And I have the same question for pigment primary colors (magenta/cyan/yellow).
In: Physics
Yes, these are the primary colors of light, **for human eyes**. While the electromagnetic spectrum is continuous, and the eye sees color in a narrow spectrum, and there are relationships between the color sensing cells inside the eye. These cells allow the eye to sense a specific color space, the [CIE 1931 space](https://en.wikipedia.org/wiki/CIE_1931_color_space#CIE_xy_chromaticity_diagram_and_the_CIE_xyY_color_space ). This chromaticity diagram shows the relationship between color frequency and the eye’s perception of it. You could use many colors, but due to the shape of the space you can cover most of it with combinations only three colors if those colors are red, green, and blue. You can use other colors of light, and cover other parts of the space, but red, yellow, and blue only covers the lower right half of the space, so it’s not as good as red green and blue.
Human eyes have 2 types of light-sensitive cells. Rods distinguish lightness and darkness, while Cones distinguish color. About 95% of people have 3 types of cones each tuned to a wavelength of visible light. (Colorblind people have faulty cone cells so one or more wavelengths is not picked up by the brain.) In a normal eye one type of cone picks up red wavelength, one type green, and one type picks up blue. When red and green cones are activated it creates the image of colors between those two wavelengths, like oranges and yellows.
So in light-mixing, red-green-blue is the least amount of colors needed to create all other visible colors/hues, since the human eye can only detect these three, due to only three types of light-sensitive cells.
Our eyes have three different types of “cones” that respond to slightly different wavelengths of light. Light looks red, green, or blue depending on which cones it stimulates.
It’s not so much a property of the colors as it is a property of our eyes.
Our eyes have sensors in them that detect red, green, and blue light. As well as sensors detecting light intensity, or black and white.
Many animals have different eyes, but humans built screens that worked with theirs.
Wrong, wrong, wrong. The three cones detect: blue, green, and yellow-green. The last one detects red at the edge of its sensitivity. That is why there are so many wavelengths seen as blue-green (because they stimulate all three cones) and why red seems to fade from combinations of pigments (because it is detected at low sensitivity).
People who have had a crystalline lens removed can see ultraviolet light. The lens normally filters it out, but the blue cone reacts to it.
Carmine is one color that cannot be expressed as an RGB value. It requires a “super” Red to make it from a mixture of primary colors. There are others that require a “super” Blue. The “tongue” or CIE diagram shows this by going outside the ordinary maximum lines.
So, RGB is an approximation for computer screens; CYMK for printing. Neither is good enough to describe all colors that normal humans can see.
> And I have the same question for pigment primary colors (magenta/cyan/yellow).
What the primary pigments do is *remove* one of the red/green/blue colors from white light, while allowing the two others to remain. Magenta is opposite green, cyan opposite red, and yellow opposite blue. If you combine two of these at full strength, you only allow one of the primary lights: for instance, mixing magenta and cyan gives a blue color. (The reverse also holds true—if you combine red and blue light, you get a magenta color, and so on.) A fourth black pigment is sometimes added to reduce how much of the other pigments are needed for dark colors.
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