Legacy ImageMagick Discussions Archive

I have a GIF image that has only 4 colors and one is a white background. If I add an alpha channel to it, both histogram and -unique colors show transparent black rather than transparent white. Perhaps this is just a limitation of GIF?

Input:
http://www.fmwconcepts.com/misc_tests/u ... esign4.gif

Code: Select all

convert design4.gif -format "%c" histogram:info:

181054: ( 16, 3, 78) #10034E srgb(16,3,78)
51286: (178, 32, 24) #B22018 srgb(178,32,24)
1277: (178,211,239) #B2D3EF srgb(178,211,239)
565759: (255,255,255) #FFFFFF white

Code: Select all

convert design4.gif -unique-colors txt:

0,0: (16,3,78) #10034E srgb(16,3,78)
1,0: (178,32,24) #B22018 srgb(178,32,24)
2,0: (178,211,239) #B2D3EF srgb(178,211,239)
3,0: (255,255,255) #FFFFFF white

Now if I add a binary alpha channel so that the white background is transparent, I get:

Code: Select all

convert design4.gif \
\( -clone 0 -fill black +opaque white -negate \) \
-alpha off -compose copy_opacity -composite \
design4a.gif

http://www.fmwconcepts.com/misc_tests/u ... sign4a.gif

Code: Select all

convert design4a.gif -format "%c" histogram:info:

565759: ( 0, 0, 0, 0) #00000000 none
181054: ( 16, 3, 78,255) #10034E srgba(16,3,78,1)
51286: (178, 32, 24,255) #B22018 srgba(178,32,24,1)
1277: (178,211,239,255) #B2D3EF srgba(178,211,239,1)

Code: Select all

convert design4a.gif -unique-colors txt:

0,0: (16,3,78,1) #10034E srgba(16,3,78,1)
1,0: (178,32,24,1) #B22018 srgba(178,32,24,1)
2,0: (178,211,239,1) #B2D3EF srgba(178,211,239,1)
3,0: (0,0,0,0) #00000000 none

See my answer here: viewtopic.php?f=3&p=118548#p118548. I think it is the same issue.

Legacy ImageMagick Discussions Archive

possible bug GIF and transparency IM 6.9.0.3 Mac OSX SnowLeopard

possible bug GIF and transparency IM 6.9.0.3 Mac OSX SnowLeopard

Re: possible bug GIF and transparency IM 6.9.0.3 Mac OSX SnowLeopard