Coding theory: Difference between revisions

Revision as of 07:11, 14 February 2006

Revision as of 14:11, 17 February 2006

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== Source encoding ==

The aim of source encoding is to take the source data and make it smaller. FAX transmission which has been around for many years uses a simple run length code. The principle is to recognize that most documents are white space with brief interruptions for the black typing. So FAX compresses a document by adding a repeat count to the next transition. It may tell the receiver that 100 of the next pixels are white. Another common encoding technique is string compression. This is used for data files. The encoder has a dictionary of strings. It matches the incoming text to the strings in the dictionary and when found, it will send a single number to the receiver which is the index to the string. All knowknown implementations of string compression are adaptive in nature and allow the encoder to create new strings and transmit them to the decoder so the two dictionaries remain the same.

== Channel encoding ==