LZW

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LZW (Lempel-Ziv-Welch) is a lossless compression algorithm based on [[LZ78]]. It was developed by Terry Welch in 1984. It is infamous for being widely used in various standard formats (especially [[GIF]]) by developers unaware that it was encumbered by [[patents]]. The patents expired around 2003.
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'''LZW''' (Lempel-Ziv-Welch) is a lossless compression algorithm based on [[LZ78]]. It was developed by Terry Welch in 1984. It is infamous for being widely used in various standard formats (especially [[GIF]]) by developers unaware that it was encumbered by [[patents]]. The patents expired around 2003.
  
 
There are many variations of LZW in use. In general, LZW compresses a stream of ''symbols'' into a stream of bits. For general-purpose file compression, the symbols are usually taken to be bytes, but for GIF format the symbols are pixels.
 
There are many variations of LZW in use. In general, LZW compresses a stream of ''symbols'' into a stream of bits. For general-purpose file compression, the symbols are usually taken to be bytes, but for GIF format the symbols are pixels.
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* [http://www.cs.duke.edu/courses/spring03/cps296.5/papers/welch_1984_technique_for.pdf A Technique for High-Performance Data Compression] Welch, Terry A.  Computer, Vol. 17, No. 6 (June 1984): pp. 8-19
 
* [http://www.cs.duke.edu/courses/spring03/cps296.5/papers/welch_1984_technique_for.pdf A Technique for High-Performance Data Compression] Welch, Terry A.  Computer, Vol. 17, No. 6 (June 1984): pp. 8-19
 
* [http://en.wikipedia.org/wiki/LZW Lempel-Ziv-Welch : Wikipedia]
 
* [http://en.wikipedia.org/wiki/LZW Lempel-Ziv-Welch : Wikipedia]
* [http://www.digitalpreservation.gov/formats/fdd/fdd000135.shtml LZW Compression Encoding, from Library of Congress resource on Sustainability of Digital Formats]
 
 
* [http://marknelson.us/2011/11/08/lzw-revisited/ LZW Revisited] a 2011 update to an article by Mark Nelson written 20 years earlier.
 
* [http://marknelson.us/2011/11/08/lzw-revisited/ LZW Revisited] a 2011 update to an article by Mark Nelson written 20 years earlier.
* [http://www.fileformat.info/mirror/egff/ch09_04.htm Lempel-Ziv-Welch (LZW) Compression] From Encyclopedia of Graphics File Formats at FileFormat.Info (1996)
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* [http://www.fileformat.info/mirror/egff/ch09_04.htm Lempel-Ziv-Welch (LZW) Compression], from the [[Encyclopedia of Graphics File Formats]]
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* [http://www.infinitepartitions.com/cgi-bin/showarticle.cgi?article=art010 How LZW (GIF) Compression Works]
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* [http://www.google.com/patents/US4558302 US Patent 4,558,302]

Revision as of 17:52, 4 January 2014

File Format
Name LZW
Ontology
LoCFDD fdd000135
PRONOM x-cmp/12
Released 1984

LZW (Lempel-Ziv-Welch) is a lossless compression algorithm based on LZ78. It was developed by Terry Welch in 1984. It is infamous for being widely used in various standard formats (especially GIF) by developers unaware that it was encumbered by patents. The patents expired around 2003.

There are many variations of LZW in use. In general, LZW compresses a stream of symbols into a stream of bits. For general-purpose file compression, the symbols are usually taken to be bytes, but for GIF format the symbols are pixels.

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