https://bugzilla.wikimedia.org/show_bug.cgi?id=28631

--- Comment #5 from Brion Vibber <[email protected]> 2011-04-28 00:54:48 UTC 
---
I can confirm here with ImageMagick 6.6.2-6 (Ubuntu 10.10 x86_64).

The '+map' (along with the -fuzz and layer optimization) was added in r71354
for bug 11822:

  "I also tried adding +map to reduce to prevent per
  frame colortables, but this option doesn't deal very well with transparency
  unfortunately (because it does significantly reduce filesize)."


My current man pages don't list the '+map' option for convert, but older ones
floating on the internet do:

==========================
-map filename
    choose a particular set of colors from this image.

    By default, color reduction chooses an optimal set of colors that best
represent the original image. Alternatively, you can choose a particular set of
colors from an image file with this option. Use +map to reduce all images
provided on the command line to a single optimal set of colors that best
represent all the images.
==========================

The '+map' tells it to rebuild the colormap from the input files, so presumably
this is behaving differently from the default (given that it's the same input
file, still). Somehow in the process of converting colors we lose some of the
transparency, and various chunks of various frames are getting mapped to a
non-transparent color by mistake.

In theory an animated GIF can have different color maps for each frame, but I
don't know if that's a case that's actually hitting stuff.

I'm a bit unclear on if/where there's a bug tracker for ImageMagick, but there
are forums where you can report bugs in the 'bugs' section. I don't see any
entries searching for 'map animated gif'.

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