Xerox DocuPrint 92C NPS, Руководство по устранению неисправностей

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ADJUSTING PRINT QUALITY AND PERFORMANCE
XEROX DOCUPRINT 92C NPS TROUBLESHOOTING GUIDE 6-11
when an application provides its own halftone specifications, it
sacrifices portability. Associated with every device is a default
halftone definition that is appropriate for most applications.”
In addition to the device-dependent nature of halftoning, a spot
function is used by
setscreen and setcolorscreen to determine the
order of pixel darkening in the halftone cell. When two pixels have the
same spot function value, their ordering values are determined
arbitrarily. Duplicate spot function values are very common. In fact,
almost all the various default spot functions generate duplicate
values. Therefore, different PostScript implementations yield
different halftone patterns, resulting in visual differences in the
output.
Gray shading—settransfer and transfer function
The PostScript operators settransfer and setcolortransfer are
used to change the procedure for mapping perceived color values in
the output of the print device into specified color values in the
PostScript master. PostScript devices use an internal transfer array
or procedure that takes into account the printing characteristics of
their marking engines in order to produce levels of color.
Transfer functions are called by the setcmykcolo r, setbsbcolor ,
setrgbcolor , and setgray operator before processing of the desired
color level that is specified in the master. The transfer function takes
a value from the stack and leaves another value on the stack for each
color component (red, green, blue, and gray).
The PostScript language provides a scheme for overwriting the
internal transfer function of a printing device by providing the
settransfer and setcolortransfer operators. However, some Xerox
PostScript devices do not allow you to overwrite their internal transfer
function.
Typically, a master tries to replace the internal transfer function with
a null transfer function such as:
{} settransfer , or
{} {} {} {} setcolortransfer
If either of the above procedures is successful, the transfer functions
return the same color levels that are passed to them without
modifying or mapping the level. On printers that do not allow the
overwriting of the transfer function, the
settransfer operator does not
affect the mapping of gray values between the output of the print
device and specified levels of color.
Note: Settransfer actually sets the transfer functions for all four
color components (red, green, blue, and gray) to the same value. The
setcolortransfer operator sets the transfer functions
individually.
Smooth curves—setflat
PostScript masters that use the PostScript operator setflat produce
inconsistent output across different PostScript printers. setflat
controls curve rendering smoothness. PostScript curve operators
use cubic Bezier control points to define the curve shape. These
curves can be rendered from straight line segments. Normally the
line segments are so short that the curve appears smooth. The
setflat operator indirectly controls the length of the straight line