src/pkg/image/image.go - go - Git at Google

 // 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.

 // The image package implements a basic 2-D image library.
 package image

 // 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
 	// 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 of RGBAColor values.
 type RGBA struct {
 	// 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) Bounds() Rectangle { return p.Rect }

 func (p *RGBA) At(x, y int) Color {
 	if !p.Rect.Contains(Point{x, y}) {
 		return RGBAColor{}
 	}
 	return p.Pix[y*p.Stride+x]
 }

 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 {
 	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
 }

 // NewRGBA returns a new RGBA with the given width and height.
 func NewRGBA(w, h int) *RGBA {
 	buf := make([]RGBAColor, w*h)
 	return &RGBA{buf, w, Rectangle{ZP, Point{w, h}}}
 }

 // An RGBA64 is an in-memory image of RGBA64Color values.
 type RGBA64 struct {
 	// 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) Bounds() Rectangle { return p.Rect }

 func (p *RGBA64) At(x, y int) Color {
 	if !p.Rect.Contains(Point{x, y}) {
 		return RGBA64Color{}
 	}
 	return p.Pix[y*p.Stride+x]
 }

 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 {
 	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 {
 	pix := make([]RGBA64Color, w*h)
 	return &RGBA64{pix, w, Rectangle{ZP, Point{w, h}}}
 }

 // An NRGBA is an in-memory image of NRGBAColor values.
 type NRGBA struct {
 	// 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) Bounds() Rectangle { return p.Rect }

 func (p *NRGBA) At(x, y int) Color {
 	if !p.Rect.Contains(Point{x, y}) {
 		return NRGBAColor{}
 	}
 	return p.Pix[y*p.Stride+x]
 }

 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 {
 	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 {
 	pix := make([]NRGBAColor, w*h)
 	return &NRGBA{pix, w, Rectangle{ZP, Point{w, h}}}
 }

 // An NRGBA64 is an in-memory image of NRGBA64Color values.
 type NRGBA64 struct {
 	// 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) Bounds() Rectangle { return p.Rect }

 func (p *NRGBA64) At(x, y int) Color {
 	if !p.Rect.Contains(Point{x, y}) {
 		return NRGBA64Color{}
 	}
 	return p.Pix[y*p.Stride+x]
 }

 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 {
 	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 {
 	pix := make([]NRGBA64Color, w*h)
 	return &NRGBA64{pix, w, Rectangle{ZP, Point{w, h}}}
 }

 // An Alpha is an in-memory image of AlphaColor values.
 type Alpha struct {
 	// 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) Bounds() Rectangle { return p.Rect }

 func (p *Alpha) At(x, y int) Color {
 	if !p.Rect.Contains(Point{x, y}) {
 		return AlphaColor{}
 	}
 	return p.Pix[y*p.Stride+x]
 }

 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 {
 	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 {
 	pix := make([]AlphaColor, w*h)
 	return &Alpha{pix, w, Rectangle{ZP, Point{w, h}}}
 }

 // An Alpha16 is an in-memory image of Alpha16Color values.
 type Alpha16 struct {
 	// 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) Bounds() Rectangle { return p.Rect }

 func (p *Alpha16) At(x, y int) Color {
 	if !p.Rect.Contains(Point{x, y}) {
 		return Alpha16Color{}
 	}
 	return p.Pix[y*p.Stride+x]
 }

 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 {
 	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 {
 	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 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.
 type PalettedColorModel []Color

 func diff(a, b uint32) uint32 {
 	if a > b {
 		return a - b
 	}
 	return b - a
 }

 // Convert returns the palette color closest to c in Euclidean R,G,B space.
 func (p PalettedColorModel) Convert(c Color) Color {
 	if len(p) == 0 {
 		return nil
 	}
 	cr, cg, cb, _ := c.RGBA()
 	// Shift by 1 bit to avoid potential uint32 overflow in sum-squared-difference.
 	cr >>= 1
 	cg >>= 1
 	cb >>= 1
 	result := Color(nil)
 	bestSSD := uint32(1<<32 - 1)
 	for _, v := range p {
 		vr, vg, vb, _ := v.RGBA()
 		vr >>= 1
 		vg >>= 1
 		vb >>= 1
 		dr, dg, db := diff(cr, vr), diff(cg, vg), diff(cb, vb)
 		ssd := (dr * dr) + (dg * dg) + (db * db)
 		if ssd < bestSSD {
 			bestSSD = ssd
 			result = v
 		}
 	}
 	return result
 }

 // A Paletted is an in-memory image backed by a 2-D slice of uint8 values and a PalettedColorModel.
 type Paletted struct {
 	// 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) 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 p.Palette[p.Pix[y*p.Stride+x]]
 }

 func (p *Paletted) ColorIndexAt(x, y int) uint8 {
 	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) {
 	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.
 func (p *Paletted) Opaque() bool {
 	for _, c := range p.Palette {
 		_, _, _, a := c.RGBA()
 		if a != 0xffff {
 			return false
 		}
 	}
 	return true
 }

 // NewPaletted returns a new Paletted with the given width, height and palette.
 func NewPaletted(w, h int, m PalettedColorModel) *Paletted {
 	pix := make([]uint8, w*h)
 	return &Paletted{pix, w, Rectangle{ZP, Point{w, h}}, m}
 }
	// 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.

	// The image package implements a basic 2-D image library.
	package image

	// 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
	// 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 of RGBAColor values.
	type RGBA struct {
	// 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) Bounds() Rectangle { return p.Rect }

	func (p *RGBA) At(x, y int) Color {
	if !p.Rect.Contains(Point{x, y}) {
	return RGBAColor{}
	}
	return p.Pix[y*p.Stride+x]
	}

	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 {
	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
	}

	// NewRGBA returns a new RGBA with the given width and height.
	func NewRGBA(w, h int) *RGBA {
	buf := make([]RGBAColor, w*h)
	return &RGBA{buf, w, Rectangle{ZP, Point{w, h}}}
	}

	// An RGBA64 is an in-memory image of RGBA64Color values.
	type RGBA64 struct {
	// 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) Bounds() Rectangle { return p.Rect }

	func (p *RGBA64) At(x, y int) Color {
	if !p.Rect.Contains(Point{x, y}) {
	return RGBA64Color{}
	}
	return p.Pix[y*p.Stride+x]
	}

	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 {
	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 {
	pix := make([]RGBA64Color, w*h)
	return &RGBA64{pix, w, Rectangle{ZP, Point{w, h}}}
	}

	// An NRGBA is an in-memory image of NRGBAColor values.
	type NRGBA struct {
	// 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) Bounds() Rectangle { return p.Rect }

	func (p *NRGBA) At(x, y int) Color {
	if !p.Rect.Contains(Point{x, y}) {
	return NRGBAColor{}
	}
	return p.Pix[y*p.Stride+x]
	}

	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 {
	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 {
	pix := make([]NRGBAColor, w*h)
	return &NRGBA{pix, w, Rectangle{ZP, Point{w, h}}}
	}

	// An NRGBA64 is an in-memory image of NRGBA64Color values.
	type NRGBA64 struct {
	// 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) Bounds() Rectangle { return p.Rect }

	func (p *NRGBA64) At(x, y int) Color {
	if !p.Rect.Contains(Point{x, y}) {
	return NRGBA64Color{}
	}
	return p.Pix[y*p.Stride+x]
	}

	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 {
	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 {
	pix := make([]NRGBA64Color, w*h)
	return &NRGBA64{pix, w, Rectangle{ZP, Point{w, h}}}
	}

	// An Alpha is an in-memory image of AlphaColor values.
	type Alpha struct {
	// 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) Bounds() Rectangle { return p.Rect }

	func (p *Alpha) At(x, y int) Color {
	if !p.Rect.Contains(Point{x, y}) {
	return AlphaColor{}
	}
	return p.Pix[y*p.Stride+x]
	}

	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 {
	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 {
	pix := make([]AlphaColor, w*h)
	return &Alpha{pix, w, Rectangle{ZP, Point{w, h}}}
	}

	// An Alpha16 is an in-memory image of Alpha16Color values.
	type Alpha16 struct {
	// 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) Bounds() Rectangle { return p.Rect }

	func (p *Alpha16) At(x, y int) Color {
	if !p.Rect.Contains(Point{x, y}) {
	return Alpha16Color{}
	}
	return p.Pix[y*p.Stride+x]
	}

	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 {
	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 {
	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 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.
	type PalettedColorModel []Color

	func diff(a, b uint32) uint32 {
	if a > b {
	return a - b
	}
	return b - a
	}

	// Convert returns the palette color closest to c in Euclidean R,G,B space.
	func (p PalettedColorModel) Convert(c Color) Color {
	if len(p) == 0 {
	return nil
	}
	cr, cg, cb, _ := c.RGBA()
	// Shift by 1 bit to avoid potential uint32 overflow in sum-squared-difference.
	cr >>= 1
	cg >>= 1
	cb >>= 1
	result := Color(nil)
	bestSSD := uint32(1<<32 - 1)
	for _, v := range p {
	vr, vg, vb, _ := v.RGBA()
	vr >>= 1
	vg >>= 1
	vb >>= 1
	dr, dg, db := diff(cr, vr), diff(cg, vg), diff(cb, vb)
	ssd := (dr * dr) + (dg * dg) + (db * db)
	if ssd < bestSSD {
	bestSSD = ssd
	result = v
	}
	}
	return result
	}

	// A Paletted is an in-memory image backed by a 2-D slice of uint8 values and a PalettedColorModel.
	type Paletted struct {
	// 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) 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 p.Palette[p.Pix[y*p.Stride+x]]
	}

	func (p *Paletted) ColorIndexAt(x, y int) uint8 {
	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) {
	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.
	func (p *Paletted) Opaque() bool {
	for _, c := range p.Palette {
	_, _, _, a := c.RGBA()
	if a != 0xffff {
	return false
	}
	}
	return true
	}

	// NewPaletted returns a new Paletted with the given width, height and palette.
	func NewPaletted(w, h int, m PalettedColorModel) *Paletted {
	pix := make([]uint8, w*h)
	return &Paletted{pix, w, Rectangle{ZP, Point{w, h}}, m}
	}