Data Compression


Criteria

Survey Formats

Basics

Basic Terms

Symbol

Set of Symbols

Alphabet

Code

Coding

Redundancy

Information Theory

Message

Probability

Information

Entropy

Redundancy Reduction

Irrelevance Reduction

Entropy Coding

Variable Length Codes

Code Trees

Compression Methods

Data Formats


Glossary

Index


Download


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Redundancy Reduction


Compression procedures intended for redundancy reduction try to adapt the internal data structure without affecting information or contents respectively. Original data will be transformed into a more efficient form to enable better usage of resources. Procedures belonging to this category are totally reversible. After decoding data will be obtained back without any difference to the original ones.


The focal point of this technology is file compression for data transfer or archiving purposes, e.g. for downloads. In this field the most important format is ZIP.


Synonymously entropy coding is in use for redundancy reduction. Strictly speaking the term entropy focusses on a smaller range of procedures. Normally it will be used for Huffman, Shannon Fano or arithmetic coding.


Examples for corresponding file formats:

zip - arj - sit - rar - tar - uc - lha - lzh


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Survey Basic Terms Diagram: Entropy of a binary Information Source Irrelevance Reduction