Update to current version of Go library.

From-SVN: r173931

25 files changed, 2307 insertions, 114 deletions

diff --git a/libgo/go/image/decode_test.go b/libgo/go/image/decode_test.go
index 0716ad9..fee537c 100644
--- a/libgo/go/image/decode_test.go
+++ b/libgo/go/image/decode_test.go
@@ -10,9 +10,11 @@ import (
 	"os"
 	"testing"
 
-	// TODO(nigeltao): implement bmp, gif and tiff decoders.
+	// TODO(nigeltao): implement bmp decoder.
+	_ "image/gif"
 	_ "image/jpeg"
 	_ "image/png"
+	_ "image/tiff"
 )
 
 const goldenFile = "testdata/video-001.png"
@@ -26,11 +28,11 @@ var imageTests = []imageTest{
 	//{"testdata/video-001.bmp", 0},
 	// GIF images are restricted to a 256-color palette and the conversion
 	// to GIF loses significant image quality.
-	//{"testdata/video-001.gif", 64<<8},
+	{"testdata/video-001.gif", 64 << 8},
 	// 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) {
diff --git a/libgo/go/image/format.go b/libgo/go/image/format.go
index 1d541b0..b485932 100644
--- a/libgo/go/image/format.go
+++ b/libgo/go/image/format.go
@@ -25,7 +25,8 @@ var formats []format
 
 // RegisterFormat registers an image format for use by Decode.
 // Name is the name of the format, like "jpeg" or "png".
-// Magic is the magic prefix that identifies the format's encoding.
+// Magic is the magic prefix that identifies the format's encoding. The magic
+// string can contain "?" wildcards that each match any one byte.
 // Decode is the function that decodes the encoded image.
 // DecodeConfig is the function that decodes just its configuration.
 func RegisterFormat(name, magic string, decode func(io.Reader) (Image, os.Error), decodeConfig func(io.Reader) (Config, os.Error)) {
@@ -46,11 +47,24 @@ func asReader(r io.Reader) reader {
 	return bufio.NewReader(r)
 }
 
-// sniff determines the format of r's data.
+// Match returns whether magic matches b. Magic may contain "?" wildcards.
+func match(magic string, b []byte) bool {
+	if len(magic) != len(b) {
+		return false
+	}
+	for i, c := range b {
+		if magic[i] != c && magic[i] != '?' {
+			return false
+		}
+	}
+	return true
+}
+
+// Sniff determines the format of r's data.
 func sniff(r reader) format {
 	for _, f := range formats {
-		s, err := r.Peek(len(f.magic))
-		if err == nil && string(s) == f.magic {
+		b, err := r.Peek(len(f.magic))
+		if err == nil && match(f.magic, b) {
 			return f
 		}
 	}
diff --git a/libgo/go/image/gif/reader.go b/libgo/go/image/gif/reader.go
new file mode 100644
index 0000000..d37f526
--- /dev/null
+++ b/libgo/go/image/gif/reader.go
@@ -0,0 +1,392 @@
+// 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 gif implements a GIF image decoder.
+//
+// The GIF specification is at http://www.w3.org/Graphics/GIF/spec-gif89a.txt.
+package gif
+
+import (
+	"bufio"
+	"compress/lzw"
+	"fmt"
+	"image"
+	"io"
+	"os"
+)
+
+// If the io.Reader does not also have ReadByte, then decode will introduce its own buffering.
+type reader interface {
+	io.Reader
+	io.ByteReader
+}
+
+// Masks etc.
+const (
+	// Fields.
+	fColorMapFollows = 1 << 7
+
+	// Image fields.
+	ifInterlace = 1 << 6
+
+	// Graphic control flags.
+	gcTransparentColorSet = 1 << 0
+)
+
+// Section indicators.
+const (
+	sExtension       = 0x21
+	sImageDescriptor = 0x2C
+	sTrailer         = 0x3B
+)
+
+// Extensions.
+const (
+	eText           = 0x01 // Plain Text
+	eGraphicControl = 0xF9 // Graphic Control
+	eComment        = 0xFE // Comment
+	eApplication    = 0xFF // Application
+)
+
+// decoder is the type used to decode a GIF file.
+type decoder struct {
+	r reader
+
+	// From header.
+	vers            string
+	width           int
+	height          int
+	flags           byte
+	headerFields    byte
+	backgroundIndex byte
+	loopCount       int
+	delayTime       int
+
+	// Unused from header.
+	aspect byte
+
+	// From image descriptor.
+	imageFields byte
+
+	// From graphics control.
+	transparentIndex byte
+
+	// Computed.
+	pixelSize      uint
+	globalColorMap image.PalettedColorModel
+
+	// Used when decoding.
+	delay []int
+	image []*image.Paletted
+	tmp   [1024]byte // must be at least 768 so we can read color map
+}
+
+// blockReader parses the block structure of GIF image data, which
+// comprises (n, (n bytes)) blocks, with 1 <= n <= 255.  It is the
+// reader given to the LZW decoder, which is thus immune to the
+// blocking.  After the LZW decoder completes, there will be a 0-byte
+// block remaining (0, ()), but under normal execution blockReader
+// doesn't consume it, so it is handled in decode.
+type blockReader struct {
+	r     reader
+	slice []byte
+	tmp   [256]byte
+}
+
+func (b *blockReader) Read(p []byte) (n int, err os.Error) {
+	if len(p) == 0 {
+		return
+	}
+	if len(b.slice) > 0 {
+		n = copy(p, b.slice)
+		b.slice = b.slice[n:]
+		return
+	}
+	var blockLen uint8
+	blockLen, err = b.r.ReadByte()
+	if err != nil {
+		return
+	}
+	if blockLen == 0 {
+		return 0, os.EOF
+	}
+	b.slice = b.tmp[0:blockLen]
+	if _, err = io.ReadFull(b.r, b.slice); err != nil {
+		return
+	}
+	return b.Read(p)
+}
+
+// decode reads a GIF image from r and stores the result in d.
+func (d *decoder) decode(r io.Reader, configOnly bool) os.Error {
+	// Add buffering if r does not provide ReadByte.
+	if rr, ok := r.(reader); ok {
+		d.r = rr
+	} else {
+		d.r = bufio.NewReader(r)
+	}
+
+	err := d.readHeaderAndScreenDescriptor()
+	if err != nil {
+		return err
+	}
+	if configOnly {
+		return nil
+	}
+
+	if d.headerFields&fColorMapFollows != 0 {
+		if d.globalColorMap, err = d.readColorMap(); err != nil {
+			return err
+		}
+	}
+
+	d.image = nil
+
+Loop:
+	for err == nil {
+		var c byte
+		c, err = d.r.ReadByte()
+		if err == os.EOF {
+			break
+		}
+		switch c {
+		case sExtension:
+			err = d.readExtension()
+
+		case sImageDescriptor:
+			var m *image.Paletted
+			m, err = d.newImageFromDescriptor()
+			if err != nil {
+				break
+			}
+			if d.imageFields&fColorMapFollows != 0 {
+				m.Palette, err = d.readColorMap()
+				if err != nil {
+					break
+				}
+				// TODO: do we set transparency in this map too? That would be
+				// d.setTransparency(m.Palette)
+			} else {
+				m.Palette = d.globalColorMap
+			}
+			var litWidth uint8
+			litWidth, err = d.r.ReadByte()
+			if err != nil {
+				return err
+			}
+			if litWidth > 8 {
+				return fmt.Errorf("gif: pixel size in decode out of range: %d", litWidth)
+			}
+			// A wonderfully Go-like piece of magic. Unfortunately it's only at its
+			// best for 8-bit pixels.
+			lzwr := lzw.NewReader(&blockReader{r: d.r}, lzw.LSB, int(litWidth))
+			if _, err = io.ReadFull(lzwr, m.Pix); err != nil {
+				break
+			}
+
+			// There should be a "0" block remaining; drain that.
+			c, err = d.r.ReadByte()
+			if err != nil {
+				return err
+			}
+			if c != 0 {
+				return os.ErrorString("gif: extra data after image")
+			}
+			d.image = append(d.image, m)
+			d.delay = append(d.delay, d.delayTime)
+			d.delayTime = 0 // TODO: is this correct, or should we hold on to the value?
+
+		case sTrailer:
+			break Loop
+
+		default:
+			err = fmt.Errorf("gif: unknown block type: 0x%.2x", c)
+		}
+	}
+	if err != nil {
+		return err
+	}
+	if len(d.image) == 0 {
+		return io.ErrUnexpectedEOF
+	}
+	return nil
+}
+
+func (d *decoder) readHeaderAndScreenDescriptor() os.Error {
+	_, err := io.ReadFull(d.r, d.tmp[0:13])
+	if err != nil {
+		return err
+	}
+	d.vers = string(d.tmp[0:6])
+	if d.vers != "GIF87a" && d.vers != "GIF89a" {
+		return fmt.Errorf("gif: can't recognize format %s", d.vers)
+	}
+	d.width = int(d.tmp[6]) + int(d.tmp[7])<<8
+	d.height = int(d.tmp[8]) + int(d.tmp[9])<<8
+	d.headerFields = d.tmp[10]
+	d.backgroundIndex = d.tmp[11]
+	d.aspect = d.tmp[12]
+	d.loopCount = -1
+	d.pixelSize = uint(d.headerFields&7) + 1
+	return nil
+}
+
+func (d *decoder) readColorMap() (image.PalettedColorModel, os.Error) {
+	if d.pixelSize > 8 {
+		return nil, fmt.Errorf("gif: can't handle %d bits per pixel", d.pixelSize)
+	}
+	numColors := 1 << d.pixelSize
+	numValues := 3 * numColors
+	_, err := io.ReadFull(d.r, d.tmp[0:numValues])
+	if err != nil {
+		return nil, fmt.Errorf("gif: short read on color map: %s", err)
+	}
+	colorMap := make(image.PalettedColorModel, numColors)
+	j := 0
+	for i := range colorMap {
+		colorMap[i] = image.RGBAColor{d.tmp[j+0], d.tmp[j+1], d.tmp[j+2], 0xFF}
+		j += 3
+	}
+	return colorMap, nil
+}
+
+func (d *decoder) readExtension() os.Error {
+	extension, err := d.r.ReadByte()
+	if err != nil {
+		return err
+	}
+	size := 0
+	switch extension {
+	case eText:
+		size = 13
+	case eGraphicControl:
+		return d.readGraphicControl()
+	case eComment:
+		// nothing to do but read the data.
+	case eApplication:
+		b, err := d.r.ReadByte()
+		if err != nil {
+			return err
+		}
+		// The spec requires size be 11, but Adobe sometimes uses 10.
+		size = int(b)
+	default:
+		return fmt.Errorf("gif: unknown extension 0x%.2x", extension)
+	}
+	if size > 0 {
+		if _, err := d.r.Read(d.tmp[0:size]); err != nil {
+			return err
+		}
+	}
+
+	// Application Extension with "NETSCAPE2.0" as string and 1 in data means
+	// this extension defines a loop count.
+	if extension == eApplication && string(d.tmp[:size]) == "NETSCAPE2.0" {
+		n, err := d.readBlock()
+		if n == 0 || err != nil {
+			return err
+		}
+		if n == 3 && d.tmp[0] == 1 {
+			d.loopCount = int(d.tmp[1]) | int(d.tmp[2])<<8
+		}
+	}
+	for {
+		n, err := d.readBlock()
+		if n == 0 || err != nil {
+			return err
+		}
+	}
+	panic("unreachable")
+}
+
+func (d *decoder) readGraphicControl() os.Error {
+	if _, err := io.ReadFull(d.r, d.tmp[0:6]); err != nil {
+		return fmt.Errorf("gif: can't read graphic control: %s", err)
+	}
+	d.flags = d.tmp[1]
+	d.delayTime = int(d.tmp[2]) | int(d.tmp[3])<<8
+	if d.flags&gcTransparentColorSet != 0 {
+		d.transparentIndex = d.tmp[4]
+		d.setTransparency(d.globalColorMap)
+	}
+	return nil
+}
+
+func (d *decoder) setTransparency(colorMap image.PalettedColorModel) {
+	if int(d.transparentIndex) < len(colorMap) {
+		colorMap[d.transparentIndex] = image.RGBAColor{}
+	}
+}
+
+func (d *decoder) newImageFromDescriptor() (*image.Paletted, os.Error) {
+	if _, err := io.ReadFull(d.r, d.tmp[0:9]); err != nil {
+		return nil, fmt.Errorf("gif: can't read image descriptor: %s", err)
+	}
+	_ = int(d.tmp[0]) + int(d.tmp[1])<<8 // TODO: honor left value
+	_ = int(d.tmp[2]) + int(d.tmp[3])<<8 // TODO: honor top value
+	width := int(d.tmp[4]) + int(d.tmp[5])<<8
+	height := int(d.tmp[6]) + int(d.tmp[7])<<8
+	d.imageFields = d.tmp[8]
+	if d.imageFields&ifInterlace != 0 {
+		return nil, os.ErrorString("gif: can't handle interlaced images")
+	}
+	return image.NewPaletted(width, height, nil), nil
+}
+
+func (d *decoder) readBlock() (int, os.Error) {
+	n, err := d.r.ReadByte()
+	if n == 0 || err != nil {
+		return 0, err
+	}
+	return io.ReadFull(d.r, d.tmp[0:n])
+}
+
+// Decode reads a GIF image from r and returns the first embedded
+// image as an image.Image.
+// Limitation: The file must be 8 bits per pixel and have no interlacing.
+func Decode(r io.Reader) (image.Image, os.Error) {
+	var d decoder
+	if err := d.decode(r, false); err != nil {
+		return nil, err
+	}
+	return d.image[0], nil
+}
+
+// GIF represents the possibly multiple images stored in a GIF file.
+type GIF struct {
+	Image     []*image.Paletted // The successive images.
+	Delay     []int             // The successive delay times, one per frame, in 100ths of a second.
+	LoopCount int               // The loop count.
+}
+
+// DecodeAll reads a GIF image from r and returns the sequential frames
+// and timing information.
+// Limitation: The file must be 8 bits per pixel and have no interlacing.
+func DecodeAll(r io.Reader) (*GIF, os.Error) {
+	var d decoder
+	if err := d.decode(r, false); err != nil {
+		return nil, err
+	}
+	gif := &GIF{
+		Image:     d.image,
+		LoopCount: d.loopCount,
+		Delay:     d.delay,
+	}
+	return gif, nil
+}
+
+// DecodeConfig returns the color model and dimensions of a GIF image without
+// decoding the entire image.
+func DecodeConfig(r io.Reader) (image.Config, os.Error) {
+	var d decoder
+	if err := d.decode(r, true); err != nil {
+		return image.Config{}, err
+	}
+	colorMap := d.globalColorMap
+	return image.Config{colorMap, d.width, d.height}, nil
+}
+
+func init() {
+	image.RegisterFormat("gif", "GIF8?a", Decode, DecodeConfig)
+}
diff --git a/libgo/go/image/image.go b/libgo/go/image/image.go
index c0e96e1..4350acc 100644
--- a/libgo/go/image/image.go
+++ b/libgo/go/image/image.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// The image package implements a basic 2-D image library.
+// Package image implements a basic 2-D image library.
 package image
 
 // A Config consists of an image's color model and dimensions.
@@ -51,6 +51,13 @@ func (p *RGBA) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toRGBAColor(c).(RGBAColor)
 }
 
+func (p *RGBA) SetRGBA(x, y int, c RGBAColor) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *RGBA) Opaque() bool {
 	if p.Rect.Empty() {
@@ -103,6 +110,13 @@ func (p *RGBA64) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toRGBA64Color(c).(RGBA64Color)
 }
 
+func (p *RGBA64) SetRGBA64(x, y int, c RGBA64Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *RGBA64) Opaque() bool {
 	if p.Rect.Empty() {
@@ -155,6 +169,13 @@ func (p *NRGBA) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toNRGBAColor(c).(NRGBAColor)
 }
 
+func (p *NRGBA) SetNRGBA(x, y int, c NRGBAColor) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *NRGBA) Opaque() bool {
 	if p.Rect.Empty() {
@@ -207,6 +228,13 @@ func (p *NRGBA64) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toNRGBA64Color(c).(NRGBA64Color)
 }
 
+func (p *NRGBA64) SetNRGBA64(x, y int, c NRGBA64Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *NRGBA64) Opaque() bool {
 	if p.Rect.Empty() {
@@ -259,6 +287,13 @@ func (p *Alpha) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toAlphaColor(c).(AlphaColor)
 }
 
+func (p *Alpha) SetAlpha(x, y int, c AlphaColor) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *Alpha) Opaque() bool {
 	if p.Rect.Empty() {
@@ -311,6 +346,13 @@ func (p *Alpha16) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toAlpha16Color(c).(Alpha16Color)
 }
 
+func (p *Alpha16) SetAlpha16(x, y int, c Alpha16Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *Alpha16) Opaque() bool {
 	if p.Rect.Empty() {
@@ -363,6 +405,13 @@ func (p *Gray) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toGrayColor(c).(GrayColor)
 }
 
+func (p *Gray) SetGray(x, y int, c GrayColor) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *Gray) Opaque() bool {
 	return true
@@ -401,6 +450,13 @@ func (p *Gray16) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toGray16Color(c).(Gray16Color)
 }
 
+func (p *Gray16) SetGray16(x, y int, c Gray16Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *Gray16) Opaque() bool {
 	return true
diff --git a/libgo/go/image/jpeg/fdct.go b/libgo/go/image/jpeg/fdct.go
new file mode 100644
index 0000000..3f8be4e
--- /dev/null
+++ b/libgo/go/image/jpeg/fdct.go
@@ -0,0 +1,190 @@
+// 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 jpeg
+
+// This file implements a Forward Discrete Cosine Transformation.
+
+/*
+It is based on the code in jfdctint.c from the Independent JPEG Group,
+found at http://www.ijg.org/files/jpegsrc.v8c.tar.gz.
+
+The "LEGAL ISSUES" section of the README in that archive says:
+
+In plain English:
+
+1. We don't promise that this software works.  (But if you find any bugs,
+   please let us know!)
+2. You can use this software for whatever you want.  You don't have to pay us.
+3. You may not pretend that you wrote this software.  If you use it in a
+   program, you must acknowledge somewhere in your documentation that
+   you've used the IJG code.
+
+In legalese:
+
+The authors make NO WARRANTY or representation, either express or implied,
+with respect to this software, its quality, accuracy, merchantability, or
+fitness for a particular purpose.  This software is provided "AS IS", and you,
+its user, assume the entire risk as to its quality and accuracy.
+
+This software is copyright (C) 1991-2011, Thomas G. Lane, Guido Vollbeding.
+All Rights Reserved except as specified below.
+
+Permission is hereby granted to use, copy, modify, and distribute this
+software (or portions thereof) for any purpose, without fee, subject to these
+conditions:
+(1) If any part of the source code for this software is distributed, then this
+README file must be included, with this copyright and no-warranty notice
+unaltered; and any additions, deletions, or changes to the original files
+must be clearly indicated in accompanying documentation.
+(2) If only executable code is distributed, then the accompanying
+documentation must state that "this software is based in part on the work of
+the Independent JPEG Group".
+(3) Permission for use of this software is granted only if the user accepts
+full responsibility for any undesirable consequences; the authors accept
+NO LIABILITY for damages of any kind.
+
+These conditions apply to any software derived from or based on the IJG code,
+not just to the unmodified library.  If you use our work, you ought to
+acknowledge us.
+
+Permission is NOT granted for the use of any IJG author's name or company name
+in advertising or publicity relating to this software or products derived from
+it.  This software may be referred to only as "the Independent JPEG Group's
+software".
+
+We specifically permit and encourage the use of this software as the basis of
+commercial products, provided that all warranty or liability claims are
+assumed by the product vendor.
+*/
+
+// Trigonometric constants in 13-bit fixed point format.
+const (
+	fix_0_298631336 = 2446
+	fix_0_390180644 = 3196
+	fix_0_541196100 = 4433
+	fix_0_765366865 = 6270
+	fix_0_899976223 = 7373
+	fix_1_175875602 = 9633
+	fix_1_501321110 = 12299
+	fix_1_847759065 = 15137
+	fix_1_961570560 = 16069
+	fix_2_053119869 = 16819
+	fix_2_562915447 = 20995
+	fix_3_072711026 = 25172
+)
+
+const (
+	constBits     = 13
+	pass1Bits     = 2
+	centerJSample = 128
+)
+
+// fdct performs a forward DCT on an 8x8 block of coefficients, including a
+// level shift.
+func fdct(b *block) {
+	// Pass 1: process rows.
+	for y := 0; y < 8; y++ {
+		x0 := b[y*8+0]
+		x1 := b[y*8+1]
+		x2 := b[y*8+2]
+		x3 := b[y*8+3]
+		x4 := b[y*8+4]
+		x5 := b[y*8+5]
+		x6 := b[y*8+6]
+		x7 := b[y*8+7]
+
+		tmp0 := x0 + x7
+		tmp1 := x1 + x6
+		tmp2 := x2 + x5
+		tmp3 := x3 + x4
+
+		tmp10 := tmp0 + tmp3
+		tmp12 := tmp0 - tmp3
+		tmp11 := tmp1 + tmp2
+		tmp13 := tmp1 - tmp2
+
+		tmp0 = x0 - x7
+		tmp1 = x1 - x6
+		tmp2 = x2 - x5
+		tmp3 = x3 - x4
+
+		b[y*8+0] = (tmp10 + tmp11 - 8*centerJSample) << pass1Bits
+		b[y*8+4] = (tmp10 - tmp11) << pass1Bits
+		z1 := (tmp12 + tmp13) * fix_0_541196100
+		z1 += 1 << (constBits - pass1Bits - 1)
+		b[y*8+2] = (z1 + tmp12*fix_0_765366865) >> (constBits - pass1Bits)
+		b[y*8+6] = (z1 - tmp13*fix_1_847759065) >> (constBits - pass1Bits)
+
+		tmp10 = tmp0 + tmp3
+		tmp11 = tmp1 + tmp2
+		tmp12 = tmp0 + tmp2
+		tmp13 = tmp1 + tmp3
+		z1 = (tmp12 + tmp13) * fix_1_175875602
+		z1 += 1 << (constBits - pass1Bits - 1)
+		tmp0 = tmp0 * fix_1_501321110
+		tmp1 = tmp1 * fix_3_072711026
+		tmp2 = tmp2 * fix_2_053119869
+		tmp3 = tmp3 * fix_0_298631336
+		tmp10 = tmp10 * -fix_0_899976223
+		tmp11 = tmp11 * -fix_2_562915447
+		tmp12 = tmp12 * -fix_0_390180644
+		tmp13 = tmp13 * -fix_1_961570560
+
+		tmp12 += z1
+		tmp13 += z1
+		b[y*8+1] = (tmp0 + tmp10 + tmp12) >> (constBits - pass1Bits)
+		b[y*8+3] = (tmp1 + tmp11 + tmp13) >> (constBits - pass1Bits)
+		b[y*8+5] = (tmp2 + tmp11 + tmp12) >> (constBits - pass1Bits)
+		b[y*8+7] = (tmp3 + tmp10 + tmp13) >> (constBits - pass1Bits)
+	}
+	// Pass 2: process columns.
+	// We remove pass1Bits scaling, but leave results scaled up by an overall factor of 8.
+	for x := 0; x < 8; x++ {
+		tmp0 := b[0*8+x] + b[7*8+x]
+		tmp1 := b[1*8+x] + b[6*8+x]
+		tmp2 := b[2*8+x] + b[5*8+x]
+		tmp3 := b[3*8+x] + b[4*8+x]
+
+		tmp10 := tmp0 + tmp3 + 1<<(pass1Bits-1)
+		tmp12 := tmp0 - tmp3
+		tmp11 := tmp1 + tmp2
+		tmp13 := tmp1 - tmp2
+
+		tmp0 = b[0*8+x] - b[7*8+x]
+		tmp1 = b[1*8+x] - b[6*8+x]
+		tmp2 = b[2*8+x] - b[5*8+x]
+		tmp3 = b[3*8+x] - b[4*8+x]
+
+		b[0*8+x] = (tmp10 + tmp11) >> pass1Bits
+		b[4*8+x] = (tmp10 - tmp11) >> pass1Bits
+
+		z1 := (tmp12 + tmp13) * fix_0_541196100
+		z1 += 1 << (constBits + pass1Bits - 1)
+		b[2*8+x] = (z1 + tmp12*fix_0_765366865) >> (constBits + pass1Bits)
+		b[6*8+x] = (z1 - tmp13*fix_1_847759065) >> (constBits + pass1Bits)
+
+		tmp10 = tmp0 + tmp3
+		tmp11 = tmp1 + tmp2
+		tmp12 = tmp0 + tmp2
+		tmp13 = tmp1 + tmp3
+		z1 = (tmp12 + tmp13) * fix_1_175875602
+		z1 += 1 << (constBits + pass1Bits - 1)
+		tmp0 = tmp0 * fix_1_501321110
+		tmp1 = tmp1 * fix_3_072711026
+		tmp2 = tmp2 * fix_2_053119869
+		tmp3 = tmp3 * fix_0_298631336
+		tmp10 = tmp10 * -fix_0_899976223
+		tmp11 = tmp11 * -fix_2_562915447
+		tmp12 = tmp12 * -fix_0_390180644
+		tmp13 = tmp13 * -fix_1_961570560
+
+		tmp12 += z1
+		tmp13 += z1
+		b[1*8+x] = (tmp0 + tmp10 + tmp12) >> (constBits + pass1Bits)
+		b[3*8+x] = (tmp1 + tmp11 + tmp13) >> (constBits + pass1Bits)
+		b[5*8+x] = (tmp2 + tmp11 + tmp12) >> (constBits + pass1Bits)
+		b[7*8+x] = (tmp3 + tmp10 + tmp13) >> (constBits + pass1Bits)
+	}
+}
diff --git a/libgo/go/image/jpeg/idct.go b/libgo/go/image/jpeg/idct.go
index 5189931..e5a2f40 100644
--- a/libgo/go/image/jpeg/idct.go
+++ b/libgo/go/image/jpeg/idct.go
@@ -63,7 +63,7 @@ const (
 //
 // For more on the actual algorithm, see Z. Wang, "Fast algorithms for the discrete W transform and
 // for the discrete Fourier transform", IEEE Trans. on ASSP, Vol. ASSP- 32, pp. 803-816, Aug. 1984.
-func idct(b *[blockSize]int) {
+func idct(b *block) {
 	// Horizontal 1-D IDCT.
 	for y := 0; y < 8; y++ {
 		// If all the AC components are zero, then the IDCT is trivial.
diff --git a/libgo/go/image/jpeg/reader.go b/libgo/go/image/jpeg/reader.go
index fb9cb11..21a6fff 100644
--- a/libgo/go/image/jpeg/reader.go
+++ b/libgo/go/image/jpeg/reader.go
@@ -2,18 +2,22 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// The jpeg package implements a decoder for JPEG images, as defined in ITU-T T.81.
+// Package jpeg implements a JPEG image decoder and encoder.
+//
+// JPEG is defined in ITU-T T.81: http://www.w3.org/Graphics/JPEG/itu-t81.pdf.
 package jpeg
 
-// See http://www.w3.org/Graphics/JPEG/itu-t81.pdf
-
 import (
 	"bufio"
 	"image"
+	"image/ycbcr"
 	"io"
 	"os"
 )
 
+// TODO(nigeltao): fix up the doc comment style so that sentences start with
+// the name of the type or function that they annotate.
+
 // A FormatError reports that the input is not a valid JPEG.
 type FormatError string
 
@@ -26,12 +30,14 @@ func (e UnsupportedError) String() string { return "unsupported JPEG feature: "
 
 // Component specification, specified in section B.2.2.
 type component struct {
+	h  int   // Horizontal sampling factor.
+	v  int   // Vertical sampling factor.
 	c  uint8 // Component identifier.
-	h  uint8 // Horizontal sampling factor.
-	v  uint8 // Vertical sampling factor.
 	tq uint8 // Quantization table destination selector.
 }
 
+type block [blockSize]int
+
 const (
 	blockSize = 64 // A DCT block is 8x8.
 
@@ -84,13 +90,13 @@ type Reader interface {
 type decoder struct {
 	r             Reader
 	width, height int
-	image         *image.RGBA
+	img           *ycbcr.YCbCr
 	ri            int // Restart Interval.
 	comps         [nComponent]component
 	huff          [maxTc + 1][maxTh + 1]huffman
-	quant         [maxTq + 1][blockSize]int
+	quant         [maxTq + 1]block
 	b             bits
-	blocks        [nComponent][maxH * maxV][blockSize]int
+	blocks        [nComponent][maxH * maxV]block
 	tmp           [1024]byte
 }
 
@@ -130,9 +136,9 @@ func (d *decoder) processSOF(n int) os.Error {
 	}
 	for i := 0; i < nComponent; i++ {
 		hv := d.tmp[7+3*i]
+		d.comps[i].h = int(hv >> 4)
+		d.comps[i].v = int(hv & 0x0f)
 		d.comps[i].c = d.tmp[6+3*i]
-		d.comps[i].h = hv >> 4
-		d.comps[i].v = hv & 0x0f
 		d.comps[i].tq = d.tmp[8+3*i]
 		// We only support YCbCr images, and 4:4:4, 4:2:2 or 4:2:0 chroma downsampling ratios. This implies that
 		// the (h, v) values for the Y component are either (1, 1), (2, 1) or (2, 2), and the
@@ -176,71 +182,47 @@ func (d *decoder) processDQT(n int) os.Error {
 	return nil
 }
 
-// Set the Pixel (px, py)'s RGB value, based on its YCbCr value.
-func (d *decoder) calcPixel(px, py, lumaBlock, lumaIndex, chromaIndex int) {
-	y, cb, cr := d.blocks[0][lumaBlock][lumaIndex], d.blocks[1][0][chromaIndex], d.blocks[2][0][chromaIndex]
-	// The JFIF specification (http://www.w3.org/Graphics/JPEG/jfif3.pdf, page 3) gives the formula
-	// for translating YCbCr to RGB as:
-	//   R = Y + 1.402 (Cr-128)
-	//   G = Y - 0.34414 (Cb-128) - 0.71414 (Cr-128)
-	//   B = Y + 1.772 (Cb-128)
-	yPlusHalf := 100000*y + 50000
-	cb -= 128
-	cr -= 128
-	r := (yPlusHalf + 140200*cr) / 100000
-	g := (yPlusHalf - 34414*cb - 71414*cr) / 100000
-	b := (yPlusHalf + 177200*cb) / 100000
-	if r < 0 {
-		r = 0
-	} else if r > 255 {
-		r = 255
+// Clip x to the range [0, 255] inclusive.
+func clip(x int) uint8 {
+	if x < 0 {
+		return 0
 	}
-	if g < 0 {
-		g = 0
-	} else if g > 255 {
-		g = 255
+	if x > 255 {
+		return 255
 	}
-	if b < 0 {
-		b = 0
-	} else if b > 255 {
-		b = 255
-	}
-	d.image.Pix[py*d.image.Stride+px] = image.RGBAColor{uint8(r), uint8(g), uint8(b), 0xff}
+	return uint8(x)
 }
 
-// Convert the MCU from YCbCr to RGB.
-func (d *decoder) convertMCU(mx, my, h0, v0 int) {
-	lumaBlock := 0
+// Store the MCU to the image.
+func (d *decoder) storeMCU(mx, my int) {
+	h0, v0 := d.comps[0].h, d.comps[0].v
+	// Store the luma blocks.
 	for v := 0; v < v0; v++ {
 		for h := 0; h < h0; h++ {
-			chromaBase := 8*4*v + 4*h
-			py := 8 * (v0*my + v)
-			for y := 0; y < 8 && py < d.height; y++ {
-				px := 8 * (h0*mx + h)
-				lumaIndex := 8 * y
-				chromaIndex := chromaBase + 8*(y/v0)
-				for x := 0; x < 8 && px < d.width; x++ {
-					d.calcPixel(px, py, lumaBlock, lumaIndex, chromaIndex)
-					if h0 == 1 {
-						chromaIndex += 1
-					} else {
-						chromaIndex += x % 2
-					}
-					lumaIndex++
-					px++
+			p := 8 * ((v0*my+v)*d.img.YStride + (h0*mx + h))
+			for y := 0; y < 8; y++ {
+				for x := 0; x < 8; x++ {
+					d.img.Y[p] = clip(d.blocks[0][h0*v+h][8*y+x])
+					p++
 				}
-				py++
+				p += d.img.YStride - 8
 			}
-			lumaBlock++
 		}
 	}
+	// Store the chroma blocks.
+	p := 8 * (my*d.img.CStride + mx)
+	for y := 0; y < 8; y++ {
+		for x := 0; x < 8; x++ {
+			d.img.Cb[p] = clip(d.blocks[1][0][8*y+x])
+			d.img.Cr[p] = clip(d.blocks[2][0][8*y+x])
+			p++
+		}
+		p += d.img.CStride - 8
+	}
 }
 
 // Specified in section B.2.3.
 func (d *decoder) processSOS(n int) os.Error {
-	if d.image == nil {
-		d.image = image.NewRGBA(d.width, d.height)
-	}
 	if n != 4+2*nComponent {
 		return UnsupportedError("SOS has wrong length")
 	}
@@ -255,7 +237,6 @@ func (d *decoder) processSOS(n int) os.Error {
 		td uint8 // DC table selector.
 		ta uint8 // AC table selector.
 	}
-	h0, v0 := int(d.comps[0].h), int(d.comps[0].v) // The h and v values from the Y components.
 	for i := 0; i < nComponent; i++ {
 		cs := d.tmp[1+2*i] // Component selector.
 		if cs != d.comps[i].c {
@@ -265,17 +246,42 @@ func (d *decoder) processSOS(n int) os.Error {
 		scanComps[i].ta = d.tmp[2+2*i] & 0x0f
 	}
 	// mxx and myy are the number of MCUs (Minimum Coded Units) in the image.
-	mxx := (d.width + 8*int(h0) - 1) / (8 * int(h0))
-	myy := (d.height + 8*int(v0) - 1) / (8 * int(v0))
+	h0, v0 := d.comps[0].h, d.comps[0].v // The h and v values from the Y components.
+	mxx := (d.width + 8*h0 - 1) / (8 * h0)
+	myy := (d.height + 8*v0 - 1) / (8 * v0)
+	if d.img == nil {
+		var subsampleRatio ycbcr.SubsampleRatio
+		n := h0 * v0
+		switch n {
+		case 1:
+			subsampleRatio = ycbcr.SubsampleRatio444
+		case 2:
+			subsampleRatio = ycbcr.SubsampleRatio422
+		case 4:
+			subsampleRatio = ycbcr.SubsampleRatio420
+		default:
+			panic("unreachable")
+		}
+		b := make([]byte, mxx*myy*(1*8*8*n+2*8*8))
+		d.img = &ycbcr.YCbCr{
+			Y:              b[mxx*myy*(0*8*8*n+0*8*8) : mxx*myy*(1*8*8*n+0*8*8)],
+			Cb:             b[mxx*myy*(1*8*8*n+0*8*8) : mxx*myy*(1*8*8*n+1*8*8)],
+			Cr:             b[mxx*myy*(1*8*8*n+1*8*8) : mxx*myy*(1*8*8*n+2*8*8)],
+			SubsampleRatio: subsampleRatio,
+			YStride:        mxx * 8 * h0,
+			CStride:        mxx * 8,
+			Rect:           image.Rect(0, 0, d.width, d.height),
+		}
+	}
 
 	mcu, expectedRST := 0, uint8(rst0Marker)
-	var allZeroes [blockSize]int
+	var allZeroes block
 	var dc [nComponent]int
 	for my := 0; my < myy; my++ {
 		for mx := 0; mx < mxx; mx++ {
 			for i := 0; i < nComponent; i++ {
 				qt := &d.quant[d.comps[i].tq]
-				for j := 0; j < int(d.comps[i].h*d.comps[i].v); j++ {
+				for j := 0; j < d.comps[i].h*d.comps[i].v; j++ {
 					d.blocks[i][j] = allZeroes
 
 					// Decode the DC coefficient, as specified in section F.2.2.1.
@@ -299,20 +305,20 @@ func (d *decoder) processSOS(n int) os.Error {
 						if err != nil {
 							return err
 						}
-						v0 := value >> 4
-						v1 := value & 0x0f
-						if v1 != 0 {
-							k += int(v0)
+						val0 := value >> 4
+						val1 := value & 0x0f
+						if val1 != 0 {
+							k += int(val0)
 							if k > blockSize {
 								return FormatError("bad DCT index")
 							}
-							ac, err := d.receiveExtend(v1)
+							ac, err := d.receiveExtend(val1)
 							if err != nil {
 								return err
 							}
 							d.blocks[i][j][unzig[k]] = ac * qt[k]
 						} else {
-							if v0 != 0x0f {
+							if val0 != 0x0f {
 								break
 							}
 							k += 0x0f
@@ -322,7 +328,7 @@ func (d *decoder) processSOS(n int) os.Error {
 					idct(&d.blocks[i][j])
 				} // for j
 			} // for i
-			d.convertMCU(mx, my, int(d.comps[0].h), int(d.comps[0].v))
+			d.storeMCU(mx, my)
 			mcu++
 			if d.ri > 0 && mcu%d.ri == 0 && mcu < mxx*myy {
 				// A more sophisticated decoder could use RST[0-7] markers to resynchronize from corrupt input,
@@ -431,7 +437,7 @@ func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, os.Error) {
 			return nil, err
 		}
 	}
-	return d.image, nil
+	return d.img, nil
 }
 
 // Decode reads a JPEG image from r and returns it as an image.Image.
diff --git a/libgo/go/image/jpeg/writer.go b/libgo/go/image/jpeg/writer.go
new file mode 100644
index 0000000..52b3dc4
--- /dev/null
+++ b/libgo/go/image/jpeg/writer.go
@@ -0,0 +1,553 @@
+// 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 jpeg
+
+import (
+	"bufio"
+	"image"
+	"image/ycbcr"
+	"io"
+	"os"
+)
+
+// min returns the minimum of two integers.
+func min(x, y int) int {
+	if x < y {
+		return x
+	}
+	return y
+}
+
+// div returns a/b rounded to the nearest integer, instead of rounded to zero.
+func div(a int, b int) int {
+	if a >= 0 {
+		return (a + (b >> 1)) / b
+	}
+	return -((-a + (b >> 1)) / b)
+}
+
+// bitCount counts the number of bits needed to hold an integer.
+var bitCount = [256]byte{
+	0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
+	5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
+	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
+	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
+	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+}
+
+type quantIndex int
+
+const (
+	quantIndexLuminance quantIndex = iota
+	quantIndexChrominance
+	nQuantIndex
+)
+
+// unscaledQuant are the unscaled quantization tables. Each encoder copies and
+// scales the tables according to its quality parameter.
+var unscaledQuant = [nQuantIndex][blockSize]byte{
+	// Luminance.
+	{
+		16, 11, 10, 16, 24, 40, 51, 61,
+		12, 12, 14, 19, 26, 58, 60, 55,
+		14, 13, 16, 24, 40, 57, 69, 56,
+		14, 17, 22, 29, 51, 87, 80, 62,
+		18, 22, 37, 56, 68, 109, 103, 77,
+		24, 35, 55, 64, 81, 104, 113, 92,
+		49, 64, 78, 87, 103, 121, 120, 101,
+		72, 92, 95, 98, 112, 100, 103, 99,
+	},
+	// Chrominance.
+	{
+		17, 18, 24, 47, 99, 99, 99, 99,
+		18, 21, 26, 66, 99, 99, 99, 99,
+		24, 26, 56, 99, 99, 99, 99, 99,
+		47, 66, 99, 99, 99, 99, 99, 99,
+		99, 99, 99, 99, 99, 99, 99, 99,
+		99, 99, 99, 99, 99, 99, 99, 99,
+		99, 99, 99, 99, 99, 99, 99, 99,
+		99, 99, 99, 99, 99, 99, 99, 99,
+	},
+}
+
+type huffIndex int
+
+const (
+	huffIndexLuminanceDC huffIndex = iota
+	huffIndexLuminanceAC
+	huffIndexChrominanceDC
+	huffIndexChrominanceAC
+	nHuffIndex
+)
+
+// huffmanSpec specifies a Huffman encoding.
+type huffmanSpec struct {
+	// count[i] is the number of codes of length i bits.
+	count [16]byte
+	// value[i] is the decoded value of the i'th codeword.
+	value []byte
+}
+
+// theHuffmanSpec is the Huffman encoding specifications.
+// This encoder uses the same Huffman encoding for all images.
+var theHuffmanSpec = [nHuffIndex]huffmanSpec{
+	// Luminance DC.
+	{
+		[16]byte{0, 1, 5, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0},
+		[]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
+	},
+	// Luminance AC.
+	{
+		[16]byte{0, 2, 1, 3, 3, 2, 4, 3, 5, 5, 4, 4, 0, 0, 1, 125},
+		[]byte{
+			0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12,
+			0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07,
+			0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xa1, 0x08,
+			0x23, 0x42, 0xb1, 0xc1, 0x15, 0x52, 0xd1, 0xf0,
+			0x24, 0x33, 0x62, 0x72, 0x82, 0x09, 0x0a, 0x16,
+			0x17, 0x18, 0x19, 0x1a, 0x25, 0x26, 0x27, 0x28,
+			0x29, 0x2a, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39,
+			0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49,
+			0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59,
+			0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
+			0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79,
+			0x7a, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89,
+			0x8a, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98,
+			0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
+			0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6,
+			0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3, 0xc4, 0xc5,
+			0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4,
+			0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe1, 0xe2,
+			0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea,
+			0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,
+			0xf9, 0xfa,
+		},
+	},
+	// Chrominance DC.
+	{
+		[16]byte{0, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0},
+		[]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
+	},
+	// Chrominance AC.
+	{
+		[16]byte{0, 2, 1, 2, 4, 4, 3, 4, 7, 5, 4, 4, 0, 1, 2, 119},
+		[]byte{
+			0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21,
+			0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71,
+			0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91,
+			0xa1, 0xb1, 0xc1, 0x09, 0x23, 0x33, 0x52, 0xf0,
+			0x15, 0x62, 0x72, 0xd1, 0x0a, 0x16, 0x24, 0x34,
+			0xe1, 0x25, 0xf1, 0x17, 0x18, 0x19, 0x1a, 0x26,
+			0x27, 0x28, 0x29, 0x2a, 0x35, 0x36, 0x37, 0x38,
+			0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
+			0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
+			0x59, 0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
+			0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,
+			0x79, 0x7a, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
+			0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95, 0x96,
+			0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5,
+			0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4,
+			0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3,
+			0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2,
+			0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda,
+			0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9,
+			0xea, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,
+			0xf9, 0xfa,
+		},
+	},
+}
+
+// huffmanLUT is a compiled look-up table representation of a huffmanSpec.
+// Each value maps to a uint32 of which the 8 most significant bits hold the
+// codeword size in bits and the 24 least significant bits hold the codeword.
+// The maximum codeword size is 16 bits.
+type huffmanLUT []uint32
+
+func (h *huffmanLUT) init(s huffmanSpec) {
+	maxValue := 0
+	for _, v := range s.value {
+		if int(v) > maxValue {
+			maxValue = int(v)
+		}
+	}
+	*h = make([]uint32, maxValue+1)
+	code, k := uint32(0), 0
+	for i := 0; i < len(s.count); i++ {
+		nBits := uint32(i+1) << 24
+		for j := uint8(0); j < s.count[i]; j++ {
+			(*h)[s.value[k]] = nBits | code
+			code++
+			k++
+		}
+		code <<= 1
+	}
+}
+
+// theHuffmanLUT are compiled representations of theHuffmanSpec.
+var theHuffmanLUT [4]huffmanLUT
+
+func init() {
+	for i, s := range theHuffmanSpec {
+		theHuffmanLUT[i].init(s)
+	}
+}
+
+// writer is a buffered writer.
+type writer interface {
+	Flush() os.Error
+	Write([]byte) (int, os.Error)
+	WriteByte(byte) os.Error
+}
+
+// encoder encodes an image to the JPEG format.
+type encoder struct {
+	// w is the writer to write to. err is the first error encountered during
+	// writing. All attempted writes after the first error become no-ops.
+	w   writer
+	err os.Error
+	// buf is a scratch buffer.
+	buf [16]byte
+	// bits and nBits are accumulated bits to write to w.
+	bits  uint32
+	nBits uint8
+	// quant is the scaled quantization tables.
+	quant [nQuantIndex][blockSize]byte
+}
+
+func (e *encoder) flush() {
+	if e.err != nil {
+		return
+	}
+	e.err = e.w.Flush()
+}
+
+func (e *encoder) write(p []byte) {
+	if e.err != nil {
+		return
+	}
+	_, e.err = e.w.Write(p)
+}
+
+func (e *encoder) writeByte(b byte) {
+	if e.err != nil {
+		return
+	}
+	e.err = e.w.WriteByte(b)
+}
+
+// emit emits the least significant nBits bits of bits to the bitstream.
+// The precondition is bits < 1<<nBits && nBits <= 16.
+func (e *encoder) emit(bits uint32, nBits uint8) {
+	nBits += e.nBits
+	bits <<= 32 - nBits
+	bits |= e.bits
+	for nBits >= 8 {
+		b := uint8(bits >> 24)
+		e.writeByte(b)
+		if b == 0xff {
+			e.writeByte(0x00)
+		}
+		bits <<= 8
+		nBits -= 8
+	}
+	e.bits, e.nBits = bits, nBits
+}
+
+// emitHuff emits the given value with the given Huffman encoder.
+func (e *encoder) emitHuff(h huffIndex, value int) {
+	x := theHuffmanLUT[h][value]
+	e.emit(x&(1<<24-1), uint8(x>>24))
+}
+
+// emitHuffRLE emits a run of runLength copies of value encoded with the given
+// Huffman encoder.
+func (e *encoder) emitHuffRLE(h huffIndex, runLength, value int) {
+	a, b := value, value
+	if a < 0 {
+		a, b = -value, value-1
+	}
+	var nBits uint8
+	if a < 0x100 {
+		nBits = bitCount[a]
+	} else {
+		nBits = 8 + bitCount[a>>8]
+	}
+	e.emitHuff(h, runLength<<4|int(nBits))
+	if nBits > 0 {
+		e.emit(uint32(b)&(1<<nBits-1), nBits)
+	}
+}
+
+// writeMarkerHeader writes the header for a marker with the given length.
+func (e *encoder) writeMarkerHeader(marker uint8, markerlen int) {
+	e.buf[0] = 0xff
+	e.buf[1] = marker
+	e.buf[2] = uint8(markerlen >> 8)
+	e.buf[3] = uint8(markerlen & 0xff)
+	e.write(e.buf[:4])
+}
+
+// writeDQT writes the Define Quantization Table marker.
+func (e *encoder) writeDQT() {
+	markerlen := 2
+	for _, q := range e.quant {
+		markerlen += 1 + len(q)
+	}
+	e.writeMarkerHeader(dqtMarker, markerlen)
+	for i, q := range e.quant {
+		e.writeByte(uint8(i))
+		e.write(q[:])
+	}
+}
+
+// writeSOF0 writes the Start Of Frame (Baseline) marker.
+func (e *encoder) writeSOF0(size image.Point) {
+	markerlen := 8 + 3*nComponent
+	e.writeMarkerHeader(sof0Marker, markerlen)
+	e.buf[0] = 8 // 8-bit color.
+	e.buf[1] = uint8(size.Y >> 8)
+	e.buf[2] = uint8(size.Y & 0xff)
+	e.buf[3] = uint8(size.X >> 8)
+	e.buf[4] = uint8(size.X & 0xff)
+	e.buf[5] = nComponent
+	for i := 0; i < nComponent; i++ {
+		e.buf[3*i+6] = uint8(i + 1)
+		// We use 4:2:0 chroma subsampling.
+		e.buf[3*i+7] = "\x22\x11\x11"[i]
+		e.buf[3*i+8] = "\x00\x01\x01"[i]
+	}
+	e.write(e.buf[:3*(nComponent-1)+9])
+}
+
+// writeDHT writes the Define Huffman Table marker.
+func (e *encoder) writeDHT() {
+	markerlen := 2
+	for _, s := range theHuffmanSpec {
+		markerlen += 1 + 16 + len(s.value)
+	}
+	e.writeMarkerHeader(dhtMarker, markerlen)
+	for i, s := range theHuffmanSpec {
+		e.writeByte("\x00\x10\x01\x11"[i])
+		e.write(s.count[:])
+		e.write(s.value)
+	}
+}
+
+// writeBlock writes a block of pixel data using the given quantization table,
+// returning the post-quantized DC value of the DCT-transformed block.
+func (e *encoder) writeBlock(b *block, q quantIndex, prevDC int) int {
+	fdct(b)
+	// Emit the DC delta.
+	dc := div(b[0], (8 * int(e.quant[q][0])))
+	e.emitHuffRLE(huffIndex(2*q+0), 0, dc-prevDC)
+	// Emit the AC components.
+	h, runLength := huffIndex(2*q+1), 0
+	for k := 1; k < blockSize; k++ {
+		ac := div(b[unzig[k]], (8 * int(e.quant[q][k])))
+		if ac == 0 {
+			runLength++
+		} else {
+			for runLength > 15 {
+				e.emitHuff(h, 0xf0)
+				runLength -= 16
+			}
+			e.emitHuffRLE(h, runLength, ac)
+			runLength = 0
+		}
+	}
+	if runLength > 0 {
+		e.emitHuff(h, 0x00)
+	}
+	return dc
+}
+
+// toYCbCr converts the 8x8 region of m whose top-left corner is p to its
+// YCbCr values.
+func toYCbCr(m image.Image, p image.Point, yBlock, cbBlock, crBlock *block) {
+	b := m.Bounds()
+	xmax := b.Max.X - 1
+	ymax := b.Max.Y - 1
+	for j := 0; j < 8; j++ {
+		for i := 0; i < 8; i++ {
+			r, g, b, _ := m.At(min(p.X+i, xmax), min(p.Y+j, ymax)).RGBA()
+			yy, cb, cr := ycbcr.RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))
+			yBlock[8*j+i] = int(yy)
+			cbBlock[8*j+i] = int(cb)
+			crBlock[8*j+i] = int(cr)
+		}
+	}
+}
+
+// rgbaToYCbCr is a specialized version of toYCbCr for image.RGBA images.
+func rgbaToYCbCr(m *image.RGBA, p image.Point, yBlock, cbBlock, crBlock *block) {
+	b := m.Bounds()
+	xmax := b.Max.X - 1
+	ymax := b.Max.Y - 1
+	for j := 0; j < 8; j++ {
+		sj := p.Y + j
+		if sj > ymax {
+			sj = ymax
+		}
+		yoff := sj * m.Stride
+		for i := 0; i < 8; i++ {
+			sx := p.X + i
+			if sx > xmax {
+				sx = xmax
+			}
+			col := &m.Pix[yoff+sx]
+			yy, cb, cr := ycbcr.RGBToYCbCr(col.R, col.G, col.B)
+			yBlock[8*j+i] = int(yy)
+			cbBlock[8*j+i] = int(cb)
+			crBlock[8*j+i] = int(cr)
+		}
+	}
+}
+
+// scale scales the 16x16 region represented by the 4 src blocks to the 8x8
+// dst block.
+func scale(dst *block, src *[4]block) {
+	for i := 0; i < 4; i++ {
+		dstOff := (i&2)<<4 | (i&1)<<2
+		for y := 0; y < 4; y++ {
+			for x := 0; x < 4; x++ {
+				j := 16*y + 2*x
+				sum := src[i][j] + src[i][j+1] + src[i][j+8] + src[i][j+9]
+				dst[8*y+x+dstOff] = (sum + 2) >> 2
+			}
+		}
+	}
+}
+
+// sosHeader is the SOS marker "\xff\xda" followed by 12 bytes:
+//	- the marker length "\x00\x0c",
+//	- the number of components "\x03",
+//	- component 1 uses DC table 0 and AC table 0 "\x01\x00",
+//	- component 2 uses DC table 1 and AC table 1 "\x02\x11",
+//	- component 3 uses DC table 1 and AC table 1 "\x03\x11",
+//	- padding "\x00\x00\x00".
+var sosHeader = []byte{
+	0xff, 0xda, 0x00, 0x0c, 0x03, 0x01, 0x00, 0x02,
+	0x11, 0x03, 0x11, 0x00, 0x00, 0x00,
+}
+
+// writeSOS writes the StartOfScan marker.
+func (e *encoder) writeSOS(m image.Image) {
+	e.write(sosHeader)
+	var (
+		// Scratch buffers to hold the YCbCr values.
+		yBlock  block
+		cbBlock [4]block
+		crBlock [4]block
+		cBlock  block
+		// DC components are delta-encoded.
+		prevDCY, prevDCCb, prevDCCr int
+	)
+	bounds := m.Bounds()
+	rgba, _ := m.(*image.RGBA)
+	for y := bounds.Min.Y; y < bounds.Max.Y; y += 16 {
+		for x := bounds.Min.X; x < bounds.Max.X; x += 16 {
+			for i := 0; i < 4; i++ {
+				xOff := (i & 1) * 8
+				yOff := (i & 2) * 4
+				p := image.Point{x + xOff, y + yOff}
+				if rgba != nil {
+					rgbaToYCbCr(rgba, p, &yBlock, &cbBlock[i], &crBlock[i])
+				} else {
+					toYCbCr(m, p, &yBlock, &cbBlock[i], &crBlock[i])
+				}
+				prevDCY = e.writeBlock(&yBlock, 0, prevDCY)
+			}
+			scale(&cBlock, &cbBlock)
+			prevDCCb = e.writeBlock(&cBlock, 1, prevDCCb)
+			scale(&cBlock, &crBlock)
+			prevDCCr = e.writeBlock(&cBlock, 1, prevDCCr)
+		}
+	}
+	// Pad the last byte with 1's.
+	e.emit(0x7f, 7)
+}
+
+// DefaultQuality is the default quality encoding parameter.
+const DefaultQuality = 75
+
+// Options are the encoding parameters.
+// Quality ranges from 1 to 100 inclusive, higher is better.
+type Options struct {
+	Quality int
+}
+
+// Encode writes the Image m to w in JPEG 4:2:0 baseline format with the given
+// options. Default parameters are used if a nil *Options is passed.
+func Encode(w io.Writer, m image.Image, o *Options) os.Error {
+	b := m.Bounds()
+	if b.Dx() >= 1<<16 || b.Dy() >= 1<<16 {
+		return os.NewError("jpeg: image is too large to encode")
+	}
+	var e encoder
+	if ww, ok := w.(writer); ok {
+		e.w = ww
+	} else {
+		e.w = bufio.NewWriter(w)
+	}
+	// Clip quality to [1, 100].
+	quality := DefaultQuality
+	if o != nil {
+		quality = o.Quality
+		if quality < 1 {
+			quality = 1
+		} else if quality > 100 {
+			quality = 100
+		}
+	}
+	// Convert from a quality rating to a scaling factor.
+	var scale int
+	if quality < 50 {
+		scale = 5000 / quality
+	} else {
+		scale = 200 - quality*2
+	}
+	// Initialize the quantization tables.
+	for i := range e.quant {
+		for j := range e.quant[i] {
+			x := int(unscaledQuant[i][j])
+			x = (x*scale + 50) / 100
+			if x < 1 {
+				x = 1
+			} else if x > 255 {
+				x = 255
+			}
+			e.quant[i][j] = uint8(x)
+		}
+	}
+	// Write the Start Of Image marker.
+	e.buf[0] = 0xff
+	e.buf[1] = 0xd8
+	e.write(e.buf[:2])
+	// Write the quantization tables.
+	e.writeDQT()
+	// Write the image dimensions.
+	e.writeSOF0(b.Size())
+	// Write the Huffman tables.
+	e.writeDHT()
+	// Write the image data.
+	e.writeSOS(m)
+	// Write the End Of Image marker.
+	e.buf[0] = 0xff
+	e.buf[1] = 0xd9
+	e.write(e.buf[:2])
+	e.flush()
+	return e.err
+}
diff --git a/libgo/go/image/jpeg/writer_test.go b/libgo/go/image/jpeg/writer_test.go
new file mode 100644
index 0000000..7aec70f
--- /dev/null
+++ b/libgo/go/image/jpeg/writer_test.go
@@ -0,0 +1,115 @@
+// 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 jpeg
+
+import (
+	"bytes"
+	"image"
+	"image/png"
+	"io/ioutil"
+	"rand"
+	"os"
+	"testing"
+)
+
+var testCase = []struct {
+	filename  string
+	quality   int
+	tolerance int64
+}{
+	{"../testdata/video-001.png", 1, 24 << 8},
+	{"../testdata/video-001.png", 20, 12 << 8},
+	{"../testdata/video-001.png", 60, 8 << 8},
+	{"../testdata/video-001.png", 80, 6 << 8},
+	{"../testdata/video-001.png", 90, 4 << 8},
+	{"../testdata/video-001.png", 100, 2 << 8},
+}
+
+func delta(u0, u1 uint32) int64 {
+	d := int64(u0) - int64(u1)
+	if d < 0 {
+		return -d
+	}
+	return d
+}
+
+func readPng(filename string) (image.Image, os.Error) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	return png.Decode(f)
+}
+
+func TestWriter(t *testing.T) {
+	for _, tc := range testCase {
+		// Read the image.
+		m0, err := readPng(tc.filename)
+		if err != nil {
+			t.Error(tc.filename, err)
+			continue
+		}
+		// Encode that image as JPEG.
+		buf := bytes.NewBuffer(nil)
+		err = Encode(buf, m0, &Options{Quality: tc.quality})
+		if err != nil {
+			t.Error(tc.filename, err)
+			continue
+		}
+		// Decode that JPEG.
+		m1, err := Decode(buf)
+		if err != nil {
+			t.Error(tc.filename, err)
+			continue
+		}
+		// Compute the average delta in RGB space.
+		b := m0.Bounds()
+		var sum, n int64
+		for y := b.Min.Y; y < b.Max.Y; y++ {
+			for x := b.Min.X; x < b.Max.X; x++ {
+				c0 := m0.At(x, y)
+				c1 := m1.At(x, y)
+				r0, g0, b0, _ := c0.RGBA()
+				r1, g1, b1, _ := c1.RGBA()
+				sum += delta(r0, r1)
+				sum += delta(g0, g1)
+				sum += delta(b0, b1)
+				n += 3
+			}
+		}
+		// Compare the average delta to the tolerance level.
+		if sum/n > tc.tolerance {
+			t.Errorf("%s, quality=%d: average delta is too high", tc.filename, tc.quality)
+			continue
+		}
+	}
+}
+
+func BenchmarkEncodeRGBOpaque(b *testing.B) {
+	b.StopTimer()
+	img := image.NewRGBA(640, 480)
+	// Set all pixels to 0xFF alpha to force opaque mode.
+	bo := img.Bounds()
+	rnd := rand.New(rand.NewSource(123))
+	for y := bo.Min.Y; y < bo.Max.Y; y++ {
+		for x := bo.Min.X; x < bo.Max.X; x++ {
+			img.Set(x, y, image.RGBAColor{
+				uint8(rnd.Intn(256)),
+				uint8(rnd.Intn(256)),
+				uint8(rnd.Intn(256)),
+				255})
+		}
+	}
+	if !img.Opaque() {
+		panic("expected image to be opaque")
+	}
+	b.SetBytes(640 * 480 * 4)
+	b.StartTimer()
+	options := &Options{Quality: 90}
+	for i := 0; i < b.N; i++ {
+		Encode(ioutil.Discard, img, options)
+	}
+}
diff --git a/libgo/go/image/png/reader.go b/libgo/go/image/png/reader.go
index eee4eac..8c76afa 100644
--- a/libgo/go/image/png/reader.go
+++ b/libgo/go/image/png/reader.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// The png package implements a PNG image decoder and encoder.
+// Package png implements a PNG image decoder and encoder.
 //
 // The PNG specification is at http://www.libpng.org/pub/png/spec/1.2/PNG-Contents.html
 package png
@@ -378,7 +378,7 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 			for x := 0; x < d.width; x += 8 {
 				b := cdat[x/8]
 				for x2 := 0; x2 < 8 && x+x2 < d.width; x2++ {
-					gray.Set(x+x2, y, image.GrayColor{(b >> 7) * 0xff})
+					gray.SetGray(x+x2, y, image.GrayColor{(b >> 7) * 0xff})
 					b <<= 1
 				}
 			}
@@ -386,7 +386,7 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 			for x := 0; x < d.width; x += 4 {
 				b := cdat[x/4]
 				for x2 := 0; x2 < 4 && x+x2 < d.width; x2++ {
-					gray.Set(x+x2, y, image.GrayColor{(b >> 6) * 0x55})
+					gray.SetGray(x+x2, y, image.GrayColor{(b >> 6) * 0x55})
 					b <<= 2
 				}
 			}
@@ -394,22 +394,22 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 			for x := 0; x < d.width; x += 2 {
 				b := cdat[x/2]
 				for x2 := 0; x2 < 2 && x+x2 < d.width; x2++ {
-					gray.Set(x+x2, y, image.GrayColor{(b >> 4) * 0x11})
+					gray.SetGray(x+x2, y, image.GrayColor{(b >> 4) * 0x11})
 					b <<= 4
 				}
 			}
 		case cbG8:
 			for x := 0; x < d.width; x++ {
-				gray.Set(x, y, image.GrayColor{cdat[x]})
+				gray.SetGray(x, y, image.GrayColor{cdat[x]})
 			}
 		case cbGA8:
 			for x := 0; x < d.width; x++ {
 				ycol := cdat[2*x+0]
-				nrgba.Set(x, y, image.NRGBAColor{ycol, ycol, ycol, cdat[2*x+1]})
+				nrgba.SetNRGBA(x, y, image.NRGBAColor{ycol, ycol, ycol, cdat[2*x+1]})
 			}
 		case cbTC8:
 			for x := 0; x < d.width; x++ {
-				rgba.Set(x, y, image.RGBAColor{cdat[3*x+0], cdat[3*x+1], cdat[3*x+2], 0xff})
+				rgba.SetRGBA(x, y, image.RGBAColor{cdat[3*x+0], cdat[3*x+1], cdat[3*x+2], 0xff})
 			}
 		case cbP1:
 			for x := 0; x < d.width; x += 8 {
@@ -456,25 +456,25 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 			}
 		case cbTCA8:
 			for x := 0; x < d.width; x++ {
-				nrgba.Set(x, y, image.NRGBAColor{cdat[4*x+0], cdat[4*x+1], cdat[4*x+2], cdat[4*x+3]})
+				nrgba.SetNRGBA(x, y, image.NRGBAColor{cdat[4*x+0], cdat[4*x+1], cdat[4*x+2], cdat[4*x+3]})
 			}
 		case cbG16:
 			for x := 0; x < d.width; x++ {
 				ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
-				gray16.Set(x, y, image.Gray16Color{ycol})
+				gray16.SetGray16(x, y, image.Gray16Color{ycol})
 			}
 		case cbGA16:
 			for x := 0; x < d.width; x++ {
 				ycol := uint16(cdat[4*x+0])<<8 | uint16(cdat[4*x+1])
 				acol := uint16(cdat[4*x+2])<<8 | uint16(cdat[4*x+3])
-				nrgba64.Set(x, y, image.NRGBA64Color{ycol, ycol, ycol, acol})
+				nrgba64.SetNRGBA64(x, y, image.NRGBA64Color{ycol, ycol, ycol, acol})
 			}
 		case cbTC16:
 			for x := 0; x < d.width; x++ {
 				rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
 				gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
 				bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
-				rgba64.Set(x, y, image.RGBA64Color{rcol, gcol, bcol, 0xffff})
+				rgba64.SetRGBA64(x, y, image.RGBA64Color{rcol, gcol, bcol, 0xffff})
 			}
 		case cbTCA16:
 			for x := 0; x < d.width; x++ {
@@ -482,7 +482,7 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 				gcol := uint16(cdat[8*x+2])<<8 | uint16(cdat[8*x+3])
 				bcol := uint16(cdat[8*x+4])<<8 | uint16(cdat[8*x+5])
 				acol := uint16(cdat[8*x+6])<<8 | uint16(cdat[8*x+7])
-				nrgba64.Set(x, y, image.NRGBA64Color{rcol, gcol, bcol, acol})
+				nrgba64.SetNRGBA64(x, y, image.NRGBA64Color{rcol, gcol, bcol, acol})
 			}
 		}
 
diff --git a/libgo/go/image/png/reader_test.go b/libgo/go/image/png/reader_test.go
index efa6336..bcc1a3d 100644
--- a/libgo/go/image/png/reader_test.go
+++ b/libgo/go/image/png/reader_test.go
@@ -28,6 +28,7 @@ var filenames = []string{
 	"basn3p02",
 	"basn3p04",
 	"basn3p08",
+	"basn3p08-trns",
 	"basn4a08",
 	"basn4a16",
 	"basn6a08",
@@ -98,17 +99,30 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
 	// (the PNG spec section 11.3 says "Ancillary chunks may be ignored by a decoder").
 	io.WriteString(w, "gAMA {1.0000}\n")
 
-	// Write the PLTE (if applicable).
+	// Write the PLTE and tRNS (if applicable).
 	if cpm != nil {
+		lastAlpha := -1
 		io.WriteString(w, "PLTE {\n")
-		for i := 0; i < len(cpm); i++ {
-			r, g, b, _ := cpm[i].RGBA()
+		for i, c := range cpm {
+			r, g, b, a := c.RGBA()
+			if a != 0xffff {
+				lastAlpha = i
+			}
 			r >>= 8
 			g >>= 8
 			b >>= 8
 			fmt.Fprintf(w, "    (%3d,%3d,%3d)     # rgb = (0x%02x,0x%02x,0x%02x)\n", r, g, b, r, g, b)
 		}
 		io.WriteString(w, "}\n")
+		if lastAlpha != -1 {
+			io.WriteString(w, "tRNS {\n")
+			for i := 0; i <= lastAlpha; i++ {
+				_, _, _, a := cpm[i].RGBA()
+				a >>= 8
+				fmt.Fprintf(w, " %d", a)
+			}
+			io.WriteString(w, "}\n")
+		}
 	}
 
 	// Write the IMAGE.
diff --git a/libgo/go/image/png/testdata/pngsuite/README b/libgo/go/image/png/testdata/pngsuite/README
index abe3ecb..c0f78bd 100644
--- a/libgo/go/image/png/testdata/pngsuite/README
+++ b/libgo/go/image/png/testdata/pngsuite/README
@@ -10,6 +10,9 @@ The files basn0g01-30.png, basn0g02-29.png and basn0g04-31.png are in fact
 not part of pngsuite but were created from files in pngsuite. Their non-power-
 of-two sizes makes them useful for testing bit-depths smaller than a byte.
 
+basn3a08.png was generated from basn6a08.png using the pngnq tool, which
+converted it to the 8-bit paletted image with alpha values in tRNS chunk.
+
 The *.sng files in this directory were generated from the *.png files
 by the sng command-line tool and some hand editing. The files
 basn0g0{1,2,4}.sng were actually generated by first converting the PNG
diff --git a/libgo/go/image/png/writer.go b/libgo/go/image/png/writer.go
index 081d06b..a27586f 100644
--- a/libgo/go/image/png/writer.go
+++ b/libgo/go/image/png/writer.go
@@ -130,12 +130,8 @@ func (e *encoder) writePLTE(p image.PalettedColorModel) {
 		e.err = FormatError("bad palette length: " + strconv.Itoa(len(p)))
 		return
 	}
-	for i := 0; i < len(p); i++ {
-		r, g, b, a := p[i].RGBA()
-		if a != 0xffff {
-			e.err = UnsupportedError("non-opaque palette color")
-			return
-		}
+	for i, c := range p {
+		r, g, b, _ := c.RGBA()
 		e.tmp[3*i+0] = uint8(r >> 8)
 		e.tmp[3*i+1] = uint8(g >> 8)
 		e.tmp[3*i+2] = uint8(b >> 8)
@@ -143,6 +139,21 @@ func (e *encoder) writePLTE(p image.PalettedColorModel) {
 	e.writeChunk(e.tmp[0:3*len(p)], "PLTE")
 }
 
+func (e *encoder) maybeWritetRNS(p image.PalettedColorModel) {
+	last := -1
+	for i, c := range p {
+		_, _, _, a := c.RGBA()
+		if a != 0xffff {
+			last = i
+		}
+		e.tmp[i] = uint8(a >> 8)
+	}
+	if last == -1 {
+		return
+	}
+	e.writeChunk(e.tmp[:last+1], "tRNS")
+}
+
 // An encoder is an io.Writer that satisfies writes by writing PNG IDAT chunks,
 // including an 8-byte header and 4-byte CRC checksum per Write call. Such calls
 // should be relatively infrequent, since writeIDATs uses a bufio.Writer.
@@ -263,7 +274,12 @@ func writeImage(w io.Writer, m image.Image, cb int) os.Error {
 	defer zw.Close()
 
 	bpp := 0 // Bytes per pixel.
+
+	// Used by fast paths for common image types
 	var paletted *image.Paletted
+	var rgba *image.RGBA
+	rgba, _ = m.(*image.RGBA)
+
 	switch cb {
 	case cbG8:
 		bpp = 1
@@ -303,12 +319,24 @@ func writeImage(w io.Writer, m image.Image, cb int) os.Error {
 				cr[0][x+1] = c.Y
 			}
 		case cbTC8:
-			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][3*x+1] = uint8(r >> 8)
-				cr[0][3*x+2] = uint8(g >> 8)
-				cr[0][3*x+3] = uint8(b >> 8)
+			// 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
+				}
+			} 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)
+				}
 			}
 		case cbP8:
 			rowOffset := y * paletted.Stride
@@ -430,6 +458,7 @@ func Encode(w io.Writer, m image.Image) os.Error {
 	e.writeIHDR()
 	if pal != nil {
 		e.writePLTE(pal.Palette)
+		e.maybeWritetRNS(pal.Palette)
 	}
 	e.writeIDATs()
 	e.writeIEND()
diff --git a/libgo/go/image/png/writer_test.go b/libgo/go/image/png/writer_test.go
index 4d9929f..6b054aa 100644
--- a/libgo/go/image/png/writer_test.go
+++ b/libgo/go/image/png/writer_test.go
@@ -5,10 +5,10 @@
 package png
 
 import (
-	"bytes"
 	"fmt"
 	"image"
 	"io"
+	"io/ioutil"
 	"os"
 	"testing"
 )
@@ -81,10 +81,42 @@ func BenchmarkEncodePaletted(b *testing.B) {
 			image.RGBAColor{0, 0, 0, 255},
 			image.RGBAColor{255, 255, 255, 255},
 		})
+	b.SetBytes(640 * 480 * 1)
 	b.StartTimer()
-	buffer := new(bytes.Buffer)
 	for i := 0; i < b.N; i++ {
-		buffer.Reset()
-		Encode(buffer, img)
+		Encode(ioutil.Discard, img)
+	}
+}
+
+func BenchmarkEncodeRGBOpaque(b *testing.B) {
+	b.StopTimer()
+	img := image.NewRGBA(640, 480)
+	// Set all pixels to 0xFF alpha to force opaque mode.
+	bo := img.Bounds()
+	for y := bo.Min.Y; y < bo.Max.Y; y++ {
+		for x := bo.Min.X; x < bo.Max.X; x++ {
+			img.Set(x, y, image.RGBAColor{0, 0, 0, 255})
+		}
+	}
+	if !img.Opaque() {
+		panic("expected image to be opaque")
+	}
+	b.SetBytes(640 * 480 * 4)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		Encode(ioutil.Discard, img)
+	}
+}
+
+func BenchmarkEncodeRGBA(b *testing.B) {
+	b.StopTimer()
+	img := image.NewRGBA(640, 480)
+	if img.Opaque() {
+		panic("expected image to not be opaque")
+	}
+	b.SetBytes(640 * 480 * 4)
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		Encode(ioutil.Discard, img)
 	}
 }
diff --git a/libgo/go/image/testdata/video-001.bmp b/libgo/go/image/testdata/video-001.bmp
new file mode 100644
index 0000000..ca3dd42
--- /dev/null
+++ b/libgo/go/image/testdata/video-001.bmp
diff --git a/libgo/go/image/testdata/video-001.gif b/libgo/go/image/testdata/video-001.gif
new file mode 100644
index 0000000..ca06af6
--- /dev/null
+++ b/libgo/go/image/testdata/video-001.gif
diff --git a/libgo/go/image/testdata/video-001.jpeg b/libgo/go/image/testdata/video-001.jpeg
new file mode 100644
index 0000000..1b87c93
--- /dev/null
+++ b/libgo/go/image/testdata/video-001.jpeg
diff --git a/libgo/go/image/testdata/video-001.png b/libgo/go/image/testdata/video-001.png
new file mode 100644
index 0000000..d3468bb
--- /dev/null
+++ b/libgo/go/image/testdata/video-001.png
diff --git a/libgo/go/image/testdata/video-001.tiff b/libgo/go/image/testdata/video-001.tiff
new file mode 100644
index 0000000..0dd6cd9
--- /dev/null
+++ b/libgo/go/image/testdata/video-001.tiff
diff --git a/libgo/go/image/tiff/buffer.go b/libgo/go/image/tiff/buffer.go
new file mode 100644
index 0000000..7c07142
--- /dev/null
+++ b/libgo/go/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),
+	}
+}
diff --git a/libgo/go/image/tiff/buffer_test.go b/libgo/go/image/tiff/buffer_test.go
new file mode 100644
index 0000000..4f3e68e
--- /dev/null
+++ b/libgo/go/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)
+		}
+	}
+}
diff --git a/libgo/go/image/tiff/consts.go b/libgo/go/image/tiff/consts.go
new file mode 100644
index 0000000..761ac9d
--- /dev/null
+++ b/libgo/go/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
+)
diff --git a/libgo/go/image/tiff/reader.go b/libgo/go/image/tiff/reader.go
new file mode 100644
index 0000000..40f659c
--- /dev/null
+++ b/libgo/go/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)
+}
diff --git a/libgo/go/image/ycbcr/ycbcr.go b/libgo/go/image/ycbcr/ycbcr.go
new file mode 100644
index 0000000..cda4599
--- /dev/null
+++ b/libgo/go/image/ycbcr/ycbcr.go
@@ -0,0 +1,174 @@
+// 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 ycbcr provides images from the Y'CbCr color model.
+//
+// JPEG, VP8, the MPEG family and other codecs use this color model. Such
+// codecs often use the terms YUV and Y'CbCr interchangeably, but strictly
+// speaking, the term YUV applies only to analog video signals.
+//
+// Conversion between RGB and Y'CbCr is lossy and there are multiple, slightly
+// different formulae for converting between the two. This package follows
+// the JFIF specification at http://www.w3.org/Graphics/JPEG/jfif3.pdf.
+package ycbcr
+
+import (
+	"image"
+)
+
+// RGBToYCbCr converts an RGB triple to a YCbCr triple. All components lie
+// within the range [0, 255].
+func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8) {
+	// The JFIF specification says:
+	//	Y' =  0.2990*R + 0.5870*G + 0.1140*B
+	//	Cb = -0.1687*R - 0.3313*G + 0.5000*B + 128
+	//	Cr =  0.5000*R - 0.4187*G - 0.0813*B + 128
+	// http://www.w3.org/Graphics/JPEG/jfif3.pdf says Y but means Y'.
+	r1 := int(r)
+	g1 := int(g)
+	b1 := int(b)
+	yy := (19595*r1 + 38470*g1 + 7471*b1 + 1<<15) >> 16
+	cb := (-11056*r1 - 21712*g1 + 32768*b1 + 257<<15) >> 16
+	cr := (32768*r1 - 27440*g1 - 5328*b1 + 257<<15) >> 16
+	if yy < 0 {
+		yy = 0
+	} else if yy > 255 {
+		yy = 255
+	}
+	if cb < 0 {
+		cb = 0
+	} else if cb > 255 {
+		cb = 255
+	}
+	if cr < 0 {
+		cr = 0
+	} else if cr > 255 {
+		cr = 255
+	}
+	return uint8(yy), uint8(cb), uint8(cr)
+}
+
+// YCbCrToRGB converts a YCbCr triple to an RGB triple. All components lie
+// within the range [0, 255].
+func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8) {
+	// The JFIF specification says:
+	//	R = Y' + 1.40200*(Cr-128)
+	//	G = Y' - 0.34414*(Cb-128) - 0.71414*(Cr-128)
+	//	B = Y' + 1.77200*(Cb-128)
+	// http://www.w3.org/Graphics/JPEG/jfif3.pdf says Y but means Y'.
+	yy1 := int(y)<<16 + 1<<15
+	cb1 := int(cb) - 128
+	cr1 := int(cr) - 128
+	r := (yy1 + 91881*cr1) >> 16
+	g := (yy1 - 22554*cb1 - 46802*cr1) >> 16
+	b := (yy1 + 116130*cb1) >> 16
+	if r < 0 {
+		r = 0
+	} else if r > 255 {
+		r = 255
+	}
+	if g < 0 {
+		g = 0
+	} else if g > 255 {
+		g = 255
+	}
+	if b < 0 {
+		b = 0
+	} else if b > 255 {
+		b = 255
+	}
+	return uint8(r), uint8(g), uint8(b)
+}
+
+// YCbCrColor represents a fully opaque 24-bit Y'CbCr color, having 8 bits for
+// each of one luma and two chroma components.
+type YCbCrColor struct {
+	Y, Cb, Cr uint8
+}
+
+func (c YCbCrColor) RGBA() (uint32, uint32, uint32, uint32) {
+	r, g, b := YCbCrToRGB(c.Y, c.Cb, c.Cr)
+	return uint32(r) * 0x101, uint32(g) * 0x101, uint32(b) * 0x101, 0xffff
+}
+
+func toYCbCrColor(c image.Color) image.Color {
+	if _, ok := c.(YCbCrColor); ok {
+		return c
+	}
+	r, g, b, _ := c.RGBA()
+	y, u, v := RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))
+	return YCbCrColor{y, u, v}
+}
+
+// YCbCrColorModel is the color model for YCbCrColor.
+var YCbCrColorModel image.ColorModel = image.ColorModelFunc(toYCbCrColor)
+
+// SubsampleRatio is the chroma subsample ratio used in a YCbCr image.
+type SubsampleRatio int
+
+const (
+	SubsampleRatio444 SubsampleRatio = iota
+	SubsampleRatio422
+	SubsampleRatio420
+)
+
+// YCbCr is an in-memory image of YCbCr colors. There is one Y sample per pixel,
+// but each Cb and Cr sample can span one or more pixels.
+// YStride is the Y slice index delta between vertically adjacent pixels.
+// CStride is the Cb and Cr slice index delta between vertically adjacent pixels
+// that map to separate chroma samples.
+// It is not an absolute requirement, but YStride and len(Y) are typically
+// multiples of 8, and:
+//	For 4:4:4, CStride == YStride/1 && len(Cb) == len(Cr) == len(Y)/1.
+//	For 4:2:2, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/2.
+//	For 4:2:0, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/4.
+type YCbCr struct {
+	Y              []uint8
+	Cb             []uint8
+	Cr             []uint8
+	YStride        int
+	CStride        int
+	SubsampleRatio SubsampleRatio
+	Rect           image.Rectangle
+}
+
+func (p *YCbCr) ColorModel() image.ColorModel {
+	return YCbCrColorModel
+}
+
+func (p *YCbCr) Bounds() image.Rectangle {
+	return p.Rect
+}
+
+func (p *YCbCr) At(x, y int) image.Color {
+	if !p.Rect.Contains(image.Point{x, y}) {
+		return YCbCrColor{}
+	}
+	switch p.SubsampleRatio {
+	case SubsampleRatio422:
+		i := x / 2
+		return YCbCrColor{
+			p.Y[y*p.YStride+x],
+			p.Cb[y*p.CStride+i],
+			p.Cr[y*p.CStride+i],
+		}
+	case SubsampleRatio420:
+		i, j := x/2, y/2
+		return YCbCrColor{
+			p.Y[y*p.YStride+x],
+			p.Cb[j*p.CStride+i],
+			p.Cr[j*p.CStride+i],
+		}
+	}
+	// Default to 4:4:4 subsampling.
+	return YCbCrColor{
+		p.Y[y*p.YStride+x],
+		p.Cb[y*p.CStride+x],
+		p.Cr[y*p.CStride+x],
+	}
+}
+
+func (p *YCbCr) Opaque() bool {
+	return true
+}
diff --git a/libgo/go/image/ycbcr/ycbcr_test.go b/libgo/go/image/ycbcr/ycbcr_test.go
new file mode 100644
index 0000000..2e60a6f
--- /dev/null
+++ b/libgo/go/image/ycbcr/ycbcr_test.go
@@ -0,0 +1,33 @@
+// 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 ycbcr
+
+import (
+	"testing"
+)
+
+func delta(x, y uint8) uint8 {
+	if x >= y {
+		return x - y
+	}
+	return y - x
+}
+
+// Test that a subset of RGB space can be converted to YCbCr and back to within
+// 1/256 tolerance.
+func TestRoundtrip(t *testing.T) {
+	for r := 0; r < 255; r += 7 {
+		for g := 0; g < 255; g += 5 {
+			for b := 0; b < 255; b += 3 {
+				r0, g0, b0 := uint8(r), uint8(g), uint8(b)
+				y, cb, cr := RGBToYCbCr(r0, g0, b0)
+				r1, g1, b1 := YCbCrToRGB(y, cb, cr)
+				if delta(r0, r1) > 1 || delta(g0, g1) > 1 || delta(b0, b1) > 1 {
+					t.Fatalf("r0, g0, b0 = %d, %d, %d   r1, g1, b1 = %d, %d, %d", r0, g0, b0, r1, g1, b1)
+				}
+			}
+		}
+	}
+}