Merge branch 'charlievieth-master'

converter.go

@@ -16,10 +16,7 @@ THIS SOFTWARE.
 
 package resize
 
-import (
+import "image"
-	"image"
-	"image/color"
-)
 
 // Keep value in [0,255] range.
 func clampUint8(in int32) uint8 {
@@ -43,33 +40,36 @@ func clampUint16(in int64) uint16 {
 	return uint16(in)
 }
 
-func resizeGeneric(in image.Image, out *image.RGBA64, scale float64, coeffs []int32, filterLength int) {
+func resizeGeneric(in image.Image, out *image.RGBA64, scale float64, coeffs []int32, offset []int, filterLength int) {
 	oldBounds := in.Bounds()
 	newBounds := out.Bounds()
 
 	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
 		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
-			interpX := scale*(float64(y)+0.5) + float64(oldBounds.Min.X)
-			start := int(interpX) - filterLength/2 + 1
-
 			var rgba [4]int64
 			var sum int64
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
 			for i := 0; i < filterLength; i++ {
-				xx := start + i
+				coeff := coeffs[ci+i]
-				if xx < oldBounds.Min.X {
+				if coeff != 0 {
-					xx = oldBounds.Min.X
+					xi := start + i
-				} else if xx >= oldBounds.Max.X {
+					switch {
-					xx = oldBounds.Max.X - 1
+					case uint(xi) < uint(oldBounds.Max.X):
+						break
+					case xi >= oldBounds.Max.X:
+						xi = oldBounds.Min.X
+					default:
+						xi = oldBounds.Max.X - 1
 					}
-
+					r, g, b, a := in.At(xi, x).RGBA()
-				coeff := coeffs[(y-newBounds.Min.Y)*filterLength+i]
-				r, g, b, a := in.At(xx, x).RGBA()
 					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)
 				}
+			}
 
 			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
 			value := clampUint16(rgba[0] / sum)
@@ -88,115 +88,127 @@ func resizeGeneric(in image.Image, out *image.RGBA64, scale float64, coeffs []in
 	}
 }
 
-func resizeRGBA(in *image.RGBA, out *image.RGBA, scale float64, coeffs []int16, filterLength int) {
+func resizeRGBA(in *image.RGBA, out *image.RGBA, scale float64, coeffs []int16, offset []int, filterLength int) {
 	oldBounds := in.Bounds()
 	newBounds := out.Bounds()
+	minX := oldBounds.Min.X * 4
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 4
 
 	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
 		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
 		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
-			interpX := scale*(float64(y)+0.5) + float64(oldBounds.Min.X)
-			start := int(interpX) - filterLength/2 + 1
-
 			var rgba [4]int32
 			var sum int32
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
 			for i := 0; i < filterLength; i++ {
-				xx := start + i
+				coeff := coeffs[ci+i]
-				if xx < oldBounds.Min.X {
+				if coeff != 0 {
-					xx = oldBounds.Min.X
+					xi := start + i
-				} else if xx >= oldBounds.Max.X {
+					switch {
-					xx = oldBounds.Max.X - 1
+					case uint(xi) < uint(oldBounds.Max.X):
+						xi *= 4
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
 					}
-
+					rgba[0] += int32(coeff) * int32(row[xi+0])
-				coeff := coeffs[(y-newBounds.Min.Y)*filterLength+i]
+					rgba[1] += int32(coeff) * int32(row[xi+1])
-				offset := (xx - oldBounds.Min.X) * 4
+					rgba[2] += int32(coeff) * int32(row[xi+2])
-				rgba[0] += int32(coeff) * int32(row[offset+0])
+					rgba[3] += int32(coeff) * int32(row[xi+3])
-				rgba[1] += int32(coeff) * int32(row[offset+1])
-				rgba[2] += int32(coeff) * int32(row[offset+2])
-				rgba[3] += int32(coeff) * int32(row[offset+3])
 					sum += int32(coeff)
 				}
+			}
 
-			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
-			out.Pix[offset+0] = clampUint8(rgba[0] / sum)
+			out.Pix[xo+0] = clampUint8(rgba[0] / sum)
-			out.Pix[offset+1] = clampUint8(rgba[1] / sum)
+			out.Pix[xo+1] = clampUint8(rgba[1] / sum)
-			out.Pix[offset+2] = clampUint8(rgba[2] / sum)
+			out.Pix[xo+2] = clampUint8(rgba[2] / sum)
-			out.Pix[offset+3] = clampUint8(rgba[3] / sum)
+			out.Pix[xo+3] = clampUint8(rgba[3] / sum)
 		}
 	}
 }
 
-func resizeRGBA64(in *image.RGBA64, out *image.RGBA64, scale float64, coeffs []int32, filterLength int) {
+func resizeRGBA64(in *image.RGBA64, out *image.RGBA64, scale float64, coeffs []int32, offset []int, filterLength int) {
 	oldBounds := in.Bounds()
 	newBounds := out.Bounds()
+	minX := oldBounds.Min.X * 8
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 8
 
 	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
 		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
 		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
-			interpX := scale*(float64(y)+0.5) + float64(oldBounds.Min.X)
-			start := int(interpX) - filterLength/2 + 1
-
 			var rgba [4]int64
 			var sum int64
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
 			for i := 0; i < filterLength; i++ {
-				xx := start + i
+				coeff := coeffs[ci+i]
-				if xx < oldBounds.Min.X {
+				if coeff != 0 {
-					xx = oldBounds.Min.X
+					xi := start + i
-				} else if xx >= oldBounds.Max.X {
+					switch {
-					xx = oldBounds.Max.X - 1
+					case uint(xi) < uint(oldBounds.Max.X):
+						xi *= 8
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
 					}
-
+					rgba[0] += int64(coeff) * int64(uint16(row[xi+0])<<8|uint16(row[xi+1]))
-				coeff := coeffs[(y-newBounds.Min.Y)*filterLength+i]
+					rgba[1] += int64(coeff) * int64(uint16(row[xi+2])<<8|uint16(row[xi+3]))
-				offset := (xx - oldBounds.Min.X) * 8
+					rgba[2] += int64(coeff) * int64(uint16(row[xi+4])<<8|uint16(row[xi+5]))
-				rgba[0] += int64(coeff) * int64(uint16(row[offset+0])<<8|uint16(row[offset+1]))
+					rgba[3] += int64(coeff) * int64(uint16(row[xi+6])<<8|uint16(row[xi+7]))
-				rgba[1] += int64(coeff) * int64(uint16(row[offset+2])<<8|uint16(row[offset+3]))
-				rgba[2] += int64(coeff) * int64(uint16(row[offset+4])<<8|uint16(row[offset+5]))
-				rgba[3] += int64(coeff) * int64(uint16(row[offset+6])<<8|uint16(row[offset+7]))
 					sum += int64(coeff)
 				}
+			}
 
-			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
 			value := clampUint16(rgba[0] / sum)
-			out.Pix[offset+0] = uint8(value >> 8)
+			out.Pix[xo+0] = uint8(value >> 8)
-			out.Pix[offset+1] = uint8(value)
+			out.Pix[xo+1] = uint8(value)
 			value = clampUint16(rgba[1] / sum)
-			out.Pix[offset+2] = uint8(value >> 8)
+			out.Pix[xo+2] = uint8(value >> 8)
-			out.Pix[offset+3] = uint8(value)
+			out.Pix[xo+3] = uint8(value)
 			value = clampUint16(rgba[2] / sum)
-			out.Pix[offset+4] = uint8(value >> 8)
+			out.Pix[xo+4] = uint8(value >> 8)
-			out.Pix[offset+5] = uint8(value)
+			out.Pix[xo+5] = uint8(value)
 			value = clampUint16(rgba[3] / sum)
-			out.Pix[offset+6] = uint8(value >> 8)
+			out.Pix[xo+6] = uint8(value >> 8)
-			out.Pix[offset+7] = uint8(value)
+			out.Pix[xo+7] = uint8(value)
 		}
 	}
 }
 
-func resizeGray(in *image.Gray, out *image.Gray, scale float64, coeffs []int16, filterLength int) {
+func resizeGray(in *image.Gray, out *image.Gray, scale float64, coeffs []int16, offset []int, filterLength int) {
 	oldBounds := in.Bounds()
 	newBounds := out.Bounds()
+	minX := oldBounds.Min.X
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1)
 
 	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
 		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
 		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
-			interpX := scale*(float64(y)+0.5) + float64(oldBounds.Min.X)
-			start := int(interpX) - filterLength/2 + 1
-
 			var gray int32
 			var sum int32
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
 			for i := 0; i < filterLength; i++ {
-				xx := start + i
+				coeff := coeffs[ci+i]
-				if xx < oldBounds.Min.X {
+				if coeff != 0 {
-					xx = oldBounds.Min.X
+					xi := start + i
-				} else if xx >= oldBounds.Max.X {
+					switch {
-					xx = oldBounds.Max.X - 1
+					case uint(xi) < uint(oldBounds.Max.X):
+						break
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
 					}
-
+					gray += int32(coeff) * int32(row[xi])
-				coeff := coeffs[(y-newBounds.Min.Y)*filterLength+i]
-				offset := (xx - oldBounds.Min.X)
-				gray += int32(coeff) * int32(row[offset])
 					sum += int32(coeff)
 				}
+			}
 
 			offset := (y-newBounds.Min.Y)*out.Stride + (x - newBounds.Min.X)
 			out.Pix[offset] = clampUint8(gray / sum)
@@ -204,31 +216,35 @@ func resizeGray(in *image.Gray, out *image.Gray, scale float64, coeffs []int16,
 	}
 }
 
-func resizeGray16(in *image.Gray16, out *image.Gray16, scale float64, coeffs []int32, filterLength int) {
+func resizeGray16(in *image.Gray16, out *image.Gray16, scale float64, coeffs []int32, offset []int, filterLength int) {
 	oldBounds := in.Bounds()
 	newBounds := out.Bounds()
+	minX := oldBounds.Min.X * 2
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 2
 
 	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
 		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
 		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
-			interpX := scale*(float64(y)+0.5) + float64(oldBounds.Min.X)
-			start := int(interpX) - filterLength/2 + 1
-
 			var gray int64
 			var sum int64
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
 			for i := 0; i < filterLength; i++ {
-				xx := start + i
+				coeff := coeffs[ci+i]
-				if xx < oldBounds.Min.X {
+				if coeff != 0 {
-					xx = oldBounds.Min.X
+					xi := start + i
-				} else if xx >= oldBounds.Max.X {
+					switch {
-					xx = oldBounds.Max.X - 1
+					case uint(xi) < uint(oldBounds.Max.X):
+						xi *= 2
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
 					}
-
+					gray += int64(coeff) * int64(uint16(row[xi+0])<<8|uint16(row[xi+1]))
-				coeff := coeffs[(y-newBounds.Min.Y)*filterLength+i]
-				offset := (xx - oldBounds.Min.X) * 2
-				gray += int64(coeff) * int64(uint16(row[offset+0])<<8|uint16(row[offset+1]))
 					sum += int64(coeff)
 				}
+			}
 
 			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*2
 			value := clampUint16(gray / sum)
@@ -238,19 +254,81 @@ func resizeGray16(in *image.Gray16, out *image.Gray16, scale float64, coeffs []i
 	}
 }
 
-func convertYCbCrToRGBA(in *image.YCbCr) *image.RGBA {
+func resizeYCbCr(in *ycc, out *ycc, scale float64, coeffs []int16, offset []int, filterLength int) {
-	out := image.NewRGBA(in.Bounds())
+	oldBounds := in.Bounds()
-	for y := 0; y < out.Bounds().Dy(); y++ {
+	newBounds := out.Bounds()
-		for x := 0; x < out.Bounds().Dx(); x++ {
+	minX := oldBounds.Min.X * 3
-			p := out.Pix[y*out.Stride+4*x:]
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 3
-			yi := in.YOffset(x, y)
+
-			ci := in.COffset(x, y)
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
-			r, g, b := color.YCbCrToRGB(in.Y[yi], in.Cb[ci], in.Cr[ci])
+		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
-			p[0] = r
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
-			p[1] = g
+			var p [3]int32
-			p[2] = b
+			var sum int32
-			p[3] = 0xff
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
+			for i := 0; i < filterLength; i++ {
+				coeff := coeffs[ci+i]
+				if coeff != 0 {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(oldBounds.Max.X):
+						xi *= 3
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
+					}
+					p[0] += int32(coeff) * int32(row[xi+0])
+					p[1] += int32(coeff) * int32(row[xi+1])
+					p[2] += int32(coeff) * int32(row[xi+2])
+					sum += int32(coeff)
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*3
+			out.Pix[xo+0] = clampUint8(p[0] / sum)
+			out.Pix[xo+1] = clampUint8(p[1] / sum)
+			out.Pix[xo+2] = clampUint8(p[2] / sum)
+		}
+	}
+}
+
+func nearestYCbCr(in *ycc, out *ycc, scale float64, coeffs []bool, offset []int, filterLength int) {
+	oldBounds := in.Bounds()
+	newBounds := out.Bounds()
+	minX := oldBounds.Min.X * 3
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 3
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var p [3]float32
+			var sum float32
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(oldBounds.Max.X):
+						xi *= 3
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
+					}
+					p[0] += float32(row[xi+0])
+					p[1] += float32(row[xi+1])
+					p[2] += float32(row[xi+2])
+					sum++
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*3
+			out.Pix[xo+0] = floatToUint8(p[0] / sum)
+			out.Pix[xo+1] = floatToUint8(p[1] / sum)
+			out.Pix[xo+2] = floatToUint8(p[2] / sum)
 		}
 	}
-	return out
 }

filters.go

@@ -80,37 +80,64 @@ func lanczos3(in float64) float64 {
 }
 
 // range [-256,256]
-func createWeights8(dy, minx, filterLength int, blur, scale float64, kernel func(float64) float64) ([]int16, int) {
+func createWeights8(dy, minx, filterLength int, blur, scale float64, kernel func(float64) float64) ([]int16, []int, int) {
 	filterLength = filterLength * int(math.Max(math.Ceil(blur*scale), 1))
 	filterFactor := math.Min(1./(blur*scale), 1)
 
 	coeffs := make([]int16, dy*filterLength)
+	start := make([]int, dy)
 	for y := 0; y < dy; y++ {
 		interpX := scale*(float64(y)+0.5) + float64(minx)
-		start := int(interpX) - filterLength/2 + 1
+		start[y] = int(interpX) - filterLength/2 + 1
+		interpX -= float64(start[y])
 		for i := 0; i < filterLength; i++ {
-			in := (interpX - float64(start) - float64(i)) * filterFactor
+			in := (interpX - float64(i)) * filterFactor
 			coeffs[y*filterLength+i] = int16(kernel(in) * 256)
 		}
 	}
 
-	return coeffs, filterLength
+	return coeffs, start, filterLength
 }
 
 // range [-65536,65536]
-func createWeights16(dy, minx, filterLength int, blur, scale float64, kernel func(float64) float64) ([]int32, int) {
+func createWeights16(dy, minx, filterLength int, blur, scale float64, kernel func(float64) float64) ([]int32, []int, int) {
 	filterLength = filterLength * int(math.Max(math.Ceil(blur*scale), 1))
 	filterFactor := math.Min(1./(blur*scale), 1)
 
 	coeffs := make([]int32, dy*filterLength)
+	start := make([]int, dy)
 	for y := 0; y < dy; y++ {
 		interpX := scale*(float64(y)+0.5) + float64(minx)
-		start := int(interpX) - filterLength/2 + 1
+		start[y] = int(interpX) - filterLength/2 + 1
+		interpX -= float64(start[y])
 		for i := 0; i < filterLength; i++ {
-			in := (interpX - float64(start) - float64(i)) * filterFactor
+			in := (interpX - float64(i)) * filterFactor
 			coeffs[y*filterLength+i] = int32(kernel(in) * 65536)
 		}
 	}
 
-	return coeffs, filterLength
+	return coeffs, start, filterLength
+}
+
+func createWeightsNearest(dy, minx, filterLength int, blur, scale float64) ([]bool, []int, int) {
+	filterLength = filterLength * int(math.Max(math.Ceil(blur*scale), 1))
+	filterFactor := math.Min(1./(blur*scale), 1)
+
+	coeffs := make([]bool, dy*filterLength)
+	start := make([]int, dy)
+	for y := 0; y < dy; y++ {
+		interpX := scale*(float64(y)+0.5) + float64(minx)
+		start[y] = int(interpX) - filterLength/2 + 1
+		interpX -= float64(start[y])
+		for i := 0; i < filterLength; i++ {
+			in := (interpX - float64(i)) * filterFactor
+			if in >= -0.5 && in < 0.5 {
+				coeffs[y*filterLength+i] = true
+			} else {
+				coeffs[y*filterLength+i] = false
+			}
+		}
+	}
+
+	return coeffs, start, filterLength
 }

nearest.go

@@ -0,0 +1,244 @@
+/*
+Copyright (c) 2014, Charlie Vieth <charlie.vieth@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+package resize
+
+import "image"
+
+func floatToUint8(x float32) uint8 {
+	// Nearest-neighbor values are always
+	// positive no need to check lower-bound.
+	if x > 0xfe {
+		return 0xff
+	}
+	return uint8(x)
+}
+
+func floatToUint16(x float32) uint16 {
+	if x > 0xfffe {
+		return 0xffff
+	}
+	return uint16(x)
+}
+
+func nearestGeneric(in image.Image, out *image.RGBA64, scale float64, coeffs []bool, offset []int, filterLength int) {
+	oldBounds := in.Bounds()
+	newBounds := out.Bounds()
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]float32
+			var sum float32
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(oldBounds.Max.X):
+						break
+					case xi >= oldBounds.Max.X:
+						xi = oldBounds.Min.X
+					default:
+						xi = oldBounds.Max.X - 1
+					}
+					r, g, b, a := in.At(xi, x).RGBA()
+					rgba[0] += float32(r)
+					rgba[1] += float32(g)
+					rgba[2] += float32(b)
+					rgba[3] += float32(a)
+					sum++
+				}
+			}
+
+			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
+			value := floatToUint16(rgba[0] / sum)
+			out.Pix[offset+0] = uint8(value >> 8)
+			out.Pix[offset+1] = uint8(value)
+			value = floatToUint16(rgba[1] / sum)
+			out.Pix[offset+2] = uint8(value >> 8)
+			out.Pix[offset+3] = uint8(value)
+			value = floatToUint16(rgba[2] / sum)
+			out.Pix[offset+4] = uint8(value >> 8)
+			out.Pix[offset+5] = uint8(value)
+			value = floatToUint16(rgba[3] / sum)
+			out.Pix[offset+6] = uint8(value >> 8)
+			out.Pix[offset+7] = uint8(value)
+		}
+	}
+}
+
+func nearestRGBA(in *image.RGBA, out *image.RGBA, scale float64, coeffs []bool, offset []int, filterLength int) {
+	oldBounds := in.Bounds()
+	newBounds := out.Bounds()
+	minX := oldBounds.Min.X * 4
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 4
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]float32
+			var sum float32
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(oldBounds.Max.X):
+						xi *= 4
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
+					}
+					rgba[0] += float32(row[xi+0])
+					rgba[1] += float32(row[xi+1])
+					rgba[2] += float32(row[xi+2])
+					rgba[3] += float32(row[xi+3])
+					sum++
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
+			out.Pix[xo+0] = floatToUint8(rgba[0] / sum)
+			out.Pix[xo+1] = floatToUint8(rgba[1] / sum)
+			out.Pix[xo+2] = floatToUint8(rgba[2] / sum)
+			out.Pix[xo+3] = floatToUint8(rgba[3] / sum)
+		}
+	}
+}
+
+func nearestRGBA64(in *image.RGBA64, out *image.RGBA64, scale float64, coeffs []bool, offset []int, filterLength int) {
+	oldBounds := in.Bounds()
+	newBounds := out.Bounds()
+	minX := oldBounds.Min.X * 8
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 8
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var rgba [4]float32
+			var sum float32
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(oldBounds.Max.X):
+						xi *= 8
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
+					}
+					rgba[0] += float32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
+					rgba[1] += float32(uint16(row[xi+2])<<8 | uint16(row[xi+3]))
+					rgba[2] += float32(uint16(row[xi+4])<<8 | uint16(row[xi+5]))
+					rgba[3] += float32(uint16(row[xi+6])<<8 | uint16(row[xi+7]))
+					sum++
+				}
+			}
+
+			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
+			value := floatToUint16(rgba[0] / sum)
+			out.Pix[xo+0] = uint8(value >> 8)
+			out.Pix[xo+1] = uint8(value)
+			value = floatToUint16(rgba[1] / sum)
+			out.Pix[xo+2] = uint8(value >> 8)
+			out.Pix[xo+3] = uint8(value)
+			value = floatToUint16(rgba[2] / sum)
+			out.Pix[xo+4] = uint8(value >> 8)
+			out.Pix[xo+5] = uint8(value)
+			value = floatToUint16(rgba[3] / sum)
+			out.Pix[xo+6] = uint8(value >> 8)
+			out.Pix[xo+7] = uint8(value)
+		}
+	}
+}
+
+func nearestGray(in *image.Gray, out *image.Gray, scale float64, coeffs []bool, offset []int, filterLength int) {
+	oldBounds := in.Bounds()
+	newBounds := out.Bounds()
+	minX := oldBounds.Min.X
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1)
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var gray float32
+			var sum float32
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(oldBounds.Max.X):
+						break
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
+					}
+					gray += float32(row[xi])
+					sum++
+				}
+			}
+
+			offset := (y-newBounds.Min.Y)*out.Stride + (x - newBounds.Min.X)
+			out.Pix[offset] = floatToUint8(gray / sum)
+		}
+	}
+}
+
+func nearestGray16(in *image.Gray16, out *image.Gray16, scale float64, coeffs []bool, offset []int, filterLength int) {
+	oldBounds := in.Bounds()
+	newBounds := out.Bounds()
+	minX := oldBounds.Min.X * 2
+	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 2
+
+	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
+		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
+		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
+			var gray float32
+			var sum float32
+			start := offset[y]
+			ci := (y - newBounds.Min.Y) * filterLength
+			for i := 0; i < filterLength; i++ {
+				if coeffs[ci+i] {
+					xi := start + i
+					switch {
+					case uint(xi) < uint(oldBounds.Max.X):
+						xi *= 2
+					case xi >= oldBounds.Max.X:
+						xi = maxX
+					default:
+						xi = minX
+					}
+					gray += float32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
+					sum++
+				}
+			}
+
+			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*2
+			value := floatToUint16(gray / sum)
+			out.Pix[offset+0] = uint8(value >> 8)
+			out.Pix[offset+1] = uint8(value)
+		}
+	}
+}

nearest_test.go

@@ -0,0 +1,57 @@
+/*
+Copyright (c) 2014, Charlie Vieth <charlie.vieth@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+package resize
+
+import "testing"
+
+func Test_FloatToUint8(t *testing.T) {
+	var testData = []struct {
+		in       float32
+		expected uint8
+	}{
+		{0, 0},
+		{255, 255},
+		{128, 128},
+		{1, 1},
+		{256, 255},
+	}
+	for _, test := range testData {
+		actual := floatToUint8(test.in)
+		if actual != test.expected {
+			t.Fail()
+		}
+	}
+}
+
+func Test_FloatToUint16(t *testing.T) {
+	var testData = []struct {
+		in       float32
+		expected uint16
+	}{
+		{0, 0},
+		{65535, 65535},
+		{128, 128},
+		{1, 1},
+		{65536, 65535},
+	}
+	for _, test := range testData {
+		actual := floatToUint16(test.in)
+		if actual != test.expected {
+			t.Fail()
+		}
+	}
+}

resize.go

@@ -33,36 +33,41 @@ import (
 // An InterpolationFunction provides the parameters that describe an
 // interpolation kernel. It returns the number of samples to take
 // and the kernel function to use for sampling.
-type InterpolationFunction func() (int, func(float64) float64)
+type InterpolationFunction int
 
+// InterpolationFunction constants
+const (
 	// Nearest-neighbor interpolation
-func NearestNeighbor() (int, func(float64) float64) {
+	NearestNeighbor InterpolationFunction = iota
+	// Bilinear interpolation
+	Bilinear
+	// Bicubic interpolation (with cubic hermite spline)
+	Bicubic
+	// Mitchell-Netravali interpolation
+	MitchellNetravali
+	// Lanczos interpolation (a=2)
+	Lanczos2
+	// Lanczos interpolation (a=3)
+	Lanczos3
+)
+
+// kernal, returns an InterpolationFunctions taps and kernel.
+func (i InterpolationFunction) kernel() (int, func(float64) float64) {
+	switch i {
+	case Bilinear:
+		return 2, linear
+	case Bicubic:
+		return 4, cubic
+	case MitchellNetravali:
+		return 4, mitchellnetravali
+	case Lanczos2:
+		return 4, lanczos2
+	case Lanczos3:
+		return 6, lanczos3
+	default:
+		// Default to NearestNeighbor.
 		return 2, nearest
 	}
-
-// Bilinear interpolation
-func Bilinear() (int, func(float64) float64) {
-	return 2, linear
-}
-
-// Bicubic interpolation (with cubic hermite spline)
-func Bicubic() (int, func(float64) float64) {
-	return 4, cubic
-}
-
-// Mitchell-Netravali interpolation
-func MitchellNetravali() (int, func(float64) float64) {
-	return 4, mitchellnetravali
-}
-
-// Lanczos interpolation (a=2)
-func Lanczos2() (int, func(float64) float64) {
-	return 4, lanczos2
-}
-
-// Lanczos interpolation (a=3)
-func Lanczos3() (int, func(float64) float64) {
-	return 6, lanczos3
 }
 
 // values <1 will sharpen the image
@@ -81,8 +86,11 @@ func Resize(width, height uint, img image.Image, interp InterpolationFunction) i
 	if height == 0 {
 		height = uint(0.7 + float64(img.Bounds().Dy())/scaleY)
 	}
+	if interp == NearestNeighbor {
+		return resizeNearest(width, height, scaleX, scaleY, img, interp)
+	}
 
-	taps, kernel := interp()
+	taps, kernel := interp.kernel()
 	cpus := runtime.NumCPU()
 	wg := sync.WaitGroup{}
 
@@ -95,25 +103,25 @@ func Resize(width, height uint, img image.Image, interp InterpolationFunction) i
 		result := image.NewRGBA(image.Rect(0, 0, int(width), int(height)))
 
 		// horizontal filter, results in transposed temporary image
-		coeffs, filterLength := createWeights8(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
+		coeffs, offset, filterLength := createWeights8(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(temp, i, cpus).(*image.RGBA)
 			go func() {
 				defer wg.Done()
-				resizeRGBA(input, slice, scaleX, coeffs, filterLength)
+				resizeRGBA(input, slice, scaleX, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
 
 		// horizontal filter on transposed image, result is not transposed
-		coeffs, filterLength = createWeights8(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
+		coeffs, offset, filterLength = createWeights8(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(result, i, cpus).(*image.RGBA)
 			go func() {
 				defer wg.Done()
-				resizeRGBA(temp, slice, scaleY, coeffs, filterLength)
+				resizeRGBA(temp, slice, scaleY, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
@@ -121,60 +129,58 @@ func Resize(width, height uint, img image.Image, interp InterpolationFunction) i
 	case *image.YCbCr:
 		// 8-bit precision
 		// accessing the YCbCr arrays in a tight loop is slow.
-		// converting the image before filtering will improve performance.
+		// converting the image to ycc increases performance by 2x.
-		inputAsRGBA := convertYCbCrToRGBA(input)
+		temp := newYCC(image.Rect(0, 0, input.Bounds().Dy(), int(width)), input.SubsampleRatio)
-		temp := image.NewRGBA(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := newYCC(image.Rect(0, 0, int(width), int(height)), input.SubsampleRatio)
-		result := image.NewRGBA(image.Rect(0, 0, int(width), int(height)))
 
-		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeights8(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
-		coeffs, filterLength := createWeights8(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
+		in := imageYCbCrToYCC(input)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
-			slice := makeSlice(temp, i, cpus).(*image.RGBA)
+			slice := makeSlice(temp, i, cpus).(*ycc)
 			go func() {
 				defer wg.Done()
-				resizeRGBA(inputAsRGBA, slice, scaleX, coeffs, filterLength)
+				resizeYCbCr(in, slice, scaleX, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
 
-		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeights8(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
-		coeffs, filterLength = createWeights8(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
-			slice := makeSlice(result, i, cpus).(*image.RGBA)
+			slice := makeSlice(result, i, cpus).(*ycc)
 			go func() {
 				defer wg.Done()
-				resizeRGBA(temp, slice, scaleY, coeffs, filterLength)
+				resizeYCbCr(temp, slice, scaleY, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
-		return result
+		return result.YCbCr()
 	case *image.RGBA64:
 		// 16-bit precision
 		temp := image.NewRGBA64(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
 		result := image.NewRGBA64(image.Rect(0, 0, int(width), int(height)))
 
 		// horizontal filter, results in transposed temporary image
-		coeffs, filterLength := createWeights16(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
+		coeffs, offset, filterLength := createWeights16(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(temp, i, cpus).(*image.RGBA64)
 			go func() {
 				defer wg.Done()
-				resizeRGBA64(input, slice, scaleX, coeffs, filterLength)
+				resizeRGBA64(input, slice, scaleX, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
 
 		// horizontal filter on transposed image, result is not transposed
-		coeffs, filterLength = createWeights16(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
+		coeffs, offset, filterLength = createWeights16(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(result, i, cpus).(*image.RGBA64)
 			go func() {
 				defer wg.Done()
-				resizeGeneric(temp, slice, scaleY, coeffs, filterLength)
+				resizeGeneric(temp, slice, scaleY, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
@@ -185,25 +191,25 @@ func Resize(width, height uint, img image.Image, interp InterpolationFunction) i
 		result := image.NewGray(image.Rect(0, 0, int(width), int(height)))
 
 		// horizontal filter, results in transposed temporary image
-		coeffs, filterLength := createWeights8(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
+		coeffs, offset, filterLength := createWeights8(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(temp, i, cpus).(*image.Gray)
 			go func() {
 				defer wg.Done()
-				resizeGray(input, slice, scaleX, coeffs, filterLength)
+				resizeGray(input, slice, scaleX, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
 
 		// horizontal filter on transposed image, result is not transposed
-		coeffs, filterLength = createWeights8(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
+		coeffs, offset, filterLength = createWeights8(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(result, i, cpus).(*image.Gray)
 			go func() {
 				defer wg.Done()
-				resizeGray(temp, slice, scaleY, coeffs, filterLength)
+				resizeGray(temp, slice, scaleY, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
@@ -214,25 +220,25 @@ func Resize(width, height uint, img image.Image, interp InterpolationFunction) i
 		result := image.NewGray16(image.Rect(0, 0, int(width), int(height)))
 
 		// horizontal filter, results in transposed temporary image
-		coeffs, filterLength := createWeights16(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
+		coeffs, offset, filterLength := createWeights16(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(temp, i, cpus).(*image.Gray16)
 			go func() {
 				defer wg.Done()
-				resizeGray16(input, slice, scaleX, coeffs, filterLength)
+				resizeGray16(input, slice, scaleX, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
 
 		// horizontal filter on transposed image, result is not transposed
-		coeffs, filterLength = createWeights16(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
+		coeffs, offset, filterLength = createWeights16(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(result, i, cpus).(*image.Gray16)
 			go func() {
 				defer wg.Done()
-				resizeGray16(temp, slice, scaleY, coeffs, filterLength)
+				resizeGray16(temp, slice, scaleY, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
@@ -243,25 +249,25 @@ func Resize(width, height uint, img image.Image, interp InterpolationFunction) i
 		result := image.NewRGBA64(image.Rect(0, 0, int(width), int(height)))
 
 		// horizontal filter, results in transposed temporary image
-		coeffs, filterLength := createWeights16(temp.Bounds().Dy(), img.Bounds().Min.X, taps, blur, scaleX, kernel)
+		coeffs, offset, filterLength := createWeights16(temp.Bounds().Dy(), img.Bounds().Min.X, taps, blur, scaleX, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(temp, i, cpus).(*image.RGBA64)
 			go func() {
 				defer wg.Done()
-				resizeGeneric(img, slice, scaleX, coeffs, filterLength)
+				resizeGeneric(img, slice, scaleX, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
 
 		// horizontal filter on transposed image, result is not transposed
-		coeffs, filterLength = createWeights16(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
+		coeffs, offset, filterLength = createWeights16(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY, kernel)
 		wg.Add(cpus)
 		for i := 0; i < cpus; i++ {
 			slice := makeSlice(result, i, cpus).(*image.RGBA64)
 			go func() {
 				defer wg.Done()
-				resizeRGBA64(temp, slice, scaleY, coeffs, filterLength)
+				resizeRGBA64(temp, slice, scaleY, coeffs, offset, filterLength)
 			}()
 		}
 		wg.Wait()
@@ -269,6 +275,191 @@ func Resize(width, height uint, img image.Image, interp InterpolationFunction) i
 	}
 }
 
+func resizeNearest(width, height uint, scaleX, scaleY float64, img image.Image, interp InterpolationFunction) image.Image {
+	taps, _ := interp.kernel()
+	cpus := runtime.NumCPU()
+	wg := sync.WaitGroup{}
+
+	switch input := img.(type) {
+	case *image.RGBA:
+		// 8-bit precision
+		temp := image.NewRGBA(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewRGBA(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA)
+			go func() {
+				defer wg.Done()
+				nearestRGBA(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA)
+			go func() {
+				defer wg.Done()
+				nearestRGBA(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.YCbCr:
+		// 8-bit precision
+		// accessing the YCbCr arrays in a tight loop is slow.
+		// converting the image to ycc increases performance by 2x.
+		temp := newYCC(image.Rect(0, 0, input.Bounds().Dy(), int(width)), input.SubsampleRatio)
+		result := newYCC(image.Rect(0, 0, int(width), int(height)), input.SubsampleRatio)
+
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX)
+		in := imageYCbCrToYCC(input)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*ycc)
+			go func() {
+				defer wg.Done()
+				nearestYCbCr(in, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*ycc)
+			go func() {
+				defer wg.Done()
+				nearestYCbCr(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result.YCbCr()
+	case *image.RGBA64:
+		// 16-bit precision
+		temp := image.NewRGBA64(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewRGBA64(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				nearestRGBA64(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				nearestGeneric(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.Gray:
+		// 8-bit precision
+		temp := image.NewGray(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewGray(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.Gray)
+			go func() {
+				defer wg.Done()
+				nearestGray(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.Gray)
+			go func() {
+				defer wg.Done()
+				nearestGray(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	case *image.Gray16:
+		// 16-bit precision
+		temp := image.NewGray16(image.Rect(0, 0, input.Bounds().Dy(), int(width)))
+		result := image.NewGray16(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), input.Bounds().Min.X, taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.Gray16)
+			go func() {
+				defer wg.Done()
+				nearestGray16(input, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.Gray16)
+			go func() {
+				defer wg.Done()
+				nearestGray16(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	default:
+		// 16-bit precision
+		temp := image.NewRGBA64(image.Rect(0, 0, img.Bounds().Dy(), int(width)))
+		result := image.NewRGBA64(image.Rect(0, 0, int(width), int(height)))
+
+		// horizontal filter, results in transposed temporary image
+		coeffs, offset, filterLength := createWeightsNearest(temp.Bounds().Dy(), img.Bounds().Min.X, taps, blur, scaleX)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(temp, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				nearestGeneric(img, slice, scaleX, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+
+		// horizontal filter on transposed image, result is not transposed
+		coeffs, offset, filterLength = createWeightsNearest(result.Bounds().Dy(), temp.Bounds().Min.X, taps, blur, scaleY)
+		wg.Add(cpus)
+		for i := 0; i < cpus; i++ {
+			slice := makeSlice(result, i, cpus).(*image.RGBA64)
+			go func() {
+				defer wg.Done()
+				nearestRGBA64(temp, slice, scaleY, coeffs, offset, filterLength)
+			}()
+		}
+		wg.Wait()
+		return result
+	}
+
+}
+
 // Calculates scaling factors using old and new image dimensions.
 func calcFactors(width, height uint, oldWidth, oldHeight float64) (scaleX, scaleY float64) {
 	if width == 0 {

ycc.go

@@ -0,0 +1,226 @@
+/*
+Copyright (c) 2014, Charlie Vieth <charlie.vieth@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+package resize
+
+import (
+	"image"
+	"image/color"
+)
+
+// ycc is an in memory YCbCr image.  The Y, Cb and Cr samples are held in a
+// single slice to increase resizing performance.
+type ycc struct {
+	// Pix holds the image's pixels, in Y, Cb, Cr order. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*3].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect image.Rectangle
+	// SubsampleRatio is the subsample ratio of the original YCbCr image.
+	SubsampleRatio image.YCbCrSubsampleRatio
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *ycc) PixOffset(x, y int) int {
+	return (y * p.Stride) + (x * 3)
+}
+
+func (p *ycc) Bounds() image.Rectangle {
+	return p.Rect
+}
+
+func (p *ycc) ColorModel() color.Model {
+	return color.YCbCrModel
+}
+
+func (p *ycc) At(x, y int) color.Color {
+	if !(image.Point{x, y}.In(p.Rect)) {
+		return color.YCbCr{}
+	}
+	i := p.PixOffset(x, y)
+	return color.YCbCr{
+		p.Pix[i+0],
+		p.Pix[i+1],
+		p.Pix[i+2],
+	}
+}
+
+func (p *ycc) Opaque() bool {
+	return true
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *ycc) SubImage(r image.Rectangle) image.Image {
+	r = r.Intersect(p.Rect)
+	if r.Empty() {
+		return &ycc{SubsampleRatio: p.SubsampleRatio}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &ycc{
+		Pix:            p.Pix[i:],
+		Stride:         p.Stride,
+		Rect:           r,
+		SubsampleRatio: p.SubsampleRatio,
+	}
+}
+
+// newYCC returns a new ycc with the given bounds and subsample ratio.
+func newYCC(r image.Rectangle, s image.YCbCrSubsampleRatio) *ycc {
+	w, h := r.Dx(), r.Dy()
+	buf := make([]uint8, 3*w*h)
+	return &ycc{Pix: buf, Stride: 3 * w, Rect: r, SubsampleRatio: s}
+}
+
+// YCbCr converts ycc to a YCbCr image with the same subsample ratio
+// as the YCbCr image that ycc was generated from.
+func (p *ycc) YCbCr() *image.YCbCr {
+	ycbcr := image.NewYCbCr(p.Rect, p.SubsampleRatio)
+	var off int
+
+	switch ycbcr.SubsampleRatio {
+	case image.YCbCrSubsampleRatio422:
+		for y := ycbcr.Rect.Min.Y; y < ycbcr.Rect.Max.Y; y++ {
+			yy := (y - ycbcr.Rect.Min.Y) * ycbcr.YStride
+			cy := (y - ycbcr.Rect.Min.Y) * ycbcr.CStride
+			for x := ycbcr.Rect.Min.X; x < ycbcr.Rect.Max.X; x++ {
+				xx := (x - ycbcr.Rect.Min.X)
+				yi := yy + xx
+				ci := cy + xx/2
+				ycbcr.Y[yi] = p.Pix[off+0]
+				ycbcr.Cb[ci] = p.Pix[off+1]
+				ycbcr.Cr[ci] = p.Pix[off+2]
+				off += 3
+			}
+		}
+	case image.YCbCrSubsampleRatio420:
+		for y := ycbcr.Rect.Min.Y; y < ycbcr.Rect.Max.Y; y++ {
+			yy := (y - ycbcr.Rect.Min.Y) * ycbcr.YStride
+			cy := (y/2 - ycbcr.Rect.Min.Y/2) * ycbcr.CStride
+			for x := ycbcr.Rect.Min.X; x < ycbcr.Rect.Max.X; x++ {
+				xx := (x - ycbcr.Rect.Min.X)
+				yi := yy + xx
+				ci := cy + xx/2
+				ycbcr.Y[yi] = p.Pix[off+0]
+				ycbcr.Cb[ci] = p.Pix[off+1]
+				ycbcr.Cr[ci] = p.Pix[off+2]
+				off += 3
+			}
+		}
+	case image.YCbCrSubsampleRatio440:
+		for y := ycbcr.Rect.Min.Y; y < ycbcr.Rect.Max.Y; y++ {
+			yy := (y - ycbcr.Rect.Min.Y) * ycbcr.YStride
+			cy := (y/2 - ycbcr.Rect.Min.Y/2) * ycbcr.CStride
+			for x := ycbcr.Rect.Min.X; x < ycbcr.Rect.Max.X; x++ {
+				xx := (x - ycbcr.Rect.Min.X)
+				yi := yy + xx
+				ci := cy + xx
+				ycbcr.Y[yi] = p.Pix[off+0]
+				ycbcr.Cb[ci] = p.Pix[off+1]
+				ycbcr.Cr[ci] = p.Pix[off+2]
+				off += 3
+			}
+		}
+	default:
+		// Default to 4:4:4 subsampling.
+		for y := ycbcr.Rect.Min.Y; y < ycbcr.Rect.Max.Y; y++ {
+			yy := (y - ycbcr.Rect.Min.Y) * ycbcr.YStride
+			cy := (y - ycbcr.Rect.Min.Y) * ycbcr.CStride
+			for x := ycbcr.Rect.Min.X; x < ycbcr.Rect.Max.X; x++ {
+				xx := (x - ycbcr.Rect.Min.X)
+				yi := yy + xx
+				ci := cy + xx
+				ycbcr.Y[yi] = p.Pix[off+0]
+				ycbcr.Cb[ci] = p.Pix[off+1]
+				ycbcr.Cr[ci] = p.Pix[off+2]
+				off += 3
+			}
+		}
+	}
+	return ycbcr
+}
+
+// imageYCbCrToYCC converts a YCbCr image to a ycc image for resizing.
+func imageYCbCrToYCC(in *image.YCbCr) *ycc {
+	w, h := in.Rect.Dx(), in.Rect.Dy()
+	buf := make([]uint8, 3*w*h)
+	p := ycc{Pix: buf, Stride: 3 * w, Rect: in.Rect, SubsampleRatio: in.SubsampleRatio}
+	var off int
+
+	switch in.SubsampleRatio {
+	case image.YCbCrSubsampleRatio422:
+		for y := in.Rect.Min.Y; y < in.Rect.Max.Y; y++ {
+			yy := (y - in.Rect.Min.Y) * in.YStride
+			cy := (y - in.Rect.Min.Y) * in.CStride
+			for x := in.Rect.Min.X; x < in.Rect.Max.X; x++ {
+				xx := (x - in.Rect.Min.X)
+				yi := yy + xx
+				ci := cy + xx/2
+				p.Pix[off+0] = in.Y[yi]
+				p.Pix[off+1] = in.Cb[ci]
+				p.Pix[off+2] = in.Cr[ci]
+				off += 3
+			}
+		}
+	case image.YCbCrSubsampleRatio420:
+		for y := in.Rect.Min.Y; y < in.Rect.Max.Y; y++ {
+			yy := (y - in.Rect.Min.Y) * in.YStride
+			cy := (y/2 - in.Rect.Min.Y/2) * in.CStride
+			for x := in.Rect.Min.X; x < in.Rect.Max.X; x++ {
+				xx := (x - in.Rect.Min.X)
+				yi := yy + xx
+				ci := cy + xx/2
+				p.Pix[off+0] = in.Y[yi]
+				p.Pix[off+1] = in.Cb[ci]
+				p.Pix[off+2] = in.Cr[ci]
+				off += 3
+			}
+		}
+	case image.YCbCrSubsampleRatio440:
+		for y := in.Rect.Min.Y; y < in.Rect.Max.Y; y++ {
+			yy := (y - in.Rect.Min.Y) * in.YStride
+			cy := (y/2 - in.Rect.Min.Y/2) * in.CStride
+			for x := in.Rect.Min.X; x < in.Rect.Max.X; x++ {
+				xx := (x - in.Rect.Min.X)
+				yi := yy + xx
+				ci := cy + xx
+				p.Pix[off+0] = in.Y[yi]
+				p.Pix[off+1] = in.Cb[ci]
+				p.Pix[off+2] = in.Cr[ci]
+				off += 3
+			}
+		}
+	default:
+		// Default to 4:4:4 subsampling.
+		for y := in.Rect.Min.Y; y < in.Rect.Max.Y; y++ {
+			yy := (y - in.Rect.Min.Y) * in.YStride
+			cy := (y - in.Rect.Min.Y) * in.CStride
+			for x := in.Rect.Min.X; x < in.Rect.Max.X; x++ {
+				xx := (x - in.Rect.Min.X)
+				yi := yy + xx
+				ci := cy + xx
+				p.Pix[off+0] = in.Y[yi]
+				p.Pix[off+1] = in.Cb[ci]
+				p.Pix[off+2] = in.Cr[ci]
+				off += 3
+			}
+		}
+	}
+	return &p
+}

ycc_test.go

@@ -0,0 +1,121 @@
+/*
+Copyright (c) 2014, Charlie Vieth <charlie.vieth@gmail.com>
+
+Permission to use, copy, modify, and/or distribute this software for any purpose
+with or without fee is hereby granted, provided that the above copyright notice
+and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
+OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
+THIS SOFTWARE.
+*/
+
+package resize
+
+import (
+	"image"
+	"testing"
+)
+
+type Image interface {
+	image.Image
+	SubImage(image.Rectangle) image.Image
+}
+
+func TestImage(t *testing.T) {
+	testImage := []Image{
+		newYCC(image.Rect(0, 0, 10, 10), image.YCbCrSubsampleRatio420),
+		newYCC(image.Rect(0, 0, 10, 10), image.YCbCrSubsampleRatio422),
+		newYCC(image.Rect(0, 0, 10, 10), image.YCbCrSubsampleRatio440),
+		newYCC(image.Rect(0, 0, 10, 10), image.YCbCrSubsampleRatio444),
+	}
+	for _, m := range testImage {
+		if !image.Rect(0, 0, 10, 10).Eq(m.Bounds()) {
+			t.Errorf("%T: want bounds %v, got %v",
+				m, image.Rect(0, 0, 10, 10), m.Bounds())
+			continue
+		}
+		m = m.SubImage(image.Rect(3, 2, 9, 8)).(Image)
+		if !image.Rect(3, 2, 9, 8).Eq(m.Bounds()) {
+			t.Errorf("%T: sub-image want bounds %v, got %v",
+				m, image.Rect(3, 2, 9, 8), m.Bounds())
+			continue
+		}
+		// Test that taking an empty sub-image starting at a corner does not panic.
+		m.SubImage(image.Rect(0, 0, 0, 0))
+		m.SubImage(image.Rect(10, 0, 10, 0))
+		m.SubImage(image.Rect(0, 10, 0, 10))
+		m.SubImage(image.Rect(10, 10, 10, 10))
+	}
+}
+
+func TestConvertYCbCr(t *testing.T) {
+	testImage := []Image{
+		image.NewYCbCr(image.Rect(0, 0, 50, 50), image.YCbCrSubsampleRatio420),
+		image.NewYCbCr(image.Rect(0, 0, 50, 50), image.YCbCrSubsampleRatio422),
+		image.NewYCbCr(image.Rect(0, 0, 50, 50), image.YCbCrSubsampleRatio440),
+		image.NewYCbCr(image.Rect(0, 0, 50, 50), image.YCbCrSubsampleRatio444),
+	}
+
+	for _, img := range testImage {
+		m := img.(*image.YCbCr)
+		for y := m.Rect.Min.Y; y < m.Rect.Max.Y; y++ {
+			for x := m.Rect.Min.X; x < m.Rect.Max.X; x++ {
+				yi := m.YOffset(x, y)
+				ci := m.COffset(x, y)
+				m.Y[yi] = uint8(16*y + x)
+				m.Cb[ci] = uint8(y + 16*x)
+				m.Cr[ci] = uint8(y + 16*x)
+			}
+		}
+
+		// test conversion from YCbCr to ycc
+		yc := imageYCbCrToYCC(m)
+		for y := m.Rect.Min.Y; y < m.Rect.Max.Y; y++ {
+			for x := m.Rect.Min.X; x < m.Rect.Max.X; x++ {
+				ystride := 3 * (m.Rect.Max.X - m.Rect.Min.X)
+				xstride := 3
+				yi := m.YOffset(x, y)
+				ci := m.COffset(x, y)
+				si := (y * ystride) + (x * xstride)
+				if m.Y[yi] != yc.Pix[si] {
+					t.Errorf("Err Y - found: %d expected: %d x: %d y: %d yi: %d si: %d",
+						m.Y[yi], yc.Pix[si], x, y, yi, si)
+				}
+				if m.Cb[ci] != yc.Pix[si+1] {
+					t.Errorf("Err Cb - found: %d expected: %d x: %d y: %d ci: %d si: %d",
+						m.Cb[ci], yc.Pix[si+1], x, y, ci, si+1)
+				}
+				if m.Cr[ci] != yc.Pix[si+2] {
+					t.Errorf("Err Cr - found: %d expected: %d x: %d y: %d ci: %d si: %d",
+						m.Cr[ci], yc.Pix[si+2], x, y, ci, si+2)
+				}
+			}
+		}
+
+		// test conversion from ycc back to YCbCr
+		ym := yc.YCbCr()
+		for y := m.Rect.Min.Y; y < m.Rect.Max.Y; y++ {
+			for x := m.Rect.Min.X; x < m.Rect.Max.X; x++ {
+				yi := m.YOffset(x, y)
+				ci := m.COffset(x, y)
+				if m.Y[yi] != ym.Y[yi] {
+					t.Errorf("Err Y - found: %d expected: %d x: %d y: %d yi: %d",
+						m.Y[yi], ym.Y[yi], x, y, yi)
+				}
+				if m.Cb[ci] != ym.Cb[ci] {
+					t.Errorf("Err Cb - found: %d expected: %d x: %d y: %d ci: %d",
+						m.Cb[ci], ym.Cb[ci], x, y, ci)
+				}
+				if m.Cr[ci] != ym.Cr[ci] {
+					t.Errorf("Err Cr - found: %d expected: %d x: %d y: %d ci: %d",
+						m.Cr[ci], ym.Cr[ci], x, y, ci)
+				}
+			}
+		}
+	}
+}