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Precalculate bicubic factors, save some cycles.

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jst 2013-04-09 21:31:31 +02:00
parent 6448fff2ee
commit 62777ac833
1 changed files with 9 additions and 2 deletions
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11
filters.go
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@ -170,12 +170,19 @@ func Bilinear(img image.Image, factor [2]float32) Filter {
}
func splineKernel(B, C float32) func(float32) float32 {
factorA := 2.0-1.5*B-C
factorB := -3.0+2.0*B+C
factorC := 1.0-1.0/3.0*B
factorD := -B/6.0-C
factorE := B+5.0*C
factorF := -2.0*B-8.0*C
factorG := 4.0/3.0*B + 4.0*C
return func(x float32) (y float32) {
absX := float32(math.Abs(float64(x)))
if absX <= 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
y = absX*absX*(factorA*absX+factorB) +factorC
} else if absX <= 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
y = absX*(absX*(absX*factorD+factorE)+factorF) + factorG
} else {
y = 0
}