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image/gif: decoding of some GIFs fails with error gif: invalid pixel value yet they open alright. #15059

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odeke-em opened this issue Apr 1, 2016 · 3 comments
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image/gif: decoding of some GIFs fails with error gif: invalid pixel value yet they open alright. #15059

odeke-em opened this issue Apr 1, 2016 · 3 comments
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Go1.7

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@odeke-em
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odeke-em commented Apr 1, 2016

Please answer these questions before submitting your issue. Thanks!

  1. What version of Go are you using (go version)?
    go version devel +ea306ae Fri Apr 1 04:13:44 2016 +0000 darwin/amd64
  2. What operating system and processor architecture are you using (go env)?
    GOARCH="amd64"
    GOBIN="/Users/emmanuelodeke/go/bin"
    GOEXE=""
    GOHOSTARCH="amd64"
    GOHOSTOS="darwin"
    GOOS="darwin"
    GOPATH="/Users/emmanuelodeke/go"
    GORACE=""
    GOROOT="/Users/emmanuelodeke/go/src/go.googlesource.com/go"
    GOTOOLDIR="/Users/emmanuelodeke/go/src/go.googlesource.com/go/pkg/tool/darwin_amd64"
    CC="clang"
    GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -gno-record-gcc-switches -fno-common"
    CXX="clang++"
    CGO_ENABLED="1"
  3. What did you do?
    If possible, provide a recipe for reproducing the error.
    A complete runnable program is good http://play.golang.org/p/_8PzZ6RffI.
    A link on play.golang.org is best.
    Tried to decode a gif https://brobible.files.wordpress.com/2016/03/joker1.gif but it failed with error gif: invalid pixel value.
    Complete runnable program here http://play.golang.org/p/_8PzZ6RffI
  4. What did you expect to see?
    Successful GIF decoding
  5. What did you see instead?
    error gif: invalid pixel value
@bradfitz bradfitz added this to the Go1.7 milestone Apr 7, 2016
@nigeltao
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It is indeed an invalid GIF image: the frame's palette only has 128 entries (i.e. valid values are from 0 to 127 inclusive), but the 'transparent index' is given as 128, which is outside the range [0, 127]. The GIF spec at https://www.w3.org/Graphics/GIF/spec-gif89a.txt says in section 22, Table Based Image Data, "Each index must be within the range of the size of the active color table".

Imagemagick similarly complains:

$ convert joker1.gif x.png
convert.im6: invalid colormap index `joker1.gif' @ error/colormap-private.h/ConstrainColormapIndex/34.

Nonetheless, it treats it as a warning, not an error. Furthemore, joker1.gif is viewable (with no visible error message) in both Firefox and Google Chrome, and by Eye-of-Gnome (which uses gdk-pixbuf). I suppose that it's a case of reality trumping the standard, and we should 'fix' this for Go.

@gopherbot
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CL https://golang.org/cl/22546 mentions this issue.

@odeke-em
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odeke-em commented Apr 28, 2016 •
edited by bradfitz
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Thank you @nigeltao, this helps me quite a lot as I was encountering a lot of such gifs on the web and needed to import them

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