3.4 Vertical Master Units

The Ydpi control contains the value that specifies the vertical master
unit. This value is the least-common multiple of the selected line spacing
and graphics resolutions.

In the example for the Diconix printer, the vertical master unit is 576
dpi. This value is the least common multiple of the following line spacing
and graphics resolutions:

o   1/288-inch (line spacing)

o   1/96-inch (normal-mode graphics)

As mentioned previously, a minidriver for a dot-matrix printer typically
supports three graphics resolutions: low, medium, and high. However, in the
case of the Diconix printer, there are only two vertical graphics
resolutions, and the higher of the two requires that a dip switch in the
printer be toggled from its default factory setting. (Minidrivers should
ideally support the default switch settings for printers. However, in some
cases this may not be possible.) In addition, the higher resolution
requires interlaced output in the y-direction. Because the higher
resolution would force the user to alter the factory settings and because
this higher resolution results in slower printing (due to the interlaced
graphics), the lower resolution (96 dpi) was chosen.

The Diconix printer supports six line-spacing commands which provide the
following vertical resolutions:

o   1/8-inch (line spacing)

o   7/72-inch (line spacing)

o   7/96-inch (line spacing)

o   1/6-inch (line spacing)

o   n/216-inch (line spacing)

o   n/288-inch (line spacing)

Of these resolutions, the finest (288 dpi) was chosen for the Diconix.

In the case of the HP LaserJet IIP, the resolution used for the
line-spacing command and the vertical resolution for graphics output are
equivalent (300 dpi).


Diconix 150 Plus

The Ydpi box contains the value 576. This value is the least common
multiple of the 1/288 inch Line Spacing command and the 1/96 inch vertical
graphics resolution.


HP LaserJet IIP

The Ydpi box contains the value 300.

NOTEÿA printer's aspect ratio is the ratio formed by the x- and the
y-printer resolution values. The aspect ratio for most printers is 1 (for
example, the HP LaserJet IIP supports a 300 dpi resolution in both the
vertical and horizontal directions). However, in the case of the Diconix
printer, this ratio is 3.333 (320/96) for the highest resolution. Whenever
possible, avoid using aspect ratios greater than 2 in order to produce the
highest quality.