Dot Patterns; Eight-Pin Graphics; Twenty-Four-Pin Graphics; Pin Labels - Epson LQ-800 User Manual

Dot patterns

The LQ's print head is able to print graphics as well as text because
graphic images are formed on the LQ about the same way that pic-
tures in newspapers and magazines are printed. If you look closely at a
newspaper photograph, you can see that it is made up of many small
dots. The LQ also forms its images with patterns of dots, as many as
360 dot positions per inch horizontally and 180 dots vertically. The
images printed by the LQ can, therefore, be as finely detailed as the
one on the first page of this chapter.

Eight-pin graphics

So that it is compatible with the many programs written for such
printers such as the Epson FX and RX series, the LQ has an 8-pin
graphics mode with six densities. Although this mode uses only one
third of the LQ's pins, it produces good quality graphics and allows
you to use the many programs written for 8-pin graphics.

Twenty-four-pin graphics

The graphics mode that takes full advantage of the LQ's print head
is 24-pin graphics. It has five densities, but for simplicity this explana-
tion will begin with only one of them, triple-density.
Triple-density prints up to 180 dots per inch horizontally. As the
print head moves across the paper, every 1/180th of an inch it must
receive instructions about which of its 24 pins to fire. At each position
it can fire any number of pins from none to 24. This means that the
printer must receive 24 bits of information for each column it prints.
Since the LQ uses 8-bit bytes of information in its communication
with a computer, it needs three bytes of information for each position.

Pin labels

To tell the printer which pins to fire in each column, you first divide
each of the vertical columns into three sections of eight pins each and
consider each section separately. Since there are 256 possible combina-
tions of the eight pins in each section, you need a numbering system
that allows you to use a single number to specify which of the 256
possible patterns you want. This numbering system is shown in Figure
6-1.
6-3