Xerox DocuPrint 155, Troubleshooting Manual

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Optimizing print quality
6-4 Troubleshooting Guide
Product features that affect PostScript print quality
You can improve the appearance of your documents by being
aware of potential problems created through the use of
proprietary PostScript extensions and device-dependent
operators.
Proprietary PostScript extensions
PostScript masters that use proprietary printer features may
cause appearance inconsistencies between different PostScript
printers. Some PostScript printers contain proprietary PostScript
extensions. For example, some versions of the Apple Macintosh
PostScript driver download encrypted proprietary image
“smoothing” operators to Apple LaserWriters. The downloaded
PostScript code uses the product operator to determine if it is
being used on a LaserWriter. If not, the proprietary code is
bypassed by doing a flushfile. This allows the PostScript master
to print on non–LaserWriter products. As a result, PostScript
masters generated on a Macintosh with Apple proprietary
features may produce output that varies between LaserWriter
and non–LaserWriter PostScript printers.
Device-dependent operators
Some PostScript operators result in device-dependent PostScript
files. “Device dependence” means that devices having different
output characteristics may produce different-looking output even
though they use the same software. This section documents the
most serious examples of device dependence. The PostScript
Language Reference Manual, second edition, lists all of the
graphics state operators that are considered device-dependent.
Gray shading—setscreen and setcolorscreen
The PostScript operators setscreen and setcolorscreen control
the PostScript halftone software that simulates various intensity
levels of gray and color inks. Since each PostScript product may
have a different default halftone definition, the halftone patterns
and gray scale range may differ also. Because setscreen is
inherently device dependent (especially when used for pattern
fills), PostScript masters look different on almost every different
model of PostScript printer.