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Adobe PostScript language

Adobe PostScript language

Adobe PostScript language is a computer language with the primary purpose of generating graphical images (including text) in a device independent manner.

It describes these graphical images by describing how they are drawn with lines and curves and fillings of areas, by placing bitmap images or bitmap image overlays.

PostScript can describe an image in terms of its component elements. It can take full advantage of graphical engine capacities such as resolution and color. Conversely, it can ignore or select alternatives to circumvent graphical engine deficencies such as being black and white or if the interpreter lacks access to a particular font description.

Because PostScript is a full capacity computer language, it is has the same constraints which all programming languages have. In general, it is impossible to write a program to analyze other programs and determine whether those programs will produce any predetermined result, such as halt. In computer science, this is known as the Halting Problem. Therefore, in general, it is impossible to write a program to analyze an Adobe PostScript file with a view to changing that file’s behavior in some predetermined manner.

This also implies, in the general case, that it is impossible to determine how many pages a PostScript print file will print. In fact, it is possible to write a program that prints a random number of pages each time it is executed. As examples of programs with clearly visible different behavior each time they execute, display or print the eyechart program mentioned below or redisplay the same page of the `Just a little PostScript’ seminars and watch the Fermilab logo change color.

Non-Adobe PostScript material, such as setting an HP printer to Adobe PostScript mode should not be included with an Adobe PostScript file. Such operations are the responsibility of the print spooler or the printer manager.

Illustrations should be EPS files and should be generated and tested as such! Many PC applications, both IBM and Apple compatible, violate this rule. These application frequently do not offer an option to generate EPS files. Or, the option to generate EPS files is not selected. Or, the option is selected; but it does not generate proper EPS files. Possibly this occurs because the artist wants to print the image to see how it looks rather then generating the EPS file and then using as it is to be used. As a direct result, many illustrations generated using these programs are not proper EPS files and have extranous printer control material. The result is problems when these files are used in an attempt to illustrate a document.

Slides, tranparencies, etc. are single page documents and should be prepared as such. That is, the EPS file should be encapsulated into a single page file, be properly places, sized and oriented and then printed as a print document.

Adobe PostScript files are intended to be written in 7-bit printable ASCII text using UNIX, Apple MacIntosh or MSDOS line terminators. But, it is possible to include binary information or extremely long lines in these files. Such conditions may cause problems with print spoolers and viewer managers such as Ghostview.