What is « Encapsulated PostScript » (« EPS »)?¶
PostScript has been for many years a lingua franca of powerful printers (though modern high-quality printers now tend to require some constrained form of Adobe Acrobat, instead); since PostScript is also a powerful graphical programming language, it is commonly used as an output medium for drawing (and other) packages.
However, since PostScript is such a powerful language, some rules need to be imposed, so that the output drawing may be included in a document as a figure without « leaking » (and thereby destroying the surrounding document, or failing to draw at all).
Appendix H of the PostScript Language Reference Manual (second and subsequent editions), specifies a set of rules for PostScript to be used as figures in this way. The important features are:
certain « structured comments » are required; important ones are
the identification of the file type, and information about the "bounding box" of the figure (i.e., the minimum rectangle enclosing it);
some commands are forbidden — for example, a
command will cause the image to disappear, in most TeX-output environments; and
« preview information » is permitted, for the benefit of things
such as word processors that don't have the ability to draw PostScript in their own right --- this preview information may be in any one of a number of system-specific formats, and any viewing program may choose to ignore it.
A PostScript figure that conforms to these rules is said to be in « Encapsulated PostScript » (EPS) format. Most (La)TeX packages for including PostScript are structured to use Encapsulated PostScript; which of course leads to much hilarity as exasperated (La)TeX users struggle to cope with the output of drawing software whose authors don’t know the rules.