HP PCL 5 Reference Manual page 315

Figure 15-3 Raster Graphics Expansion - at 300 dpi
Note Rectangular area fills and character data are not affected by changes
in resolution. Rectangular Area fills and character data always print at
the maximum resolution, regardless of the resolution setting.
When configured for 600 dpi resolution, the printer automatically
expands raster graphics transferred at resolutions less than 600
dots-per-inch to 600 dots-per-inch during printing. illustrates how a
single bit is translated into the corresponding printed dots in various
graphics resolutions when the printer is configured for 600 dpi.
Figure 15-4 Raster Graphics Expansion - at 600 dpi
EN
Raster Graphics Resolution Command 15-7