compression

1. application (Or "compaction") The coding of data to save

storage space or transmission time. Although data is already

coded in digital form for computer processing, it can often be

coded more efficiently (using fewer bits). For example,

run-length encoding replaces strings of repeated characters

(or other units of data) with a single character and a count.

There are many compression algorithms and utilities.

Compressed data must be decompressed before it can be used.

The standard Unix compression utilty is called compress

though GNU's superior gzip has largely replaced it. Other

compression utilties include pack, zip and PKZIP.

When compressing several similar files, it is usually better

to join the files together into an archive of some kind

(using tar for example) and then compress them, rather than

to join together individually compressed files. This is

because some common compression algorithms build up tables

based on the data from their current input which they have

already compressed. They then use this table to compress

subsequent data more efficiently.

See also TIFF, JPEG, MPEG, Lempel-Ziv Welch,

"lossy", "lossless".

Compression FAQ.

Usenet newsgroups: news:comp.compression,

news:comp.compression.research.

2. multimedia Reducing the dynamic range of an audio signal,

making quiet sounds louder and loud sounds quieter. Thus,

when discussing digital audio, the preferred term for reducing

the total amount of data is "compaction". Some advocate this

term in all contexts.

(2001-01-30)