Editor › Learn › What is CMYK? A Practical Explanation for Print
What is CMYK?
CMYK is a subtractive colour model that builds an image from four printing inks — cyan, magenta, yellow and black (K for "key"). Each ink absorbs light rather than emitting it, so more ink means a darker result, which is the opposite of how a screen works.
Why four inks and not three
In theory cyan, magenta and yellow together absorb all light and produce black. In practice inks are impure, so overlapping all three gives a muddy dark brown. A dedicated black ink fixes that, and it also saves ink and keeps small text crisp — text printed as a single black plate stays sharp, whereas text built from three plates shows any misregistration as coloured fringes.
Total ink and why presses care
Every press has a limit on how much ink a sheet can absorb, usually expressed as total area coverage — the sum of the four percentages. Exceed it and ink fails to dry, offsets onto the next sheet, or muddies shadow detail. This is why a profile-driven conversion matters: the profile encodes how much black to substitute for the other three inks, keeping the total within the press limit.
What this means when you convert
- Bright saturated screen colours — especially vivid greens, oranges and blues — cannot be reproduced in CMYK and will shift.
- The same CMYK numbers print differently on different papers, which is why the profile describes a printing condition and not just "CMYK".
- Converting is lossy and one-way in practice. Keep your RGB master.
Checking your own work
The useful habits are: soft-proof against the profile your printer supplies, look at each plate separately to confirm black text is on the K plate alone, and check that shadow areas have not gone over the total ink limit.
Questions
- Does K stand for black or key?
- Key — the key plate that carries detail. It happens to be black ink.
- Should I design in CMYK from the start?
- Usually no. Work in RGB, keep the master, and convert for a specific printing condition at the end.