Comment on Significance of Compression Rate Method

Wed, 02 Jun 2010 01:02:04 GMT

But jpeg is being judged by a slightly different figure of merit, which changes the relevant considerations.

Like other lossy image compression schemes, jpeg is judged based on how much of the source picture it is that a human notices as being lost. So, for that problem, the relevant "source" to be encoded is really the human perception of the image, not the bitstream of the image file.

And really, since all phenomena pass through someone's senses before they're observed, this is the relevant metric for any MML formalism: whether you can come up with a way to briefly describe what you have experienced. It's just that in typical lossless tests, they've eliminated the impact of human cognition by making it possible to compare directly to a specific string and determine if that string can be completely reproduced.

So I don't condemn jpeg or regard it as meaningless; I'm saying it can be directly compared to lossless methods if you either a) penalize it by the amount of data needed to go from the jpeg to the source image, or b) penalize it by the amount of data needed, on average, to restore the image to something a human would not remember differently (which in many cases is very little if any data).

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