go.image/tiff: use optimized routines for RGBA and NRGBA

Performance for an RGBA image:

benchmark          old ns/op    new ns/op    delta
BenchmarkEncode      1633495         7897  -99.52%

benchmark           old MB/s     new MB/s  speedup
BenchmarkEncode        37.83      7824.96  206.85x

NRGBA images are now encoded as such, the spec calls it
"unassociated alpha".

R=nigeltao, rsc
CC=golang-dev
https://golang.org/cl/6308049
This commit is contained in:
Benny Siegert 2012-06-13 10:40:38 +10:00 committed by Nigel Tao
parent de792da79c
commit c35a1ecb6c
3 changed files with 57 additions and 9 deletions

View File

@ -58,14 +58,17 @@ func TestUnpackBits(t *testing.T) {
}
func compare(t *testing.T, img0, img1 image.Image) {
b := img1.Bounds()
if !b.Eq(img0.Bounds()) {
t.Fatalf("wrong image size: want %s, got %s", img0.Bounds(), b)
b0 := img0.Bounds()
b1 := img1.Bounds()
if b0.Dx() != b1.Dx() || b0.Dy() != b1.Dy() {
t.Fatalf("wrong image size: want %s, got %s", b0, b1)
}
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; x < b.Max.X; x++ {
x1 := b1.Min.X - b0.Min.X
y1 := b1.Min.Y - b0.Min.Y
for y := b0.Min.Y; y < b0.Max.Y; y++ {
for x := b0.Min.X; x < b0.Max.X; x++ {
c0 := img0.At(x, y)
c1 := img1.At(x, y)
c1 := img1.At(x+x1, y+y1)
r0, g0, b0, a0 := c0.RGBA()
r1, g1, b1, a1 := c1.RGBA()
if r0 != r1 || g0 != g1 || b0 != b1 || a0 != a1 {

View File

@ -73,6 +73,20 @@ func writeImgData(w io.Writer, m image.Image) error {
return nil
}
func writePix(w io.Writer, pix []byte, nrows, length, stride int) error {
if length == stride {
_, err := w.Write(pix[:nrows*length])
return err
}
for ; nrows > 0; nrows-- {
if _, err := w.Write(pix[:length]); err != nil {
return err
}
pix = pix[stride:]
}
return nil
}
func writeIFD(w io.Writer, ifdOffset int, d []ifdEntry) error {
var buf [ifdLen]byte
// Make space for "pointer area" containing IFD entry data
@ -126,8 +140,9 @@ func writeIFD(w io.Writer, ifdOffset int, d []ifdEntry) error {
return err
}
// Encode writes the image m to w in uncompressed RGBA format.
// Encode writes the image m to w in uncompressed 8-bit RGBA or NRGBA format.
func Encode(w io.Writer, m image.Image) error {
var extrasamples uint32
_, err := io.WriteString(w, leHeader)
if err != nil {
return err
@ -142,7 +157,19 @@ func Encode(w io.Writer, m image.Image) error {
if err != nil {
return err
}
switch img := m.(type) {
case *image.NRGBA:
extrasamples = 2 // Unassociated alpha.
off := img.PixOffset(img.Rect.Min.X, img.Rect.Min.Y)
err = writePix(w, img.Pix[off:], img.Rect.Dy(), 4*img.Rect.Dx(), img.Stride)
case *image.RGBA:
extrasamples = 1 // Associated alpha.
off := img.PixOffset(img.Rect.Min.X, img.Rect.Min.Y)
err = writePix(w, img.Pix[off:], img.Rect.Dy(), 4*img.Rect.Dx(), img.Stride)
default:
extrasamples = 1 // Associated alpha.
err = writeImgData(w, m)
}
if err != nil {
return err
}
@ -161,6 +188,6 @@ func Encode(w io.Writer, m image.Image) error {
{tXResolution, dtRational, []uint32{72, 1}},
{tYResolution, dtRational, []uint32{72, 1}},
{tResolutionUnit, dtShort, []uint32{resPerInch}},
{tExtraSamples, dtShort, []uint32{1}}, // RGBA.
{tExtraSamples, dtShort, []uint32{extrasamples}},
})
}

View File

@ -46,6 +46,24 @@ func TestRoundtrip(t *testing.T) {
}
}
// TestRoundtrip2 tests that encoding and decoding an image whose
// origin is not (0, 0) gives the same thing.
func TestRoundtrip2(t *testing.T) {
m0 := image.NewRGBA(image.Rect(3, 4, 9, 8))
for i := range m0.Pix {
m0.Pix[i] = byte(i)
}
out := new(bytes.Buffer)
if err := Encode(out, m0); err != nil {
t.Fatal(err)
}
m1, err := Decode(&buffer{buf: out.Bytes()})
if err != nil {
t.Fatal(err)
}
compare(t, m0, m1)
}
// BenchmarkEncode benchmarks the encoding of an image.
func BenchmarkEncode(b *testing.B) {
img, err := openImage("video-001.tiff")