CMYK stands for the four printing colours cyan, magenta, yellow and ‘key’ (black or black component). These four printing colours form the basis for four-colour printing. At least these four printing colours are required for printing colourful photos.
CMYK is a subtractive colour model: colours are created by absorbing light. When printing, colours are applied to white paper and the different colours absorb different parts of the light to achieve the desired colour. By combining cyan, magenta and yellow, a wide range of colours can be produced.
CMYK colour spaces depend on the printer and the paper used and therefore require colour profiles to accurately describe the colour reproduction.
High-quality image brochures on art paper are produced in CMYK in exactly the same way as an inexpensive advertising newspaper with a large print run, but the colour reproduction is completely different. If, for example, an image was printed with identical CMYK values in both the high-quality image brochure and the newspaper print, the print result would certainly be completely different. In the image brochure, deep blacks and saturated colours are achieved, whereas the colourfulness in newspaper printing is very pale and no deep black can be achieved, only a ‘dark grey’ as the darkest printing tone.
These differences in colour reproduction can be mapped using CMYK proof profiles and thus also partially matched in print. If, for example, the same RGB image is separated according to PSOCoatedV3 for a high-quality image brochure and according to ISONewspaper26v5 for newspaper printing, the differences in the achievable gamut will of course still exist, but the images will be adjusted so that the motif does not become colour-sticky or ‘drown’, i.e. the dark tonal values run out.
The most important CMYK colour spaces are
- ISOCoatedV2 and PSOCoatedV3 for offset printing on picture printing
- PSOUncoated and PSOUncoatedV3 for offset printing on uncoated paper
- ISO newsprint 26v4 and 26v5 for newspaper printing
- Numerous PSO and PSR standards for web offset and gravure printing
However, the CMYK colour model is not really optimal; for example, it cannot display all colours in the visible spectrum well. In particular, bright and intense colours such as a bright green or orange can hardly be printed with CMYK. In such cases, additional printing colours, such as CMYKOGV with orange, green and violet in seven-colour printing, can increase the colour gamut. However, multicolour printing, such as FOGRA55 with seven or more colours, has not yet become widespread on the market, as it is noticeably more expensive and requires a great deal of expertise and technology in terms of retouching and printing. However, Proof GmbH was the first company to be certified for proofing with an extended colour space according to FOGRA55 CMYKOGV in 2022.
In proof printing, we also work not only with the 4 CMYK colours, but also with orange, green, violet, light cyan, light magenta, light grey and two shades of black for gloss black and matt black. This means that colour gamuts can be achieved in proof printing that are almost double the range of even high-quality image printing CMYK colour spaces.