Understanding CMYK v RGB Colour


A typical printing press uses 4 colours of ink to create full-colour photographic images. The four inks are placed on the paper in layers of dots that combine to create the illusion of many more colours. CMYK refers to the 4 ink colors used by the printing press. C is cyan, M is magenta, Y is yellow, and K is black. Cyan, Magenta, Yellow and Black are called subtractive colours. Consumer ink-jet printers use CMYK toners in much the same way to produce full-colour printing. Combining them all gives the colour black. When combined in various percentages, these four inks will create an entire spectrum of colours.

The CMYK offset printing method is also known as “four-colour process” or simply “process” colour. All of the colours in the printable portion of the colour spectrum can be achieved by overlapping “tints” of cyan, magenta, yellow and black inks. A tint is a screen of tiny dots appearing as a percentage of a solid color. When various tints of the four colors are printed in overlapping patterns it gives the illusion of continuous tones - like a photograph.


Computer, television, and smartphone screens use a different colour model called RGB (Red-Green-Blue) that is the contrast of CMYK. It is important to understand that it is impossible to print RGB. In RGB, the convergence of the three primary additive colours produces white. In CMYK, the convergence of the three primary subtractive colors produces black. Additionally, the colours in RGB are much brighter than the colours in CMYK. It is possible to attain a much larger percentage of the visible spectrum with RGB, as RGB uses transmitted light while the CMYK uses reflected light. See colour gamut image below.


It is important to choose the right colour model for the job. Use RGB for screen displays so the full gamut will be available. In printed materials, this light combination cannot be directly reproduced; so computer-generated images and artwork  MUST be converted to the CMYK equivalent. Because both models can be available at the same time in some applications, it is easy to make a mistake and choose the wrong palette or set of colour swatches.

Offset Printing: MUST be CMYK

Screen or Monitor: Use RGB

Digital Printing: Is more forgiving as we can convert your RGB artwork to CMYK "In-RIP" if required.

 We are very happy to advise you on how best to produce printable CMYK artwork files.