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image/png: fix encoding of images that don't start at (0, 0).

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R=r
CC=golang-dev
https://golang.org/cl/4560049
This commit is contained in:
Nigel Tao 2011-05-30 10:55:37 +10:00
parent 5d5d84f3df
commit a479bc8d02
2 changed files with 90 additions and 57 deletions
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74
src/pkg/image/png/writer.go
View File

@ -174,7 +174,7 @@ func (e *encoder) Write(b []byte) (int, os.Error) {
// Chooses the filter to use for encoding the current row, and applies it.
// The return value is the index of the filter and also of the row in cr that has had it applied.
func filter(cr [][]byte, pr []byte, bpp int) int {
func filter(cr *[nFilter][]byte, pr []byte, bpp int) int {
// We try all five filter types, and pick the one that minimizes the sum of absolute differences.
// This is the same heuristic that libpng uses, although the filters are attempted in order of
// estimated most likely to be minimal (ftUp, ftPaeth, ftNone, ftSub, ftAverage), rather than
@ -304,7 +304,7 @@ func writeImage(w io.Writer, m image.Image, cb int) os.Error {
// The +1 is for the per-row filter type, which is at cr[*][0].
b := m.Bounds()
var cr [nFilter][]uint8
for i := 0; i < len(cr); i++ {
for i := range cr {
cr[i] = make([]uint8, 1+bpp*b.Dx())
cr[i][0] = uint8(i)
}
@ -312,78 +312,84 @@ func writeImage(w io.Writer, m image.Image, cb int) os.Error {
for y := b.Min.Y; y < b.Max.Y; y++ {
// Convert from colors to bytes.
i := 1
switch cb {
case cbG8:
for x := b.Min.X; x < b.Max.X; x++ {
c := image.GrayColorModel.Convert(m.At(x, y)).(image.GrayColor)
cr[0][x+1] = c.Y
cr[0][i] = c.Y
i++
}
case cbTC8:
// We have previously verified that the alpha value is fully opaque.
cr0 := cr[0]
if rgba != nil {
yoff := y * rgba.Stride
xoff := 3*b.Min.X + 1
for _, color := range rgba.Pix[yoff+b.Min.X : yoff+b.Max.X] {
cr0[xoff] = color.R
cr0[xoff+1] = color.G
cr0[xoff+2] = color.B
xoff += 3
cr0[i+0] = color.R
cr0[i+1] = color.G
cr0[i+2] = color.B
i += 3
}
} else {
for x := b.Min.X; x < b.Max.X; x++ {
r, g, b, _ := m.At(x, y).RGBA()
cr0[3*x+1] = uint8(r >> 8)
cr0[3*x+2] = uint8(g >> 8)
cr0[3*x+3] = uint8(b >> 8)
cr0[i+0] = uint8(r >> 8)
cr0[i+1] = uint8(g >> 8)
cr0[i+2] = uint8(b >> 8)
i += 3
}
}
case cbP8:
rowOffset := y * paletted.Stride
copy(cr[0][b.Min.X+1:], paletted.Pix[rowOffset+b.Min.X:rowOffset+b.Max.X])
copy(cr[0][1:], paletted.Pix[rowOffset+b.Min.X:rowOffset+b.Max.X])
case cbTCA8:
// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
for x := b.Min.X; x < b.Max.X; x++ {
c := image.NRGBAColorModel.Convert(m.At(x, y)).(image.NRGBAColor)
cr[0][4*x+1] = c.R
cr[0][4*x+2] = c.G
cr[0][4*x+3] = c.B
cr[0][4*x+4] = c.A
cr[0][i+0] = c.R
cr[0][i+1] = c.G
cr[0][i+2] = c.B
cr[0][i+3] = c.A
i += 4
}
case cbG16:
for x := b.Min.X; x < b.Max.X; x++ {
c := image.Gray16ColorModel.Convert(m.At(x, y)).(image.Gray16Color)
cr[0][2*x+1] = uint8(c.Y >> 8)
cr[0][2*x+2] = uint8(c.Y)
cr[0][i+0] = uint8(c.Y >> 8)
cr[0][i+1] = uint8(c.Y)
i += 2
}
case cbTC16:
// We have previously verified that the alpha value is fully opaque.
for x := b.Min.X; x < b.Max.X; x++ {
// We have previously verified that the alpha value is fully opaque.
r, g, b, _ := m.At(x, y).RGBA()
cr[0][6*x+1] = uint8(r >> 8)
cr[0][6*x+2] = uint8(r)
cr[0][6*x+3] = uint8(g >> 8)
cr[0][6*x+4] = uint8(g)
cr[0][6*x+5] = uint8(b >> 8)
cr[0][6*x+6] = uint8(b)
cr[0][i+0] = uint8(r >> 8)
cr[0][i+1] = uint8(r)
cr[0][i+2] = uint8(g >> 8)
cr[0][i+3] = uint8(g)
cr[0][i+4] = uint8(b >> 8)
cr[0][i+5] = uint8(b)
i += 6
}
case cbTCA16:
// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
for x := b.Min.X; x < b.Max.X; x++ {
c := image.NRGBA64ColorModel.Convert(m.At(x, y)).(image.NRGBA64Color)
cr[0][8*x+1] = uint8(c.R >> 8)
cr[0][8*x+2] = uint8(c.R)
cr[0][8*x+3] = uint8(c.G >> 8)
cr[0][8*x+4] = uint8(c.G)
cr[0][8*x+5] = uint8(c.B >> 8)
cr[0][8*x+6] = uint8(c.B)
cr[0][8*x+7] = uint8(c.A >> 8)
cr[0][8*x+8] = uint8(c.A)
cr[0][i+0] = uint8(c.R >> 8)
cr[0][i+1] = uint8(c.R)
cr[0][i+2] = uint8(c.G >> 8)
cr[0][i+3] = uint8(c.G)
cr[0][i+4] = uint8(c.B >> 8)
cr[0][i+5] = uint8(c.B)
cr[0][i+6] = uint8(c.A >> 8)
cr[0][i+7] = uint8(c.A)
i += 8
}
}
// Apply the filter.
f := filter(cr[0:nFilter], pr, bpp)
f := filter(&cr, pr, bpp)
// Write the compressed bytes.
_, err = zw.Write(cr[f])

73
src/pkg/image/png/writer_test.go
View File

@ -5,9 +5,9 @@
package png
import (
"bytes"
"fmt"
"image"
"io"
"io/ioutil"
"os"
"testing"
@ -15,21 +15,38 @@ import (
func diff(m0, m1 image.Image) os.Error {
b0, b1 := m0.Bounds(), m1.Bounds()
if !b0.Eq(b1) {
if !b0.Size().Eq(b1.Size()) {
return fmt.Errorf("dimensions differ: %v vs %v", b0, b1)
}
dx := b1.Min.X - b0.Min.X
dy := 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++ {
r0, g0, b0, a0 := m0.At(x, y).RGBA()
r1, g1, b1, a1 := m1.At(x, y).RGBA()
c0 := m0.At(x, y)
c1 := m1.At(x+dx, y+dy)
r0, g0, b0, a0 := c0.RGBA()
r1, g1, b1, a1 := c1.RGBA()
if r0 != r1 || g0 != g1 || b0 != b1 || a0 != a1 {
return fmt.Errorf("colors differ at (%d, %d): %v vs %v", x, y, m0.At(x, y), m1.At(x, y))
return fmt.Errorf("colors differ at (%d, %d): %v vs %v", x, y, c0, c1)
}
}
}
return nil
}
func encodeDecode(m image.Image) (image.Image, os.Error) {
b := bytes.NewBuffer(nil)
err := Encode(b, m)
if err != nil {
return nil, err
}
m, err = Decode(b)
if err != nil {
return nil, err
}
return m, nil
}
func TestWriter(t *testing.T) {
// The filenames variable is declared in reader_test.go.
names := filenames
@ -44,26 +61,16 @@ func TestWriter(t *testing.T) {
t.Error(fn, err)
continue
}
// Read the image again, and push it through a pipe that encodes at the write end, and decodes at the read end.
pr, pw := io.Pipe()
defer pr.Close()
go func() {
defer pw.Close()
m1, err := readPng(qfn)
if err != nil {
t.Error(fn, err)
return
}
err = Encode(pw, m1)
if err != nil {
t.Error(fn, err)
return
}
}()
m2, err := Decode(pr)
// Read the image again, encode it, and decode it.
m1, err := readPng(qfn)
if err != nil {
t.Error(fn, err)
continue
return
}
m2, err := encodeDecode(m1)
if err != nil {
t.Error(fn, err)
return
}
// Compare the two.
err = diff(m0, m2)
@ -74,6 +81,26 @@ func TestWriter(t *testing.T) {
}
}
func TestSubimage(t *testing.T) {
m0 := image.NewRGBA(256, 256)
for y := 0; y < 256; y++ {
for x := 0; x < 256; x++ {
m0.Set(x, y, image.RGBAColor{uint8(x), uint8(y), 0, 255})
}
}
m0.Rect = image.Rect(50, 30, 250, 130)
m1, err := encodeDecode(m0)
if err != nil {
t.Error(err)
return
}
err = diff(m0, m1)
if err != nil {
t.Error(err)
return
}
}
func BenchmarkEncodePaletted(b *testing.B) {
b.StopTimer()
img := image.NewPaletted(640, 480,