As far as I could read, the MedianCutQuantizer's generated palette does not have space for a transparent color.
Given non-paletted img, this is what I do -- tell the quantizer to generate a paletted image, then prepend it with transparent color (I like having transparency as the zeroth color in the palette).
It makes me uneasy that dst.Set() is not skippable, given I have no use for the actual pixels, but I've chosen that's still fine as I still get a palette back:
quantizer := gogif.MedianCutQuantizer{NumColor: 255} // Up to 255 colors plus 1 space for transparency.
pal := image.NewPaletted(img.Bounds(), nil)
quantizer.Quantize(pal, img.Bounds(), img, image.ZP)
// Create a version of paletted image with color.Transparent in it. That's the first
// color so the empty image defaults to it.
palTransparent := image.NewPaletted(img.Bounds(), append(color.Palette([]color.Color{color.Transparent}), pal.Palette...))
// Now use draw.Draw() to create a version of the image which has the
// MedianCutQuantizer's palette plus transparent color.
draw.Draw(palTransparent, img.Bounds(), img, image.ZP, draw.Over)
g.Image = append(g.Image, palTransparent)
g.Delay = append(g.Delay, 50)
g.Disposal = append(g.Disposal, gif.DisposalBackground)
g.BackgroundIndex = 0 // image.Transparent
draw.Draw is from image/draw, naturally. g is an image/gif.GIF.
As far as I could read, the
MedianCutQuantizer's generated palette does not have space for a transparent color.Given non-paletted
img, this is what I do -- tell the quantizer to generate a paletted image, then prepend it with transparent color (I like having transparency as the zeroth color in the palette).It makes me uneasy that
dst.Set()is not skippable, given I have no use for the actual pixels, but I've chosen that's still fine as I still get a palette back:draw.Drawis fromimage/draw, naturally.gis animage/gif.GIF.