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.

3045 View(s), 10 Comment(s)   

Index

Copyright © by Shelwien, 2008-2009
28.10.09 00:57  Introduction to Rangecoding 5994/1
27.08.09 13:05  Counter state quantization 2926/1
26.07.09 19:30  Counter evolution /1 3294/1
10.07.09 02:42  On universal counters 3065/1
06.11.08 00:34  Collecting the Statistics on Context Occurences 3741/2
26.10.08 21:58  Data Structures for Context Model Statistics 5330/2
04.07.08 13:10  PPM/CM optimal parsing 3411/4
01.07.08 01:57  Hashes vs Trees /2 3727/3
30.06.08 08:32  CM vs LZ 3793/1
29.06.08 02:47  Parameter optimization 3322/1
28.06.08 04:27  Hashes vs Trees 1802/1
27.06.08 02:49  AI opinion 3529/4
26.06.08 05:17  About escapes 3604/1
25.06.08 06:55  BWT output compression test 3993/0
24.06.08 04:59  Linear mixing with "indirect updates" 3701/1
23.06.08 02:37  Fast compression and compilers 3386/0
22.06.08 01:25  About fast compression 3734/1
22.06.08 01:18  Secondary Symbol Estimation /2 3272/1
21.06.08 00:59  Secondary Symbol Estimation 3569/15
20.06.08 01:09  GPGPU compression 8029/9
18.06.08 18:11  Optimized parameters for bitwise order0 with multiplication-based counter update 3764/1
17.06.08 00:03  multi-threaded implementation of order0 CM 3299/1
16.06.08 22:21  CM Audio compression 3482/1
16.06.08 00:07  Counters article from the old encode.ru forum 3652/1
26.07.08 15:34  Mix v6 - delayed counter test 4055/9
17.07.08 17:44  Mix v5 - SSE test [link fixed] 3542/14
14.07.08 16:27  Mix v4 - some failures 5790/20
12.07.08 14:24  Mix v3 3476/26
10.07.08 14:03  Mix v2 4395/48
08.07.08 13:27  Mix v1 - an improvement? 3542/4
05.07.08 13:47  Mix v0 - a collection of order2-6 CM coders 3942/12
05.07.08 10:27  SSE & unary coding thread 3356/5
03.07.08 02:46  CCM/LPAQ competitor thread 4612/26
02.07.08 07:25  o1rc9g released  
01.07.08 06:07  o1rc9f released 3678/1
19.06.08 02:08  ST2rc story 3843/2