Gourt > Computers > Algorithms > Compression (5)
In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits (or other information-bearing units) than an unencoded representation would use through use of specific encoding schemes. For example, this article could be encoded with fewer bits if we accept the convention that the word "compression" be encoded as "comp". One popular instance of compression that many computer users are familiar with is the ZIP file format, which, as well as providing compression, acts as an archiver, storing many files in a single output file.
As is the case with any form of communication, compressed data communication only works when both the sender and receiver of the information understand the encoding scheme. For example, this text makes sense only if the receiver understands that it is intended to be interpreted as characters representing the English language. Similarly, compressed data can only be understood if the decoding method is known by the receiver. Some compression algorithms exploit this property in order to encrypt data during the compression process so that decompression can only be achieved by an authorized party (eg. through the use of a password).
Compression is possible because most real-world data has statistical redundancy. For example, the letter 'e' is much more common in English text than the letter 'z', and the probability that the letter 'q' will be followed by the letter 'z' is rather small. Lossless compression algorithms usually exploit statistical redundancy in such a way as to represent the sender's data more concisely, but nevertheless perfectly.
More on [ Data compression ]
GIF :: 2D
JPEG :: 2D
PNG :: 2D
MPEG :: Multimedia
Audio Formats :: Music and Audio
Data Compression :: Software
Coding Theory :: Communication Theory
Wavelets :: Numerical Analysis
Data Coding and Compression :: Image Processing
Data Deduplication, did you say 20% or 20 times? - InformationWeek
Tue, 20 May 2008 01:27:48 -0000
Data Deduplication, did you say 20% or 20 times?InformationWeek, NY - May 19, 2008Add onto that clever algorithms to decide what block size to use and you can imagine systems that yield wildly different data compression ratios. ...
Size matters: Yahoo claims 2-petabyte database is world's biggest ... - Computerworld
Thu, 22 May 2008 09:33:23 -0000
Size matters: Yahoo claims 2-petabyte database is world's biggest ...Computerworld, MA - 19 minutes agoYahoo brought the database in-house and continued to enhance it: tighter data compression, more parallel data processing, and more optimized queries. ...
Midmarket Gearing Up for WAN Compression - eWeek
Sat, 26 Apr 2008 19:03:49 -0000
Midmarket Gearing Up for WAN CompressioneWeek, NY - Apr 26, 2008The study showed 32 percent of the Fortune 1000 are currently using WAN data compression and acceleration technologies, while another 45 percent were ...
Data Domain Joins SNIA Europe - FOXBusiness
Tue, 20 May 2008 07:41:08 -0000
Data Domain Joins SNIA EuropeFOXBusiness - May 20, 2008Data Domain, the Data Domain logo and Global Compression are trademarks or registered trademarks of Data Domain, Inc. All other trademarks used or mentioned ...
A scientific first: A supernova explosion is observed in real time - Hindu
Thu, 22 May 2008 09:42:19 -0000
A scientific first: A supernova explosion is observed in real timeHindu, India - 10 minutes agoThis extreme compression is followed by a rebound, creating a shock wave that bounces off the surface of the newly-formed neutron star and rips through its ...
Compressing DNA sequence databases with coil - 7thSpace Interactive (press release)
Tue, 20 May 2008 05:13:17 -0000
Compressing DNA sequence databases with coil7thSpace Interactive (press release), NY - May 19, 2008Currently, sequence data is usually kept in large "flat files," which are then compressed using standard Lempel-Ziv (gzip) compression - an approach which ...
3D Graphics Compression Homepage - A directory of 3D graphics compression information, researchers, and commercial products on the web.
ACM Crossroads Data Compression Issue - Data Compression issue of ACM Crossroads, the student magazine of the Association for Computing Machinery.
Meta Description: [ ACM Crossroads 6.3: Data Compression ]
Arturo Campos: Compression Programming - Articles on various compression algorithms.
Meta Description: [ The home of Arturo Campos, student and programmer interested
in data compression, not only programming, but also writing articles. ]
comp.compression Frequently Asked Questions - List from Usenet.
Compression - Computing Reference - Explanation of compression and various compression schemes at eLook Computing Reference.
Meta Description: [ Information and links on Compression ]
Compression via Arithmetic Coding in Java - Unrestricted open-source Java implementation of the PPM (prediction by partial matching) algorithm for text and data compression by Bob Carpenter. Builds with ant.
Data Compression - From PC Webopedia definition and links.
Meta Description: [ This page describes the term data compression and lists other pages on the Web where you can find additional information. ]
Data Compression Reference Center - Basic facts, algorithms, hardware, links, and a glossary.
Data-Compression.com - A website devoted to the principles and practice of data compression.
DataCompression.info - Directory of data compression sites. Allows user to rate the listed sites.
Meta Description: [ DataCompression.info is a comprehensive
set of links to resources on the Internet related to Data Compression. These
include web pages, source code, papers, newsgroup posts, books, and more.
Compression topics covered here include Huffman and arithmetic coding, LZ77,
LZ78, LZW, LZSS and variants... ]
Dr Ross's Compression Crypt - LZRW* text compression algorithms. Links to other compression sites.
Meta Description: [ Dr Ross's Compression crypt contains compression algorithms
by Ross Williams, and other information about compression. ]
Groovyweb Compression Tutorials - Compression tutorials, links to other compression sites and compression downloads.
How Stuff Works: How File Compression Works - Detailed narrative fully describes how a file is actually deflated, or compressed to get rid of redundancy - and save space.
Meta Description: [ File compression allows users to make one or more files into a smaller zip file. Learn about file compression, zip files and compression algorithms. ]
Lossless Image Compression with Switched Linear Prediction - By Shinji Wakasugi. A simple method for lossless image compression using switched linear prediction. Report in PDF with code in C.
Meta Description: [ A simple method for lossless image compression ]
MacKiDo - Provides brief overview of shape compression, run-length encoding, and Lempel-Ziv.
Mitsuharu Arimura's Data Compression Pointers - Very large list of links, including books and lecture notes, benchmarkings, archives, image/graphic compression, fractal compression, wavelets, video and audio compression, and links to other link lists.
PKZIP Application Note - Describes the compression and decompression algorithms used by PKZIP.
Meta Description: [ PKWARE, Inc. - Data Security and File Compression Solutions for Home and Enterprise Users, In order to ensure the continued interoperability of the .ZIP file format for all users, PKWARE publishes an Application Note on the .ZIP file format . The APPNOTE provides developers a general description ... ]
Practical Huffman Coding - A tutorial by Michael Schindler.
Meta Description: [ This page gives hints for
efficient huffman codings from practical view. Most of this stuff
you will not find in textbooks ]
SPIHT - The Set Partitioning In Hierarchical Trees algorithm for image and video compression. Documentation and resources.
The Art of Lossless Data Compression - Results of tests performed to compare lossless compression of various data by all known good enough programs. Descriptions of test terms and files. Links to related programs, and pages.
The Canterbury Corpus - A set of benchmark results for various lossless compression methods. Includes test files and compression test results for many research compression methods.
The Data Compression Resource - Algorithms, links, comparisons, conferences, corpora and the home of the compressor ABC.
Meta Description: [ The central resource for data compression with informations and links to algorithms, corpora, comparisons, the compressor ABC, books and conferences. ]
The LBE Data Compression Algorithm - A Huffman like algorithm that uses triangular matrices, rather than binary trees, for string substitution. Free source code available.
Tutorial on Image Compression - A tutorial on Image Compression, with step by step procedural examples and list of references, along with sample code.
Vcodex - Video and image coding tutorials, links, resources and research.
Meta Description: [ image and video coding research, consultancy and analysis ]
| SmartLearn - How To Use File Compression Features In Win XP |
