In the graphic arts community, four-colour process printing is used primarily to reproduce full-colour continuous-tone images such as photographs, transparencies, and paintings.
This form of printing uses specific colours, called "process colours", consisting of the three primary colours cyan, magenta, and yellow plus black.
When printed, the four process colours appear as thousands of microscopic dots of solid colour which when combined in various sizes and patterns duplicate the full range of colours found in the original image.
These dots range in general size depending on how they are printed: 80 to 100 screen (coarse) for newspaper; 133 to 150 (average); and 175 to 200 line for fine detail lithography.
In this way, colours are created not by physical mixing of inks, but rather by the optical mixing of the four process colours by the viewer's eye. The actual colour or shading perceived is dictated by the size of the dots, the manner in which they overlap and their relation to one another.
The operating principle is that any conceivable shade found in the colour spectrum can be faithfully reproduced by means of the proper concentrations of the four process colours.
Quality paper plays and important role in your ability to reproduce an original.
Don't underestimate the effect paper has on the outcome of the printed piece.
Digital colour copies work much the same way.
Using the primary colours plus black, in a dry powder toner, each colour is digitally transferred via laser to the main drum of the machine electrostatically.
The toner is then applied or 'fused' to the sheet.