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image/gif: don't encode local color tables if they're the same as the
global color table. Change-Id: Ia38f75708ed5e5b430680a1eecafb4fc8047269c Reviewed-on: https://go-review.googlesource.com/9467 Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Nigel Tao
parent
10f6d30315
commit
4ddd751c92
@ -6,6 +6,7 @@ package gif
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import (
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"bufio"
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"bytes"
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"compress/lzw"
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"errors"
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"image"
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@ -53,8 +54,12 @@ type encoder struct {
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err error
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// g is a reference to the data that is being encoded.
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g GIF
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// buf is a scratch buffer. It must be at least 768 so we can write the color map.
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buf [1024]byte
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// globalCT is the size in bytes of the global color table.
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globalCT int
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// buf is a scratch buffer. It must be at least 256 for the blockWriter.
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buf [256]byte
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globalColorTable [3 * 256]byte
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localColorTable [3 * 256]byte
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}
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// blockWriter writes the block structure of GIF image data, which
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@ -127,7 +132,8 @@ func (e *encoder) writeHeader() {
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e.buf[1] = e.g.BackgroundIndex
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e.buf[2] = 0x00 // Pixel Aspect Ratio.
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e.write(e.buf[:3])
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e.writeColorTable(p, paddedSize)
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e.globalCT = encodeColorTable(e.globalColorTable[:], p, paddedSize)
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e.write(e.globalColorTable[:e.globalCT])
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} else {
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// All frames have a local color table, so a global color table
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// is not needed.
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@ -155,25 +161,22 @@ func (e *encoder) writeHeader() {
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}
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}
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func (e *encoder) writeColorTable(p color.Palette, size int) {
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if e.err != nil {
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return
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}
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for i := 0; i < log2Lookup[size]; i++ {
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func encodeColorTable(dst []byte, p color.Palette, size int) int {
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n := log2Lookup[size]
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for i := 0; i < n; i++ {
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if i < len(p) {
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r, g, b, _ := p[i].RGBA()
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e.buf[3*i+0] = uint8(r >> 8)
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e.buf[3*i+1] = uint8(g >> 8)
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e.buf[3*i+2] = uint8(b >> 8)
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dst[3*i+0] = uint8(r >> 8)
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dst[3*i+1] = uint8(g >> 8)
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dst[3*i+2] = uint8(b >> 8)
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} else {
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// Pad with black.
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e.buf[3*i+0] = 0x00
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e.buf[3*i+1] = 0x00
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e.buf[3*i+2] = 0x00
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dst[3*i+0] = 0x00
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dst[3*i+1] = 0x00
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dst[3*i+2] = 0x00
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}
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}
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e.write(e.buf[:3*log2Lookup[size]])
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return 3 * n
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}
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func (e *encoder) writeImageBlock(pm *image.Paletted, delay int, disposal byte) {
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@ -232,11 +235,15 @@ func (e *encoder) writeImageBlock(pm *image.Paletted, delay int, disposal byte)
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e.write(e.buf[:9])
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paddedSize := log2(len(pm.Palette)) // Size of Local Color Table: 2^(1+n).
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// Interlacing is not supported.
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e.writeByte(0x80 | uint8(paddedSize))
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// Local Color Table.
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e.writeColorTable(pm.Palette, paddedSize)
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ct := encodeColorTable(e.localColorTable[:], pm.Palette, paddedSize)
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if ct != e.globalCT || !bytes.Equal(e.globalColorTable[:ct], e.localColorTable[:ct]) {
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// Use a local color table.
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e.writeByte(fColorTable | uint8(paddedSize))
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e.write(e.localColorTable[:ct])
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} else {
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// Use the global color table.
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e.writeByte(0)
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}
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litWidth := paddedSize + 1
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if litWidth < 2 {
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@ -357,7 +357,60 @@ func TestEncodeImplicitConfigSize(t *testing.T) {
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}
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}
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// TODO: add test for when a frame has the same color map (palette) as the global one.
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func TestEncodePalettes(t *testing.T) {
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const w, h = 5, 5
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pals := []color.Palette{{
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color.RGBA{0x00, 0x00, 0x00, 0xff},
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color.RGBA{0x01, 0x00, 0x00, 0xff},
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color.RGBA{0x02, 0x00, 0x00, 0xff},
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}, {
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color.RGBA{0x00, 0x00, 0x00, 0xff},
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color.RGBA{0x00, 0x01, 0x00, 0xff},
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}, {
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color.RGBA{0x00, 0x00, 0x03, 0xff},
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color.RGBA{0x00, 0x00, 0x02, 0xff},
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color.RGBA{0x00, 0x00, 0x01, 0xff},
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color.RGBA{0x00, 0x00, 0x00, 0xff},
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}, {
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color.RGBA{0x10, 0x07, 0xf0, 0xff},
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color.RGBA{0x20, 0x07, 0xf0, 0xff},
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color.RGBA{0x30, 0x07, 0xf0, 0xff},
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color.RGBA{0x40, 0x07, 0xf0, 0xff},
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color.RGBA{0x50, 0x07, 0xf0, 0xff},
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}}
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g0 := &GIF{
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Image: []*image.Paletted{
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image.NewPaletted(image.Rect(0, 0, w, h), pals[0]),
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image.NewPaletted(image.Rect(0, 0, w, h), pals[1]),
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image.NewPaletted(image.Rect(0, 0, w, h), pals[2]),
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image.NewPaletted(image.Rect(0, 0, w, h), pals[3]),
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},
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Delay: make([]int, len(pals)),
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Disposal: make([]byte, len(pals)),
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Config: image.Config{
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ColorModel: pals[2],
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Width: w,
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Height: h,
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},
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}
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var buf bytes.Buffer
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if err := EncodeAll(&buf, g0); err != nil {
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t.Fatalf("EncodeAll: %v", err)
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}
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g1, err := DecodeAll(&buf)
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if err != nil {
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t.Fatalf("DecodeAll: %v", err)
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}
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if len(g0.Image) != len(g1.Image) {
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t.Fatalf("image lengths differ: %d and %d", len(g0.Image), len(g1.Image))
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}
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for i, m := range g1.Image {
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if got, want := m.Palette, pals[i]; !palettesEqual(got, want) {
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t.Errorf("frame %d:\ngot %v\nwant %v", i, got, want)
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}
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}
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}
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func BenchmarkEncode(b *testing.B) {
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b.StopTimer()
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