6 ms·

Color wheels are wrong? How color vision actually works

214 points by tobyjsullivan 14y ago

strebler 14y ago
It's definitely an interesting topic and a nice high level overview of the problems of colour and colour spaces. I like the 4 point colour wheel in some way, but I don't entirely see the benefits. From a computer vision perspective, this representation still has problems (as do all colour spaces). Look at how massive the green space is. There's 4-5 greenish slices that are close to each other, yet only 1 slice for yellow and 2ish for red. Red is the colour humans see "best", physiologically it should have the largest representation, whereas blue should be smallest. From the simpler side (i.e. a basic colour wheel application), I'm not sure if this makes it much easier or faster for me to find a colour. In any case, the article is very nice high level overview of a fascinating problem.
- AceJohnny2 14y ago
  "look at how massive the green space is..." This is why, in non-symmetric color coding systems, Green is given the largest share. For example 16-bit image formats give 5 bits for Red and Blue, but 6 bits for Green. The Bayer color pattern pattern used on CMOS sensors (basically all sensors on consumer devices) has interleaved rows of Green and Red and rows of Blue and Green: twice as much green as the other colors! Finally, green represents more than 50% of Luminance! From an evolutionary perspective, it makes sense to be more sensitive in the green spectrum: we were surrounded by green plants. Better catch the nuances to better identify predators or prey!
- evincarofautumn 14y ago
  I thought green was the colour humans saw best, if best means brightest. For instance, when converting from RGB to greyscale the usual weights are 30% red, 59% green, and 11% blue. (Though I always found it kind of unfortunate that these weights are wrong for people with nonstandard colour receptors.) In that sense, green should (seem to) be the largest because we perceive more colours as greenish than as reddish or bluish.
sp332 14y ago
In the S/M/L chart (this one http://asmartbear.wpengine.netdna-cdn.com/wp-content/uploads/Cone-fundamentals-with-srgb-spectrum.png http://asmartbear.wpengine.netdna-cdn.com/wp-content/uploads...) you can see that at the right-hand side, the M (green) activation is pretty low and goes to zero where L (red) is still strong enough to be visible. But there's no frequency on that graph where M (green) is active all by itself. So you've probably never in your whole life experienced a pure "green" sense input! CIE takes this into account when defining visible color spaces. Since you have 3 "primaries" you would expect the colorspace to be bounded by a triangle, each corner being a pure input of each primary. But you can see here https://en.wikipedia.org/wiki/International_Commission_on_Illumination https://en.wikipedia.org/wiki/International_Commission_on_Il... that the top green corner is missing. That's because there are no frequencies of light that would let you see any color that is "greener" or further toward where that corner would be. OK one last thing before I get to my proposal :) Your eyes gradually adapt against the colors you are looking at. For example if you're wearing red/blue 3d glasses for a while, when you take them off things will look greenish out of the "red" eye and yellower out of the "blue" eye. You can play tricks like this http://wxerfm.com/blogs/post/jfrieders/2012/jan/25/picture-cool-optical-illusion-star-negative-photo-/ http://wxerfm.com/blogs/post/jfrieders/2012/jan/25/picture-c... In fact it's possible to exhaust some of your photoreceptors, like the "spot" from a camera flash or the streak from a glare of sunlight. So here's my idea: if you strobe a really bright red & blue light, enough to temporarily blind the S & L receptors in your eyes, you should be able to see a green that is more pure and intense than you have ever experienced, right off the CIE chart of visible colors! Who's up for experimenting? :)
- hammock 14y ago
  >But there's no frequency on that graph where M (green) is active all by itself. So you've probably never in your whole life experienced a pure "green" sense input! I wonder if there is a medical condition out there where someone is missing the L (red) cones in their eyes - in that case they COULD see pure green sense input. In fact despite being disabled, they could see colors that everyone else is unable to see! edit: It does seem to exist, protanopes (a severe form of red-green colorblind) are missing the red cones. So if I understand correctly, while we tend to think of them as having a restricted spectrum, they may actually see some colors that others can't.
teilo 14y ago
I'm somewhat surprised that no mention was made of L * a * b color, since the four point color wheel corresponds to the a and b channels.
ken 14y ago
> Every seven-year-old kid in America is taught that “the opposite of red is green” and “the opposite of blue is yellow.” Did I sleep through second grade or something? I've spent the first 30+ years of my life in America and I've never heard of this.
- jrockway 14y ago
  Same. I know this, but only from looking at negatives.
- evincarofautumn 14y ago
  Different schools teach different things; many don’t introduce colour theory at all. And it’s an odd thing, but most people don’t know intuitively how colours combine or invert. Of course, as a synesthete and maybe a tetrachromat, I’m not really statistically relevant to this discussion. ;)
  - deleted 14y ago
    [deleted]
- Evbn 14y ago
  It's wrong. The opposite of blue is orange=red+yellow. Yellow is the opposite of purple=blue+red. Red is the opposite of green=yellow+blue, as written above. In paint pigments, in second grade.
- ianstormtaylor 14y ago
  Not only that, but I'm pretty sure everyone was taught that the opposite of blue was orange and the opposite of purple as yellow.
derekp7 14y ago
He's got one minor thing wrong -- in CMYK, black isn't there to save money, it is because that in theory, CMY mixed will produce black, but in reality the ink's aren't "pure" enough, so they end up being a muddy color. So the K is there to produce the darker blacks. Also, a) Ink is translucent; light goes through the ink, reflects off the white paper, goes back through, and that affects the color change of the light. Therefore ink uses CMYK. Pigments in paint are opaque, so light reflects directly off them. In this mode, Red-Yellow-Blue-Black works. For monitors, light is emitted not reflected at all, so that is why they use RGB. Oh, and many colors can translate from one model to another, but not all of them. Some can only be expressed in RGB but not CMYK, others can only be made in RYB.
- praptak 14y ago
  True, and not even the K in CMYK is 100% black, hence the notion of "rich black", which is a collective name for colors produced when K is at maximum and yet other colors are added to the mix. It even has its own Wikipedia page: http://en.wikipedia.org/wiki/Rich_black http://en.wikipedia.org/wiki/Rich_black
- jonhendry 14y ago
  And when painting, you often don't want to use black, because it's too dark, but clearly it would be painful, and probably impossible, to try to obtain a rich, almost-black-red by mixing CYM paints. (But it's easy to get by mixing red and a dark navy blue.)
idspispopd 14y ago
Wow, just wow. This is what happens when someone who knows a little bit about how the eyes and brain interpret colour decides to write an article where they fill their gaps of knowledge with mistakes instead of doing some research. Since the author wanted to talk about the eye, they should have kept to additive colour only and not tried to be confusing by introducing subtractive colour, which they neither understand or present factually.
- idspispopd 14y ago
  Here's a few of the factual errors: >They’ll launch into a treatise about how the Three Primary Colors They'll try to teach you Subtractive colour theory. Artists don't actually work in three primaries, however the idea of 3 primaries form the basis of subtractive colour theory. An artists knows you simply don't get brighter colours out of darker ones. >Primary Colors produces the Secondary Colors (orange, green, and purple): The colours shown here are additive colour mixes, not subtractive. E.g. Magenta is not Purple. Purple has a single wavelength, magenta does not. >infamous color wheel you probably learned in school It's based on Goethe's colour wheel, it's artistic not scientific. (As limited by the few amounts of colours available in earlier times.) Although it's still a decent representation of colour than the result this author produced. >Doesn't stand up to scrutiny/ Three colors of ink which, when combined, produce all others: cyan, magenta, and yellow. (Black is included as a money-saver — black is the cheapest and most common color; it’s cheaper to have a black cartridge than to dump ink from the other three.) CMYK does not produce a full gamut of colour, not anywhere near it. Black is not included as a money saver, but because CMY simply doesn't produce a decent 'black' and there can be registration issues. What CMYK does produce is a nice compromise of commonly occurring colours, however you won't get a vivid blue, green or red out of it - there is simply no building blocks in those colours to produce a good version of each. Instead you'll get a purplish blue, a yellowy green and an orangey red. This is why printers have 'spot colours'. >But wait! I thought the “Primary” colors were red, blue, and yellow, not cyan (bluish-green), magenta (bluish-red), and yellow. Not only does the diagram falsely misrepresent the results of mixing of CMY colours(e.g. it should be a dark mess in the centre), but it also falsely represents the individual colours themselves. It's actually pretty difficult to get a computer screen to display a true Cyan, which is not, in any stretch of the imagination "bluish-green". At this stage the author has created a bunch of confusion, seemingly his own because he doesn't truly understand what is going on here. The actual difference between additive and subtractive colour aren't explored or explained. There are lots of common school boy mistakes like assuming subtractive mixing produces similar colours to additive mixing, e.g. he shows that purple is akin to magenta(it's not), or that you can get any colour your want out of mixing three primaries(you can't). Or that RGB, or CMY allows for a full gamut (neither do.) >This isn’t adding up. Let’s turn to science. From here the article gets better, but it trips a few times before getting to actual physiology. For a short while he talks about the 'magenta' problem, which actually is well resolved. It's called an extra-spectral colour, it's not generated via a single wavelength, but rather the absence of wavelengths from white light. Oddly later he mentions this. >Opposites "Complements" rather, are well resolved scientifically, there are two sets of complements and two colour wheels to demo these. Since he's talking about eyes, he should just focus on additive colour. The wheel the author has created is utter rubbish, it skips swaths of wavelengths and is only interested in preserving 'opposites', which are represented by incorrect renditions of those colours anyway.
mbostock 14y ago
If you want a good introduction to color theory, see Marc Levoy's lecture notes from CS 248 (Introduction to Computer Graphics). The notes are quite dense but contain a lot of good information. http://graphics.stanford.edu/courses/cs248-08/color/color1.html http://graphics.stanford.edu/courses/cs248-08/color/color1.h... http://graphics.stanford.edu/courses/cs248-08/color/color2.html http://graphics.stanford.edu/courses/cs248-08/color/color2.h...
gcb 14y ago
could be a much better article if not so sensationalist about kindergarten learning not being perfect.
commieneko 14y ago
I knew when I saw the title I was in trouble. I've got stuff to do tonight, and don't have time to write a real response. And a real response isn't even really necessary; there's nothing wrong with the all the various color theories and models that paper the floor of the world. They are all imperfect, but often useful, approximations generally designed by trial and error usually for specific use cases. So the notion that those wacky, touchy feely artists (aren't they cute!) don't know jack about color is specious. Their knowledge is specific to their domain and tools they use. While many of them could use some touch up here and there, it's really not necessary because ... dramatic pause ... It doesn't matter! No artist is trying to produce a particular color found in nature. They are trying to produce the appearance of a perceived color of a certain local color source under certain lighting conditions, and, here's the kicker, under certain psychological conditions. A good artist can make you think you see any color they want to using nearly any available palette. The more colors the better, up to a point; limited palettes can be a very powerful tool. And the color interactions you get when mixing pigment paint is not just an optical problem, it's a chemical problems as well. Artists do some very odd things to get the colors they need. I'm reminded of a story about the MIT hackers back in the 50s/60s who found out that a radio produced interesting sounds depending on what the computer next to it was doing. The electronics would produce radio noise that would be played as sound. With a little experimentation the hackers found out what kind of operations produced what kinds of noises, and at what frequencies. So they wrote one of the first computer music programs using this system. Needless to say, they needed to make the computers do some pretty odd and complicated things to get the radio "noise" they needed. The chemicals we use for pigments are the ones that "happen" to reflect, re-emit, or transmit light at particular frequencies. Finding the colors is hard enough, but you also have to worry about how they interact chemically with each other, for both stability (boom!) light fastness, or toxicity. In the early days, toxicity wasn't too big a considerations, and many, many artists died from rather nasty chemical poisoning. If you are interested, get a book on oil painting. Creative Illustration by Andrew Loomis is a pretty good place to start. I also highly recommend John Gurney's books on painting or artistic color usage. These are good things to read even if you have no intention of every picking up a brush, because they are not at all about the physics of color. They are about using color to communicate and create a certain kind of perceptual experience. If optics and physics were what was needed to understand the mechanics of picture and image making, anyone with a good camera could do the job. But a good photographer knows that their job is not to perfectly transcribe whatever may be happening in front their lens at any old arbitrary time. (As an alternative, you can learn a lot about practical color theory by studying older photography books.) As for CMYK and RGB color spaces, these are simple but quite effective tools for dealing with color in a purely mechanical way. And they dovetail rather nicely with the artistic color models used in the past by painters and photographers. It is important to know that these are abstract color models intended to produce an approximation that is almost always good enough for most everyday usage by non-specialists. Specialists use tools that are often similar, but with more special cases and provisions for calibration and feed back situations. If you really need a color model more closely tied to how human visual physiology works, LAB was designed as a good approximation of that. Specialists sometimes use other, often proprietary systems. If you need this level of knowledge, you got some book larnin' to do. No blog posts or comments on HN is going to help you too much. Finally, speaking of human physiology, the model of filters he describes seems to make it impossible to distinguish red from green. In other words it seems to be describing a system that exhibits red/green color blindness. I have a suspicion that the author read a complicated article, got hung up on the part that talked about r/g color blindness, and thought that was the general case. When I've talked to specialists about this kind of thing, the answers I get are all the equivalent to "It's complicated ..." Human visual physiology is real complicated, even the purely mechanical aspects of it, and frankly not a lot is known about some aspects of it. What I've been told is that when you reduce the complicated aspects of what is known into a workable set of approximations, for specific use cases, you get something very similar to ... wait for it ... Artistic color wheels and paint mixing systems.
arundelo 14y ago
Terminology note: This is called the opponent process theory. http://en.wikipedia.org/wiki/Opponent_process http://en.wikipedia.org/wiki/Opponent_process
duopixel 14y ago
Previous discussion (more than a year ago) http://news.ycombinator.com/item?id=2166494 http://news.ycombinator.com/item?id=2166494
nsns 14y ago
Nice article, even better comments. But am I the only one who thinks explaining stuff by "it's because your brain tells you that..." doesn't really solve anything, simply relocates the mystery?
adrianhoward 14y ago
Ask any artist to explain how color works, and they’ll launch into a treatise about how the Three Primary Colors Nope. If you ask an artist or designer about how colour works when you'll usually get is a deep sigh, followed by "it's complicated", followed by a looooooooooong explanation of some of the options presented here and a good few more besides. (Fascinating bit of trivia: There is some moderatly persuasive evidence that some folk have more varient cone cells and can see more colours than people with "normal" vision. See http://www.post-gazette.com/stories/news/health/some-women-may-see-100-million-colors-thanks-to-their-genes-450179/ http://www.post-gazette.com/stories/news/health/some-women-m... and http://www.klab.caltech.edu/cns186/papers/Jameson01.pdf http://www.klab.caltech.edu/cns186/papers/Jameson01.pdf). It's usually developers who have the broken models of colour perception because, unsurprisingly, they're not trained in it :-) Artists and designers deal with multiple colour models all of the time - just go look at how many of the preferences in things like Photoshop are about managing colour... and that's just in the digital editing space.
idan 14y ago
I had a short bit about this in my datavis talk at Pycon. Youtube link directly to the explanation of vision / color physiology: http://youtu.be/vfYul2E56fo?t=18m31s http://youtu.be/vfYul2E56fo?t=18m31s.
SonicSoul 14y ago
awesome post. this is not 100% related, but if you're interested in color as it pertains to human perception (and how to cure color blindess and how a mantis shrimp can perceive 6x more color) there is a great podcast on RadioLab! http://www.radiolab.org/2012/may/21/ http://www.radiolab.org/2012/may/21/

214 points by tobyjsullivan 14y ago

It's definitely an interesting topic and a nice high level overview of the problems of colour and colour spaces. I like the 4 point colour wheel in some way, but I don't entirely see the benefits. From a computer vision perspective, this representation still has problems (as do all colour spaces). Look at how massive the green space is. There's 4-5 greenish slices that are close to each other, yet only 1 slice for yellow and 2ish for red. Red is the colour humans see "best", physiologically it should have the largest representation, whereas blue should be smallest. From the simpler side (i.e. a basic colour wheel application), I'm not sure if this makes it much easier or faster for me to find a colour. In any case, the article is very nice high level overview of a fascinating problem.

AceJohnny2 14y ago
"look at how massive the green space is..." This is why, in non-symmetric color coding systems, Green is given the largest share. For example 16-bit image formats give 5 bits for Red and Blue, but 6 bits for Green. The Bayer color pattern pattern used on CMOS sensors (basically all sensors on consumer devices) has interleaved rows of Green and Red and rows of Blue and Green: twice as much green as the other colors! Finally, green represents more than 50% of Luminance! From an evolutionary perspective, it makes sense to be more sensitive in the green spectrum: we were surrounded by green plants. Better catch the nuances to better identify predators or prey!
evincarofautumn 14y ago
I thought green was the colour humans saw best, if best means brightest. For instance, when converting from RGB to greyscale the usual weights are 30% red, 59% green, and 11% blue. (Though I always found it kind of unfortunate that these weights are wrong for people with nonstandard colour receptors.) In that sense, green should (seem to) be the largest because we perceive more colours as greenish than as reddish or bluish.

sp332 14y ago

In the S/M/L chart (this one http://asmartbear.wpengine.netdna-cdn.com/wp-content/uploads/Cone-fundamentals-with-srgb-spectrum.png http://asmartbear.wpengine.netdna-cdn.com/wp-content/uploads...) you can see that at the right-hand side, the M (green) activation is pretty low and goes to zero where L (red) is still strong enough to be visible. But there's no frequency on that graph where M (green) is active all by itself. So you've probably never in your whole life experienced a pure "green" sense input! CIE takes this into account when defining visible color spaces. Since you have 3 "primaries" you would expect the colorspace to be bounded by a triangle, each corner being a pure input of each primary. But you can see here https://en.wikipedia.org/wiki/International_Commission_on_Illumination https://en.wikipedia.org/wiki/International_Commission_on_Il... that the top green corner is missing. That's because there are no frequencies of light that would let you see any color that is "greener" or further toward where that corner would be. OK one last thing before I get to my proposal :) Your eyes gradually adapt against the colors you are looking at. For example if you're wearing red/blue 3d glasses for a while, when you take them off things will look greenish out of the "red" eye and yellower out of the "blue" eye. You can play tricks like this http://wxerfm.com/blogs/post/jfrieders/2012/jan/25/picture-cool-optical-illusion-star-negative-photo-/ http://wxerfm.com/blogs/post/jfrieders/2012/jan/25/picture-c... In fact it's possible to exhaust some of your photoreceptors, like the "spot" from a camera flash or the streak from a glare of sunlight. So here's my idea: if you strobe a really bright red & blue light, enough to temporarily blind the S & L receptors in your eyes, you should be able to see a green that is more pure and intense than you have ever experienced, right off the CIE chart of visible colors! Who's up for experimenting? :)

hammock 14y ago
>But there's no frequency on that graph where M (green) is active all by itself. So you've probably never in your whole life experienced a pure "green" sense input! I wonder if there is a medical condition out there where someone is missing the L (red) cones in their eyes - in that case they COULD see pure green sense input. In fact despite being disabled, they could see colors that everyone else is unable to see! edit: It does seem to exist, protanopes (a severe form of red-green colorblind) are missing the red cones. So if I understand correctly, while we tend to think of them as having a restricted spectrum, they may actually see some colors that others can't.

teilo 14y ago

I'm somewhat surprised that no mention was made of L * a * b color, since the four point color wheel corresponds to the a and b channels.

ken 14y ago

> Every seven-year-old kid in America is taught that “the opposite of red is green” and “the opposite of blue is yellow.” Did I sleep through second grade or something? I've spent the first 30+ years of my life in America and I've never heard of this.

jrockway 14y ago
Same. I know this, but only from looking at negatives.
evincarofautumn 14y ago
Different schools teach different things; many don’t introduce colour theory at all. And it’s an odd thing, but most people don’t know intuitively how colours combine or invert. Of course, as a synesthete and maybe a tetrachromat, I’m not really statistically relevant to this discussion. ;)
- deleted 14y ago
  [deleted]
Evbn 14y ago
It's wrong. The opposite of blue is orange=red+yellow. Yellow is the opposite of purple=blue+red. Red is the opposite of green=yellow+blue, as written above. In paint pigments, in second grade.
ianstormtaylor 14y ago
Not only that, but I'm pretty sure everyone was taught that the opposite of blue was orange and the opposite of purple as yellow.

derekp7 14y ago

He's got one minor thing wrong -- in CMYK, black isn't there to save money, it is because that in theory, CMY mixed will produce black, but in reality the ink's aren't "pure" enough, so they end up being a muddy color. So the K is there to produce the darker blacks. Also, a) Ink is translucent; light goes through the ink, reflects off the white paper, goes back through, and that affects the color change of the light. Therefore ink uses CMYK. Pigments in paint are opaque, so light reflects directly off them. In this mode, Red-Yellow-Blue-Black works. For monitors, light is emitted not reflected at all, so that is why they use RGB. Oh, and many colors can translate from one model to another, but not all of them. Some can only be expressed in RGB but not CMYK, others can only be made in RYB.

praptak 14y ago
True, and not even the K in CMYK is 100% black, hence the notion of "rich black", which is a collective name for colors produced when K is at maximum and yet other colors are added to the mix. It even has its own Wikipedia page: http://en.wikipedia.org/wiki/Rich_black http://en.wikipedia.org/wiki/Rich_black
jonhendry 14y ago
And when painting, you often don't want to use black, because it's too dark, but clearly it would be painful, and probably impossible, to try to obtain a rich, almost-black-red by mixing CYM paints. (But it's easy to get by mixing red and a dark navy blue.)

idspispopd 14y ago

Wow, just wow. This is what happens when someone who knows a little bit about how the eyes and brain interpret colour decides to write an article where they fill their gaps of knowledge with mistakes instead of doing some research. Since the author wanted to talk about the eye, they should have kept to additive colour only and not tried to be confusing by introducing subtractive colour, which they neither understand or present factually.

idspispopd 14y ago
Here's a few of the factual errors: >They’ll launch into a treatise about how the Three Primary Colors They'll try to teach you Subtractive colour theory. Artists don't actually work in three primaries, however the idea of 3 primaries form the basis of subtractive colour theory. An artists knows you simply don't get brighter colours out of darker ones. >Primary Colors produces the Secondary Colors (orange, green, and purple): The colours shown here are additive colour mixes, not subtractive. E.g. Magenta is not Purple. Purple has a single wavelength, magenta does not. >infamous color wheel you probably learned in school It's based on Goethe's colour wheel, it's artistic not scientific. (As limited by the few amounts of colours available in earlier times.) Although it's still a decent representation of colour than the result this author produced. >Doesn't stand up to scrutiny/ Three colors of ink which, when combined, produce all others: cyan, magenta, and yellow. (Black is included as a money-saver — black is the cheapest and most common color; it’s cheaper to have a black cartridge than to dump ink from the other three.) CMYK does not produce a full gamut of colour, not anywhere near it. Black is not included as a money saver, but because CMY simply doesn't produce a decent 'black' and there can be registration issues. What CMYK does produce is a nice compromise of commonly occurring colours, however you won't get a vivid blue, green or red out of it - there is simply no building blocks in those colours to produce a good version of each. Instead you'll get a purplish blue, a yellowy green and an orangey red. This is why printers have 'spot colours'. >But wait! I thought the “Primary” colors were red, blue, and yellow, not cyan (bluish-green), magenta (bluish-red), and yellow. Not only does the diagram falsely misrepresent the results of mixing of CMY colours(e.g. it should be a dark mess in the centre), but it also falsely represents the individual colours themselves. It's actually pretty difficult to get a computer screen to display a true Cyan, which is not, in any stretch of the imagination "bluish-green". At this stage the author has created a bunch of confusion, seemingly his own because he doesn't truly understand what is going on here. The actual difference between additive and subtractive colour aren't explored or explained. There are lots of common school boy mistakes like assuming subtractive mixing produces similar colours to additive mixing, e.g. he shows that purple is akin to magenta(it's not), or that you can get any colour your want out of mixing three primaries(you can't). Or that RGB, or CMY allows for a full gamut (neither do.) >This isn’t adding up. Let’s turn to science. From here the article gets better, but it trips a few times before getting to actual physiology. For a short while he talks about the 'magenta' problem, which actually is well resolved. It's called an extra-spectral colour, it's not generated via a single wavelength, but rather the absence of wavelengths from white light. Oddly later he mentions this. >Opposites "Complements" rather, are well resolved scientifically, there are two sets of complements and two colour wheels to demo these. Since he's talking about eyes, he should just focus on additive colour. The wheel the author has created is utter rubbish, it skips swaths of wavelengths and is only interested in preserving 'opposites', which are represented by incorrect renditions of those colours anyway.

mbostock 14y ago

If you want a good introduction to color theory, see Marc Levoy's lecture notes from CS 248 (Introduction to Computer Graphics). The notes are quite dense but contain a lot of good information. http://graphics.stanford.edu/courses/cs248-08/color/color1.html http://graphics.stanford.edu/courses/cs248-08/color/color1.h... http://graphics.stanford.edu/courses/cs248-08/color/color2.html http://graphics.stanford.edu/courses/cs248-08/color/color2.h...

gcb 14y ago

could be a much better article if not so sensationalist about kindergarten learning not being perfect.

commieneko 14y ago

I knew when I saw the title I was in trouble. I've got stuff to do tonight, and don't have time to write a real response. And a real response isn't even really necessary; there's nothing wrong with the all the various color theories and models that paper the floor of the world. They are all imperfect, but often useful, approximations generally designed by trial and error usually for specific use cases. So the notion that those wacky, touchy feely artists (aren't they cute!) don't know jack about color is specious. Their knowledge is specific to their domain and tools they use. While many of them could use some touch up here and there, it's really not necessary because ... dramatic pause ... It doesn't matter! No artist is trying to produce a particular color found in nature. They are trying to produce the appearance of a perceived color of a certain local color source under certain lighting conditions, and, here's the kicker, under certain psychological conditions. A good artist can make you think you see any color they want to using nearly any available palette. The more colors the better, up to a point; limited palettes can be a very powerful tool. And the color interactions you get when mixing pigment paint is not just an optical problem, it's a chemical problems as well. Artists do some very odd things to get the colors they need. I'm reminded of a story about the MIT hackers back in the 50s/60s who found out that a radio produced interesting sounds depending on what the computer next to it was doing. The electronics would produce radio noise that would be played as sound. With a little experimentation the hackers found out what kind of operations produced what kinds of noises, and at what frequencies. So they wrote one of the first computer music programs using this system. Needless to say, they needed to make the computers do some pretty odd and complicated things to get the radio "noise" they needed. The chemicals we use for pigments are the ones that "happen" to reflect, re-emit, or transmit light at particular frequencies. Finding the colors is hard enough, but you also have to worry about how they interact chemically with each other, for both stability (boom!) light fastness, or toxicity. In the early days, toxicity wasn't too big a considerations, and many, many artists died from rather nasty chemical poisoning. If you are interested, get a book on oil painting. Creative Illustration by Andrew Loomis is a pretty good place to start. I also highly recommend John Gurney's books on painting or artistic color usage. These are good things to read even if you have no intention of every picking up a brush, because they are not at all about the physics of color. They are about using color to communicate and create a certain kind of perceptual experience. If optics and physics were what was needed to understand the mechanics of picture and image making, anyone with a good camera could do the job. But a good photographer knows that their job is not to perfectly transcribe whatever may be happening in front their lens at any old arbitrary time. (As an alternative, you can learn a lot about practical color theory by studying older photography books.) As for CMYK and RGB color spaces, these are simple but quite effective tools for dealing with color in a purely mechanical way. And they dovetail rather nicely with the artistic color models used in the past by painters and photographers. It is important to know that these are abstract color models intended to produce an approximation that is almost always good enough for most everyday usage by non-specialists. Specialists use tools that are often similar, but with more special cases and provisions for calibration and feed back situations. If you really need a color model more closely tied to how human visual physiology works, LAB was designed as a good approximation of that. Specialists sometimes use other, often proprietary systems. If you need this level of knowledge, you got some book larnin' to do. No blog posts or comments on HN is going to help you too much. Finally, speaking of human physiology, the model of filters he describes seems to make it impossible to distinguish red from green. In other words it seems to be describing a system that exhibits red/green color blindness. I have a suspicion that the author read a complicated article, got hung up on the part that talked about r/g color blindness, and thought that was the general case. When I've talked to specialists about this kind of thing, the answers I get are all the equivalent to "It's complicated ..." Human visual physiology is real complicated, even the purely mechanical aspects of it, and frankly not a lot is known about some aspects of it. What I've been told is that when you reduce the complicated aspects of what is known into a workable set of approximations, for specific use cases, you get something very similar to ... wait for it ... Artistic color wheels and paint mixing systems.

arundelo 14y ago

Terminology note: This is called the opponent process theory. http://en.wikipedia.org/wiki/Opponent_process http://en.wikipedia.org/wiki/Opponent_process

duopixel 14y ago

Previous discussion (more than a year ago) http://news.ycombinator.com/item?id=2166494 http://news.ycombinator.com/item?id=2166494

nsns 14y ago

Nice article, even better comments. But am I the only one who thinks explaining stuff by "it's because your brain tells you that..." doesn't really solve anything, simply relocates the mystery?

adrianhoward 14y ago

Ask any artist to explain how color works, and they’ll launch into a treatise about how the Three Primary Colors Nope. If you ask an artist or designer about how colour works when you'll usually get is a deep sigh, followed by "it's complicated", followed by a looooooooooong explanation of some of the options presented here and a good few more besides. (Fascinating bit of trivia: There is some moderatly persuasive evidence that some folk have more varient cone cells and can see more colours than people with "normal" vision. See http://www.post-gazette.com/stories/news/health/some-women-may-see-100-million-colors-thanks-to-their-genes-450179/ http://www.post-gazette.com/stories/news/health/some-women-m... and http://www.klab.caltech.edu/cns186/papers/Jameson01.pdf http://www.klab.caltech.edu/cns186/papers/Jameson01.pdf). It's usually developers who have the broken models of colour perception because, unsurprisingly, they're not trained in it :-) Artists and designers deal with multiple colour models all of the time - just go look at how many of the preferences in things like Photoshop are about managing colour... and that's just in the digital editing space.

idan 14y ago

I had a short bit about this in my datavis talk at Pycon. Youtube link directly to the explanation of vision / color physiology: http://youtu.be/vfYul2E56fo?t=18m31s http://youtu.be/vfYul2E56fo?t=18m31s.

SonicSoul 14y ago

awesome post. this is not 100% related, but if you're interested in color as it pertains to human perception (and how to cure color blindess and how a mantis shrimp can perceive 6x more color) there is a great podcast on RadioLab! http://www.radiolab.org/2012/may/21/ http://www.radiolab.org/2012/may/21/