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Optimizing GIF has reverse effect (makes file size larger)

Mar 5, 2011, 22:51
Post: #1
Optimizing GIF has reverse effect (makes file size larger)
I've been using GIMP to make GIFS for a long time now, but recently the "optimize for difference" option I've used is having the reverse effect it should have- ie, it's making the file larger. Here's an example. It's the exact same image, same dimensions, same amount of colors. The first one is unoptimized, each frame is a full picture, and it's file size it ~149kb. The second one is the same as the first, except optimized with about ~50% of the pixels removed from each frame (except the first frame obviously), and yet it's file size is ~155kb. I can not for the life of me figure out why an image with most of it's pixels removed is creating a larger file size. It's driving me crazy.

http://i.imgur.com/hkLRm.gif (unoptimized)

http://i.imgur.com/42Irf.gif (optimized)
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Mar 7, 2011, 00:48
Post: #2
RE: Optimizing GIF has reverse effect (makes file size larger)
Nobody has any explanation for why this is happening?
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Mar 7, 2011, 00:53
Post: #3
RE: Optimizing GIF has reverse effect (makes file size larger)
I have no idea really
The only thing I could think of is maybe the plugin is not working correctly, you could always try re-installing GIMP... only answer I can think of

Sorry mate
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Mar 7, 2011, 15:20
Post: #4
RE: Optimizing GIF has reverse effect (makes file size larger)
I would assume (without testing) that the "difference" optimization is really replacing full frames by smaller layers moving over a fixed background. This would work very well with pure CGI, but since in your case the input is video, the optimizer may have trouble finding a "fixed" background (slight variations of color on a pixel would disqualify it as a background pixel). So you get no optimization, and some additional metadata (comments, etc..).

(in a similar vein, if you try to zip a .ZIP, you get a slightly bigger file...)

Now answering your questions on
https://Gimp-Forum.net
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