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It is insufficiently considered that men more often require to be reminded than informed. Samuel Johnson This file is part 1 of a set of Frequently Asked Questions (FAQ) for the groups comp.compression and comp.compression.research. If you can't find part 2 or 3, see item 53 below. A copy of this FAQ is available by ftp in ftp://rtfm.mit.edu/pub/usenet/news.answers/compression-faq/ files part1 to part3. This FAQ is also accessible in the World Wide Web at http://www.faqs.org/faqs/compression-faq/part1/preamble.html or http://www.cis.ohio-state.edu/hypertext/faq/usenet/compression-faq/top.html Certain questions get asked time and again, and this is an attempt to reduce the bandwidth taken up by these posts and their associated replies. If you have a question, *please* check this file before you post. It may save a lot of peoples time. If you have not already read the overall Usenet introductory material posted to "news.announce.newusers", please do. It is also available by ftp in ftp://garbo.uwasa.fi/pc/doc-net/usenews.zip (see item 2 below about .zip). If you don't want to see this FAQ regularly, please add the subject line to your kill file. If you don't know what a kill file is, get by ftp the file ftp://rtfm.mit.edu/pub/usenet/news.answers/killfile-faq If you have corrections or suggestions for this FAQ, send them to Jean-loup Gailly <jloup at gzip.org>. (Replace " at " with "@". This is a protection against junk mail. Sorry for the inconvenience.) Part 1 is oriented towards practical usage of compression programs. Part 2 is more intended for people who want to know how compression works. Part 3 is a long (but somewhat obsolete) list of image compression hardware. Main changes relative to the previous version: - LZO page moved [item 2] - new url for the File Format Collection [items 2 & 54] - new url for ACE [item 2] - new pkzip version [item 3] - fixed url for arithmetic coder [item 13] - add url for DjVu, an image compression library [item 15] - remove obsolete link [item 15] - new url for DCT algorithms [item 15] - add url for lossless image compression benchmarks [item 16] - added urls for the MP3 audio compression standard, and for benchmarks of lossless audio compression programs [item 26] Contents ======== General questions:  What are these newsgroups about?  What is this .xxx file type? Where can I find the corresponding compression program?  What is the latest pkzip version?  What is an archiver?  What is the best general purpose compression program?  Which books should I read?  What about patents on data compression algorithms?  Compression of random data (WEB, Gilbert and others)  Fake compression programs (OWS, WIC)  What is the V.42bis standard?  I need source for the winners of the Dr Dobbs compression contest  I need source for arithmetic coding Image and audio compression:  Where can I get image compression programs?  What is the state of the art in lossless image compression?  What is the state of fractal compression?  I need specs and source for TIFF and CCITT group 4 Fax.  What is JPEG?  I am looking for source of an H.261/H.263 codec and MPEG  Fast DCT (Discrete Cosine Transform) algorithms  Are there algorithms and standards for audio compression? Common problems:  My archive is corrupted!  pkunzip reports a CRC error!  VMS zip is not compatible with pkzip!  I have a problem with Stacker or DoubleSpace! Questions which do not really belong to comp.compression:  What is this 'tar' compression program?  I need a CRC algorithm  What about those people who continue to ask frequently asked questions?  Where are FAQ lists archived?  I need specs for graphics formats  Where can I find Lenna and other images?  I am looking for a message digest algorithm  I have lost my password on a .zip file Part 2: (Long) introductions to data compression techniques  Introduction to data compression (long) Huffman and Related Compression Techniques Arithmetic Coding Substitutional Compressors The LZ78 family of compressors The LZ77 family of compressors  Introduction to MPEG (long) What is MPEG? Does it have anything to do with JPEG? Then what's JBIG and MHEG? What has MPEG accomplished? So how does MPEG I work? What about the audio compression? So how much does it compress? What's phase II? When will all this be finished? How do I join MPEG? How do I get the documents, like the MPEG I draft?  What is wavelet theory?  What is the theoretical compression limit?  Introduction to JBIG  Introduction to JPEG  What is Vector Quantization?  Introduction to Fractal compression  The Burrows-Wheeler block sorting algorithm Part 3: (Long) list of image compression hardware  Image compression hardware  Acknowledgments Search for "Subject: [#]" to get to question number # quickly. Some news readers can also take advantage of the message digest format used here. If you know very little about data compression, read question 70 in part 2 first.