JPEG’s Reply to Microsoft WMP: Better JPEG?
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 Richter posted some comparison results with both JPEG and JPEG2000.
Guido Vollbeding mentioned at comp.compression that Q15 is patent free. It removes some of the patented QM features (such as conditional exchange) and compensates for compression performance with use of an alternative probability estimation table (”Fast Attack”) and bit-stuffing technique instead of byte-stuffing (also regarding the latency issue).
There are some more developments/proposals due (like this one). A new extension ‘.jpa’ is also under consideration but they may stick with ‘.jpg’ like they did when progressive algorithms were introduced without changing file extension.
What I would like to see is a head-2-head comparison of old JPEG, new JPEG, JPEG2000, MS WMP and some of the other proprietary image formats, not just on compression ratio but also the relative ‘visual’ quality and speed.
Although we already have many image formats, only few were important enough to be bothered with. But now, the image formats domain is all set to become as crowded at audio/video formats. We have a mess of old/new open standards and a few proprietary ’standards’ have also showed up and will gain atleast some traction due to marketing muscle behind them.
Its going to be hard to say which format will win, but average users will now surely get more format choices and better technology (if they don’t go insane trying to find support for viewing their images in all the devices they use and all the software solutions they like). But I am not complaining, everything has a price :-)