An automated way of comparing gifs?

[Ben Zwycky]

I have some nice animated logos I did a long time ago, before I learned the wisdom of using relative frames (leave previous frame, next frame is transparent except for changes from previous frame) to minimize the overall file size. Now I could in theory go through and manually create those frames, but some of these animations have around 70 frames, no it's just not practical. If anyone knows of a way of automatically comparing two gif images so that only the changed pixels are selected, then I might just do it. I have Photoshop 4.0 and the Gimp, so if there's some feature I've missed in those or a free application somewhere that can do it, I'd be grateful for some pointers. If it can be done, I might be able to get them under the avatar size limit here. (One of the logos is now my current avatar, but it's not my favourite one)

[Ben Zwycky]

I finally noticed that there's an automated option in the Gimp to do this in one step (compare and remove the part that has not changed from the previous frame) for all frames in an animation.

1. Open up your animated gif ion in The Gimp

2. Select Filters>Animation>Optimise (Difference)

3. Rename the new image file that is created (either overwriting the previous file or giving it a slightly different name), saving as a gif

4. Choosing save as animation from the menu (and as indexed file, but that's selected by default)

That's it! Now to just check that those images display properly on the forum:

CIOPSloop2.gif


Defenceloop2.gif

Yep, looking good.