Imaging and Color - The Graphic Design: Reference and Specification - page 15

h a l f to n e s c r e e n s
The halftone screens that are used to convert a continuous-tone image to one that can
be printed come in a variety of densities measured by lines per inch (lpi), a term the
industry uses for referring to the size of a screen's halftone dot. High screen rulings
of 175 or 200 lpi have more halftone dots per inch and, therefore, smaller dots. Low
screen rulings such as 65 or 85 lpi have larger dots. The size of a halftone dot can
affect an image's quality. Those with a high lpi show more detail. However, the choice of
halftone screen is often dictated by the type of paper used. Paper with a low degree of
absorbency, such as coated stocks, tend to resist dot gain or the spreading of halftone
dots in a halftone screen and are suitable for high lpi halftone screens. Printing images
on inexpensive uncoated stocks, such as newsprint, tends to result in dot gain and
requires a halftone screen with a low lpi.
Enlarged halftone screen.