The act of decomposing a color graphic or photo into single-color layers. For example, to print full-color photos with an offset printing press, one must first separate the photo into the four basic ink colors: cyan, magenta, yellow, and black (CMYK). Each single-color layer is then printed separately, one on top of the other, to give the impression of infinite colors.
This type of color separation, mixing three or four colors to produce an infinite variety of colors, is called process color separation. Another type of color separation, called spot color separation, is used to separate colors that are not to be mixed. In this case, each spot color is represented by its own ink, which is specially mixed. Spot colors are effective for highlighting text but they cannot be used to reproduce full-color images.
Traditionally, process color separation has been performed photographically with different colored filters. However, many modern desktop publishing systems are now capable of producing color separations for graphics stored electronically. This capability is essential if you want to create full-color documents on your computer and then print them using an offset printer. You don’t need to perform color separation if you are printing directly to a color printer because in this case the printer itself performs the color separation internally.
Recommended Reading: Webopedia’s The Science of Color and the Digital Camera Quick Reference.