GIF partially broken? about image HOT 10 CLOSED

i'll look into it

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Is this fixed?

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No.

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From comment #58 (comment)

The bug is in the LZW decoder and the documentation for LZW is really…brief. This is why I didn't do much on TIFF lately because I also ran into problems with it and couldn't figure out how exactly LZW is supposed to work in detail.

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Maybe http://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Welch will help?

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I've done some rudimentary testing (about 10 images) and it seems this works with gifs encoded with 89a but fails those encoded with 87a

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Interesting finding. I had a look at the specs. At least until decompression it looks like it should be correct and the same for both standards.

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I'm wondering if it the dependent on the starting location of the actual image data blocks, based off this documentation

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No this doesn't matter. Until the actual image data it is read correctly. As far as I can see every gif 87a image should be a valid gif 89a image.

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Maybe there is really something wrong with the reading of the image data blocks. It seems to fail too if the images are too big…

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