A
page description language (PDL) developed by Adobe Systems. PostScript is primarily a
language for printing
documents on
laser printers, but it can be adapted to produce images on other types of
devices. PostScript is the
standard for
desktop publishing because it is
supported by
imagesetters, the very
high-resolution printers used by
service bureaus to produce
camera-ready copy.
PostScript is an object-oriented language, meaning that it treats images, including fonts, as collections of geometrical objects rather than as bit maps. PostScript fonts are called outline fonts because the outline of each character is defined. They are also called scalable fonts because their size can be changed with PostScript commands. Given a single typeface definition, a PostScript printer can thus produce a multitude of fonts. In contrast, many non-PostScript printers represent fonts with bit maps. To print a bit-mapped typeface with different sizes, these printers require a complete set of bit maps for each size.
The principal advantage of object-oriented (vector) graphics over bit-mapped graphics is that object-oriented images take advantage of high-resolution output devices whereas bit-mapped images do not. A PostScript drawing looks much better when printed on a 600-dpi printer than on a 300-dpi printer. A bit-mapped image looks the same on both printers.
Every PostScript printer contains a built-in interpreter that executes PostScript instructions. If your laser printer does not come with PostScript support, you may be able to purchase a cartridge that contains PostScript.
There are three basic versions of PostScript: Level 1, Level 2 and PostScript 3. Level 2 PostScript, which was released in 1992, has better support for color printing. PostScript 3, release in 1997, supports more fonts, better graphics handling, and includes several features to speed up PostScript printing.
