- Lempel-Ziv-Storer-Szymanski
Lempel-Ziv-Storer-Szymanski (LZSS) is a
lossless data compression algorithm , a derivative ofLZ77 , that was created in 1982 byJames Storer andThomas Szymanski . LZSS was described in article "Data compression via textual substitution" published in "Journal of the ACM" (pp. 928-951).LZSS is a dictionary encoding technique. It attempts to replace a string of symbols with a reference to a dictionary location of the same string.
The main difference between LZ77 and LZSS is that in LZ77 the dictionary reference could actually be longer than the string it was replacing. In LZSS, such references are omitted if the length is less than the "break even" point. Furthermore, LZSS uses one-bit flags to indicate whether the next chunk of data is a literal (byte) or a reference to an offset/length pair.
Example
Here is the beginning of
Dr. Seuss 'sGreen eggs and ham , with character numbers at the beginning of lines for convenience.0: I am Sam9:10: Sam I am19:20: That Sam-I-am!35: That Sam-I-am!50: I do not like64: that Sam-I-am!79: 80: Do you like green eggs and ham?112:113: I do not like them, Sam-I-am.143: I do not like green eggs and ham.This text takes 177 bytes in uncompressed form. Assuming a break even point of 2 bytes (and thus 2 byte pointer/offset pairs), and one byte newlines, this text compressed with LZSS becomes 96 bytes long:
0: I am Sam9:10: (6,3) (0,4)16:17: That(5,4)-I-am!30: (20,15)I do not like46: t(21,14)49: Do you(58,5) green eggs and ham?79: (49,14) them,(24,9).(49,14)(93,18).Note: this does not include a few bytes (3-4) of flags indicating whether the next chunk of text is a pointer or a literal. Adding it, the text becomes just over 100 bytes long, which is much shorter than the original 177 bytes.
Implementations
Many popular archivers like
PKZip ,ARJ , ZOO,LHarc use LZSS rather than LZ77 as primary compression algorithm; the encoding of literal characters and of length-distance pairs varies, with the most common option beingHuffman coding . TheAllegro library can encode and decode an LZSS format, [Hargreaves, Shawn, et al. [http://alleg.svn.sourceforge.net/viewvc/alleg/allegro/branches/4.2/src/lzss.c?revision=7522&view=markup Allegro source code: lzss.c, revision 7522] . Accessed onAugust 3 ,2008 .] and theGame Boy Advance BIOS can decode a slightly different LZSS format. [Korth, Martin. [http://nocash.emubase.de/gbatek.htm#biosdecompressionfunctions GBATEK: GBA BIOS Decompression Functions] . Accessed onAugust 3 ,2008 .]References
See also
*
LZ77
*Lempel-Ziv-Welch (LZW)External links
* [http://babelfish.altavista.com/babelfish/trurl_pagecontent?lp=es_en&url=http%3A%2F%2Fes.wikipedia.org%2Fwiki%2FLZSS More information] translated from Spanish language Wikipedia
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