Adobe Systems and the Postscript Language

John Markoff and Phillip Robinson
BYTE Magazine

February 1985

Adobe Systems Inc., of Palo Alto, California, was started by a number of researchers who left Xerox's PARC (Palo Alto Research Center). In particular, John Warnock, president of Adobe, was a principal scientist at PARC for raster-graphic display techniques. Charles Geschke, the executive vice-president, was a manager of the Imaging Sciences Laboratory at PARC.

Adobe is trying to make PostScript—their text and graphics language—a business standard. Unlike most print-file description languages, PostScript is not a static, data-structured written description: it is a programming language. When the Macintosh communicates with the LaserWriter, it actually sends a program across AppleTalk.

According to Geschke, "When the program arrives at the 68000 in the printer and begins executing, it has one very interesting side effect, namely, it drives the video on that laser and produces output. But it is really a program description that is generated on the Macintosh and is executed on the printer." By using PostScript, the amount of information sent across AppleTalk can be trimmed, in some cases, to just 10 percent more than the raw ASCII (American Standard Code for Information Interchange) data.

PostScript is completely encoded in the printable character subset of 7-bit ASCII code and so is completely invisible across any kind of communications line, not just AppleTalk. PostScript can handle any material: text, line-art, photographics, and even color (for printers that can use it). While photographic images are sent as bit maps, graphics are sent as commands and the fonts are sent as mathematical outlines (based on Bezier cubics) that can be stroked, filled, scaled, oriented, or used as clipping boundaries. And it is flexible, as Geschke pointed out. "If you're really into graphic art you can adjust the shape of the half-tone dot, the shape of the tonal production curve, the orientation of the screen, and its frequency."

Adobe isn't only working with Apple. You'll be seeing PostScript in other systems from other companies.