Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Adaptive coding
open-in-new
<h2 id="adaptive-method">Adaptive method</h2> <p>The operating method of adaptive encoding algorithms is as follows:<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p> <h3>Encoder</h3> <ol><li>Initialize the data model as per agreement.</li> <li>While there is more data to send <ol><li>Encode the next symbol using the data model and send it.</li> <li>Modify the data model based on the last symbol.</li></ol></li></ol> <h3>Decoder</h3> <ol><li>Initialize the data model as per agreement.</li> <li>While there is more data to receive <ol><li>Decode the next symbol using the data model and output it.</li> <li>Modify the data model based on the decoded symbol.</li></ol></li></ol> <p>Any adaptive coding method has a corresponding <i>static model</i> method, in which the data model is precalculated and then transmitted with the data. </p> <h2 id="static-method">Static method</h2> <h3>Encoder</h3> <ol><li>Initialize the data model based on a first pass over the data.</li> <li>Transmit the data model.</li> <li>While there is more data to send <ol><li>Encode the next symbol using the data model and send it.</li></ol></li></ol> <h3>Decoder</h3> <ol><li>Receive the data model.</li> <li>While there is more data to receive <ol><li>Decode the next symbol using the data model and output it.</li></ol></li></ol> <h2 id="examples">Examples</h2> <p>Adaptive image coding was used by the <a href="/facts/Cassini-Huygens/PWknrDeY">Cassini-Huygens</a> craft to relay images from <a href="/facts/Saturn/D54LcGJ9">Saturn</a>. Only about 5% of the images show any visual signs of damage. As the spacecraft has an error correcting <a href="/facts/Solid-state_drive/aMHBy8gU">Flash drive</a> 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.[<i>needs update</i>] </p> <h3>Cassini Lossless Compression</h3> <ul><li>Both converted (8-bit) and unconverted (12-bit) data can be losslessly compressed. The Cassini hardware data compressor uses a modified Huffman encoding scheme as part of its adaptive compressor.</li> <li>Each compressed image can be reconstructed on the ground with no loss to the information content of the image, provided the image entropy does not exceed the threshold where 2:1 compression is reached.</li> <li>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.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Williams, Ross N. (1991). Adaptive Data Compression. Springer Science & Business Media. ISBN 978-0-7923-9085-5. <a href="978-0-7923-9085-5" target="_blank">978-0-7923-9085-5</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Williams, Ross N. (1991). Adaptive Data Compression. Springer Science & Business Media. ISBN 978-0-7923-9085-5. <a href="978-0-7923-9085-5" target="_blank">978-0-7923-9085-5</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> </ol>