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They increase compression ratio? That's counter-intuitive. You're effectively imposing an ordering requiring certain information to be available first, so you'd
by darkmighty 11y ago
They increase compression ratio? That's counter-intuitive. You're effectively imposing an ordering requiring certain information to be available first, so you'd expect the compression be at most as good as non-progressive. I guess the changed ordering makes the statistics simpler and easier to compress, or something like that.
- mzs 11y agoThe initial passes are lower freq, so they compress better. More over you have control over them when encoding so you can optimize there (and there are tools that do so), but the defaults used by all encoders are very good across most all images.
- cbr 11y agoThe downside is memory usage during compression. A non-progressive jpeg can be compressed locally but a progressive encoding requires the whole image. But this is only a small downside. (Converting JPEG images to progressive format is one of the optimizations mod_pagespeed makes.)