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 6325/4
27.08.09 13:05  Counter state quantization 3106/3
26.07.09 19:30  Counter evolution /1 3501/3
10.07.09 02:42  On universal counters 3256/3
06.11.08 00:34  Collecting the Statistics on Context Occurences 3956/4
26.10.08 21:58  Data Structures for Context Model Statistics 5503/5
04.07.08 13:10  PPM/CM optimal parsing 3595/6
01.07.08 01:57  Hashes vs Trees /2 3944/5
30.06.08 08:32  CM vs LZ 4005/3
29.06.08 02:47  Parameter optimization 3554/3
28.06.08 04:27  Hashes vs Trees 2150/3
27.06.08 02:49  AI opinion 3807/6
26.06.08 05:17  About escapes 3858/3
25.06.08 06:55  BWT output compression test 4233/2
24.06.08 04:59  Linear mixing with "indirect updates" 3980/4
23.06.08 02:37  Fast compression and compilers 3696/2
22.06.08 01:25  About fast compression 3949/3
22.06.08 01:18  Secondary Symbol Estimation /2 3482/3
21.06.08 00:59  Secondary Symbol Estimation 3773/18
20.06.08 01:09  GPGPU compression 9509/12
18.06.08 18:11  Optimized parameters for bitwise order0 with multiplication-based counter update 4021/3
17.06.08 00:03  multi-threaded implementation of order0 CM 3530/3
16.06.08 22:21  CM Audio compression 3710/3
16.06.08 00:07  Counters article from the old encode.ru forum 3861/4
26.07.08 15:34  Mix v6 - delayed counter test 4264/11
17.07.08 17:44  Mix v5 - SSE test [link fixed] 3759/16
14.07.08 16:27  Mix v4 - some failures 5999/22
12.07.08 14:24  Mix v3 3730/28
10.07.08 14:03  Mix v2 4586/50
08.07.08 13:27  Mix v1 - an improvement? 3812/6
05.07.08 13:47  Mix v0 - a collection of order2-6 CM coders 4112/17
05.07.08 10:27  SSE & unary coding thread 3970/7
03.07.08 02:46  CCM/LPAQ competitor thread 4964/29
02.07.08 07:25  o1rc9g released  
01.07.08 06:07  o1rc9f released 3880/3
19.06.08 02:08  ST2rc story 4085/4