Why do printers have CMYK ink instead of RYB & black ink?


Why do printers have CMYK ink instead of RYB & black ink?

In: 2442

CMYK has a wider *gamut* (the set of colors that can be represented using mixes of primaries) than RYB does. So if you want to put as many different colors as possible in your prints, that’s a better way to do it.

Because Red, Yellow, and Blue are not really primary colors of pigments. [Look at this graphic.](https://www.wtamu.edu/~cbaird/sq/images/color_mixing.png)

The top shows red, green, and blue which are the primary colors of light. That is additive color which is how light works, where by mixing different amounts of each of those colors of light you can make any other color. Mixing all the colors of light together gets you the color white.

The bottom shows cyan, magenta, and yellow which are the primary colors of pigments, which is how subtractive color works. Pigments absorb certain colors of light and reflect the rest for you to see. Mixing all the colors of pigment together gets you the color black.

Note how mixing adjacent primary additive colors together gets you cyan, magenta, and yellow as secondary colors. Also notice how mixing the adjacent primary subtractive colors together gets you red, green, and blue as secondary colors.

Red, yellow, blue just isn’t really a proper set of primary colors at all. I mean in concept you can use any three colors as primary colors (red, orange, and yellow for example) but it would just leave you with a reduced color gamut and the inability to produce some colors. Unfortunately many people are still taught this system simply through weight of tradition.

RGB is a subtractive model, using light. R+G+B = white. It is not physically possible to print with light. Ink uses an additive model that mixes inks. The addition of black widens the gamut a bit, and allows for darker darks.

It is a *smaller* gamut than RGB, but since we can’t print with light, it is the standard for printing on paper.

A monitor emits light so red, green, and blue are added together. So red and green light have the same visual effect on humans as yellow light. This is an additive colors model

Printing use ink that when illuminated by white light reflects back some light and absorbed other. So if you use twixt two ink color only the light both reflect are reflected, this is a subtractive color model

Look at https://www.simplypsychology.org/wp-content/uploads/eye-color-sensitivity.png which shows the color sensitivity of the three types of cones in a human eye.

RGB monitor works by having a color that primarily stimulates one of the cones and you can trick it so that we see color in between. With ink of just three colors, we need to do the same with the three cone types, it just had to do by absorbing parts of red light


For ink where light is removed, you reflect light that stimulates two cones in one ink.

Yellow ink in reflecting back both green and red light, that mean is absorbed the light that stimulates the “blue” cone

Cyan lighter reflects blue and green light, so it absorbed red.

Magenta reflects blue and red light, so it absorbed green.

So think of the ink as removing, red, green, and blue light from white. Yellow ink does not reflect back just yellow light, it reflects back light from green to red light includes yellow, it absorbed blue light

The spectra of the ink look like https://www.researchgate.net/publication/359777295/figure/fig4/AS:1143362056929291@1649610165431/Spectral-reflection-analysis-of-cyan-magenta-and-yellow-inks-illuminated-with-31-LED.png so reality us a bit messier than the text above but the general idea is correct

The result is if you what green when you print you use the inks that absorbed red and blue light. Cyan absorbed red and yellow absorbed blue but both reflect green. So cyan ink + yellow ink = green color when illuminated by white light

So the colors that are used are a result of how our eye works and the difference between absorbing light that hit something compared to emitting light