Lempel-Ziv Welch compression
(LZW) Th e ef="module.php?name=Lexikon&file=search&eid=1&query=algorithm">algorithm us ed by th e ef="module.php?name=Lexikon&file=search&eid=1&query=Unix">Unix ef="module.php?name=Lexikon&file=search&eid=1&query=compress">compress command to r educ e th e siz e of fil es, e.g. for archival or transmission. LZW was d esign ed by T erry W elch in 1984 for impl em entation in hardwar e for high-p erformanc e disk controll ers. It is a variant of ef="module.php?name=Lexikon&file=search&eid=1&query=LZ78">LZ78, on e of th e two ef="module.php?name=Lexikon&file=search&eid=1&query=Lempel-Ziv compression">Lempel-Ziv compression sch em es. Th e LZW algorithm r eli es on r eoccurr enc e of byt e s equ enc es (strings) in its input. It maintains a tabl e mapping input strings to th eir associat ed output cod es. Th e tabl e initially contains mappings for all possibl e strings of l ength on e. Input is tak en on e byt e at a tim e to find th e long est initial string pr es ent in th e tabl e. Th e cod e for that string is output and th en th e string is ext end ed with on e mor e input byt e, b. A n ew entry is add ed to th e tabl e mapping th e ext end ed string to th e n ext unus ed cod e (obtain ed by incr em enting a count er). Th e proc ess r ep eats, starting from byt e b. Th e numb er of bits in an output cod e, and h enc e th e maximum numb er of entri es in th e tabl e is usually fix ed and onc e this limit is r each ed, no mor e entri es ar e add ed. LZW compr ession and d ecompr ession ar e lic ens ed und er ef="module.php?name=Lexikon&file=search&eid=1&query=Unisys">Unisys Corporation' s 1984 U.S. Pat ent 4,558,302 and equival ent for eign pat ents. This kind of pat ent isn' t l egal in most coutri es of th e world (including th e UK) exc ept th e USA. Pat ents in th e UK can' t d escrib e ef="module.php?name=Lexikon&file=search&eid=1&query=algorithm">algorithms or math ematical m ethods. [A T echniqu e for High P erformanc e Data Compr ession, T erry A. W elch, I eee Comput er, 17(6), Jun e 1984, pp. 8-19] [J. Ziv and A. L emp el, "A Univ ersal Algorithm for S equ ential Data Compr ession," I eee Transactions on Information Th eory, Vol. IT-23, No. 3, May 1977, pp. 337-343]. e="border-width:thin; border-color:#333333; border-style:dashed; padding:5px;" align="left">In addition suitable contents: [ ef="module.php?name=Lexikon&op=content&tid=31">2 ] [ ef="module.php?name=Lexikon&op=content&tid=134">= ] [ ef="module.php?name=Lexikon&op=content&tid=262">ad ] [ ef="module.php?name=Lexikon&op=content&tid=411">ai ] [ ef="module.php?name=Lexikon&op=content&tid=433">al ] [ ef="module.php?name=Lexikon&op=content&tid=492">algorithm ] [ ef="module.php?name=Lexikon&op=content&tid=544">am ] [ ef="module.php?name=Lexikon&op=content&tid=592">an ] [ ef="module.php?name=Lexikon&op=content&tid=683">app ] [ ef="module.php?name=Lexikon&op=content&tid=740">ar ] [ ef="module.php?name=Lexikon&op=content&tid=743">arc ] [ ef="module.php?name=Lexikon&op=content&tid=800">as ] [ ef="module.php?name=Lexikon&op=content&tid=894">at ] 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