Why do printers combine cyan, magenta and yellow to create a colour image while video displays like TVs and Monitors use Red, Green and Blue?
In: Technology
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There are fundamental differences in how these two machines produce colour.
Video displays make their own light. In a completely dark room, you can see them, and when off they look black. They use red, green and blue because those are the colours our eyes are sensitive to, and their purpose is to stimulate those things in your eyes directly so you see the colours they want.
Printers are the opposite. You can’t see a print-out in the dark. The paper with nothing on it is white and if you look at a print-out under any colour of light other than white it looks wrong. You’re mixing inks in order to take white light, bounce it off the pigments, and get the colour you want to bounce back. C, M, and Y are the ideal colours to use for this purpose. If you mix any 2 of red, green or blue together on a monitor, you will get back either cyan, yellow, or magenta depending on which 2 monitor colours you used.
Mixing all 3 ink colours *should* produce black… but in practice, mixing inks causes dilution of the them and it ends up being a grey colour instead. So a separate black ink is used for good blacks instead. It also makes printing in black+white much cheaper since you can just use the one ink type.
It’s the difference between adding light from nothing – which is black – to everything – which is white. The fundamental colours of that system are red, green, and blue, the *additive* colour system, you’re starting with no light and adding it in, and red, green, and blue and lower
With printing you’re (usually) starting with a white sheet of paper, and adding pigments to filter that white paper down to other colours, and the primaries for that system are cyan, magenta, and yellow (with Key usually, but not always, meaning black). It’s a *subtractive* system, whatever you do you’re removing light.
Why are the primary colours different?
If you imagine printing red paint onto a paper. What paint does is filter out any light that *isn’t* red and that’s what you end up seeing.
So…what happens if you want to print any other colours onto that answer is you can’t, because you’re already down to a “lower” point than a lot of other colours sit.
But in printing, you can *make* red with yellow and cyan mixed together, so having yellow and cyan as some of your primary colours gives you more options for colour.
Similarly, if you tried to have a “cyan” pixel on a monitor, cyan is a mixture of green and blue light added together, so if you start with cyan, you now have no way to make green, or blue because you’re already “higher” than that, closer to white than green or blue sit.
This is why when you’re a kid you mix paints together expecting great colours, and often end up with a murky brown/black. This is typically because getting kids to understand the distinction between “Red” “Blue” and “Yellow” compared to “Magenta” “Cyan” and “Yellow” is tough, so you ended up with that less than optimal solution of Red blue and yellow.
TVs and monitors selectively emit light.
Inks and dyes selectively absorb light.
Cyan absorbs red.
Magenta absorbs green.
Yellow absorbs blue.
If you used RGB ink, you wouldn’t be able to show magenta at full brightness, but if you use CMY, you can show red by using both magenta and yellow.
The difference is additive vs subtractive colour mixing.
– Mixing all colours of light makes white.
– Mixing all colours of paint makes brownblack.
It’s like that because “white light” is a mix of all the colours. Video screens shine the colours of light that you see.
Paintprintersink work by absorbing all the colours of white light *except* the colours you see. Red ink absorbs all the colours except red, and bounces the red part to your eye. Same for blue etc.
That’s why colour mixing works differently for screens vs ink pigments. Screens are adding light together. Ink is removing different combos from white light hitting the printed object and you see what’s left.
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