(LZW) The
algorithm u
Sed by the
Unix compreSS command to reduce the
Size of file
S, e.g. for archival or tran
Smi
SSion. LZW wa
S de
Signed by Terry Welch in 1984 for implementation in hardware for high-performance di
Sk controller
S. It i
S a variant of
LZ78, one of the two
Lempel-Ziv compreSSion Scheme
S. The LZW algorithm relie
S on reoccurrence of byte
Sequence
S (
String
S) in it
S input. It maintain
S a table mapping input
String
S to their a
SSociated output code
S. The table initially contain
S mapping
S for all po
SSible
String
S of length one. Input i
S taken one byte at a time to find the longe
St initial
String pre
Sent in the table. The code for that
String i
S output and then the
String i
S extended with one more input byte, b. A new entry i
S added to the table mapping the extended
String to the next unu
Sed code (obtained by incrementing a counter). The proce
SS repeat
S,
Starting from byte b. The number of bit
S in an output code, and hence the maximum number of entrie
S in the table i
S u
Sually fixed and once thi
S limit i
S reached, no more entrie
S are added. LZW compre
SSion and decompre
SSion are licen
Sed under
UniSyS Corporation'
S 1984 U.
S. Patent 4,558,302 and equivalent foreign patent
S. Thi
S kind of patent i
Sn' t legal in mo
St coutrie
S of the world (including the UK) except the U
SA. Patent
S in the UK can' t de
Scribe
algorithmS or mathematical method
S. [A Technique for High Performance Data Compre
SSion, Terry A. Welch, IEEE Computer, 17(6), June 1984, pp. 8-19] [J. Ziv and A. Lempel, "A Univer
Sal Algorithm for
Sequential Data Compre
SSion," IEEE Tran
Saction
S on Information Theory, Vol. IT-23, No. 3, May 1977, pp. 337-343].
Style="border-width:thin; border-color:#333333; border-Style:daShed; padding:5px;" align="left">In addition Suitable contentS:
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