Can Animated GIFs be reduced in filesize by comparing regions that actually changed?

Can GIFs be optimized so that only the changed regions (pixels within certain rectangular bounds per frame) are rendered / calculated in the final filesize?

This is assuming that by default – each frames are fully included in an animated GIF (I’m guessing this is the case when exporting from Photoshop’s “Save for Web”…)

Does such compression exists that would also remain compatible to playback in any browsers (like a normal animated GIF)?

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Answer

I’m guessing this is the case

actually, no, that’s not the case. Animated GIFs are optimized in exactly this way…each frame only contains the parts of the image that actually changed from the previous frame.

Wikipedia doesn’t go deep into detail, but does mention it here:

Some economy of data is possible where a frame need only rewrite a portion of the pixels of the display, because the Image Descriptor can define a smaller rectangle to be rescanned instead of the whole image.

Attribution
Source : Link , Question Author : bigp , Answer Author : DA01

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