Page 194 - Graphic Design and Print Production Fundamentals

182 Chapter 6. Imaging
a device independent language. The interpreter processes the PostScript instructions to create a raster
image the device can render. The interpreter is often referred to as a RIP or raster image processor
for this reason. It is possible to write valid PostScript code from scratch, but it is impractical as page
composition applications can either generate the PostScript code directly or can utilize a print driver,
which can convert the page to the PostScript language.

Since PostScript is a general-purpose programming language, it includes many elements that you
wouldn’t associate specifically with printing such as data types (numbers, arrays, and strings) and
control primitives (conditionals, loops, and procedures). It also has an interesting feature called
dictionary, which stores information in a table consisting of a collection of key and value pairs.
The values can be entered into the dictionary while the keys are used to reference the information
needed. These features made possible documents that acted like an application which could generate
pages dynamically from data directly on the printer itself. These printer-based applications were stored
temporarily in memory or permanently in the printer’s hard drive, and triggered by a command in the
print stream. These capabilities made variable data printing possible using PostScript and are still being
used today for that purpose.

The first printer to use PostScript was the Apple LaserWriter in 1985. The same day that Apple
announced the LaserWriter, Aldus Corporation announced PageMaker, a page layout application
developed to take advantage of the Apple Macintosh computer’s GUI (graphical user interface) and the
PostScript PDL. This series of events is considered by many as the genesis of the desktop publishing
revolution. In fact, the term desktop publishing is attributed to the founder of Aldus Corporation.

PDF

Portable document format (PDF) is one of the most popular file formats for displaying and printing
documents. When this format was released by Adobe in 1993, it shared many of the same concepts and
components of PostScript. But where PostScript was designed primarily to provide device independent
consistency in print output, PDF was focused on maintaining the visual appearance of a document
onscreen, independent of the operating system displaying it. Over the years, PDF has expanded to more
specific-use specifications for engineering, archiving, health care, universal access, and printing.

PDF/X is a branch of PDF and an ISO standard that deals specifically with print. It was developed by
the Committee for Graphic Arts Technologies Standards (CGATS). Table 6.5 shows the evolution of the
standard.