A mixture of light and dark areas fool the eye into seeing gray values.
A halftone can be produced photographically using a process camera or digitally using imagesetters.
Halftones can be produced with different dot sizes, called screen rulings. The finer the screen, the smaller and less visible, the dot. Usually, the smallest dot possible is desired. However, the type of paper the image will be printed on is a determining factor, as the ink tends to spread on absorbent papers ( a phenomenon called "dot gain"). Also, the ability of a press to "hold" a dot is an important factor.
Screen rulings vary from 65 lines per inch (common in newspaper) to above 300 lpi (used in high quality press work). Lines per inch is not to be confused with dots per inch (dpi) or pixels per inch (ppi) both used to describe computer screen and output device resolutions.
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