Adobe ILLUSTRATOR 6.0, Online Manual, Page: 752 / 893

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Specifying the halftone screen ruling
The Halftone menu displays one or
more sets of line screens (lines per inch,
or lpi) and resolutions (dots per inch, or
dpi) available on the printer or image-
setter that will be used to print the color
separations.
A high line-screen ruling (for example,
150 lpi) spaces the dots used to create
an image closely together to create a
finely rendered image on the press; a
low screen ruling (60 lpi to 85 lpi)
spaces the dots farther apart to create a
coarser image. The size of the dots is
also determined by the line screen. A
high line-screen ruling uses small dots;
a low screen ruling uses large dots. The
most important factor in choosing a
line-screen ruling is the type of printing
press on which your job will be printed.
Ask your print shop how fine a line
screen its press can hold, and make
your choices accordingly.