Adaptive coding: Difference between revisions

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{{unreferencedMore citations needed|date=JuneMarch 2009|bot=yes2025}}

'''Adaptive coding''' refers to variants of [[entropy encoding]] methods of [[lossless data compression]].{{Citation needed|date=March 2025}} They are particularly suited to [[streaming data]], as they adapt to localized changes in the characteristics of the data,{{Citation needed|date=March 2025}} and don't require a first pass over the data to calculate a probability model.<ref name=":0">{{Cite book |last=Williams |first=Ross N. |url=https://www.google.com/books/edition/Adaptive_Data_Compression/lBY6CcXU59EC?hl=en&gbpv=1&pg=PR11&printsec=frontcover |title=Adaptive Data Compression |date=1991 |publisher=Springer Science & Business Media |isbn=978-0-7923-9085-5 |language=en}}</ref> The cost paid for these advantages is that the encoder and decoder must be more complex to keep their states synchronized, and more computational power is needed to keep adapting the encoder/decoder state.

Almost all [[data compression]] methods involve the use of a ''model'', a prediction of the composition of the data. When the data matches the prediction made by the model, the encoder can usually transmit the content of the data at a lower information cost, by making reference to the model.

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==Adaptive method==

The operating method of adaptive encoding algorithms is as follows:<ref name=":0" />

===Encoder===

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Adaptive image coding was used by the [[Cassini-Huygens]] craft to relay images from [[Saturn]]. Only about 5% of the images show any visual signs of damage. As the spacecraft has an error correcting [[Solid-state drive|Flash drive]] and long timeframes between image taking events, damaged images like this can be present. It is assumed that the number of damaged, but unrecoverable images from the Cassini mission is about 0.01% or less.{{Update inline|date=December 2019|reason=How many of the images were actually damaged, now that the mission has ended?}}

[[Image:Damaged N00153918.jpg|thumb|center|450px|The Cassini camera was pointing toward DIONE[[Dione (moon)|Dione]] at a distance of approximately 548,210 kilometers. The image was taken using the CL1 and CL2 filters on May 17, 2010.|alt=]]

=== Cassini Lossless Compression ===

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* Due to camera problems and the need to reduce file size, there is a slight modification to the image coding scheme so that each compressed line is effectively bandwidth limited on the number of bits available to encode it.

==References==

{{Reflist}}

{{Compression Methods}}

{{CCSDS}}

[[Category:Lossless compression algorithms]]

[[Category:Data compression]]