Encapsulated PostScript

Encapsulated PostScript, or EPS is a file format combining two files, one is the "real" PostScript file that will be sent to the printer, and the other is a small bitmap for displaying on the screen. The idea is to allow a simple preview of the final output in any application that can draw a bitmap (which is to say, just about everything). Sadly, EPS is one of the worst "standards" to ever be created.

When it was first implemented the only machines widely using PostScript were Apple Macintoshes, and EPS was invented to allow libraries of PS clip art to be easily manipulated on these machines because they were not powerful enough to render the PS directly. To solve the problem Adobe included a Mac-standard PICT file as the bitmap, stored in the Mac's non-standard resource fork. On the Mac this had a number of advatages, practically every Mac program could draw a PICT (it was built into the operating system) while the use of the resource fork made the two files "stick together" automatically as they were moved around.

But neither of these pieces of technology exist on any other operating system. When faced with the same problems on new Microsoft Windows based versions of their programs, Adobe chose to instead include a TIFF file encoded into the header section of the PostScript. Sometimes, just for ease of use apparently, they used the WMF (Windows MetaFile) instead.

The result was three separate types of EPS, all of them incompatible. Realizing the problem, Adobe attempted to solve it. Instead of simply picking one of the existing formats (the TIFF version could easily be used on all platforms) they invented yet another version inluding an ASCII-encoded bitmap known as a EPSI'. This format allowed for black-and-white previews only, and, thankfully, has been largely ignored.

Given this confusion, it's not surprising that the EPS format is not widely used. Today most programs used clip-art in either TIFF or some native format (PICT or WMF), and then convert everything to PS when needed for printing.

Note: the author is unaware of any program that supports EPSI.

External links:

The EPS file format

The Graphics File Formats Page

- has the actual EPS standard as a downloadable file