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Possible bug writing small .gif images
Posted: 2011-04-04T07:15:14-07:00
by odrm
Code: Select all
$ convert -version
Version: ImageMagick 6.6.9-1 2011-04-04 Q8 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2011 ImageMagick Studio LLC
Features: OpenMP OpenCL
Small images with a transparent background are incorrectly saved with a black background. To reproduce:
Code: Select all
$ convert -size 16x16 xc:none -fill blue -draw 'rectangle 4,4 8,8' s.gif
$ identify -verbose s.gif
...
Histogram:
230: ( 0, 0, 0,255) #000000 black
1: ( 0, 0, 0, 0) #00000000 none
25: ( 0, 0,255,255) #0000FF blue
...
The transparency wasn't saved, but was replaced with black. For a larger image, this doesn't appear to happen:
Code: Select all
$ convert -size 32x32 xc:none -fill blue -draw 'rectangle 4,4 8,8' m.gif
$ identify -verbose m.gif
...
Histogram:
999: ( 0, 0, 0, 0) #00000000 none
25: ( 0, 0,255,255) #0000FF blue
...
Re: Possible bug writing small .gif images
Posted: 2011-04-04T07:53:15-07:00
by magick
We'll add a patch to fix this problem to the next point release of ImageMagick. Thanks.
Re: Possible bug writing small .gif images
Posted: 2011-04-14T08:09:11-07:00
by sas
I might be hitting the same bug (also using ImageMagick 6.6.9-1).
In my case it doesn't replace transparent pixels with black, however, but rather with the "Alpha" background color saved with the image:
bullet.png 
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$ identify -verbose bullet.png | grep "Alpha: "
Alpha: rgba(255,0,0,0) #FF000000
-->
bullet.gif:
(Also note the top-left pixel being set to grey)
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$ identify -verbose bullet.gif | grep "Alpha: "
Alpha: none #00000000
This happens to me for images of size 10 x 25px or smaller, but not with larges ones.
Re: Possible bug writing small .gif images
Posted: 2011-04-14T09:35:09-07:00
by fmw42
The following works fine for me under IM 6.6.9.4 Q16 Mac OSX Tiger.
convert -size 16x16 xc:none -fill blue -draw 'rectangle 4,4 8,8' tmp.gif
identify -verbose tmp.gif
Code: Select all
Format: GIF (CompuServe graphics interchange format)
Class: PseudoClass
Geometry: 16x16+0+0
Resolution: 72x72
Print size: 0.222222x0.222222
Units: Undefined
Type: PaletteMatte
Endianess: Undefined
Colorspace: RGB
Depth: 8/1-bit
...
Histogram:
231: ( 0, 0, 0, 0) #00000000 none
25: ( 0, 0,255,255) #0000FF blue
Colormap: 2
0: ( 0, 0,255,255) #0000FF blue
1: ( 0, 0, 0, 0) #00000000 none
Re: Possible bug writing small .gif images
Posted: 2011-04-14T13:07:14-07:00
by sas
After upgrading to ImageMagick 6.6.9-4 2011-04-11 Q16, it works as expected now. Great!
fmw42 wrote:convert -size 16x16 xc:none -fill blue -draw 'rectangle 4,4 8,8' tmp.gif
That probably always worked, the problem was only with images with width ≤10px and height ≤ 25px (at least for me).
Re: Possible bug writing small .gif images
Posted: 2011-04-16T01:03:00-07:00
by anthony
Small GIF files with transparency is still broken!!!!
Code: Select all
convert -size 9x9 xc:none png: | convert - -scale 1000% show:
will show a transparent image which is what I asked for.
Code: Select all
convert -size 9x9 xc:none gif: | convert - -scale 1000% show:
shows an all black image but for a single transparent pixel in the top-left
Re: Possible bug writing small .gif images
Posted: 2012-08-07T21:33:06-07:00
by anthony
This is still broken!!!!
Re: Possible bug writing small .gif images
Posted: 2012-08-07T21:36:19-07:00
by fmw42
anthony wrote:This is still broken!!!!
see also
viewtopic.php?f=1&t=21583
Re: Possible bug writing small .gif images
Posted: 2012-08-08T06:43:29-07:00
by magick
We can reproduce the problem you posted and have a patch in ImageMagick 6.7.8-9 Beta. Thanks.