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.
