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Generalize spline based filters

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This also fixes a quality issue with Mitchell-Netravali: A factor was
missing in the calculation.
This commit is contained in:
jst 2013-04-04 22:32:33 +02:00
parent 5290c4773b
commit 6448fff2ee
1 changed files with 11 additions and 18 deletions
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29
filters.go
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@ -169,36 +169,29 @@ func Bilinear(img image.Image, factor [2]float32) Filter {
}) })
} }
// Bicubic interpolation (with cubic hermite spline) func splineKernel(B, C float32) func(float32) float32 {
func Bicubic(img image.Image, factor [2]float32) Filter { return func(x float32) (y float32) {
return createFilter(img, factor, 4, func(x float32) (y float32) {
absX := float32(math.Abs(float64(x))) absX := float32(math.Abs(float64(x)))
if absX <= 1 { if absX <= 1 {
y = absX*absX*(1.5*absX-2.5) + 1 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
} else if absX <= 2 { } else if absX <= 2 {
y = absX*(absX*(2.5-0.5*absX)-4) + 2 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
} else { } else {
y = 0 y = 0
} }
return return
}) }
}
// Bicubic interpolation (with cubic hermite spline)
func Bicubic(img image.Image, factor [2]float32) Filter {
return createFilter(img, factor, 4, splineKernel(0, 0.5))
} }
// Mitchell-Netravali interpolation // Mitchell-Netravali interpolation
func MitchellNetravali(img image.Image, factor [2]float32) Filter { func MitchellNetravali(img image.Image, factor [2]float32) Filter {
return createFilter(img, factor, 4, func(x float32) (y float32) { return createFilter(img, factor, 4, splineKernel(1.0/3.0, 1.0/3.0))
absX := float32(math.Abs(float64(x)))
if absX <= 1 {
y = absX*absX*(7*absX-12) + 16.0/3
} else if absX <= 2 {
y = -(absX - 2) * (absX - 2) / 3 * (7*absX - 8)
} else {
y = 0
}
return
})
} }
func lanczosKernel(a uint) func(float32) float32 { func lanczosKernel(a uint) func(float32) float32 {