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Reverse alpha-premultiplication for image.RGBA, image.RGBA64 and generic images

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types.
This commit is contained in:
nfnt 2015-05-12 15:19:11 +02:00
parent 5a6676c19e
commit c3c062672a
1 changed files with 51 additions and 8 deletions
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59
converter.go
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@ -64,6 +64,17 @@ func resizeGeneric(in image.Image, out *image.NRGBA64, scale float64, coeffs []i
xi = maxX xi = maxX
} }
r, g, b, a := in.At(xi+in.Bounds().Min.X, x+in.Bounds().Min.Y).RGBA() r, g, b, a := in.At(xi+in.Bounds().Min.X, x+in.Bounds().Min.Y).RGBA()
// reverse alpha-premultiplication.
if a != 0 {
r *= 0xffff
r /= a
g *= 0xffff
g /= a
b *= 0xffff
b /= a
}
rgba[0] += int64(coeff) * int64(r) rgba[0] += int64(coeff) * int64(r)
rgba[1] += int64(coeff) * int64(g) rgba[1] += int64(coeff) * int64(g)
rgba[2] += int64(coeff) * int64(b) rgba[2] += int64(coeff) * int64(b)
@ -112,10 +123,26 @@ func resizeRGBA(in *image.RGBA, out *image.NRGBA, scale float64, coeffs []int16,
default: default:
xi = 0 xi = 0
} }
rgba[0] += int32(coeff) * int32(row[xi+0])
rgba[1] += int32(coeff) * int32(row[xi+1]) r := uint32(row[xi+0])
rgba[2] += int32(coeff) * int32(row[xi+2]) g := uint32(row[xi+1])
rgba[3] += int32(coeff) * int32(row[xi+3]) b := uint32(row[xi+2])
a := uint32(row[xi+3])
// reverse alpha-premultiplication.
if a != 0 {
r *= 0xffff
r /= a
g *= 0xffff
g /= a
b *= 0xffff
b /= a
}
rgba[0] += int32(coeff) * int32(r)
rgba[1] += int32(coeff) * int32(g)
rgba[2] += int32(coeff) * int32(b)
rgba[3] += int32(coeff) * int32(a)
sum += int32(coeff) sum += int32(coeff)
} }
} }
@ -192,10 +219,26 @@ func resizeRGBA64(in *image.RGBA64, out *image.NRGBA64, scale float64, coeffs []
default: default:
xi = 0 xi = 0
} }
rgba[0] += int64(coeff) * int64(uint16(row[xi+0])<<8|uint16(row[xi+1]))
rgba[1] += int64(coeff) * int64(uint16(row[xi+2])<<8|uint16(row[xi+3])) r := uint32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
rgba[2] += int64(coeff) * int64(uint16(row[xi+4])<<8|uint16(row[xi+5])) g := uint32(uint16(row[xi+2])<<8 | uint16(row[xi+3]))
rgba[3] += int64(coeff) * int64(uint16(row[xi+6])<<8|uint16(row[xi+7])) b := uint32(uint16(row[xi+4])<<8 | uint16(row[xi+5]))
a := uint32(uint16(row[xi+6])<<8 | uint16(row[xi+7]))
// reverse alpha-premultiplication.
if a != 0 {
r *= 0xffff
r /= a
g *= 0xffff
g /= a
b *= 0xffff
b /= a
}
rgba[0] += int64(coeff) * int64(r)
rgba[1] += int64(coeff) * int64(g)
rgba[2] += int64(coeff) * int64(b)
rgba[3] += int64(coeff) * int64(a)
sum += int64(coeff) sum += int64(coeff)
} }
} }