Fwd: Corrupt image when identify gif image

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The command:

        gm identify test.gif

The output in terminal:

        gm identify: Corrupt image (test.gif)

However, Imagemagicks does well.

So, I gdb GM and IM and then I found the difference.

In GM.1.3.22 coders/gif.c:

     1011     if (opacity >= (long) image->colors)
     1012       image->colors=opacity+1;

In IM:

     1259     if (opacity >= (ssize_t) image->colors)
     1260       opacity=(-1);

------

This difference will cause mistakes when allocating local colormaps.
Moreover I scaned spec-gif89a.txt
<http://www.w3.org/Graphics/GIF/spec-gif89a.txt> and didn't find anything
about this. So I'm not sure whether it's a bug.


image URL:  http://bigfile.b0.upaiyun.com/test.gif

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<div dir=3D"ltr"><div class=3D"gmail_quote"><br><div dir=3D"ltr">The comman=
d:<div>=C2=A0=C2=A0</div><div>=C2=A0 =C2=A0 =C2=A0 =C2=A0 gm identify test.=
gif</div><div><br></div><div>The output in terminal:</div><div><br></div><d=
iv>=C2=A0 =C2=A0 =C2=A0 =C2=A0 gm identify: Corrupt image (test.gif)<br></d=
iv><div><br></div><div>However, Imagemagicks does well.</div><div><br></div=
><div>So, I gdb GM and IM and then I found the difference.</div><div><br></=
div><div>In GM.1.3.22 coders/gif.c:</div><div><br></div><div><div>=C2=A0 =
=C2=A0 =C2=A01011 =C2=A0 =C2=A0 if (opacity &gt;=3D (long) image-&gt;colors=
)</div><div>=C2=A0 =C2=A0 =C2=A01012 =C2=A0 =C2=A0 =C2=A0 image-&gt;colors=
=3Dopacity+1;</div></div><div><br></div><div>In IM:</div><div><br></div><di=
v>=C2=A0 =C2=A0 =C2=A01259 =C2=A0 =C2=A0 if (opacity &gt;=3D (ssize_t) imag=
e-&gt;colors)</div><div>=C2=A0 =C2=A0 =C2=A01260 =C2=A0 =C2=A0 =C2=A0 opaci=
ty=3D(-1);</div><div><br></div><div>------</div><div><br></div><div>This di=
fference will cause mistakes when allocating local colormaps. Moreover I sc=
aned=C2=A0<a href=3D"http://www.w3.org/Graphics/GIF/spec-gif89a.txt" target=
=3D"_blank">spec-gif89a.txt</a>=C2=A0and didn&#39;t find anything about thi=
s. So I&#39;m not sure whether it&#39;s a bug.</div><div><br></div><div><br=
></div><div>image URL: =C2=A0<a href=3D"http://bigfile.b0.upaiyun.com/test.=
gif">http://bigfile.b0.upaiyun.com/test.gif</a></div><div><br></div><div><b=
r></div><div><br></div><div><br></div><div><br></div><div><br></div><div><b=
r></div><div><br></div></div>
</div><br></div>

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