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More On The BBC's Codec 'Dirac'
TioHoltzman writes "El Reg is reporting about a new codec that is built on top of wavelet technology and seems to offer performance that is "roughly in line with the Video Codec 9" from Microsoft. The project has been released as open source on SourceForge. This looks like it might be really interesting." (Previously mentioned a few weeks back.)
The standard way to compress both audio and video is with the Discrete Cosine Transform, or DCT. MPEG audio and video are based on DCT.
The basic idea of DCT is to transform the data into a series of waves, which tends to concentrate the data. Then you throw away part of the data, and then use lossless encoding on what is left. If you just threw away pixels, the result would be obvious in an image; but if you throw away part of the wave specification data, the results are not as obvious.
With DCT, consistent data sets compress very well (e.g., a blue sky or a white wall). Pictures with lots of sharp little edges (e.g., a field of blades of grass) compress much less well.
My understanding is that potentially wavelets will compress even better than the DCT. However, they are not enough better to be a huge win at the moment.
steveha
lf(1): it's like ls(1) but sorts filenames by extension, tersely
as for wavelet compression being a novel codec, what about apple's pixlet technology?
Some drink at the fountain of knowledge. Others just gargle.
Nothing to do with the government. The BBC is granted a charter from Parliment, but is not government run or funded. The BBc is funded by a compulsory license fee for owning equipment capable of recieving and decoding their broadcasts such as a TV or tuner card. Basically it's a tax on virtually every household and business in the UK. There is a discount for black & white TV's, pensioners and those with vision based disabilities. In the 'old days' you used to need a 'wireless licence' as well for radios!
Pixlet is designed for real-time editing, so it has minimal artifacts and no interframe compression. Dirac is for broadcast, so it is much more agressive about compression and can take advantage of motion compensation and other computationally expensive compression techniques.
You are right, however, that wavelets are not at all a new compression technology. People started playing with it at least 10 years ago and JPEG-2000 uses wavelets for still photo compression. I think that the computational load has prevented their use in video until recently.
What's the problem with distributing patented technology in source form? I believe this is legal. As an example VTK distributes the marching cube patented method (among others) with no problem.
Unisys never had a problem with any of the LZW implementation in source form. They never asked for them to be pulled out of any site, and neither could they legally. What they asked is if you were using this technology for anything other than research and study (i.e. if you really wanted to compress some file with it for redistribution) *then* you needed a license from them.
The use of patented methods for research and study is legal, this is the whole point of patenting technology. Patenting is a publication process, in exchange for exclusive control of the technology *in applications*. The idea is that other people can study this technology and improve on it.
If you as a user take some source code floating on the net implementing some patented technology, and add it to some application, be the application free or not, you are responsible for obtaining a license from the holder of the patent, but AFAIK the author of the code is in the clear, and so are the distributors.