09-17-08 - 2

Block-based compressors can be lapped and use fancy coders and all that to compete with wavelets in most every way. But there is a really nice thing about wavelet compression as opposed to block-based. It's the resolution independence. If I take a photo at 1024x1024, and take the same photo at 2048x2048 and compress them both - the wavelet coder has the smaller one as a subset of what it does; it basically just keep doing the same thing, it still codes the LL DPCM band at the same resolution, 32x32 or whatever you chose. In contrast, the block-based coder is now working on very different data. It still works on 8x8 blocks, but they are now half as big in real space, they contain detail at a different scale. The DC coefficient set is now 256x256 instead of 128x128 and the DPCM properties of it are quite different.

One thing this means is that the block based coders that are super tuned (like JPEG,MPEG,H264) are actually dialed in for a certain era and a certain typical image resolution.

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old rants