Go語言中對映像進行縮放

由Google開發，簡潔、高效、開源的Go語言日漸成為語言新寵。它專門針對多處理器系統應用程式的編程進行最佳化，使得Go編譯的程式與C或C++代碼的速度相媲美，且更安全、支援並行進程。Go語言在Go1版本上支援Windows, 蘋果Mac OS X, Linux和FreeBSD作業系統。Go支援物件導向，而且具有真正的封裝(closures)和反射 (reflection)等功能。

在學習曲線方面,派克認為Go與Java類似,對於Java開發人員來說,應該能夠輕鬆學會 Go。同樣，對於C#開發人員來說，也很輕鬆學會GO語言。

筆者對圖形映像研究高度興趣，讓我們來看看Go語言中對映像進行縮放的解決方案：

package resize

import (
"image"
"image/color"
)

// average convert the sums to averages and returns the result.
func average(sum []uint64, w, h int, n uint64) *image.RGBA {
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)
pix := ret.Pix[y*ret.Stride+x*4:]
pix[0] = uint8(sum[index+0] / n)
pix[1] = uint8(sum[index+1] / n)
pix[2] = uint8(sum[index+2] / n)
pix[3] = uint8(sum[index+3] / n)
}
}
return ret
}

// 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.RGBA {
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++ {
pix := m.Pix[(y-r.Min.Y)*m.Stride:]
for x := r.Min.X; x < r.Max.X; x++ {
// Get the source pixel.
p := pix[(x-r.Min.X)*4:]
r64 := uint64(p[0])
g64 := uint64(p[1])
b64 := uint64(p[2])
a64 := uint64(p[3])
// 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)
}

// ResizeNRGBA returns a scaled copy of the RGBA image slice r of m.
// The returned image has width w and height h.
func ResizeNRGBA(m *image.NRGBA, r image.Rectangle, w, h int) *image.RGBA {
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++ {
pix := m.Pix[(y-r.Min.Y)*m.Stride:]
for x := r.Min.X; x < r.Max.X; x++ {
// Get the source pixel.
p := pix[(x-r.Min.X)*4:]
r64 := uint64(p[0])
g64 := uint64(p[1])
b64 := uint64(p[2])
a64 := uint64(p[3])
r64 = (r64 * a64) / 255
g64 = (g64 * a64) / 255
b64 = (b64 * a64) / 255
// 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.RGBA {
if w < 0 || h < 0 {
return nil
}
if w == 0 || h == 0 || r.Dx() <= 0 || r.Dy() <= 0 {
return image.NewRGBA(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

}

（龍崗民生網 http://www.lgms.net）

有了上面的基礎，下文講解 利用Go語言上傳映像並產生縮圖。