CtxModel.Net

Context Modeling is a divide-and-conquer method based on separation of data into subsequences by context, so that each subsequence can be approximated with a simple model (usually memoryless) while still providing a good overall precision. Most widely used CM subclass is PPM, which concentrates on a single context model due to performance considerations and switches to other contexts only if the main model fails. This allows PPM compressors to keep competitive speed at the cost of some prediction imprecision showing as redundancy. Another known subclass is Context Mixing, which linearly combines the predictions of several submodels. More complex schemes with secondary models using the primary predictions as context seem to remain anonymous. Then, there's yet another approach which also approximates complex data with simple model but by a static data transformation (LZ, Block Sorting, Symbol Ranking). Strange as it may seem, CM too is only a speed/redundancy tradeoff stage, as an ultimate modelling method is to find a function which generates given data. There're even some practical applications for this in the cases with known source model, then parameters can be determined by maximum likelihood.

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Index

Copyright © by Shelwien, 2008-2009
28.10.09 00:57  Introduction to Rangecoding 6189/3
27.08.09 13:05  Counter state quantization 3034/2
26.07.09 19:30  Counter evolution /1 3402/2
10.07.09 02:42  On universal counters 3178/2
06.11.08 00:34  Collecting the Statistics on Context Occurences 3842/3
26.10.08 21:58  Data Structures for Context Model Statistics 5422/4
04.07.08 13:10  PPM/CM optimal parsing 3519/5
01.07.08 01:57  Hashes vs Trees /2 3856/4
30.06.08 08:32  CM vs LZ 3902/2
29.06.08 02:47  Parameter optimization 3434/2
28.06.08 04:27  Hashes vs Trees 1998/2
27.06.08 02:49  AI opinion 3681/5
26.06.08 05:17  About escapes 3742/2
25.06.08 06:55  BWT output compression test 4115/1
24.06.08 04:59  Linear mixing with "indirect updates" 3825/3
23.06.08 02:37  Fast compression and compilers 3502/1
22.06.08 01:25  About fast compression 3848/2
22.06.08 01:18  Secondary Symbol Estimation /2 3387/2
21.06.08 00:59  Secondary Symbol Estimation 3689/16
20.06.08 01:09  GPGPU compression 8854/11
18.06.08 18:11  Optimized parameters for bitwise order0 with multiplication-based counter update 3892/2
17.06.08 00:03  multi-threaded implementation of order0 CM 3426/2
16.06.08 22:21  CM Audio compression 3606/2
16.06.08 00:07  Counters article from the old encode.ru forum 3762/3
26.07.08 15:34  Mix v6 - delayed counter test 4161/10
17.07.08 17:44  Mix v5 - SSE test [link fixed] 3652/15
14.07.08 16:27  Mix v4 - some failures 5916/21
12.07.08 14:24  Mix v3 3598/27
10.07.08 14:03  Mix v2 4490/49
08.07.08 13:27  Mix v1 - an improvement? 3672/5
05.07.08 13:47  Mix v0 - a collection of order2-6 CM coders 4052/15
05.07.08 10:27  SSE & unary coding thread 3754/6
03.07.08 02:46  CCM/LPAQ competitor thread 4857/28
02.07.08 07:25  o1rc9g released  
01.07.08 06:07  o1rc9f released 3782/2
19.06.08 02:08  ST2rc story 3983/3