He came up with the idea of using lossy compression techniques to compress the original file, then calculating the difference between the approximate reconstruction and the original file and compressing that data; by combining the two pieces, you have a lossless compressor.
This type of approach can work, Misra said, but, in most cases, would not be more efficient than a standard lossless compression algorithm, because coding the error usually isn’t any easier than coding the data.
Well, this is almost how MPEG movie compresion works - and it really does work! MPEG works by partly describing the next picture from the previous using motion vectors. These vectors described how the next picture will look based on movements of small-ish macroblocks on the original picture. Now, if that was the only element of the algorithm movies would look kind of strange (like paper-doll characters being moved about)! So the secret to make it work is to send extra information allowing the client to calculate the final picture. This is done by subracted the predicted picture from the actual next frame. This difference-picture will (if the difference between the two frames was indeed mostly due to movement) be mostly black but it will contain some information due to noise, things that have become visible due to the movement, rotation etc. So MPEG also contains an algorithm that can very efficiently encode this "difference picture". Basically an algorithm that is very efficient for encoding an almost black picture.
So there you have it - MPEG works by applying a very crude, lossy compression (only describing the picture difference in terms of motion vectors) and in addition transmitting the information required to correct the errors and allow reconstruction of the actual frame.
The only part where the comparison breaks down is that MPEG is not lossless. Even when transmitting the difference picture, further compression and reduction takes place (depending on bandwidth) so that the actual frame can not be reconstructed 100%. Still MPEG is evidence that the basic principle of using a crude lossy compressor combined with sending a compensation, works.
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