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Color wheels are wrong? How color vision actually works (asmartbear.com)
214 points by tobyjsullivan on June 27, 2012 | hide | past | favorite | 44 comments

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.

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.


"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.

In a way I appreciate your pedantry (though not your tone), but I must also say that the details you add seem to be technical, specific to printing and not particularly important to the point of the post.

Half the article is about subtractive colour, which happens to be print/painting/any kind of colour mixing which isn't combining light sources.

The author (is it you?) has done zero research on the topics they don't understand, and deserves any amount of critical writing in response.

The whole point of the internet is that it represented the end of people waffling bullshit, access to accurate information is there, and if people want to run around spreading incorrect information they deserve to be taken down as many notches as possible.

I might also add that this is important to the authors conclusion, should the author has done any real research they'd see that not only does a colour wheel that addresses their concern exist, but that they've misrepresented the foundation of their entire argument to begin with.

But every one of his illustrations has a "pin" button on it. And that's really the point, isn't it?

I believe the author goes by "asmartbear" or something similar here on HN.

Yeah, I started interested, like maybe there was a new take on this, but when he pulled out CMYK that way, I knew there was trouble. Thanks for pointing out the specifics.

Yeah, I felt the exact same way. The combination of pseudoscience, blatent speculation, and lack of research made me want to barf.

In the S/M/L chart (this one 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_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-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? :)

Since you can burn out the receptors temporarily simply by viewing saturated color in the same place in your visual field for a while, you can just do this sort of thing: http://www.moillusions.com/2006/03/eclipse-of-mars-illusion....

Don't expect miracles of color, but it's sort of neat. This site claims to have more color variants, but these I haven't tried: http://www.skytopia.com/project/illusion/ipage-et.html

Also, given the diversity of modern monitors and resolutions, you may need to hit CTRL-+ or CTRL-- a time or two for best effect

It's a similar effect! But those in particular are showing limitations of monitors, specifically the sRGB colorspace. You can see how the sRGB space compares: https://en.wikipedia.org/wiki/SRGB The large not-quite-triangular blob represents all visible colors, and the little triangle inside it is how much sRGB covers.

> 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

Note: you probably shouldn't try this


Good to know :) Just to clarify, I just meant flash, or strobe once.

>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.

In some sense, everybody sees colors that others don't. "Color" is purely perceptual; it does not exist outside the visual system. Objects radiate/reflect/refract light in various ways, and the way they do depends on the wave length of photons. Many flowers 'are' ultraviolet, so that insects can see them well, but humans cannot see that.

Not quite. The spectrum is completely covered by our common set of sensors, as you can see. There are no gaps on that S/M/L chart. So someone missing a receptor might experience a color in a different way, but they won't see extra colors.

No, they wouldn't be able to see colors most people can't -- they'd be able to experience colors most people can't. It's an important difference. Their "ultra-green" would really correspond to our "yellow".

Thanks for clarifying. That's exactly what I meant.

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.

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

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.)

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.

"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!

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.

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.

> 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.

Not at all. The filter R-G will be be positive for reds, and negative for greens. You might have been thinking of the R+G component of the R+G-B filter.

This actually explains why yellow is a a combination of green + reed, and how it is so un-intuitive. Yellow wouldn't really be the middle ground between red and green, but the absence of blue. Or something.

I agree that this blog post takes a sort of silly tone, and also that many artists are very sophisticated in their understanding and use of color.

He goes wrong in a few places, for instance in using quite confusing coloration of his diagrams, and he really shouldn’t put the labels R, G, B on cone responses: these are too evocative and are likely to confuse as much as they enlighten.

But to be fair, basic paint mixing models in artists’ heads often aren’t very good, and many artists would really benefit from studying human color vision more seriously. Explaining how vision works to visual artists, especially amateurs, is one of the more rewarding things I ever do: you can see these lightbulbs going off in their heads as a bunch of stuff that they know “intuitively” and experientially is given proper names and ordered into a comprehensible model.

> As for CMYK and RGB color spaces, these are simple but quite effective tools for dealing with color in a purely mechanical way.

I think these spaces have no place being taught to non-specialists. They are not intuitive to humans, being based on particular technology rather than on human vision. Any user interface which exposes these color spaces to non-experts is letting them down. Just as bad is using HSL or HSV or some similar trivial derivative space. Image editing software, in particular, is dramatically harder to use than it would be if the dimensions were at all relevant to vision.

> 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.

Specialists looking for models related to vision mostly use open, publicly developed and specified models. At root, most of modern colorimetry is based on the CIE system, which has served very well since the 1930s. Recent fairly effective models that would be useful for software include CIECAM02 and IPT, which behave better in some ways than CIELAB, but are a bit more computationally expensive.

> 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.

That’s reasonable. Let’s start with some pointers to good sources!

For this audience, Maureen Stone’s SIGGRAPH notes from 2001 are a nice first start, with lots of pointers to other good resrouces: http://graphics.stanford.edu/courses/cs448b-02-spring/04cdro...

For anyone who wants to really dive deep, I recommend http://www.handprint.com/LS/CVS/color.html (edit: Actually, I see that the blogger does link there. So that’s nice.)

Also, anyone looking for pointers to books, feel free to email me (address in profile), and I can point you in some direction based on your specific interests.

Artist's color mixing models aren't simple mechanical ratios. They use emergent properties of chemicals that just happen to be a particularly useful color. In fact, artist try to do as little color mixing as possible. Mixed pigments of the types artists use do work like the inks used in printing and the dyes used in RGB displays. Color wheels are guides and approximations. Learning a color theory that is more accurate is counter productive because you can't find pigments that behave that way. And if you ever get a chance to see a painting in the flesh and compare it to even a very good reproduction, you will see that the simple color model primaries used in printing and on screen reproduction are only loose approximations of the real colors.

Now what an artist does need to know is how color works perceptually. And the models used for this are pretty good. And remember the intended result is seldom "photo realism"; not that photos are particularly realistic. But that's another discussion altogether.

If you are talking about amateur artists, or beginners, then, sure, lecture away, but if you talk to someone who's been successfully painting for 40 years, my advice is to listen to him/her. They may or may not know much about the physiology of human vision, but don't be surprised if they do, but they certainly know the ins and outs of making you think you see what they want you to see.

The nice thing about standards are there are so many of them. I've spent more time than I cared to writing software to convert and compare between systems. They are a few lingua franca systems, but if you are doing serious, critical color work, your special cases are going to be the bulk of your job. Which only makes sense if you think about it. The sources I used are going to be about 30 years out of date, and the chemistries and optical systems no longer relevant.

Doing mechanical color reproduction is a specialty and few people need to know more than the basic RGB/CMY model and whatever specific systems that they need for their domain of activity. These days these models are very good and well tuned for their domains. Unless it's a brand new technology (Or NTSC; don't get me started!) This usually means working with a specific palette and color gamut.

And while a lot of people in the various industries feel that they are dealing with the real color models, and the rest mere approximations, there is no such thing. In the end it all breaks down and you are left with making specific measurements with specific types of equipment for use with specific use cases. And then you calibrate.

Color theory is very much a case of the map not being the territory.

> Learning a color theory that is more accurate is counter productive because you can't find pigments that behave that way

Learning theories can be tremendously helpful for crystalizing existing knowledge. Ultimately the only way to learn is to make visual art and look at it, a whole heck of a lot. But having theoretical models can help guide that thinking and looking, and can forestall a lot of confusion.

There are two kinds of models an artist needs to learn to deal with color:

(1) How the human eye sees color. This is so that texture and shape can be made to convey the desired effect of the picture. It’s helpful to learn about simultaneous contrast, adaptation effects, and even more obscure things like Ralph Evans’ (Kodak) theories about what he called “brilliance”. Learning this doesn’t tell you how to mix the paint, but it helps you figure out what results you should aim for.

(2) Color reproduction technology: the physical properties of paint / displays / printers / whatever.

Many people in the general public, including many artists, don’t properly understand the distinction between (1) and (2), and also take the radically oversimple concept of primary and secondary colors, etc. (whether it’s elementary school teachers with their red, yellow, blue, or programmers with their sRGB) as some kind of ultimate truth.

All of our models of color are approximations. Color is complex and contingent, depending on observer, lighting, viewing conditions, temporal effects, and so on.

My point is not that artists shouldn't learn about color and learn color theories. And I'm not saying that they shouldn't learn how human's see and process information. What I'm saying is that they already do that. But they are doing it with different models and techniques that are keyed to their domain and tools.

Sure, learn about RGB/CMY. It doesn't hurt. And printing technology, which is a different domain is very similar, though not the same in critical areas.

There's nothing magic or even very special about the methods and models you are talking about outside their domain of use.

If you are a designer who is working in print or onscreen display, you will learn to think in RGB/CMY(K). But there's nothing universal or special about that system compared to other systems. It's not more science compared to the systems artists use in their various working practices.

It's not more keyed to human physiology, in fact I'd argue that it is less intuitive and useful. I'll agree that it's not a numeric model and it's not a model designed for accuracy; and reproducibility. But it is a model tightly coupled with human perception, expression, and communication.

(As a designer working with digital imagery and renderings, I make major use of HSB style color models. I've written many special purpose tools for giving me effects I want, using all kinds of hair brained models, and then converting the results into RGB.)

To create a numeric model of how artists use color would be very difficult. If it weren't we'd be able to make cameras that made illustrations. And we can't and don't.

What an artist does is make an observation, and I mean this in both an abstract and practical sense. He or she then takes that observation and creates an abstraction of it, and then tries to make a work that communicates that abstraction. With the tools and mental model at hand.

There's a photo floating on Reddit right now of where a hair stylist has arranged hair clippings found on the floor in the shape of a dog. It's a wonderful piece of throwaway art. Now you could sit down and say, "If I take these hairs and arrange them with these percentages, I'll be able to get this range of colors and represent these textures ..."

But that's silly. The artist sees the hair, it reminds them of something, like a dog, and they spontaneously arrange them, making corrections and following intuition as they go.


Now if you are going to start an artistic tradition of arranging hair clippings for art, you might come up with some theories to model different effects. But I don't think you are going to be making numeric models. For one thing you never know what kinds of hairs you are going to find on the floor. Instead you are going to learn to "fake" it by using the relative and comparative artifacts of the human's visual and perceptual system. But it will almost certainly be intuitive and spontaneous. Lots of trial and error.

If this art form becomes a tradition, then special markets will develop in hair clippings, special dealers selling hair patches arranged nicely in special ways, maybe even a bit like RGB/CMY. (But don't push it.) Hair dyeing might become a specialty, but purists will insist on nature hair and natural hair colors. There will be much arguing about it and many bar fights.

And if you decide that there's a market in selling hair floor arrangements in mass quantities, then you might see something akin to what you see in modern printing or broadcast. Specialists will arise.

And most artists will say, "It's hard enough to make a pile of dog hair look like something interesting while worrying about all that. I'll make a good pile of hair and leave it up to the specialists to mass produce it. Maybe I'll use standard hair patches to make things easier, I do like it when the reproduction is well done. But I hate limiting my choices and opportunities, and besides the reproduced hair piles never look as good as the original anyway. After all, it's just a copy."

I think you’re misunderstanding me, because I mostly agree with you.

> There's nothing magic or even very special about the methods and models you are talking about outside their domain of use.

Learning about how cones & brains interpret light into the colors we perceive is definitely “special” compared to models designed around some particular physical medium like ink or dye or CRT displays, and the domain of use is “any time you want humans to look at colors”.

> [RGB/CMYK] is not more keyed to human physiology, in fact I'd argue that it is less intuitive and useful.

Sure. Which is why what I advocate teaching is the physiology and models aimed at approximating it (something with dimensions like the Munsell system or CIECAM02, etc.) ... which is absolutely more “intuitive” than RGB or CMYK or some paint mixing model, in the sense that it tracks perceived color attributes directly.

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.



Ask any artist to explain how color works, and they’ll launch into a treatise about how the Three Primary Colors


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-m... and 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.

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.

> 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.

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. ;)

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.

Same. I know this, but only from looking at negatives.

Terminology note: This is called the opponent process theory.


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.

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?

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

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/

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

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