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[Note: the appropriate group for discussing software patents is comp.patents or misc.legal.computing, not comp.compression.] Only a very small subset of all patents on data compression are mentioned here; there are several hundred patents on lossless data compression alone. All patents mentioned here are US patents, and thus probably not applicable outside the US. The abstracts and claims of all recent US patents can be obtained from http://patent.womplex.ibm.com/ See item 70, "Introduction to data compression" for the meaning of LZ77, LZ78 or LZW. (a) Run length encoding - Tsukiyama has two patents on run length encoding: 4,586,027 and 4,872,009 granted in 1986 and 1989 respectively. The first one covers run length encoding in its most primitive form: a length byte followed by the repeated byte. The second patent covers the 'invention' of limiting the run length to 16 bytes and thus the encoding of the length on 4 bits. Here is the start of claim 1 of patent 4,872,009, just for pleasure: 1. A method of transforming an input data string comprising a plurality of data bytes, said plurality including portions of a plurality of consecutive data bytes identical to one another, wherein said data bytes may be of a plurality of types, each type representing different information, said method comprising the steps of: [...] - O'Brien has patented (4,988,998) run length encoding followed by LZ77. (b) LZ77 - Waterworth patented (4,701,745) the algorithm now known as LZRW1, because Ross Williams reinvented it later and posted it on comp.compression on April 22, 1991. (See item 5 for the ftp site with all LZRW derivatives.) The *same* algorithm has later been patented by Gibson & Graybill (see below). 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. The Waterworth patent is now owned by Stac Inc, which won a lawsuit against Microsoft, concerning the compression feature of MSDOS 6.0. Damages awarded were $120 million. (Microsoft and Stac later settled out of court.) - Fiala and Greene obtained in 1990 a patent (4,906,991) on all implementations of LZ77 using a tree data structure. Claim 1 of the patent is much broader than the algorithms published by Fiala and Greene in Comm.ACM, April 89. The patent covers the algorithm published by Rodeh and Pratt in 1981 (J. of the ACM, vol 28, no 1, pp 16-24). It also covers the algorithms used in lharc, lha and zoo. - Notenboom (from Microsoft) 4,955,066 uses three levels of compression, starting with run length encoding. - The Gibson & Graybill patent 5,049,881 covers the LZRW1 algorithm previously patented by Waterworth and reinvented by Ross Williams. Claims 4 and 12 are very general and could be interpreted as applying to any LZ algorithm using hashing (including all variants of LZ78): 4. A compression method for compressing a stream of input data into a compressed stream of output data based on a minimum number of characters in each input data string to be compressed, said compression method comprising the creation of a hash table, hashing each occurrence of a string of input data and subsequently searching for identical strings of input data and if such an identical string of input data is located whose string size is at least equal to the minimum compression size selected, compressing the second and all subsequent occurrences of such identical string of data, if a string of data is located which does not match to a previously compressed string of data, storing such data as uncompressed data, and for each input strings after each hash is used to find a possible previous match location of the string, the location of the string is stored in the hash table, thereby using the previously processed data to act as a compression dictionary. Claim 12 is identical, with 'method' replaced with 'apparatus'. Since the 'minimal compression size' can be as small as 2, the claim could cover any dictionary technique of the LZ family. However the text of the patent and the other claims make clear that the patent should cover the LZRW1 algorithm only. (In any case the Gibson & Graybill patent is likely to be invalid because of the prior art in the Waterworth patent.) - 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. - IBM patented (5,001,478) the idea of combining a history buffer (the LZ77 technique) and a lexicon (as in LZ78). - Stac Inc patented (5,016,009 and 5,126,739) yet another variation of LZ77 with hashing. The '009 patent was used in the lawsuit against Microsoft (see above). Stac also has a patent on LZ77 with parallel lookup in hardware (5,003,307). - Robert Jung, author of 'arj', has been granted patent 5,140,321 for one variation of LZ77 with hashing. This patent is very close to the LZRW3-A algorithm, also previously discovered by Ross Williams. LZRW3-A was posted on comp.compression on July 15, 1991. The patent was filed two months later on Sept 4, 1991. Microsoft has patented a similar idea (two level table with pseudo-LRU managment of slots inside the level-2 table) in 5,455,577 (filed in 1993). - Chambers 5,155,484 is yet another variation of LZ77 with hashing. The hash function is just the juxtaposition of two input bytes, this is the 'invention' being patented. The hash table is named 'direct lookup table'. (c) LZ78 - One form of the original LZ78 algorithm was patented (4,464,650) by its authors Lempel, Ziv, Cohn and Eastman. This patent is owned by Unisys. - The LZW algorithm used in 'compress' is patented by IBM (4,814,746) and Unisys (4,558,302). It is also used in the V.42bis compression standard (see question 11 on V.42bis below), in Postscript Level 2, in GIF and TIFF. Unisys sells the license to modem manufacturers for a onetime fee (contact: Welch Patent Desk, Unisys Corp., P.O. Box 500, Bluebell, PA 19424 Mailcode C SW 19). CompuServe is licensing the usage of LZW in GIF products for 1.5% of the product price, of which 1% goes to Unisys; usage of LZW in non-GIF products must be licensed directly from Unisys. For more information, see http://www.unisys.com/ or email to email@example.com. The IBM patent application was first filed three weeks before that of Unisys, but the US patent office failed to recognize that they covered the same algorithm. (The IBM patent is more general, but its claim 7 is exactly LZW.) - Klaus Holtz also claims that patent 4,366,551 for his "autosophy" data compression method covers LZ78 and LZW. According to Holtz, most of the largest V.42bis modem manufacturers have paid for patent licenses. - AP coding is patented by Storer (4,876,541). (Get the yabba package for source code, see question 2 above, file type .Y) Storer also claims that his patent covers V.42bis. (d) arithmetic coding - IBM holds many patents on arithmetic coding (4,122,440 4,286,256 4,295,125 4,463,342 4,467,317 4,633,490 4,652,856 4,792,954 4,891,643 4,901,363 4,905,297 4,933,883 4,935,882 5,045,852 5,099,440 5,142,283 5,210,536 5,414,423 5,546,080). It has patented in particular the Q-coder implementation of arithmetic coding. The JBIG standard, and the arithmetic coding option of the JPEG standard requires use of the patented algorithm. No JPEG-compatible method is possible without infringing the patent, because what IBM actually claims rights to is the underlying probability model (the heart of an arithmetic coder). (See item 75 for details.) See also below details on many other patents on arithmetic coding (4,973,961 4,989,000 5,023,611 5,025,258 5,272,478 5,307,062 5,309,381 5,311,177 5,363,099 5,404,140 5,406,282 5,418,532). The list is not exhaustive. (e) predictor - The 'predictor' algorithm was first described in the paper Raita, T. and Teuhola, J. (1987), "Predictive text compression by hashing", ACM Conference on Information Retrieval This algorithm has been patented (5,229,768) by K. Thomas in 1993. It is used in the Internet Draft "PPP Predictor Compression Protocol" (see ftp://venera.isi.edu/internet-drafts/). (f) compression of random data - The US patent office no longer grants patents on perpetual motion machines, but has recently granted a patent on a mathematically impossible process (compression of truly random data): 5,533,051 "Method for Data Compression". See item 9.5 of this FAQ for details. As can be seen from the above list, some of the most popular compression programs (compress, pkzip, zoo, lha, arj) are now covered by patents. (This says nothing about the validity of these patents.) Here are some references on data compression patents. Some of them are taken from the list ftp://prep.ai.mit.edu/pub/lpf/patent-list. 3,914,586 Data compression method and apparatus filed 10/25/73, granted 10/21/75 General Motors Corporation, Detroit MI Duane E. McIntosh, Santa Ynez CA Data compression apparatus is disclosed is operable in either a bit pair coding mode of a word coding mode depending on the degree of redundancy of the data to be encoded. 3,976,844 Data communication system for transmitting data in compressed form filed Apr. 4, 1975, granted Aug. 24, 1976 inventor Bernard K. Betz, assignee Honeywell Information Systems, Inc. [encode differences with previous line] 4,021,782 Data compaction system and apparatus inventor Hoerning filed 04/30/1975, granted 05/03/1977 [A primitive form of LZ77 with implicit offsets (compare with previous record)] 4,054,951 Data expansion apparatus inventor R.D. Jackson, assignee IBM filed Jun. 30, 1976, granted Oct. 18, 1977 [Covers only decompression of data compressed with a variant of LZ77.] 4,087,788 Data compression system filed 1/14/77, granted 5/2/78 NCR Canada LTD - NCR Canada Ltee, Mississauga CA Brian J. Johannesson, Waterloo CA A data compression system is disclosed in which the left hand boundary of a character is developed in the form of a sequence of Freeman direction codes, the codes being stored in digital form within a processor. 4,122,440 Method and means for arithmetic string coding assignee IBM filed 1977/03/04, granted 1978/10/24 [This is the basic idea of arithmetic coding. Note that the patent is expired now.] 4,286,256 Method and means for arithmetic coding using a reduced number of operations. granted Aug 25, 1981 assignee IBM 4,295,125 A method and means for pipeline decoding of the high to low order pairwise combined digits of a decodable set of relatively shifted finite number of strings granted Oct 13, 1981 assignee IBM 4,366,551 Associative Memory Search System filed June 16, 1975, granted Dec. 28, 1982. inventor Klaus Holtz, assignee Omni Dimensional Networks. 4,412,306 System for minimizing space requirements for storage and transmission of digital signals filed May 14, 1981, granted Oct. 25, 1983 inventor Edward W. Moll 4,463,342 A method and means for carry-over control in a high order to low order combining of digits of a decodable set of relatively shifted finite number strings. granted Jul 31, 1984 assignee IBM 4,491,934 Data compression process filed May 12, 1982, granted Jan. 1, 1985 inventor Karl E. Heinz 4,464,650 Apparatus and method for compressing data signals and restoring the compressed data signals inventors Lempel, Ziv, Cohn, Eastman assignee Sperry Corporation (now Unisys) filed 8/10/81, granted 8/7/84 A compressor parses the input data stream into segments where each segment comprises a prefix and the next symbol in the data stream following the prefix. [This is the original LZ78 algorithm.] 4,467,317 High-speed arithmetic compression using using concurrent value updating. granted Aug 21, 1984 assignee IBM 4,494,108 Adaptive source modeling for data file compression within bounded memory filed Jun. 5, 1984, granted Jan. 15, 1985 invntors Glen G. Langdon, Jorma J. Rissanen assignee IBM order 1 Markov modeling 4,558,302 High speed data compression and decompression apparatus and method inventor Welch assignee Sperry Corporation (now Unisys) filed 6/20/83, granted 12/10/85 re-examined: filed 12/14/92, granted 4/1/94. The text of the original 1985 patent can be ftped from ftp://ftp.uni-stuttgart.de/pub/doc/comp-patents/US4558302.Z There is also a European Patent 0,129,439 1/2/89 for DE, FR, GB, IT and patent pending for Japan. 4,560,976 Data compression filed 6/5/84, granted 12/24/85 Codex Corporation, Mansfield MA Steven G. Finn, Framingham, MA A stream of source characters, which occur with varying relative frequencies, is encoded into a compressed stream of codewords, each having one, two or three subwords, by ranking the source characters by their current frequency of appearance, encoding the source characters having ranks no higher than a first number as one subword codewords, source characters having ranks higher than the first number but no higher than a second number as two subword codewords, and the remaining source characters as three subword codewords. 4,586,027 Method and system for data compression and restoration inventor Tsukimaya et al. assignee Hitachi filed 08/07/84, granted 04/29/86 patents run length encoding 4,597,057 System for compressed storate of 8-bit ascii bytes using coded strings of 4-bit nibbles. inventor Snow, assignee System Development corporation. filed 12/31/1981, granted 06/24/1986. Compression using static dictionary of common words, prefixes and suffixes. 4,612,532 Data compression apparatus and method inventor Bacon, assignee Telebyte Corportion filed Jun. 19, 1984, granted Sep. 16, 1986 [Uses followsets as in the pkzip 0.92 'reduce' algorithm, but the followsets are dynamically updated. This is in effect a sort of order-1 Markov modeling.] 4,622,545 Method and apparatus for image compression and Manipulation inventor William D. Atkinson assignee Apple computer Inc. filed 9/30/82 granted 11/11/86 4,633,490 Symmetrical adaptive data compression/decompression system. granted Dec 30, 1985 assignee IBM 4,652,856 A multiplication-free multi-alphabet arithmetic code. granted Feb 4, 1986 assignee IBM 4,667,649 Data receiving apparatus filed 4/18/84, granted 6/30/87 inventors Kunishi et al. assignee Canon Kabushiki Kaisha, Tokyo Japan compression of Fax images. 4,682,150 Data compression method and apparatus inventors Mathes and Protheroe, assignee NCR Corporation, Dayton OH A system and apparatus for compressing redundant and nonredundant binary data generated as part of an operation of a time and attendance terminal in which the data represents the time an employee is present during working hours. 4,701,745 Data compression system inventor Waterworth John R assignee Ferranti PLC GB, patent rights now acquired by Stac Inc. filed 03/03/1986 (03/06/1985 in GB), granted 10/20/1987 Algorithm now known as LZRW1 (see above) I claim: 1. A data compression system comprising an input store for receiving and storing a plurality of bytes of uncompressed data from an outside source, and data processing means for processing successive bytes of data from the input store; the data processing means including circuit means operable to check whether a sequence of successive bytes to be processed identical with a sequence of bytes already processed, and including hash generating means responsive to the application of a predetermined number of bytes in sequence to derive a hash code appropriate to those bytes, a temporary store in which the hash code may represent the address of a storage location, and a pointer counter operable to store in the temporary store at said address a pointer indicative of the position in the input store of one of the predetermined number of bytes; output means operable to apply to a transfer medium each byte of data not forming part of such an identical sequence; and encoding means responsive to the identification of such a sequence to apply to the transfer medium an identification signal which identifies both the location in the input store of the previous occurrence of the sequence of bytes and the number of bytes contained in the sequence. 4,730,348 Adaptive data compression system inventor MacCrisken, assignee Adaptive Computer Technologies filed Sep. 19, 1986, granted Mar. 8, 1988 [order-1 Markov modeling + Huffman coding + LZ77] 4,758,899 Data compression control device inventor Tsukiyama, assignee Hitachi filed 11/20/1985, granted 07/19/1988 Limits compression to ensure that tape drive stays busy. 4,792,954 Concurrent detection of errors in arithmetic data compression coding assignee IBM filed 1986/10/31, granted 1988/12/20 4,809,350 Data compression system filed Jan. 30, 1987, granted Feb. 28, 1989 inventor Yair Shimoni & Ron Niv assignee Elscint Ltd., Haifa, Israel [Image compression via variable length encoding of differences with predicted data.] 4,814,746 Data compression method inventors Victor S. Miller, Mark N. Wegman assignee IBM filed 8/11/86, granted 3/21/89 A previous application was filed on 6/1/83, three weeks before the application by Welch (4,558,302) Communications between a Host Computing System and a number of remote terminals is enhanced by a data compression method which modifies the data compression method of Lempel and Ziv by addition of new character and new string extensions to improve the compression ratio, and deletion of a least recently used routine to limit the encoding tables to a fixed size to significantly improve data transmission efficiency. 4,841,092 continued in 5,003,307 4,853,696 Code converter for data compression/decompression filed 4/13/87, granted 8/1/89 inventor Amar Mukherjee, Maitland FL assignee University of Central Florida, Orlando FL Another hardware Huffman encoder: A code converter has a network of logic circuits connected in reverse binary tree fashion with logic paths between leaf nodes and a common root node. 4,872,009 Method and apparatus for data compression and restoration inventor Tsukimaya et al. assignee Hitachi filed 12/07/87, granted 10/03/89 This patent on run length encoding covers the 'invention' of limiting the run length to 16 bytes and thus the encoding of the length on 4 bits. 4,876,541 Stem [sic] for dynamically compressing and decompressing electronic data filed 10/15/87, granted 10/24/89 inventor James A. Storer assignee Data Compression Corporation A data compression system for encoding and decoding textual data, including an encoder for encoding the data and for a decoder for decoding the encoded data. 4,891,643 Arithmetic coding data compression/de-compression by selectively employed, diverse arithmetic encoders and decoders. file 1986/09/15, granted 1990/01/02 assignee IBM 4,901,363 System for compressing bi-level data assignee IBM [arithmetic coding] 4,905,297 Arithmetic coding encoder and decoder system. granted Feb 27, 1990 assignee IBM 4,906,991 Textual substitution data compression with finite length search window filed 4/29/1988, granted 3/6/1990 inventors Fiala,E.R., and Greene,D.H. assignee Xerox Corporation extended in 5,058,144 4,933,883 Probability adaptation for arithmetic coders. granted Jun 12, 1990 assignee IBM 4,935,882 Probability adaptation for arithmetic coders. granted Jun 19, 1990 assignee IBM 4,941,193 Barnsley, fractal compression. 4,943,869 Compression Method for Dot Image Data filed 1988-05-04, granted 1990-07-24 assignee Fuji Photo Film Co. Lossy and lossless image compression schemes. 4,955,066 Compressing and Decompressing Text Files filed 10/13/89, granted 09/04/90 inventor Notenboom, L.A. assignee Microsoft Now extended as 5,109,433 [Noted in signon screen of Word 5.5 and on the outside of the MS-DOS 5.0 Upgrade.] A method of compressing a text file in digital form is disclosed. A full text file having characters formed into phrases is provided by an author. The characters are digitally represented by bytes. A first pass compression is sequentially followed by a second pass compression of the text which has previously been compressed. A third or fourth level of compression is serially performed on the compressed text. For example, in a first pass, the text is run-length compressed. In a second pass, the compressed text is further compressed with key phrase compression. In a third pass, the compressed text is further compressed with Huffman compression. The compressed text is stored in a text file having a Huffman decode tree, a key phrase table, and a topic index. The data is decompressed in a single pass and provided one line at a time as an output. Sequential compressing of the text minimizes the storage space required for the file. Decompressing of the text is performed in a single pass. As a complete line is decompressed, it is output rapidly, providing full text to the user. 4,973,961 Method and apparatus for carry-over control in arithmetic coding. granted Nov 27, 1990 assignee AT&T 4,988,998 Data compression system for successively applying at least two data compression methods to an input data stream. inventor O'Brien assignee Storage Technology Corporation, Louisville, Colorado filed Sep 5, 1989, granted Jan 29, 1991. Run length encoding followed by LZ77. 4,989,000 Data string compression using arithmetic encoding with simplified probability subinterval estimation filed 1989/06/19, granted 1991/01/29] [shift & add instead of multiply] 5,001,478 Method of Encoding Compressed Data filed 12/28/89, granted 03/19/91 inventor Michael E. Nagy assignee IBM 1. A method of encoding a compressed data stream made up of a sequence of literal references, lexicon references and history references, which comprises the steps of: assigning to each literal reference a literal identifier; assigning to each history reference a history identifier; assigning to each lexicon reference a lexicon identifier; and emitting a data stream with said identifiers assigned to said references. Gordon Irlam <firstname.lastname@example.org> says: The invention can probably be best understood by considering the decompressor. It consists of a history buffer, and a lexicon buffer, both of which are initially empty. The history buffer contains the last n symbols emitted. Whenever a history buffer reference is to be output the string so referenced is subsequently moved to the lexicon buffer for future reference. Thus the history buffer keeps track of strings that may be repeated on a very short term basis, while the lexicon buffer stores items for a longer time. Furthermore a history reference involves specifying both the offset and length within the history buffer, whereas a lexicon reference simply specifies a number denoting the string. Both buffers have a finite size. 5,003,307 Data compression apparatus with shift register search means filed Oct. 6, 1989, granted Mar. 26, 1991 inventors George Glen A, Ivey Glen E, Whiting Douglas L assignee Stac Inc continuation of 4,841,092 5,016,009 Data compression apparatus and method filed 01/13/1989, granted 05/14/1991 inventors George Glen A, Ivey Glen E, Whiting Douglas L assignee Stac Inc LZ77 with offset hash table (extended in 5,126,739) 5,023,611 Entropy encoder/decoder including a context extractor. granted Jun 11, 1991 assignee AT&T 5,025,258 Adaptive probability estimator for entropy encoder/decoder. granted Jun 18, 1991 assignee AT&T 5,045,852 Dynamic model selection during data compression assignee IBM [arithmetic coding] 5,049,881 Apparatus and method for very high data rate-compression incorporating lossless data compression and expansion utilizing a hashing technique inventors Dean K. Gibson, Mark D. Graybill assignee Intersecting Concepts, Inc. filed 6/18/90, granted 9/17/91 [covers lzrw1, almost identical with Waterworth 4,701,745] 5,051,745 String searcher, and compressor using same filed 8/21/90, granted 9/24/91 inventor Phillip W. Katz (author of pkzip) In the string search method and apparatus pointers to the string to be searched are indexed via a hashing function and organized according to the hashing values of the string elements pointed to. The hashing function is also run on the string desired to be found, and the resulting hashing value is used to access the index. If the resulting hashing value is not in the index, it is known that the target string does not appear in the string being searched. Otherwise the index is used to determine the pointers which correspond to the target hashing value, these pointers pointing to likely candidates for matching the target string. The pointers are then used to sequentially compare each of the locations in the string being searched to the target string, to determine whether each location contains a match to the target string. In the method and apparatus for compressing a stream of data symbols, a fixed length search window, comprising a predetermined contiguous portion of the symbol stream, is selected as the string to be searched by the string searcher. If a string to be compressed is found in the symbol stream, a code is output designating the location within the search window of the matching string and the length of the matching string. 5,065,447 (continued in 5,347,600) Method and apparatus for processing digital data filed Jul. 5, 1989, granted Nov. 12, 1991 inventors Michael F. Barnsley and Alan D. Sloan [Patents image compression with the "Fractal Transform"] 5,099,440 Probability adaptation for arithmetic coders 5,109,433 Compressing and decompressing text files inventor Notenboom assignee Microsoft extension of 4,955,066 5,126,739 Data Compression Apparatus and Method filed Nov. 27, 1990, granted June 30, 1992. inventor Whiting et. al assignee Stac Inc LZ77 with offset hash table (extension of 5,016,009) 5,140,321 Data compression/decompression method and apparatus filed 9/4/91, granted 8/18/92 inventor Robert Jung assignee Prime Computer 5,142,283 Arithmetic compression coding using interpolation for ambiguous symbols filed 1990/07/10, granted 1992/08/25 assignee IBM 5,155,484 Fast data compressor with direct lookup table indexing into history buffer filed 9/13/1991, granted 10/13/1992 inventor Chambers, IV, Lloyd L., Menlo Park, California assignee Salient Software, Inc., Palo Alto, California (02) Uses a 64K hash table indexed by the first two characters of the input string. Includes several claims on the LZ77 file format (literal or pair offset,length). 5,179,378 file Jul. 30, 1991, granted Jan. 12, 1993 inventor Ranganathan assignee University of South Florida Method and apparatus for the compression and decompression of data using Lempel-Ziv based techniques. [This covers LZ77 hardware compression with a systolic array of processors working in parallel.] 5,210,536 Data compression/coding method and device for implementing said method assignee IBM [PPM + arithmetic coding] 5,229,768 Adaptive data compression system granted Jul. 20, 1993 inventor Kasman E. Thomas assignee Traveling Software, Inc. A system for data compression and decompression is disclosed. A series of fixed length overlapping segments, called hash strings, are formed from an input data sequence. A retrieved character is the next character in the input data sequence after a particular hash string. A hash function relates a particular hash string to a unique address in a look-up table (LUT). An associated character for the particular hash string is stored in the LUT at the address. When a particular hash string is considered, the content of the LUT address associated with the hash string is checked to determine whether the associated character matches the retrieved character following the hash string. If there is a match, a Boolean TRUE is output; if there is no match, a Boolean FALSE along with the retrieved character is output. Furthermore, if there is no match, then the LUT is updated by replacing the associated character in the LUT with the retrieved character. [...] [This algorithm is used in the Internet draft "PPP Predictor Compression Protocol".] 5,272,478 Method and apparatus for entropy coding assignee Ricoh [arithmetic coding with finite state machine] 5,307,062 Coding system filed 1992/12/15, granted 1994/04/26 assignee Mitsubishi [binary arithmetic coding, see also 5,404,140] 5,309,381 Probability estimation table apparatus filed 1992/04/08, granted 1994/05/03 assignee Ricoh [arithmetic coding] 5,311,177 Code transmitting apparatus with limited carry propagation filed 1992/06/19, granted 1994/05/10 assignee Mitsubishi [arithmetic coding] 5,347,600 (continuation of 5,065,447) Method and apparatus for compression and decompression of digital image filed 10/23/1991, granted 09/13/1994 inventors Barnsley and Sloan 5,363,099 Method and apparatus for entropy coding [arithmetic coding with state machine] 5,384,867 (continued in 5,430,812) filed 10/23/1991, granted 01/24/1995 Fractal transform compression board inventors Barnsley et al. 5,404,140 Coding system filed 1994/01/13, granted 1995/04/04 assignee Mitsubishi [binary arithmetic coding, see also 5,307,062] 5,406,282 Data coding and decoding with improved efficiency assignee Ricoh [PPM & arithmedic coding] 5,414,423 Stabilization of probability estimates by conditioning on prior decisions of a given context assignee IBM arithmetic coding] 5,416,856 Method of encoding a digital image using iterated image transformations to form an eventually contractive map filed 1992/03/30, granted 1995/05/16 inventors Jacobs, Boss and Fisher 5,418,532 Method and system for efficient, multiplication-free arithmetic coding filed 1993/05/13, granted 1995/05/23. inventors Lei & Shaw-Min assignee Bell Communications Research, Inc. (Livingston, NJ). 5,430,812 (continuation of 5,384,867) Fractal transform compression board filed 1994/05/18, granted 1995/07/04 inventors Barnsley et al. 5,455,577 Method and system for data compression filed 1993/03/12, granted 1995/10/03 inventors Slivka & Rashid, assignee Microsoft LZ77 with two-level search data structure 5,533,051 Method for Data Compression filed 1993/03/12, granted 1996/07/02 inventor David C. James, assignee The James Group This is a patent on compression of random data, see item 9.5 below. Japan 2-46275 Coding system granted Feb 26, 1990 [Patents one form of arithmetic coding.]
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