Before the advent of laser and inkjet technology, impact
printers could only print standard, justified text with no
variation in letter size or font style. Today, printers are able to
process complex documents with embedded images, charts, and tables
in multiple frames and in several languages, all on one page. Such
complexity must adhere to some format conventions. This is what
spurred the development of the page
description language (or PDL) — a specialized document
formatting language specially made for computer communication with
printers.
Over the years, printer manufacturers have developed their own
proprietary languages to describe document formats. However, such
proprietary languages applied only to the printers that the
manufacturers created themselves. If, for example, you were to send
a print-ready file using a proprietary PDL to a professional press,
there was no guarantee that your file would be compatible with the
printer's machines. The issue of portability came into
question.
Xerox® developed the
Interpress™ protocol for their
line of printers, but full adoption of the language by the rest of
the printing industry was never realized. Two original developers
of Interpress left Xerox and formed Adobe®, a software company catering mostly
to electronic graphics and document professionals. At Adobe, they
developed a widely-adopted PDL called PostScript™,
which uses a markup language to describe text formatting and image
information that could be processed by printers. At the same time,
the Hewlett-Packard® Company
developed the Printer
Control Language™ (or PCL) for use in their
ubiquitous laser and inkjet printer lines. PostScript and PCL are
now widely adopted PDLs and are supported by most printer
manufacturers.
PDLs work on the same principle as computer programming
languages. When a document is ready for printing, the PC or
workstation takes the images, typographical information, and
document layout, and uses them as objects that form instructions
for the printer to process. The printer then translates those
objects into rasters, a series of scanned
lines that form an image of the document (called Raster Image Processing or RIP), and prints the
output onto the page as one image, complete with text and any
graphics included. This process makes printed documents more
consistent, resulting in little or no variation when printing the
same document on different model printers. PDLs are designed to be
portable to any format, and scalable to fit different paper
sizes.
Choosing the right printer is a matter of determining what
standards the various departments in your organization have adopted
for their needs. Most departments use word processing and other
productivity software that use the PostScript language for
outputting to printers. However, if your graphics department
requires PCL or some proprietary form of printing, you must take
that into consideration as well.
