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June 22, 2006

The new ITU-T Recommendation T.851 offers better (and faster) compression by introducing a new (backward incompatible) alternative Q15 arithmetic coding. Color precision is increased to maximum 16 bits per color component.

The change is only in the final lossless entropy coding stage. Thus current JPEGs can be losslessly encoded to use new algorithm and the lossiness of this new variant (the blockiness etc…) will be same as that of existing JPEGs.

Work on the new compression algorithm was started in 2004 by ITU-T Study Group 16. An alpha open source implementation is available.

Official results claim around 10% improvement in ratio over old JPEG. StuffIt’s JPEG recompression technology deserves a mention here, they claim a 30% better ratio by taking a similar approach. Thomas Ritcher posted some comparison results with both JPEG and JPEG2000.