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We know that RGB is additive color model and CMYK is subtractive color model. RGB starts with darkness (black) and we gradually add light; an CMY(K) image requires to be illuminated by white light.

When a printer performs printing operation, how do CMYK and RGB work together to print on white paper? And why does CMYK technology need both, white paper and white color?

N. B. - I want to understand the intuition rather than details. Please don't use too much technical term.

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    I’m voting to close this question because it is not about software engineering
    – mmathis
    Feb 10 at 18:46
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    @mmathis where should I ask?
    – Alok Maity
    Feb 10 at 18:47
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    @AlokMaity: sounds like a good question for graphicdesign.stackexchange.com but before you ask, make sure it was not already asked and answered there. Currently, I found 187 questions on that site for the keywords RGB and CMYK, you may filter them further and check them first.
    – Doc Brown
    Feb 10 at 20:29
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    @JacquesB please insert your comments in answer, your comments like answer and deserve upvote.
    – Alok Maity
    Feb 11 at 19:01
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    TLDR: Ink works by subtracting colors from white light shining on white paper. If you subtract the red wavelengths from white light, you are left with cyan. If you subtract the green, you are left with magenta, and if you subtract the blue, you are left with yellow. Black ink is an optimization: When you want to absorb all of the light, black ink does a slightly better job than if you layered cyan on top of magenta on top of yellow. Also, the black ink costs less than the colored inks. Feb 11 at 20:16

1 Answer 1

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If you are working on image editing or graphic software, you probably wonder why you'd need to provide some more thoughts about color models:

  • Colors you see on a screen are sent from a light source. No light is black. Adding light to the source is the simplest way to change the color.

  • Colors you see on a paper are reflected from the ink. No ink reflects the paper color (usually white). But in reality the ink does not reflect a certain color: It absorbs a color and reflect more or less the other ones. The absorption corresponds to a subtractive effect, i.e. you add on paper ink that would subtract some light from the reflection.
    ( If the paper is not white, it already absorbs some colors of the white light spectrum. So it subtracts already something and substracting, say yellow, would then subtract even more, leading to a different color. )

This is why RGB color model is popular for screens and light and CMYK for printing. (Fortunately, device drivers are making the conversion for us: most of the time we do not really need to know about such differences).

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    Plus for that it is a real technical, physical phenomena of additive/subtractive color. And monitors are mainly RGB pixels whereas printers use CMYK ink.
    – Joop Eggen
    Feb 10 at 19:34
  • @Christophe "If the paper is not white, it already absorbs some colors of the white light spectrum. So it subtracts already something and substracting, say yellow, would then subtract even more, leading to a different color. "--- in CMYK we need C, M, Y, K ink to subtract R,G,B from white light. My question is ""yellow is subtracting""-- don't understand? Please give one example where yellow is subtracting on without white paper and produce unexpected color?
    – Alok Maity
    Feb 11 at 1:00
  • @Christophe when white light incident on cyan ink it absorbs red light and reflects green and blue—remember then green + blue light = cyan. My question is it only reflects green and blue light among 7 colors (white light) ? Remaining lights is absorbed like red color?
    – Alok Maity
    Feb 11 at 1:12
  • @AlokMaity Yes. I suggest to read the link behind "It absorbs color". The principle is that the white light is made of all the colors. When the white light hits the paper, nothing is absorbed and all the colors bounce back to your eye: you see white. When you have color yellow, the ink absorbs all the other colors but yellow and this is why you see only yellow. The colors that you see is the color that is not absorbed. At the other extreme: if you ink your paper with all possible colors, then the white light is completely absorbed, and you see nothing: the sheet appears black.
    – Christophe
    Feb 11 at 1:18
  • @Christophe "it subtracts already something and substracting, say yellow, would then subtract even more"--- from this statement I understand that if paper is yellow then when white light incident on yellow paper we only see yellow color paper. If we want a printed surface to appear cyan then it absorbs red light and reflects green and blue—remember than green + blue light = cyan. Then cyan + yellow= green. We don't get cyan color on paper instead we get green color which isn't not expected. Am I correct?
    – Alok Maity
    Feb 12 at 10:49

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