Generalize spline based filters
This also fixes a quality issue with Mitchell-Netravali: A factor was missing in the calculation.
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5290c4773b
commit
6448fff2ee
29
filters.go
29
filters.go
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@ -169,36 +169,29 @@ func Bilinear(img image.Image, factor [2]float32) Filter {
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})
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}
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// Bicubic interpolation (with cubic hermite spline)
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func Bicubic(img image.Image, factor [2]float32) Filter {
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return createFilter(img, factor, 4, func(x float32) (y float32) {
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func splineKernel(B, C float32) func(float32) float32 {
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return func(x float32) (y float32) {
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absX := float32(math.Abs(float64(x)))
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if absX <= 1 {
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y = absX*absX*(1.5*absX-2.5) + 1
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y = (absX*absX*((12.0-9.0*B-6.0*C)*absX+(-18.0+12.0*B+6.0*C)) + (6.0 - 2.0*B)) / 6.0
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} else if absX <= 2 {
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y = absX*(absX*(2.5-0.5*absX)-4) + 2
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y = (absX*(absX*(absX*(-B-6.0*C)+(6.0*B+30.0*C))+(-12.0*B-48.0*C)) + (8.0*B + 24.0*C)) / 6.0
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} else {
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y = 0
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}
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return
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})
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}
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}
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// Bicubic interpolation (with cubic hermite spline)
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func Bicubic(img image.Image, factor [2]float32) Filter {
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return createFilter(img, factor, 4, splineKernel(0, 0.5))
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}
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// Mitchell-Netravali interpolation
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func MitchellNetravali(img image.Image, factor [2]float32) Filter {
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return createFilter(img, factor, 4, func(x float32) (y float32) {
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absX := float32(math.Abs(float64(x)))
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if absX <= 1 {
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y = absX*absX*(7*absX-12) + 16.0/3
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} else if absX <= 2 {
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y = -(absX - 2) * (absX - 2) / 3 * (7*absX - 8)
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} else {
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y = 0
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}
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return
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})
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return createFilter(img, factor, 4, splineKernel(1.0/3.0, 1.0/3.0))
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}
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func lanczosKernel(a uint) func(float32) float32 {
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