6.1.7 Interlaced Graphics

In some cases it is possible to create a higher resolution than a native
one by vertically interlacing graphics (rendering each block of graphics
data in two passes). In order to accomplish this, the printer must support
a vertical cursor-movement command that uses a resolution at least twice as
fine as the native vertical-graphics resolution being used. The Universal
Printer Driver accomplishes this by sending the first block of raster data
as normal, but during the second pass, the print-head position is
incremented in the y-direction by a value that is less than or equal to the
height of a single pin or jet. In order to render bitmaps correctly, the
Universal Printer Driver requires the number of pins used by the printer
for interlaced graphics. If the height of a block of graphics data is less
than the height of the specified pins, the Universal Printer Driver will
add null graphics data to the block.

An example of this is found in many 9-pin dot-matrix drivers. Typically, a
9-pin printer will support a 240 X 72 dpi resolution as its highest native
mode, but also has a vertical-movement command that operates in 1/144 inch.
The Universal Printer Driver may support a 240 X 144 dpi resolutions if the
driver sets sPinsPerPass to 8 (the number of pins fired in one pass), sets
sNPins to 16 (the number of pins fired in two passes), and supports the
1/144-inch vertical command.


Diconix 150 Plus

For the Diconix 150 Plus printer, the sNPins box contains the value 8; this
is the number of jets used by the printer for noninterlaced graphics.


HP LaserJet IIP

For the HP LaserJet IIP printer, the sNPins box contains the value 1.