, the question about saturation can't be answered because it depends entirely on the spectral distributions of the two colours. If the red and the blue were both saturated enough to have no wavelengths in common, the red object would appear black.
So, in practice when painting, we either have to just look at what's happening, or guess/work out the spectral distribution (based on things like material or how things have looked to us in similar situations)?

[briggsy@ashtons]

I've heard it's impossible to paint a red rose in bright sunlight accurately (as in both realistic values and realistic 'colours' - i.e. chroma/hues - at the same time). So is this the reason for it? As in, to achieve the effect of both high saturation and high brightness, you would have to dull everything else.

Yes, though I'd add that to preserve the colour relationships needed to create a realistic effect of light in most subjects, you need to paint most things somewhat darker than people first assume.


Also, I recall you mentioning on your site that value had a specific meaning and you mostly used lightness or brightness (depending on whether you were talking about light or surfaces), but I couldn't find it. What is the technical definition of value? Is it just a shorthand for lightness/brightness and can mean either?

Value is a synonym of lightness. I didn't correct your use of "value' in this context because you can talk about the components of a subject either in terms of the brightness and saturation of the light coming from them, or the value/lightness and chroma of the paint you would use to represent them.


So, in practice when painting, we either have to just look at what's happening, or guess/work out the spectral distribution (based on things like material or how things have looked to us in similar situations)?

I'd take it to mean that there is a (certain) range of colours that could result, and so we're free to use any of those (including the ones we get using multiply mode) and they should look right.

[grapholic]

hi
again david
now i include the sample of my painting about subtractive and additive mixing
it says if the red subtract with green surface or blue light subtract with green surface resulting "black" color did you mean by "neutral or gray" color?

i want to ask, which picture is the correct one sir?

http://i93.photobucket.com/albums/l59/Grapholic/Subtractive.jpg
or
http://i93.photobucket.com/albums/l59/Grapholic/additive.jpg

and why sir?
thanks before

[briggsy@ashtons]

Ah, trick question! Both additive and subtractive processes are involved. Can you follow this? -

[grapholic]

hi david, thanks for the explanation
did you mean by this?
http://i93.photobucket.com/albums/l59/Grapholic/subtractiveplusadditiveanswer.jpg

at no 1. i see the green became more yellowish at the diffuse reflection, is that because the RED + GREEN? also the number two, the green became more blue (lets say cyan) is that because G + B?

then what happened to the subtractive mixing theory that say if between two color that has no wavelength in common will appear black? EX. R + G = Black or G + B = Black?
or is there any example in real object where we can see this "black" happen between light and surface color?

what if a yellow surface got blue light?
http://i93.photobucket.com/albums/l59/Grapholic/SubtractiveyellowVSbluelight.jpg
how the subtractive mixing going on?
the hue of yellow value is higher than the hue of blue light, is the yellow surface became lower in value if it got blue light?

could you please include the formula for me like the one u've did before at the upper of this picture?
http://i93.photobucket.com/albums/l59/Grapholic/5-2copy.jpg

thanks before david for your helping. i really appreciate that. :)

[briggsy@ashtons]

With subtractive mixing you get the wavelengths that are in common to the two colours, so the result depends on the actual spectral distributions. With a non-monochromatic blue light and a typical yellow surface you're likely to get a green reflection (first example). With a desaturated red light and a typical green surface you might get a slightly more yellowish green than the local colour (second example).

You might like to try out other combinations yourself with the online applet I used to make these diagrams. Choose the option you want (e.g. "Run with browser Java) and then click and drag on the diagrams to create your spectra.

http://www.cs.brown.edu/exploratories/freeSoftware/repository/edu/brown/cs/exploratories/applets/spectrum/reflection_guide.html

[grapholic]

thanks dave, but i'm not really understand how to used the diagram, the incoming light, reflectance, and product.

[briggsy@ashtons]

No problem g. In each set of three graphs, "Incoming Light" represents the spectrum of the coloured light source (I don't know why they didn't add the spectrum colours to that graph - it's a bit confusing), "Reflectance" represents the wavelengths of the spectrum that the colored object can reflect, and "Product" is the result of multiplying those two graphs together, wavelength by wavelength, and represents how much of that coloured light will be reflected by that coloured object. (For example, in the second diagram, for a middle green wavelength we get incoming light (0.4) times reflectance (1.0) gives a product of 0.4, while for an extreme violet wavelength we get incoming light (0.4) times reflectance (0.0) gives a product of 0.0).

I just made up the reflectance spectra, but they represent rather ideal bright yellow and bright green objects.

[Elwell]

David, have you seen this?
http://io9.com/5904487/why-does-this-blue-stone-have-yellow-light-coming-out-of-it

[briggsy@ashtons]

I don't know what it is, but I want one! It's described in the article both as "stone" and "glass" but it looks very pale for a volcanic glass, so it seems more likely to be artificial.

Very cool site!

[Elwell]

I suspect it is, although I've seen similar, but less dramatic, effects with moonstone.

[grapholic]

yes, the incoming light got no color
do we identify the color by seeing the highest mount at the diagram?
let say, what monochromatic blue light beam into monochromatic yellow surface

does the diagram look like this?
http://i93.photobucket.com/albums/l59/Grapholic/bluelightyellowsurface.jpg

then what the result of product's diagram saying?

thanks for helping dave.