Pixel Placement Command
This command determines how pixels are rendered in images.
Two models are used for rendering pixels when an image is placed on
• Grid Intersection Model
• Grid Centered Model
This command can be invoked multiple times during a page. It has no
effect except to switch the model being used for imaging.
The PCL Pixel Placement command determines how pixels are
placed for both PCL and HP-GL/2 operation.
The example shown in Figure 2-1 illustrates the concepts of the two
models. Assume a rectangle extends from coordinate position (1,1) to
position (3,4). As shown below, each model produces a different
result. (Since PCL printers print only at intersections, grid centered
pixel placement is implemented as shown on the right.)
- Grid intersection
- Grid centered
= 0, 1 (command is ignored for other values)
Printer-Specific Differences 2-25
The grid centered model produces a rectangle that is one dot row
thinner and one dot row shorter than the grid intersection model. The
grid intersection model is the PCL default.
The grid centered method is used by Microsoft Windows.
2-26 Printer-Specific Differences
PCL and HP-GL/2 (see following pages for HP-GL/2 pixel placement
command description) provide two pixel placement modes: grid
intersection (the default) and grid centered. Grid intersection places
pixels on the intersections of the grid (see Figure 2-2). Grid centered
places pixels in the center of the grid. In Figure 2-2, a rectangle
extends from position (1,1) to (3,4). The grid centered model
produces a rectangle one dot thinner and one dot shorter then the
grid intersection model.
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
Since PCL printers print only at intersections, grid centered is
implemented as shown on the right.
Pixel Placement Variations
Printer-Specific Differences 2-27