Xerox DocuPrint Network Printer Series Guide, Руководство пользователя, Страница: 57 / 72

POSTSCRIPT
XEROX DOCUPRINT NPS GUIDE TO USING PAGE DESCRIPTION LANGUAGES 2-31
Considerations
The scan order of an image relative to the content of the image is not
important. It is important that the scan order of the image in the
desired orientation is relative to the scan order of the page.
There are circumstances when a transformation cannot be avoided
by any ordering of image data (such as when the image sides are not
parallel to the sides of the paper, or when the image is skewed), but
for many cases a rotation can be avoided by ensuring that the data
in the image is in the correct order.
Ensuring optimum image data order is complicated by the fact that
the rotations are not tied to the use of the
rotate operator in a
PostScript program, or to implied rotations in the image-to-user
space transformation. The transformations specified in PostScript
are part of a specification of the desired position of an image in terms
of the default user coordinate system.
DocuPrint NPS only performs an image rotation when one is
required. Rotations of multiples of 90 degrees are optimized so that
the impact is not too great.
Because the data is already aligned with the printing orientation,
DocuPrint NPS does not perform any rotation of the image. In the
default user coordinate system, a rotate operation is required.
Without the rotate operation, the PostScript specifies that the image
be placed on the page with its left edge (fast scan dimension) parallel
to the short edge of the paper. A 90 degree counterclockwise rotation
of the coordinate system is needed to correctly specify the image
orientation on the page.
It may be possible to arrange an appropriate order for the data by
correctly arranging the original when a scan is performed. It is
assumed that scanners produce data from a portrait scan in left-to-
right (fast scan), top-to-bottom (slow scan) order.
By rotating the original 90 degrees clockwise, you can obtain data
from the scanner with the fast scan direction bottom-to-top (relative
to the original), and the slow scan direction left-to-right, matching the
page scan directions for the correct output orientation. Alternatively,
you can have the data reordered by a program before the PostScript
master is created.
After determining that a certain scan orientation produces data in the
optimum order for printing, you can scan an image and import it into
an emitter. Some rotation may be necessary to place the image
correctly.
If the emitter performs a rotation by manipulating the data, then the
resulting PostScript master may have the data in the incorrect order.
It is also possible that the emitter may not alter the data and change
the transformations specified in PostScript so that the initial ordering
is preserved.
Summary
To minimize imaging time, make sure that no data transformations
need to be performed at the printer. Order the image data so that the
fast and slow scan directions match the output fast and slow scan
directions when the image is in the correct orientation on the page.
With the image data correctly ordered, arrange the PostScript
transformations so that they specify the position and orientation of