Reverse alpha premultiplication
This commit is contained in:
Eugene Zagidullin
nfnt
parent
579058ccc0
commit
5311ab3c51
129
converter.go
129
converter.go
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@ -63,18 +63,9 @@ func resizeGeneric(in image.Image, out *image.NRGBA64, scale float64, coeffs []i
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case xi >= maxX:
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case xi >= maxX:
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xi = maxX
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xi = maxX
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}
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}
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// Forward alpha-premultiplication (if needed)
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r, g, b, a := in.At(xi+in.Bounds().Min.X, x+in.Bounds().Min.Y).RGBA()
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r, g, b, a := in.At(xi+in.Bounds().Min.X, x+in.Bounds().Min.Y).RGBA()
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// reverse alpha-premultiplication.
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if a != 0 {
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r *= 0xffff
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r /= a
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g *= 0xffff
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g /= a
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b *= 0xffff
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b /= a
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}
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rgba[0] += int64(coeff) * int64(r)
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rgba[0] += int64(coeff) * int64(r)
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rgba[1] += int64(coeff) * int64(g)
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rgba[1] += int64(coeff) * int64(g)
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rgba[2] += int64(coeff) * int64(b)
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rgba[2] += int64(coeff) * int64(b)
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@ -84,16 +75,18 @@ func resizeGeneric(in image.Image, out *image.NRGBA64, scale float64, coeffs []i
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}
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}
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offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
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offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
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value := clampUint16(rgba[0] / sum)
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// Reverse alpha-premultiplication
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a := rgba[3] / sum
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value := clampUint16(rgba[0] * 0xffff / a / sum)
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out.Pix[offset+0] = uint8(value >> 8)
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out.Pix[offset+0] = uint8(value >> 8)
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out.Pix[offset+1] = uint8(value)
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out.Pix[offset+1] = uint8(value)
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value = clampUint16(rgba[1] / sum)
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value = clampUint16(rgba[1] * 0xffff / a / sum)
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out.Pix[offset+2] = uint8(value >> 8)
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out.Pix[offset+2] = uint8(value >> 8)
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out.Pix[offset+3] = uint8(value)
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out.Pix[offset+3] = uint8(value)
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value = clampUint16(rgba[2] / sum)
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value = clampUint16(rgba[2] * 0xffff / a / sum)
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out.Pix[offset+4] = uint8(value >> 8)
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out.Pix[offset+4] = uint8(value >> 8)
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out.Pix[offset+5] = uint8(value)
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out.Pix[offset+5] = uint8(value)
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value = clampUint16(rgba[3] / sum)
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value = clampUint16(a)
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out.Pix[offset+6] = uint8(value >> 8)
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out.Pix[offset+6] = uint8(value >> 8)
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out.Pix[offset+7] = uint8(value)
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out.Pix[offset+7] = uint8(value)
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}
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}
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@ -124,34 +117,21 @@ func resizeRGBA(in *image.RGBA, out *image.NRGBA, scale float64, coeffs []int16,
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xi = 0
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xi = 0
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}
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}
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r := uint32(row[xi+0])
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rgba[0] += int32(coeff) * int32(row[xi+0])
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g := uint32(row[xi+1])
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rgba[1] += int32(coeff) * int32(row[xi+1])
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b := uint32(row[xi+2])
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rgba[2] += int32(coeff) * int32(row[xi+2])
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a := uint32(row[xi+3])
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rgba[3] += int32(coeff) * int32(row[xi+3])
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// reverse alpha-premultiplication.
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if a != 0 {
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r *= 0xff
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r /= a
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g *= 0xff
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g /= a
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b *= 0xff
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b /= a
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}
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rgba[0] += int32(coeff) * int32(r)
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rgba[1] += int32(coeff) * int32(g)
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rgba[2] += int32(coeff) * int32(b)
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rgba[3] += int32(coeff) * int32(a)
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sum += int32(coeff)
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sum += int32(coeff)
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}
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}
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}
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}
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xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
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xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
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out.Pix[xo+0] = clampUint8(rgba[0] / sum)
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// Reverse alpha-premultiplication
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out.Pix[xo+1] = clampUint8(rgba[1] / sum)
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a := rgba[3] / sum
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out.Pix[xo+2] = clampUint8(rgba[2] / sum)
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out.Pix[xo+0] = clampUint8(rgba[0] * 0xff / a / sum)
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out.Pix[xo+3] = clampUint8(rgba[3] / sum)
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out.Pix[xo+1] = clampUint8(rgba[1] * 0xff / a / sum)
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out.Pix[xo+2] = clampUint8(rgba[2] * 0xff / a / sum)
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out.Pix[xo+3] = clampUint8(a)
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}
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}
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}
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}
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}
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}
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@ -179,19 +159,24 @@ func resizeNRGBA(in *image.NRGBA, out *image.NRGBA, scale float64, coeffs []int1
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default:
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default:
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xi = 0
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xi = 0
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}
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}
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rgba[0] += int32(coeff) * int32(row[xi+0])
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rgba[1] += int32(coeff) * int32(row[xi+1])
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// Forward alpha-premultiplication
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rgba[2] += int32(coeff) * int32(row[xi+2])
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a := int32(row[xi+3])
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rgba[3] += int32(coeff) * int32(row[xi+3])
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rgba[0] += int32(coeff) * int32(row[xi+0]) * a / 0xff
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rgba[1] += int32(coeff) * int32(row[xi+1]) * a / 0xff
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rgba[2] += int32(coeff) * int32(row[xi+2]) * a / 0xff
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rgba[3] += int32(coeff) * a
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sum += int32(coeff)
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sum += int32(coeff)
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}
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}
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}
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}
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xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
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xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
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out.Pix[xo+0] = clampUint8(rgba[0] / sum)
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// Reverse alpha-premultiplication
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out.Pix[xo+1] = clampUint8(rgba[1] / sum)
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a := rgba[3] / sum
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out.Pix[xo+2] = clampUint8(rgba[2] / sum)
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out.Pix[xo+0] = clampUint8(rgba[0] * 0xff / a / sum)
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out.Pix[xo+3] = clampUint8(rgba[3] / sum)
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out.Pix[xo+1] = clampUint8(rgba[1] * 0xff / a / sum)
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out.Pix[xo+2] = clampUint8(rgba[2] * 0xff / a / sum)
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out.Pix[xo+3] = clampUint8(a)
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}
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}
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}
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}
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}
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}
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@ -220,40 +205,27 @@ func resizeRGBA64(in *image.RGBA64, out *image.NRGBA64, scale float64, coeffs []
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xi = 0
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xi = 0
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}
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}
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r := uint32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
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rgba[0] += int64(coeff) * (int64(row[xi+0])<<8 | int64(row[xi+1]))
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g := uint32(uint16(row[xi+2])<<8 | uint16(row[xi+3]))
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rgba[1] += int64(coeff) * (int64(row[xi+2])<<8 | int64(row[xi+3]))
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b := uint32(uint16(row[xi+4])<<8 | uint16(row[xi+5]))
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rgba[2] += int64(coeff) * (int64(row[xi+4])<<8 | int64(row[xi+5]))
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a := uint32(uint16(row[xi+6])<<8 | uint16(row[xi+7]))
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rgba[3] += int64(coeff) * (int64(row[xi+6])<<8 | int64(row[xi+7]))
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// reverse alpha-premultiplication.
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if a != 0 {
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r *= 0xffff
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r /= a
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g *= 0xffff
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g /= a
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b *= 0xffff
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b /= a
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}
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rgba[0] += int64(coeff) * int64(r)
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rgba[1] += int64(coeff) * int64(g)
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rgba[2] += int64(coeff) * int64(b)
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rgba[3] += int64(coeff) * int64(a)
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sum += int64(coeff)
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sum += int64(coeff)
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}
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}
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}
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}
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xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
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xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
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value := clampUint16(rgba[0] / sum)
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// Reverse alpha-premultiplication
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a := rgba[3] / sum
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value := clampUint16(rgba[0] * 0xffff / a / sum)
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out.Pix[xo+0] = uint8(value >> 8)
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out.Pix[xo+0] = uint8(value >> 8)
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out.Pix[xo+1] = uint8(value)
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out.Pix[xo+1] = uint8(value)
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value = clampUint16(rgba[1] / sum)
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value = clampUint16(rgba[1] * 0xffff / a / sum)
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out.Pix[xo+2] = uint8(value >> 8)
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out.Pix[xo+2] = uint8(value >> 8)
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out.Pix[xo+3] = uint8(value)
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out.Pix[xo+3] = uint8(value)
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value = clampUint16(rgba[2] / sum)
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value = clampUint16(rgba[2] * 0xffff / a / sum)
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out.Pix[xo+4] = uint8(value >> 8)
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out.Pix[xo+4] = uint8(value >> 8)
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out.Pix[xo+5] = uint8(value)
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out.Pix[xo+5] = uint8(value)
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value = clampUint16(rgba[3] / sum)
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value = clampUint16(a)
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out.Pix[xo+6] = uint8(value >> 8)
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out.Pix[xo+6] = uint8(value >> 8)
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out.Pix[xo+7] = uint8(value)
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out.Pix[xo+7] = uint8(value)
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}
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}
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@ -283,25 +255,30 @@ func resizeNRGBA64(in *image.NRGBA64, out *image.NRGBA64, scale float64, coeffs
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default:
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default:
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xi = 0
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xi = 0
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}
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}
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rgba[0] += int64(coeff) * int64(uint16(row[xi+0])<<8|uint16(row[xi+1]))
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rgba[1] += int64(coeff) * int64(uint16(row[xi+2])<<8|uint16(row[xi+3]))
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// Forward alpha-premultiplication
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rgba[2] += int64(coeff) * int64(uint16(row[xi+4])<<8|uint16(row[xi+5]))
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a := int64(row[xi+6])<<8 | int64(row[xi+7])
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rgba[3] += int64(coeff) * int64(uint16(row[xi+6])<<8|uint16(row[xi+7]))
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rgba[0] += int64(coeff) * (int64(row[xi+0])<<8 | int64(row[xi+1])) * a / 0xffff
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rgba[1] += int64(coeff) * (int64(row[xi+2])<<8 | int64(row[xi+3])) * a / 0xffff
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rgba[2] += int64(coeff) * (int64(row[xi+4])<<8 | int64(row[xi+5])) * a / 0xffff
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rgba[3] += int64(coeff) * a
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sum += int64(coeff)
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sum += int64(coeff)
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}
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}
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}
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}
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xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
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xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
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value := clampUint16(rgba[0] / sum)
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// Reverse alpha-premultiplication
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a := rgba[3] / sum
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value := clampUint16(rgba[0] * 0xffff / a / sum)
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out.Pix[xo+0] = uint8(value >> 8)
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out.Pix[xo+0] = uint8(value >> 8)
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out.Pix[xo+1] = uint8(value)
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out.Pix[xo+1] = uint8(value)
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value = clampUint16(rgba[1] / sum)
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value = clampUint16(rgba[1] * 0xffff / a / sum)
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out.Pix[xo+2] = uint8(value >> 8)
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out.Pix[xo+2] = uint8(value >> 8)
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out.Pix[xo+3] = uint8(value)
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out.Pix[xo+3] = uint8(value)
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value = clampUint16(rgba[2] / sum)
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value = clampUint16(rgba[2] * 0xffff / a / sum)
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out.Pix[xo+4] = uint8(value >> 8)
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out.Pix[xo+4] = uint8(value >> 8)
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out.Pix[xo+5] = uint8(value)
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out.Pix[xo+5] = uint8(value)
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value = clampUint16(rgba[3] / sum)
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value = clampUint16(a)
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out.Pix[xo+6] = uint8(value >> 8)
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out.Pix[xo+6] = uint8(value >> 8)
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out.Pix[xo+7] = uint8(value)
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out.Pix[xo+7] = uint8(value)
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}
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}
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