Four Color Process
Four-color process printing is the method used to reproduce full-color continuous-tone copy, such as transparencies, color prints, and paintings. Four-color process printing should not be confused with four-color printing, discussed earlier in this section. Whereas four-color printing can be done with any four flat colors, four-color process printing uses four specific colors, called process colors, which consist of the three primary colors, yellow, magenta (process red), cyan (process blue) and black. Note: although most printers refer to the process colors simply as yellow, red, blue, and black, we shall use the correct terminology, yellow, magenta, cyan, and black, so as not to confuse the reader when discussing separations.
When printed, the four process colors appear as dots of solid color which combined in various sizes and patterns duplicate the full range of colors found in the original image. It is interesting to note that the colors are created not by a physical mixing of the inks, but by the optical mixing of the four original colors by the viewer's eye (similar to the principle of the pointillist technique developed by impressionist painter Georges Seurat).
PROCESS COLOR AS FLAT COLOR Although process color is used primarily for the reproduction of full-color continuous-tone images, it can also be used to reproduce black and white line copy in color. This is possible because any flat color can be approximated by combining various tints of the four process colors. This technique is commonly used for jobs such as ads, posters, magazines, and book covers.
Note: when combining process-color tints, keep in mind that the more ink applied to the paper's surface, the muddier the colors become. The total percentage of tints should not exceed 240%. For example, 100% yellow, 100% magenta, and 40% cyan would be acceptable, whereas 100% yellow, 100% magenta, and 100% cyan would not be.