HP PCL/PJL reference (PCL 5 Color) - Technical Reference Manual

6-36 Raster Graphics EN
Raster Scaling
Raster scaling provides the ability to enlarge or reduce raster images
using the Destination Raster Width and Destination Raster Height
commands. The Start Raster command (
?*r#A) with a value field of
2 or 3 turns on scale mode. Scaling is independent of device
resolution.
Note To use raster scaling, the Configure Image Data command (?*r#W)
must be sent prior to the Start Raster command (
?*r#A), which must
have a value field of 2 or 3 to enable scaling.
There are two types of raster scaling: Resolution and Arbitrary. The
scaling type is selected by the argument to the Start Raster
command. If either 0 or 1 are used then resolution scaling is
performed. If either 2 or 3 is used then arbitrary scaling is performed.
Resolution Scaling
This scaling is performed using the raster resolution in combination
with the device resolution. For example, if the raster resolution is set
to 300 dpi and the device resolution is 600 dpi, then the image is
scaled by a factor of two. This type of scaling does not depend on the
source or destination raster dimensions.
Arbitrary Scaling
This scaling is performed without regard to the raster resolution which
is unaffected by scale calculations. The scaling factor is determined
by the source and destination raster dimensions. If the destination
dimensions are not specified the graphics margin and printable area
are used to calculated destination dimensions while maintaining
isotropic scaling so that the entire image fits on the page. If only one
destination boundary is specified the other is calculated to maintain
isotropic scaling.
The destination width and height commands accept real numbers
with up to four decimal places of precision. This level of precision is
necessary when converting from decipoints to pixels so that round off
errors will not create visible print artifacts such as lines within the
image.