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Topic: LZW (algorithm)

	[70] Introduction to data compression (long)
		LZW decompression takes the stream of codes and uses it to exactly recreate the original input data.
		LZW is more commonly encountered today in a variant known as LZC, after its use in the UNIX "compress" program.
		The most commonly used algorithms are derived from the LZSS scheme described by James Storer and Thomas Szymanski in 1982.
	www.faqs.org /faqs/compression-faq/part2/section-1.html (1700 words)

	LZW - Encyclopedia, History, Geography and Biography
		LZW (Lempel-Ziv-Welch) is a universal lossless data compression algorithm created by Abraham Lempel, Jacob Ziv, and Terry Welch.
		Two US patents were issued for the LZW algorithm: U.S. Patent 4,814,746 by Victor S. Miller and Mark N. Wegman and assigned to IBM, originally filed on June 1, 1983, and U.S. Patent 4,558,302 by Welch, assigned to Sperry Corporation, later Unisys Corporation, filed on June 20, 1983.
		On June 20, 2003, this patent on the LZW algorithm expired [1].
	www.arikah.com /encyclopedia/LZW (1469 words)

	LZW Data Compression
		LZW is a data compression method that takes advantage of this repetition.
		LZW starts out with a dictionary of 256 characters (in the case of 8 bits) and uses those as the "standard" character set.
		Although LZW generally does not require a pseudo-eof (normally, it reads data until it can read no more), it is a good idea to use one.
	www.cs.duke.edu /csed/curious/compression/lzw.html (1296 words)

	» LZW Data Compression Mark Nelson: Programming, mostly.
		The companion algorithm for compression is the decompression algorithm.
		One reason for the efficiency of the LZW algorithm is that it does not need to pass the string table to the decompression code.
		LZW is still going to pick up on that by generating codes for all the strings that start with 'A' more frequently than other codes.
	www.dogma.net /markn/articles/lzw/lzw.htm (9419 words)

	CodeNotes® - Article Display
		LZW file decompression does not require the presence of the unique identifier table; it does not have to be stored in the compressed file.
		The LZW table-based algorithm was invented and patented by Abraham Lempel, Jacob Ziv, and Terry Welch.
		The original LZW approach to data compression was first published in 1977; Terry Welch's refinements to the algorithm were published in 1984.
	www.codenotes.com /articles/articleAction.aspx?articleID=442 (469 words)

	LZW Data Compression
		The code that the LZW algorithm outputs can be of any arbitrary length, but it must have more bits in it than a single character.
		Stepping through the start of the algorithm for this string, you can see that the first pass through the loop, a check is performed to see if the string "/W" is in the table.
		One reason for the efficiency of the LZW algorithm is that it does not need to pass the string table to the decompression code.
	www.eg.bucknell.edu /~cs350/S06/lzw.html (3965 words)

	LZW (Xj3D Code Library)
		LZW compression recognizes sequences that have already appeared in the data, and replaces each later appearance by a unique code.
		LZW compression is effective with data having many and / or lengthy repeat sequences, such as text, and graphics with areas of solid color or patterns.
		The LZW algorithm used in 'compress' is patented, both by IBM (4,814,746) and Unisys (4,558,302).
	www.xj3d.org /javadoc/org/web3d/vrml/export/compressors/LZW.html (455 words)

	LZW4P - LZW Data Compression Library for Pascal (Site not responding. Last check: 2007-10-31)
		It is a data compression library for Turbo Pascal programmers which uses the LZW algorithm as published in research papers by Lempel, Ziv, and Welch.
		The LZW algorithm is probably the best generic compression algorithm known today.
		The LZW algorithm is considered to be one of the best general purpose algorithms available today.
	www.sources.ru /pascal/archives/lzw4p13.htm (363 words)

	DOUGPACK - interpretation of the LZW algorithm
		The DOUGPACK unit implements an interpretation of the LZW algorithm.
		This incarnation of the algorithm is optimized for speed, as much as is possible in a high level language like pascal, and to a lesser degree at this experimental stage, flexibility, not readability.
		CRC assembly language routines were furnished by: Edwin T. Floyd [76067,747] This unit allows the user to compress data using a variation on the standard LZW compression format, or conversely to decompress data that was previously compressed by this unit.
	pascal.sources.ru /archives/lzw1.htm (522 words)

	LZW - Sonic Retro
		LZW (Lempel-Ziv-Welch) is a lossless data compression algorithm.
		It was developed by Terry Welch in 1984 as an improved version of the LZ77 and LZ78 dictionary coding algorithms developed by Abraham Lempel and Jacob Ziv.
		Although the LZW acronym obviously refers to the inventors as Lempel, Ziv and Welch, some people claim the intellectual property rights go to Ziv first, so the method must be called the Ziv-Lempel-Welch algorithm, and not the Lempel-Ziv-Welch algorithm.
	info.sonicretro.org /LZW (871 words)

	The GIF Controversy: A Software Developer's Perspective (lzw.info)
		LZW itself is a refinement of other algorithms published in the years before (Ziv-Lempel and others).
		The LZW patent, as well as its international counterparts, and similar patents filed by others, are expected to remain valid for at least 20 years from the original filing date of June 20, 1983, i.e.
		While the original article on LZW was published in 1984, the LZW patent issue first surfaced in the press in 1989, when the BTLZ algorithm (a procedure similar to LZW developed and patented by British Telecom) was to be approved for data compression into the V.42bis modem standard.
	www.cloanto.com /users/mcb/19950127giflzw.html (4892 words)

	The LZW compression algorithm (Site not responding. Last check: 2007-10-31)
		LZW is named after Abraham Lempel, Jakob Ziv and Terry Welch, the scientists who developed this compression algorithm.
		The code that the LZW algorithm outputs can be of any arbitrary length, but it must have more bits in it than a single character.
		The remaining codes are assigned to strings as the algorithm proceeds.
	www.prepressure.com /techno/compressionlzw.htm (546 words)

	Lempel-Ziv-Welch (LZW) Encoding Discussion and Implementation
		Entries in the LZW dictionary are strings, and every LZW code word is a reference to a string in the dictionary.
		However, the LZW algorithm does not impose a limit on the length of strings that are encoded.
		Further discussion of LZW with links to other documentation and libraries may be found at http://www.datacompression.info/lzw.shtml.
	michael.dipperstein.com /lzw (4219 words)

	LZW Compression: A Short Summary
		Lempel-Ziv Welch (LZW) first began its existence in 1977, with the publication of the theorems and algorithms of Jacob Ziv and Abraham Lempel, as Lempel-Ziv compression.
		LZW is called a substitutional or dictionary based coding algorithm because the algorithm constructs a data table of the characters and their associated codes.
		The algorithm, being known as a "greedy" parser, needs only to pass over the data once, which is an obvious advantage over such algorithms as Huffman coding.
	www.cs.mcgill.ca /~jkelih/works/cs251.html (1151 words)

	Dr. Dobb's \| Replacing a Dictionary with a Square Root \| April 9, 2002
		The algorithm I propose here is derived by studying the input-output behavior of LZW over runs of a single input value, but without depending on its implementation in any way.
		LZW happens to exploit the repeated is and si because of the particular behavior of its dictionary, as shown in the compress method.
		It prints the LZW encoding of the strings that are from 1 to 20 repetitions of the single character "a." Figure 1 is the output of generateCompressMapping (Listing Two).
	www.ddj.com /184404817 (1670 words)

	Public Domain liblzw (Site not responding. Last check: 2007-10-31)
		Many may be familiar with this compression algorithm via the classical UNIX programs compress and uncompress which manipulate files named with a.Z extension, or perhaps the usage of LZW in compressing GIF/TIFF image data.
		Since I ripped the compression algorithms out of the public-domain package ncompress (google for ncompress-4.2.4.tar.gz as it no longer has a homepage), I've also released liblzw into the public-domain for people to do with as they will.
		One last note for those of you coming late to the party; all existing patents on the LZW algorithm have expired world-wide.
	freestdf.sourceforge.net /liblzw.php (204 words)

	Glossary - Document scanning, data conversion and document retrieval - Compact Data Management
		LZW is "lossless" which means it will not compress as well as JPEG, but will retain all of the image's quality.
		Refers to a data compression algorithm that actually reduces the amount of information in the data, rather than just the number of bits used to represent that information.
		The lost information is usually removed because it is subjectively less important to the quality of the data (usually an image or sound) or because it can be recovered reasonably by interpolation from the remaining data.
	www.compact.uk.com /glossary (1304 words)

	CS 1501 Programming Project 5
		Purpose: The purpose of this assignment is for you to fully understand the LZW compression algorithm, its performance and its implementation.
		Be sure to read not only the top level LZW document, but also the more detailed paper in http://www.dogma.net/markn/articles/lzw/lzw.htm.
		For all algorithms, indicate which of the test files gave the best and worst compression ratios, and speculate as to why this was the case.
	www.cs.pitt.edu /~kirk/cs1501/assignments/lzw/lzw-04-2.html (1666 words)

	[No title] (Site not responding. Last check: 2007-10-31)
		Because the LZW algorithm had been so widely described in printed articles and other references, the programmers at CompuServe assumed that the algorithm was in the public domain.
		CompuServe had alternatives to LZW compression when it created the GIF standard, but they were less appealing, and there appeared to be no compelling reason not to use LZW, since it was mistakenly assumed to be patent-free.
		The LZW case illustrates one of the biggest problems with software patents--the very nature of software and algorithms leads programmers and scientists to freely adopt and exchange ideas that have been published in academic and non-academic literature.
	cse.stanford.edu /class/cs201/projects-99-00/software-patents/lzw.html (980 words)

	An Introduction to Data Compression
		LZW is a way of compressing data that takes advantage of repetition of strings in the data.
		LZW manipulates three objects in both compression and decompression: the charstream, the codestream, and the string table.
		Also, note that "straight LZW" compression runs the risk of overflowing the string table - getting to a code which can't be represented in the number of bits you've set aside for codes.
	www.cis.udel.edu /~amer/CISC651/lzw.and.gif.explained.html (2491 words)

	LZW coding algorithm
		The LZW algorithm uses the same principles and ideas as LZ78 does, while adding several technical improvements over LZ78.
		The second problem is that the algorithm does not work for one abnormal case.
		Therefore these algorithms are usually applied to compress relatively long sequences.
	www.cs.technion.ac.il /Labs/Isl/Project/Projects_done/VisionClasses/DIP/Lossless_Compression/node18.html (634 words)

	LZW compression algorithm (Site not responding. Last check: 2007-10-31)
		Unisys presently requires anyone who uses the algorithm in a commercial application to purchase from them a license to do so.
		Basic overview: LZW compression creates a table of strings commonly occurring in the data being compressed, and replaces the actual data with references into the table.
		The table is formed during compression at the same time at which the data is encoded and during decompression at the same time as the data is decoded.
	www.cs.usyd.edu.au /~loki/cs2csys/gif-info/algorithm-lzw.htm (370 words)

	[No title]
		In this algorithm, a tree (NOT binary tree) is introduced to represent the whole dictionary.
		As the name implies, it is an algorithm used to sorting with respect to the occurrence.
		Because of the nature of LZW dictionary, you may find that a branch's occurrence equals to the sum of sub-branches occurrences.
	www.math.niu.edu /~rusin/known-math/00_incoming/lzw (1836 words)

	What is LZW and what are the issues surrounding it? - Knowledge Base
		LZW (Lempel-Ziv-Welch) is a popular compression algorithm used by a number of formats, including GIF, TIFF, PostScript, PDF, Unix Compress, and V.42bis.
		Unisys used to hold the patent for LZW, though many companies and developers, including CompuServe, mistakenly believed it to be in the public domain.
		Unisys had always required licenses from companies that used LZW in their hardware (e.g., modem manufacturers), but for many years it overlooked LZW implementations in software.
	kb.iu.edu /data/aghf.html (307 words)

	LZW Data Compression at Mark Nelson
		The companion algorithm for compression is the decompression algorithm.
		One reason for the efficiency of the LZW algorithm is that it does not need to pass the string table to the decompression code.
		Most compression algorithms either use a bit stream of some kind or write words of varying size, so they are all going to have an output_code() routine of some kind.
	marknelson.us /1989/10/01/lzw-data-compression (8377 words)

	Decompression algorithms
		The LZW algorithm itself, when used for compression or decompression in an apparatus (sic) designed for compression and decompression, has been patented by Unisys in Japan, Europe, and the United States.
		This algorithm is based on the Deflate algorithm described in the Internet RFC 1951 (see also RFC 1950 for related material).
		The algorithms listed as UNKNOWN-x have not yet been mapped to actual algorithms but are known to be used by the games.
	freesci.linuxgames.com /scihtml/x386.html (490 words)

	Interactive LZW Compression
		The LZW algorithm is what we are going to talk about here.
		The nice thing is that the decompressor builds its own dictionary on its side, that matches exactly the compressor's, so that only the codes need to be sent.
		If you want more detail, there is an article on LZW Compression by Mark Nelson, the author of the Data Compression Book.
	www.cs.sfu.ca /cs/CC/365/li/squeeze/LZW.html (573 words)

	NewsForge \| Bringing back LZW compression
		LZW has other more vital uses, chief among them being that it is the default compression algorithim for the Tagged Image File Format (TIFF) file format.
		Furthermore, they could also still supply a working LZW function separately, for those who needed it, which could be implemented with a single patch to the library.
		There was some debate last year over whether IBM also held a patent on the LZW algorithm, but it has been settled -- IBM's patented compression is a cousin to LZW, but different.
	software.newsforge.com /software/05/06/23/2150233.shtml?tid=130 (1944 words)

	[No title]
		LZW - A sophisticated data compression algorithm based on work done by Lempel-Ziv & Welch which has the feature of very efficient one-pass encoding and decoding.
		COMPRESSION The LZW algorithm converts a series of data values into a series of codes which may be raw values or a code designating a series of values.
		Whenever the LZW code value would exceed the current code length, the code length is increased by one.
	www.cs.cmu.edu /~cil/lzw.and.gif.txt (5491 words)

	The LZW algorithm
		In this algorithm, the same terms are used as in LZ78, with the following addendum:
		During the decoding this string is not yet present in the dictionary.
		The LZW method is patented -- the owner of the patent is the Unisys company.
	oldwww.rasip.fer.hr /research/compress/algorithms/fund/lz/lzw.html (614 words)

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