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.
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)
Nearby terms:
compress « Compressed SLIP « compressed video «
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