Epson LQ-850 User Manual

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 pictures 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 ones at the beginning of this section.

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.

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
explanation 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.

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