RGB ↔ CMYK Converter
Convert between RGB (screen) and CMYK (print) color formats. Note: this is a device-independent mathematical conversion — actual print results depend on your ink profile and paper stock.
About RGB ↔ CMYK Conversion
CMYK is a subtractive color model — colors are created by subtracting light using inks (Cyan, Magenta, Yellow) plus a Key (Black) plate for depth and economy. RGB is an additive model — colors are created by combining red, green, and blue light. The two models occupy different gamuts (ranges of possible colors), so direct conversion is an approximation.
RGB to CMYK Formula
Normalize: \( r' = R/255,\ g' = G/255,\ b' = B/255 \).
\[ K = 1 - \max(r', g', b') \]
If \( K = 1 \) (pure black), then \( C = M = Y = 0 \). Otherwise:
\[ C = \frac{1 - r' - K}{1 - K}, \quad M = \frac{1 - g' - K}{1 - K}, \quad Y = \frac{1 - b' - K}{1 - K} \]
All four values \( \in [0, 1] \), typically expressed as percentages.
CMYK to RGB Formula
\[ R = 255 \times (1 - C)(1 - K) \] \[ G = 255 \times (1 - M)(1 - K) \] \[ B = 255 \times (1 - Y)(1 - K) \]
Why Results Differ from Photoshop
Professional tools apply ICC color profiles that map specific ink formulations on specific paper types. The formula above is the device-independent mathematical relationship — a useful baseline, but not a substitute for profile-based color management in print workflows.
Frequently Asked Questions
Can every RGB color be reproduced in CMYK?
No. The CMYK gamut (range of reproducible colors) is smaller than the sRGB gamut. Bright, saturated colors like neon blue or electric green exist in RGB but fall outside what standard process inks can produce. These out-of-gamut colors are mapped to the nearest printable equivalent (gamut compression).
Why is there a separate K (black) channel?
Theoretically, equal amounts of CMY produce black. In practice, ink absorption varies, producing a muddy brown. Using pure black ink (K) gives cleaner text and shadows, saves ink costs, and reduces drying time.
What does "Key" mean in CMYK?
In traditional printing, the key plate carries the detail and outline information — historically the black plate. The name comes from "key" as in the component that other plates are keyed (aligned) to, not from "black" directly.
Should I convert my logo colors from RGB to CMYK for printing?
This calculator gives you a mathematical starting point, but for professional print work, always work with a printer and use ICC profiles. Ask your print provider for their CMYK color profile and convert in Photoshop or Illustrator using that profile.