image/tiff: implement a decoder.

The current iteration can decode 8-bit images in
grayscale, paletted, RGB, RGBA and NRGBA mode. LZW compression
is implemented but does not work on my test images.
Deflate (i.e. zlib) compression with or without a horizontal
predictor is supported.

R=nigeltao, nigeltao_gnome
CC=golang-dev, mpl
https://golang.org/cl/4240051

src/pkg/Makefile

@@ -107,6 +107,7 @@ DIRS=\
 	image\
 	image/jpeg\
 	image/png\
+	image/tiff\
 	image/ycbcr\
 	index/suffixarray\
 	io\

src/pkg/image/decode_test.go

@@ -10,9 +10,10 @@ import (
 	"os"
 	"testing"
 
-	// TODO(nigeltao): implement bmp, gif and tiff decoders.
+	// TODO(nigeltao): implement bmp and gif decoders.
 	_ "image/jpeg"
 	_ "image/png"
+	_ "image/tiff"
 )
 
 const goldenFile = "testdata/video-001.png"
@@ -30,7 +31,7 @@ var imageTests = []imageTest{
 	// JPEG is a lossy format and hence needs a non-zero tolerance.
 	{"testdata/video-001.jpeg", 8 << 8},
 	{"testdata/video-001.png", 0},
-	//{"testdata/video-001.tiff", 0},
+	{"testdata/video-001.tiff", 0},
 }
 
 func decode(filename string) (image.Image, string, os.Error) {

src/pkg/image/tiff/Makefile

@@ -0,0 +1,13 @@
+# 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.
+
+include ../../../Make.inc
+
+TARG=image/tiff
+GOFILES=\
+	buffer.go\
+	consts.go\
+	reader.go\
+
+include ../../../Make.pkg

src/pkg/image/tiff/buffer.go

@@ -0,0 +1,57 @@
+// 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
+
+import (
+	"io"
+	"os"
+)
+
+// buffer buffers an io.Reader to satisfy io.ReaderAt.
+type buffer struct {
+	r   io.Reader
+	buf []byte
+}
+
+func (b *buffer) ReadAt(p []byte, off int64) (int, os.Error) {
+	o := int(off)
+	end := o + len(p)
+	if int64(end) != off+int64(len(p)) {
+		return 0, os.EINVAL
+	}
+
+	m := len(b.buf)
+	if end > m {
+		if end > cap(b.buf) {
+			newcap := 1024
+			for newcap < end {
+				newcap *= 2
+			}
+			newbuf := make([]byte, end, newcap)
+			copy(newbuf, b.buf)
+			b.buf = newbuf
+		} else {
+			b.buf = b.buf[:end]
+		}
+		if n, err := io.ReadFull(b.r, b.buf[m:end]); err != nil {
+			end = m + n
+			b.buf = b.buf[:end]
+			return copy(p, b.buf[o:end]), err
+		}
+	}
+
+	return copy(p, b.buf[o:end]), nil
+}
+
+// newReaderAt converts an io.Reader into an io.ReaderAt.
+func newReaderAt(r io.Reader) io.ReaderAt {
+	if ra, ok := r.(io.ReaderAt); ok {
+		return ra
+	}
+	return &buffer{
+		r:   r,
+		buf: make([]byte, 0, 1024),
+	}
+}

src/pkg/image/tiff/buffer_test.go

@@ -0,0 +1,36 @@
+// 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
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+var readAtTests = []struct {
+	n   int
+	off int64
+	s   string
+	err os.Error
+}{
+	{2, 0, "ab", nil},
+	{6, 0, "abcdef", nil},
+	{3, 3, "def", nil},
+	{3, 5, "f", os.EOF},
+	{3, 6, "", os.EOF},
+}
+
+func TestReadAt(t *testing.T) {
+	r := newReaderAt(strings.NewReader("abcdef"))
+	b := make([]byte, 10)
+	for _, test := range readAtTests {
+		n, err := r.ReadAt(b[:test.n], test.off)
+		s := string(b[:n])
+		if s != test.s || err != test.err {
+			t.Errorf("buffer.ReadAt(<%v bytes>, %v): got %v, %q; want %v, %q", test.n, test.off, err, s, test.err, test.s)
+		}
+	}
+}

src/pkg/image/tiff/consts.go

@@ -0,0 +1,102 @@
+// 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
+
+// A tiff image file contains one or more images. The metadata
+// of each image is contained in an Image File Directory (IFD),
+// which contains entries of 12 bytes each and is described
+// on page 14-16 of the specification. An IFD entry consists of
+//
+//  - a tag, which describes the signification of the entry,
+//  - the data type and length of the entry,
+//  - the data itself or a pointer to it if it is more than 4 bytes.
+//
+// The presence of a length means that each IFD is effectively an array.
+
+const (
+	leHeader = "II\x2A\x00" // Header for little-endian files.
+	beHeader = "MM\x00\x2A" // Header for big-endian files.
+
+	ifdLen = 12 // Length of an IFD entry in bytes.
+)
+
+// Data types (p. 14-16 of the spec).
+const (
+	dtByte     = 1
+	dtASCII    = 2
+	dtShort    = 3
+	dtLong     = 4
+	dtRational = 5
+)
+
+// The length of one instance of each data type in bytes.
+var lengths = [...]uint32{0, 1, 1, 2, 4, 8}
+
+// Tags (see p. 28-41 of the spec).
+const (
+	tImageWidth                = 256
+	tImageLength               = 257
+	tBitsPerSample             = 258
+	tCompression               = 259
+	tPhotometricInterpretation = 262
+
+	tStripOffsets    = 273
+	tSamplesPerPixel = 277
+	tRowsPerStrip    = 278
+	tStripByteCounts = 279
+
+	tXResolution    = 282
+	tYResolution    = 283
+	tResolutionUnit = 296
+
+	tPredictor    = 317
+	tColorMap     = 320
+	tExtraSamples = 338
+)
+
+// Compression types (defined in various places in the spec and supplements).
+const (
+	cNone       = 1
+	cCCITT      = 2
+	cG3         = 3 // Group 3 Fax.
+	cG4         = 4 // Group 4 Fax.
+	cLZW        = 5
+	cJPEGOld    = 6 // Superseded by cJPEG.
+	cJPEG       = 7
+	cDeflate    = 8 // zlib compression.
+	cPackBits   = 32773
+	cDeflateOld = 32946 // Superseded by cDeflate.
+)
+
+// Photometric interpretation values (see p. 37 of the spec).
+const (
+	pWhiteIsZero = 0
+	pBlackIsZero = 1
+	pRGB         = 2
+	pPaletted    = 3
+	pTransMask   = 4 // transparency mask
+	pCMYK        = 5
+	pYCbCr       = 6
+	pCIELab      = 8
+)
+
+// Values for the tPredictor tag (page 64-65 of the spec).
+const (
+	prNone       = 1
+	prHorizontal = 2
+)
+
+// imageMode represents the mode of the image.
+type imageMode int
+
+const (
+	mBilevel imageMode = iota
+	mPaletted
+	mGray
+	mGrayInvert
+	mRGB
+	mRGBA
+	mNRGBA
+)

src/pkg/image/tiff/reader.go

@@ -0,0 +1,385 @@
+// 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)
+}