| slovo | definícia |
compression
(mass) | compression
- zhustenie, kompresia |
compression
(encz) | compression,komprese Vladimír Pilný |
compression
(encz) | compression,komprimace Zdeněk Brož |
compression
(encz) | compression,propružení Pavel Cvrček |
compression
(encz) | compression,stisknutí Zdeněk Brož |
compression
(encz) | compression,stlačení Zdeněk Brož |
compression
(encz) | compression,stlačování Zdeněk Brož |
compression
(encz) | compression,zhuštění Pavel Cvrček |
Compression
(gcide) | Compression \Com*pres"sion\, n. [L. compressio: cf. F.
compression.]
1. The act of compressing, or state of being compressed.
"Compression of thought." --Johnson.
[1913 Webster]
2. (Computers) reduction of the space required for storage
(of binary data) by an algorithm which converts the data
to a smaller number of bits while preserving the
information content. The act of compressing [3].
Note: Compression may be lossless compression, in which all
of the information in the original data is preserved,
and the original data may be recovered in form
identical to its original form; or lossy compression,
in which some of the information in the original data
is lost, and decompression results in a data form
slightly different from the original. {Lossy
compression} is used, for example, to compress audio or
video recordings, and sometimes images, where the
slight differences in the original data and the data
recovered after lossy compression may be
imperceptable to the human eye or ear. The JPEG
format is produced by a lossy compression algorithm.
[PJC] |
compression
(wn) | compression
n 1: an increase in the density of something [syn: compaction,
compression, concretion, densification]
2: the process or result of becoming smaller or pressed
together; "the contraction of a gas on cooling" [syn:
compression, condensation, contraction]
3: encoding information while reducing the bandwidth or bits
required [ant: decompression]
4: applying pressure [syn: compression, compressing] [ant:
decompressing, decompression] |
compression
(foldoc) | compression
compaction
uncompression
1. (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
(ftp://rtfm.mit.edu/pub/usenet/news.answers/compression-faq/)}.
{Web Content Compression FAQ
(http://perl.apache.org/docs/tutorials/client/compression/compression.html)}.
Usenet newsgroups: news:comp.compression,
news:comp.compression.research.
2. 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)
|
| | podobné slovo | definícia |
compression bandage
(encz) | compression bandage, n: |
compression fracture
(encz) | compression fracture, n: |
compressional
(encz) | compressional,stlačující adj: Zdeněk Brož |
decompression
(encz) | decompression,dekomprese n: Zdeněk Broždecompression,dekomprimování n: Zdeněk Brož |
decompression sickness
(encz) | Decompression Sickness,Kesonová nemoc [med.] Michal AmbrožDecompression Sickness,Nemoc z dekomprese [med.] Michal Ambrož |
image compression
(encz) | image compression, n: |
nerve compression
(encz) | nerve compression, n: |
decompression sickness
(czen) | Decompression Sickness,DCS[zkr.] Michal Ambrož |
Compression
(gcide) | Compression \Com*pres"sion\, n. [L. compressio: cf. F.
compression.]
1. The act of compressing, or state of being compressed.
"Compression of thought." --Johnson.
[1913 Webster]
2. (Computers) reduction of the space required for storage
(of binary data) by an algorithm which converts the data
to a smaller number of bits while preserving the
information content. The act of compressing [3].
Note: Compression may be lossless compression, in which all
of the information in the original data is preserved,
and the original data may be recovered in form
identical to its original form; or lossy compression,
in which some of the information in the original data
is lost, and decompression results in a data form
slightly different from the original. {Lossy
compression} is used, for example, to compress audio or
video recordings, and sometimes images, where the
slight differences in the original data and the data
recovered after lossy compression may be
imperceptable to the human eye or ear. The JPEG
format is produced by a lossy compression algorithm.
[PJC] |
Compression member
(gcide) | Member \Mem"ber\, n. [OE. membre, F. membre, fr. L. membrum; cf.
Goth. mimz flesh, Skr. mamsa.]
[1913 Webster]
1. (Anat.) A part of an animal capable of performing a
distinct office; an organ; a limb.
[1913 Webster]
We have many members in one body, and all members
have not the same office. --Rom. xii. 4.
[1913 Webster]
2. Hence: A part of a whole; an independent constituent of a
body; as:
(a) A part of a discourse or of a period or sentence; a
clause; a part of a verse.
(b) (Math.) Either of the two parts of an algebraic
equation, connected by the sign of equality.
(c) (Engin.) Any essential part, as a post, tie rod,
strut, etc., of a framed structure, as a bridge truss.
(d) (Arch.) Any part of a building, whether
constructional, as a pier, column, lintel, or the
like, or decorative, as a molding, or group of
moldings.
(e) One of the persons composing a society, community, or
the like; an individual forming part of an
association; as, a member of the society of Friends.
(f) (Math.) one of the elements which, taken together,
comprise a set.
(g) (Math.) one of the individual objects which comprise a
group or class.
[1913 Webster +PJC]
Compression member, Tension member (Engin.), a member, as
a rod, brace, etc., which is subjected to compression or
tension, respectively.
[1913 Webster] |
Compression projectile
(gcide) | Compression projectile \Com*pres"sion pro*jec"tile\
A projectile constructed so as to take the grooves of a rifle
by means of a soft copper band firmly attached near its base
or, formerly, by means of an envelope of soft metal. In small
arms the modern projectile, having a soft core and harder
jacket, is subjected to compression throughout the entire
cylindrical part.
[Webster 1913 Suppl.] |
decompression
(gcide) | decompression \decompression\ n.
1. the process of experiencing decompression; the act or
process of relieving or reducing pressure.
Syn: decompressing.
[WordNet 1.5 +PJC]
2. the reduction of atmospheric pressure experienced by
divers rising from deep water to the surface, thus
reducing the concentration of dissolved atmospheric gases
in the blood; -- especially applied to a gradual reduction
of such pressure.
[PJC]
3. the process, analogous to sense 2, undergone by divers in
a decompression chamber, in which an artificially high
atmospheric pressure is gradually lowered to normal
pressure.
[PJC]
4. a return to a normal, more relaxed state after a period of
intense stress, psychological pressure, or urgent
activity; -- of people.
[PJC]
5. (Computers) the process of converting digitally encoded
data from a more compact (compressed) form to its
original, larger size.
Note: The process of compression and decompression may
completely recover all of the original data (called
lossless compression), or may lose some of the original
data in order to achieve higher degress of compression
(lossy compression). The latter is used especially with
images or video data, which may be of very large size
relative to text, and for which small changes may be
imperceptible to the human eye. The JPEG data
compression format is a lossy format.
[PJC] |
decompression sickness
(gcide) | Caisson disease \Cais"son dis*ease"\ (Med.)
A disease frequently induced by remaining for some time in an
atmosphere of high pressure, as in caissons, diving bells,
etc. It is characterized by neuralgic pains and paralytic
symptoms. It is caused by the release of bubbles of gas,
usually nitrogen, from bodily fluids into the blood and
tissues, when a person, having been in an environment with
high air pressure, moves to a lower pressure environment too
rapidly for the excess dissolved gases to be released through
normal breathing. It may be fatal, but can be reversed or
alleviated by returning the affected person to a high air
pressure, and then gradually decreasing the pressure to allow
the gases to be released from the body fluids. It is a danger
well known to divers. It is also called the bends and
decompression sickness. It can be prevented in divers by a
slow return to normal pressure, or by using a breathing
mixture of oxygen combined with a gas having low solubility
in water, such as helium.
[Webster 1913 Suppl. +PJC] |
Globe of compression
(gcide) | Globe \Globe\ (gl[=o]b), n. [L. globus, perh. akin to L. glomus
a ball of yarn, and E. clump, golf: cf. F. globe.]
1. A round or spherical body, solid or hollow; a body whose
surface is in every part equidistant from the center; a
ball; a sphere.
[1913 Webster]
2. Anything which is nearly spherical or globular in shape;
as, the globe of the eye; the globe of a lamp.
[1913 Webster]
3. The earth; the terraqueous ball; -- usually preceded by
the definite article. --Locke.
[1913 Webster]
4. A round model of the world; a spherical representation of
the earth or heavens; as, a terrestrial or celestial
globe; -- called also artificial globe.
[1913 Webster]
5. A body of troops, or of men or animals, drawn up in a
circle; -- a military formation used by the Romans,
answering to the modern infantry square.
[1913 Webster]
Him round
A globe of fiery seraphim inclosed. --Milton.
[1913 Webster]
Globe amaranth (Bot.), a plant of the genus Gomphrena
(G. globosa), bearing round heads of variously colored
flowers, which long retain color when gathered.
Globe animalcule, a small, globular, locomotive organism
(Volvox globator), once throught to be an animal,
afterward supposed to be a colony of microscopic alg[ae].
Globe of compression (Mil.), a kind of mine producing a
wide crater; -- called also overcharged mine.
Globe daisy (Bot.), a plant or flower of the genus
Globularing, common in Europe. The flowers are minute
and form globular heads.
Globe sight, a form of front sight placed on target rifles.
Globe slater (Zool.), an isopod crustacean of the genus
Spheroma.
Globe thistle (Bot.), a thistlelike plant with the flowers
in large globular heads (Cynara Scolymus); also, certain
species of the related genus Echinops.
Globe valve.
(a) A ball valve.
(b) A valve inclosed in a globular chamber. --Knight.
[1913 Webster]
Syn: Globe, Sphere, Orb, Ball.
Usage: Globe denotes a round, and usually a solid body;
sphere is the term applied in astronomy to such a
body, or to the concentric spheres or orbs of the old
astronomers; orb is used, especially in poetry, for
globe or sphere, and also for the pathway of a
heavenly body; ball is applied to the heavenly bodies
concieved of as impelled through space.
[1913 Webster] |
lossless compression
(gcide) | Compression \Com*pres"sion\, n. [L. compressio: cf. F.
compression.]
1. The act of compressing, or state of being compressed.
"Compression of thought." --Johnson.
[1913 Webster]
2. (Computers) reduction of the space required for storage
(of binary data) by an algorithm which converts the data
to a smaller number of bits while preserving the
information content. The act of compressing [3].
Note: Compression may be lossless compression, in which all
of the information in the original data is preserved,
and the original data may be recovered in form
identical to its original form; or lossy compression,
in which some of the information in the original data
is lost, and decompression results in a data form
slightly different from the original. {Lossy
compression} is used, for example, to compress audio or
video recordings, and sometimes images, where the
slight differences in the original data and the data
recovered after lossy compression may be
imperceptable to the human eye or ear. The JPEG
format is produced by a lossy compression algorithm.
[PJC] |
Lossy compression
(gcide) | Compression \Com*pres"sion\, n. [L. compressio: cf. F.
compression.]
1. The act of compressing, or state of being compressed.
"Compression of thought." --Johnson.
[1913 Webster]
2. (Computers) reduction of the space required for storage
(of binary data) by an algorithm which converts the data
to a smaller number of bits while preserving the
information content. The act of compressing [3].
Note: Compression may be lossless compression, in which all
of the information in the original data is preserved,
and the original data may be recovered in form
identical to its original form; or lossy compression,
in which some of the information in the original data
is lost, and decompression results in a data form
slightly different from the original. {Lossy
compression} is used, for example, to compress audio or
video recordings, and sometimes images, where the
slight differences in the original data and the data
recovered after lossy compression may be
imperceptable to the human eye or ear. The JPEG
format is produced by a lossy compression algorithm.
[PJC]lossy compression \los"sy com*pres"sion\, n. (Computers)
The compression of binary data into a form which, when it is
re-expanded, has most, but not all, of the original
information. It is used primarily for compression of images
and sounds, and is designed to provide a high degree of
compression at the cost of a slight loss of data. It is
expemplified by the JPEG compression standard. Images
compressed by a lossy compression algorithm are re-expanded
into an image close, but not identical to the original image;
the difference between the original and the reconstructed
image may be imperceptible to normal viewing by the eye.
[PJC] |
lossy compression
(gcide) | Compression \Com*pres"sion\, n. [L. compressio: cf. F.
compression.]
1. The act of compressing, or state of being compressed.
"Compression of thought." --Johnson.
[1913 Webster]
2. (Computers) reduction of the space required for storage
(of binary data) by an algorithm which converts the data
to a smaller number of bits while preserving the
information content. The act of compressing [3].
Note: Compression may be lossless compression, in which all
of the information in the original data is preserved,
and the original data may be recovered in form
identical to its original form; or lossy compression,
in which some of the information in the original data
is lost, and decompression results in a data form
slightly different from the original. {Lossy
compression} is used, for example, to compress audio or
video recordings, and sometimes images, where the
slight differences in the original data and the data
recovered after lossy compression may be
imperceptable to the human eye or ear. The JPEG
format is produced by a lossy compression algorithm.
[PJC]lossy compression \los"sy com*pres"sion\, n. (Computers)
The compression of binary data into a form which, when it is
re-expanded, has most, but not all, of the original
information. It is used primarily for compression of images
and sounds, and is designed to provide a high degree of
compression at the cost of a slight loss of data. It is
expemplified by the JPEG compression standard. Images
compressed by a lossy compression algorithm are re-expanded
into an image close, but not identical to the original image;
the difference between the original and the reconstructed
image may be imperceptible to normal viewing by the eye.
[PJC] |
compression bandage
(wn) | compression bandage
n 1: bandage that stops the flow of blood from an artery by
applying pressure [syn: compression bandage,
tourniquet] |
compression fracture
(wn) | compression fracture
n 1: fracture in which the bone collapses (especially in short
bones such as vertebrae) |
decompression
(wn) | decompression
n 1: restoring compressed information to its normal form for use
or display [ant: compression]
2: relieving pressure (especially bringing a compressed person
gradually back to atmospheric pressure) [syn:
decompression, decompressing] [ant: compressing,
compression] |
decompression sickness
(wn) | decompression sickness
n 1: pain resulting from rapid change in pressure [syn:
decompression sickness, aeroembolism, air embolism,
gas embolism, caisson disease, bends] |
image compression
(wn) | image compression
n 1: the compression of graphics for storage or transmission |
nerve compression
(wn) | nerve compression
n 1: harmful pressure on a nerve (especially in nerves that pass
over rigid prominences); causes nerve damage and muscle
weakness |
data compression
(foldoc) | data compression
compression. Probably to distinguish it from
(electronic) signal compression.
(1995-04-02)
|
deflate compression
(foldoc) | deflate
deflate compression
deflate/inflate compression
inflate
A compression standard derived
from LZ77; it is reportedly used in zip, gzip, PKZIP,
and png, among others.
Unlike LZW, deflate compression does not use patented
compression algorithms.
Used as a verb to mean to compress (not decompress!) a file
which has been compressed using deflate compression. The
opposite, inflate, means to decompress data which has been
deflated.
Deflate is described in RFC 1951.
(1997-06-21)
|
deflate/inflate compression
(foldoc) | deflate
deflate compression
deflate/inflate compression
inflate
A compression standard derived
from LZ77; it is reportedly used in zip, gzip, PKZIP,
and png, among others.
Unlike LZW, deflate compression does not use patented
compression algorithms.
Used as a verb to mean to compress (not decompress!) a file
which has been compressed using deflate compression. The
opposite, inflate, means to decompress data which has been
deflated.
Deflate is described in RFC 1951.
(1997-06-21)
|
file compression
(foldoc) | file compression
The compression of data in a file, usually to
reduce storage requirements.
(1995-04-06)
|
fractal compression
(foldoc) | fractal compression
A technique for encoding images using
fractals.
{Yuval Fisher's fractal image compression site
(http://inls.ucsd.edu/y/Fractals/)}.
[Summary?]
(1998-03-27)
|
lempel-ziv compression
(foldoc) | Lempel-Ziv compression
LZ compression
Substitutional compression schemes proposed by Jakob Ziv and
Abraham Lempel in 1977 and 1978. There are two main schemes,
LZ77 and LZ78. Lempel-Ziv Welch compression is a
variant of LZ78.
|
lempel-ziv welch compression
(foldoc) | Lempel-Ziv Welch compression
LZW compression
(LZW) The algorithm used by the Unix compress command to
reduce the size of files, e.g. for archival or transmission.
LZW was designed by Terry Welch in 1984 for implementation in
hardware for high-performance disk controllers. It is a
variant of LZ78, one of the two Lempel-Ziv compression
schemes.
The LZW algorithm relies on reoccurrence of byte sequences
(strings) in its input. It maintains a table mapping input
strings to their associated output codes. The table initially
contains mappings for all possible strings of length one.
Input is taken one byte at a time to find the longest initial
string present in the table. The code for that string is
output and then the string is extended with one more input
byte, b. A new entry is added to the table mapping the
extended string to the next unused code (obtained by
incrementing a counter). The process repeats, starting from
byte b. The number of bits in an output code, and hence the
maximum number of entries in the table is usually fixed and
once this limit is reached, no more entries are added.
LZW compression and decompression are licensed under Unisys
Corporation's 1984 U.S. Patent 4,558,302 and equivalent
foreign patents. This kind of patent isn't legal in most
coutries of the world (including the UK) except the USA.
Patents in the UK can't describe algorithms or mathematical
methods.
[A Technique for High Performance Data Compression, Terry A.
Welch, IEEE Computer, 17(6), June 1984, pp. 8-19]
[J. Ziv and A. Lempel, "A Universal Algorithm for Sequential
Data Compression," IEEE Transactions on Information Theory,
Vol. IT-23, No. 3, May 1977, pp. 337-343].
|
lossless audio compression
(foldoc) | lossless audio compression
Any kind of audio compression in which
the original signal and the decoded signal are bitwise
identical. Lossless audio compression algorithms are usually
based on a data compression algorithm like PKzip or gzip
but specialized for PCM audio data. The signal is divided
into predictable tonal components and unpredictable noisy
components. Tonal components are stored as coefficients of a
predictor, the remaining signal is coded by Rice coding,
Huffman coding or arithmetic coding.
(2001-12-24)
|
lossless predictive audio compression
(foldoc) | Lossless Predictive Audio Compression
(LPAC) A lossless audio compression
algorithm with compression ratios from 1.5 to 4, depending
on the input. Software is available for Microsoft Windows,
Linux and Solaris. LPAC files (*.pac) can be played with
a Winamp plug-in.
(http://www-ft.ee.tu-berlin.de/~liebchen/lpac.html).
(2001-12-17)
|
lossy audio compression
(foldoc) | lossy audio compression
Any audio compression algorithm which
does not retain every bit of data but only reproduces a signal
that sounds more or less like the original. Examples are
MP1, MP2, MP3, AAC.
(2001-12-24)
|
lz compression
(foldoc) | Lempel-Ziv compression
LZ compression
Substitutional compression schemes proposed by Jakob Ziv and
Abraham Lempel in 1977 and 1978. There are two main schemes,
LZ77 and LZ78. Lempel-Ziv Welch compression is a
variant of LZ78.
|
lz77 compression
(foldoc) | LZ77 compression
The first algorithm to use the Lempel-Ziv {substitutional
compression} schemes, proposed in 1977. LZ77 compression
keeps track of the last n bytes of data seen, and when a
phrase is encountered that has already been seen, it outputs a
pair of values corresponding to the position of the phrase in
the previously-seen buffer of data, and the length of the
phrase. In effect the compressor moves a fixed-size "window"
over the data (generally referred to as a "sliding window"),
with the position part of the (position, length) pair
referring to the position of the phrase within the window.
The most commonly used algorithms are derived from the
LZSS scheme described by James Storer and Thomas Szymanski
in 1982. In this the compressor maintains a window of size N
bytes and a "lookahead buffer", the contents of which it tries
to find a match for in the window:
while (lookAheadBuffer not empty)
{
get a pointer (position, match) to the longest match in
the window for the lookahead buffer;
if (length > MINIMUM_MATCH_LENGTH)
{
output a (position, length) pair;
shift the window length characters along;
}
else
{
output the first character in the lookahead buffer;
shift the window 1 character along;
}
}
Decompression is simple and fast: whenever a (POSITION,
LENGTH) pair is encountered, go to that POSITION in the window
and copy LENGTH bytes to the output.
Sliding-window-based schemes can be simplified by numbering
the input text characters mod N, in effect creating a circular
buffer. The sliding window approach automatically creates the
LRU effect which must be done explicitly in LZ78 schemes.
Variants of this method apply additional compression to the
output of the LZSS compressor, which include a simple
variable-length code (LZB), dynamic Huffman coding
(LZH), and Shannon-Fano coding (ZIP 1.x), all of which
result in a certain degree of improvement over the basic
scheme, especially when the data are rather random and the
LZSS compressor has little effect. An algorithm was developed
which combines the ideas behind LZ77 and LZ78 to produce a
hybrid called LZFG. LZFG uses the standard sliding window,
but stores the data in a modified trie data structure and
produces as output the position of the text in the trie.
Since LZFG only inserts complete *phrases* into the
dictionary, it should run faster than other LZ77-based
compressors.
All popular archivers (arj, lha, zip, zoo) are
variations on LZ77.
[comp.compression FAQ].
(1995-04-07)
|
lz78 compression
(foldoc) | LZ78 compression
A substitutional compression scheme which works by entering
phrases into a dictionary and then, when a reoccurrence of
that particular phrase is found, outputting the dictionary
index instead of the phrase. Several algorithms are based
on this principle, differing mainly in the manner in which
they manage the dictionary.
The most well-known Lempel-Ziv scheme is Terry Welch's
Lempel-Ziv Welch variant of LZ78.
[comp.compression FAQ].
|
lzh compression
(foldoc) | LZH compression
(After Lempel-Ziv and Haruyasu, the inventors) A
compression algorithm derived from the LZSS scheme with
a sliding window and additional compression applied to the
output of the LZSS compressor by dynamic Huffman coding.
(1995-04-07)
|
lzw compression
(foldoc) | Lempel-Ziv Welch compression
LZW compression
(LZW) The algorithm used by the Unix compress command to
reduce the size of files, e.g. for archival or transmission.
LZW was designed by Terry Welch in 1984 for implementation in
hardware for high-performance disk controllers. It is a
variant of LZ78, one of the two Lempel-Ziv compression
schemes.
The LZW algorithm relies on reoccurrence of byte sequences
(strings) in its input. It maintains a table mapping input
strings to their associated output codes. The table initially
contains mappings for all possible strings of length one.
Input is taken one byte at a time to find the longest initial
string present in the table. The code for that string is
output and then the string is extended with one more input
byte, b. A new entry is added to the table mapping the
extended string to the next unused code (obtained by
incrementing a counter). The process repeats, starting from
byte b. The number of bits in an output code, and hence the
maximum number of entries in the table is usually fixed and
once this limit is reached, no more entries are added.
LZW compression and decompression are licensed under Unisys
Corporation's 1984 U.S. Patent 4,558,302 and equivalent
foreign patents. This kind of patent isn't legal in most
coutries of the world (including the UK) except the USA.
Patents in the UK can't describe algorithms or mathematical
methods.
[A Technique for High Performance Data Compression, Terry A.
Welch, IEEE Computer, 17(6), June 1984, pp. 8-19]
[J. Ziv and A. Lempel, "A Universal Algorithm for Sequential
Data Compression," IEEE Transactions on Information Theory,
Vol. IT-23, No. 3, May 1977, pp. 337-343].
|
non-uniform quantising logarithmic compression
(foldoc) | non-uniform quantising logarithmic compression
The kind of compression often applied to a sound waveform.
Logarithmic compression is a good match for the human ear's
sensitivity but cannot handle zero amplitude (for which the
logarithm is negative infinity). There are two standard
compression functions which give a smooth transition between
the logarithmic function and a linear segment passing through
the origin: mu-law (North America) and A-law (ITU-T).
(1995-02-21)
|
stac compression
(foldoc) | stac compression
A data compression technique from STAC,
used with modems. Stac compression is capable of
compressing data by a factor of about four.
[Details?]
(1998-06-08)
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uncompression
(foldoc) | compression
compaction
uncompression
1. (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
(ftp://rtfm.mit.edu/pub/usenet/news.answers/compression-faq/)}.
{Web Content Compression FAQ
(http://perl.apache.org/docs/tutorials/client/compression/compression.html)}.
Usenet newsgroups: news:comp.compression,
news:comp.compression.research.
2. 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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video compression
(foldoc) | video compression
compressed video
Compression of sequences of images. Video compression
algorithms use the fact that there are usually only small
changes from one "frame" to the next so they only need to
encode the starting frame and a sequence of differences
between frames. This is known as "inter-frame coding" or "3D
coding".
MPEG is a committee producing standards in this area and
also the name of their standard algorithm. H.261 is
another standard.
See also Integrated Information Technology, 3DO,
full-motion video, Online Media.
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