8 ms·

Color wheels are wrong? How color vision actually works

225 points by akkartik 16y ago

diiq 16y ago
I'm happy to see someone investigating color, and the way we perceive it. So many color theory books are more mystical than scientific; it's wonderful to see a physiological model. I suspect that we continue to teach the RGB, RBY, and CYMK color wheels because they behave correctly with respect to the behavior of particular physical media. Yellow-looking paint and blue-looking paint do make green-looking paint. Red-looking light and green-looking light do make yellow-looking light. The (physiologically accurate?) four-primary-color model proposed here does not correctly predict the world: yellow and blue act as additive color opposites; red and green act as subtractive color opposites. No one set of pigments or lights will ever consistently behave the way this 4 color wheel predicts. We need multiple systems because colored objects mix by multiple mechanisms.
- sedachv 16y ago
  It's not really a new thing. Rudolf Arnheim's Art and Visual Perception (published in 1974, widely read in art school from what I understand) had a whole chapter about exactly the same material as in that blog post. But before that it had a chapter on the psychology of color, and why the color wheel is in fact useful.
  - diiq 16y ago
    Right! I used "proposed" to mean "argued for" rather than "set forth for the first time". Arnheim is kind enough to distinguish between "generative complements" and what he calls "fundamental complements", (though I would prefer they be called "perceptual"). He warns specifically against confusing perceptual color and color-in-the-world. By making that distinction, Arnheim validates BOTH systems, rather than attempting to invalidate three-primary systems (as this article appears to do). The article calls RGB and RBY color "wrong" and unable to "stand up to even minor scrutiny". Arnheim calls them "generative". I claim their generative nature (that they inform how to create color) is why they are taught in schools. I'm not denying the four-color idea; I'm just saying it is based on a different definition of color, and different intended use of color.
sfphotoarts 16y ago
while the article looks like a mashup of text-books and wikipedia (not to mention the self-aggrandization) and is interesting, this looks like SEO spam, one of these sites that sells you some book on how to get rich quick or how to start your startup. I think I'll stick with my Johannes Itten.
- michael_dorfman 16y ago
  You talk about what the article "looks like", but have you actually read it? I found it to be a well-written, well-researched introduction to some of the problems in color theory. If that's what you mean by "a mashup", then I guess all secondary literature is. As for the site, asmartbear is no stranger to these parts, and Jason's posts are well-regarded.
  - sfphotoarts 16y ago
    possibly my British grammar is stumping you, but yes, to read something you have to look at it. This article might appear well researched here, but this is the hello-world equivalent on an art forum. Maybe if Jason believes he has something meaningful to contribute to color theory, he should consider updating the Wikipedia page rather than promoting his own self interest by advertising his book & blog on HN.
    - barrkel 16y ago
      > to read something you have to look at it. It seems basic logic is stumping you: when A implies B, and B is true, it does not follow that A is true. You assert that you've looked at the article, and certainly one needs to look at the article to read it, but that doesn't imply that you've read it. > this is the hello-world equivalent on an art forum I fear you might be at the wrong place - Hacker News isn't an art forum.
    - jacobolus 16y ago
      > he should consider updating the Wikipedia page Please note that anyone enthusiastic to learn and contribute is extremely welcome on the color-related Wikipedia articles; many of them are in a pretty sorry state.
wccrawford 16y ago
The budding designer in me loves these articles. While I can intellectually understand the color wheel(s), I'm still having issues grasping it emotionally and creatively.
lukev 16y ago
I wish I could upvote this twice. I hadn't realized that our actual perception of color was so filtered from the physical spectrum. I find it incredibly fascinating, from a philosophical perspective, that there are literally color combinations (i.e, greenish-red) that, despite lying within the physical spectrum to which our eyes are sensitive, we cannot see, cannot even imagine.
- NonMint 16y ago
  The thing that will really blow your mind is are there things that are red, or a group of things that have a common appearance that our minds just label "red." And what if what if the signals that reach my brain when I view "red" are shifted one to the left on the color wheel? The gradual perception of color change would be perceived but we would be looking at different colors even though we both agree that it is "Red."
  - foljs 16y ago
    Yes, it would blow my mind, if that wasn't the kind of stuff 12 years old sci-fi fans talk about, you know, the kind confusing semantics games with reality...
  - apl 16y ago
    > The thing that will really blow your mind is [...] Only if "you" refers to a stoned college kid. The realization that qualia -- such as the redness of red -- are fundamentally subjective is, quite frankly, an old hat.
sambeau 16y ago
The checkerboard illusion at the end amazes me every time I see it.
joeld42 16y ago
This article tries to sensationalize and obfuscate something that is pretty simple in reality. RGB are the primaries in light. By mixing these three colors you can create any color the human vision system can perceive (yes, because of tristimulus). When white light hits a material, some of those RGB wavelengths are absorbed (subtracted). RGB - GB(Cyan) = Red, RGB - RG(Yellow) = Blue, RGB - RB(Magenta) = Green. Thus, Cyan, Magenta and Yellow act as primaries (colors from which you can construct any visible color) for materials that absorb, not emit light. The forth primary in print media, Black, is simply added because inks are imperfect and a mix of CMY inks yields a kind of murky black (plus it wastes ink). It's a historical simplification to say that "red, yellow and blue" are the primaries for paint, the red works like a magenta, the blue works like a cyan. They sell Cyan/Yellow/Magenta primaries for oil/acrylics and if you paint with these you'll get a brighter, wider palette but you can get there with a traditional palette by adding whites and other pigments. The tone of the article is awful. The opening sentence, "Ask any artist..." is flatly untrue, this stuff is basic for most visual artists (I first learned about the CMY primaries in a community ed. Painting I class). It's not that the article is factually wrong, it's just basic stuff presented as if it were obscure or clever. None of this makes the color wheel or any other color theory any less valid. The "four color" wheel he lists at the end is not wrong, it's just silly: you could pick any points on the wheel and their opposites and have the same thing.
- sfphotoarts 16y ago
  You said it with more finesse, but exactly. This is just an badly written article on a subject that is clearly not understood by the author trying to grab eyeballs through sensationalism. Using printer inks as an example was the first big cue that this was link bait to a self-aggrandizing blog.
- bobds 16y ago
  > just basic stuff presented as if it were obscure or clever. I think the part about the three filters is at least somewhat obscure and probably the most useful thing I learned from the article.
- speleding 16y ago
  Can you explain why your statement "pretty simple... RGB are the primaries in light" is true, his explanation in his article "complex... RGB is just a rough approximation" is false? He gives a plausible physiological explanation.
kylec 16y ago
I must have missed something as a seven-year-old, because this is the first I've heard that blue and yellow were supposed to be opposites. To me, it always made sense that blue and orange were opposites, both conceptually and visually. The same with purple and yellow.
- Zaak 16y ago
  It's possible you're an anomalous trichromat: http://en.wikipedia.org/wiki/Color_blindness#Anomalous_trichromacy http://en.wikipedia.org/wiki/Color_blindness#Anomalous_trich...
- KevinMS 16y ago
  Yes I don't understand why this mistake is being made. The opposites are blue-orange, purple-yellow(easter colors), red-green(christmas colors).
jessriedel 16y ago
EDIT: joeld42 answered my question elsewhere on this page: http://news.ycombinator.com/item?id=2166782 http://news.ycombinator.com/item?id=2166782 The artists reds and blues are just approximations to the magenta and cyan of printers. ---- So I understand that in order to mimic the electromagnetic stimulation to the cones you only need to control the amount of RGB light hitting the retina. And I understand that propagating light is additive, so that for light producing displays you mix amounts of RGB, whereas pigments subtract light, so that for printing you mix amounts of CMY. (C paint absorbs non-R light, M paint absorbs non-G light, and Y paint absorbs non-B light.) I further (kind of) understand that once printing and CRT screens are explained, there are additional properties of light due to the filters described in the article. But can someone explain why the artist's paints are different from the CMY ink pigments? It seems like it's either (a) something weird about the way paints mix, (b) artists use paints which somehow take advantage of the filters in the eye, or (c) a combination.
- lutorm 16y ago
  Maybe you mistyped, but cyan paint absorbs red light, it reflects everything but red, i.e. cyan.
  - jessriedel 16y ago
    yes I did
- kronusaturn 16y ago
  Partly because cyan and magenta pigments good enough that you can mix them with yellow and get a decent red and green are a relatively modern invention. Partly because the reds and greens you get still aren't nearly as vivid as unmixed pigments. Partly because it's easier to start with a pigment that's close to what you want and adjust it than to start from scratch with only CMY.
bobds 16y ago
Site was temporarily unavailable when I tried to post a comment, so here it goes: This post clears up a few misconceptions for me, thanks for that. I think you will enjoy the following link about "context" related illusions: http://www.psy.ritsumei.ac.jp/~akitaoka/color12e.html http://www.psy.ritsumei.ac.jp/~akitaoka/color12e.html Akiyoshi Kitaoka is a university professor from Japan that has created a very extensive and amazing collection of illusions, documenting so many subtle ways our eyes play tricks on us. His homepage is really worth exploring: http://www.psy.ritsumei.ac.jp/~akitaoka/index-e.html http://www.psy.ritsumei.ac.jp/~akitaoka/index-e.html
nollidge 16y ago
I'm getting a 503 error. Obligatory Google cache: http://webcache.googleusercontent.com/search?q=cache:oS8AaG3vxYQJ:blog.asmartbear.com/color-wheels.html+http://blog.asmartbear.com/color-wheels.html&cd=1&hl=en&ct=clnk&gl=us&source=www.google.com http://webcache.googleusercontent.com/search?q=cache:oS8AaG3...
martian 16y ago
In the early 20th century Albert Munsell did a series of empirical studies to determine exactly how people see colors relative to one another. The results are expected, but fascinating. http://en.wikipedia.org/wiki/Munsell_color_system http://en.wikipedia.org/wiki/Munsell_color_system
- jacobolus 16y ago
  Why are the results expected? (Also, I really need to expand the Munsell Wikipedia article, but Albert Munsell was dead before much of the empirical work that went into the 1929 Munsell Book of Color – by that point his son was running the company – or into the 1943 Munsell Renotations, which were based on the work of the Optical Society of America.)
mattmillr 16y ago
It's interesting that Red/Green and Blue/Yellow colorblindness correlate to the opposite color pairs that Jason points out. Does anyone know why this is? Are these types of colorblindness related to a deficiency in the filters (#s 1 and 2) he describes?
knutae 16y ago
I find the CIE Standard Observer graph enlightening: http://en.wikipedia.org/wiki/CIE_1931_color_space#Color_matching_functions http://en.wikipedia.org/wiki/CIE_1931_color_space#Color_matc... As far as I understand this, the red function, which corresponds to the red receptors in a typical human eye, reacts mostly to high wavelengths, but also has a small spike in the lower end of the spectrum. This explains why the violet end of the spectrum looks similar to red to human eyes, and this is probably why color wheels seem so natural. After all, a color wheel is almost the same as rainbow that wraps around. I also find it fascinating that the CIE color space was defined as early as 1931.
- jacobolus 16y ago
  No, the CIE standard observer is not the same as the responsivities of cone cells in the eye. That article you linked describes how it was arrived at: 1. Match monochromatic (narrow wavelength band) light sources of each wavelength with three particular monochromatic lights (called “R”, “G”, “B”), in some cases needing to add some of one of those three to the monochromatic source in order to get the two sides to match – this is a “negative” component. This process results in three (r(λ), g(λ), b(λ)) functions of wavelength. 2. Take three linear combinations of those three functions and call them (x(λ), y(λ), z(λ)), such that (a) the y(λ) function is approximately the same as the photopic luminance function as best it could be computed at the time, (b) all three of x, y, and z had only positive values, and (c) integrating each of the three yields the same value, so that an equal-energy stimulus will have the same X, Y, and Z values. The red receptors in the human eye do not really have this kind of spike in response in the lower end of the spectrum. * * * However, “red” the “psychological primary” or “unique hue” does have some violet/blue in it. Any monochromatic red light source is a bit on the orange side.
steadicat 16y ago
Why does he conclude that we need 4 primary colors? He knows that our eyes have three kinds of 'sensors', which roughly correspond to [R, G, B]. How the brain processes the initial perceptions, allegedly [R-G, (R+G)-B, R+G+B], doesn't change the fact that you can approximate all colors by mixing quantities of R, G and B. What I'd find more interesting is a proposal (or a mention) of a color space that's based on what are, according to him, the 'computed' values. Something like NTL (tiNt/Temperature/Luminance), where N is R-G, T is (R+G)-B, and L is R+G+B. (The names 'tint' and 'temperature' are taken from photo editing software, as they are the only tools I can think of that come close to this system.)
- cwp 16y ago
  Actually, this kind of encoding is quite common. Analog television, digital video and JPEG images are all encoded using brightness, red-green and blue-yellow channels. The details vary (eg. between YUV, YCbCr and YPbPr) but they all take advantage of the fact that our eyes are more sensitive to variations in brightness than to variations in colour. As a result, we can subject the colour data to higher levels of compression without noticing any visual degradation of the image.
armandososa 16y ago
Artists get it wrong I kinda get upset about all his use of "artist" as a derogatory term. Have he ever painted anything in real life? Beleive it or not, just a canvas plus red, blue and yellow acrylic paint will be enough. Oh, and some kind of talent.
- jackolas 16y ago
  I'm not sure that understanding color as we experience it is required to be a good artist, but it might help the more engineer-ish of us.
- icegreentea 16y ago
  Agreed. The fact that artists make stuff that 'works' at all should be hint enough that they aren't completely wrong. Just working with a useful approximation/abstraction layer.
- KevinMS 16y ago
  Beleive it or not, just a canvas plus red, blue and yellow acrylic paint will be enough. This is actually not completely true, but I appreciate the point you are making. Something we shouldn't overlook is that there no pigments that fit perfectly on a color wheel. In other words, there's no blue pigment, its always blueish green or blueish purple. This has been a challenge for pigment makers for centuries and has a complicated history. Maybe sometimes a perfect pigment or dye is found, color wise, but then it turns out to easily fade, aka 'fugitive', so artists, the ones who expect their art work to last for more than a few years, are stuck with certain colors. Why does this matter? Its because of mixing. You might think you have paints of the primaries, blue, yellow, and red, and you need a bright green, so you mix the blue with the yellow, and you end up with an muddy olive color. Turns out your blue was leaning towards being purplish, and when mixed with the yellow, a component of grey was produced, because they are opposite. So how do you get a nice bright green? You need to mix a greenish blue with a greenish yellow. In practice this results in artists, who want to paint with a full range of colors, need 6 primary colors. For example, two good lightfast (not destroyed by light) blues are ultramarine (very old pigment), and a newer phthalo blue (much more modern). The ultramarine leans towards the violet and the phthalo, to varying degrees, towards green. In the old days I think prussian blue was the greenish blue of choice, but its a weak color and is easily overpowered. Cobalt blue, if I'm not mistaken, is the closest thing we have to a lightfast primary color. Artist really hit the jackpot with blues. Some are very old. They are also nicely transparent, which can make a difference in technique The bright reds and bright yellows aren't so good, and the ones that are lightfast are supposed to be toxic. And not very transparent either. If you don't care about the brightness of your reds and yellows you are in luck, there are plenty of rust and dirt pigments like iron oxide, sienna and umber. This is a complicated subject. Here's a book about it http://www.amazon.com/Blue-Yellow-Dont-Make-Green/dp/0967962870 http://www.amazon.com/Blue-Yellow-Dont-Make-Green/dp/0967962...
m-photonic 16y ago
>And magenta? It comes from full R and B with no G, activating Filter #1 full-positive, Filter #2 at zero. This doesn't seem right to me. If the second filter were at zero, you should have a pure red and not something with blue content in it like magenta clearly has. I think he may be representing the second filter as R+G-B, when R+G-2B would make more sense. The latter system shows FFFFFF as being neutral on the yellow-blue axis, while the former erroneously puts it in the yellow region.
- jacobolus 16y ago
  None of these are straight-forward “linear” sums: there are differing amounts of each type of cone cell in the retina (and the proportions vary from one part of the retina to another), there are several levels of combination of signals which we don’t fully understand currently, the eye/brain adapts to what it’s just been looking at, what else is in the visual field, what it knows the light source to be, what “memory colors” it expects for an object, and so forth. Thinking of the mechanisms of the eye operating directly on “FFFFFF” is a very imprecise model for what’s happening.
apl 16y ago
> But I digress, and besides I did promise to be all gross > and irresponsible, so I’ll stick with that. > So there are R, G, and B cones. Cute and all, but so very wrong. There are acceptable simplifications; this is not one of them.
mambodog 16y ago
A while ago I submitted an article[1] about the YUV colour system, which takes into account human perception of brightness/luminance, and how it differs between colours. It's also an interesting colour system to work with, as the 'Y' channel just stores luminance, so discarding the other two channels gives you a greyscale image. I recommend reading it if you haven't already. [1] http://nreynolds.co.uk/blog/hsv-is-dead/ http://nreynolds.co.uk/blog/hsv-is-dead/
blahblahblah 16y ago
So there’s no such thing as "red with a little green" -- there’s just a less intense red. The brain physically cannot see "greenish-red" because the filter removes that information. Under ordinary circumstances this is true. However, it has been shown that the human brain can be made to see reddish-green, yellowish-blue, etc. Scientific American published an article about this strange hack of human visual perception just last year. http://www.scientificamerican.com/article.cfm?id=seeing-forbidden-colors http://www.scientificamerican.com/article.cfm?id=seeing-forb...
thret 16y ago
If you enjoyed that article, you may also like http://www.designersreviewofbooks.com/2010/10/interaction-of-color-by-josef-albers/ http://www.designersreviewofbooks.com/2010/10/interaction-of... It is a beautiful book.

225 points by akkartik 16y ago

diiq 16y ago

I'm happy to see someone investigating color, and the way we perceive it. So many color theory books are more mystical than scientific; it's wonderful to see a physiological model. I suspect that we continue to teach the RGB, RBY, and CYMK color wheels because they behave correctly with respect to the behavior of particular physical media. Yellow-looking paint and blue-looking paint do make green-looking paint. Red-looking light and green-looking light do make yellow-looking light. The (physiologically accurate?) four-primary-color model proposed here does not correctly predict the world: yellow and blue act as additive color opposites; red and green act as subtractive color opposites. No one set of pigments or lights will ever consistently behave the way this 4 color wheel predicts. We need multiple systems because colored objects mix by multiple mechanisms.

sedachv 16y ago
It's not really a new thing. Rudolf Arnheim's Art and Visual Perception (published in 1974, widely read in art school from what I understand) had a whole chapter about exactly the same material as in that blog post. But before that it had a chapter on the psychology of color, and why the color wheel is in fact useful.
- diiq 16y ago
  Right! I used "proposed" to mean "argued for" rather than "set forth for the first time". Arnheim is kind enough to distinguish between "generative complements" and what he calls "fundamental complements", (though I would prefer they be called "perceptual"). He warns specifically against confusing perceptual color and color-in-the-world. By making that distinction, Arnheim validates BOTH systems, rather than attempting to invalidate three-primary systems (as this article appears to do). The article calls RGB and RBY color "wrong" and unable to "stand up to even minor scrutiny". Arnheim calls them "generative". I claim their generative nature (that they inform how to create color) is why they are taught in schools. I'm not denying the four-color idea; I'm just saying it is based on a different definition of color, and different intended use of color.

sfphotoarts 16y ago

while the article looks like a mashup of text-books and wikipedia (not to mention the self-aggrandization) and is interesting, this looks like SEO spam, one of these sites that sells you some book on how to get rich quick or how to start your startup. I think I'll stick with my Johannes Itten.

michael_dorfman 16y ago
You talk about what the article "looks like", but have you actually read it? I found it to be a well-written, well-researched introduction to some of the problems in color theory. If that's what you mean by "a mashup", then I guess all secondary literature is. As for the site, asmartbear is no stranger to these parts, and Jason's posts are well-regarded.
- sfphotoarts 16y ago
  possibly my British grammar is stumping you, but yes, to read something you have to look at it. This article might appear well researched here, but this is the hello-world equivalent on an art forum. Maybe if Jason believes he has something meaningful to contribute to color theory, he should consider updating the Wikipedia page rather than promoting his own self interest by advertising his book & blog on HN.
  - barrkel 16y ago
    > to read something you have to look at it. It seems basic logic is stumping you: when A implies B, and B is true, it does not follow that A is true. You assert that you've looked at the article, and certainly one needs to look at the article to read it, but that doesn't imply that you've read it. > this is the hello-world equivalent on an art forum I fear you might be at the wrong place - Hacker News isn't an art forum.
  - jacobolus 16y ago
    > he should consider updating the Wikipedia page Please note that anyone enthusiastic to learn and contribute is extremely welcome on the color-related Wikipedia articles; many of them are in a pretty sorry state.

wccrawford 16y ago

The budding designer in me loves these articles. While I can intellectually understand the color wheel(s), I'm still having issues grasping it emotionally and creatively.

lukev 16y ago

I wish I could upvote this twice. I hadn't realized that our actual perception of color was so filtered from the physical spectrum. I find it incredibly fascinating, from a philosophical perspective, that there are literally color combinations (i.e, greenish-red) that, despite lying within the physical spectrum to which our eyes are sensitive, we cannot see, cannot even imagine.

NonMint 16y ago
The thing that will really blow your mind is are there things that are red, or a group of things that have a common appearance that our minds just label "red." And what if what if the signals that reach my brain when I view "red" are shifted one to the left on the color wheel? The gradual perception of color change would be perceived but we would be looking at different colors even though we both agree that it is "Red."
- foljs 16y ago
  Yes, it would blow my mind, if that wasn't the kind of stuff 12 years old sci-fi fans talk about, you know, the kind confusing semantics games with reality...
- apl 16y ago
  > The thing that will really blow your mind is [...] Only if "you" refers to a stoned college kid. The realization that qualia -- such as the redness of red -- are fundamentally subjective is, quite frankly, an old hat.

sambeau 16y ago

The checkerboard illusion at the end amazes me every time I see it.

joeld42 16y ago

This article tries to sensationalize and obfuscate something that is pretty simple in reality. RGB are the primaries in light. By mixing these three colors you can create any color the human vision system can perceive (yes, because of tristimulus). When white light hits a material, some of those RGB wavelengths are absorbed (subtracted). RGB - GB(Cyan) = Red, RGB - RG(Yellow) = Blue, RGB - RB(Magenta) = Green. Thus, Cyan, Magenta and Yellow act as primaries (colors from which you can construct any visible color) for materials that absorb, not emit light. The forth primary in print media, Black, is simply added because inks are imperfect and a mix of CMY inks yields a kind of murky black (plus it wastes ink). It's a historical simplification to say that "red, yellow and blue" are the primaries for paint, the red works like a magenta, the blue works like a cyan. They sell Cyan/Yellow/Magenta primaries for oil/acrylics and if you paint with these you'll get a brighter, wider palette but you can get there with a traditional palette by adding whites and other pigments. The tone of the article is awful. The opening sentence, "Ask any artist..." is flatly untrue, this stuff is basic for most visual artists (I first learned about the CMY primaries in a community ed. Painting I class). It's not that the article is factually wrong, it's just basic stuff presented as if it were obscure or clever. None of this makes the color wheel or any other color theory any less valid. The "four color" wheel he lists at the end is not wrong, it's just silly: you could pick any points on the wheel and their opposites and have the same thing.

sfphotoarts 16y ago
You said it with more finesse, but exactly. This is just an badly written article on a subject that is clearly not understood by the author trying to grab eyeballs through sensationalism. Using printer inks as an example was the first big cue that this was link bait to a self-aggrandizing blog.
bobds 16y ago
> just basic stuff presented as if it were obscure or clever. I think the part about the three filters is at least somewhat obscure and probably the most useful thing I learned from the article.
speleding 16y ago
Can you explain why your statement "pretty simple... RGB are the primaries in light" is true, his explanation in his article "complex... RGB is just a rough approximation" is false? He gives a plausible physiological explanation.

kylec 16y ago

I must have missed something as a seven-year-old, because this is the first I've heard that blue and yellow were supposed to be opposites. To me, it always made sense that blue and orange were opposites, both conceptually and visually. The same with purple and yellow.

Zaak 16y ago
It's possible you're an anomalous trichromat: http://en.wikipedia.org/wiki/Color_blindness#Anomalous_trichromacy http://en.wikipedia.org/wiki/Color_blindness#Anomalous_trich...
KevinMS 16y ago
Yes I don't understand why this mistake is being made. The opposites are blue-orange, purple-yellow(easter colors), red-green(christmas colors).

jessriedel 16y ago

EDIT: joeld42 answered my question elsewhere on this page: http://news.ycombinator.com/item?id=2166782 http://news.ycombinator.com/item?id=2166782 The artists reds and blues are just approximations to the magenta and cyan of printers. ---- So I understand that in order to mimic the electromagnetic stimulation to the cones you only need to control the amount of RGB light hitting the retina. And I understand that propagating light is additive, so that for light producing displays you mix amounts of RGB, whereas pigments subtract light, so that for printing you mix amounts of CMY. (C paint absorbs non-R light, M paint absorbs non-G light, and Y paint absorbs non-B light.) I further (kind of) understand that once printing and CRT screens are explained, there are additional properties of light due to the filters described in the article. But can someone explain why the artist's paints are different from the CMY ink pigments? It seems like it's either (a) something weird about the way paints mix, (b) artists use paints which somehow take advantage of the filters in the eye, or (c) a combination.

lutorm 16y ago
Maybe you mistyped, but cyan paint absorbs red light, it reflects everything but red, i.e. cyan.
- jessriedel 16y ago
  yes I did
kronusaturn 16y ago
Partly because cyan and magenta pigments good enough that you can mix them with yellow and get a decent red and green are a relatively modern invention. Partly because the reds and greens you get still aren't nearly as vivid as unmixed pigments. Partly because it's easier to start with a pigment that's close to what you want and adjust it than to start from scratch with only CMY.

bobds 16y ago

Site was temporarily unavailable when I tried to post a comment, so here it goes: This post clears up a few misconceptions for me, thanks for that. I think you will enjoy the following link about "context" related illusions: http://www.psy.ritsumei.ac.jp/~akitaoka/color12e.html http://www.psy.ritsumei.ac.jp/~akitaoka/color12e.html Akiyoshi Kitaoka is a university professor from Japan that has created a very extensive and amazing collection of illusions, documenting so many subtle ways our eyes play tricks on us. His homepage is really worth exploring: http://www.psy.ritsumei.ac.jp/~akitaoka/index-e.html http://www.psy.ritsumei.ac.jp/~akitaoka/index-e.html

nollidge 16y ago

I'm getting a 503 error. Obligatory Google cache: http://webcache.googleusercontent.com/search?q=cache:oS8AaG3vxYQJ:blog.asmartbear.com/color-wheels.html+http://blog.asmartbear.com/color-wheels.html&cd=1&hl=en&ct=clnk&gl=us&source=www.google.com http://webcache.googleusercontent.com/search?q=cache:oS8AaG3...

martian 16y ago

In the early 20th century Albert Munsell did a series of empirical studies to determine exactly how people see colors relative to one another. The results are expected, but fascinating. http://en.wikipedia.org/wiki/Munsell_color_system http://en.wikipedia.org/wiki/Munsell_color_system

jacobolus 16y ago
Why are the results expected? (Also, I really need to expand the Munsell Wikipedia article, but Albert Munsell was dead before much of the empirical work that went into the 1929 Munsell Book of Color – by that point his son was running the company – or into the 1943 Munsell Renotations, which were based on the work of the Optical Society of America.)

mattmillr 16y ago

It's interesting that Red/Green and Blue/Yellow colorblindness correlate to the opposite color pairs that Jason points out. Does anyone know why this is? Are these types of colorblindness related to a deficiency in the filters (#s 1 and 2) he describes?

knutae 16y ago

I find the CIE Standard Observer graph enlightening: http://en.wikipedia.org/wiki/CIE_1931_color_space#Color_matching_functions http://en.wikipedia.org/wiki/CIE_1931_color_space#Color_matc... As far as I understand this, the red function, which corresponds to the red receptors in a typical human eye, reacts mostly to high wavelengths, but also has a small spike in the lower end of the spectrum. This explains why the violet end of the spectrum looks similar to red to human eyes, and this is probably why color wheels seem so natural. After all, a color wheel is almost the same as rainbow that wraps around. I also find it fascinating that the CIE color space was defined as early as 1931.

jacobolus 16y ago
No, the CIE standard observer is not the same as the responsivities of cone cells in the eye. That article you linked describes how it was arrived at: 1. Match monochromatic (narrow wavelength band) light sources of each wavelength with three particular monochromatic lights (called “R”, “G”, “B”), in some cases needing to add some of one of those three to the monochromatic source in order to get the two sides to match – this is a “negative” component. This process results in three (r(λ), g(λ), b(λ)) functions of wavelength. 2. Take three linear combinations of those three functions and call them (x(λ), y(λ), z(λ)), such that (a) the y(λ) function is approximately the same as the photopic luminance function as best it could be computed at the time, (b) all three of x, y, and z had only positive values, and (c) integrating each of the three yields the same value, so that an equal-energy stimulus will have the same X, Y, and Z values. The red receptors in the human eye do not really have this kind of spike in response in the lower end of the spectrum. * * * However, “red” the “psychological primary” or “unique hue” does have some violet/blue in it. Any monochromatic red light source is a bit on the orange side.

steadicat 16y ago

Why does he conclude that we need 4 primary colors? He knows that our eyes have three kinds of 'sensors', which roughly correspond to [R, G, B]. How the brain processes the initial perceptions, allegedly [R-G, (R+G)-B, R+G+B], doesn't change the fact that you can approximate all colors by mixing quantities of R, G and B. What I'd find more interesting is a proposal (or a mention) of a color space that's based on what are, according to him, the 'computed' values. Something like NTL (tiNt/Temperature/Luminance), where N is R-G, T is (R+G)-B, and L is R+G+B. (The names 'tint' and 'temperature' are taken from photo editing software, as they are the only tools I can think of that come close to this system.)

cwp 16y ago
Actually, this kind of encoding is quite common. Analog television, digital video and JPEG images are all encoded using brightness, red-green and blue-yellow channels. The details vary (eg. between YUV, YCbCr and YPbPr) but they all take advantage of the fact that our eyes are more sensitive to variations in brightness than to variations in colour. As a result, we can subject the colour data to higher levels of compression without noticing any visual degradation of the image.

armandososa 16y ago

Artists get it wrong I kinda get upset about all his use of "artist" as a derogatory term. Have he ever painted anything in real life? Beleive it or not, just a canvas plus red, blue and yellow acrylic paint will be enough. Oh, and some kind of talent.

jackolas 16y ago
I'm not sure that understanding color as we experience it is required to be a good artist, but it might help the more engineer-ish of us.
icegreentea 16y ago
Agreed. The fact that artists make stuff that 'works' at all should be hint enough that they aren't completely wrong. Just working with a useful approximation/abstraction layer.
KevinMS 16y ago
Beleive it or not, just a canvas plus red, blue and yellow acrylic paint will be enough. This is actually not completely true, but I appreciate the point you are making. Something we shouldn't overlook is that there no pigments that fit perfectly on a color wheel. In other words, there's no blue pigment, its always blueish green or blueish purple. This has been a challenge for pigment makers for centuries and has a complicated history. Maybe sometimes a perfect pigment or dye is found, color wise, but then it turns out to easily fade, aka 'fugitive', so artists, the ones who expect their art work to last for more than a few years, are stuck with certain colors. Why does this matter? Its because of mixing. You might think you have paints of the primaries, blue, yellow, and red, and you need a bright green, so you mix the blue with the yellow, and you end up with an muddy olive color. Turns out your blue was leaning towards being purplish, and when mixed with the yellow, a component of grey was produced, because they are opposite. So how do you get a nice bright green? You need to mix a greenish blue with a greenish yellow. In practice this results in artists, who want to paint with a full range of colors, need 6 primary colors. For example, two good lightfast (not destroyed by light) blues are ultramarine (very old pigment), and a newer phthalo blue (much more modern). The ultramarine leans towards the violet and the phthalo, to varying degrees, towards green. In the old days I think prussian blue was the greenish blue of choice, but its a weak color and is easily overpowered. Cobalt blue, if I'm not mistaken, is the closest thing we have to a lightfast primary color. Artist really hit the jackpot with blues. Some are very old. They are also nicely transparent, which can make a difference in technique The bright reds and bright yellows aren't so good, and the ones that are lightfast are supposed to be toxic. And not very transparent either. If you don't care about the brightness of your reds and yellows you are in luck, there are plenty of rust and dirt pigments like iron oxide, sienna and umber. This is a complicated subject. Here's a book about it http://www.amazon.com/Blue-Yellow-Dont-Make-Green/dp/0967962870 http://www.amazon.com/Blue-Yellow-Dont-Make-Green/dp/0967962...

m-photonic 16y ago

>And magenta? It comes from full R and B with no G, activating Filter #1 full-positive, Filter #2 at zero. This doesn't seem right to me. If the second filter were at zero, you should have a pure red and not something with blue content in it like magenta clearly has. I think he may be representing the second filter as R+G-B, when R+G-2B would make more sense. The latter system shows FFFFFF as being neutral on the yellow-blue axis, while the former erroneously puts it in the yellow region.

jacobolus 16y ago
None of these are straight-forward “linear” sums: there are differing amounts of each type of cone cell in the retina (and the proportions vary from one part of the retina to another), there are several levels of combination of signals which we don’t fully understand currently, the eye/brain adapts to what it’s just been looking at, what else is in the visual field, what it knows the light source to be, what “memory colors” it expects for an object, and so forth. Thinking of the mechanisms of the eye operating directly on “FFFFFF” is a very imprecise model for what’s happening.

apl 16y ago

> But I digress, and besides I did promise to be all gross > and irresponsible, so I’ll stick with that. > So there are R, G, and B cones. Cute and all, but so very wrong. There are acceptable simplifications; this is not one of them.

mambodog 16y ago

A while ago I submitted an article[1] about the YUV colour system, which takes into account human perception of brightness/luminance, and how it differs between colours. It's also an interesting colour system to work with, as the 'Y' channel just stores luminance, so discarding the other two channels gives you a greyscale image. I recommend reading it if you haven't already. [1] http://nreynolds.co.uk/blog/hsv-is-dead/ http://nreynolds.co.uk/blog/hsv-is-dead/

blahblahblah 16y ago

So there’s no such thing as "red with a little green" -- there’s just a less intense red. The brain physically cannot see "greenish-red" because the filter removes that information. Under ordinary circumstances this is true. However, it has been shown that the human brain can be made to see reddish-green, yellowish-blue, etc. Scientific American published an article about this strange hack of human visual perception just last year. http://www.scientificamerican.com/article.cfm?id=seeing-forbidden-colors http://www.scientificamerican.com/article.cfm?id=seeing-forb...

thret 16y ago

If you enjoyed that article, you may also like http://www.designersreviewofbooks.com/2010/10/interaction-of-color-by-josef-albers/ http://www.designersreviewofbooks.com/2010/10/interaction-of... It is a beautiful book.