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A weird thing about apng is it doesn't do any interframe compression. Even GIF has that. It's just a series of png images crammed into a single file.

• Dylan16807 9y ago
  That's not true. It has basic controls to use/clear/revert the last frame and whether the new frame draws on top or replaces part of it. It's still useless when things are moving, but it's no worse than gif.
  • Houshalter 9y ago
    Oh, huh my mistake. I was thinking about how PNG compression is entirely based around using the previous pixels to predict the next one. But as far as I know, apng doesn't update the filters to use information from the previous frame. I guess you can use transparent pixels to compress pixels that don't change though.
    • Dylan16807 9y ago
      Oh, yeah, it definitely resets the compression context between frames. But so does a video format. No format that I'm aware of supports lossless compression that spans frames. Which leads to a funny situation where some images compress best by custom outputting a .gif or .png with no compression, and then zipping it.
      • Houshalter 9y ago
        As I understand it all video compression uses delta compression between frames. And you mention another issue I forgot, that it can't reuse Huffman codes or any common segments between frames. Since they are independently compressed.
        • Dylan16807 9y ago
          > As I understand it all video compression uses delta compression between frames. And so does apng, more or less, via alpha. But that's less important than motion interpolation, which it utterly lacks.