Craig Birkmaier wrote: >Shannon can help us predict the highest frequency that >can be represented (without aliasing) for any given raster >size. So in theory we could create some diabolical image >that totally saturates the spectra that can be represented >in a single frame. I believe you are referring to the Nyquist limit here. That does apply to images, of course. But Shannon's Law refers to the limiting bit rate that can be transferred in a given channel width, as a function of signal to noise ratio. The analogous limit in image compression might be stated as "given the pixel count, frequency content, color content, of a given image, what is the smallest file size that can be achieved, in theory (i.e. not restricted to any existing algorithm), with no loss of image information? >But this is just for one frame. Shannon tells us noting >about the next frame, except that it can contain no >more information than the previous "diabolical" frame. This different form of Shannon's law would be repeated for all frames in the moving image sequence, in principle, and information content change would then become a factor too. >But the next frame can be equally challenging, but >totally different. From a compression perspective this >is truly diabolical - that is there is no relationship from >one frame to the next, thus very little opportunity to >take advantage of interframe entropy coding. Yes, I think this does relate. If you remember the results of the 4th and 5th gen 8-VSB equalizers, there were examples where they beat the 14.9 dB C/N for solid reception. Not that 14.9 is any sort of Shannon limit, it's not, but the message was that if the "noise" is somehow correlated to the signal, it can be used to enhance reception. The Shannon limit is not violated, though. Because when it appears as if the Shannon liimit might have been exceeded, it turns out that some of that "noise" was actually signal, as in S/(N+I). On the other hand, if the noise is gaussian, i.e. uncorrelated, then it cannot be used to enhance reception. So I agree that whatever this new law looked like, it would have to take into account how much information change occurred between frames, when it was applied to moving images. Analogous concepts here. >In other words, there is no correct answer to Bert's >question. Any limits will change dynamically based on >the ability of the compression algorithm to deal with >specific types of image pathology. John Shutt's question, actually. I don't know that anyone has come up with any sort of Shannonesque law to answer John's question, but I would be surprised if such a law were undevelopable(?). Again, the answer would not be related to any one compression algorithm. And I agree that we are most likely nowhere close to the limit, with existing algorithms. But that's only a wild*ss guess. Bert _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today - it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.