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Source file src/image/image.go

Documentation: image

  // 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:
  // https://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 color.Palette p,
  // then m.At(x, y) should be equivalent to p[m.ColorIndexAt(x, y)]. If m's
  // color model is not a color.Palette, 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 image 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 image 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 image 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 image 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 image 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.Alpha16 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 image 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 image 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 image 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}
  }
  
  // CMYK is an in-memory image whose At method returns color.CMYK values.
  type CMYK struct {
  	// Pix holds the image's pixels, in C, M, Y, K 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 *CMYK) ColorModel() color.Model { return color.CMYKModel }
  
  func (p *CMYK) Bounds() Rectangle { return p.Rect }
  
  func (p *CMYK) At(x, y int) color.Color {
  	return p.CMYKAt(x, y)
  }
  
  func (p *CMYK) CMYKAt(x, y int) color.CMYK {
  	if !(Point{x, y}.In(p.Rect)) {
  		return color.CMYK{}
  	}
  	i := p.PixOffset(x, y)
  	return color.CMYK{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 *CMYK) PixOffset(x, y int) int {
  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*4
  }
  
  func (p *CMYK) Set(x, y int, c color.Color) {
  	if !(Point{x, y}.In(p.Rect)) {
  		return
  	}
  	i := p.PixOffset(x, y)
  	c1 := color.CMYKModel.Convert(c).(color.CMYK)
  	p.Pix[i+0] = c1.C
  	p.Pix[i+1] = c1.M
  	p.Pix[i+2] = c1.Y
  	p.Pix[i+3] = c1.K
  }
  
  func (p *CMYK) SetCMYK(x, y int, c color.CMYK) {
  	if !(Point{x, y}.In(p.Rect)) {
  		return
  	}
  	i := p.PixOffset(x, y)
  	p.Pix[i+0] = c.C
  	p.Pix[i+1] = c.M
  	p.Pix[i+2] = c.Y
  	p.Pix[i+3] = c.K
  }
  
  // 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 *CMYK) 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 &CMYK{}
  	}
  	i := p.PixOffset(r.Min.X, r.Min.Y)
  	return &CMYK{
  		Pix:    p.Pix[i:],
  		Stride: p.Stride,
  		Rect:   r,
  	}
  }
  
  // Opaque scans the entire image and reports whether it is fully opaque.
  func (p *CMYK) Opaque() bool {
  	return true
  }
  
  // NewCMYK returns a new CMYK image with the given bounds.
  func NewCMYK(r Rectangle) *CMYK {
  	w, h := r.Dx(), r.Dy()
  	buf := make([]uint8, 4*w*h)
  	return &CMYK{buf, 4 * 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 image 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}
  }
  

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