HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part II

EN PCL Raster Graphics 24-7
PCL Raster Graphics
To minimize I/O transmission time and conserve memory, avoid
sending unnecessary raster data to the printer that represents white
space. This is accomplished using the raster compression modes and
raster reduction techniques available with the raster picture area.
Set resolution prior to the start raster graphics command. Once the
start raster command is received, the resolution cannot be set until
after a subsequent end raster graphics command.
Set presentation mode prior to the Start Raster Graphics command.
Once the start raster command is received, the presentation mode
cannot be set until after a subsequent End Raster Graphics
Command.
Some applications and I/O drivers insert carriage returns or line feeds
into the data stream sent to the printer. This modification of the data
stream must be suppressed for correct printer operation.
The most efficient way to draw lines (horizontal and vertical) is using
graphics rules (black-fill rectangular areas). The most efficient way to
draw diagonal lines is using HP-GL/2 vector graphics.