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jpeg: speed up RGBA encoding ~%50

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Avoids image.At(), color.RGBA(), opposing 8 bit shifts,
and min function calls in a loop.  Not as pretty as before,
but the pure version is still there to revert back to
later if/when the compiler gets better.

before (best of 5)
jpeg.BenchmarkEncodeRGBOpaque   50   64781360 ns/op   18.97 MB/s

after (best of 5)
jpeg.BenchmarkEncodeRGBOpaque   50   42044300 ns/op   29.23 MB/s

(benchmarked on an HP z600; 16 core Xeon E5520 @ 2.27Ghz)

R=r, r2, nigeltao
CC=golang-dev
https://golang.org/cl/4433088
This commit is contained in:
Brad Fitzpatrick 2011-05-02 07:26:40 -07:00
parent 437015bbed
commit 807ce2719c
1 changed files with 31 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
src/pkg/image/jpeg/writer.go
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@ -391,6 +391,31 @@ func toYCbCr(m image.Image, p image.Point, yBlock, cbBlock, crBlock *block) {
}
}
// rgbaToYCbCr is a specialized version of toYCbCr for image.RGBA images.
func rgbaToYCbCr(m *image.RGBA, p image.Point, yBlock, cbBlock, crBlock *block) {
b := m.Bounds()
xmax := b.Max.X - 1
ymax := b.Max.Y - 1
for j := 0; j < 8; j++ {
sj := p.Y + j
if sj > ymax {
sj = ymax
}
yoff := sj * m.Stride
for i := 0; i < 8; i++ {
sx := p.X + i
if sx > xmax {
sx = xmax
}
col := &m.Pix[yoff+sx]
yy, cb, cr := ycbcr.RGBToYCbCr(col.R, col.G, col.B)
yBlock[8*j+i] = int(yy)
cbBlock[8*j+i] = int(cb)
crBlock[8*j+i] = int(cr)
}
}
}
// scale scales the 16x16 region represented by the 4 src blocks to the 8x8
// dst block.
func scale(dst *block, src *[4]block) {
@ -431,13 +456,18 @@ func (e *encoder) writeSOS(m image.Image) {
prevDCY, prevDCCb, prevDCCr int
)
bounds := m.Bounds()
rgba, _ := m.(*image.RGBA)
for y := bounds.Min.Y; y < bounds.Max.Y; y += 16 {
for x := bounds.Min.X; x < bounds.Max.X; x += 16 {
for i := 0; i < 4; i++ {
xOff := (i & 1) * 8
yOff := (i & 2) * 4
p := image.Point{x + xOff, y + yOff}
if rgba != nil {
rgbaToYCbCr(rgba, p, &yBlock, &cbBlock[i], &crBlock[i])
} else {
toYCbCr(m, p, &yBlock, &cbBlock[i], &crBlock[i])
}
prevDCY = e.writeBlock(&yBlock, 0, prevDCY)
}
scale(&cBlock, &cbBlock)