User Guide

657
Screen frequency
Although separate from resolution,
screen frequency also affects the sharp-
ness of a printed image. Also known as
screen ruling, screen frequency refers to
the number of halftone cells per inch in
the halftone (or line) screen used to
print a grayscale image or color separa-
tion. The line screen arranges the image
in each separation into rows of halftone
dots for printing. The frequency of
these rows of dots is described in lines
per inch, or lpi.
A low lpi setting (e.g., 65 lpi) creates a
coarse screen that produces large, well-
separated dots. This is useful for print-
ing newspapers, for example, because
that kind of paper absorbs ink quickly,
and the dots tend to spread.
A high lpi setting (e.g., 177 lpi) pro-
duces many small dots, which is useful
for printing fine shadings and detailed
images, such as those found in art
books and magazines. The appropriate
line screen setting depends on the reso-
lution of the printer, and on the type of
paper, press, and inks that will be used
to print the artwork.