138 lines
3.4 KiB
Go
138 lines
3.4 KiB
Go
/*
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Copyright (c) 2012, Jan Schlicht <jan.schlicht@gmail.com>
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Permission to use, copy, modify, and/or distribute this software for any purpose
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with or without fee is hereby granted, provided that the above copyright notice
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and this permission notice appear in all copies.
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THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
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REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
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FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
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INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
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OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
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TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
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THIS SOFTWARE.
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*/
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package resize
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import (
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"image"
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"image/color"
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"math"
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)
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// color.RGBA64 as array
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type RGBA [4]uint16
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// build RGBA from an arbitrary color
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func toRGBA(c color.Color) RGBA {
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r, g, b, a := c.RGBA()
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return RGBA{uint16(r), uint16(g), uint16(b), uint16(a)}
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}
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func clampToUint16(x float32) (y uint16) {
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y = uint16(x)
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if x < 0 {
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y = 0
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} else if x > float32(0xfffe) {
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y = 0xffff
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}
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return
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}
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func convolution1d(x float32, kernel func(float32, int) float32, p []RGBA) (c RGBA) {
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x -= float32(int(x))
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var k float32
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var sum float32 = 0
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l := [4]float32{0.0, 0.0, 0.0, 0.0}
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for j := range p {
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k = kernel(x, j)
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sum += k
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for i := range c {
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l[i] += float32(p[j][i]) * k
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}
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}
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for i := range c {
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c[i] = clampToUint16(l[i] / sum)
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}
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return
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}
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func filter(x, y float32, img image.Image, n int, kernel func(x float32, j int) float32) color.RGBA64 {
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xf, yf := int(x)-n/2+1, int(y)-n/2+1
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row := make([]RGBA, n)
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col := make([]RGBA, n)
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for i := 0; i < n; i++ {
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for j := 0; j < n; j++ {
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row[j] = toRGBA(img.At(xf+j, yf+i))
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}
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col[i] = convolution1d(x, kernel, row)
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}
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c := convolution1d(y, kernel, col)
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return color.RGBA64{c[0], c[1], c[2], c[3]}
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}
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// Nearest-neighbor interpolation.
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// Approximates a value by returning the value of the nearest point.
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func NearestNeighbor(x, y float32, img image.Image) color.RGBA64 {
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n := 2
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kernel := func(x float32, j int) (y float32) {
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if x+0.5 >= float32(j) && x+0.5 < float32(j)+1 {
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y = 1
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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 filter(x, y, img, n, kernel)
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}
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// Bicubic interpolation
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func Bilinear(x, y float32, img image.Image) color.RGBA64 {
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n := 2
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kernel := func(x float32, j int) float32 {
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xa := float32(math.Abs(float64(x - float32(j))))
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return 1 - xa
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}
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return filter(x, y, img, n, kernel)
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}
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// Bicubic interpolation
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func Bicubic(x, y float32, img image.Image) color.RGBA64 {
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n := 4
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kernel := func(x float32, j int) (y float32) {
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xa := float32(math.Abs(float64(x - float32(j-1))))
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if xa <= 1 {
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y = 1.5*xa*xa*xa - 2.5*xa*xa + 1
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} else {
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y = -0.5*xa*xa*xa + 2.5*xa*xa - 4*xa + 2
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}
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return
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}
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return filter(x, y, img, n, kernel)
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}
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// Lanczos interpolation (a=2).
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func Lanczos2(x, y float32, img image.Image) color.RGBA64 {
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n := 4
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kernel := func(x float32, j int) float32 {
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return float32(Sinc(float64(x-float32(j-1)))) * float32(Sinc(float64((x-float32(j-1))/float32(2))))
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}
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return filter(x, y, img, n, kernel)
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}
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// Lanczos interpolation (a=3).
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func Lanczos3(x, y float32, img image.Image) color.RGBA64 {
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n := 6
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kernel := func(x float32, j int) float32 {
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return float32(Sinc(float64(x-float32(j-2)))) * float32(Sinc(float64((x-float32(j-2))/float32(3))))
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}
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return filter(x, y, img, n, kernel)
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}
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