1 files changed, 936 insertions, 0 deletions
diff --git a/src/image/image.go b/src/image/image.go
new file mode 100644
index 000000000..6b8e5c487
--- /dev/null
+++ b/src/image/image.go
@@ -0,0 +1,936 @@
+// Copyright 2009 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 implements a basic 2-D image library.
+//
+// The fundamental interface is called Image. An Image contains colors, which
+// are described in the image/color package.
+//
+// Values of the Image interface are created either by calling functions such
+// as NewRGBA and NewPaletted, or by calling Decode on an io.Reader containing
+// image data in a format such as GIF, JPEG or PNG. Decoding any particular
+// image format requires the prior registration of a decoder function.
+// Registration is typically automatic as a side effect of initializing that
+// format's package so that, to decode a PNG image, it suffices to have
+//	import _ "image/png"
+// in a program's main package. The _ means to import a package purely for its
+// initialization side effects.
+//
+// See "The Go image package" for more details:
+// http://golang.org/doc/articles/image_package.html
+package image
+
+import (
+	"image/color"
+)
+
+// Config holds an image's color model and dimensions.
+type Config struct {
+	ColorModel    color.Model
+	Width, Height int
+}
+
+// Image is a finite rectangular grid of color.Color values taken from a color
+// model.
+type Image interface {
+	// ColorModel returns the Image's color model.
+	ColorModel() color.Model
+	// 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.Color
+}
+
+// PalettedImage is an image whose colors may come from a limited palette.
+// If m is a PalettedImage and m.ColorModel() returns a PalettedColorModel p,
+// then m.At(x, y) should be equivalent to p[m.ColorIndexAt(x, y)]. If m's
+// color model is not a PalettedColorModel, then ColorIndexAt's behavior is
+// undefined.
+type PalettedImage interface {
+	// ColorIndexAt returns the palette index of the pixel at (x, y).
+	ColorIndexAt(x, y int) uint8
+	Image
+}
+
+// RGBA is an in-memory image whose At method returns color.RGBA values.
+type RGBA struct {
+	// Pix holds the image's pixels, in R, G, B, A order. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*4].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *RGBA) ColorModel() color.Model { return color.RGBAModel }
+
+func (p *RGBA) Bounds() Rectangle { return p.Rect }
+
+func (p *RGBA) At(x, y int) color.Color {
+	return p.RGBAAt(x, y)
+}
+
+func (p *RGBA) RGBAAt(x, y int) color.RGBA {
+	if !(Point{x, y}.In(p.Rect)) {
+		return color.RGBA{}
+	}
+	i := p.PixOffset(x, y)
+	return color.RGBA{p.Pix[i+0], p.Pix[i+1], p.Pix[i+2], p.Pix[i+3]}
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *RGBA) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*4
+}
+
+func (p *RGBA) Set(x, y int, c color.Color) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	c1 := color.RGBAModel.Convert(c).(color.RGBA)
+	p.Pix[i+0] = c1.R
+	p.Pix[i+1] = c1.G
+	p.Pix[i+2] = c1.B
+	p.Pix[i+3] = c1.A
+}
+
+func (p *RGBA) SetRGBA(x, y int, c color.RGBA) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i+0] = c.R
+	p.Pix[i+1] = c.G
+	p.Pix[i+2] = c.B
+	p.Pix[i+3] = c.A
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *RGBA) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &RGBA{}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &RGBA{
+		Pix:    p.Pix[i:],
+		Stride: p.Stride,
+		Rect:   r,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *RGBA) Opaque() bool {
+	if p.Rect.Empty() {
+		return true
+	}
+	i0, i1 := 3, p.Rect.Dx()*4
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for i := i0; i < i1; i += 4 {
+			if p.Pix[i] != 0xff {
+				return false
+			}
+		}
+		i0 += p.Stride
+		i1 += p.Stride
+	}
+	return true
+}
+
+// NewRGBA returns a new RGBA with the given bounds.
+func NewRGBA(r Rectangle) *RGBA {
+	w, h := r.Dx(), r.Dy()
+	buf := make([]uint8, 4*w*h)
+	return &RGBA{buf, 4 * w, r}
+}
+
+// RGBA64 is an in-memory image whose At method returns color.RGBA64 values.
+type RGBA64 struct {
+	// Pix holds the image's pixels, in R, G, B, A order and big-endian format. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*8].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *RGBA64) ColorModel() color.Model { return color.RGBA64Model }
+
+func (p *RGBA64) Bounds() Rectangle { return p.Rect }
+
+func (p *RGBA64) At(x, y int) color.Color {
+	return p.RGBA64At(x, y)
+}
+
+func (p *RGBA64) RGBA64At(x, y int) color.RGBA64 {
+	if !(Point{x, y}.In(p.Rect)) {
+		return color.RGBA64{}
+	}
+	i := p.PixOffset(x, y)
+	return color.RGBA64{
+		uint16(p.Pix[i+0])<<8 | uint16(p.Pix[i+1]),
+		uint16(p.Pix[i+2])<<8 | uint16(p.Pix[i+3]),
+		uint16(p.Pix[i+4])<<8 | uint16(p.Pix[i+5]),
+		uint16(p.Pix[i+6])<<8 | uint16(p.Pix[i+7]),
+	}
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *RGBA64) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*8
+}
+
+func (p *RGBA64) Set(x, y int, c color.Color) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	c1 := color.RGBA64Model.Convert(c).(color.RGBA64)
+	p.Pix[i+0] = uint8(c1.R >> 8)
+	p.Pix[i+1] = uint8(c1.R)
+	p.Pix[i+2] = uint8(c1.G >> 8)
+	p.Pix[i+3] = uint8(c1.G)
+	p.Pix[i+4] = uint8(c1.B >> 8)
+	p.Pix[i+5] = uint8(c1.B)
+	p.Pix[i+6] = uint8(c1.A >> 8)
+	p.Pix[i+7] = uint8(c1.A)
+}
+
+func (p *RGBA64) SetRGBA64(x, y int, c color.RGBA64) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i+0] = uint8(c.R >> 8)
+	p.Pix[i+1] = uint8(c.R)
+	p.Pix[i+2] = uint8(c.G >> 8)
+	p.Pix[i+3] = uint8(c.G)
+	p.Pix[i+4] = uint8(c.B >> 8)
+	p.Pix[i+5] = uint8(c.B)
+	p.Pix[i+6] = uint8(c.A >> 8)
+	p.Pix[i+7] = uint8(c.A)
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *RGBA64) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &RGBA64{}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &RGBA64{
+		Pix:    p.Pix[i:],
+		Stride: p.Stride,
+		Rect:   r,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *RGBA64) Opaque() bool {
+	if p.Rect.Empty() {
+		return true
+	}
+	i0, i1 := 6, p.Rect.Dx()*8
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for i := i0; i < i1; i += 8 {
+			if p.Pix[i+0] != 0xff || p.Pix[i+1] != 0xff {
+				return false
+			}
+		}
+		i0 += p.Stride
+		i1 += p.Stride
+	}
+	return true
+}
+
+// NewRGBA64 returns a new RGBA64 with the given bounds.
+func NewRGBA64(r Rectangle) *RGBA64 {
+	w, h := r.Dx(), r.Dy()
+	pix := make([]uint8, 8*w*h)
+	return &RGBA64{pix, 8 * w, r}
+}
+
+// NRGBA is an in-memory image whose At method returns color.NRGBA values.
+type NRGBA struct {
+	// Pix holds the image's pixels, in R, G, B, A order. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*4].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *NRGBA) ColorModel() color.Model { return color.NRGBAModel }
+
+func (p *NRGBA) Bounds() Rectangle { return p.Rect }
+
+func (p *NRGBA) At(x, y int) color.Color {
+	return p.NRGBAAt(x, y)
+}
+
+func (p *NRGBA) NRGBAAt(x, y int) color.NRGBA {
+	if !(Point{x, y}.In(p.Rect)) {
+		return color.NRGBA{}
+	}
+	i := p.PixOffset(x, y)
+	return color.NRGBA{p.Pix[i+0], p.Pix[i+1], p.Pix[i+2], p.Pix[i+3]}
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *NRGBA) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*4
+}
+
+func (p *NRGBA) Set(x, y int, c color.Color) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	c1 := color.NRGBAModel.Convert(c).(color.NRGBA)
+	p.Pix[i+0] = c1.R
+	p.Pix[i+1] = c1.G
+	p.Pix[i+2] = c1.B
+	p.Pix[i+3] = c1.A
+}
+
+func (p *NRGBA) SetNRGBA(x, y int, c color.NRGBA) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i+0] = c.R
+	p.Pix[i+1] = c.G
+	p.Pix[i+2] = c.B
+	p.Pix[i+3] = c.A
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *NRGBA) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &NRGBA{}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &NRGBA{
+		Pix:    p.Pix[i:],
+		Stride: p.Stride,
+		Rect:   r,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *NRGBA) Opaque() bool {
+	if p.Rect.Empty() {
+		return true
+	}
+	i0, i1 := 3, p.Rect.Dx()*4
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for i := i0; i < i1; i += 4 {
+			if p.Pix[i] != 0xff {
+				return false
+			}
+		}
+		i0 += p.Stride
+		i1 += p.Stride
+	}
+	return true
+}
+
+// NewNRGBA returns a new NRGBA with the given bounds.
+func NewNRGBA(r Rectangle) *NRGBA {
+	w, h := r.Dx(), r.Dy()
+	pix := make([]uint8, 4*w*h)
+	return &NRGBA{pix, 4 * w, r}
+}
+
+// NRGBA64 is an in-memory image whose At method returns color.NRGBA64 values.
+type NRGBA64 struct {
+	// Pix holds the image's pixels, in R, G, B, A order and big-endian format. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*8].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *NRGBA64) ColorModel() color.Model { return color.NRGBA64Model }
+
+func (p *NRGBA64) Bounds() Rectangle { return p.Rect }
+
+func (p *NRGBA64) At(x, y int) color.Color {
+	return p.NRGBA64At(x, y)
+}
+
+func (p *NRGBA64) NRGBA64At(x, y int) color.NRGBA64 {
+	if !(Point{x, y}.In(p.Rect)) {
+		return color.NRGBA64{}
+	}
+	i := p.PixOffset(x, y)
+	return color.NRGBA64{
+		uint16(p.Pix[i+0])<<8 | uint16(p.Pix[i+1]),
+		uint16(p.Pix[i+2])<<8 | uint16(p.Pix[i+3]),
+		uint16(p.Pix[i+4])<<8 | uint16(p.Pix[i+5]),
+		uint16(p.Pix[i+6])<<8 | uint16(p.Pix[i+7]),
+	}
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *NRGBA64) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*8
+}
+
+func (p *NRGBA64) Set(x, y int, c color.Color) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	c1 := color.NRGBA64Model.Convert(c).(color.NRGBA64)
+	p.Pix[i+0] = uint8(c1.R >> 8)
+	p.Pix[i+1] = uint8(c1.R)
+	p.Pix[i+2] = uint8(c1.G >> 8)
+	p.Pix[i+3] = uint8(c1.G)
+	p.Pix[i+4] = uint8(c1.B >> 8)
+	p.Pix[i+5] = uint8(c1.B)
+	p.Pix[i+6] = uint8(c1.A >> 8)
+	p.Pix[i+7] = uint8(c1.A)
+}
+
+func (p *NRGBA64) SetNRGBA64(x, y int, c color.NRGBA64) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i+0] = uint8(c.R >> 8)
+	p.Pix[i+1] = uint8(c.R)
+	p.Pix[i+2] = uint8(c.G >> 8)
+	p.Pix[i+3] = uint8(c.G)
+	p.Pix[i+4] = uint8(c.B >> 8)
+	p.Pix[i+5] = uint8(c.B)
+	p.Pix[i+6] = uint8(c.A >> 8)
+	p.Pix[i+7] = uint8(c.A)
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *NRGBA64) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &NRGBA64{}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &NRGBA64{
+		Pix:    p.Pix[i:],
+		Stride: p.Stride,
+		Rect:   r,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *NRGBA64) Opaque() bool {
+	if p.Rect.Empty() {
+		return true
+	}
+	i0, i1 := 6, p.Rect.Dx()*8
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for i := i0; i < i1; i += 8 {
+			if p.Pix[i+0] != 0xff || p.Pix[i+1] != 0xff {
+				return false
+			}
+		}
+		i0 += p.Stride
+		i1 += p.Stride
+	}
+	return true
+}
+
+// NewNRGBA64 returns a new NRGBA64 with the given bounds.
+func NewNRGBA64(r Rectangle) *NRGBA64 {
+	w, h := r.Dx(), r.Dy()
+	pix := make([]uint8, 8*w*h)
+	return &NRGBA64{pix, 8 * w, r}
+}
+
+// Alpha is an in-memory image whose At method returns color.Alpha values.
+type Alpha struct {
+	// Pix holds the image's pixels, as alpha values. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*1].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *Alpha) ColorModel() color.Model { return color.AlphaModel }
+
+func (p *Alpha) Bounds() Rectangle { return p.Rect }
+
+func (p *Alpha) At(x, y int) color.Color {
+	return p.AlphaAt(x, y)
+}
+
+func (p *Alpha) AlphaAt(x, y int) color.Alpha {
+	if !(Point{x, y}.In(p.Rect)) {
+		return color.Alpha{}
+	}
+	i := p.PixOffset(x, y)
+	return color.Alpha{p.Pix[i]}
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *Alpha) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*1
+}
+
+func (p *Alpha) Set(x, y int, c color.Color) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i] = color.AlphaModel.Convert(c).(color.Alpha).A
+}
+
+func (p *Alpha) SetAlpha(x, y int, c color.Alpha) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i] = c.A
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *Alpha) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &Alpha{}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &Alpha{
+		Pix:    p.Pix[i:],
+		Stride: p.Stride,
+		Rect:   r,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *Alpha) Opaque() bool {
+	if p.Rect.Empty() {
+		return true
+	}
+	i0, i1 := 0, p.Rect.Dx()
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for i := i0; i < i1; i++ {
+			if p.Pix[i] != 0xff {
+				return false
+			}
+		}
+		i0 += p.Stride
+		i1 += p.Stride
+	}
+	return true
+}
+
+// NewAlpha returns a new Alpha with the given bounds.
+func NewAlpha(r Rectangle) *Alpha {
+	w, h := r.Dx(), r.Dy()
+	pix := make([]uint8, 1*w*h)
+	return &Alpha{pix, 1 * w, r}
+}
+
+// Alpha16 is an in-memory image whose At method returns color.Alpha64 values.
+type Alpha16 struct {
+	// Pix holds the image's pixels, as alpha values in big-endian format. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*2].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *Alpha16) ColorModel() color.Model { return color.Alpha16Model }
+
+func (p *Alpha16) Bounds() Rectangle { return p.Rect }
+
+func (p *Alpha16) At(x, y int) color.Color {
+	return p.Alpha16At(x, y)
+}
+
+func (p *Alpha16) Alpha16At(x, y int) color.Alpha16 {
+	if !(Point{x, y}.In(p.Rect)) {
+		return color.Alpha16{}
+	}
+	i := p.PixOffset(x, y)
+	return color.Alpha16{uint16(p.Pix[i+0])<<8 | uint16(p.Pix[i+1])}
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *Alpha16) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*2
+}
+
+func (p *Alpha16) Set(x, y int, c color.Color) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	c1 := color.Alpha16Model.Convert(c).(color.Alpha16)
+	p.Pix[i+0] = uint8(c1.A >> 8)
+	p.Pix[i+1] = uint8(c1.A)
+}
+
+func (p *Alpha16) SetAlpha16(x, y int, c color.Alpha16) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i+0] = uint8(c.A >> 8)
+	p.Pix[i+1] = uint8(c.A)
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *Alpha16) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &Alpha16{}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &Alpha16{
+		Pix:    p.Pix[i:],
+		Stride: p.Stride,
+		Rect:   r,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *Alpha16) Opaque() bool {
+	if p.Rect.Empty() {
+		return true
+	}
+	i0, i1 := 0, p.Rect.Dx()*2
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for i := i0; i < i1; i += 2 {
+			if p.Pix[i+0] != 0xff || p.Pix[i+1] != 0xff {
+				return false
+			}
+		}
+		i0 += p.Stride
+		i1 += p.Stride
+	}
+	return true
+}
+
+// NewAlpha16 returns a new Alpha16 with the given bounds.
+func NewAlpha16(r Rectangle) *Alpha16 {
+	w, h := r.Dx(), r.Dy()
+	pix := make([]uint8, 2*w*h)
+	return &Alpha16{pix, 2 * w, r}
+}
+
+// Gray is an in-memory image whose At method returns color.Gray values.
+type Gray struct {
+	// Pix holds the image's pixels, as gray values. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*1].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *Gray) ColorModel() color.Model { return color.GrayModel }
+
+func (p *Gray) Bounds() Rectangle { return p.Rect }
+
+func (p *Gray) At(x, y int) color.Color {
+	return p.GrayAt(x, y)
+}
+
+func (p *Gray) GrayAt(x, y int) color.Gray {
+	if !(Point{x, y}.In(p.Rect)) {
+		return color.Gray{}
+	}
+	i := p.PixOffset(x, y)
+	return color.Gray{p.Pix[i]}
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *Gray) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*1
+}
+
+func (p *Gray) Set(x, y int, c color.Color) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i] = color.GrayModel.Convert(c).(color.Gray).Y
+}
+
+func (p *Gray) SetGray(x, y int, c color.Gray) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i] = c.Y
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *Gray) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &Gray{}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &Gray{
+		Pix:    p.Pix[i:],
+		Stride: p.Stride,
+		Rect:   r,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *Gray) Opaque() bool {
+	return true
+}
+
+// NewGray returns a new Gray with the given bounds.
+func NewGray(r Rectangle) *Gray {
+	w, h := r.Dx(), r.Dy()
+	pix := make([]uint8, 1*w*h)
+	return &Gray{pix, 1 * w, r}
+}
+
+// Gray16 is an in-memory image whose At method returns color.Gray16 values.
+type Gray16 struct {
+	// Pix holds the image's pixels, as gray values in big-endian format. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*2].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+}
+
+func (p *Gray16) ColorModel() color.Model { return color.Gray16Model }
+
+func (p *Gray16) Bounds() Rectangle { return p.Rect }
+
+func (p *Gray16) At(x, y int) color.Color {
+	return p.Gray16At(x, y)
+}
+
+func (p *Gray16) Gray16At(x, y int) color.Gray16 {
+	if !(Point{x, y}.In(p.Rect)) {
+		return color.Gray16{}
+	}
+	i := p.PixOffset(x, y)
+	return color.Gray16{uint16(p.Pix[i+0])<<8 | uint16(p.Pix[i+1])}
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *Gray16) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*2
+}
+
+func (p *Gray16) Set(x, y int, c color.Color) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	c1 := color.Gray16Model.Convert(c).(color.Gray16)
+	p.Pix[i+0] = uint8(c1.Y >> 8)
+	p.Pix[i+1] = uint8(c1.Y)
+}
+
+func (p *Gray16) SetGray16(x, y int, c color.Gray16) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i+0] = uint8(c.Y >> 8)
+	p.Pix[i+1] = uint8(c.Y)
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *Gray16) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &Gray16{}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &Gray16{
+		Pix:    p.Pix[i:],
+		Stride: p.Stride,
+		Rect:   r,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *Gray16) Opaque() bool {
+	return true
+}
+
+// NewGray16 returns a new Gray16 with the given bounds.
+func NewGray16(r Rectangle) *Gray16 {
+	w, h := r.Dx(), r.Dy()
+	pix := make([]uint8, 2*w*h)
+	return &Gray16{pix, 2 * w, r}
+}
+
+// Paletted is an in-memory image of uint8 indices into a given palette.
+type Paletted struct {
+	// Pix holds the image's pixels, as palette indices. The pixel at
+	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*1].
+	Pix []uint8
+	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
+	Stride int
+	// Rect is the image's bounds.
+	Rect Rectangle
+	// Palette is the image's palette.
+	Palette color.Palette
+}
+
+func (p *Paletted) ColorModel() color.Model { return p.Palette }
+
+func (p *Paletted) Bounds() Rectangle { return p.Rect }
+
+func (p *Paletted) At(x, y int) color.Color {
+	if len(p.Palette) == 0 {
+		return nil
+	}
+	if !(Point{x, y}.In(p.Rect)) {
+		return p.Palette[0]
+	}
+	i := p.PixOffset(x, y)
+	return p.Palette[p.Pix[i]]
+}
+
+// PixOffset returns the index of the first element of Pix that corresponds to
+// the pixel at (x, y).
+func (p *Paletted) PixOffset(x, y int) int {
+	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*1
+}
+
+func (p *Paletted) Set(x, y int, c color.Color) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i] = uint8(p.Palette.Index(c))
+}
+
+func (p *Paletted) ColorIndexAt(x, y int) uint8 {
+	if !(Point{x, y}.In(p.Rect)) {
+		return 0
+	}
+	i := p.PixOffset(x, y)
+	return p.Pix[i]
+}
+
+func (p *Paletted) SetColorIndex(x, y int, index uint8) {
+	if !(Point{x, y}.In(p.Rect)) {
+		return
+	}
+	i := p.PixOffset(x, y)
+	p.Pix[i] = index
+}
+
+// SubImage returns an image representing the portion of the image p visible
+// through r. The returned value shares pixels with the original image.
+func (p *Paletted) SubImage(r Rectangle) Image {
+	r = r.Intersect(p.Rect)
+	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
+	// either r1 or r2 if the intersection is empty. Without explicitly checking for
+	// this, the Pix[i:] expression below can panic.
+	if r.Empty() {
+		return &Paletted{
+			Palette: p.Palette,
+		}
+	}
+	i := p.PixOffset(r.Min.X, r.Min.Y)
+	return &Paletted{
+		Pix:     p.Pix[i:],
+		Stride:  p.Stride,
+		Rect:    p.Rect.Intersect(r),
+		Palette: p.Palette,
+	}
+}
+
+// Opaque scans the entire image and reports whether it is fully opaque.
+func (p *Paletted) Opaque() bool {
+	var present [256]bool
+	i0, i1 := 0, p.Rect.Dx()
+	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
+		for _, c := range p.Pix[i0:i1] {
+			present[c] = true
+		}
+		i0 += p.Stride
+		i1 += p.Stride
+	}
+	for i, c := range p.Palette {
+		if !present[i] {
+			continue
+		}
+		_, _, _, a := c.RGBA()
+		if a != 0xffff {
+			return false
+		}
+	}
+	return true
+}
+
+// NewPaletted returns a new Paletted with the given width, height and palette.
+func NewPaletted(r Rectangle, p color.Palette) *Paletted {
+	w, h := r.Dx(), r.Dy()
+	pix := make([]uint8, 1*w*h)
+	return &Paletted{pix, 1 * w, r, p}
+}