Specifications

CHAPTER 3
LaserWriter Pro Software
Page Device Parameters 35
To use this capability, you must allocate a 4-bit-per-pixel frame buffer instead of the
usual 1-bit-per-pixel buffer.
Note
Allocating this amount of memory to the frame buffer places an
additional computational burden on the host computer. It may also
cause some degradation in performance, especially if you are rendering
images with the image or imagemask operators. ◆
The PhotoGrade technology is invoked before PostScript language objects are rendered
to the frame buffer. This is why it is considered pre-rendering enhancement.
The PreRenderingEnhance entry in the page device dictionary is treated as a request,
not an assertion. The rendering enhancement request is considered in conjunction with
the page size request, the value of HWResolution, and the amount of memory installed.
See Table 3-2.
To make the best use of the special hardware required by PhotoGrade, you should select
a different halftone screen frequency. To do this, the default Install procedure used by
the setpagedevice operator reads the value of ActualPreRenderingEnhance. If it
is false, the halftone dictionary specified by Install is used as an argument to the
sethalftone operator. If it is true, the name of a Halftone resource instance is
obtained from the PreRenderingEnhanceDetails dictionary and that name is used
to fetch a Halftone resource instance. The PostScript Language Reference Manual
provides more information on available halftone resources. Table 3-6 shows frequently
used entries in the PreRenderingEnhanceDetails dictionary.
Table 3-5 PhotoGrade device parameters
Device parameter Description
Install
Performs graphics state setup for the page device. If
PreRenderingEnhance is true and the request is satisfied,
Install sets the halftone in the graphics state to the
dictionary identified by DefaultHalftone in
PreRenderingEnhanceDetails. Otherwise, a standard
halftone dictionary is used, with a frequency of 60 at 300 dpi,
and 85 at 600 dpi.
PreRenderingEnhance
Indicates whether or not you have requested PhotoGrade.
Page descriptions can change this value within save/restore
boundaries.
PreRenderingEnhanceDetails
Contains information specific to PhotoGrade technology.
See Tables 3-6 and 3-7.
Table 3-6 Frequently used entries in the PreRenderingEnhanceDetails dictionary
Key Type Default Description
DefaultHalftone name 106 x 45 Name of a valid Halftone resource instance
used by Install
Type integer 1 Indicates where PhotoGrade information is found
and how it is represented