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

EN The PCL Print Model 5-25
Figure 5-5 Pixel Placement
Note The grid-centered method is used by Microsoft Windows.
When rectangular area fills are used and grid intersection is used, an
overlapping of pixels can occur if rectangular area fills are placed
adjacent to one another (as shown below). Depending on the raster
operation presently in effect, this overlap can produce undesirable
results in the final printed image. To avoid this problem, use the
grid-centered method.