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image/color: Palette ignores alpha channel #9902

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magical opened this issue Feb 17, 2015 · 0 comments
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image/color: Palette ignores alpha channel #9902

magical opened this issue Feb 17, 2015 · 0 comments
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@magical
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@magical magical commented Feb 17, 2015

Palette.Index, and by extension image.Paletted.Set, cannot distinguish between image.Black and image.Transparent (and in general, any fully-transparent color or partially-transparent black) because it ignores the alpha channel of the colors when searching for the closet match.

This makes it impossible to draw a black pixel onto an image.Paletted whose palette contains color.Transparent, even if it also contains color.Black (or the other way around, depending on the order of the colors in the palette).

See this example program: http://play.golang.org/p/29G2978Px7

In general, it seems like p.Convert(c) should equal c, for every color.Palette p and color.Color c in p.

@rsc rsc added this to the Go1.5Maybe milestone Apr 10, 2015
@nigeltao nigeltao closed this in 28388c4 Apr 16, 2015
@mikioh mikioh modified the milestones: Go1.5, Go1.5Maybe May 27, 2015
@golang golang locked and limited conversation to collaborators Jun 25, 2016
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