aw/go-resize
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Merge branch 'alpha_channel_fix'

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Colors in image.RGBA, image.RGBA64 and generic types with alpha channel should
now resize correctly. There's a small performance hit for these image types even
if they don't use alpha channels though.
Fixes bug #26.
This commit is contained in:
nfnt 2015-05-12 16:00:13 +02:00
commit f2d1b73023
2 changed files with 66 additions and 8 deletions
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59
converter.go
View File

@ -64,6 +64,17 @@ func resizeGeneric(in image.Image, out *image.NRGBA64, scale float64, coeffs []i
xi = maxX
}
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[1] += int64(coeff) * int64(g)
rgba[2] += int64(coeff) * int64(b)
@ -112,10 +123,26 @@ func resizeRGBA(in *image.RGBA, out *image.NRGBA, scale float64, coeffs []int16,
default:
xi = 0
}
rgba[0] += int32(coeff) * int32(row[xi+0])
rgba[1] += int32(coeff) * int32(row[xi+1])
rgba[2] += int32(coeff) * int32(row[xi+2])
rgba[3] += int32(coeff) * int32(row[xi+3])
r := uint32(row[xi+0])
g := uint32(row[xi+1])
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)
}
}
@ -192,10 +219,26 @@ func resizeRGBA64(in *image.RGBA64, out *image.NRGBA64, scale float64, coeffs []
default:
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]))
rgba[2] += int64(coeff) * int64(uint16(row[xi+4])<<8|uint16(row[xi+5]))
rgba[3] += int64(coeff) * int64(uint16(row[xi+6])<<8|uint16(row[xi+7]))
r := uint32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
g := uint32(uint16(row[xi+2])<<8 | uint16(row[xi+3]))
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)
}
}

15
resize_test.go
View File

@ -105,6 +105,21 @@ func Test_PixelCoordinates(t *testing.T) {
}
}
func Test_ResizeWithPremultipliedAlpha(t *testing.T) {
img := image.NewRGBA(image.Rect(0, 0, 1, 4))
for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ {
// 0x80 = 0.5 * 0xFF.
img.SetRGBA(0, y, color.RGBA{0x80, 0x80, 0x80, 0x80})
}
out := Resize(1, 2, img, MitchellNetravali)
outputColor := out.At(0, 0).(color.NRGBA)
if outputColor.R != 0xFF {
t.Fail()
}
}
const (
// Use a small image size for benchmarks. We don't want memory performance
// to affect the benchmark results.