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Topic: LZ77 and LZ78 (algorithms)

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	LZ77 and LZ78 (algorithms) \| English \| Dictionary & Translation by Babylon
		LZ77 and LZ78 are the names for the two lossless data compression algorithms published in papers by Abraham Lempel and Jacob Ziv in 1977 and 1978.
		These two algorithms form the basis for most of the LZ variations including LZW, LZSS and others.
		LZ77 is the "sliding window" compression algorithm, which was later shown to be equivalent to the explicit dictionary technique first given in LZ78.
	www.babylon.com /definition/LZ77_and_LZ78_(algorithms) (97 words)

	LZ77 and LZ78 (algorithms) - Encyclopedia, History, Geography and Biography
		LZ77 and LZ78 are the names for the two lossless data compression algorithms published in papers by Abraham Lempel and Jacob Ziv in 1977 and 1978.
		LZ77 is the "sliding window" compression algorithm, which was later shown to be equivalent to the explicit dictionary technique first given in LZ78.
		The LZ77 algorithm works by keeping a history window of the most recently seen data and comparing the current data being encoded with the data in the history window.What is actually placed into the compressed stream are references to the position in the history window, and the length of the match.
	www.arikah.net /encyclopedia/LZ78 (1107 words)

	LZ77
		LZ77 and LZ78 are the names for the two lossless algorithms published in papers by Abraham Lempel[?] and Jacob Ziv[?] in 1977 and 1978.
		The LZ77 algorithm works by keeping a history window of the most recently seen data and comparing the current data being encoded with the data in the history window.
		LZ78 never became as popular as LZ77 because for the first few decades after it was introduced, LZ78 was somewhat of a patent minefield in the United States, while LZ77 is not patented.
	www.ebroadcast.com.au /lookup/encyclopedia/lz/LZ78.html (287 words)

	LZ77
		These two algorithms form the basis for most of the LZ variations including LZW, LZSS and others.\nThey are both dictionary coders, unlike minimum redundancy coders or run length coders.
		The LZ77 algorithm works by keeping a history window of the most recently seen data and comparing the current data being encoded with the data in the history window.\nWhat is actually placed into the compressed stream are references to the position in the history window, and the length of the match.
		The most popular form of LZ78 compression was the LZW algorithm, a modification of the LZ78 algorithm made by Terry Welch, which proved to be a patent minefield.
	encyclopedia.codeboy.net /wikipedia/l/lz/lz77.html (388 words)

	Data Compression Reference Center
		A refineme nt of this algorithm which is the basis for practically all the later methods in this group is the LZSS algorithm developed in 1982 by Storer and Szymanski.
		LZ77 solves this problem this way: after each pointer it outputs the first character in the lookahead buffer after the match.
		The LZSS algorithm solves this problem in a more efficient manner: the pointer is output only if it points to a match longer than the pointer itself; otherwise, explicit characters are sent.
	compress.rasip.fer.hr /algorithms_dictionary_methods.htm (2751 words)

	Lossless Data Compression: LZ78
		In LZ77, the dictionary of phrases was defined by a fixed-length window of previously seen text.
		LZ78-based schemes work by entering phrases into a ‘dictionary’ and then, when a repeat occurrence of that particular phrase is found, outputting a token that consists of the dictionary index instead of the phrase, as well as a single character that follows that phrase.
		Unlike LZ77, there is no need to pass the phrase length as a parameter because decoder already has this information.
	cse.stanford.edu /class/sophomore-college/projects-00/data-compression/lossless/lz78/concept.htm (362 words)

	LZ77 and LZ78 (algorithms) - Wikipedia, the free encyclopedia
		These two algorithms form the basis for most of the LZ variations including LZW, LZSS and others.
		What is actually placed into the compressed stream are references to the position in the history window, and the length of the match.
		By the reasoning presented in the above example this is the only case were the newly-created symbol is sent immediately.
	en.wikipedia.org /wiki/LZ77 (1107 words)

	[No title] (Site not responding. Last check: 2007-10-26)
		LZ78 differs from LZ77 in that the text compression is achieved by parsing the data being compressed into phrases which are entered into a compression dictionary.
		In the LZ78 algorithm of the preferred embodiment, text is compressed, as was shown in FIGURE 2, using a compression dictionary which is expanded during the compression process whereby references to the compression dictionary are transmitted in place of the original text.
		This limits the usefulness of the algorithm somewhat, as is the case with conventional LZ78, since decompressing a portion of data requires that the preceding portion be decompressed in its entirety.
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=98/06028.980611&ELEMENT_SET=DECL (14897 words)

	Certified Medical Coder -- Recommendations and Resources (Site not responding. Last check: 2007-10-26)
		A dictionary coder, also sometimes known as a substitution coder, is any of a number of data compression algorithms which operate by searching for matches between the text to be compressed and a set of strings contained in a data structure (called the 'dictionary') maintained by the encoder.
		In LZ77, a data structure called the "sliding window" is used to hold the last ''N'' bytes of data processed; this window serves as the dictionary, effectively storing ''every'' substring that has appeared in the past ''N'' bytes as dictionary entries.
		LZ78 uses a more explicit dictionary structure; at the beginning of the encoding process, the dictionary only needs to contain entries for the symbols of the alphabet used in the text to be compressed,
	www.becomingapediatrician.com /health/29/certified-medical-coder.html (390 words)

	Towards Analytical Information Theory: Recent Results on Lempel-Ziv Data Compression Schemes
		The Lempel-Ziv algorithms are well-known dynamic dictionary algorithms of use in data compression.
		As these examples demonstrate, the LZ77 algorithm ``learns'' faster but, the implied dictionary being larger, references are more costly as their encodings require more bits.
		The redundancy of a compression scheme is a measure of its distance to the information-theoretic lower bound (2).
	pauillac.inria.fr /algo/seminars/sem96-97/szpankowski.html (2207 words)

	Class notes CS251B -- Winter 1997
		LZ77 and LZ78, two dictionary-based data compression techniques described by these two researchers, provided a whole new way of viewing the world of data compression.
		The highly innovative LZ77 and LZ78 methods, although usually referred to as the singular Lempel-Ziv (LZ) or Ziv-Lempel method, are in fact considerably different.
		Both algorithms are based on the principle of storing pointers to the data.
	www.cs.mcgill.ca /~cs251/OldCourses/1997/topic23 (1472 words)

	:::► Dictionary of Meaning www.mauspfeil.net ◄::: (Site not responding. Last check: 2007-10-26)
		It was developed by Terry Welch in 1984 as an improved version of the LZ77 and LZ78 (algorithms) LZ78 dictionary coding algorithm developed by Abraham Lempel and Jacob Ziv.
		A variant of this algorithm is widely used in the *.zip save format which is used in OpenOffice.org save formates, PDF files, and NTFS drives.
		LZ78 was covered by {{US patent4,464,650}} by Lempel, Ziv, Cohn, and Eastman, assigned to Sperry Corporation, later Unisys Corporation, filed on August 10, 1981, and presumably now expired.
	www.mauspfeil.net /LZW.html (955 words)

	Hacking Data Compression - Lesson 7
		They are known as LZ77 and LZ78, referring to the papers published by Ziv and Lempel in 1977 and 1978, respectively (the transposition of 'L' and 'Z' was made early and propagated widely).
		All LZ78-class algorithms and many LZ77-class algorithms are the victims of software patents, meaning that if you use them you will have to pay the patent holders or face a court challenge.
		Instead of encoding an index referring to a dictionary full of strings, it encodes a triple , where "off" is the file offset at which the string starts, "len" is the length of the match, and "char" is the first character that didn't match.
	www.fadden.com /techmisc/hdc/lesson07.htm (3137 words)

	[No title] (Site not responding. Last check: 2007-10-26)
		That is, the algorithms do not affect, update or otherwise change the dictionary for a given unit of text.
		In semi-static compression algorithms, the dictionary is occasionally updated or changed according to the text based on a selected scheme.
		To this end, the data decompressor 28 uses a decompression algorithm that is complementary to the compression algorithm used by the data compressor 22.
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=00/38098.000629&ELEMENT_SET=DECL (6006 words)

	Citations: Text compression using antidictionaries - Crochemore, Mignosi, Restivo, Salemi (ResearchIndex) (Site not responding. Last check: 2007-10-26)
		Although these algorithms result asymptotically faster than the classical scan based methods, their overall time requirement may be yet too high since they rely on a full scan of the compressed text.
		The algorithm can be applied to the problem for any compression methods, such as the Ziv Lempel fam ily, the RE PAIR [20] and static dictionary based methods.
		A collection of algorithms is currently known to solve eciently (possibly optimally) this problem on text compressed by means of various schemes: e.g.
	citeseer.ist.psu.edu /context/663563/216370 (2594 words)

	Lossless data compression theory and algorithms
		A dictionary coder, also sometimes known as a substitution coder, is any of a number of lossless data compression algorithms which operate by searching for matches between the text to be compressed and a set of strings contained in a data structure (called the 'dictionary') maintained by the encoder.
		In LZ77, a data structure called the "sliding window" is used to hold the last N bytes of data processed; this window serves as the dictionary, effectively storing every substring that has appeared in the past N bytes as dictionary entries.
		Context mixing is a type of data compression algorithm in which the next-symbol predictions of two or more statistical models are combined to yield a prediction that is often more accurate than any of the individual predictions.
	www.maximumcompression.com /algoritms.php (2676 words)

	IRNIS on the NET - glossary
		Message digest algorithms have much in common with techniques used in encryption, but to a different end; verification that data have not been altered since the signature was published.
		The most commonly used present-day message digest algorithm is the 128 bit MD5 algorithm, developed by Ron Rivest of the MIT Laboratory for Computer Science and RSA Data Security, Inc. The algorithm, with a reference implementation, was published as Internet RFC 1321 in April 1992, and was placed into the public domain at that time.
		This algorithm is simple enough to be translated into a number of different languages and assembly languages very easily.
	www.irnis.net /gloss/all.shtml (2725 words)

	Towards Analytical Information Theory: Recent Results on Lempel-Ziv Data Compression Schemes
		The Lempel-Ziv algorithms are well-known dynamic dictionary algorithms of use in data compression.
		As these examples demonstrate, the LZ77 algorithm ``learns'' faster but, the implied dictionary being larger, references are more costly as their encodings require more bits.
		The redundancy of a compression scheme is a measure of its distance to the information-theoretic lower bound (2).
	algo.inria.fr /seminars/sem96-97/szpankowski.html (2207 words)

	LZ77
		LZ78 never became as popular as LZ77 because for the first few decades after it was introduced, LZ78 was somewhat of a patent minefield in the United States, while LZ77 isn't patented.
		Long did I toss from side.html">side to side as I visited with the divine wrath--to be struck with sudden death, thought occurred to me: "Why should I not drive out to the make a second confession?" Thereafter I grew calmer.
		All is still licensed under the GNU FDL.
	www.wordlookup.net /lz/lz77.html (429 words)

	LZ77 (algorithm) - TheBestLinks.com - LZ78, Algorithm, Huffman coding, Lossless data compression, ... (Site not responding. Last check: 2007-10-26)
		LZ77 (algorithm) - TheBestLinks.com - LZ78, Algorithm, Huffman coding, Lossless data compression,...
		LZ78, LZ77 (algorithm), Algorithm, Huffman coding, Lossless data compression...
		Abraham Lempel, Jacob Ziv; A Universal Algorithm for Sequential Data Compression (http://www.cs.duke.edu/courses/spring03/cps296.5/papers/ziv_lempel_1977_universal_algorithm.pdf), IEEE Transactions on Information Theory, May 1977.
	www.thebestlinks.com /LZ78.html (425 words)

	Compression Algorithms
		The drawbacks are that dynamic versions of the algorithms tend to be complicated, and that coders often are slower than the non-dynamic versions.
		The algorithm states that one is to combine nodes containing the lowest probability.
		Most variations on these dynamic coding algorithms, stem from one of two methods known as LZ77 and LZ78, which were published by Jacob Ziv and Abraham Lempel in IEEE Transactions on Information Theory [84] [85].
	www.ifi.uio.no /~ftp/publications/cand-scient-theses/SHuseby/html/node43.html (1698 words)

	Algorithms in the Real World: Compression
		The theory is not as strong as Sayood's book (below), and the algorithms are sometimes not described in enough depth to implement them, but the number of algorithms covered is impressive, including Burrows-Wheeler, ABC, and about a dozen variants of Lempel-Ziv.
		Source code for many of the algorithms is supposed to be here, but the connection timed out last time I tried.
		The GIF format is patented by ComputServe and the LZW algorithm used by the format is patented by Unisys.
	www.cs.cmu.edu /afs/cs/project/pscico-guyb/realworld/www/compress.html (672 words)

	[No title]
		Fiddling with various parameters in the algorithms might give better results, and it might be the case that small tricks could be used some places to push the performance a little further.
		There is a whole class of algorithms that use the fact that when we get a letter from the input, we can say that certain characters most likely will follow.
		One possibility is that the encoder has a dictionary of often-used character sequences (for example including common words like "what", "where", etc.), and then instead of outputting each character separately, it tries to match blocks of the input with dictionary entries and then outputs the positions in the dictionary where the text blocks are.
	www.rebolforces.com /articles/compression/6/source.txt (1363 words)

	The LZW compression algorithm (Site not responding. Last check: 2007-10-26)
		He developed a rather simple algorithm that was based on the LZ78 algorithm and that is now called LZW.
		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)

	LZ77 compression (Site not responding. Last check: 2007-10-26)
		LZ77 compression keeps track of the last n bytes of data seen, and when a phrase is encountered that has already been seen, it outputs a pair of values corresponding to the position of the phrase in the previously-seen buffer of data, and the length of the phrase.
		In effect the compressor moves a fixed-size "window" over the data (generally referred to as a "sliding window"), with the position part of the (position, length) pair referring to the position of the phrase within the window.
		The most commonly used algorithms are derived from the LZSS scheme described by James Storer and Thomas Szymanski in 1982.
	burks.brighton.ac.uk /burks/foldoc/44/69.htm (296 words)

	Chapter 4: Compression techniques (Site not responding. Last check: 2007-10-26)
		Compression algorithms which need information from previous packets cannot be used since it is possible that one of those previous packets did not reach the destination.
		The current position is then incremented by L. Next, the algorithm outputs a double <i,c> with `i' being the index of the found entry and `c' being the character at the current position.
		The Huffman algorithm constructs such a tree in which the leafs are marked with the values that need to be encoded.
	research.edm.luc.ac.be /jori/thesis/onlinethesis/chapter4.html (5247 words)

	Data Compression: The Complete Reference
		Although the coder component of compression algorithms are typically limited to one of a few types of code (e.g.
		Lempel-Ziv 78 (LZ78) after the years in which they were published.
		Because the LZ algorithms do not use probabilities more carefully, the algorithms as originally specified are not very effective in practice.
	www.cs.cmu.edu /People/aladdin/xml/gdepot/comp.xml (1386 words)

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