I’m not saying there isn’t some phenomena in which the eye/brain system doesn’t add something novel to the perception of color, but one would have to concede that whatever we perceive as color comes strictly from the electromagnetic spectrum (whether reproduced using a color model/system or from nature itself).
That said, in the human experience, you’re right, color perception is a complex, relative, subjective, not entirely understood and yet fascinating area. But you can’t understand one side of the phenomena without understanding the other.
In that sense, the physics of light is incredibly relevant.
I think he’s saying there no pink wavelength of light you can point to, the color “pink” is only perceived optically by humans as a contextual color seen adjacent to a specific contrasting surface.
The physics side is irrelevant. There is nothing that is known in any theory of physics which would prohibit a truly infinite number of possible peak wavelengths for a spectrum. Therefore, if the OP has any known answer, it must come from physiology or psychology, not from physics.
A given intersection of physical phenomena is perceived as pink. Take away the human observer; what do you call those phenomena? What does the butterfly see?
That we do not “fully understand,” cannot define or explain hardly bears on its reality, of course.
And, of course I understand this, since on a linear spectrum, how can violet smoothly transition back around to red (AKA the famous Color Wheel), which is something that happens within our physiology?*
I’m not disputing that. But still, it is the EM spectrum that excites our eyes/brain into perceiving “pink” just like any other mixed color.
*rhetorical question to confirm agreement.
Regarding the OPs question, consider the Macadam Ellipses. These are regions on the CIE chromaticity diagram where the color in indistinguishable from the one at the center.
Presumably if you could “tile” the CIE diagram with Macadam ellipses you could come up with a number of distinguishable colors that the human eye can see. But Macadam himself* only looked at 25 points on the CIE plot. Like all results in color, his are averaged results for a “typical” human eye, and YMMV. I suspect that “ellipse” is just a convenient designation for "region’, the boundaries of which are nebulous but roughly elliptical. If we took the picture in the Wikipedia article (which looks exactly like others I’ve seen), then we’re probably talking about 100-200 ellipses to cover the space.
If you want to get into physics, I note that all of the curved periphery of the CIE region is the “spectral locus”, corresponding to the visible spectrum, and that it is essentially infinitely divided into individual wavelengths, and that your eye can’t distinguish ones that are too close together, I’ll also observe that this is just a convenient way to plot color on a two-dimensional surface. The plot ought realy to be three-dimensional, since color vision is a thre-parameter function, but the coordinates used in CIE are normalized, so the third is ignored. In the process, we essentialy ignore the intensity, which is a part of the viewing experience. To claim that there is no color “pink” because it’s not on the diagram isn’t true – pink is a light red, and if we had a complete plot we would include the degree of color saturation that made that light red look pink. Certainly your monitor, which doesn’t even hit all the points on a CIE plot, can make a perfectly serviceable pink.
*Prof. David Macadam had the office down the hall from me when I was in grad school, and I used to see him all the time. His lab, with its color viewing booths painted neutral gray, with stacks of color chip cards in them, stood open a lot of the time.
Yes, even on the quantum level. What you may be thinking of is that any given system, such as a hydrogen atom, can only produce a spectrum peaked around some discrete values. But you can still get other values: Just start with a different system. Or take the system you’ve already got, and Doppler shift it appropriately. A continuum of velocities are possible, so a continuum of Doppler shifts are also possible.
The proof that “color” can’t be reduced to physics is found in the fact that color optical illusions exist.
If the exact same combinations of wavelengths can be perceived as two different colors at the same time, then you can’t say that color is reducible to wavelengths.
Even more to the point, there are infinite number of colors that appear to be identical that can be produced by different spectra.
But I take issue with you “color can’t be reduced to physics” claim. I can use physics to produce those many different spectra. And I can take any spectrum and use it to predict which color will be produced.
That colors appear different on different backgrounds, or that you can even see colors where they don’t exist is a subtler set of phenomena, but there’s a vast body of research on how they are generated, and the limits on their applicability.
If you want to really mess with your head, look up the Land Effect.
[QUOTE=A Note from Biotele]
It has come to my attention that some readers are confused by Liz Elliot’s title of this article. Some readers have debated that magenta is a color, especially important in reflective media like paper. And many printers are based on the CMYK color scheme, where M stands for magenta. It is my opinion that the people debating the title have missed the point of the article.
Magenta is an “extraspectral” color. Sir Isaac Newton noticed that magenta did not exist in the spectrum of colors from white light when he played with prisms. But when he superimposed the red end of the spectrum on to the blue end, he saw the color magenta (this can be done with two prisms to make two spectral spreads, “rainbows”):
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Years ago I wrote photo retouching software. (Basically it was a proprietary system that did what Photoshop did before Photoshop existed.) In order to maximize picture quality we didn’t store pictures as RGB. We stored them using three special primaries that were designed to be visually linear, i.e the same amount of numeric difference equaled the same amount of visual difference everywhere in the color space. (More or less. It was as linear as we could make it.) With this system, 8 bits per primary were not quite enough to create smooth gradients to the trained eye. You could still see slight banding. However, storing 10 bits per primary was.
2^24 = 16 million
2^30 = 1 billion
Based on my experience the number of distinguishable colors is closer to the bottom of this range than the top. A 1-bit difference between two colors in a visually linear color space was just barely visible to the trained eye. And only at the middle of the brightness range. Color discrimination broke down with very bright or very dim colors. I’d guess someone with excellent color sense could distinguish at most 20 million distinct colors. (This is close to the value of 10 million given in the Wikipedia article on color vision.)
Of course, this sort of discrimination requires the colors to be next to each other. If you’re talking about how many colors we can distinguish from memory, the number is much, much lower.
njtt and others are correct. Colors do not exist in any real way in physics. They are an emergent property of psychology and neuroscience (both of which can be just as much of a hard science as anything else) and they are irreducible below that level. That is hard thing for many people to accept, even very educated ones, but it is true.
Optical illusions are a good example but even better ones are everyday experiences that we all have. There is a whole category of colors that are supposedly can’t be understood through physics alone yet every non-colorblind person knows that they are real because they are all around us. They are called ‘impossible colors’.
You can design careful experiments to carefully define how many colors people can see in a gradient but it isn’t always useful and sometimes culturally dependent. For example, green and blue are lumped into the same word in Japan even though they are clearly different colors to most people. There is a big difference between between able to distinguish between fine shades of different colors in a lab setting and having different words for them in everyday life.
There are lots of optical illusions out there that work a little bit like this: They start by saying “Point to the part of this picture that is white.” Then they color the rest of the picture with a correct “true white” and you say “Holy crap! That was yellow!”
So white is NOT perceived because there’s a mixture of all wavelengths. It’s much more complicated than that, and it relies as much (or more) on the brain as it does on the photons received by the eyes.
Other examples include the blind spot that nobody notices is there. Or the fact that your field of vision appears to be stationary even though your eyes are constantly making tiny micro-movements.
This is maybe a tangent, but it’s why “Seeing is believing” needs to be dragged out back and shot. What you see is not comparable to a photograph of reality; it’s a simulation of reality constructed by your brain, using some external inputs as a suggestion.
You’re talking about color constancy. Purely within our head.
The blind spot is where the optic nerve, or disc, is. There’s no light sensitive cells there, and our brain is good at filling in this blind spot, unless we explicitly expose it through various tricks (like staring at one finger, and moving the other finger into its place).
And yes, all our perceptions of reality are a simulacrum of sorts—yet distinguishing where our perceptions of reality and reality itself diverge has always been of great import to understanding our physiology. Color being just one of these.
