Imported Upstream version 2011.01.12upstream/2011.01.12

13 files changed, 1118 insertions, 353 deletions

diff --git a/src/pkg/image/Makefile b/src/pkg/image/Makefile
index 9c886f9f9..739ad804b 100644
--- a/src/pkg/image/Makefile
+++ b/src/pkg/image/Makefile
@@ -2,11 +2,13 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
-include ../../Make.$(GOARCH)
+include ../../Make.inc
 
 TARG=image
 GOFILES=\
 	color.go\
+	format.go\
+	geom.go\
 	image.go\
 	names.go\
 
diff --git a/src/pkg/image/color.go b/src/pkg/image/color.go
index 8a865a8a0..c1345c025 100644
--- a/src/pkg/image/color.go
+++ b/src/pkg/image/color.go
@@ -103,6 +103,27 @@ func (c Alpha16Color) RGBA() (r, g, b, a uint32) {
 	return a, a, a, a
 }
 
+// A GrayColor represents an 8-bit grayscale color.
+type GrayColor struct {
+	Y uint8
+}
+
+func (c GrayColor) RGBA() (r, g, b, a uint32) {
+	y := uint32(c.Y)
+	y |= y << 8
+	return y, y, y, 0xffff
+}
+
+// A Gray16Color represents a 16-bit grayscale color.
+type Gray16Color struct {
+	Y uint16
+}
+
+func (c Gray16Color) RGBA() (r, g, b, a uint32) {
+	y := uint32(c.Y)
+	return y, y, y, 0xffff
+}
+
 // A ColorModel can convert foreign Colors, with a possible loss of precision,
 // to a Color from its own color model.
 type ColorModel interface {
@@ -187,6 +208,24 @@ func toAlpha16Color(c Color) Color {
 	return Alpha16Color{uint16(a)}
 }
 
+func toGrayColor(c Color) Color {
+	if _, ok := c.(GrayColor); ok {
+		return c
+	}
+	r, g, b, _ := c.RGBA()
+	y := (299*r + 587*g + 114*b + 500) / 1000
+	return GrayColor{uint8(y >> 8)}
+}
+
+func toGray16Color(c Color) Color {
+	if _, ok := c.(Gray16Color); ok {
+		return c
+	}
+	r, g, b, _ := c.RGBA()
+	y := (299*r + 587*g + 114*b + 500) / 1000
+	return Gray16Color{uint16(y)}
+}
+
 // The ColorModel associated with RGBAColor.
 var RGBAColorModel ColorModel = ColorModelFunc(toRGBAColor)
 
@@ -204,3 +243,9 @@ var AlphaColorModel ColorModel = ColorModelFunc(toAlphaColor)
 
 // The ColorModel associated with Alpha16Color.
 var Alpha16ColorModel ColorModel = ColorModelFunc(toAlpha16Color)
+
+// The ColorModel associated with GrayColor.
+var GrayColorModel ColorModel = ColorModelFunc(toGrayColor)
+
+// The ColorModel associated with Gray16Color.
+var Gray16ColorModel ColorModel = ColorModelFunc(toGray16Color)
diff --git a/src/pkg/image/format.go b/src/pkg/image/format.go
new file mode 100644
index 000000000..1d541b094
--- /dev/null
+++ b/src/pkg/image/format.go
@@ -0,0 +1,86 @@
+// Copyright 2010 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 image
+
+import (
+	"bufio"
+	"io"
+	"os"
+)
+
+// An UnknownFormatErr indicates that decoding encountered an unknown format.
+var UnknownFormatErr = os.NewError("image: unknown format")
+
+// A format holds an image format's name, magic header and how to decode it.
+type format struct {
+	name, magic  string
+	decode       func(io.Reader) (Image, os.Error)
+	decodeConfig func(io.Reader) (Config, os.Error)
+}
+
+// Formats is the list of registered formats.
+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.
+// 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)) {
+	formats = append(formats, format{name, magic, decode, decodeConfig})
+}
+
+// A reader is an io.Reader that can also peek ahead.
+type reader interface {
+	io.Reader
+	Peek(int) ([]byte, os.Error)
+}
+
+// AsReader converts an io.Reader to a reader.
+func asReader(r io.Reader) reader {
+	if rr, ok := r.(reader); ok {
+		return rr
+	}
+	return bufio.NewReader(r)
+}
+
+// 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 {
+			return f
+		}
+	}
+	return format{}
+}
+
+// Decode decodes an image that has been encoded in a registered format.
+// The string returned is the format name used during format registration.
+// Format registration is typically done by the init method of the codec-
+// specific package.
+func Decode(r io.Reader) (Image, string, os.Error) {
+	rr := asReader(r)
+	f := sniff(rr)
+	if f.decode == nil {
+		return nil, "", UnknownFormatErr
+	}
+	m, err := f.decode(rr)
+	return m, f.name, err
+}
+
+// DecodeConfig decodes the color model and dimensions of an image that has
+// been encoded in a registered format. The string returned is the format name
+// used during format registration. Format registration is typically done by
+// the init method of the codec-specific package.
+func DecodeConfig(r io.Reader) (Config, string, os.Error) {
+	rr := asReader(r)
+	f := sniff(rr)
+	if f.decodeConfig == nil {
+		return Config{}, "", UnknownFormatErr
+	}
+	c, err := f.decodeConfig(rr)
+	return c, f.name, err
+}
diff --git a/src/pkg/image/geom.go b/src/pkg/image/geom.go
new file mode 100644
index 000000000..ccfe9cdb0
--- /dev/null
+++ b/src/pkg/image/geom.go
@@ -0,0 +1,223 @@
+// Copyright 2010 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 image
+
+import (
+	"strconv"
+)
+
+// A Point is an X, Y coordinate pair. The axes increase right and down.
+type Point struct {
+	X, Y int
+}
+
+// String returns a string representation of p like "(3,4)".
+func (p Point) String() string {
+	return "(" + strconv.Itoa(p.X) + "," + strconv.Itoa(p.Y) + ")"
+}
+
+// Add returns the vector p+q.
+func (p Point) Add(q Point) Point {
+	return Point{p.X + q.X, p.Y + q.Y}
+}
+
+// Sub returns the vector p-q.
+func (p Point) Sub(q Point) Point {
+	return Point{p.X - q.X, p.Y - q.Y}
+}
+
+// Mul returns the vector p*k.
+func (p Point) Mul(k int) Point {
+	return Point{p.X * k, p.Y * k}
+}
+
+// Div returns the vector p/k.
+func (p Point) Div(k int) Point {
+	return Point{p.X / k, p.Y / k}
+}
+
+// Mod returns the point q in r such that p.X-q.X is a multiple of r's width
+// and p.Y-q.Y is a multiple of r's height.
+func (p Point) Mod(r Rectangle) Point {
+	w, h := r.Dx(), r.Dy()
+	p = p.Sub(r.Min)
+	p.X = p.X % w
+	if p.X < 0 {
+		p.X += w
+	}
+	p.Y = p.Y % h
+	if p.Y < 0 {
+		p.Y += h
+	}
+	return p.Add(r.Min)
+}
+
+// Eq returns whether p and q are equal.
+func (p Point) Eq(q Point) bool {
+	return p.X == q.X && p.Y == q.Y
+}
+
+// ZP is the zero Point.
+var ZP Point
+
+// Pt is shorthand for Point{X, Y}.
+func Pt(X, Y int) Point {
+	return Point{X, Y}
+}
+
+// A Rectangle contains the points with Min.X <= X < Max.X, Min.Y <= Y < Max.Y.
+// It is well-formed if Min.X <= Max.X and likewise for Y. Points are always
+// well-formed. A rectangle's methods always return well-formed outputs for
+// well-formed inputs.
+type Rectangle struct {
+	Min, Max Point
+}
+
+// String returns a string representation of r like "(3,4)-(6,5)".
+func (r Rectangle) String() string {
+	return r.Min.String() + "-" + r.Max.String()
+}
+
+// Dx returns r's width.
+func (r Rectangle) Dx() int {
+	return r.Max.X - r.Min.X
+}
+
+// Dy returns r's height.
+func (r Rectangle) Dy() int {
+	return r.Max.Y - r.Min.Y
+}
+
+// Size returns r's width and height.
+func (r Rectangle) Size() Point {
+	return Point{
+		r.Max.X - r.Min.X,
+		r.Max.Y - r.Min.Y,
+	}
+}
+
+// Add returns the rectangle r translated by p.
+func (r Rectangle) Add(p Point) Rectangle {
+	return Rectangle{
+		Point{r.Min.X + p.X, r.Min.Y + p.Y},
+		Point{r.Max.X + p.X, r.Max.Y + p.Y},
+	}
+}
+
+// Add returns the rectangle r translated by -p.
+func (r Rectangle) Sub(p Point) Rectangle {
+	return Rectangle{
+		Point{r.Min.X - p.X, r.Min.Y - p.Y},
+		Point{r.Max.X - p.X, r.Max.Y - p.Y},
+	}
+}
+
+// Inset returns the rectangle r inset by n, which may be negative. If either
+// of r's dimensions is less than 2*n then an empty rectangle near the center
+// of r will be returned.
+func (r Rectangle) Inset(n int) Rectangle {
+	if r.Dx() < 2*n {
+		r.Min.X = (r.Min.X + r.Max.X) / 2
+		r.Max.X = r.Min.X
+	} else {
+		r.Min.X += n
+		r.Max.X -= n
+	}
+	if r.Dy() < 2*n {
+		r.Min.Y = (r.Min.Y + r.Max.Y) / 2
+		r.Max.Y = r.Min.Y
+	} else {
+		r.Min.Y += n
+		r.Max.Y -= n
+	}
+	return r
+}
+
+// Intersect returns the largest rectangle contained by both r and s. If the
+// two rectangles do not overlap then the zero rectangle will be returned.
+func (r Rectangle) Intersect(s Rectangle) Rectangle {
+	if r.Min.X < s.Min.X {
+		r.Min.X = s.Min.X
+	}
+	if r.Min.Y < s.Min.Y {
+		r.Min.Y = s.Min.Y
+	}
+	if r.Max.X > s.Max.X {
+		r.Max.X = s.Max.X
+	}
+	if r.Max.Y > s.Max.Y {
+		r.Max.Y = s.Max.Y
+	}
+	if r.Min.X > r.Max.X || r.Min.Y > r.Max.Y {
+		return ZR
+	}
+	return r
+}
+
+// Union returns the smallest rectangle that contains both r and s.
+func (r Rectangle) Union(s Rectangle) Rectangle {
+	if r.Min.X > s.Min.X {
+		r.Min.X = s.Min.X
+	}
+	if r.Min.Y > s.Min.Y {
+		r.Min.Y = s.Min.Y
+	}
+	if r.Max.X < s.Max.X {
+		r.Max.X = s.Max.X
+	}
+	if r.Max.Y < s.Max.Y {
+		r.Max.Y = s.Max.Y
+	}
+	return r
+}
+
+// Empty returns whether the rectangle contains no points.
+func (r Rectangle) Empty() bool {
+	return r.Min.X >= r.Max.X || r.Min.Y >= r.Max.Y
+}
+
+// Eq returns whether r and s are equal.
+func (r Rectangle) Eq(s Rectangle) bool {
+	return r.Min.X == s.Min.X && r.Min.Y == s.Min.Y &&
+		r.Max.X == s.Max.X && r.Max.Y == s.Max.Y
+}
+
+// Overlaps returns whether r and s have a non-empty intersection.
+func (r Rectangle) Overlaps(s Rectangle) bool {
+	return r.Min.X < s.Max.X && s.Min.X < r.Max.X &&
+		r.Min.Y < s.Max.Y && s.Min.Y < r.Max.Y
+}
+
+// Contains returns whether r contains p.
+func (r Rectangle) Contains(p Point) bool {
+	return p.X >= r.Min.X && p.X < r.Max.X &&
+		p.Y >= r.Min.Y && p.Y < r.Max.Y
+}
+
+// Canon returns the canonical version of r. The returned rectangle has minimum
+// and maximum coordinates swapped if necessary so that it is well-formed.
+func (r Rectangle) Canon() Rectangle {
+	if r.Max.X < r.Min.X {
+		r.Min.X, r.Max.X = r.Max.X, r.Min.X
+	}
+	if r.Max.Y < r.Min.Y {
+		r.Min.Y, r.Max.Y = r.Max.Y, r.Min.Y
+	}
+	return r
+}
+
+// ZR is the zero Rectangle.
+var ZR Rectangle
+
+// Rect is shorthand for Rectangle{Pt(x0, y0), Pt(x1, y1)}.
+func Rect(x0, y0, x1, y1 int) Rectangle {
+	if x0 > x1 {
+		x0, x1 = x1, x0
+	}
+	if y0 > y1 {
+		y0, y1 = y1, y0
+	}
+	return Rectangle{Point{x0, y0}, Point{x1, y1}}
+}
diff --git a/src/pkg/image/image.go b/src/pkg/image/image.go
index decf1ce43..c0e96e1f7 100644
--- a/src/pkg/image/image.go
+++ b/src/pkg/image/image.go
@@ -5,50 +5,67 @@
 // The image package implements a basic 2-D image library.
 package image
 
-// An Image is a rectangular grid of Colors drawn from a ColorModel.
+// A Config consists of an image's color model and dimensions.
+type Config struct {
+	ColorModel    ColorModel
+	Width, Height int
+}
+
+// An Image is a finite rectangular grid of Colors drawn from a ColorModel.
 type Image interface {
+	// ColorModel returns the Image's ColorModel.
 	ColorModel() ColorModel
-	Width() int
-	Height() int
-	// At(0, 0) returns the upper-left pixel of the grid.
-	// At(Width()-1, Height()-1) returns the lower-right pixel.
+	// Bounds returns the domain for which At can return non-zero color.
+	// The bounds do not necessarily contain the point (0, 0).
+	Bounds() Rectangle
+	// At returns the color of the pixel at (x, y).
+	// At(Bounds().Min.X, Bounds().Min.Y) returns the upper-left pixel of the grid.
+	// At(Bounds().Max.X-1, Bounds().Max.Y-1) returns the lower-right one.
 	At(x, y int) Color
 }
 
-// An RGBA is an in-memory image backed by a 2-D slice of RGBAColor values.
+// An RGBA is an in-memory image of RGBAColor values.
 type RGBA struct {
-	// The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
-	Pixel [][]RGBAColor
+	// Pix holds the image's pixels. The pixel at (x, y) is Pix[y*Stride+x].
+	Pix    []RGBAColor
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
 }
 
 func (p *RGBA) ColorModel() ColorModel { return RGBAColorModel }
 
-func (p *RGBA) Width() int {
-	if len(p.Pixel) == 0 {
-		return 0
+func (p *RGBA) Bounds() Rectangle { return p.Rect }
+
+func (p *RGBA) At(x, y int) Color {
+	if !p.Rect.Contains(Point{x, y}) {
+		return RGBAColor{}
 	}
-	return len(p.Pixel[0])
+	return p.Pix[y*p.Stride+x]
 }
 
-func (p *RGBA) Height() int { return len(p.Pixel) }
-
-func (p *RGBA) At(x, y int) Color { return p.Pixel[y][x] }
-
-func (p *RGBA) Set(x, y int, c Color) { p.Pixel[y][x] = toRGBAColor(c).(RGBAColor) }
+func (p *RGBA) Set(x, y int, c Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = toRGBAColor(c).(RGBAColor)
+}
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *RGBA) Opaque() bool {
-	h := len(p.Pixel)
-	if h > 0 {
-		w := len(p.Pixel[0])
-		for y := 0; y < h; y++ {
-			pix := p.Pixel[y]
-			for x := 0; x < w; x++ {
-				if pix[x].A != 0xff {
-					return false
-				}
+	if p.Rect.Empty() {
+		return true
+	}
+	base := p.Rect.Min.Y * p.Stride
+	i0, i1 := base+p.Rect.Min.X, base+p.Rect.Max.X
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for _, c := range p.Pix[i0:i1] {
+			if c.A != 0xff {
+				return false
 			}
 		}
+		i0 += p.Stride
+		i1 += p.Stride
 	}
 	return true
 }
@@ -56,251 +73,343 @@ func (p *RGBA) Opaque() bool {
 // NewRGBA returns a new RGBA with the given width and height.
 func NewRGBA(w, h int) *RGBA {
 	buf := make([]RGBAColor, w*h)
-	pix := make([][]RGBAColor, h)
-	for y := range pix {
-		pix[y] = buf[w*y : w*(y+1)]
-	}
-	return &RGBA{pix}
+	return &RGBA{buf, w, Rectangle{ZP, Point{w, h}}}
 }
 
-// An RGBA64 is an in-memory image backed by a 2-D slice of RGBA64Color values.
+// An RGBA64 is an in-memory image of RGBA64Color values.
 type RGBA64 struct {
-	// The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
-	Pixel [][]RGBA64Color
+	// Pix holds the image's pixels. The pixel at (x, y) is Pix[y*Stride+x].
+	Pix    []RGBA64Color
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
 }
 
 func (p *RGBA64) ColorModel() ColorModel { return RGBA64ColorModel }
 
-func (p *RGBA64) Width() int {
-	if len(p.Pixel) == 0 {
-		return 0
+func (p *RGBA64) Bounds() Rectangle { return p.Rect }
+
+func (p *RGBA64) At(x, y int) Color {
+	if !p.Rect.Contains(Point{x, y}) {
+		return RGBA64Color{}
 	}
-	return len(p.Pixel[0])
+	return p.Pix[y*p.Stride+x]
 }
 
-func (p *RGBA64) Height() int { return len(p.Pixel) }
-
-func (p *RGBA64) At(x, y int) Color { return p.Pixel[y][x] }
-
-func (p *RGBA64) Set(x, y int, c Color) { p.Pixel[y][x] = toRGBA64Color(c).(RGBA64Color) }
+func (p *RGBA64) Set(x, y int, c Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = toRGBA64Color(c).(RGBA64Color)
+}
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *RGBA64) Opaque() bool {
-	h := len(p.Pixel)
-	if h > 0 {
-		w := len(p.Pixel[0])
-		for y := 0; y < h; y++ {
-			pix := p.Pixel[y]
-			for x := 0; x < w; x++ {
-				if pix[x].A != 0xffff {
-					return false
-				}
+	if p.Rect.Empty() {
+		return true
+	}
+	base := p.Rect.Min.Y * p.Stride
+	i0, i1 := base+p.Rect.Min.X, base+p.Rect.Max.X
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for _, c := range p.Pix[i0:i1] {
+			if c.A != 0xffff {
+				return false
 			}
 		}
+		i0 += p.Stride
+		i1 += p.Stride
 	}
 	return true
 }
 
 // NewRGBA64 returns a new RGBA64 with the given width and height.
 func NewRGBA64(w, h int) *RGBA64 {
-	buf := make([]RGBA64Color, w*h)
-	pix := make([][]RGBA64Color, h)
-	for y := range pix {
-		pix[y] = buf[w*y : w*(y+1)]
-	}
-	return &RGBA64{pix}
+	pix := make([]RGBA64Color, w*h)
+	return &RGBA64{pix, w, Rectangle{ZP, Point{w, h}}}
 }
 
-// A NRGBA is an in-memory image backed by a 2-D slice of NRGBAColor values.
+// An NRGBA is an in-memory image of NRGBAColor values.
 type NRGBA struct {
-	// The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
-	Pixel [][]NRGBAColor
+	// Pix holds the image's pixels. The pixel at (x, y) is Pix[y*Stride+x].
+	Pix    []NRGBAColor
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
 }
 
 func (p *NRGBA) ColorModel() ColorModel { return NRGBAColorModel }
 
-func (p *NRGBA) Width() int {
-	if len(p.Pixel) == 0 {
-		return 0
+func (p *NRGBA) Bounds() Rectangle { return p.Rect }
+
+func (p *NRGBA) At(x, y int) Color {
+	if !p.Rect.Contains(Point{x, y}) {
+		return NRGBAColor{}
 	}
-	return len(p.Pixel[0])
+	return p.Pix[y*p.Stride+x]
 }
 
-func (p *NRGBA) Height() int { return len(p.Pixel) }
-
-func (p *NRGBA) At(x, y int) Color { return p.Pixel[y][x] }
-
-func (p *NRGBA) Set(x, y int, c Color) { p.Pixel[y][x] = toNRGBAColor(c).(NRGBAColor) }
+func (p *NRGBA) Set(x, y int, c Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = toNRGBAColor(c).(NRGBAColor)
+}
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *NRGBA) Opaque() bool {
-	h := len(p.Pixel)
-	if h > 0 {
-		w := len(p.Pixel[0])
-		for y := 0; y < h; y++ {
-			pix := p.Pixel[y]
-			for x := 0; x < w; x++ {
-				if pix[x].A != 0xff {
-					return false
-				}
+	if p.Rect.Empty() {
+		return true
+	}
+	base := p.Rect.Min.Y * p.Stride
+	i0, i1 := base+p.Rect.Min.X, base+p.Rect.Max.X
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for _, c := range p.Pix[i0:i1] {
+			if c.A != 0xff {
+				return false
 			}
 		}
+		i0 += p.Stride
+		i1 += p.Stride
 	}
 	return true
 }
 
 // NewNRGBA returns a new NRGBA with the given width and height.
 func NewNRGBA(w, h int) *NRGBA {
-	buf := make([]NRGBAColor, w*h)
-	pix := make([][]NRGBAColor, h)
-	for y := range pix {
-		pix[y] = buf[w*y : w*(y+1)]
-	}
-	return &NRGBA{pix}
+	pix := make([]NRGBAColor, w*h)
+	return &NRGBA{pix, w, Rectangle{ZP, Point{w, h}}}
 }
 
-// A NRGBA64 is an in-memory image backed by a 2-D slice of NRGBA64Color values.
+// An NRGBA64 is an in-memory image of NRGBA64Color values.
 type NRGBA64 struct {
-	// The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
-	Pixel [][]NRGBA64Color
+	// Pix holds the image's pixels. The pixel at (x, y) is Pix[y*Stride+x].
+	Pix    []NRGBA64Color
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
 }
 
 func (p *NRGBA64) ColorModel() ColorModel { return NRGBA64ColorModel }
 
-func (p *NRGBA64) Width() int {
-	if len(p.Pixel) == 0 {
-		return 0
+func (p *NRGBA64) Bounds() Rectangle { return p.Rect }
+
+func (p *NRGBA64) At(x, y int) Color {
+	if !p.Rect.Contains(Point{x, y}) {
+		return NRGBA64Color{}
 	}
-	return len(p.Pixel[0])
+	return p.Pix[y*p.Stride+x]
 }
 
-func (p *NRGBA64) Height() int { return len(p.Pixel) }
-
-func (p *NRGBA64) At(x, y int) Color { return p.Pixel[y][x] }
-
-func (p *NRGBA64) Set(x, y int, c Color) { p.Pixel[y][x] = toNRGBA64Color(c).(NRGBA64Color) }
+func (p *NRGBA64) Set(x, y int, c Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = toNRGBA64Color(c).(NRGBA64Color)
+}
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *NRGBA64) Opaque() bool {
-	h := len(p.Pixel)
-	if h > 0 {
-		w := len(p.Pixel[0])
-		for y := 0; y < h; y++ {
-			pix := p.Pixel[y]
-			for x := 0; x < w; x++ {
-				if pix[x].A != 0xffff {
-					return false
-				}
+	if p.Rect.Empty() {
+		return true
+	}
+	base := p.Rect.Min.Y * p.Stride
+	i0, i1 := base+p.Rect.Min.X, base+p.Rect.Max.X
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for _, c := range p.Pix[i0:i1] {
+			if c.A != 0xffff {
+				return false
 			}
 		}
+		i0 += p.Stride
+		i1 += p.Stride
 	}
 	return true
 }
 
 // NewNRGBA64 returns a new NRGBA64 with the given width and height.
 func NewNRGBA64(w, h int) *NRGBA64 {
-	buf := make([]NRGBA64Color, w*h)
-	pix := make([][]NRGBA64Color, h)
-	for y := range pix {
-		pix[y] = buf[w*y : w*(y+1)]
-	}
-	return &NRGBA64{pix}
+	pix := make([]NRGBA64Color, w*h)
+	return &NRGBA64{pix, w, Rectangle{ZP, Point{w, h}}}
 }
 
-// An Alpha is an in-memory image backed by a 2-D slice of AlphaColor values.
+// An Alpha is an in-memory image of AlphaColor values.
 type Alpha struct {
-	// The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
-	Pixel [][]AlphaColor
+	// Pix holds the image's pixels. The pixel at (x, y) is Pix[y*Stride+x].
+	Pix    []AlphaColor
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
 }
 
 func (p *Alpha) ColorModel() ColorModel { return AlphaColorModel }
 
-func (p *Alpha) Width() int {
-	if len(p.Pixel) == 0 {
-		return 0
+func (p *Alpha) Bounds() Rectangle { return p.Rect }
+
+func (p *Alpha) At(x, y int) Color {
+	if !p.Rect.Contains(Point{x, y}) {
+		return AlphaColor{}
 	}
-	return len(p.Pixel[0])
+	return p.Pix[y*p.Stride+x]
 }
 
-func (p *Alpha) Height() int { return len(p.Pixel) }
-
-func (p *Alpha) At(x, y int) Color { return p.Pixel[y][x] }
-
-func (p *Alpha) Set(x, y int, c Color) { p.Pixel[y][x] = toAlphaColor(c).(AlphaColor) }
+func (p *Alpha) Set(x, y int, c Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = toAlphaColor(c).(AlphaColor)
+}
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *Alpha) Opaque() bool {
-	h := len(p.Pixel)
-	if h > 0 {
-		w := len(p.Pixel[0])
-		for y := 0; y < h; y++ {
-			pix := p.Pixel[y]
-			for x := 0; x < w; x++ {
-				if pix[x].A != 0xff {
-					return false
-				}
+	if p.Rect.Empty() {
+		return true
+	}
+	base := p.Rect.Min.Y * p.Stride
+	i0, i1 := base+p.Rect.Min.X, base+p.Rect.Max.X
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for _, c := range p.Pix[i0:i1] {
+			if c.A != 0xff {
+				return false
 			}
 		}
+		i0 += p.Stride
+		i1 += p.Stride
 	}
 	return true
 }
 
 // NewAlpha returns a new Alpha with the given width and height.
 func NewAlpha(w, h int) *Alpha {
-	buf := make([]AlphaColor, w*h)
-	pix := make([][]AlphaColor, h)
-	for y := range pix {
-		pix[y] = buf[w*y : w*(y+1)]
-	}
-	return &Alpha{pix}
+	pix := make([]AlphaColor, w*h)
+	return &Alpha{pix, w, Rectangle{ZP, Point{w, h}}}
 }
 
-// An Alpha16 is an in-memory image backed by a 2-D slice of Alpha16Color values.
+// An Alpha16 is an in-memory image of Alpha16Color values.
 type Alpha16 struct {
-	// The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
-	Pixel [][]Alpha16Color
+	// Pix holds the image's pixels. The pixel at (x, y) is Pix[y*Stride+x].
+	Pix    []Alpha16Color
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
 }
 
 func (p *Alpha16) ColorModel() ColorModel { return Alpha16ColorModel }
 
-func (p *Alpha16) Width() int {
-	if len(p.Pixel) == 0 {
-		return 0
+func (p *Alpha16) Bounds() Rectangle { return p.Rect }
+
+func (p *Alpha16) At(x, y int) Color {
+	if !p.Rect.Contains(Point{x, y}) {
+		return Alpha16Color{}
 	}
-	return len(p.Pixel[0])
+	return p.Pix[y*p.Stride+x]
 }
 
-func (p *Alpha16) Height() int { return len(p.Pixel) }
-
-func (p *Alpha16) At(x, y int) Color { return p.Pixel[y][x] }
-
-func (p *Alpha16) Set(x, y int, c Color) { p.Pixel[y][x] = toAlpha16Color(c).(Alpha16Color) }
+func (p *Alpha16) Set(x, y int, c Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = toAlpha16Color(c).(Alpha16Color)
+}
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *Alpha16) Opaque() bool {
-	h := len(p.Pixel)
-	if h > 0 {
-		w := len(p.Pixel[0])
-		for y := 0; y < h; y++ {
-			pix := p.Pixel[y]
-			for x := 0; x < w; x++ {
-				if pix[x].A != 0xffff {
-					return false
-				}
+	if p.Rect.Empty() {
+		return true
+	}
+	base := p.Rect.Min.Y * p.Stride
+	i0, i1 := base+p.Rect.Min.X, base+p.Rect.Max.X
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for _, c := range p.Pix[i0:i1] {
+			if c.A != 0xffff {
+				return false
 			}
 		}
+		i0 += p.Stride
+		i1 += p.Stride
 	}
 	return true
 }
 
 // NewAlpha16 returns a new Alpha16 with the given width and height.
 func NewAlpha16(w, h int) *Alpha16 {
-	buf := make([]Alpha16Color, w*h)
-	pix := make([][]Alpha16Color, h)
-	for y := range pix {
-		pix[y] = buf[w*y : w*(y+1)]
+	pix := make([]Alpha16Color, w*h)
+	return &Alpha16{pix, w, Rectangle{ZP, Point{w, h}}}
+}
+
+// A Gray is an in-memory image of GrayColor values.
+type Gray struct {
+	// Pix holds the image's pixels. The pixel at (x, y) is Pix[y*Stride+x].
+	Pix    []GrayColor
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *Gray) ColorModel() ColorModel { return GrayColorModel }
+
+func (p *Gray) Bounds() Rectangle { return p.Rect }
+
+func (p *Gray) At(x, y int) Color {
+	if !p.Rect.Contains(Point{x, y}) {
+		return GrayColor{}
 	}
-	return &Alpha16{pix}
+	return p.Pix[y*p.Stride+x]
+}
+
+func (p *Gray) Set(x, y int, c Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = toGrayColor(c).(GrayColor)
+}
+
+// Opaque scans the entire image and returns whether or not it is fully opaque.
+func (p *Gray) Opaque() bool {
+	return true
+}
+
+// NewGray returns a new Gray with the given width and height.
+func NewGray(w, h int) *Gray {
+	pix := make([]GrayColor, w*h)
+	return &Gray{pix, w, Rectangle{ZP, Point{w, h}}}
+}
+
+// A Gray16 is an in-memory image of Gray16Color values.
+type Gray16 struct {
+	// Pix holds the image's pixels. The pixel at (x, y) is Pix[y*Stride+x].
+	Pix    []Gray16Color
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *Gray16) ColorModel() ColorModel { return Gray16ColorModel }
+
+func (p *Gray16) Bounds() Rectangle { return p.Rect }
+
+func (p *Gray16) At(x, y int) Color {
+	if !p.Rect.Contains(Point{x, y}) {
+		return Gray16Color{}
+	}
+	return p.Pix[y*p.Stride+x]
+}
+
+func (p *Gray16) Set(x, y int, c Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = toGray16Color(c).(Gray16Color)
+}
+
+// Opaque scans the entire image and returns whether or not it is fully opaque.
+func (p *Gray16) Opaque() bool {
+	return true
+}
+
+// NewGray16 returns a new Gray16 with the given width and height.
+func NewGray16(w, h int) *Gray16 {
+	pix := make([]Gray16Color, w*h)
+	return &Gray16{pix, w, Rectangle{ZP, Point{w, h}}}
 }
 
 // A PalettedColorModel represents a fixed palette of colors.
@@ -342,30 +451,41 @@ func (p PalettedColorModel) Convert(c Color) Color {
 
 // A Paletted is an in-memory image backed by a 2-D slice of uint8 values and a PalettedColorModel.
 type Paletted struct {
-	// The Pixel field's indices are y first, then x, so that At(x, y) == Palette[Pixel[y][x]].
-	Pixel   [][]uint8
+	// Pix holds the image's pixels. The pixel at (x, y) is Pix[y*Stride+x].
+	Pix    []uint8
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+	// Palette is the image's palette.
 	Palette PalettedColorModel
 }
 
 func (p *Paletted) ColorModel() ColorModel { return p.Palette }
 
-func (p *Paletted) Width() int {
-	if len(p.Pixel) == 0 {
-		return 0
+func (p *Paletted) Bounds() Rectangle { return p.Rect }
+
+func (p *Paletted) At(x, y int) Color {
+	if len(p.Palette) == 0 {
+		return nil
+	}
+	if !p.Rect.Contains(Point{x, y}) {
+		return p.Palette[0]
 	}
-	return len(p.Pixel[0])
+	return p.Palette[p.Pix[y*p.Stride+x]]
 }
 
-func (p *Paletted) Height() int { return len(p.Pixel) }
-
-func (p *Paletted) At(x, y int) Color { return p.Palette[p.Pixel[y][x]] }
-
 func (p *Paletted) ColorIndexAt(x, y int) uint8 {
-	return p.Pixel[y][x]
+	if !p.Rect.Contains(Point{x, y}) {
+		return 0
+	}
+	return p.Pix[y*p.Stride+x]
 }
 
 func (p *Paletted) SetColorIndex(x, y int, index uint8) {
-	p.Pixel[y][x] = index
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = index
 }
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
@@ -381,10 +501,6 @@ func (p *Paletted) Opaque() bool {
 
 // NewPaletted returns a new Paletted with the given width, height and palette.
 func NewPaletted(w, h int, m PalettedColorModel) *Paletted {
-	buf := make([]uint8, w*h)
-	pix := make([][]uint8, h)
-	for y := range pix {
-		pix[y] = buf[w*y : w*(y+1)]
-	}
-	return &Paletted{pix, m}
+	pix := make([]uint8, w*h)
+	return &Paletted{pix, w, Rectangle{ZP, Point{w, h}}, m}
 }
diff --git a/src/pkg/image/jpeg/Makefile b/src/pkg/image/jpeg/Makefile
index c84811d6a..5c5f97e71 100644
--- a/src/pkg/image/jpeg/Makefile
+++ b/src/pkg/image/jpeg/Makefile
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
-include $(GOROOT)/src/Make.$(GOARCH)
+include ../../../Make.inc
 
 TARG=image/jpeg
 GOFILES=\
@@ -10,4 +10,4 @@ GOFILES=\
 	idct.go\
 	reader.go\
 
-include $(GOROOT)/src/Make.pkg
+include ../../../Make.pkg
diff --git a/src/pkg/image/jpeg/reader.go b/src/pkg/image/jpeg/reader.go
index ec036ef4d..fb9cb11bb 100644
--- a/src/pkg/image/jpeg/reader.go
+++ b/src/pkg/image/jpeg/reader.go
@@ -147,7 +147,6 @@ func (d *decoder) processSOF(n int) os.Error {
 			}
 		}
 	}
-	d.image = image.NewRGBA(d.width, d.height)
 	return nil
 }
 
@@ -206,7 +205,7 @@ func (d *decoder) calcPixel(px, py, lumaBlock, lumaIndex, chromaIndex int) {
 	} else if b > 255 {
 		b = 255
 	}
-	d.image.Pixel[py][px] = image.RGBAColor{uint8(r), uint8(g), uint8(b), 0xff}
+	d.image.Pix[py*d.image.Stride+px] = image.RGBAColor{uint8(r), uint8(g), uint8(b), 0xff}
 }
 
 // Convert the MCU from YCbCr to RGB.
@@ -240,7 +239,7 @@ func (d *decoder) convertMCU(mx, my, h0, v0 int) {
 // Specified in section B.2.3.
 func (d *decoder) processSOS(n int) os.Error {
 	if d.image == nil {
-		return FormatError("missing SOF segment")
+		d.image = image.NewRGBA(d.width, d.height)
 	}
 	if n != 4+2*nComponent {
 		return UnsupportedError("SOS has wrong length")
@@ -365,9 +364,8 @@ func (d *decoder) processDRI(n int) os.Error {
 	return nil
 }
 
-// Decode reads a JPEG formatted image from r and returns it as an image.Image.
-func Decode(r io.Reader) (image.Image, os.Error) {
-	var d decoder
+// decode reads a JPEG image from r and returns it as an image.Image.
+func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, os.Error) {
 	if rr, ok := r.(Reader); ok {
 		d.r = rr
 	} else {
@@ -411,6 +409,9 @@ func Decode(r io.Reader) (image.Image, os.Error) {
 		switch {
 		case marker == sof0Marker: // Start Of Frame (Baseline).
 			err = d.processSOF(n)
+			if configOnly {
+				return nil, err
+			}
 		case marker == sof2Marker: // Start Of Frame (Progressive).
 			err = UnsupportedError("progressive mode")
 		case marker == dhtMarker: // Define Huffman Table.
@@ -432,3 +433,23 @@ func Decode(r io.Reader) (image.Image, os.Error) {
 	}
 	return d.image, nil
 }
+
+// Decode reads a JPEG image from r and returns it as an image.Image.
+func Decode(r io.Reader) (image.Image, os.Error) {
+	var d decoder
+	return d.decode(r, false)
+}
+
+// DecodeConfig returns the color model and dimensions of a JPEG 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
+	}
+	return image.Config{image.RGBAColorModel, d.width, d.height}, nil
+}
+
+func init() {
+	image.RegisterFormat("jpeg", "\xff\xd8", Decode, DecodeConfig)
+}
diff --git a/src/pkg/image/names.go b/src/pkg/image/names.go
index 0b621cff5..c309684ce 100644
--- a/src/pkg/image/names.go
+++ b/src/pkg/image/names.go
@@ -4,53 +4,64 @@
 
 package image
 
-// Colors from the HTML 4.01 specification: http://www.w3.org/TR/REC-html40/types.html#h-6.5
-// These names do not necessarily match those from other lists, such as the X11 color names.
 var (
-	Aqua    = ColorImage{RGBAColor{0x00, 0xff, 0xff, 0xff}}
-	Black   = ColorImage{RGBAColor{0x00, 0x00, 0x00, 0xff}}
-	Blue    = ColorImage{RGBAColor{0x00, 0x00, 0xff, 0xff}}
-	Fuchsia = ColorImage{RGBAColor{0xff, 0x00, 0xff, 0xff}}
-	Gray    = ColorImage{RGBAColor{0x80, 0x80, 0x80, 0xff}}
-	Green   = ColorImage{RGBAColor{0x00, 0x80, 0x00, 0xff}}
-	Lime    = ColorImage{RGBAColor{0x00, 0xff, 0x00, 0xff}}
-	Maroon  = ColorImage{RGBAColor{0x80, 0x00, 0x00, 0xff}}
-	Navy    = ColorImage{RGBAColor{0x00, 0x00, 0x80, 0xff}}
-	Olive   = ColorImage{RGBAColor{0x80, 0x80, 0x00, 0xff}}
-	Red     = ColorImage{RGBAColor{0xff, 0x00, 0x00, 0xff}}
-	Purple  = ColorImage{RGBAColor{0x80, 0x00, 0x80, 0xff}}
-	Silver  = ColorImage{RGBAColor{0xc0, 0xc0, 0xc0, 0xff}}
-	Teal    = ColorImage{RGBAColor{0x00, 0x80, 0x80, 0xff}}
-	White   = ColorImage{RGBAColor{0xff, 0xff, 0xff, 0xff}}
-	Yellow  = ColorImage{RGBAColor{0xff, 0xff, 0x00, 0xff}}
-
-	// These synonyms are not in HTML 4.01.
-	Cyan    = Aqua
-	Magenta = Fuchsia
+	// Black is an opaque black ColorImage.
+	Black = NewColorImage(Gray16Color{0})
+	// White is an opaque white ColorImage.
+	White = NewColorImage(Gray16Color{0xffff})
+	// Transparent is a fully transparent ColorImage.
+	Transparent = NewColorImage(Alpha16Color{0})
+	// Opaque is a fully opaque ColorImage.
+	Opaque = NewColorImage(Alpha16Color{0xffff})
 )
 
-// A ColorImage is a practically infinite-sized Image of uniform Color.
+// A ColorImage is an infinite-sized Image of uniform Color.
 // It implements both the Color and Image interfaces.
 type ColorImage struct {
 	C Color
 }
 
-func (c ColorImage) RGBA() (r, g, b, a uint32) {
+func (c *ColorImage) RGBA() (r, g, b, a uint32) {
 	return c.C.RGBA()
 }
 
-func (c ColorImage) ColorModel() ColorModel {
+func (c *ColorImage) ColorModel() ColorModel {
 	return ColorModelFunc(func(Color) Color { return c.C })
 }
 
-func (c ColorImage) Width() int { return 1e9 }
+func (c *ColorImage) Bounds() Rectangle { return Rectangle{Point{-1e9, -1e9}, Point{1e9, 1e9}} }
 
-func (c ColorImage) Height() int { return 1e9 }
-
-func (c ColorImage) At(x, y int) Color { return c.C }
+func (c *ColorImage) At(x, y int) Color { return c.C }
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
-func (c ColorImage) Opaque() bool {
+func (c *ColorImage) Opaque() bool {
 	_, _, _, a := c.C.RGBA()
 	return a == 0xffff
 }
+
+func NewColorImage(c Color) *ColorImage {
+	return &ColorImage{c}
+}
+
+// A Tiled is an infinite-sized Image that repeats another Image in both
+// directions. Tiled{i, p}.At(x, y) will equal i.At(x+p.X, y+p.Y) for all
+// points {x+p.X, y+p.Y} within i's Bounds.
+type Tiled struct {
+	I      Image
+	Offset Point
+}
+
+func (t *Tiled) ColorModel() ColorModel {
+	return t.I.ColorModel()
+}
+
+func (t *Tiled) Bounds() Rectangle { return Rectangle{Point{-1e9, -1e9}, Point{1e9, 1e9}} }
+
+func (t *Tiled) At(x, y int) Color {
+	p := Point{x, y}.Add(t.Offset).Mod(t.I.Bounds())
+	return t.I.At(p.X, p.Y)
+}
+
+func NewTiled(i Image, offset Point) *Tiled {
+	return &Tiled{i, offset}
+}
diff --git a/src/pkg/image/png/Makefile b/src/pkg/image/png/Makefile
index 3ba0f44d3..4101f77e1 100644
--- a/src/pkg/image/png/Makefile
+++ b/src/pkg/image/png/Makefile
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
-include ../../../Make.$(GOARCH)
+include ../../../Make.inc
 
 TARG=image/png
 GOFILES=\
diff --git a/src/pkg/image/png/reader.go b/src/pkg/image/png/reader.go
index fddb70423..e2d679bb4 100644
--- a/src/pkg/image/png/reader.go
+++ b/src/pkg/image/png/reader.go
@@ -9,6 +9,7 @@ package png
 
 import (
 	"compress/zlib"
+	"fmt"
 	"hash"
 	"hash/crc32"
 	"image"
@@ -25,6 +26,18 @@ const (
 	ctTrueColorAlpha = 6
 )
 
+// A cb is a combination of color type and bit depth.
+const (
+	cbInvalid = iota
+	cbG8
+	cbTC8
+	cbP8
+	cbTCA8
+	cbG16
+	cbTC16
+	cbTCA16
+)
+
 // Filter type, as per the PNG spec.
 const (
 	ftNone    = 0
@@ -50,20 +63,25 @@ const (
 
 const pngHeader = "\x89PNG\r\n\x1a\n"
 
+type imgOrErr struct {
+	img image.Image
+	err os.Error
+}
+
 type decoder struct {
 	width, height int
-	image         image.Image
-	colorType     uint8
+	palette       image.PalettedColorModel
+	cb            int
 	stage         int
 	idatWriter    io.WriteCloser
-	idatDone      chan os.Error
+	idatDone      chan imgOrErr
 	tmp           [3 * 256]byte
 }
 
 // A FormatError reports that the input is not a valid PNG.
 type FormatError string
 
-func (e FormatError) String() string { return "invalid PNG format: " + string(e) }
+func (e FormatError) String() string { return "png: invalid format: " + string(e) }
 
 var chunkOrderError = FormatError("chunk out of order")
 
@@ -72,12 +90,12 @@ type IDATDecodingError struct {
 	Err os.Error
 }
 
-func (e IDATDecodingError) String() string { return "IDAT decoding error: " + e.Err.String() }
+func (e IDATDecodingError) String() string { return "png: IDAT decoding error: " + e.Err.String() }
 
 // An UnsupportedError reports that the input uses a valid but unimplemented PNG feature.
 type UnsupportedError string
 
-func (e UnsupportedError) String() string { return "unsupported PNG feature: " + string(e) }
+func (e UnsupportedError) String() string { return "png: unsupported feature: " + string(e) }
 
 // Big-endian.
 func parseUint32(b []uint8) uint32 {
@@ -107,9 +125,6 @@ func (d *decoder) parseIHDR(r io.Reader, crc hash.Hash32, length uint32) os.Erro
 		return err
 	}
 	crc.Write(d.tmp[0:13])
-	if d.tmp[8] != 8 {
-		return UnsupportedError("bit depth")
-	}
 	if d.tmp[10] != 0 || d.tmp[11] != 0 || d.tmp[12] != 0 {
 		return UnsupportedError("compression, filter or interlace method")
 	}
@@ -122,16 +137,31 @@ func (d *decoder) parseIHDR(r io.Reader, crc hash.Hash32, length uint32) os.Erro
 	if nPixels != int64(int(nPixels)) {
 		return UnsupportedError("dimension overflow")
 	}
-	d.colorType = d.tmp[9]
-	switch d.colorType {
-	case ctTrueColor:
-		d.image = image.NewRGBA(int(w), int(h))
-	case ctPaletted:
-		d.image = image.NewPaletted(int(w), int(h), nil)
-	case ctTrueColorAlpha:
-		d.image = image.NewNRGBA(int(w), int(h))
-	default:
-		return UnsupportedError("color type")
+	d.cb = cbInvalid
+	switch d.tmp[8] {
+	case 8:
+		switch d.tmp[9] {
+		case ctGrayscale:
+			d.cb = cbG8
+		case ctTrueColor:
+			d.cb = cbTC8
+		case ctPaletted:
+			d.cb = cbP8
+		case ctTrueColorAlpha:
+			d.cb = cbTCA8
+		}
+	case 16:
+		switch d.tmp[9] {
+		case ctGrayscale:
+			d.cb = cbG16
+		case ctTrueColor:
+			d.cb = cbTC16
+		case ctTrueColorAlpha:
+			d.cb = cbTCA16
+		}
+	}
+	if d.cb == cbInvalid {
+		return UnsupportedError(fmt.Sprintf("bit depth %d, color type %d", d.tmp[8], d.tmp[9]))
 	}
 	d.width, d.height = int(w), int(h)
 	return nil
@@ -147,17 +177,15 @@ func (d *decoder) parsePLTE(r io.Reader, crc hash.Hash32, length uint32) os.Erro
 		return err
 	}
 	crc.Write(d.tmp[0:n])
-	switch d.colorType {
-	case ctPaletted:
-		palette := make([]image.Color, np)
+	switch d.cb {
+	case cbP8:
+		d.palette = image.PalettedColorModel(make([]image.Color, np))
 		for i := 0; i < np; i++ {
-			palette[i] = image.RGBAColor{d.tmp[3*i+0], d.tmp[3*i+1], d.tmp[3*i+2], 0xff}
+			d.palette[i] = image.RGBAColor{d.tmp[3*i+0], d.tmp[3*i+1], d.tmp[3*i+2], 0xff}
 		}
-		d.image.(*image.Paletted).Palette = image.PalettedColorModel(palette)
-	case ctTrueColor, ctTrueColorAlpha:
+	case cbTC8, cbTCA8, cbTC16, cbTCA16:
 		// As per the PNG spec, a PLTE chunk is optional (and for practical purposes,
 		// ignorable) for the ctTrueColor and ctTrueColorAlpha color types (section 4.1.2).
-		return nil
 	default:
 		return FormatError("PLTE, color type mismatch")
 	}
@@ -173,19 +201,20 @@ func (d *decoder) parsetRNS(r io.Reader, crc hash.Hash32, length uint32) os.Erro
 		return err
 	}
 	crc.Write(d.tmp[0:n])
-	switch d.colorType {
-	case ctTrueColor:
-		return UnsupportedError("TrueColor transparency")
-	case ctPaletted:
-		p := d.image.(*image.Paletted).Palette
-		if n > len(p) {
+	switch d.cb {
+	case cbG8, cbG16:
+		return UnsupportedError("grayscale transparency")
+	case cbTC8, cbTC16:
+		return UnsupportedError("truecolor transparency")
+	case cbP8:
+		if n > len(d.palette) {
 			return FormatError("bad tRNS length")
 		}
 		for i := 0; i < n; i++ {
-			rgba := p[i].(image.RGBAColor)
-			p[i] = image.RGBAColor{rgba.R, rgba.G, rgba.B, d.tmp[i]}
+			rgba := d.palette[i].(image.RGBAColor)
+			d.palette[i] = image.RGBAColor{rgba.R, rgba.G, rgba.B, d.tmp[i]}
 		}
-	case ctTrueColorAlpha:
+	case cbTCA8, cbTCA16:
 		return FormatError("tRNS, color type mismatch")
 	}
 	return nil
@@ -205,30 +234,54 @@ func paeth(a, b, c uint8) uint8 {
 	return c
 }
 
-func (d *decoder) idatReader(idat io.Reader) os.Error {
+func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 	r, err := zlib.NewReader(idat)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	defer r.Close()
 	bpp := 0 // Bytes per pixel.
 	maxPalette := uint8(0)
 	var (
+		gray     *image.Gray
 		rgba     *image.RGBA
-		nrgba    *image.NRGBA
 		paletted *image.Paletted
+		nrgba    *image.NRGBA
+		gray16   *image.Gray16
+		rgba64   *image.RGBA64
+		nrgba64  *image.NRGBA64
+		img      image.Image
 	)
-	switch d.colorType {
-	case ctTrueColor:
+	switch d.cb {
+	case cbG8:
+		bpp = 1
+		gray = image.NewGray(d.width, d.height)
+		img = gray
+	case cbTC8:
 		bpp = 3
-		rgba = d.image.(*image.RGBA)
-	case ctPaletted:
+		rgba = image.NewRGBA(d.width, d.height)
+		img = rgba
+	case cbP8:
 		bpp = 1
-		paletted = d.image.(*image.Paletted)
-		maxPalette = uint8(len(paletted.Palette) - 1)
-	case ctTrueColorAlpha:
+		paletted = image.NewPaletted(d.width, d.height, d.palette)
+		img = paletted
+		maxPalette = uint8(len(d.palette) - 1)
+	case cbTCA8:
 		bpp = 4
-		nrgba = d.image.(*image.NRGBA)
+		nrgba = image.NewNRGBA(d.width, d.height)
+		img = nrgba
+	case cbG16:
+		bpp = 2
+		gray16 = image.NewGray16(d.width, d.height)
+		img = gray16
+	case cbTC16:
+		bpp = 6
+		rgba64 = image.NewRGBA64(d.width, d.height)
+		img = rgba64
+	case cbTCA16:
+		bpp = 8
+		nrgba64 = image.NewNRGBA64(d.width, d.height)
+		img = nrgba64
 	}
 	// cr and pr are the bytes for the current and previous row.
 	// The +1 is for the per-row filter type, which is at cr[0].
@@ -239,7 +292,7 @@ func (d *decoder) idatReader(idat io.Reader) os.Error {
 		// Read the decompressed bytes.
 		_, err := io.ReadFull(r, cr)
 		if err != nil {
-			return err
+			return nil, err
 		}
 
 		// Apply the filter.
@@ -271,32 +324,56 @@ func (d *decoder) idatReader(idat io.Reader) os.Error {
 				cdat[i] += paeth(cdat[i-bpp], pdat[i], pdat[i-bpp])
 			}
 		default:
-			return FormatError("bad filter type")
+			return nil, FormatError("bad filter type")
 		}
 
 		// Convert from bytes to colors.
-		switch d.colorType {
-		case ctTrueColor:
+		switch d.cb {
+		case cbG8:
+			for x := 0; x < d.width; x++ {
+				gray.Set(x, y, image.GrayColor{cdat[x]})
+			}
+		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})
 			}
-		case ctPaletted:
+		case cbP8:
 			for x := 0; x < d.width; x++ {
 				if cdat[x] > maxPalette {
-					return FormatError("palette index out of range")
+					return nil, FormatError("palette index out of range")
 				}
 				paletted.SetColorIndex(x, y, cdat[x])
 			}
-		case ctTrueColorAlpha:
+		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]})
 			}
+		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})
+			}
+		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})
+			}
+		case cbTCA16:
+			for x := 0; x < d.width; x++ {
+				rcol := uint16(cdat[8*x+0])<<8 | uint16(cdat[8*x+1])
+				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})
+			}
 		}
 
 		// The current row for y is the previous row for y+1.
 		pr, cr = cr, pr
 	}
-	return nil
+	return img, nil
 }
 
 func (d *decoder) parseIDAT(r io.Reader, crc hash.Hash32, length uint32) os.Error {
@@ -308,14 +385,14 @@ func (d *decoder) parseIDAT(r io.Reader, crc hash.Hash32, length uint32) os.Erro
 	if d.idatWriter == nil {
 		pr, pw := io.Pipe()
 		d.idatWriter = pw
-		d.idatDone = make(chan os.Error)
+		d.idatDone = make(chan imgOrErr)
 		go func() {
-			err := d.idatReader(pr)
+			img, err := d.idatReader(pr)
 			if err == os.EOF {
 				err = FormatError("too little IDAT")
 			}
 			pr.CloseWithError(FormatError("too much IDAT"))
-			d.idatDone <- err
+			d.idatDone <- imgOrErr{img, err}
 		}()
 	}
 	var buf [4096]byte
@@ -386,7 +463,7 @@ func (d *decoder) parseChunk(r io.Reader) os.Error {
 		}
 		err = d.parsetRNS(r, crc, length)
 	case "IDAT":
-		if d.stage < dsSeenIHDR || d.stage > dsSeenIDAT || (d.colorType == ctPaletted && d.stage == dsSeenIHDR) {
+		if d.stage < dsSeenIHDR || d.stage > dsSeenIDAT || (d.cb == cbP8 && d.stage == dsSeenIHDR) {
 			return chunkOrderError
 		}
 		d.stage = dsSeenIDAT
@@ -438,7 +515,7 @@ func (d *decoder) checkHeader(r io.Reader) os.Error {
 	return nil
 }
 
-// Decode reads a PNG formatted image from r and returns it as an image.Image.
+// Decode reads a PNG image from r and returns it as an image.Image.
 // The type of Image returned depends on the PNG contents.
 func Decode(r io.Reader) (image.Image, os.Error) {
 	var d decoder
@@ -446,21 +523,66 @@ func Decode(r io.Reader) (image.Image, os.Error) {
 	if err != nil {
 		return nil, err
 	}
-	for d.stage = dsStart; d.stage != dsSeenIEND; {
+	for d.stage != dsSeenIEND {
 		err = d.parseChunk(r)
 		if err != nil {
 			break
 		}
 	}
+	var img image.Image
 	if d.idatWriter != nil {
 		d.idatWriter.Close()
-		err1 := <-d.idatDone
+		ie := <-d.idatDone
 		if err == nil {
-			err = err1
+			img, err = ie.img, ie.err
 		}
 	}
 	if err != nil {
 		return nil, err
 	}
-	return d.image, nil
+	return img, nil
+}
+
+// DecodeConfig returns the color model and dimensions of a PNG image without
+// decoding the entire image.
+func DecodeConfig(r io.Reader) (image.Config, os.Error) {
+	var d decoder
+	err := d.checkHeader(r)
+	if err != nil {
+		return image.Config{}, err
+	}
+	for {
+		err = d.parseChunk(r)
+		if err != nil {
+			return image.Config{}, err
+		}
+		if d.stage == dsSeenIHDR && d.cb != cbP8 {
+			break
+		}
+		if d.stage == dsSeenPLTE && d.cb == cbP8 {
+			break
+		}
+	}
+	var cm image.ColorModel
+	switch d.cb {
+	case cbG8:
+		cm = image.GrayColorModel
+	case cbTC8:
+		cm = image.RGBAColorModel
+	case cbP8:
+		cm = d.palette
+	case cbTCA8:
+		cm = image.NRGBAColorModel
+	case cbG16:
+		cm = image.Gray16ColorModel
+	case cbTC16:
+		cm = image.RGBA64ColorModel
+	case cbTCA16:
+		cm = image.NRGBA64ColorModel
+	}
+	return image.Config{cm, d.width, d.height}, nil
+}
+
+func init() {
+	image.RegisterFormat("png", pngHeader, Decode, DecodeConfig)
 }
diff --git a/src/pkg/image/png/reader_test.go b/src/pkg/image/png/reader_test.go
index 1dc45992e..fefceee3a 100644
--- a/src/pkg/image/png/reader_test.go
+++ b/src/pkg/image/png/reader_test.go
@@ -14,23 +14,24 @@ import (
 )
 
 // The go PNG library currently supports only a subset of the full PNG specification.
-// In particular, bit depths other than 8 are not supported, and neither are grayscale images.
+// In particular, bit depths other than 8 or 16 are not supported, nor are grayscale-
+// alpha images.
 var filenames = []string{
-	//"basn0g01",	// bit depth is not 8
-	//"basn0g02",	// bit depth is not 8
-	//"basn0g04",	// bit depth is not 8
-	//"basn0g08",	// grayscale color model
-	//"basn0g16",	// bit depth is not 8
+	//"basn0g01",	// bit depth is not 8 or 16
+	//"basn0g02",	// bit depth is not 8 or 16
+	//"basn0g04",	// bit depth is not 8 or 16
+	"basn0g08",
+	"basn0g16",
 	"basn2c08",
-	//"basn2c16",	// bit depth is not 8
-	//"basn3p01",	// bit depth is not 8
-	//"basn3p02",	// bit depth is not 8
-	//"basn3p04",	// bit depth is not 8
+	"basn2c16",
+	//"basn3p01",	// bit depth is not 8 or 16
+	//"basn3p02",	// bit depth is not 8 or 16
+	//"basn3p04",	// bit depth is not 8 or 16
 	"basn3p08",
-	//"basn4a08",	// grayscale color model
-	//"basn4a16",	// bit depth is not 8
+	//"basn4a08",	// grayscale-alpha color model
+	//"basn4a16",	// grayscale-alpha color model
 	"basn6a08",
-	//"basn6a16",	// bit depth is not 8
+	"basn6a16",
 }
 
 func readPng(filename string) (image.Image, os.Error) {
@@ -45,23 +46,34 @@ func readPng(filename string) (image.Image, os.Error) {
 // An approximation of the sng command-line tool.
 func sng(w io.WriteCloser, filename string, png image.Image) {
 	defer w.Close()
-	// For now, the go PNG parser only reads bitdepths of 8.
-	bitdepth := 8
+	bounds := png.Bounds()
+	cm := png.ColorModel()
+	var bitdepth int
+	switch cm {
+	case image.RGBAColorModel, image.NRGBAColorModel, image.AlphaColorModel, image.GrayColorModel:
+		bitdepth = 8
+	default:
+		bitdepth = 16
+	}
+	cpm, _ := cm.(image.PalettedColorModel)
+	var paletted *image.Paletted
+	if cpm != nil {
+		bitdepth = 8
+		paletted = png.(*image.Paletted)
+	}
 
 	// Write the filename and IHDR.
 	io.WriteString(w, "#SNG: from "+filename+".png\nIHDR {\n")
-	fmt.Fprintf(w, "    width: %d; height: %d; bitdepth: %d;\n", png.Width(), png.Height(), bitdepth)
-	cm := png.ColorModel()
-	var paletted *image.Paletted
-	cpm, _ := cm.(image.PalettedColorModel)
+	fmt.Fprintf(w, "    width: %d; height: %d; bitdepth: %d;\n", bounds.Dx(), bounds.Dy(), bitdepth)
 	switch {
-	case cm == image.RGBAColorModel:
+	case cm == image.RGBAColorModel, cm == image.RGBA64ColorModel:
 		io.WriteString(w, "    using color;\n")
-	case cm == image.NRGBAColorModel:
+	case cm == image.NRGBAColorModel, cm == image.NRGBA64ColorModel:
 		io.WriteString(w, "    using color alpha;\n")
+	case cm == image.GrayColorModel, cm == image.Gray16ColorModel:
+		io.WriteString(w, "    using grayscale;\n")
 	case cpm != nil:
 		io.WriteString(w, "    using color palette;\n")
-		paletted = png.(*image.Paletted)
 	default:
 		io.WriteString(w, "unknown PNG decoder color model\n")
 	}
@@ -86,20 +98,40 @@ func sng(w io.WriteCloser, filename string, png image.Image) {
 
 	// Write the IMAGE.
 	io.WriteString(w, "IMAGE {\n    pixels hex\n")
-	for y := 0; y < png.Height(); y++ {
+	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
 		switch {
+		case cm == image.GrayColorModel:
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				gray := png.At(x, y).(image.GrayColor)
+				fmt.Fprintf(w, "%02x", gray.Y)
+			}
+		case cm == image.Gray16ColorModel:
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				gray16 := png.At(x, y).(image.Gray16Color)
+				fmt.Fprintf(w, "%04x ", gray16.Y)
+			}
 		case cm == image.RGBAColorModel:
-			for x := 0; x < png.Width(); x++ {
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
 				rgba := png.At(x, y).(image.RGBAColor)
 				fmt.Fprintf(w, "%02x%02x%02x ", rgba.R, rgba.G, rgba.B)
 			}
+		case cm == image.RGBA64ColorModel:
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				rgba64 := png.At(x, y).(image.RGBA64Color)
+				fmt.Fprintf(w, "%04x%04x%04x ", rgba64.R, rgba64.G, rgba64.B)
+			}
 		case cm == image.NRGBAColorModel:
-			for x := 0; x < png.Width(); x++ {
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
 				nrgba := png.At(x, y).(image.NRGBAColor)
 				fmt.Fprintf(w, "%02x%02x%02x%02x ", nrgba.R, nrgba.G, nrgba.B, nrgba.A)
 			}
+		case cm == image.NRGBA64ColorModel:
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
+				nrgba64 := png.At(x, y).(image.NRGBA64Color)
+				fmt.Fprintf(w, "%04x%04x%04x%04x ", nrgba64.R, nrgba64.G, nrgba64.B, nrgba64.A)
+			}
 		case cpm != nil:
-			for x := 0; x < png.Width(); x++ {
+			for x := bounds.Min.X; x < bounds.Max.X; x++ {
 				fmt.Fprintf(w, "%02x", paletted.ColorIndexAt(x, y))
 			}
 		}
diff --git a/src/pkg/image/png/writer.go b/src/pkg/image/png/writer.go
index e186ca819..081d06bf5 100644
--- a/src/pkg/image/png/writer.go
+++ b/src/pkg/image/png/writer.go
@@ -15,13 +15,13 @@ import (
 )
 
 type encoder struct {
-	w         io.Writer
-	m         image.Image
-	colorType uint8
-	err       os.Error
-	header    [8]byte
-	footer    [4]byte
-	tmp       [3 * 256]byte
+	w      io.Writer
+	m      image.Image
+	cb     int
+	err    os.Error
+	header [8]byte
+	footer [4]byte
+	tmp    [3 * 256]byte
 }
 
 // Big-endian.
@@ -32,10 +32,18 @@ func writeUint32(b []uint8, u uint32) {
 	b[3] = uint8(u >> 0)
 }
 
+type opaquer interface {
+	Opaque() bool
+}
+
 // Returns whether or not the image is fully opaque.
 func opaque(m image.Image) bool {
-	for y := 0; y < m.Height(); y++ {
-		for x := 0; x < m.Width(); x++ {
+	if o, ok := m.(opaquer); ok {
+		return o.Opaque()
+	}
+	b := m.Bounds()
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		for x := b.Min.X; x < b.Max.X; x++ {
 			_, _, _, a := m.At(x, y).RGBA()
 			if a != 0xffff {
 				return false
@@ -84,10 +92,33 @@ func (e *encoder) writeChunk(b []byte, name string) {
 }
 
 func (e *encoder) writeIHDR() {
-	writeUint32(e.tmp[0:4], uint32(e.m.Width()))
-	writeUint32(e.tmp[4:8], uint32(e.m.Height()))
-	e.tmp[8] = 8 // bit depth
-	e.tmp[9] = e.colorType
+	b := e.m.Bounds()
+	writeUint32(e.tmp[0:4], uint32(b.Dx()))
+	writeUint32(e.tmp[4:8], uint32(b.Dy()))
+	// Set bit depth and color type.
+	switch e.cb {
+	case cbG8:
+		e.tmp[8] = 8
+		e.tmp[9] = ctGrayscale
+	case cbTC8:
+		e.tmp[8] = 8
+		e.tmp[9] = ctTrueColor
+	case cbP8:
+		e.tmp[8] = 8
+		e.tmp[9] = ctPaletted
+	case cbTCA8:
+		e.tmp[8] = 8
+		e.tmp[9] = ctTrueColorAlpha
+	case cbG16:
+		e.tmp[8] = 16
+		e.tmp[9] = ctGrayscale
+	case cbTC16:
+		e.tmp[8] = 16
+		e.tmp[9] = ctTrueColor
+	case cbTCA16:
+		e.tmp[8] = 16
+		e.tmp[9] = ctTrueColorAlpha
+	}
 	e.tmp[10] = 0 // default compression method
 	e.tmp[11] = 0 // default filter method
 	e.tmp[12] = 0 // non-interlaced
@@ -224,7 +255,7 @@ func filter(cr [][]byte, pr []byte, bpp int) int {
 	return filter
 }
 
-func writeImage(w io.Writer, m image.Image, ct uint8) os.Error {
+func writeImage(w io.Writer, m image.Image, cb int) os.Error {
 	zw, err := zlib.NewWriter(w)
 	if err != nil {
 		return err
@@ -233,51 +264,94 @@ func writeImage(w io.Writer, m image.Image, ct uint8) os.Error {
 
 	bpp := 0 // Bytes per pixel.
 	var paletted *image.Paletted
-	switch ct {
-	case ctTrueColor:
+	switch cb {
+	case cbG8:
+		bpp = 1
+	case cbTC8:
 		bpp = 3
-	case ctPaletted:
+	case cbP8:
 		bpp = 1
 		paletted = m.(*image.Paletted)
-	case ctTrueColorAlpha:
+	case cbTCA8:
 		bpp = 4
+	case cbTC16:
+		bpp = 6
+	case cbTCA16:
+		bpp = 8
+	case cbG16:
+		bpp = 2
 	}
 	// cr[*] and pr are the bytes for the current and previous row.
 	// cr[0] is unfiltered (or equivalently, filtered with the ftNone filter).
 	// cr[ft], for non-zero filter types ft, are buffers for transforming cr[0] under the
 	// other PNG filter types. These buffers are allocated once and re-used for each row.
 	// The +1 is for the per-row filter type, which is at cr[*][0].
+	b := m.Bounds()
 	var cr [nFilter][]uint8
 	for i := 0; i < len(cr); i++ {
-		cr[i] = make([]uint8, 1+bpp*m.Width())
+		cr[i] = make([]uint8, 1+bpp*b.Dx())
 		cr[i][0] = uint8(i)
 	}
-	pr := make([]uint8, 1+bpp*m.Width())
+	pr := make([]uint8, 1+bpp*b.Dx())
 
-	for y := 0; y < m.Height(); y++ {
+	for y := b.Min.Y; y < b.Max.Y; y++ {
 		// Convert from colors to bytes.
-		switch ct {
-		case ctTrueColor:
-			for x := 0; x < m.Width(); x++ {
+		switch cb {
+		case cbG8:
+			for x := b.Min.X; x < b.Max.X; x++ {
+				c := image.GrayColorModel.Convert(m.At(x, y)).(image.GrayColor)
+				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)
 			}
-		case ctPaletted:
-			for x := 0; x < m.Width(); x++ {
-				cr[0][x+1] = paletted.ColorIndexAt(x, y)
-			}
-		case ctTrueColorAlpha:
+		case cbP8:
+			rowOffset := y * paletted.Stride
+			copy(cr[0][b.Min.X+1:], paletted.Pix[rowOffset+b.Min.X:rowOffset+b.Max.X])
+		case cbTCA8:
 			// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
-			for x := 0; x < m.Width(); x++ {
+			for x := b.Min.X; x < b.Max.X; x++ {
 				c := image.NRGBAColorModel.Convert(m.At(x, y)).(image.NRGBAColor)
 				cr[0][4*x+1] = c.R
 				cr[0][4*x+2] = c.G
 				cr[0][4*x+3] = c.B
 				cr[0][4*x+4] = c.A
 			}
+		case cbG16:
+			for x := b.Min.X; x < b.Max.X; x++ {
+				c := image.Gray16ColorModel.Convert(m.At(x, y)).(image.Gray16Color)
+				cr[0][2*x+1] = uint8(c.Y >> 8)
+				cr[0][2*x+2] = uint8(c.Y)
+			}
+		case cbTC16:
+			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][6*x+1] = uint8(r >> 8)
+				cr[0][6*x+2] = uint8(r)
+				cr[0][6*x+3] = uint8(g >> 8)
+				cr[0][6*x+4] = uint8(g)
+				cr[0][6*x+5] = uint8(b >> 8)
+				cr[0][6*x+6] = uint8(b)
+			}
+		case cbTCA16:
+			// Convert from image.Image (which is alpha-premultiplied) to PNG's non-alpha-premultiplied.
+			for x := b.Min.X; x < b.Max.X; x++ {
+				c := image.NRGBA64ColorModel.Convert(m.At(x, y)).(image.NRGBA64Color)
+				cr[0][8*x+1] = uint8(c.R >> 8)
+				cr[0][8*x+2] = uint8(c.R)
+				cr[0][8*x+3] = uint8(c.G >> 8)
+				cr[0][8*x+4] = uint8(c.G)
+				cr[0][8*x+5] = uint8(c.B >> 8)
+				cr[0][8*x+6] = uint8(c.B)
+				cr[0][8*x+7] = uint8(c.A >> 8)
+				cr[0][8*x+8] = uint8(c.A)
+			}
 		}
 
 		// Apply the filter.
@@ -305,7 +379,7 @@ func (e *encoder) writeIDATs() {
 	if e.err != nil {
 		return
 	}
-	e.err = writeImage(bw, e.m, e.colorType)
+	e.err = writeImage(bw, e.m, e.cb)
 	if e.err != nil {
 		return
 	}
@@ -320,7 +394,7 @@ func Encode(w io.Writer, m image.Image) os.Error {
 	// Obviously, negative widths and heights are invalid. Furthermore, the PNG
 	// spec section 11.2.2 says that zero is invalid. Excessively large images are
 	// also rejected.
-	mw, mh := int64(m.Width()), int64(m.Height())
+	mw, mh := int64(m.Bounds().Dx()), int64(m.Bounds().Dy())
 	if mw <= 0 || mh <= 0 || mw >= 1<<32 || mh >= 1<<32 {
 		return FormatError("invalid image size: " + strconv.Itoa64(mw) + "x" + strconv.Itoa64(mw))
 	}
@@ -328,12 +402,28 @@ func Encode(w io.Writer, m image.Image) os.Error {
 	var e encoder
 	e.w = w
 	e.m = m
-	e.colorType = uint8(ctTrueColorAlpha)
 	pal, _ := m.(*image.Paletted)
 	if pal != nil {
-		e.colorType = ctPaletted
-	} else if opaque(m) {
-		e.colorType = ctTrueColor
+		e.cb = cbP8
+	} else {
+		switch m.ColorModel() {
+		case image.GrayColorModel:
+			e.cb = cbG8
+		case image.Gray16ColorModel:
+			e.cb = cbG16
+		case image.RGBAColorModel, image.NRGBAColorModel, image.AlphaColorModel:
+			if opaque(m) {
+				e.cb = cbTC8
+			} else {
+				e.cb = cbTCA8
+			}
+		default:
+			if opaque(m) {
+				e.cb = cbTC16
+			} else {
+				e.cb = cbTCA16
+			}
+		}
 	}
 
 	_, e.err = io.WriteString(w, pngHeader)
diff --git a/src/pkg/image/png/writer_test.go b/src/pkg/image/png/writer_test.go
index a61e1c95a..f218a5564 100644
--- a/src/pkg/image/png/writer_test.go
+++ b/src/pkg/image/png/writer_test.go
@@ -5,6 +5,7 @@
 package png
 
 import (
+	"bytes"
 	"fmt"
 	"image"
 	"io"
@@ -13,15 +14,16 @@ import (
 )
 
 func diff(m0, m1 image.Image) os.Error {
-	if m0.Width() != m1.Width() || m0.Height() != m1.Height() {
-		return os.NewError(fmt.Sprintf("dimensions differ: %dx%d vs %dx%d", m0.Width(), m0.Height(), m1.Width(), m1.Height()))
+	b0, b1 := m0.Bounds(), m1.Bounds()
+	if !b0.Eq(b1) {
+		return fmt.Errorf("dimensions differ: %v vs %v", b0, b1)
 	}
-	for y := 0; y < m0.Height(); y++ {
-		for x := 0; x < m0.Width(); x++ {
+	for y := b0.Min.Y; y < b0.Max.Y; y++ {
+		for x := b0.Min.X; x < b0.Max.X; x++ {
 			r0, g0, b0, a0 := m0.At(x, y).RGBA()
 			r1, g1, b1, a1 := m1.At(x, y).RGBA()
 			if r0 != r1 || g0 != g1 || b0 != b1 || a0 != a1 {
-				return os.NewError(fmt.Sprintf("colors differ at (%d, %d): %v vs %v", x, y, m0.At(x, y), m1.At(x, y)))
+				return fmt.Errorf("colors differ at (%d, %d): %v vs %v", x, y, m0.At(x, y), m1.At(x, y))
 			}
 		}
 	}
@@ -67,3 +69,18 @@ func TestWriter(t *testing.T) {
 		}
 	}
 }
+
+func BenchmarkEncodePaletted(b *testing.B) {
+	b.StopTimer()
+	img := image.NewPaletted(640, 480,
+		[]image.Color{
+			image.RGBAColor{0, 0, 0, 255},
+			image.RGBAColor{255, 255, 255, 255},
+		})
+	b.StartTimer()
+	buffer := new(bytes.Buffer)
+	for i := 0; i < b.N; i++ {
+		buffer.Reset()
+		Encode(buffer, img)
+	}
+}