image/gif color corruption with DecodeAll/EncodeAll

[Jason Del Ponte]

I'm seeing an odd issue with image/gif.  When an image is loaded with gif.DecodeAll, and written to a new file, with no manipulations, via gif.EncodeAll sections of each frame are black when they shouldn't be.

Not sure if i'm missing something when using image/gif, or if this is a bug in the package.  It looks like the compressed fill parts of the original image are lost, and replaced with black pixels(Default background color?) when written again. I'm not sure how to identify if this problem is happening on the encoding or decoding side.

Code example: http://play.golang.org/p/z8VwdM7jfS

Before: http://i.imgur.com/nGsYOhn.gif

After: http://imgur.com/59gSWgw.gif

(Running on Ubuntu 14.04 x86_64)

Also looks like the same issue is occurring with just gif.Encode and gif.Decode when writing just the first frame. http://i.imgur.com/IHwEXuY.gif

Cheers,

Jason

[Jason Del Ponte]

Forgot to mention I've reproduced this on 1.2.1, 1.2.2, and 1.3beta1 the same way.

[Andy Bonventre]

If you decode and then encode to another image format like jpeg, does the issue still present itself? That would help you narrow down at what step the issue is happening.

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[James Bardin]

Your gif is optimized in such a way that it uses a color palette combined with transparency over a colored background.

I don't think the Go gif coders don't really handle background color.

It looks like background color is ignored during decoding, and written ad 0x00 (black) during encoding.

[Andy Bonventre]

This is what I see when encoding the first frame to a jpeg after decoding from your original gif:

James is correct. Please file an issue for the decoder.

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[Jason Del Ponte]

I think you're right. encoding to jpeg maintains the same loose. http://i.imgur.com/ZSxA5nO.jpeg

Thanks! I'll open an issue.

[Jason Del Ponte]

submitted issue https://code.google.com/p/go/issues/detail?id=7993