--- /dev/null
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package tiff implements a TIFF image decoder.
+//
+// The TIFF specification is at http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf
+package tiff
+
+import (
+ "compress/lzw"
+ "compress/zlib"
+ "encoding/binary"
+ "image"
+ "io"
+ "io/ioutil"
+ "os"
+)
+
+// A FormatError reports that the input is not a valid TIFF image.
+type FormatError string
+
+func (e FormatError) String() string {
+ return "tiff: invalid format: " + string(e)
+}
+
+// An UnsupportedError reports that the input uses a valid but
+// unimplemented feature.
+type UnsupportedError string
+
+func (e UnsupportedError) String() string {
+ return "tiff: unsupported feature: " + string(e)
+}
+
+// An InternalError reports that an internal error was encountered.
+type InternalError string
+
+func (e InternalError) String() string {
+ return "tiff: internal error: " + string(e)
+}
+
+type decoder struct {
+ r io.ReaderAt
+ byteOrder binary.ByteOrder
+ config image.Config
+ mode imageMode
+ features map[int][]uint
+ palette []image.Color
+}
+
+// firstVal returns the first uint of the features entry with the given tag,
+// or 0 if the tag does not exist.
+func (d *decoder) firstVal(tag int) uint {
+ f := d.features[tag]
+ if len(f) == 0 {
+ return 0
+ }
+ return f[0]
+}
+
+// ifdUint decodes the IFD entry in p, which must be of the Byte, Short
+// or Long type, and returns the decoded uint values.
+func (d *decoder) ifdUint(p []byte) (u []uint, err os.Error) {
+ var raw []byte
+ datatype := d.byteOrder.Uint16(p[2:4])
+ count := d.byteOrder.Uint32(p[4:8])
+ if datalen := lengths[datatype] * count; datalen > 4 {
+ // The IFD contains a pointer to the real value.
+ raw = make([]byte, datalen)
+ _, err = d.r.ReadAt(raw, int64(d.byteOrder.Uint32(p[8:12])))
+ } else {
+ raw = p[8 : 8+datalen]
+ }
+ if err != nil {
+ return nil, err
+ }
+
+ u = make([]uint, count)
+ switch datatype {
+ case dtByte:
+ for i := uint32(0); i < count; i++ {
+ u[i] = uint(raw[i])
+ }
+ case dtShort:
+ for i := uint32(0); i < count; i++ {
+ u[i] = uint(d.byteOrder.Uint16(raw[2*i : 2*(i+1)]))
+ }
+ case dtLong:
+ for i := uint32(0); i < count; i++ {
+ u[i] = uint(d.byteOrder.Uint32(raw[4*i : 4*(i+1)]))
+ }
+ default:
+ return nil, UnsupportedError("data type")
+ }
+ return u, nil
+}
+
+// parseIFD decides whether the the IFD entry in p is "interesting" and
+// stows away the data in the decoder.
+func (d *decoder) parseIFD(p []byte) os.Error {
+ tag := d.byteOrder.Uint16(p[0:2])
+ switch tag {
+ case tBitsPerSample,
+ tExtraSamples,
+ tPhotometricInterpretation,
+ tCompression,
+ tPredictor,
+ tStripOffsets,
+ tStripByteCounts,
+ tRowsPerStrip,
+ tImageLength,
+ tImageWidth:
+ val, err := d.ifdUint(p)
+ if err != nil {
+ return err
+ }
+ d.features[int(tag)] = val
+ case tColorMap:
+ val, err := d.ifdUint(p)
+ if err != nil {
+ return err
+ }
+ numcolors := len(val) / 3
+ if len(val)%3 != 0 || numcolors <= 0 || numcolors > 256 {
+ return FormatError("bad ColorMap length")
+ }
+ d.palette = make([]image.Color, numcolors)
+ for i := 0; i < numcolors; i++ {
+ d.palette[i] = image.RGBA64Color{
+ uint16(val[i]),
+ uint16(val[i+numcolors]),
+ uint16(val[i+2*numcolors]),
+ 0xffff,
+ }
+ }
+ }
+ return nil
+}
+
+// decode decodes the raw data of an image with 8 bits in each sample.
+// It reads from p and writes the strip with ymin <= y < ymax into dst.
+func (d *decoder) decode(dst image.Image, p []byte, ymin, ymax int) os.Error {
+ spp := len(d.features[tBitsPerSample]) // samples per pixel
+ off := 0
+ width := dst.Bounds().Dx()
+
+ if len(p) < spp*(ymax-ymin)*width {
+ return FormatError("short data strip")
+ }
+
+ // Apply horizontal predictor if necessary.
+ // In this case, p contains the color difference to the preceding pixel.
+ // See page 64-65 of the spec.
+ if d.firstVal(tPredictor) == prHorizontal {
+ for y := ymin; y < ymax; y++ {
+ off += spp
+ for x := 0; x < (width-1)*spp; x++ {
+ p[off] += p[off-spp]
+ off++
+ }
+ }
+ off = 0
+ }
+
+ switch d.mode {
+ case mGray:
+ img := dst.(*image.Gray)
+ for y := ymin; y < ymax; y++ {
+ for x := img.Rect.Min.X; x < img.Rect.Max.X; x++ {
+ img.Set(x, y, image.GrayColor{p[off]})
+ off += spp
+ }
+ }
+ case mGrayInvert:
+ img := dst.(*image.Gray)
+ for y := ymin; y < ymax; y++ {
+ for x := img.Rect.Min.X; x < img.Rect.Max.X; x++ {
+ img.Set(x, y, image.GrayColor{0xff - p[off]})
+ off += spp
+ }
+ }
+ case mPaletted:
+ img := dst.(*image.Paletted)
+ for y := ymin; y < ymax; y++ {
+ for x := img.Rect.Min.X; x < img.Rect.Max.X; x++ {
+ img.SetColorIndex(x, y, p[off])
+ off += spp
+ }
+ }
+ case mRGB:
+ img := dst.(*image.RGBA)
+ for y := ymin; y < ymax; y++ {
+ for x := img.Rect.Min.X; x < img.Rect.Max.X; x++ {
+ img.Set(x, y, image.RGBAColor{p[off], p[off+1], p[off+2], 0xff})
+ off += spp
+ }
+ }
+ case mNRGBA:
+ img := dst.(*image.NRGBA)
+ for y := ymin; y < ymax; y++ {
+ for x := img.Rect.Min.X; x < img.Rect.Max.X; x++ {
+ img.Set(x, y, image.NRGBAColor{p[off], p[off+1], p[off+2], p[off+3]})
+ off += spp
+ }
+ }
+ case mRGBA:
+ img := dst.(*image.RGBA)
+ for y := ymin; y < ymax; y++ {
+ for x := img.Rect.Min.X; x < img.Rect.Max.X; x++ {
+ img.Set(x, y, image.RGBAColor{p[off], p[off+1], p[off+2], p[off+3]})
+ off += spp
+ }
+ }
+ }
+
+ return nil
+}
+
+func newDecoder(r io.Reader) (*decoder, os.Error) {
+ d := &decoder{
+ r: newReaderAt(r),
+ features: make(map[int][]uint),
+ }
+
+ p := make([]byte, 8)
+ if _, err := d.r.ReadAt(p, 0); err != nil {
+ return nil, err
+ }
+ switch string(p[0:4]) {
+ case leHeader:
+ d.byteOrder = binary.LittleEndian
+ case beHeader:
+ d.byteOrder = binary.BigEndian
+ default:
+ return nil, FormatError("malformed header")
+ }
+
+ ifdOffset := int64(d.byteOrder.Uint32(p[4:8]))
+
+ // The first two bytes contain the number of entries (12 bytes each).
+ if _, err := d.r.ReadAt(p[0:2], ifdOffset); err != nil {
+ return nil, err
+ }
+ numItems := int(d.byteOrder.Uint16(p[0:2]))
+
+ // All IFD entries are read in one chunk.
+ p = make([]byte, ifdLen*numItems)
+ if _, err := d.r.ReadAt(p, ifdOffset+2); err != nil {
+ return nil, err
+ }
+
+ for i := 0; i < len(p); i += ifdLen {
+ if err := d.parseIFD(p[i : i+ifdLen]); err != nil {
+ return nil, err
+ }
+ }
+
+ d.config.Width = int(d.firstVal(tImageWidth))
+ d.config.Height = int(d.firstVal(tImageLength))
+
+ // Determine the image mode.
+ switch d.firstVal(tPhotometricInterpretation) {
+ case pRGB:
+ d.config.ColorModel = image.RGBAColorModel
+ // RGB images normally have 3 samples per pixel.
+ // If there are more, ExtraSamples (p. 31-32 of the spec)
+ // gives their meaning (usually an alpha channel).
+ switch len(d.features[tBitsPerSample]) {
+ case 3:
+ d.mode = mRGB
+ case 4:
+ switch d.firstVal(tExtraSamples) {
+ case 1:
+ d.mode = mRGBA
+ case 2:
+ d.mode = mNRGBA
+ d.config.ColorModel = image.NRGBAColorModel
+ default:
+ // The extra sample is discarded.
+ d.mode = mRGB
+ }
+ default:
+ return nil, FormatError("wrong number of samples for RGB")
+ }
+ case pPaletted:
+ d.mode = mPaletted
+ d.config.ColorModel = image.PalettedColorModel(d.palette)
+ case pWhiteIsZero:
+ d.mode = mGrayInvert
+ d.config.ColorModel = image.GrayColorModel
+ case pBlackIsZero:
+ d.mode = mGray
+ d.config.ColorModel = image.GrayColorModel
+ default:
+ return nil, UnsupportedError("color model")
+ }
+
+ if _, ok := d.features[tBitsPerSample]; !ok {
+ return nil, FormatError("BitsPerSample tag missing")
+ }
+ for _, b := range d.features[tBitsPerSample] {
+ if b != 8 {
+ return nil, UnsupportedError("not an 8-bit image")
+ }
+ }
+
+ return d, nil
+}
+
+// DecodeConfig returns the color model and dimensions of a TIFF image without
+// decoding the entire image.
+func DecodeConfig(r io.Reader) (image.Config, os.Error) {
+ d, err := newDecoder(r)
+ if err != nil {
+ return image.Config{}, err
+ }
+ return d.config, nil
+}
+
+// Decode reads a TIFF image from r and returns it as an image.Image.
+// The type of Image returned depends on the contents of the TIFF.
+func Decode(r io.Reader) (img image.Image, err os.Error) {
+ d, err := newDecoder(r)
+ if err != nil {
+ return
+ }
+
+ // Check if we have the right number of strips, offsets and counts.
+ rps := int(d.firstVal(tRowsPerStrip))
+ numStrips := (d.config.Height + rps - 1) / rps
+ if rps == 0 || len(d.features[tStripOffsets]) < numStrips || len(d.features[tStripByteCounts]) < numStrips {
+ return nil, FormatError("inconsistent header")
+ }
+
+ switch d.mode {
+ case mGray, mGrayInvert:
+ img = image.NewGray(d.config.Width, d.config.Height)
+ case mPaletted:
+ img = image.NewPaletted(d.config.Width, d.config.Height, d.palette)
+ case mNRGBA:
+ img = image.NewNRGBA(d.config.Width, d.config.Height)
+ case mRGB, mRGBA:
+ img = image.NewRGBA(d.config.Width, d.config.Height)
+ }
+
+ var p []byte
+ for i := 0; i < numStrips; i++ {
+ ymin := i * rps
+ // The last strip may be shorter.
+ if i == numStrips-1 && d.config.Height%rps != 0 {
+ rps = d.config.Height % rps
+ }
+ offset := int64(d.features[tStripOffsets][i])
+ n := int64(d.features[tStripByteCounts][i])
+ switch d.firstVal(tCompression) {
+ case cNone:
+ // TODO(bsiegert): Avoid copy if r is a tiff.buffer.
+ p = make([]byte, 0, n)
+ _, err = d.r.ReadAt(p, offset)
+ case cLZW:
+ r := lzw.NewReader(io.NewSectionReader(d.r, offset, n), lzw.MSB, 8)
+ p, err = ioutil.ReadAll(r)
+ r.Close()
+ case cDeflate, cDeflateOld:
+ r, err := zlib.NewReader(io.NewSectionReader(d.r, offset, n))
+ if err != nil {
+ return nil, err
+ }
+ p, err = ioutil.ReadAll(r)
+ r.Close()
+ default:
+ err = UnsupportedError("compression")
+ }
+ if err != nil {
+ return
+ }
+ err = d.decode(img, p, ymin, ymin+rps)
+ }
+ return
+}
+
+func init() {
+ image.RegisterFormat("tiff", leHeader, Decode, DecodeConfig)
+ image.RegisterFormat("tiff", beHeader, Decode, DecodeConfig)
+}