aw/go-resize
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Rename Lanczos functions using look-up tables to Lanczos2Lut, Lanczos3Lut and restore Lanczos2, Lanczos3 to give users the choice between higher speed or higher accuracy.

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jst 2013-07-08 20:48:20 +02:00
parent 9e5ed35b85
commit a85ea9eaa8
1 changed files with 14 additions and 2 deletions
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16
filters.go
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@ -209,8 +209,6 @@ func MitchellNetravali(img image.Image, factor [2]float32) Filter {
} }
func splineKernel(B, C float32) func(float32) float32 { func splineKernel(B, C float32) func(float32) float32 {
const lanczosTableSize = 300
factorA := 2.0 - 1.5*B - C factorA := 2.0 - 1.5*B - C
factorB := -3.0 + 2.0*B + C factorB := -3.0 + 2.0*B + C
factorC := 1.0 - 1.0/3.0*B factorC := 1.0 - 1.0/3.0*B
@ -244,14 +242,28 @@ func lanczosKernel(a uint) func(float32) float32 {
} }
} }
const lanczosTableSize = 300
// Lanczos interpolation (a=2) // Lanczos interpolation (a=2)
func Lanczos2(img image.Image, factor [2]float32) Filter { func Lanczos2(img image.Image, factor [2]float32) Filter {
return createFilter(img, factor, 4, lanczosKernel(2))
}
// Lanczos interpolation (a=2) using a look-up table
// to speed up computation
func Lanczos2Lut(img image.Image, factor [2]float32) Filter {
return createFilter(img, factor, 4, return createFilter(img, factor, 4,
tableKernel(lanczosKernel(2), lanczosTableSize, 2.0)) tableKernel(lanczosKernel(2), lanczosTableSize, 2.0))
} }
// Lanczos interpolation (a=3) // Lanczos interpolation (a=3)
func Lanczos3(img image.Image, factor [2]float32) Filter { func Lanczos3(img image.Image, factor [2]float32) Filter {
return createFilter(img, factor, 6, lanczosKernel(3))
}
// Lanczos interpolation (a=3) using a look-up table
// to speed up computation
func Lanczos3Lut(img image.Image, factor [2]float32) Filter {
return createFilter(img, factor, 6, return createFilter(img, factor, 6,
tableKernel(lanczosKernel(3), lanczosTableSize, 3.0)) tableKernel(lanczosKernel(3), lanczosTableSize, 3.0))
} }