// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package resize
import (
"image"
"image/color"
)
// Resize returns a scaled copy of the image slice r of m.
// The returned image has width w and height h.
func Resize(m image.Image, r image.Rectangle, w, h int) image.Image {
if w < 0 || h < 0 {
return nil
}
if w == 0 || h == 0 || r.Dx() <= 0 || r.Dy() <= 0 {
return image.NewRGBA64(image.Rect(0, 0, w, h))
}
switch m := m.(type) {
case *image.RGBA:
return resizeRGBA(m, r, w, h)
case *image.YCbCr:
if m, ok := resizeYCbCr(m, r, w, h); ok {
return m
}
}
ww, hh := uint64(w), uint64(h)
dx, dy := uint64(r.Dx()), uint64(r.Dy())
// The scaling algorithm is to nearest-neighbor magnify the dx * dy source
// to a (ww*dx) * (hh*dy) intermediate image and then minify the intermediate
// image back down to a ww * hh destination with a simple box filter.
// The intermediate image is implied, we do not physically allocate a slice
// of length ww*dx*hh*dy.
// For example, consider a 4*3 source image. Label its pixels from a-l:
// abcd
// efgh
// ijkl
// To resize this to a 3*2 destination image, the intermediate is 12*6.
// Whitespace has been added to delineate the destination pixels:
// aaab bbcc cddd
// aaab bbcc cddd
// eeef ffgg ghhh
//
// eeef ffgg ghhh
// iiij jjkk klll
// iiij jjkk klll
// Thus, the 'b' source pixel contributes one third of its value to the
// (0, 0) destination pixel and two thirds to (1, 0).
// The implementation is a two-step process. First, the source pixels are
// iterated over and each source pixel's contribution to 1 or more
// destination pixels are summed. Second, the sums are divided by a scaling
// factor to yield the destination pixels.
// TODO: By interleaving the two steps, instead of doing all of
// step 1 first and all of step 2 second, we could allocate a smaller sum
// slice of length 4*w*2 instead of 4*w*h, although the resultant code
// would become more complicated.
n, sum := dx*dy, make([]uint64, 4*w*h)
for y := r.Min.Y; y < r.Max.Y; y++ {
for x := r.Min.X; x < r.Max.X; x++ {
// Get the source pixel.
r32, g32, b32, a32 := m.At(x, y).RGBA()
r64 := uint64(r32)
g64 := uint64(g32)
b64 := uint64(b32)
a64 := uint64(a32)
// Spread the source pixel over 1 or more destination rows.
py := uint64(y) * hh
for remy := hh; remy > 0; {
qy := dy - (py % dy)
if qy > remy {
qy = remy
}
// Spread the source pixel over 1 or more destination columns.
px := uint64(x) * ww
index := 4 * ((py/dy)*ww + (px / dx))
for remx := ww; remx > 0; {
qx := dx - (px % dx)
if qx > remx {
qx = remx
}
sum[index+0] += r64 * qx * qy
sum[index+1] += g64 * qx * qy
sum[index+2] += b64 * qx * qy
sum[index+3] += a64 * qx * qy
index += 4
px += qx
remx -= qx
}
py += qy
remy -= qy
}
}
}
return average(sum, w, h, n*0x0101)
}
// average convert the sums to averages and returns the result.
func average(sum []uint64, w, h int, n uint64) image.Image {
ret := image.NewRGBA(image.Rect(0, 0, w, h))
for y := 0; y < h; y++ {
for x := 0; x < w; x++ {
index := 4 * (y*w + x)
ret.SetRGBA(x, y, color.RGBA{
uint8(sum[index+0] / n),
uint8(sum[index+1] / n),
uint8(sum[index+2] / n),
uint8(sum[index+3] / n),
})
}
}
return ret
}
// resizeYCbCr returns a scaled copy of the YCbCr image slice r of m.
// The returned image has width w and height h.
func resizeYCbCr(m *image.YCbCr, r image.Rectangle, w, h int) (image.Image, bool) {
var verticalRes int
switch m.SubsampleRatio {
case image.YCbCrSubsampleRatio420:
verticalRes = 2
case image.YCbCrSubsampleRatio422:
verticalRes = 1
default:
return nil, false
}
ww, hh := uint64(w), uint64(h)
dx, dy := uint64(r.Dx()), uint64(r.Dy())
// See comment in Resize.
n, sum := dx*dy, make([]uint64, 4*w*h)
for y := r.Min.Y; y < r.Max.Y; y++ {
Y := m.Y[y*m.YStride:]
Cb := m.Cb[y/verticalRes*m.CStride:]
Cr := m.Cr[y/verticalRes*m.CStride:]
for x := r.Min.X; x < r.Max.X; x++ {
// Get the source pixel.
r8, g8, b8 := color.YCbCrToRGB(Y[x], Cb[x/2], Cr[x/2])
r64 := uint64(r8)
g64 := uint64(g8)
b64 := uint64(b8)
// Spread the source pixel over 1 or more destination rows.
py := uint64(y) * hh
for remy := hh; remy > 0; {
qy := dy - (py % dy)
if qy > remy {
qy = remy
}
// Spread the source pixel over 1 or more destination columns.
px := uint64(x) * ww
index := 4 * ((py/dy)*ww + (px / dx))
for remx := ww; remx > 0; {
qx := dx - (px % dx)
if qx > remx {
qx = remx
}
qxy := qx * qy
sum[index+0] += r64 * qxy
sum[index+1] += g64 * qxy
sum[index+2] += b64 * qxy
sum[index+3] += 0xFFFF * qxy
index += 4
px += qx
remx -= qx
}
py += qy
remy -= qy
}
}
}
return average(sum, w, h, n), true
}
// resizeRGBA returns a scaled copy of the RGBA image slice r of m.
// The returned image has width w and height h.
func resizeRGBA(m *image.RGBA, r image.Rectangle, w, h int) image.Image {
ww, hh := uint64(w), uint64(h)
dx, dy := uint64(r.Dx()), uint64(r.Dy())
// See comment in Resize.
n, sum := dx*dy, make([]uint64, 4*w*h)
for y := r.Min.Y; y < r.Max.Y; y++ {
pixOffset := m.PixOffset(r.Min.X, y)
for x := r.Min.X; x < r.Max.X; x++ {
// Get the source pixel.
r64 := uint64(m.Pix[pixOffset+0])
g64 := uint64(m.Pix[pixOffset+1])
b64 := uint64(m.Pix[pixOffset+2])
a64 := uint64(m.Pix[pixOffset+3])
pixOffset += 4
// Spread the source pixel over 1 or more destination rows.
py := uint64(y) * hh
for remy := hh; remy > 0; {
qy := dy - (py % dy)
if qy > remy {
qy = remy
}
// Spread the source pixel over 1 or more destination columns.
px := uint64(x) * ww
index := 4 * ((py/dy)*ww + (px / dx))
for remx := ww; remx > 0; {
qx := dx - (px % dx)
if qx > remx {
qx = remx
}
qxy := qx * qy
sum[index+0] += r64 * qxy
sum[index+1] += g64 * qxy
sum[index+2] += b64 * qxy
sum[index+3] += a64 * qxy
index += 4
px += qx
remx -= qx
}
py += qy
remy -= qy
}
}
}
return average(sum, w, h, n)
}
// Resample returns a resampled copy of the image slice r of m.
// The returned image has width w and height h.
func Resample(m image.Image, r image.Rectangle, w, h int) image.Image {
if w < 0 || h < 0 {
return nil
}
if w == 0 || h == 0 || r.Dx() <= 0 || r.Dy() <= 0 {
return image.NewRGBA64(image.Rect(0, 0, w, h))
}
curw, curh := r.Dx(), r.Dy()
img := image.NewRGBA(image.Rect(0, 0, w, h))
for y := 0; y < h; y++ {
for x := 0; x < w; x++ {
// Get a source pixel.
subx := x * curw / w
suby := y * curh / h
r32, g32, b32, a32 := m.At(subx, suby).RGBA()
r := uint8(r32 >> 8)
g := uint8(g32 >> 8)
b := uint8(b32 >> 8)
a := uint8(a32 >> 8)
img.SetRGBA(x, y, color.RGBA{r, g, b, a})
}
}
return img
}
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