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


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Irrelevance Reduction


If a higher compression rate is required than achievable by redundancy reduction, a decrease in quality cannot be avoided. Appropriate technologies are available especially for graphic, audio or video coding. The main characteristic of those technologies is the attempt to evaluate the relevance of a particular part of the contents. In a step by step process the most irrelevant parts will be removed. With a higher compression rate more and more relvant contents will be lost.


Irrelvance reduction is not reversible because information will be lost during the encoding process. According to the particular technology encoding and decoding cycles cannot be repeated frequently because compression artefacts could be accumulated.


Most of the technologies belonging to irrelevance reduction as MPEG or JPEG also use methods of redundancy reduction. But the main characteristics are driven by their internal basic algorithms like DCT.


Examples for corresponding formats:

mpeg - jpeg - mjpeg - fif - png - AC-3


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Survey Basic Terms Redundancy Reduction Entropy Coding