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

13-18 The PCL Print Model EN
Reserved (Byte 3)
This field, byte 3, is not currently used and must be set to 0.
Height in Pixels (Bytes 4 and 5)
This field, bytes 4 and 5, identifies the number of rows (height) of
the pattern.
Width in Pixels (Bytes 6 and 7)
This field, bytes 6 and 7, identifies the number of pixels (width) of
the pattern.
Pattern Image
This field contains the raster data for the pattern.
Master X Resolution (UI)
The Master X Resolution field is the pixel resolution in the X scan
direction at which the pattern was designed.
Master Y Resolution (UI)
The Master Y Resolution field is the pixel resolution in the Y scan
direction at which the pattern was designed.