The printing process is a collection of other discrete processes all needed to produce the end product; typically an image on paper. In reproducing a full, or four-color image a photograph is separated into four components represented on film. One film is produced representing the amount of cyan found in the image, one for the amount of magenta, and one for the amount of yellow. A fourth film is produced which represents the black portion of the photograph which typically is wherever cyan, magenta, and yellow are all present in equal amounts. In order to simulate varying amounts of a given color found in a photograph, we use dots that change diameter or total coverage. For example, if we took one spot on a photograph and broke it down into its various components we may end up with something like this :
Black =20 % Cyan =40 % Magenta =40 % Yellow =20 %
In order to reproduce this particular spot we will create films with these dot percentages, or halftones, and overlay them. Since we are using dots instead of a continuous tone method as represented in the original photograph, we have to trick our eyes and make these dots small enough so our eyes cannot notice what they actually are.
The overlay looks fairly peculiar here but if you were to make it small enough, the eye would see it as a single color. Hence the simulation of continuous tone photography.
As printers, one of our main concerns would be to control the size of the dots. It is essential that pressmen know when the dot is sharpening or growing. A 3% growth or decrease in the dot area in any or all components will be enough for our eyes to notice a change in the overall shade or hue of the reproduced image. Hence, measuring dot area and dot gain are crucial to the control of overall color.