|Department of Engineering|
|University of Cambridge > Engineering Department > computing help|
Postscript was invented decades ago by Adobe. It's a powerful format - indeed it's really a language: it has loops, etc, and commands to do masking, distortion, etc. It has vector and bitmap commands. Because of its power a complicated program (a "postscript interpreter") is needed to understand the files, and lots of memory may be required. This is why postscript printers are relatively expensive.
Postscript has evolved over the years: first to "Level II" and now to "Adobe® PostScript® 3". Encapsulated Postscript (EPS) is a slight variation on Postscript. EPS files are designed to be embedded in another document rather than printed out directly.
Programs exist to display PostScript files onscreen, but they're rather complex. Though you can embed EPS in Word documents, Word can't show you what's in the EPS file unless it has an included preview image - a simplified image used for screen display only. Preview images can be in many formats too - TIFF and WMF (Windows Metaformat) being common.
Adobe developed PDF (Portable Document Format) to overcome some of the practical restrictions of Postscript. Though it's based on Postscript, PDF files are easier for programs to understand. The free viewer (called Acrobat Reader) is available for just about all computers. PDF (unlike Postscript) was designed to make the most of files viewed online.
As well as being able to hold complete documents, PDF files can contain images that can be loaded into bigger documents.
Because of the availabilty of the Viewer and the quality plus reliability of the printed output, PDF has taken over from Postscript as the format for document transfer. PDF files are common on the WWW.
Photographs can take up a great deal of memory. The "Joint Photographic Experts Group" developed a format (officially JFIF, but usually it's called JPEG) specially designed to deal with this issue. JPEG is a "lossy" format - you can choose to sacrifice some accuracy in order to reduce file sizes. Because of the design of the format the loss of accuracy often goes unnoticed by the human eye even when space saving is considerable. See the online jpeg examples.
JPEG is well supported (even Postscript 2 interpreters understand it), and is common on the WWW but beware of using it for graphs - the fuzziness is quickly noticed.
The GIF format was common on the WWW in the early days. It's good with images that have large areas of solid colour - cartoons, icons, etc. Since then the originators have decided to invoke their patent rights, making the format increasingly unpopular.
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