CMYK
The subtractive color model used by printers. Cyan, Magenta, Yellow and Key (black) are combined on paper to produce a full-color image.
cmyk(65% 69% 0% 10%).The four channels
C — Cyan
Absorbs red light. Cyan ink reflects green and blue, producing a light blue-green appearance when applied to white paper.
M — Magenta
Absorbs green light. Magenta ink reflects red and blue, producing a vivid pink-purple appearance.
Y — Yellow
Absorbs blue light. Yellow ink reflects red and green, producing a bright yellow.
K — Key (black)
Added for sharper blacks and to reduce ink usage. On its own, K produces a neutral black. Combined with CMY it produces a deep, rich black for text and shadows.
Why K exists
Pure CMY ink should produce black in theory — each ink absorbs one of the three additive primaries, and together they absorb all. But in practice, three-color black looks muddy brown, uses a lot of ink, and never dries properly on some papers. Adding a dedicated K (black) channel:
- Produces deeper, more neutral blacks.
- Reduces ink coverage and print cost.
- Produces sharper text and finer detail (single ink dots do not smear into one another).
- Dries faster (one ink layer instead of three).
RGB vs CMYK
| Aspect | RGB | CMYK |
|---|---|---|
| Type | Additive (light) | Subtractive (ink) |
| Used for | Screens, displays | Print, paper |
| Primaries | Red, Green, Blue | Cyan, Magenta, Yellow, Key |
| Full-intensity mix | White | Black |
| Zero channel value | Black | White paper |
| Gamut | Wider in bright neon colors | Wider in some deep earth tones |
Conversion formulas
RGB to CMYK (naive, device-independent):
Let R, G, B be 0–1 values.
K = 1 − max(R, G, B)
If K = 1 (pure black):
C = M = Y = 0
Otherwise:
C = (1 − R − K) / (1 − K)
M = (1 − G − K) / (1 − K)
Y = (1 − B − K) / (1 − K)CMYK to RGB (the inverse):
Let C, M, Y, K be 0–1 values.
R = (1 − C) × (1 − K)
G = (1 − M) × (1 − K)
B = (1 − Y) × (1 − K)Why screen and print colors differ
RGB and CMYK have different gamuts — different ranges of reproducible colors. Some bright, saturated colors that look vivid on a screen simply cannot be produced with standard CMYK inks:
- Neon green — vivid RGB greens become duller in CMYK.
- Saturated blues and oranges — pure RGB blue and orange are difficult to match.
- Bright magenta and cyan — usually printable, but can differ from screen.
- Metallic and fluorescent colors — require special inks (spot colors, Pantone).
Practical syntax
/* CMYK is not a CSS color syntax, but the value format is: */
cmyk(65% 69% 0% 10%) /* violet */
/* To use a CMYK color in CSS, convert it to sRGB first: */
color: #4f46e5; /* ≈ cmyk(65% 69% 0% 10%) */
/* In design tools, use the ICC profile for your printer. */When to use CMYK
- Offset printing — books, magazines, packaging.
- Digital presses — short-run commercial print.
- Consumer printers — home and office inkjet and laser printing.
- Brand guidelines — companies often specify brand colors in both RGB and CMYK for consistent cross-medium output.
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Frequently asked questions
What is CMYK?
CMYK stands for Cyan, Magenta, Yellow and Key. It is a subtractive color model used in printing. Each channel is a percentage of ink, from 0% to 100%. Mixing all four inks produces a deep black; the K channel produces sharper blacks than CMY alone.
Why does CMYK have a black channel?
Pure CMY ink should produce black, but in practice it produces a muddy dark brown and uses a lot of ink. Adding a K (black) channel gives pure, sharp blacks and reduces ink usage. K is also cheaper and dries faster, so it is used for text and detail.
Why do RGB and CMYK produce different colors?
RGB is additive (light) and CMYK is subtractive (ink). Their gamuts are different, and some colors visible on screen cannot be reproduced on paper. This is why designs for print often look slightly different from the screen version — bright neon greens and saturated blues are particularly hard to match.
Is CMYK still used in modern printing?
Yes. CMYK is the standard for offset printing, digital presses and most consumer printers. It is also the base model for additional spot colors (Pantone, metallic, fluorescent) used when CMYK cannot achieve the desired result.
How do I convert RGB to CMYK correctly?
The naive formula (K = 1 − max(R, G, B)) gives an approximation, but real print conversion depends on the ink, paper and printer. Use an ICC profile — such as US Web Coated (SWOP) or Coated FOGRA39 — in your design tool. This is why print-ready files are always delivered with the printer's profile embedded.