Filters

• A filter transforms data as it is being read from or written to a file. The language supports filters for ASCII encoding of binary data, compression and decompression, and embedded subfiles. Properly used, these filters reduce the storage and transmission cost of page descriptions, especially ones containing sampled images. Benefits: Reduced storage requirements, greater performance.
• ASCII encoding of binary data: ASCII/85 (represent binary data in ASCII format with only a 125% expansion of data), and ASCII/HEX (current method of representing binary data in ASCII format but with a 200% expansion of data). Benefits: Compact representation of binary data in a portable ASCII representation.
• Compression and decompression filters: CCITT Group 3 & 4 (monochrome images), run-length encoding (monochrome and grayscale images), LZW ( 2:1 compression of text files), DCT (20-200:1 compression of color images using the proposed JPEG standard). Benefits: Improved performance due to reduced transmission times. PostScript files on disk can also be made much smaller, saving disk space.