Threshing Eps Files

In this article we describe the CEP package for compressing EPS files. It belongs to the public domain and was released at the GUST meeting in Bachotek, 1997. The amount of disk space occupied by bitmap graphics is a well-recognized problem. For example, a 300 dpi picture (A4) contains ca 8700000 pixels; assuming that each CMYK pixel occupies four bytes, one obtains ca 35MB of disk space needed to store the picture. Now, imagine a TEX-er, who is not allowed to use binary graphic data (because of the otherwise magnificent DVIPS); thus our poor TEX-er usually converts the binary data to hexadecimal EPS files, thus doubling the required space, and next, after compiling a document with TEX+DVIPS, the whole graphic data is put into the resulting PostScript file, so the required space is doubled again — altogether 140MB per one A4 page. The nightmare begins. . . This problem is not a new one; it was recognised by Adobe a relatively long time ago. In the PostScript Level 2 specification, they included objects called filters which enable data compression. In particular, instead of hexadecimal data, one can use ASCII85 encoding (there are explanations of abbreviations at the end of the article), run length compression, LZW compression, DCT (used in JPEG files), and many others. Why not make use of these tools? The question is not as silly as it may look at the first glance, as there exist relatively few applications capable of generating well-compressed PostScript graphics. We decided to patch somehow this gap. We developed a little package enabling the compression of “normal” (non-compressed) graphic data. The nature of the problem is more complex, however, than one might expect. In particular, a universal, always efficient compression technique does not exist. Choice of an optimal algorithm depends upon the kind of data, form of the file and the expected application. Hence, the package has several “buttons” which enable controlling various aspects of compression. Actually, the name CEP is derived from “compressed EPS”. Coincidentally, the name in Polish means “the flail”. We hope that others find threshing EPS files useful, in order to get rid of chaff, i.e., redundant data.