Here’s a decent Wikipedia article about color gamuts. The first diagram, “A typical CRT gamut”, illustrates what’s going on. From the caption:
The grayed-out horseshoe shape is the entire range of possible chromaticities. The colored triangle is the gamut available to a typical computer monitor; it does not cover the entire space.
In case you don’t like Wikipedia for cites, you can google around on “color gamut” or “color gamut rgb OR crt OR cmyk” and such. Here for example is another presentation of the topic. Here’s another article that addresses it more from a printer’s viewpoint.
Basically, any color reproduction technology that works by using a small set of primary colors — which includes the RGB light elements in a video display, or the CMYK dots of ink in typical print publishing — will not be able to cover the entire range of human color vision. Obviously though it works well enough for most purposes.
It would just take a little bit of work to add a fourth colour to our monitors, and a bit of tweaking to our visual systems. We are so close. Only a thin barrier remains between our present vision and the unimaginable glories of the universe.
Ask a Color Scientist website
How many colors can we see? (219)
This is a very popular question and it is usually answered vaguely by, “Millions and millions!” However, it is better to ask the question in a more specific way to get a more comprehensive answer.
Many of us can select a setting for our computer monitors that displays millions of colors and we see an improvement in image quality with this setting. However, if you select the colors correctly you can reduce the number of colors to a couple of hundred or even fewer (depending on the image) without noticing a degradation in quality. This would indicate that we can’t see millions of color variations simultaneously.
One way to answer the question is to measure the ability of people to discriminate colors. Many researchers have investigated chromatic discrimination by varying the wavelength of two monochromatic lights until they are just noticeably different. Other studies have used the variability of color matching to gauge discriminability and yet others have directly measured threshold differences throughout color space. Using these measures we find that our visual systems can discriminate millions of colors.
In our laboratory we are interested also in larger than threshold color differences: the type of differences that would make you reject a certain touch-up paint because it’s not a close enough match to the color of the paint of your car. Even with such a metric there are close to a million discriminable colors on a computer monitor which only can reproduce a fraction of the colors we can see out in the real world.
But CMYK isn’t RGB. CMYK has a significantly smaller color gamut than RGB. In particular, there are greens and blues that are not reproducible in CMYK that are visible in the sRGB (standard RGB) colorspace. And your monitor’s RGB is a suprisingly small sliver of the visible spectrum.
Also, all color is not made from a combination of red, green, and blue. Yellow can be either be a monochromatic light source with a wavelength of 570-580 nm, or it can be a mixture of wavelengths, like red and green.
edit: Ah, I see Bytegeist covered most of this above.
It’s a really subjective thing once you get beyond the 10 or 11 well known primaries: Red, Orange, Yellow, Green, Blue, Violet, Brown, Black, White, Gray and maybe Pink.
After that, you can get into industry terms, such as that in lithography like cyan, and magenta. Or, there’s several different terms that became popular merely through usage in everyday life and commerce (but most of these come from well known objects that naturally hold this color): Silver, gold, peach, maroon, turquoise, pistachio, salmon, charcoal, etc.
Of course, there are highly ordered color systems like Pantone, but they don’t have names, they have numbers. And it’s more about keeping a standard for reproduction and reference in the graphics industry. I’m sure there are several more that could be mentioned, but they’re all rather esoteric, besides, you get the idea.
Interesting question, but it’s true, you can’t do this.
What you can do is pick three colors such that any real color can be made with a mix of these three - IF you are allowed to use negative numbers, too.
Perhaps what is most clear to you is that, if we are using three differently tinted sensors, then obviously there is an additive linear system underlying it all. This is true, or at least pretty nearly so (an evolved animal system like vision has, not surprisingly, various deviations and oddities; for example, color - the sensation, not the distribution of wavelengths - depends a little on how large an area you are looking at).
Folks have taken advantage of this by projecting, from white, outward beyond the curve representing pure spectral colors (being colors made from a single wavelength). They imagine colors “out there” such that mixing one of these colors with white light gives you a pure spectral color. The colors are named X, Y and Z and can be thought of as versions of red, green and blue (I hope I got the order right) that are much more intense than any pure spectral color.
To be clear, I’m talking about reproducing the effect on the sensors of the human eye - obviously there are all kinds of patterns of real light that aren’t the same as an RGB combination, and mechanical sensors could tell the difference, but we couldn’t.
And I remain unconvinced by the cites about color gamuts - it seems to me that all of them are assuming a limited system that can only deliver a certain finite range of its three primary colors of light, or even making poor choices for which three color. (I’m also not dealing with mixing pigments, which has its own set of problems, but additive light.)
>To be clear, I’m talking about reproducing the effect on the sensors of the human eye - obviously there are all kinds of patterns of real light that aren’t the same as an RGB combination, and mechanical sensors could tell the difference, but we couldn’t.
Oh, yes, I understood this from the start. You can’t reproduce the effect of all real colors on the eye with three real lights. A short version of why: since all three of your sensor subsystems are at least slightly sensitive to all wavelengths, you can’t choose any wavelengths that only stimulate one. Given that three arbitrarily good wavelength choices will each stimulate all the sensors, there will be colors people can see in real life that have a lower stimulation on one of the sensor types than any nonnegative combination of the three wavelengths will match. This is less of a problem with red, as it is pretty easy to stimulate your red sensors with only slight stimulation of the green ones and practically none of the blue ones. It is somewhat more difficult with blue, but you can come pretty close. With green it is the hardest. If you think about it, this statement goes along with the fact that the chromaticity diagrams you see will all have a rounded-off vertex at the green end of the space.
>And I remain unconvinced by the cites about color gamuts - it seems to me that all of them are assuming a limited system that can only deliver a certain finite range of its three primary colors of light, or even making poor choices for which three color. (I’m also not dealing with mixing pigments, which has its own set of problems, but additive light.)
Gamuts are usually interesting because they are dealing with some significantly limited system, or choosing between different limited system. Bear in mind that people dealing with gamuts generally don’t choose wavelengths, they choose light sources, for which there is a limited range of wavelength options, and a bunch of other compromise issues too (lifetime, stability, mechanical properties that allow manufacture, cost, etc etc). For example, CRT color television pictures are especially limited because there are not good phosphors that emit lots of green light around 510 nm and little else. I think the commonest choice is a good deal yellower than that, and not so spectrally pure either. Making this work practically is a difficult compromise but people sure started buying color televisions when they were available.
Don’t be so sure. Do “pink” and “red” count as different colors, or is one just a shade of the other? For that matter, is “orange” just a shade of red? These are purely cultural questions: In Russian, for instance, there are two different words for shades of blue, that they regard as different as we do red and pink.
Just had to point out - silver and gold are not actually colors. They are effects of reflection. The actual colors, devoid of reflection, are gray and yellow.
is it also worth considering individual interpretation of colours? I notice a small but distinct difference in hues between what i can see with either eye. But then again my eyes have different prescriptions (-1.5 & -1.75) Is it possible that we all see colours differently?
The range of possible perceptual colors could be indexed as activation levels of the three types of cones: from (0%, 0%, 0%) to (100%, 100%, 100%). The ultimate monitor would bypass your cones and directly stimulate the corresponding nerves. Then it would be possible to see the color (0, 100, 0) - a green so pure that no real light can produce it.
Direct-stim monitors aren’t around the corner, but it might be possible to develop anesthetic eyedrops that selectively deadened one or two of your cone types. You could see colors you had never seen before. They would be neurologically new, but your brain would probably map then onto colors you were already familiar with.
