RGB to RYB conversion? [Archive] - ConceptArt.org Forums

GMAnimation

June 25th, 2005, 03:15 AM

Its really a common misconception that the primary colours are Red, Yellow and Blue. They are infact Cyan Yellow and Magenta.

The explanation behind this is that as you probably know, light is addative. The more light you add the brighter your colours get, so naturaly you start with the darker colours of the spectrum which happen to be Red Green and Blue. As you mix them together the colours mix to form the lighter colours of the specturm which are Cyan Yellow And Magenta.
http://www.gmanimation.com/junk/rgb.jpg
Painting on the other hand is subtractive. The more pigments you mix together the darker they become. As such you start with the lighter colours of the specturm.
http://www.gmanimation.com/junk/cym.jpg
This is a pretty simple explanation, but you should get the idea.
If you wanna learn more about it, check out this guy's book. (http://www.amazon.com/exec/obidos/tg/detail/-/0823007545/qid=1119686896/sr=8-2/ref=pd_csp_2/002-9134614-1924013?v=glance&s=books&n=507846)

Murphy ( ^.^)/~~~

Tjendol

June 25th, 2005, 09:01 AM

I'm sorry, I wasn't very clear about what I wanted to know. I'm not looking for a way to change the RGB color itself into a RYB color..well..in the end I am..but I just want to convert the hex values...or whatever they're called.

I have read a little about all the points made in this thread :)

However, I don't want to digitally edit in any program. I simply want to know if there's a way to get RGB values like 0 0 255 converted into the closest RYB value.

And although Ive also read that red yellow and blue aren't the primary colors...some ( a lot of?) people still learn to paint with these three colors when they start painting..and painters have used them for years. And I'm not certain but can't you make every possible color with this combination when painting traditionally?

Back to my initial question :) Wheter or not it is the right way to paint with red yellow and blue tradtionally and using red green and blue in a digital paint program...is there an algorithm to convert one into the other?

Looking at the above image it should be possible to make every color with with Cyan Yellow and Magenta as well.
So..if theres no calculation possible to convert rgb into ryb, maybe it's possible to convert rgb into cmy? This kind of sounds the same to me..lol..

Im thinking of another question now..which is..when you have a CMY value in a digital paint program..would using these values traditionally with real paint produce the same color?

jfrancis

June 25th, 2005, 04:58 PM

http://www.digitalartform.com/archives/images/psColorMixing_1.jpg
http://www.digitalartform.com/archives/images/psColorMixing_2.jpg
http://www.digitalartform.com/archives/images/psColorMixing_3.jpg

http://www.digitalartform.com/archives/2005/06/digital_color_m.html

Elwell

June 25th, 2005, 05:56 PM

And although Ive also read that red yellow and blue aren't the primary colors...some ( a lot of?) people still learn to paint with these three colors when they start painting..and painters have used them for years. And I'm not certain but can't you make every possible color with this combination when painting traditionally?
No.

Im thinking of another question now..which is..when you have a CMY value in a digital paint program..would using these values traditionally with real paint produce the same color?
No.

jfrancis

June 25th, 2005, 06:50 PM

If you are using Red, Yellow and Blue to mix paints, and you want to mix a saturated orange, you should start with an orangey red (like cadmium red) and mix it with an orangey yellow, like cadmium yellow.

If you want to mix a saturated purple, start with a purplish red like quinacridone red, and mix it with a purplish blue like ultramarine blue.

You'll get a desaturated, not vibrant purple if you use cadmium red and cerulean blue.

You'll get a desaturated, not vibrant orange if you use quinacridone red and hansa yellow.

We use the words red, yellow, and blue pretty loosely. The colors they describe include magenta, yellow, and cyan.

The best book for this stuff is "Blue and Yellow Don't Make Green" by Michael Wilcox.

Tjendol

June 25th, 2005, 11:35 PM

No.

No.

Please motivate...

Printers use cmy plus black to mix colors as well..why wouldn't this work.

GMAnimation

June 26th, 2005, 12:11 AM

It would have been nice if Elwell had elaborated on his answers, but he is non the less correct.

The First 'No':
Once colours have been mixed the can't be unmixed. So esentialy, unless you start with the absolute primary colours there will be certain colours that you won't be able to achive.
Try to think of it as similar to painting with light green insted of yellow. If you use this it can often achive some very interesting and plesant results, but the most yellow colour you can achive is a light green.
The same applys to Red and Blue. They arn't really primary colours. they are Pre mixed and therfore there is a certain range of the specturm that can't be utalised.

The Second 'No':
In a perfect world mixing CYM paints should theoreticaly mix the way they do on your computer screens. Unfortunately, the realworld isn't so perfect.
Cyan and Magenta are almost imposible to get perfet pigments for. Ontop of that Mixing two seperate pigments will never have quite the same quality as using a pigment that is already what you need.
This is the reson that so many pigments are avalable. You arn't expected to mix every colour you need. Working in CYM (or RYB or whatever colour scheme you want to use for that matter) is simply a guide to keep you mindful of how and why the paint is doing what it does.

Like i said, you should really read that guys book!
Murphy ( ^.^)/~~~

Elwell

June 26th, 2005, 01:14 AM

Printers use cmy plus black to mix colors as well..why wouldn't this work.
In addition to everything GMAnimation said...

Physical mixing with pigments works very differently from the optical mixing used in four-color printing. Color behaviour gets complicated and unpredictable when you move from digital models to the real world. Two pigments can look identical out of the tube yet be drastically different when tinted up with white. The difference between two colors can be undetectable under some kinds of light and obvious under others. Pigments differ in their opacity/transparency and in their tinting strength. For instance, pthalo blue, the closest pigment to a "true" cyan, is several times more powerful than any magenta or yellow, so if used in equal amounts it will totally overwhelm the mix. Tint the same color up with titanium , zinc, and lead white and you'll get three different results, and none of them will be the same as a transparent wash or glaze of the same value. Etc, etc, etc.

Pixels, print, and pigments all play by different rules, and it's important to understand all of them.

Tjendol

June 26th, 2005, 06:07 AM

Thank you guys for the helpful information.

GMAnimation, I will try and get my hands on that book you suggested.
You talked about absolute primary colors. I was wondering why these paint pigments aren't available, you would think it's possible with todays technology.

But let's say that you use a red yellow and blue or cyan magenta and yellow which come very close to the absolute primaries (don't know if those exist in paint), would it be possible to get close to being able to create almost any desired color? Suggested you take a random object color in your surroundings you want to achieve with mixing paint..can you get close to it and get fairly the same color, just starting with these primaries (although theyre never absolute)? I mean, would you be able to easily tell the difference with the human eye?

And do I understand you right when you say that mixing can't be unmixed, you can't fix a mistake even if you start with "absolute primaries" in theory?
Let's say you want a certain color but you mix a little too much blue...you can't make it right by adding more of another primary?

I just want to experiment a bit..starting with these couple of colors and seeing how close you can get to any desired color. But I get the impression that this is hard to do even with a variety of available pigments.

GMAnimation

June 26th, 2005, 09:58 AM

You talked about absolute primary colors. I was wondering why these paint pigments aren't available, you would think it's possible with todays technology.
Yeah, you'd think so, but allass. Yet another problem with the Cyan and magenta paints is that most pigments deteriorate over time, and from what i hear, the closer you get to true cyan and magenta the quicker they deteriorate.

And do I understand you right when you say that mixing can't be unmixed, you can't fix a mistake even if you start with "absolute primaries" in theory?
Let's say you want a certain color but you mix a little too much blue...you can't make it right by adding more of another primary?
This really depends on what medium you're working in. If you're premixing opaque oils or guaches on a pallet (or even strait to canvas), you can ballance it out. But this is blancing out the ratios by adding more, not unmixing what is already there.
The real problems here occur when white comes into the equasion as opaque paints need white mixed in to make them lighter. You can't unmix the white, so no matter how much colour you balance it out with, it will still have the white in it. Think you can fix it by adding black? then things just get muddy, unsaturated and shit... bad bad kama.
Waterpaints on the other hand are transparent and for this reson are a very difficult medium because you don't really know what you're going to get untill the paint is on the paper, by which point, you can't really take any of blue out and adding more of the other primarys will just make it darker.

But let's say that you use a red yellow and blue or cyan magenta and yellow which come very close to the absolute primaries (don't know if those exist in paint), would it be possible to get close to being able to create almost any desired color? Suggested you take a random object color in your surroundings you want to achieve with mixing paint..can you get close to it and get fairly the same color, just starting with these primaries (although theyre never absolute)? I mean, would you be able to easily tell the difference with the human eye?

You have to understand that there are more than just the primary colours in the specturm. It's just good to be mindfull of how colour really works at its base level.
Just looking at some of the great masters of the renaissance and the romantics should adiquately answer this question. They are proof enough that you can do absolutly amazing things with RYB school of thought.
Unless you're trying to perfectly replicate photography (which would defeat the purpose of painting anyways) you don't have to (and really shouldn't) stick to CYM (or RYB for that matter) as the be all and end all formula.
For instance, say you want to make a really cold moody blue picture, instead of simply using less red(cyan) and yellow in your picture, try actualy using Purple, Green and blue as your primary colours.

murphy ( ^.^)/~~~

p.s sorry about my shitty spelling and gramma.

Tjendol

June 27th, 2005, 10:13 AM

For instance, say you want to make a really cold moody blue picture, instead of simply using less red(cyan) and yellow in your picture, try actualy using Purple, Green and blue as your primary colours.

murphy ( ^.^)/~~~

p.s sorry about my shitty spelling and gramma.

Don't be sorry, it's perfectly understandable and my English isn't exactly top notch either :)

Aside from it being convenient to use purple as a prepared color, what's the difference compared to using RYB as purple is a result of mixing red and blue?

You should be able to get the same results right?

Although there's clearly a lot more to it than just one solid base I understand that it's not totally wrong to start practicing and experimenting with the primary RYB colors when starting to paint and learning how to mix.

I'm asking all these questions because I was thinking about creating a device that could help guide starting painters with mixing their paint on a basis level to achieve a certain hue and eventually making them understand how mixing works. Partly because I have a hard time with copying colors myself.

Therefore I would need a device that can measure colors of objects in the surrounding space and because the result will be RGB or CMY values..I would need to convert them to RYB (or leave it cmy when you choose to paint with cmy pigments). The thing is, different reds, yellows and blues exist and even without taking that into account It has become clear to me that it's virtually impossible to create such a device if you demand exact results. However, I could maybe try to use a certain brand of paint and find out which one comes closest to the rgb (or cmy results if conversion isn't possible) when mixing. Because it will not be precise, I could use a permitted margin between the RGB measured values and the RYB you will have to obtain by mixing your paint. This way you can, altough not entirely accurate, still get a feeling about how mixing in general works and maybe hopefully you will be able to pick it up faster.

CreationEdge

June 27th, 2005, 12:43 PM

Its really a common misconception that the primary colours are Red, Yellow and Blue. They are infact Cyan Yellow and Magenta.

Physically(As in Physics), that's not right.

Red Green and Blue are the primary colors of light. They make the Secondary Colors. Yellow, Cyan, and Magenta.

However, YCW are the Primary Pigments. A pigment is something that holds a color and reflects another. They're primary because, for instance, a blue pigment withholds blue and reflects red and green, thus appearing yellow to the eye. (Primary pigments absorb primary colors)

Thought I'd add that, since it's the only thing I can really add to this topic.

I know that Red paint is actually a Cyan Pigment. Green is actually a Magenta Pigment. Mixing the colors, in light, would yield yellow. But, in paint... You have Magenta(R + B) + Cyan(B + G), giving you a blackish color because you have all 3 pigments. If I remember right, when I tried it I got a very dark greenish-yellow with the paints I used.

So...

In paints, you're dealing with Pigments. It's almost backward thinking.
In digital, you're dealing with a monitor(which uses Light to display images), so you're dealing in Colors.

If you want to go from Paints to Digital, you almost have to think the opposite of what you used to. Digital is Additive, and you're dealing with the face vale of what you see. Painting is Subtractive, and the real guys at work are the Pigments underneath absorbing all the light they can of a color(s).

jfrancis

June 27th, 2005, 04:43 PM

Physically(As in Physics), that's not right.

Red Green and Blue are the primary colors of light. They make the Secondary Colors. Yellow, Cyan, and Magenta.

One way to make yellow-looking light is to superimpose red and green. Pass that light through a prism, and it will decompose back into red and green.

ANOTHER way to make yellow-looking light is to actually use yellow light.

yellow light is at about 570 nanometers.

If you generate 570 nm yellow light and pass it through a prism, it will not decompose into red and green light.

GMAnimation

June 27th, 2005, 09:50 PM

Physically(As in Physics), that's not right.

Red Green and Blue are the primary colors of light. They make the Secondary Colors. Yellow, Cyan, and Magenta.

I'm gunna have to dissagree with this. Yes in a addative situation you're right, Red Green Blue are the primarys, and make the secondary colours Cyan Yellow Magenta.
But in a subtractive situation Cyan Yellow Magenta quite definately ARE the primary colours and in a subtractive situation they make Red Green and Blue which become the secondary colours.

For instance. If i had two bright lights, and i put a green gel on one and a blue gel on the other, the light shining on the wall wall would be Cyan.
But what happens if i have one light and i use overlaping gels? In this case, if i overlap yellow and magenta gels the light shining on the wall becomes red... Yellow and magenta being the primarys and red being secondary.

So CYM are quite definately primary colours (and RGB secondary) depending on how they are being mixed.

also, red is made of Cyan and megenta, not just cyan... and true green doesn't have any magenta in it at all?!?

And to answer Tjendol's question. I think you'll find that if your working in a spasific brand of paint (Winsor Newton, Faber Castell, etc etc etc) the companys usualy produce pretty comprehensive colour wheels and charts showing all the colours and how to achive them using thier paints, which sounds just like what you need. They arn't very expencive and your art supplyer sould have them in stock, and if not, it shouldn't be to hard to get them in.
As for measuring colours of objects in the surrounding space... well, i think you'll just have to keep practacing and train your eye, which i think is a good thing. If you had something to measure the colours for you, you wouldn't learn how to do it yourself which is a very important skill.

Murphy ( ^.^)/~~~

CreationEdge

June 27th, 2005, 10:04 PM

You could also use a filter which absorbs everything but yellow light...
Pass that through a prism(after the filter) and it will stay yellow.

Doesn't quite effect painting though. Unless you're using a colored lightsource in your painting...

Shine green light on a yellow object, for example. With just paint, you'd get yellow-green. But since light is Color and the object is Pigment, you have on object keeping blue light. Thus, shining green on it, which has no blue light, will give you a green only object.

Now, with that same light. Let's say it's on a cyan object this time. Ah! Green again.

Lastly, on a magenta object. Now... you get something grayish or black.

I think I've left the topic, but it's still about colors and light. This is the first time I've actually thought about it in an art sense(I'm a graphite-only guy, for now). The whole shining light thing never really occured to me. I'll have to remember that once I start using color...

CreationEdge

June 27th, 2005, 10:17 PM

I'm gunna have to dissagree with this. Yes in a addative situation you're right, Red Green Blue are the primarys, and make the secondary colours Cyan Yellow Magenta.
But in a subtractive situation Cyan Yellow Magenta quite definately ARE the primary colours and in a subtractive situation they make Red Green and Blue which become the secondary colours.

For instance. If i had two bright lights, and i put a green gel on one and a blue gel on the other, the light shining on the wall wall would be Cyan.
But what happens if i have one light and i use overlaping gels? In this case, if i overlap yellow and magenta gels the light shining on the wall becomes red... Yellow and magenta being the primarys and red being secondary.

So CYM are quite definately primary colours (and RGB secondary) depending on how they are being mixed.

In physics(as in the class I took this past year), what I said is true.

In a Subtractive situation, you're using Pigments. All you're mixed up on is the terminology I'm using.

In your first example you're using light straight out. Mixing Colors of Light. The gels act as a filter, so you have Green and Blue Light combining. Since it's the Light combining, it's additive, and you get Cyan.

In your 2nd example, you're not mixing the light, you're filtering it. Now, the yellow gel lets through yellow light by withholding Blue Light. So now all we have is Red and Green Light hitting the Magenta Gel. Now, that gel absorbs Green light. Now all you're left with is your Red light.

So, in a subtractive situation, CYM ARE primary, but scientifically-speaking, they're primary PIGMENTS, not colors. It helps to differentiate what properties you're talking about.

I find it easier to just say "Add red and green pigments" than "mix red and green in a subtractive situation."

Hope that cleared up what I meant. I'm just speaking science here. What you said is absolutely right, we're just calling it by different names.

Gilead

June 27th, 2005, 10:36 PM

Tjendol,
The biggest problem with what you're trying to do is that It's not just a question of what colors you are mixing together, it's also a question of what method you are using to "mix" them
For example. If you have a dark surface and you want it light cyan blue you could do one of two things. You could paint the surface white, let it dry and then lay down a thin glaze of blue over it (or airbrush it or jet print it). Or you could mix the white and blue together and paint it on as a mixture. Both methods "mix" white and blue so you'd think that if you used the same amounts of paint in either case it would turn out looking the same. But they actually come out completely different. The first way gives you a clear sharp transparent looking blue. The second method gives you a dull, soft, opaque blue.
All this talk about mixing light is interesting, but I've never seen that this information has any paractical application to mixing paint. And while I'm at it, if you are going to try to get "THE ANSWER" while looking at a computer screen and then think you're just going to go out and do the same thing with pigment you are doomed from the start.
Mix actual paints first. It's the only way to see what's really going to happen. Everything else is all theory.

jfrancis

June 28th, 2005, 02:41 AM

jfrancis

June 28th, 2005, 02:46 AM

Also it's not a good idea to use the term "subtractive" when describing pigment mixing or filter stacking.

3 minus 5 does not equal 5 minus three, BUT cyan pigment mixed with green pigment isn't different from green mixed with cyan. The model isn't subtraction; it's more like multiplication.

Tjendol

June 28th, 2005, 03:14 AM

And to answer Tjendol's question. I think you'll find that if your working in a spasific brand of paint (Winsor Newton, Faber Castell, etc etc etc) the companys usualy produce pretty comprehensive colour wheels and charts showing all the colours and how to achive them using thier paints, which sounds just like what you need. They arn't very expencive and your art supplyer sould have them in stock, and if not, it shouldn't be to hard to get them in.
As for measuring colours of objects in the surrounding space... well, i think you'll just have to keep practacing and train your eye, which i think is a good thing. If you had something to measure the colours for you, you wouldn't learn how to do it yourself which is a very important skill.

Murphy ( ^.^)/~~~

The problem with using a specific brand without the use of technology is that you need a chart, which will always be limited or very large. Also, you would have to look the color up manually. Which doesn't have to be a problem of course, but since my study involves applying technology and creativity to create innovatives ideas I was wondering about how to apply it to this matter and maybe do things more efficient or create new ways of doing it. By using a device, in theory you would be able to get any color in the space you're in within a fraction of a second. Now I don't want the device to just measure and mix colors for you. My goal is in fact to learn from it by guiding the user and start off with some base information because it can be hard to even start from nothing to get to a color (that's my experience). Once you have the rgb or cmy values of a chosen object, you can try and copy it with that information, but you're still doing the mixing yourself and if you do this often enough you will start to understand how paint works and what different amount of paints mixed together will produce. Obviously you could use a color chart on the side and use the same device to see how each color is built up if you would like to mix colors in a more structural way. Keep in mind that this idea is meant for absolute beginners. In order for me to achieve it, I need to understand the basics as well to know if it's possible at all.

The biggest problem with what you're trying to do is that It's not just a question of what colors you are mixing together, it's also a question of what method you are using to "mix" them

Very much true indeed. My intention though is to help beginners and build a foundation they can work from later. From there they can learn different methods as they start to get more advanced.
The idea is to just mix different paints like done on a palette.

Hybridstar

June 28th, 2005, 06:04 AM

I do most of my mixing from the primarys, using a number of variations of each color depending on the bias. So yes you can mix every color from the primarys.

CreationEdge

June 28th, 2005, 11:53 AM

There's yellow light at 570 nanometers that is REALLY yellow light. It's not made of red and green.

There is really such a thing as orange light. It's at 590 nm.

The visible violet light has a wavelength of about 400 nm.

The visible indigo light has a wavelength of about 445 nm

Right. That just means you have to take your source into account. But very rarely will you encounter light like that. Colored lamps are usually just filtered white light.

And you can't do that with all colors, either. Sometimes to get a color you MUST combine the light(like magenta), because it's just perception. Heck, even white is just perception, there's no actual white in the spectrum. I think there's so many colors which we just perceive that specific colored light(like 570) would be impractical...

Interestingly enough, the human eye doesn't perceive yellow light as yellow, first. That wavelegth actually triggers our red and green receptors and then combines it into yellow again in out head.

It's interesting stuff.

Gilead> Yeah, what I'm talking about is pretty much the effects of light, and nothing to do with actual paints.

But what you said interests me. Sounds cool. Do you have any examples in your threads that show this? Makes me want to get into paints more and more.

jfrancis

June 29th, 2005, 10:07 AM

It's theoretically possible to make a gray filter by dividing the spectrum into many bands and letting trough only the even-numbered bands...

...and ANOTHER gray filter that lets through only the odd-numbered bands--except in the red, where it let's throught the even-numbered bands...

If you could do that, you'd have two gray filters that when sandwiched together would turn red!

I saw that idea somewhere here...
http://personales.upv.es/~gbenet/teoria%20del%20color/water_color/wcolor.html
...not sure exactly where -- but that's an interesting link

Here's another one from that same page.
Those pesky primary colors (http://personales.upv.es/~gbenet/teoria%20del%20color/water_color/color9.html#primaries)
...That guy's stuff is worth a good read.

briggsy@ashtons

June 29th, 2005, 08:51 PM

"REALLY yellow" vs "yellow-looking"

Take care, fellow colour enthusiast! It sounds as if you have fallen for the fallacy of thinking of colour as a property of light itself, rather than what it really is, an experience elicited in ourselves by that light. A monochromatic light of a certain wavelength will stimulate the three cone types in our eyes in a certain proportion to give us the experience we call "yellow"; light containing a mix of wavelengths that individually look red and green can stimulate the cones in the same proportion to give the same experience. The second "yellow" is neither more nor less real than the first; in fact the two situations are identical as far as the eye is concerned. Light has wavelengths, different surfaces reflect light of different wavelengths in different proportions, but colour exists only "in the eye of the beholder".

You should realize by the way that a "paint that only reflected 570 nm light" would not be yellow but would be dense black in appearance. A paint such as that would absorb more than 99% of the light falling on it: all of our black paints reflect a greater percentage of the visible light spectrum than that. Even a paint that reflected the whole of the more or less yellow part of the spectrum would be a very dark yellow indeed. (Actually it would have a very dark green appearance, but that's another story).

All bright yellow paints and surfaces reflect most of the red, orange, yellow and green light that hits them (to use the conventional manner of speaking, that is, meaning light wavelengths that would look those colours when seen individually). If you find yourself arguing that a lemon or a blob of cad yellow is only yellow-looking, while a black paint that just reflects light of 570 nm is really yellow, ... need i say more?

Elwell

June 29th, 2005, 09:48 PM

...It sounds as if you have fallen for the fallacy of thinking of colour as a property of light itself, rather than what it really is, an experience elicited in ourselves by that light...If you find yourself arguing that a lemon or a blob of cad yellow is only yellow-looking, while a black paint that just reflects light of 570 nm is really yellow, ... need i say more?

THANK YOU!

CreationEdge

June 29th, 2005, 10:49 PM

Actually, if you have a light that shines yellow only(570 nm), onto the surface that reflects only that, I think you'd get a very nice yellow. The only reason it'd appear dark with normal light is because that light, like you said, is of many wavelengths combined. And since there's receptors in our eyes for amounts of light...

Just saying, that if you had one of those lights it'd be shining enough of that light on it that you'd get a pure yellow.

And nah, I know what you're saying, but it's fun talking about light(which I was, moreso, than colors, IMPOV.) If you know what I mean... It was just nice talking with someone else who knew the physics of light. :}

briggsy@ashtons

June 29th, 2005, 10:57 PM

Getting back to your original question, have you thought about what you actually mean by "RYB values"? Are you assuming the existence of a defineable colour space, with RYB axes, but somehow independent of actual pigments? If so, I think you are out of luck.

We can avoid a lot of confusion by taking care to distinguish between, on the one hand, additive, ideal subtractive, and pigmentary mixing PROCESSES and their respective RGB, CMY and RYB primaries, and on the other hand, COLOUR SPACES such as RGB, CMY and all the others.

A Colour space is a framework for designating colours and understanding colour relationships. The RGB space is a good example. It is what is called a device-dependent colour space: it defines a range of colours that can be produced on a colour monitor, in which the R, G and B components can be varied independently over a range from 0 to 255. These three axes define a solid volume which, if the axes are placed at right angles to each other, takes the form of a cube.

But what sort of space do you have in mind when you talk about RYB values? Is it the range of colours you can get by mixing a red, a yellow and a blue pigment? This situation is a bit different from RGB. For a start, the three components are not independent of each other. For example, if the R and Y components are both at 0%, the B component must be 100%. So you get a colour "space" that is a triangular plane, not a solid, with R,Y, and B at the three corners. To get a solid you would need another independent component, for example white, added either as a pigment or as a ground showing through the mixture. But more to the point, the space is obviously entirely dependent on the three pigments you chose: a different space for every combination of three pigments you might think of.

You CAN of course easily go the other way: find representative RGB values for any red, yellow and blue pigments OF YOUR CHOOSING. Just paint them on a card, scan them and use a colour picker. (Obviously the exact result will depend somewhat on your settings). But don't expect these RGB colours to mix the same way in a paint program as the original colours do, because the behaviour of pigments in mixtures depends on their actual absorption curves. For example, two pigments of very similar appearance can turn out to have very different mixing complementaries. Bruce MacEvoy gives some striking examples in his "handprint" site, referred to in the last post by jfrancis.

briggsy@ashtons

June 30th, 2005, 12:22 AM

Actually, if you have a light that shines yellow only(570 nm), onto the surface that reflects only that, I think you'd get a very nice yellow.

Very good, very good! I hadn't anticipated that objection! Of course pretty much everything else in sight would be brighter or darker versions of the same yellow, so adaptation would reduce (partially) our sense of the intensity of the colour. But you're right, it would still be pretty darn yellow.

Thanks to Elwell for his speedy thank you

Bye for now (off to work)

Tjendol

June 30th, 2005, 08:50 AM

Getting back to your original question, have you thought about what you actually mean by "RYB values"? Are you assuming the existence of a defineable colour space, with RYB axes, but somehow independent of actual pigments? If so, I think you are out of luck.
jfrancis.

I'll try to give an example because all this information is too much for me too handle and I'm a bit confused as I'm too much of a noob when it comes to this matter.

Forgive me for my simple illustration.

let's say we have the rgb value (I call it value because I don't know what it's officially called) of:
R:224
G:29
B:45

Now this is on a scale from 0 till 255.

If we would convert and round off into percentages we would get:

R:88%
G:11%
B:18%

I was wondering if you would get close to the same colour as with the 0-255 scale if you digitally mix (instead of using a color picker) these percentages of each rgb value. so 88% red, 11 % green and 18% blue. I wanted to try this in painter but I don't know if it's possible to mix certain amounts of paints digitally.

Now..I want to get this same color with pigments (real paint). But I can't use the RGB values because working with paint is subtractive and I can't create yellow. So I need RYB pigments to make this work with paint. So there's my first question again..is it possible to convert the RGB percentages of a certain color R:224 G:29 B:45 or R:88% G:11% B:18% into RYB percentages in the same format to get that same color when mixed?

If converting from digital RGB value to the closest digital RYB value is not at all possible or very difficult...can it be done with CMY?

So you have the CMY values of a color..digitally obtained..for example in Photoshop.

Is it then possible to use real paint of a certain brand of which you know that the cyan, magenta and yellow have (nearly) the same value as the digital ones. And would mixing the real paint with the same percentages produce (almost) the same color as the digital color? Are the proportions comparable?

Thanks to all of you for your input!

Elwell

June 30th, 2005, 09:01 AM

Is it then possible to use real paint of a certain brand of which you know that the cyan, magenta and yellow have (nearly) the same value as the digital ones.
No.

And would mixing the real paint with the same percentages produce (almost) the same color as the digital color?
No.

Are the proportions comparable?
No.

Tjendol

June 30th, 2005, 09:35 AM

Even if all given information is very obvious to you, and since I read professional under your name, it has to be :)...it may not be to others.

Personally I think reactions like these don't add a lot of purpose to the thread (even if you find everything is very clear or that all questions have been answered in previous posts) although your answers may be right. I assume nevertheless that you mean well but some illustration is much appreciated.

jfrancis

June 30th, 2005, 09:56 AM

I'm not sure whom to answer, or even if I have much to contribute to this conversation, other than...

In talking about 570 nm laser light, by "really" yellow, I mean a prism can't split it into other colors. I know that the interpretation of that wavelength (and many other wavelength "recipes") as yellow occurs in the brain.

A 570 nm paint under normal lighting conditions would be black, yes. It would be yellow under a tremendously bright light. I was using pigment mixing and filter sandwiching interchangably, which, as long as the light is bright enough, I think I still can, no? I suppose your point is since the point on the spectrum at 570 nm is infinitely thin, no amount of light, no matter how bright, would make it show yellow? In the case of the reflectivity of a pigment, you may be right.

Do I think r-y-b defines a color space? I suppose it does define a subspace, at any rate, with a limited span.

My recommendation for a good book to ease into the topics of pigments and color mixing is Blua and Yellow Don't Make Green (http://www.amazon.com/exec/obidos/tg/detail/-/0967962870/ref=pd_sxp_f/102-5982722-4680167?v=glance&s=books) by Michael Wilcox

...he goes on at great length about why a "red" paint made from one wavelength recipe will mix differently from a "red" made from another wavelength recipe.

Elwell

June 30th, 2005, 05:25 PM

I assume nevertheless that you mean well but some illustration is much appreciated.
Like this?

Pigments differ in their opacity/transparency and in their tinting strength. For instance, pthalo blue, the closest pigment to a "true" cyan, is several times more powerful than any magenta or yellow, so if used in equal amounts it will totally overwhelm the mix. Tint the same color up with titanium , zinc, and lead white and you'll get three different results, and none of them will be the same as a transparent wash or glaze of the same value. Etc, etc, etc.

Main Loop

July 1st, 2005, 03:08 AM

tjendol, i think you're failing to account for something thats extremely importantwhen considering what color to use in your system: The light of the environment itself... if you take a colro that looks a certain way in north light, it'll look complete different in candle light, or flourescent light, or any other light...thats why colors shift so dramatically when you bring a plein air painting indoors, sure the numerical value of the hue will always be the same, but not to the eye, thats why there's no formula to painting.. aside from pigments not reacting predictably to eachother due to the chemicals reacting to eachother among other things, the only true way to know how pigments are going to behave is to practice with them.. how much painting have you done so far?

since this is such a complicated topic, i may have totally misunderstood your question, so ignore me if what i said's irrelevant..

Tjendol

July 1st, 2005, 07:26 AM

I never even thought about the paint chemicals reachting to eachother..that's a good point. Still wondering about my printer a little bit..it seems to be pretty accurate when I print stuff off my screen.

About the light..I would like to get to the color in the specific light you're working with..daylight, candlelight..whatever.

I really haven't painted that much yet. And I know I probably will learn eventually by practicing more. It's not that I don't want to do this..I was just wondering if there's a way to guide beginners in the right direction..because I started doing it and noticed it can be a hard thing to do.

When it can't be done with real paint by giving the exact proportions of CMY or RYB colors for all the given reasons, maybe you can simply let people know if they need to add more of a certain color to the mixture to get to the color measured initially.

Tjendol

July 1st, 2005, 07:36 AM

Like this?
Yeah, like that.

These are really things you can take into account though. The overwhelming blue for example..you can use formula's that will let you know to use less blue.

As for the whites, that's why I suggested using one type and brand of paint to start with to kind of know how it works together because it's a matter for beginners. This really is to advanced already, although good and interesting points.

Main Loop said it's unpredictable because of chemical reactions as well and that really makes things more complicated if you want to 'calculate' needed percentages of paint.

CreationEdge

July 1st, 2005, 08:03 AM

At my school, in the basic art class(which I haven't had here, but I saw their projects), they'd get these papers, cardstock or something, and they'd have to paint on those. They'd start with a color and slowly make it more light and more dark, so they'd get a gradient of little rectangles, and they usually fit several different colors(like red and green) on each piece of paper.

And they might have done the same with mixing colors. Like red to blue, slowly making the blue more to purple then purple to red.

Seems like a good idea to familiarize yourself with how the paints mix. First way will help with adding black and white. Second, just seeing how the colors mix. You could probably try any colors.

Like, once they're more along, you give them two colors. Then you tell them that they need to blend one into a third color which blends into the second.

Green and blue, for instance. But show them the third color, lime. And straight green and blue can't make lime, they'll obviously have to add in at least 1 more color of paint.

Even if they get it wrong, they should still learn more about the combinations of what they did mix.

briggsy@ashtons

July 1st, 2005, 09:52 AM

Is it then possible to use real paint of a certain brand of which you know that the cyan, magenta and yellow have (nearly) the same value as the digital ones. And would mixing the real paint with the same percentages produce (almost) the same color as the digital color? Are the proportions comparable?

No, I wouldn't use cyan and magenta artist's paints for your device as they do not work very well as mixing primaries. Yellow and magenta mix to give quite dull reds and oranges, unlike their digital versions. I think you would get the biggest range of mixed colours using a bright yellow and strong staining reds (such as permanent alizarin or a quinacridone) and blues (a Pthalo blue). (I don't think these will give you any problems with chemical reactions).

So, if you choose your red, yellow and blue pigments (plus a white? which, as I suggested, would give you a greater range of possible mixtures), there is nothing to stop you defining your own colour space based on the proportions of these colours. You would need to decide the kind of scaling you are using e.g. does 50Y50R mean equal amounts of red and yellow (by weight?, by volume?) or is it the mixture perceptually halfway between the two? But the only way you could relate your arbitrary colour space to RGB would be to work backwards: make up a whole bunch of charts of your R,Y,B and W pigments in carefully measured proportions and scan them.

But would it really be such a great idea?

When I paint I think of colours and colour relationships in terms of a colour space, but not one defined in terms of proportions of an arbitrary set of pigments. The colour space in my head has three dimensions: tone (lightness vs darkness), hue (i.e position around the colour wheel) and chroma (relative intensity between neutral and the maximum possible for that hue). The space is basically shaped like a double cone, with the colour wheel in the middle and white and black at the opposite ends, except that the colour wheel is tilted so that yellow, being light-toned at its greatest chroma, is high up, and blue and violet, being low-toned at their greatest intensity, are low down. (This particular system was described by Arthur Pope of Harvard in a series of papers in the early 1900s). I can not begin to say how vital I think it is to have some sort of conception of this sort in your mind when you are painting, both as a guide to mixing the colours you are after, and to understanding the colour relationships you are trying to create. I put it to you that learning to think about colour in this way would be a much better use of your enquiring mind. :wink:

madster

July 1st, 2005, 10:51 AM

Elwell

July 1st, 2005, 12:31 PM

There's a lot of good, solid information about color on Don Jusko's site. Unfortunately, it's mixed in with an equal amount of stuff that's just plain wacky, and there's no way for the beginner to tell one from the other. Half the time it reads like the the label on a Dr. Bronner's soap bottle.

Elwell

July 1st, 2005, 12:41 PM

Tjendol, you need to stop asking theoretical questions and actually do some color mixing. I think you'll find this very useful: http://www.goldenpaints.com/technicaldata/mixguide.php

Tjendol

July 1st, 2005, 01:30 PM

Tjendol, you need to stop asking theoretical questions and actually do some color mixing. I think you'll find this very useful: http://www.goldenpaints.com/technicaldata/mixguide.php

Thanks for the url.

I do need to practice with color mixing but there's nothing wrong with gathering useful theoretical information first. This topic has been very clarifying to me and I learn from almost every post made. Some people in here carry an incredible amount of knowledge and I think this will help me and others even more before actually start practicing. You're absolutely right that practise will be probably very useful next to the theoretical info.

Learning to mix myself with real paints won't provide the answer I'm looking for (not to mention whether the answer can be found or not.):
Electronically measuring colors of objects (output is RGB) and next finding a system to get to the measured color with an RYB real paint palette.

Using CMY(K) would be possible in theory because you can convert RGB into CMY although problems can occur with this method and people don't always agree on using this method, as can be read in this thread as well. Since there's no known conversion from RGB to RYB (with white) it will be a problem finding a way to use RYB pigments.

briggsy@ashtons: I'm not sure if it is a good idea, up till now I was just finding out if it's even possible. People will dispute about whether it's a good idea or not...I don't know..maybe it can be..maybe it will turn out to be useless :) Thinking and reading about it is interesting though.

I would like to see if instead of a teacher that tells me what color to add to my mix to get the desired color..a device can do the same and make it understandable for me.

Elwell

July 1st, 2005, 01:54 PM

Learning to mix myself with real paints won't provide the answer I'm looking for (not to mention whether the answer can be found or not.):
Electronically measuring colors of objects (output is RGB) and next finding a system to get to the measured color with an RYB real paint palette.

Using CMY(K) would be possible in theory because you can convert RGB into CMY although problems can occur with this method and people don't always agree on using this method, as can be read in this thread as well. Since there's no known conversion from RGB to RYB (with white) it will be a problem finding a way to use RYB pigments.
Actually, what you describe is pretty much how color matching systems for housepaints work. You can bring in a swatch of fabric, for example, and a computer scans it and then figures out the formula for mixing that color from a limited number of bases and tinting agents. I don't think such a system is practical, or for that matter desirable, for artistic painting, though.

Tjendol

July 1st, 2005, 02:13 PM

Yeah I've read about these systems when I was surfing on the web last week.
It's kind of what I mean only now I don't want the system to do all the work but interact with the user by 'watching the mixing' and support him if desired.

Judging if it will be a practical tool will be a personal preference and is maybe something that should be tested.

jfrancis

July 14th, 2005, 05:28 PM

3D renderers as old as Renderman (The Renderman Companion, Steve Upstill, p. 42) and as young as Maxwell, have had the ability to represent colors in higher than the usual 3 samples (at red, green, and blue) along the spectrum. A common practice (among those who use multi-spectral sampling) is to represent colors with 9, and sometimes 12, wavelength samples.

This is especially useful for representing colors in so-called "subtractive color" situations, such as the layering of transparent colored objects, or their interreflections against each other, or the color falloff of objects underwater, or in exotic atmospheres.

Has the idea of multi-spectral sampling made it into Painter's internal color-mixing calculations? In the artist's oils routines, for example?

I'm wondering how much real world Physics and real world paint testing and mixing has made its way into the Painter IX color engine.

Anyone know?

jfrancis

November 19th, 2005, 12:43 PM

Maxwell multispectral color picker screenshot...

http://www.maxwellrender.com/whitepaper/images/matSpec.png

At some point all color pickers, from Maya to Painter, will probably have internal multispectral sampling color math and an advanced mode with a color picker that looks something like this.

briggsy@ashtons

November 20th, 2005, 08:23 PM

I would have thought that the point of introducing this sort of sophistication into a paint program would be to try to emulate the mixing behaviour of specific pigments. The latter DOES depend on the actual spectral reflectance curves of the pigments involved, so that the results you get differ from those of ideal subtractive mixing, and you can't predict from their hue whether or not two pigments will be exact mixing complements. I haven't seen any attempt to represent specific pigments in Painter, where, based on my very limited experience, the mixing complement pairs appear to be those of ideal subtractive mixing, and where you DO know from the hue of your components which pairs will be mixing complements. Am I wrong about this?

Ilaekae

November 23rd, 2005, 01:29 PM

I really can't wait til my comp gets here so I can do something really constructive. I have just...so HELP me, Goddess...read every single damn entry in this thread...I am now ready to die...

Screw using the word "color." Screw RGB, CMY, CMYK, PMS, Focaltone, ad nauseum...

SOME THINGS CAN NOT BE DONE! No matter how much you think you can do something theoretically, no matter what opinions/knowledge/theoretical evidence you gather... IT CAN NOT BE DONE!

Use words that do not pertain to color and it's conversion, and you'll see what I mean.

Q. Can you build a wooden car?
A. Of course.
Q. Then what wood would you use to make the engine block? Or the transmission gears?

Q. All organic matter is made up of carbon, hydrogen, nitrogen, and oxygen. Right?
A. Yup.
Q. Then, if I pour a bunch of each into a milk bottle, how long do I have to shake it up to get a baby brother?

Does this give you some idea of what I'm trying to get across? The various uses/applications/existence of different types of colors are dependent on their ultimate form and use. Artists pigments are dependent on chemistry and chemical interactions AND the reflected light from those chemicals, which has absolutely friggin' nuthin' to do with RGB! Or CMYK reproduction! Or chicken soup! It's not always possible to make a "conversion" between different systems because many of the POINTS (colors) in one system you are trying to match just don't exist in the other system. Arguing about the theoretical possibilities will NOT make it any different, just as knowing you CAN make a wooden car, BUT you will still need METAL engine parts for it to work. You just CAN NOT MAKE a working internal combustion engine out of friggin' wood! Just because you think your cat is the most beautiful creature on earth doesn't mean you can take her out to the movies and then get her pregnant in the back seat of your Ford! How about a little theoretical reining in here, and a bit more common sense?

Phalanx3D

January 27th, 2007, 12:25 PM

You guys got carried away here

found this in 00:03

http://www.liquitex.com/Products/pixel2paint.cfm

-p3d

Crusoe the Painter

February 11th, 2007, 04:02 AM

Actually, painting with CMYK isn't all that hard. The only problem points with my experiments have been 'warmer' greens and true deep purples. But there are no perfect pigments. There is no "True" red or "Magenta" or "Blue", they're all biased in some fashion.

I find the muddy color problems to be much less than that from using the split RYB palletes that most books use. Even if they use split RYB palletes.

Quinacridone Magenta, Light Yellow, and Marine Blue from Holbein work quite well. Add to this a warm yellow-green, a good violet, and a good middle red, white and black and you'll be suprised at the color range of these 8 colors.

The only problem I've encountered is that these pigments tend to have HUGE tinting power, so mixing colors needs to be done carefully. The pure mixes are also very bright.