REPRO: In publication printing, all the colours in the printed image are created with a combination of the basic colours (the "subtractive primaries") yellow, magenta, and cyan, which are present in different intensities. In order to print coloured pictures, yellow, magenta, cyan and black inks have to be printed exactly in register over each other. In order to do this, the amounts of the basic colours in the original have to be separated. These colour separations are made from originals digitised in scanners or supplied from digital cameras. Each of the basic colour portions is presented in the form of higher or lower values, representing the amounts of ink needed in the subsequent printing operation. Any required colour corrections to these colour separations, re-touching and the composition of complete pages including the text are also carried out in prepress computer systems. The digital data is then supplied for the engraving of printing formes.
In packaging and decorative printing, additional separations are needed for additional inks used for special colours, such as a red or purple that is identified with a particular product brand, browns for printing wood-effects, or metallic 'silver' or 'gold'.