Unify filters and their dependencies

filters.go

@@ -41,17 +41,24 @@ func clampToUint16(x float32) (y uint16) {
 	return
 }
 
-func convolution1d(x float32, kernel func(float32) float32, p []rgba16) (c rgba16) {
+type filterModel struct {
+	src     image.Image
+	size    int
+	kernel  func(float32) float32
+	tempRow []rgba16
+	tempCol []rgba16
+}
+
+func (f *filterModel) convolution1d(x float32, p []rgba16) (c rgba16) {
 	x -= float32(int(x))
-	
-	m := float32(len(p)/2-1)
+	m := float32(f.size/2 - 1)
 
 	var k float32
 	var sum float32 = 0
 	l := [4]float32{0.0, 0.0, 0.0, 0.0}
 
 	for j := range p {
-		k = kernel(x+m-float32(j))
+		k = f.kernel(x + m - float32(j))
 		sum += k
 		for i := range c {
 			l[i] += float32(p[j][i]) * k
@@ -63,51 +70,43 @@ func convolution1d(x float32, kernel func(float32) float32, p []rgba16) (c rgba1
 	return
 }
 
-func filter(x, y float32, img image.Image, n int, kernel func(x float32) float32) color.RGBA64 {
-	xf, yf := int(x)-n/2+1, int(y)-n/2+1
+func (f *filterModel) Interpolate(x, y float32) color.RGBA64 {
+	xf, yf := int(x)-f.size/2+1, int(y)-f.size/2+1
 
-	row := make([]rgba16, n)
-	col := make([]rgba16, n)
-
-	for i := 0; i < n; i++ {
-		for j := 0; j < n; j++ {
-			row[j] = toRGBA(img.At(xf+j, yf+i))
+	for i := 0; i < f.size; i++ {
+		for j := 0; j < f.size; j++ {
+			f.tempRow[j] = toRGBA(f.src.At(xf+j, yf+i))
 		}
-		col[i] = convolution1d(x, kernel, row)
+		f.tempCol[i] = f.convolution1d(x, f.tempRow)
 	}
 
-	c := convolution1d(y, kernel, col)
+	c := f.convolution1d(y, f.tempCol)
 	return color.RGBA64{c[0], c[1], c[2], c[3]}
 }
 
 // Nearest-neighbor interpolation.
 // Approximates a value by returning the value of the nearest point.
-func NearestNeighbor(x, y float32, img image.Image) color.RGBA64 {
-	n := 2
-	kernel := func(x float32) (y float32) {
+func NearestNeighbor(img image.Image) Filter {
+	return &filterModel{img, 2, func(x float32) (y float32) {
 		if x >= -0.5 && x < 0.5 {
 			y = 1
 		} else {
 			y = 0
 		}
 		return
-	}
-	return filter(x, y, img, n, kernel)
+	}, make([]rgba16, 2), make([]rgba16, 2)}
 }
 
 // Bicubic interpolation
-func Bilinear(x, y float32, img image.Image) color.RGBA64 {
-	n := 2
-	kernel := func(x float32) float32 {
+func Bilinear(img image.Image) Filter {
+	return &filterModel{img, 2, func(x float32) float32 {
 		return 1 - float32(math.Abs(float64(x)))
-	}
-	return filter(x, y, img, n, kernel)
+	}, make([]rgba16, 2), make([]rgba16, 2)}
 }
 
 // Bicubic interpolation
-func Bicubic(x, y float32, img image.Image) color.RGBA64 {
-	n := 4
-	kernel := func(x float32) (y float32) {
+func Bicubic(img image.Image) Filter {
+	return &filterModel{img, 4, func(x float32) (y float32) {
 		absX := float32(math.Abs(float64(x)))
 		if absX <= 1 {
 			y = absX*absX*(1.5*absX-2.5) + 1
@@ -115,24 +114,19 @@ func Bicubic(x, y float32, img image.Image) color.RGBA64 {
 			y = absX*(absX*(2.5-0.5*absX)-4) + 2
 		}
 		return
-	}
-	return filter(x, y, img, n, kernel)
+	}, make([]rgba16, 4), make([]rgba16, 4)}
 }
 
 // Lanczos interpolation (a=2).
-func Lanczos2(x, y float32, img image.Image) color.RGBA64 {
-	n := 4
-	kernel := func(x float32) float32 {
+func Lanczos2(img image.Image) Filter {
+	return &filterModel{img, 4, func(x float32) float32 {
 		return float32(Sinc(float64(x))) * float32(Sinc(float64((x)/float32(2))))
-	}
-	return filter(x, y, img, n, kernel)
+	}, make([]rgba16, 4), make([]rgba16, 4)}
 }
 
 // Lanczos interpolation (a=3).
-func Lanczos3(x, y float32, img image.Image) color.RGBA64 {
-	n := 6
-	kernel := func(x float32) float32 {
+func Lanczos3(img image.Image) Filter {
+	return &filterModel{img, 6, func(x float32) float32 {
 		return float32(Sinc(float64(x))) * float32(Sinc(float64((x)/float32(3))))
-	}
-	return filter(x, y, img, n, kernel)
+	}, make([]rgba16, 6), make([]rgba16, 6)}
 }

resize.go

@@ -40,30 +40,14 @@ func (t *Trans2) Eval(x, y float32) (u, v float32) {
 	return
 }
 
-// Calculate scaling factors using old and new image dimensions.
-func calcFactors(width, height uint, oldWidth, oldHeight float32) (scaleX, scaleY float32) {
-	if width == 0 {
-		if height == 0 {
-			scaleX = 1.0
-			scaleY = 1.0
-		} else {
-			scaleY = oldHeight / float32(height)
-			scaleX = scaleY
-		}
-	} else {
-		scaleX = oldWidth / float32(width)
-		if height == 0 {
-			scaleY = scaleX
-		} else {
-			scaleY = oldHeight / float32(height)
-		}
-	}
-	return
+// Filter can interpolate at points (x,y)
+type Filter interface {
+	Interpolate(x, y float32) color.RGBA64
 }
 
-// InterpolationFunction return a color for an arbitrary point inside
-// an image
-type InterpolationFunction func(float32, float32, image.Image) color.RGBA64
+// InterpolationFunction return a Filter implementation
+// that operates on an image
+type InterpolationFunction func(image.Image) Filter
 
 // Resize an image to new width and height using the interpolation function interp.
 // A new image with the given dimensions will be returned.
@@ -85,11 +69,12 @@ func Resize(width, height uint, img image.Image, interp InterpolationFunction) i
 	c := make(chan int, n)
 	for i := 0; i < n; i++ {
 		go func(b image.Rectangle, c chan int) {
+			filter := interp(img)
 			var u, v float32
 			for y := b.Min.Y; y < b.Max.Y; y++ {
 				for x := b.Min.X; x < b.Max.X; x++ {
 					u, v = t.Eval(float32(x), float32(y))
-					resizedImg.SetRGBA64(x, y, interp(u, v, img))
+					resizedImg.SetRGBA64(x, y, filter.Interpolate(u, v))
 				}
 			}
 			c <- 1
@@ -103,6 +88,27 @@ func Resize(width, height uint, img image.Image, interp InterpolationFunction) i
 	return resizedImg
 }
 
+// Calculate scaling factors using old and new image dimensions.
+func calcFactors(width, height uint, oldWidth, oldHeight float32) (scaleX, scaleY float32) {
+	if width == 0 {
+		if height == 0 {
+			scaleX = 1.0
+			scaleY = 1.0
+		} else {
+			scaleY = oldHeight / float32(height)
+			scaleX = scaleY
+		}
+	} else {
+		scaleX = oldWidth / float32(width)
+		if height == 0 {
+			scaleY = scaleX
+		} else {
+			scaleY = oldHeight / float32(height)
+		}
+	}
+	return
+}
+
 // Set number of parallel jobs
 // but prevent resize from doing too much work
 // if #CPUs > width