# Thread: The Dimensions of Colour - a colour theory discussion thread

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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.
Last edited by D.C.; April 27th, 2010 at 08:44 PM. Reason: grammar

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3. Originally Posted by D.C.
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. With a small light source close to an object, this gradation is very evident.

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5. 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.

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7. 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...
Last edited by revenebo; May 2nd, 2010 at 06:16 AM.

8. 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.

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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.

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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!

12. 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.

13. 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.

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

16. ## color harmony

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.

17. Originally Posted by Virg
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.

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19. 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.

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