image/gif: result of EncodeAll not viewable in Eye of GNOME

[pierrre]

Go version: 1.5.2 & 1.6beta1 linux/amd64
Architecture: Linux pierre-vm 4.2.5-1-ARCH #1 SMP PREEMPT Tue Oct 27 08:13:28 CET 2015 x86_64 GNU/Linux

With this image: https://raw.githubusercontent.com/pierrre/imageserver/master/testdata/animated.gif
Run:

package main

import (
    "bytes"
    "image/gif"
    "io/ioutil"
)

func main() {
    b, err := ioutil.ReadFile("/home/pierre/Go/src/github.com/pierrre/imageserver/testdata/animated.gif")
    if err != nil {
        panic(err)
    }
    g, err := gif.DecodeAll(bytes.NewReader(b))
    if err != nil {
        panic(err)
    }
    buf := new(bytes.Buffer)
    err = gif.EncodeAll(buf, g)
    if err != nil {
        panic(err)
    }
    b = buf.Bytes()
    err = ioutil.WriteFile("test.gif", b, 0644)
    if err != nil {
        panic(err)
    }
}

If I open the encoded image (test.gif) with Eye of GNOME 3.18.1 (default image viewer on Gnome), I get an error message: "Circular table entry in GIF file".

I can open the original image with Eye of GNOME.
I can open the encoded image with Firefox, Chrome, or XnView.

[pierrre]

I have a similar issue with this code:

package main

import (
    "bytes"
    "image"
    "image/color"
    "image/gif"
    "io/ioutil"
)

func main() {
    g := &gif.GIF{
        Image: []*image.Paletted{
            image.NewPaletted(image.Rect(0, 0, 100, 100), color.Palette{color.RGBA{0xff, 0, 0, 0xff}}),
        },
        Delay: []int{
            0,
        },
    }
    buf := new(bytes.Buffer)
    err := gif.EncodeAll(buf, g)
    if err != nil {
        panic(err)
    }
    err = ioutil.WriteFile("test.gif", buf.Bytes(), 0644)
    if err != nil {
        panic(err)
    }
}

Eye of GNOME says: "GIF image loader cannot understand this image."

[rsc]

/cc @nigeltao

[rsc]

Animated GIF aficionados will have to wait for Go 1.7.

[nigeltao]

Sorry for the late reply. I've been away for some months now, for non-work-related reasons. I'll look at this for Go 1.7.

[tanepiper]

go version: go1.6.2 windows/amd64
Platform: Windows 10 Pro

Gahh! So one of the first examples in The Go Programming Language book is the lissajous example (https://github.com/adonovan/gopl.io/blob/master/ch1/lissajous/main.go) and while it outputs a file it appears to be non-valid. This would potentially explain why.

[nigeltao]

@pierrre, I believe that these are bugs with Eye-of-Gnome (i.e with gdk-pixbuf) instead of with Go. In particular, I think that gdk-pixbuf's LZW decompressor is at fault.

For example, the "GIF image loader cannot understand this image" error message comes from https://github.com/GNOME/gdk-pixbuf/blob/master/gdk-pixbuf/io-gif.c#L634 in the lzw_read_byte function, and the comment immediately above that says: "FIXME - we should handle this case".

I filed a bug on the gdk-pixbuf project: https://bugzilla.gnome.org/show_bug.cgi?id=765705

@tanepiper, I need more information than "it appears to be non-valid". What programs did you try and open that output file with? What error messages (if any) did it show? Did you try various browsers: Firefox, Google Chrome, Internet Explorer?

[pierrre]

Thank you !

[tanepiper]

@nigeltao The above example is in the first chapter of http://www.gopl.io/

The book example actually starts off without the web server, here is my version of it: https://gist.github.com/tanepiper/658606e9c424f876f284f60eeaea16cc

I've attached the output gif, the output it compiled with go version go1.6.2 windows/amd64 and as you can see it outputs a gif file of 313kb but invalid.

You are correct in that the web version does seem to work (sorry I passed this example in the book after spending a frutsrating hour trying to get the first version working) but when outputting to a file (e.g. lissajoi.exe > output.gif the writer seems to failing. I've tried various versions of the command (lissajoi.exe 1> output.gif, lissajoi.exe > output.gif 2>&1, etc) and nothing seems to work. I'm thinking now it's either an os.Stdout issue or something on Windows itself but outputting to a file like that should work :(

Anyway appreciate the response and that it's not a issue with the gif library.

[tanepiper]

Hah! So on a random whim tried it in cmd.exe rather than Powershell and it worked! So it seems it's something screwy with Powershell and Stdout. How annoying 😠