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Topic: LZ77 (algorithm)

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	LZ77 and LZ78 - Wikipedia, the free encyclopedia
		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.
		LZ77 algorithms achieve compression by replacing portions of the data with references to matching data that has already passed through both encoder and decoder.
	en.wikipedia.org /wiki/LZ77 (780 words)

	LZ77 (Site not responding. Last check: 2007-10-04)
		The LZ77 algorithm works by keeping a window of the most recently seen data comparing the current data being encoded with data in the history window.
		LZ78 never became as popular as LZ77 for the first few decades after it introduced LZ78 was somewhat of a patent minefield in the United States while LZ77 is not patented.
		The popular form of LZ78 compression was the LZW algorithm a modification of the LZ78 made by Terry Welch which proved to a patent minefield.
	www.freeglossary.com /Data_compression/LZ77_78 (346 words)

	The LZW compression algorithm (Site not responding. Last check: 2007-10-04)
		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)

	LZSS (LZ77) Discussion and Implementation (Site not responding. Last check: 2007-10-04)
		In their original LZ77 algorithm, Lempel and Ziv proposed that all strings be encoded as a length and offset, even strings with no match.
		Since the dictionary is a sliding window of the last characters encoded by the algorithm, the lists of strings starting with a given character must be updated as old characters are removed from the dictionary and new characters are added to the dictionary.
		Rather than inventing and testing a new key algorithm, I chose the key generation method discussed in K. Sadakane and H. Imai: Improving the Speed of LZ77 Compression by Hashing and Suffix Sorting, IEICE Trans.
	michael.dipperstein.com /lzss (2834 words)

	Dr. Dobb's \| An Algorithm for Online Data Compression \| April 15, 2003 (Site not responding. Last check: 2007-10-04)
		The Deflate algorithm is some combination of the LZ77 algorithm and Huffman-like encoding, and it is very popular for offline compression.
		Similar to the Deflate algorithm, it is a combination of the LZ77 algorithm and Huffman-like encoding.
		Thus, the LZ77 compressor's task is to build an intermediate stream S, such that the LZ77 decompressor, which applies the previously described instructions to S' (identical to S), will output a raw byte stream identical to the input raw byte stream of the compressor.
	www.ddj.com /184403560?pgno=5 (3744 words)

	RFC 3051
		LZJH is similar to the algorithm described in [LZ78] although it also has aspects which are similar to the algorithm described in [LZ77].
		The output of the algorithm is a new (and hopefully smaller) payload.
		The LZJH algorithm, as described in [V44], is easily modified to incorporate an adaptive compressibility test, as referenced in [RFC2393].
	www.nalanda.nitc.ac.in /misc/rfc/html/rfc3051.html (1458 words)

	LZW Compression: A Short Summary
		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 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.
	www.cs.mcgill.ca /~jkelih/works/cs251.html (1151 words)

	An Explanation of the `Deflate' Algorithm
		Each element that you could want to specify has a code made up of numbers, and because no code for one element begins with the code for any other element, you can type in that code and there will be no ambiguity about that being the one you mean.
		A Huffman algorithm starts by assembling the elements of the ``alphabet,'' each one being assigned a ``weight'' -- a number that represents its relative frequency within the data to be compressed.
		LZ77 compression works by finding sequences of data that are repeated.
	www.zlib.net /feldspar.html (2217 words)

	[No title]
		The bytecode for the chosen compression algorithm is uploaded to the UDVM as part of the compressed data.
		The compression ratio of LZ77 is improved by the remaining UDVM memory, which is used to store a history buffer containing the previously decompressed messages.
		LZW compression operates in a similar manner to LZ77 in that it maintains a circular buffer of previously received decompressed data, and each compressed character references exactly one byte string from the circular buffer.
	www.rfc-editor.org /rfc/rfc4464.txt (5706 words)

	Lossless Data Compression Program: Hybrid LZ77 RLE
		The distribution of the LZ77 offset values (pointer to a previous occurrance of a string) is not at all similar to the length distribution.
		Because LZ77 is the most frequently used primary unit, this presents a saving that more than compensates for the loss of 2-byte LZ77 matches with offsets 257..768 (which we can no longer represent, because we fixed the offset for 2-byte matches to use exactly 8 bits).
		Well, actually the algorithm proceeds from the end of the file to the beginning for efficiency reasons, but the result is the same anyway: the path that minimizes the bits emitted is determined and remembered.
	www.cs.tut.fi /~albert/Dev/pucrunch (13324 words)

	A guide to PNG optimization
		In the second stage, the filtered byte sequence is passed through the Ziv-Lempel algorithm (LZ77), producing LZ77 codes that are further compressed by the Huffman algorithm in the third and final stage.
		The output of LZ77 is fed into a buffer which is occasionally flushed by sending a static Huffman tree followed by all the Huffman codes, to the output of Deflate.
		The dynamic Huffman codes referred to by the Deflate specification are NOT built by the dynamic Huffman algorithm, as defined, for example, by Faller, Gallager and Knuth (the FGK algorithm), or by Vitter (the V algorithm).
	www.cs.toronto.edu /~cosmin/pngtech/optipng.html (3118 words)

	DataCompression.info - LZ77/LZSS and derivatives (Site not responding. Last check: 2007-10-04)
		This topic encompasses the LZ77 algorithm and its descendant, LZSS.
		This algorithm, later known as LZ77, is still one of the most widely used techniques for lossless data compression in use today.
		This is the data compression standard that implements the LZJH algorithm, and is used in V.90 and V.92 modems.
	datacompression.info /LZSS.shtml (1939 words)

	LZ77 compression (Site not responding. Last check: 2007-10-04)
		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)

	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)

	7z
		In computing, 7z is an archive format which allows data compression using a number of compression algorithms.
		The format was initially implemented by the 7-Zip archiver but the file format is public and 7-Zip's implementation of it is publicly available under the GNU LGPL licence.
		The key is generated from a user-supplied passphrase using an algorithm based on the SHA-256 hash algorithm (with a large number of iterations, to make a brute-force search for the passphrase more difficult).
	www.guajara.com /wiki/en/wikipedia/7/7z/7z.html (202 words)

	[No title] (Site not responding. Last check: 2007-10-04)
		LZ77 became the first of two compression algorithm presented by Lempel and Ziv.
		Basically a fixed-size "sliding window" is shifted across the data, while a pointer keeps track of where you are with respect to other data.
		Decompression is fast and easy: whenever a (P, L) value pair is encountered, go to that "position" in the window and copy "length" next bytes to the output.
	www.eecis.udel.edu /~staiano/ELEG867/lz77.html (242 words)

	rfc1951
		The Huffman trees for each block are independent of those for previous or subsequent blocks; the LZ77 algorithm may use a reference to a duplicated string occurring in a previous block, up to 32K input bytes before.
		Given an alphabet with known symbol frequencies, the Huffman algorithm allows the construction of an optimal prefix code (one which represents strings with those symbol frequencies using the fewest bits of any possible prefix codes for that alphabet).
		In all cases, the decoding algorithm for the actual data is as follows: do read block header from input stream.
	www.nalanda.nitc.ac.in /misc/rfc/html/rfc1951.html (2858 words)

	The Flate/deflate compression algorithm (Site not responding. Last check: 2007-10-04)
		The lossless deflate compression algorithm is based on two other compression algorithms: huffman encoding and LZ77 compression.
		Deflate is a smart algorithm that adapts the way it compresses data to the actual data themselves.
		Compression, first with LZ77 and then with a slightly modified version of Huffman coding with trees that the compressor creates and stores along with the data.
	www.prepressure.com /techno/compressionflate.htm (285 words)

	Xcell Journal Online -- Tararo and Celoxica article
		The majority of the algorithm was used with little or no modification to provide an immediate basis for prototyping and a controlled test framework in which to enhance and optimize the algorithm.
		The process for porting the GZIP algorithm to hardware was to write the code for one "module" of the system at a time in Handel-C. Note that the modules correspond to algorithmic stages in the decompression algorithm, as shown in Table 1, rather than more traditional hardware blocks.
		The GZIP decompression algorithm was used to demonstrate the platform’s ability to deliver significant acceleration and an overall performance improvement for applications.
	www.xilinx.com /publications/xcellonline/xcell_46/xc_fast46.htm (2109 words)

	LZ77 Data Compression (Site not responding. Last check: 2007-10-04)
		In effect the compressor moves a fixed-size "window" over the data (generally referred to as a "sliding window" [or "ring buffer"], with the position part of the (position, length) pair referring to the position of the phrase within the window.
		The patent office failed to recognize that the same algorithm was patented twice, even though the wording used in the two patents is very similar.
		Phil Katz, author of pkzip, also has a patent on LZ77 (5,051,745) but the claims only apply to sorted hash tables, and when the hash table is substantially smaller than the window size.
	home.earthlink.net /~neilbawd/pall.html (1265 words)

	Grand Laboratory\|Home for your research
		People realized that so called greedy algorithms can not be implemented on the routing protocols of multi-hop wireless networks which are aimed at minimize the expected hop count or maximize the probability of delivery.
		There are many well-developed algorithms of sorting at present, but they are all based on comparing between elements, which makes them impossible to surpass the limitation of time complexity of O(nlogn).
		The key idea of this algorithm is to generate the guessing function which is a mapping from elements value to their location.
	grandlab.cer.net (584 words)

	The LZ78 algorithm (Site not responding. Last check: 2007-10-04)
		In that case we output a special code word that represents an empty string, followed by this character and add this character to the dictionary.
		The biggest advantage over the LZ77 algorithm is the reduced number of string comparisons in each encoding step.
		The compression ratio is similar to the LZ77.
	oldwww.rasip.fer.hr /research/compress/algorithms/fund/lz/lz78.html (529 words)

	Copmression (not definitive but a guide to some forms) -
		The LZ78 algorithm is so called, because it was derived from the initials and year the mathematicians, Abraham Lempel and Jacob Ziv officially released it in 1978.
		Despite this, the algorithm is flexible and can be easily applied to images (ones with few colours/shades would be particularly suited to Run Length Encoding) and rather than repetitions of individual characters, the code could be adjusted to allow for repetitions of entire words or sequences.
		This has the advantage over LZ77 that the dictionary and the references have a global scope meaning that if a word is written as a series at the beginning and end of a data series then the word only needs one code throughout.
	www.belowtopsecret.com /thread169283/pglastpost (3051 words)

	LZ77 - Sonic Retro
		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.
		Abraham Lempel, Jacob Ziv; A Universal Algorithm for Sequential Data Compression, IEEE Transactions on Information Theory, May 1977.
	info.sonicretro.org /LZ77 (227 words)

	Deflate - file compression algorithm (Site not responding. Last check: 2007-10-04)
		Deflation is a means of compressing an octet sequence that combines the LZ77 algorithm for marking common substrings and Huffman coding to take advantage of the different frequencies of occurence of byte sequences in the file.
		This algorithm may not be as easy to understand or as efficient as the LZW compression algorithm but Deflate does have the important advantage in that it is not patented.
		If you have any doubt that Lisp is a better language for writing bit level algorithms you need only compare the source for this version of the Inflate algorithm with the C version found in programs such as gzip.
	opensource.franz.com /deflate/index.html (377 words)

	Millau: a binary encoding format for XML documents
		The deflate algorithm [6] uses a combination of the LZ77 compression and the Huffman coding.
		If the algorithm is adaptive (as, for example, with LZ77), the algorithm slowly learns correlations between adjacent pairs of characters, then triples, quadruples and so on.
		The algorithm rarely has a chance to take advantage of longer range correlations before either the end of input is reached or the tables maintained by the algorithms are filled to capacity, specially with small files.
	www9.org /w9cdrom/154/154.html (10473 words)

	Re: compression methods
		LZW is the first efficient implementation of the LZ78 algorithm (published by Lempel and Ziv in 1978).
		This algorithm, called LZ77, was first published in 1977.
		Hence, the LZ78 algorithm was implemented years before the LZ77 algorithm...
	www.mail-archive.com /msx@stack.nl/msg05480.html (307 words)

	[No title]
		The LZJH algorithm was modified to compress a continuous stream of data for a modem environment and this modified version is the basis for Heath & Border Informational [Page 2] RFC 3051 IP Payload Compression Using ITU-T V.44 January 2001 Recommendation V.44.
		IPComp Association (IPCA) Parameters IKE [RFC2409] MAY be used to negotiate the use of the LZJH compression algorithm to establish an IPCA, as defined in [RFC2393].
		References [LZ77] Lempel, A., and Ziv, J., "A Universal Algorithm for Sequential Data Compression", IEEE Transactions On Information Theory, Vol.
	www.ietf.org /rfc/rfc3051.txt (1788 words)

	Flash Game Programming Wiki - LZ77 Compression for XML files (Site not responding. Last check: 2007-10-04)
		Either you want to have your XML files compressed for smaller size or just for the purpose that nobody can read the contents immediately, a XML compression routine is a useful option.
		The LZ77 compression algorithm is simple and fast enough so that ActionScript can handle it easily.
		There is a LZ77 compressor and decompression routine in AS1.0 written by Strille at www.strille.net/tutorials/FlashXMLCompressor/ but the compressor executable only works if you have the Microsoft.NET Framework v1.1 installed (it does not work with the new version 2.0).
	fgpwiki.corewatch.net /wiki/LZ77_Compression_for_XML_files (393 words)

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