go.image/tiff: simplify encoding.
R=bsiegert CC=golang-dev https://golang.org/cl/5738044
This commit is contained in:
Nigel Tao
parent
f594c3aad5
commit
20e9620e99
108
tiff/writer.go
108
tiff/writer.go
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@ -47,63 +47,19 @@ func (e ifdEntry) putData(p []byte) {
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}
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}
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type ifd []ifdEntry
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type byTag []ifdEntry
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func (d ifd) Len() int {
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return len(d)
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}
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func (d byTag) Len() int { return len(d) }
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func (d byTag) Less(i, j int) bool { return d[i].tag < d[j].tag }
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func (d byTag) Swap(i, j int) { d[i], d[j] = d[j], d[i] }
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func (d ifd) Less(i, j int) bool {
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return d[i].tag < d[j].tag
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}
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func (d ifd) Swap(i, j int) {
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d[i], d[j] = d[j], d[i]
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}
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type encoder struct {
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ifd ifd
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img image.Image
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imageLen int // Length of the image in bytes.
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}
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func newEncoder(m image.Image) *encoder {
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width := m.Bounds().Dx()
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height := m.Bounds().Dy()
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imageLen := width * height * 4
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return &encoder{
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img: m,
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// For uncompressed images, imageLen is known in advance.
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// For compressed images, we would need to write the image
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// data in a buffer here to get its length.
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imageLen: imageLen,
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ifd: ifd{
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{tImageWidth, dtShort, []uint32{uint32(width)}},
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{tImageLength, dtShort, []uint32{uint32(height)}},
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{tBitsPerSample, dtShort, []uint32{8, 8, 8, 8}},
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{tCompression, dtShort, []uint32{cNone}},
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{tPhotometricInterpretation, dtShort, []uint32{pRGB}},
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{tStripOffsets, dtLong, []uint32{8}},
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{tSamplesPerPixel, dtShort, []uint32{4}},
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{tRowsPerStrip, dtShort, []uint32{uint32(height)}},
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{tStripByteCounts, dtLong, []uint32{uint32(imageLen)}},
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// There is currently no support for storing the image
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// resolution, so give a bogus value of 72x72 dpi.
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{tXResolution, dtRational, []uint32{72, 1}},
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{tYResolution, dtRational, []uint32{72, 1}},
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{tResolutionUnit, dtShort, []uint32{resPerInch}},
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{tExtraSamples, dtShort, []uint32{1}}, // RGBA.
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},
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}
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}
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func (e *encoder) writeImgData(w io.Writer) error {
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b := e.img.Bounds()
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buf := make([]byte, 4*b.Dx())
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for y := b.Min.Y; y < b.Max.Y; y++ {
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func writeImgData(w io.Writer, m image.Image) error {
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bounds := m.Bounds()
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buf := make([]byte, 4*bounds.Dx())
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for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
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i := 0
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for x := b.Min.X; x < b.Max.X; x++ {
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r, g, b, a := e.img.At(x, y).RGBA()
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for x := bounds.Min.X; x < bounds.Max.X; x++ {
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r, g, b, a := m.At(x, y).RGBA()
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buf[i+0] = uint8(r >> 8)
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buf[i+1] = uint8(g >> 8)
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buf[i+2] = uint8(b >> 8)
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@ -117,22 +73,22 @@ func (e *encoder) writeImgData(w io.Writer) error {
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return nil
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}
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func (e *encoder) writeIFD(w io.Writer) error {
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func writeIFD(w io.Writer, ifdOffset int, d []ifdEntry) error {
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var buf [ifdLen]byte
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// Make space for "pointer area" containing IFD entry data
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// longer than 4 bytes.
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parea := make([]byte, 1024)
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pstart := int(e.imageLen) + 8 + (ifdLen * len(e.ifd)) + 6
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pstart := ifdOffset + ifdLen*len(d) + 6
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var o int // Current offset in parea.
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// The IFD has to be written with the tags in ascending order.
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sort.Sort(e.ifd)
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sort.Sort(byTag(d))
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// Write the number of entries in this IFD.
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if err := binary.Write(w, enc, uint16(len(e.ifd))); err != nil {
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if err := binary.Write(w, enc, uint16(len(d))); err != nil {
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return err
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}
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for _, ent := range e.ifd {
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for _, ent := range d {
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enc.PutUint16(buf[0:2], uint16(ent.tag))
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enc.PutUint16(buf[2:4], uint16(ent.datatype))
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count := uint32(len(ent.data))
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@ -170,25 +126,41 @@ func (e *encoder) writeIFD(w io.Writer) error {
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return err
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}
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func (e *encoder) encode(w io.Writer) error {
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// Encode writes the image m to w in uncompressed RGBA format.
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func Encode(w io.Writer, m image.Image) error {
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_, err := io.WriteString(w, leHeader)
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if err != nil {
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return err
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}
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ifdOffset := e.imageLen + 8 // 8 bytes for TIFF header.
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bounds := m.Bounds()
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width, height := bounds.Dx(), bounds.Dy()
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// imageLen is the length of the image data in bytes.
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imageLen := width * height * 4
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ifdOffset := imageLen + 8 // 8 bytes for TIFF header.
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err = binary.Write(w, enc, uint32(ifdOffset))
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if err != nil {
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return err
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}
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err = e.writeImgData(w)
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err = writeImgData(w, m)
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if err != nil {
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return err
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}
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return e.writeIFD(w)
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}
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// Encode writes the image m to w in uncompressed RGBA format.
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func Encode(w io.Writer, m image.Image) error {
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return newEncoder(m).encode(w)
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return writeIFD(w, ifdOffset, []ifdEntry{
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{tImageWidth, dtShort, []uint32{uint32(width)}},
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{tImageLength, dtShort, []uint32{uint32(height)}},
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{tBitsPerSample, dtShort, []uint32{8, 8, 8, 8}},
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{tCompression, dtShort, []uint32{cNone}},
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{tPhotometricInterpretation, dtShort, []uint32{pRGB}},
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{tStripOffsets, dtLong, []uint32{8}},
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{tSamplesPerPixel, dtShort, []uint32{4}},
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{tRowsPerStrip, dtShort, []uint32{uint32(height)}},
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{tStripByteCounts, dtLong, []uint32{uint32(imageLen)}},
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// There is currently no support for storing the image
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// resolution, so give a bogus value of 72x72 dpi.
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{tXResolution, dtRational, []uint32{72, 1}},
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{tYResolution, dtRational, []uint32{72, 1}},
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{tResolutionUnit, dtShort, []uint32{resPerInch}},
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{tExtraSamples, dtShort, []uint32{1}}, // RGBA.
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})
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}
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