compression definition
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.
Web Content Compression FAQ.
Usenet newsgroups: comp.compression,
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.
(2004-04-26)
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