The laser printer was the first digital proofing system
used for desktop publishing. A document is created on the computer and
then sent to the printer in the form of a page description language
(PDL), most commonly PostScript. A PostScript laser printer includes
a raster image processor (RIP) that converts the information from the
PostScript language into information that the print engine can understand.
Through the use of positive and negative electrical charges, an image
is written onto an internal drum by a laser beam. A developer roller
picks up toner and applies it where the image is. The toner is transferred
from the drum to the paper, forming the image. The toner is then fused
to the paper by passing through a pair of heated rollers. This technology
is called Electrostatic Printing, or Xerography, which is the same technology
used for photocopiers.
Laser printers have image resolutions from 300 dots
per inch (dpi) to 1200 dpi. The printers are used during the design
stages for customer approval on initial concepts and also for proofreading
purposes. The low cost and efficiency of the printer makes it a good
choice for the initial proofing process.