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It's pretty cool how a simple encoding scheme can have profound effects on compression. This is a big part of what makes DCT-style block compression work as wel
by bob1029 4y ago
It's pretty cool how a simple encoding scheme can have profound effects on compression. This is a big part of what makes DCT-style block compression work as well as it does. You rig the game such that all of your higher frequency components wind up at the end - ideally as zeroes after quantization. So, a simple RLE scheme can do a lot more work than it otherwise could.
- benj111 4y agoSorry. Are you inferring this is how DCT works or are you making a comparison? Ive just read up about DCT and don't really have a clue, but it doesn't seems applicable? That being so. I'm not sure how RLE at the bit level would help. Surely encoding run lengths of 5ish bits isn't going to compress much of anything.
- bob1029 4y agoZigzag is a phase after DCT+quantization where you iterate through the resulting matrix in a particular order. Nothing to do with the DCT itself. https://commons.wikimedia.org/wiki/File:JPEG_example_zigzag.png https://commons.wikimedia.org/wiki/File:JPEG_example_zigzag....
- oakwhiz 4y agoThe idea behind this is to scan diagonally by frequency so that big numbers are grouped together at the start. You can choose to zero out some of the bits near the end since those only contain high frequency components that are harder to notice. RLE then has the ability to work on the trailing zeroes, or other methods can be used instead.