From: Bob Friesenhahn <bfriesen@si...> - 2010-02-16 17:06:24
On Tue, 16 Feb 2010, Dan Tsohar wrote:
> If I take the following picture:
> And resize it with the command:
> "gm convert tiger.gif -coalesce -resize 80x80+0+0% out.gif"
> I get the following result:
> (Transparency is gone and turned black)
> I have also seen that transparency sometimes turns to grey.
The problem with simple 'transparency' when the base image does not
start with a color is that the resulting color depends on whatever
background color or image the animation is played on. Undefined
pixels still need to have a color even if you can't see it. The
default background color is black. If you expect a background color
of white, then use
gm convert tiger.gif -background white -coalesce -resize 80x80+0+0% out.gif
It does seem like a bug that -coalesce does not preserve binary
transparency and I notice that recent ImageMagick does better in this
regard. If you can submit a formal bug report via the GraphicsMagick
SourceForge bug tracker, then I will work to fix this.
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/