CMYK
CMYK — Cyan, Magenta, Yellow, and Key (black) — is the four-colour subtractive process used for full-colour printing. Files supplied as RGB (the additive model used by screens and cameras) are converted to CMYK at prepress, with a colour profile that matches the press, ink, and substrate.
Also called: four-color process · 4-color process · process colour printing · CMYK printing · RGB vs CMYK
In depth
Print presses build colour by overprinting four translucent inks in halftone dots. Combinations of cyan, magenta, yellow, and black produce the visible colour gamut. Black is added as a separate "key" plate because layering CMY alone produces a muddy dark brown rather than a clean black, and uses three times the ink to do it.
The challenge in colour management is that screens use additive RGB (red, green, blue light) and produce colours that CMYK ink on paper cannot reach — bright saturated greens and electric blues, in particular. The conversion from RGB to CMYK has to make choices about how to map out-of-gamut colours into the printable range. A colour profile (ICC profile) specific to the press, ink, and stock describes those choices so the result is predictable.
For brand-critical work, Pantone spot colours can be printed as a fifth (or sixth, seventh) ink alongside CMYK. This is more expensive (extra plate, extra wash-up) but produces exact brand colours that CMYK cannot reach.
Common questions
My PDF looks great on screen but dull when printed — why?
Should I supply files as RGB or CMYK?
Related terms
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