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Comment by __alexs | Hacker News Reader

Doesn't GIF already have a differential animation mode since you can set unchanged pixels in each frame to transparent? e.g. http://www.imagemagick.org/Usage/anim_opt/#opt_trans

With PNG24 you'd at least get better colour depth. In which case why not use the same Dispose None technique in APNG (https://wiki.mozilla.org/APNG_Specification#.60fcTL.60:_The_...) and a polyfill (https://github.com/davidmz/apng-canvas) to provide cross-browser support?

Actually it might be preferable to always use the polyfill if you want to do something like the Apple thing where you can scrub around the video. Still doesn't have I-Frames to do frame-skip during fast movements though.

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GIFs standard is awesome, it is that most of the software does them wrong. To recap:

You can update multiple rectangles each with 0ms delay. Issue is that most browsers don't like dealing with 0ms updates, and will consider rectangle update a frame update. Some browsers will silently increase delays. [1]

You can pause once all necessary rectangles for frame have been updated. [2]

You can have full colour image provided that it is built from multiple rectangle updates, where each rectangle contains its own colour map. [3]

[1] : Browsers not respecting GIF rectangle update delays : http://nullsleep.tumblr.com/post/16524517190/animated-gif-mi...

[2] : gifsicle [image] --delay [delaytime] #[start]-[end] : http://linux.die.net/man/1/gifsicle

[3] : True Colour GIF : http://phil.ipal.org/tc.html

Based on my hazy understanding of the animated GIF file format, I believe that what I ended up with is very similar to animated GIFs, from a high level at least (i.e., a collection of frames, each of which containing multiple rectangles where the frame differs from the previous one). I have no idea why the animated gif encoders I tried did such a poor job size wise, it looked as if none of them even tried to find the minimal set of changes from one frame to another. I didn't spend too long looking, as 8-bit color was always going to be a show stopper.

Your example image (http://www.sublimetext.com/anim/rename2_packed.png) is in 8-bit colour. Perhaps you just only tried the awful GIF encoders that couldn't even do the dithering well :)

Indeed!

Next thing I'll find out that you actually can get a JavaScript callback when a GIF has finished animating.

I think GIFs only have one rectangle that differs per frame so a "dumb" encoder would be replacing nearly the whole frame each time, since your changes are small but distributed all over the frame.

The smarter encoders would encode most of that rectangle as transparent and let the previous frames show through.

Indeed, it is very strange that an animated GIF would be so ineffective in this case. The image does not seem to have too many colors and the animated changes are minimal. Have you tried an encoder that attempts to use at least the basic GIF optimization techniques?

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