Source file src/image/image.go

Documentation: image

		 1  // Copyright 2009 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  // Package image implements a basic 2-D image library.
		 6  //
		 7  // The fundamental interface is called Image. An Image contains colors, which
		 8  // are described in the image/color package.
		 9  //
		10  // Values of the Image interface are created either by calling functions such
		11  // as NewRGBA and NewPaletted, or by calling Decode on an io.Reader containing
		12  // image data in a format such as GIF, JPEG or PNG. Decoding any particular
		13  // image format requires the prior registration of a decoder function.
		14  // Registration is typically automatic as a side effect of initializing that
		15  // format's package so that, to decode a PNG image, it suffices to have
		16  //	import _ "image/png"
		17  // in a program's main package. The _ means to import a package purely for its
		18  // initialization side effects.
		19  //
		20  // See "The Go image package" for more details:
		21  // https://golang.org/doc/articles/image_package.html
		22  package image
		23  
		24  import (
		25  	"image/color"
		26  )
		27  
		28  // Config holds an image's color model and dimensions.
		29  type Config struct {
		30  	ColorModel		color.Model
		31  	Width, Height int
		32  }
		33  
		34  // Image is a finite rectangular grid of color.Color values taken from a color
		35  // model.
		36  type Image interface {
		37  	// ColorModel returns the Image's color model.
		38  	ColorModel() color.Model
		39  	// Bounds returns the domain for which At can return non-zero color.
		40  	// The bounds do not necessarily contain the point (0, 0).
		41  	Bounds() Rectangle
		42  	// At returns the color of the pixel at (x, y).
		43  	// At(Bounds().Min.X, Bounds().Min.Y) returns the upper-left pixel of the grid.
		44  	// At(Bounds().Max.X-1, Bounds().Max.Y-1) returns the lower-right one.
		45  	At(x, y int) color.Color
		46  }
		47  
		48  // RGBA64Image is an Image whose pixels can be converted directly to a
		49  // color.RGBA64.
		50  type RGBA64Image interface {
		51  	// RGBA64At returns the RGBA64 color of the pixel at (x, y). It is
		52  	// equivalent to calling At(x, y).RGBA() and converting the resulting
		53  	// 32-bit return values to a color.RGBA64, but it can avoid allocations
		54  	// from converting concrete color types to the color.Color interface type.
		55  	RGBA64At(x, y int) color.RGBA64
		56  	Image
		57  }
		58  
		59  // PalettedImage is an image whose colors may come from a limited palette.
		60  // If m is a PalettedImage and m.ColorModel() returns a color.Palette p,
		61  // then m.At(x, y) should be equivalent to p[m.ColorIndexAt(x, y)]. If m's
		62  // color model is not a color.Palette, then ColorIndexAt's behavior is
		63  // undefined.
		64  type PalettedImage interface {
		65  	// ColorIndexAt returns the palette index of the pixel at (x, y).
		66  	ColorIndexAt(x, y int) uint8
		67  	Image
		68  }
		69  
		70  // pixelBufferLength returns the length of the []uint8 typed Pix slice field
		71  // for the NewXxx functions. Conceptually, this is just (bpp * width * height),
		72  // but this function panics if at least one of those is negative or if the
		73  // computation would overflow the int type.
		74  //
		75  // This panics instead of returning an error because of backwards
		76  // compatibility. The NewXxx functions do not return an error.
		77  func pixelBufferLength(bytesPerPixel int, r Rectangle, imageTypeName string) int {
		78  	totalLength := mul3NonNeg(bytesPerPixel, r.Dx(), r.Dy())
		79  	if totalLength < 0 {
		80  		panic("image: New" + imageTypeName + " Rectangle has huge or negative dimensions")
		81  	}
		82  	return totalLength
		83  }
		84  
		85  // RGBA is an in-memory image whose At method returns color.RGBA values.
		86  type RGBA struct {
		87  	// Pix holds the image's pixels, in R, G, B, A order. The pixel at
		88  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*4].
		89  	Pix []uint8
		90  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
		91  	Stride int
		92  	// Rect is the image's bounds.
		93  	Rect Rectangle
		94  }
		95  
		96  func (p *RGBA) ColorModel() color.Model { return color.RGBAModel }
		97  
		98  func (p *RGBA) Bounds() Rectangle { return p.Rect }
		99  
	 100  func (p *RGBA) At(x, y int) color.Color {
	 101  	return p.RGBAAt(x, y)
	 102  }
	 103  
	 104  func (p *RGBA) RGBA64At(x, y int) color.RGBA64 {
	 105  	if !(Point{x, y}.In(p.Rect)) {
	 106  		return color.RGBA64{}
	 107  	}
	 108  	i := p.PixOffset(x, y)
	 109  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	 110  	r := uint16(s[0])
	 111  	g := uint16(s[1])
	 112  	b := uint16(s[2])
	 113  	a := uint16(s[3])
	 114  	return color.RGBA64{
	 115  		(r << 8) | r,
	 116  		(g << 8) | g,
	 117  		(b << 8) | b,
	 118  		(a << 8) | a,
	 119  	}
	 120  }
	 121  
	 122  func (p *RGBA) RGBAAt(x, y int) color.RGBA {
	 123  	if !(Point{x, y}.In(p.Rect)) {
	 124  		return color.RGBA{}
	 125  	}
	 126  	i := p.PixOffset(x, y)
	 127  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	 128  	return color.RGBA{s[0], s[1], s[2], s[3]}
	 129  }
	 130  
	 131  // PixOffset returns the index of the first element of Pix that corresponds to
	 132  // the pixel at (x, y).
	 133  func (p *RGBA) PixOffset(x, y int) int {
	 134  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*4
	 135  }
	 136  
	 137  func (p *RGBA) Set(x, y int, c color.Color) {
	 138  	if !(Point{x, y}.In(p.Rect)) {
	 139  		return
	 140  	}
	 141  	i := p.PixOffset(x, y)
	 142  	c1 := color.RGBAModel.Convert(c).(color.RGBA)
	 143  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	 144  	s[0] = c1.R
	 145  	s[1] = c1.G
	 146  	s[2] = c1.B
	 147  	s[3] = c1.A
	 148  }
	 149  
	 150  func (p *RGBA) SetRGBA64(x, y int, c color.RGBA64) {
	 151  	if !(Point{x, y}.In(p.Rect)) {
	 152  		return
	 153  	}
	 154  	i := p.PixOffset(x, y)
	 155  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	 156  	s[0] = uint8(c.R >> 8)
	 157  	s[1] = uint8(c.G >> 8)
	 158  	s[2] = uint8(c.B >> 8)
	 159  	s[3] = uint8(c.A >> 8)
	 160  }
	 161  
	 162  func (p *RGBA) SetRGBA(x, y int, c color.RGBA) {
	 163  	if !(Point{x, y}.In(p.Rect)) {
	 164  		return
	 165  	}
	 166  	i := p.PixOffset(x, y)
	 167  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	 168  	s[0] = c.R
	 169  	s[1] = c.G
	 170  	s[2] = c.B
	 171  	s[3] = c.A
	 172  }
	 173  
	 174  // SubImage returns an image representing the portion of the image p visible
	 175  // through r. The returned value shares pixels with the original image.
	 176  func (p *RGBA) SubImage(r Rectangle) Image {
	 177  	r = r.Intersect(p.Rect)
	 178  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	 179  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	 180  	// this, the Pix[i:] expression below can panic.
	 181  	if r.Empty() {
	 182  		return &RGBA{}
	 183  	}
	 184  	i := p.PixOffset(r.Min.X, r.Min.Y)
	 185  	return &RGBA{
	 186  		Pix:		p.Pix[i:],
	 187  		Stride: p.Stride,
	 188  		Rect:	 r,
	 189  	}
	 190  }
	 191  
	 192  // Opaque scans the entire image and reports whether it is fully opaque.
	 193  func (p *RGBA) Opaque() bool {
	 194  	if p.Rect.Empty() {
	 195  		return true
	 196  	}
	 197  	i0, i1 := 3, p.Rect.Dx()*4
	 198  	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
	 199  		for i := i0; i < i1; i += 4 {
	 200  			if p.Pix[i] != 0xff {
	 201  				return false
	 202  			}
	 203  		}
	 204  		i0 += p.Stride
	 205  		i1 += p.Stride
	 206  	}
	 207  	return true
	 208  }
	 209  
	 210  // NewRGBA returns a new RGBA image with the given bounds.
	 211  func NewRGBA(r Rectangle) *RGBA {
	 212  	return &RGBA{
	 213  		Pix:		make([]uint8, pixelBufferLength(4, r, "RGBA")),
	 214  		Stride: 4 * r.Dx(),
	 215  		Rect:	 r,
	 216  	}
	 217  }
	 218  
	 219  // RGBA64 is an in-memory image whose At method returns color.RGBA64 values.
	 220  type RGBA64 struct {
	 221  	// Pix holds the image's pixels, in R, G, B, A order and big-endian format. The pixel at
	 222  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*8].
	 223  	Pix []uint8
	 224  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
	 225  	Stride int
	 226  	// Rect is the image's bounds.
	 227  	Rect Rectangle
	 228  }
	 229  
	 230  func (p *RGBA64) ColorModel() color.Model { return color.RGBA64Model }
	 231  
	 232  func (p *RGBA64) Bounds() Rectangle { return p.Rect }
	 233  
	 234  func (p *RGBA64) At(x, y int) color.Color {
	 235  	return p.RGBA64At(x, y)
	 236  }
	 237  
	 238  func (p *RGBA64) RGBA64At(x, y int) color.RGBA64 {
	 239  	if !(Point{x, y}.In(p.Rect)) {
	 240  		return color.RGBA64{}
	 241  	}
	 242  	i := p.PixOffset(x, y)
	 243  	s := p.Pix[i : i+8 : i+8] // Small cap improves performance, see https://golang.org/issue/27857
	 244  	return color.RGBA64{
	 245  		uint16(s[0])<<8 | uint16(s[1]),
	 246  		uint16(s[2])<<8 | uint16(s[3]),
	 247  		uint16(s[4])<<8 | uint16(s[5]),
	 248  		uint16(s[6])<<8 | uint16(s[7]),
	 249  	}
	 250  }
	 251  
	 252  // PixOffset returns the index of the first element of Pix that corresponds to
	 253  // the pixel at (x, y).
	 254  func (p *RGBA64) PixOffset(x, y int) int {
	 255  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*8
	 256  }
	 257  
	 258  func (p *RGBA64) Set(x, y int, c color.Color) {
	 259  	if !(Point{x, y}.In(p.Rect)) {
	 260  		return
	 261  	}
	 262  	i := p.PixOffset(x, y)
	 263  	c1 := color.RGBA64Model.Convert(c).(color.RGBA64)
	 264  	s := p.Pix[i : i+8 : i+8] // Small cap improves performance, see https://golang.org/issue/27857
	 265  	s[0] = uint8(c1.R >> 8)
	 266  	s[1] = uint8(c1.R)
	 267  	s[2] = uint8(c1.G >> 8)
	 268  	s[3] = uint8(c1.G)
	 269  	s[4] = uint8(c1.B >> 8)
	 270  	s[5] = uint8(c1.B)
	 271  	s[6] = uint8(c1.A >> 8)
	 272  	s[7] = uint8(c1.A)
	 273  }
	 274  
	 275  func (p *RGBA64) SetRGBA64(x, y int, c color.RGBA64) {
	 276  	if !(Point{x, y}.In(p.Rect)) {
	 277  		return
	 278  	}
	 279  	i := p.PixOffset(x, y)
	 280  	s := p.Pix[i : i+8 : i+8] // Small cap improves performance, see https://golang.org/issue/27857
	 281  	s[0] = uint8(c.R >> 8)
	 282  	s[1] = uint8(c.R)
	 283  	s[2] = uint8(c.G >> 8)
	 284  	s[3] = uint8(c.G)
	 285  	s[4] = uint8(c.B >> 8)
	 286  	s[5] = uint8(c.B)
	 287  	s[6] = uint8(c.A >> 8)
	 288  	s[7] = uint8(c.A)
	 289  }
	 290  
	 291  // SubImage returns an image representing the portion of the image p visible
	 292  // through r. The returned value shares pixels with the original image.
	 293  func (p *RGBA64) SubImage(r Rectangle) Image {
	 294  	r = r.Intersect(p.Rect)
	 295  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	 296  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	 297  	// this, the Pix[i:] expression below can panic.
	 298  	if r.Empty() {
	 299  		return &RGBA64{}
	 300  	}
	 301  	i := p.PixOffset(r.Min.X, r.Min.Y)
	 302  	return &RGBA64{
	 303  		Pix:		p.Pix[i:],
	 304  		Stride: p.Stride,
	 305  		Rect:	 r,
	 306  	}
	 307  }
	 308  
	 309  // Opaque scans the entire image and reports whether it is fully opaque.
	 310  func (p *RGBA64) Opaque() bool {
	 311  	if p.Rect.Empty() {
	 312  		return true
	 313  	}
	 314  	i0, i1 := 6, p.Rect.Dx()*8
	 315  	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
	 316  		for i := i0; i < i1; i += 8 {
	 317  			if p.Pix[i+0] != 0xff || p.Pix[i+1] != 0xff {
	 318  				return false
	 319  			}
	 320  		}
	 321  		i0 += p.Stride
	 322  		i1 += p.Stride
	 323  	}
	 324  	return true
	 325  }
	 326  
	 327  // NewRGBA64 returns a new RGBA64 image with the given bounds.
	 328  func NewRGBA64(r Rectangle) *RGBA64 {
	 329  	return &RGBA64{
	 330  		Pix:		make([]uint8, pixelBufferLength(8, r, "RGBA64")),
	 331  		Stride: 8 * r.Dx(),
	 332  		Rect:	 r,
	 333  	}
	 334  }
	 335  
	 336  // NRGBA is an in-memory image whose At method returns color.NRGBA values.
	 337  type NRGBA struct {
	 338  	// Pix holds the image's pixels, in R, G, B, A order. The pixel at
	 339  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*4].
	 340  	Pix []uint8
	 341  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
	 342  	Stride int
	 343  	// Rect is the image's bounds.
	 344  	Rect Rectangle
	 345  }
	 346  
	 347  func (p *NRGBA) ColorModel() color.Model { return color.NRGBAModel }
	 348  
	 349  func (p *NRGBA) Bounds() Rectangle { return p.Rect }
	 350  
	 351  func (p *NRGBA) At(x, y int) color.Color {
	 352  	return p.NRGBAAt(x, y)
	 353  }
	 354  
	 355  func (p *NRGBA) RGBA64At(x, y int) color.RGBA64 {
	 356  	r, g, b, a := p.NRGBAAt(x, y).RGBA()
	 357  	return color.RGBA64{uint16(r), uint16(g), uint16(b), uint16(a)}
	 358  }
	 359  
	 360  func (p *NRGBA) NRGBAAt(x, y int) color.NRGBA {
	 361  	if !(Point{x, y}.In(p.Rect)) {
	 362  		return color.NRGBA{}
	 363  	}
	 364  	i := p.PixOffset(x, y)
	 365  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	 366  	return color.NRGBA{s[0], s[1], s[2], s[3]}
	 367  }
	 368  
	 369  // PixOffset returns the index of the first element of Pix that corresponds to
	 370  // the pixel at (x, y).
	 371  func (p *NRGBA) PixOffset(x, y int) int {
	 372  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*4
	 373  }
	 374  
	 375  func (p *NRGBA) Set(x, y int, c color.Color) {
	 376  	if !(Point{x, y}.In(p.Rect)) {
	 377  		return
	 378  	}
	 379  	i := p.PixOffset(x, y)
	 380  	c1 := color.NRGBAModel.Convert(c).(color.NRGBA)
	 381  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	 382  	s[0] = c1.R
	 383  	s[1] = c1.G
	 384  	s[2] = c1.B
	 385  	s[3] = c1.A
	 386  }
	 387  
	 388  func (p *NRGBA) SetRGBA64(x, y int, c color.RGBA64) {
	 389  	if !(Point{x, y}.In(p.Rect)) {
	 390  		return
	 391  	}
	 392  	r, g, b, a := uint32(c.R), uint32(c.G), uint32(c.B), uint32(c.A)
	 393  	if (a != 0) && (a != 0xffff) {
	 394  		r = (r * 0xffff) / a
	 395  		g = (g * 0xffff) / a
	 396  		b = (b * 0xffff) / a
	 397  	}
	 398  	i := p.PixOffset(x, y)
	 399  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	 400  	s[0] = uint8(r >> 8)
	 401  	s[1] = uint8(g >> 8)
	 402  	s[2] = uint8(b >> 8)
	 403  	s[3] = uint8(a >> 8)
	 404  }
	 405  
	 406  func (p *NRGBA) SetNRGBA(x, y int, c color.NRGBA) {
	 407  	if !(Point{x, y}.In(p.Rect)) {
	 408  		return
	 409  	}
	 410  	i := p.PixOffset(x, y)
	 411  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	 412  	s[0] = c.R
	 413  	s[1] = c.G
	 414  	s[2] = c.B
	 415  	s[3] = c.A
	 416  }
	 417  
	 418  // SubImage returns an image representing the portion of the image p visible
	 419  // through r. The returned value shares pixels with the original image.
	 420  func (p *NRGBA) SubImage(r Rectangle) Image {
	 421  	r = r.Intersect(p.Rect)
	 422  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	 423  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	 424  	// this, the Pix[i:] expression below can panic.
	 425  	if r.Empty() {
	 426  		return &NRGBA{}
	 427  	}
	 428  	i := p.PixOffset(r.Min.X, r.Min.Y)
	 429  	return &NRGBA{
	 430  		Pix:		p.Pix[i:],
	 431  		Stride: p.Stride,
	 432  		Rect:	 r,
	 433  	}
	 434  }
	 435  
	 436  // Opaque scans the entire image and reports whether it is fully opaque.
	 437  func (p *NRGBA) Opaque() bool {
	 438  	if p.Rect.Empty() {
	 439  		return true
	 440  	}
	 441  	i0, i1 := 3, p.Rect.Dx()*4
	 442  	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
	 443  		for i := i0; i < i1; i += 4 {
	 444  			if p.Pix[i] != 0xff {
	 445  				return false
	 446  			}
	 447  		}
	 448  		i0 += p.Stride
	 449  		i1 += p.Stride
	 450  	}
	 451  	return true
	 452  }
	 453  
	 454  // NewNRGBA returns a new NRGBA image with the given bounds.
	 455  func NewNRGBA(r Rectangle) *NRGBA {
	 456  	return &NRGBA{
	 457  		Pix:		make([]uint8, pixelBufferLength(4, r, "NRGBA")),
	 458  		Stride: 4 * r.Dx(),
	 459  		Rect:	 r,
	 460  	}
	 461  }
	 462  
	 463  // NRGBA64 is an in-memory image whose At method returns color.NRGBA64 values.
	 464  type NRGBA64 struct {
	 465  	// Pix holds the image's pixels, in R, G, B, A order and big-endian format. The pixel at
	 466  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*8].
	 467  	Pix []uint8
	 468  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
	 469  	Stride int
	 470  	// Rect is the image's bounds.
	 471  	Rect Rectangle
	 472  }
	 473  
	 474  func (p *NRGBA64) ColorModel() color.Model { return color.NRGBA64Model }
	 475  
	 476  func (p *NRGBA64) Bounds() Rectangle { return p.Rect }
	 477  
	 478  func (p *NRGBA64) At(x, y int) color.Color {
	 479  	return p.NRGBA64At(x, y)
	 480  }
	 481  
	 482  func (p *NRGBA64) RGBA64At(x, y int) color.RGBA64 {
	 483  	r, g, b, a := p.NRGBA64At(x, y).RGBA()
	 484  	return color.RGBA64{uint16(r), uint16(g), uint16(b), uint16(a)}
	 485  }
	 486  
	 487  func (p *NRGBA64) NRGBA64At(x, y int) color.NRGBA64 {
	 488  	if !(Point{x, y}.In(p.Rect)) {
	 489  		return color.NRGBA64{}
	 490  	}
	 491  	i := p.PixOffset(x, y)
	 492  	s := p.Pix[i : i+8 : i+8] // Small cap improves performance, see https://golang.org/issue/27857
	 493  	return color.NRGBA64{
	 494  		uint16(s[0])<<8 | uint16(s[1]),
	 495  		uint16(s[2])<<8 | uint16(s[3]),
	 496  		uint16(s[4])<<8 | uint16(s[5]),
	 497  		uint16(s[6])<<8 | uint16(s[7]),
	 498  	}
	 499  }
	 500  
	 501  // PixOffset returns the index of the first element of Pix that corresponds to
	 502  // the pixel at (x, y).
	 503  func (p *NRGBA64) PixOffset(x, y int) int {
	 504  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*8
	 505  }
	 506  
	 507  func (p *NRGBA64) Set(x, y int, c color.Color) {
	 508  	if !(Point{x, y}.In(p.Rect)) {
	 509  		return
	 510  	}
	 511  	i := p.PixOffset(x, y)
	 512  	c1 := color.NRGBA64Model.Convert(c).(color.NRGBA64)
	 513  	s := p.Pix[i : i+8 : i+8] // Small cap improves performance, see https://golang.org/issue/27857
	 514  	s[0] = uint8(c1.R >> 8)
	 515  	s[1] = uint8(c1.R)
	 516  	s[2] = uint8(c1.G >> 8)
	 517  	s[3] = uint8(c1.G)
	 518  	s[4] = uint8(c1.B >> 8)
	 519  	s[5] = uint8(c1.B)
	 520  	s[6] = uint8(c1.A >> 8)
	 521  	s[7] = uint8(c1.A)
	 522  }
	 523  
	 524  func (p *NRGBA64) SetRGBA64(x, y int, c color.RGBA64) {
	 525  	if !(Point{x, y}.In(p.Rect)) {
	 526  		return
	 527  	}
	 528  	r, g, b, a := uint32(c.R), uint32(c.G), uint32(c.B), uint32(c.A)
	 529  	if (a != 0) && (a != 0xffff) {
	 530  		r = (r * 0xffff) / a
	 531  		g = (g * 0xffff) / a
	 532  		b = (b * 0xffff) / a
	 533  	}
	 534  	i := p.PixOffset(x, y)
	 535  	s := p.Pix[i : i+8 : i+8] // Small cap improves performance, see https://golang.org/issue/27857
	 536  	s[0] = uint8(r >> 8)
	 537  	s[1] = uint8(r)
	 538  	s[2] = uint8(g >> 8)
	 539  	s[3] = uint8(g)
	 540  	s[4] = uint8(b >> 8)
	 541  	s[5] = uint8(b)
	 542  	s[6] = uint8(a >> 8)
	 543  	s[7] = uint8(a)
	 544  }
	 545  
	 546  func (p *NRGBA64) SetNRGBA64(x, y int, c color.NRGBA64) {
	 547  	if !(Point{x, y}.In(p.Rect)) {
	 548  		return
	 549  	}
	 550  	i := p.PixOffset(x, y)
	 551  	s := p.Pix[i : i+8 : i+8] // Small cap improves performance, see https://golang.org/issue/27857
	 552  	s[0] = uint8(c.R >> 8)
	 553  	s[1] = uint8(c.R)
	 554  	s[2] = uint8(c.G >> 8)
	 555  	s[3] = uint8(c.G)
	 556  	s[4] = uint8(c.B >> 8)
	 557  	s[5] = uint8(c.B)
	 558  	s[6] = uint8(c.A >> 8)
	 559  	s[7] = uint8(c.A)
	 560  }
	 561  
	 562  // SubImage returns an image representing the portion of the image p visible
	 563  // through r. The returned value shares pixels with the original image.
	 564  func (p *NRGBA64) SubImage(r Rectangle) Image {
	 565  	r = r.Intersect(p.Rect)
	 566  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	 567  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	 568  	// this, the Pix[i:] expression below can panic.
	 569  	if r.Empty() {
	 570  		return &NRGBA64{}
	 571  	}
	 572  	i := p.PixOffset(r.Min.X, r.Min.Y)
	 573  	return &NRGBA64{
	 574  		Pix:		p.Pix[i:],
	 575  		Stride: p.Stride,
	 576  		Rect:	 r,
	 577  	}
	 578  }
	 579  
	 580  // Opaque scans the entire image and reports whether it is fully opaque.
	 581  func (p *NRGBA64) Opaque() bool {
	 582  	if p.Rect.Empty() {
	 583  		return true
	 584  	}
	 585  	i0, i1 := 6, p.Rect.Dx()*8
	 586  	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
	 587  		for i := i0; i < i1; i += 8 {
	 588  			if p.Pix[i+0] != 0xff || p.Pix[i+1] != 0xff {
	 589  				return false
	 590  			}
	 591  		}
	 592  		i0 += p.Stride
	 593  		i1 += p.Stride
	 594  	}
	 595  	return true
	 596  }
	 597  
	 598  // NewNRGBA64 returns a new NRGBA64 image with the given bounds.
	 599  func NewNRGBA64(r Rectangle) *NRGBA64 {
	 600  	return &NRGBA64{
	 601  		Pix:		make([]uint8, pixelBufferLength(8, r, "NRGBA64")),
	 602  		Stride: 8 * r.Dx(),
	 603  		Rect:	 r,
	 604  	}
	 605  }
	 606  
	 607  // Alpha is an in-memory image whose At method returns color.Alpha values.
	 608  type Alpha struct {
	 609  	// Pix holds the image's pixels, as alpha values. The pixel at
	 610  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*1].
	 611  	Pix []uint8
	 612  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
	 613  	Stride int
	 614  	// Rect is the image's bounds.
	 615  	Rect Rectangle
	 616  }
	 617  
	 618  func (p *Alpha) ColorModel() color.Model { return color.AlphaModel }
	 619  
	 620  func (p *Alpha) Bounds() Rectangle { return p.Rect }
	 621  
	 622  func (p *Alpha) At(x, y int) color.Color {
	 623  	return p.AlphaAt(x, y)
	 624  }
	 625  
	 626  func (p *Alpha) RGBA64At(x, y int) color.RGBA64 {
	 627  	a := uint16(p.AlphaAt(x, y).A)
	 628  	a |= a << 8
	 629  	return color.RGBA64{a, a, a, a}
	 630  }
	 631  
	 632  func (p *Alpha) AlphaAt(x, y int) color.Alpha {
	 633  	if !(Point{x, y}.In(p.Rect)) {
	 634  		return color.Alpha{}
	 635  	}
	 636  	i := p.PixOffset(x, y)
	 637  	return color.Alpha{p.Pix[i]}
	 638  }
	 639  
	 640  // PixOffset returns the index of the first element of Pix that corresponds to
	 641  // the pixel at (x, y).
	 642  func (p *Alpha) PixOffset(x, y int) int {
	 643  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*1
	 644  }
	 645  
	 646  func (p *Alpha) Set(x, y int, c color.Color) {
	 647  	if !(Point{x, y}.In(p.Rect)) {
	 648  		return
	 649  	}
	 650  	i := p.PixOffset(x, y)
	 651  	p.Pix[i] = color.AlphaModel.Convert(c).(color.Alpha).A
	 652  }
	 653  
	 654  func (p *Alpha) SetRGBA64(x, y int, c color.RGBA64) {
	 655  	if !(Point{x, y}.In(p.Rect)) {
	 656  		return
	 657  	}
	 658  	i := p.PixOffset(x, y)
	 659  	p.Pix[i] = uint8(c.A >> 8)
	 660  }
	 661  
	 662  func (p *Alpha) SetAlpha(x, y int, c color.Alpha) {
	 663  	if !(Point{x, y}.In(p.Rect)) {
	 664  		return
	 665  	}
	 666  	i := p.PixOffset(x, y)
	 667  	p.Pix[i] = c.A
	 668  }
	 669  
	 670  // SubImage returns an image representing the portion of the image p visible
	 671  // through r. The returned value shares pixels with the original image.
	 672  func (p *Alpha) SubImage(r Rectangle) Image {
	 673  	r = r.Intersect(p.Rect)
	 674  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	 675  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	 676  	// this, the Pix[i:] expression below can panic.
	 677  	if r.Empty() {
	 678  		return &Alpha{}
	 679  	}
	 680  	i := p.PixOffset(r.Min.X, r.Min.Y)
	 681  	return &Alpha{
	 682  		Pix:		p.Pix[i:],
	 683  		Stride: p.Stride,
	 684  		Rect:	 r,
	 685  	}
	 686  }
	 687  
	 688  // Opaque scans the entire image and reports whether it is fully opaque.
	 689  func (p *Alpha) Opaque() bool {
	 690  	if p.Rect.Empty() {
	 691  		return true
	 692  	}
	 693  	i0, i1 := 0, p.Rect.Dx()
	 694  	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
	 695  		for i := i0; i < i1; i++ {
	 696  			if p.Pix[i] != 0xff {
	 697  				return false
	 698  			}
	 699  		}
	 700  		i0 += p.Stride
	 701  		i1 += p.Stride
	 702  	}
	 703  	return true
	 704  }
	 705  
	 706  // NewAlpha returns a new Alpha image with the given bounds.
	 707  func NewAlpha(r Rectangle) *Alpha {
	 708  	return &Alpha{
	 709  		Pix:		make([]uint8, pixelBufferLength(1, r, "Alpha")),
	 710  		Stride: 1 * r.Dx(),
	 711  		Rect:	 r,
	 712  	}
	 713  }
	 714  
	 715  // Alpha16 is an in-memory image whose At method returns color.Alpha16 values.
	 716  type Alpha16 struct {
	 717  	// Pix holds the image's pixels, as alpha values in big-endian format. The pixel at
	 718  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*2].
	 719  	Pix []uint8
	 720  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
	 721  	Stride int
	 722  	// Rect is the image's bounds.
	 723  	Rect Rectangle
	 724  }
	 725  
	 726  func (p *Alpha16) ColorModel() color.Model { return color.Alpha16Model }
	 727  
	 728  func (p *Alpha16) Bounds() Rectangle { return p.Rect }
	 729  
	 730  func (p *Alpha16) At(x, y int) color.Color {
	 731  	return p.Alpha16At(x, y)
	 732  }
	 733  
	 734  func (p *Alpha16) RGBA64At(x, y int) color.RGBA64 {
	 735  	a := p.Alpha16At(x, y).A
	 736  	return color.RGBA64{a, a, a, a}
	 737  }
	 738  
	 739  func (p *Alpha16) Alpha16At(x, y int) color.Alpha16 {
	 740  	if !(Point{x, y}.In(p.Rect)) {
	 741  		return color.Alpha16{}
	 742  	}
	 743  	i := p.PixOffset(x, y)
	 744  	return color.Alpha16{uint16(p.Pix[i+0])<<8 | uint16(p.Pix[i+1])}
	 745  }
	 746  
	 747  // PixOffset returns the index of the first element of Pix that corresponds to
	 748  // the pixel at (x, y).
	 749  func (p *Alpha16) PixOffset(x, y int) int {
	 750  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*2
	 751  }
	 752  
	 753  func (p *Alpha16) Set(x, y int, c color.Color) {
	 754  	if !(Point{x, y}.In(p.Rect)) {
	 755  		return
	 756  	}
	 757  	i := p.PixOffset(x, y)
	 758  	c1 := color.Alpha16Model.Convert(c).(color.Alpha16)
	 759  	p.Pix[i+0] = uint8(c1.A >> 8)
	 760  	p.Pix[i+1] = uint8(c1.A)
	 761  }
	 762  
	 763  func (p *Alpha16) SetRGBA64(x, y int, c color.RGBA64) {
	 764  	if !(Point{x, y}.In(p.Rect)) {
	 765  		return
	 766  	}
	 767  	i := p.PixOffset(x, y)
	 768  	p.Pix[i+0] = uint8(c.A >> 8)
	 769  	p.Pix[i+1] = uint8(c.A)
	 770  }
	 771  
	 772  func (p *Alpha16) SetAlpha16(x, y int, c color.Alpha16) {
	 773  	if !(Point{x, y}.In(p.Rect)) {
	 774  		return
	 775  	}
	 776  	i := p.PixOffset(x, y)
	 777  	p.Pix[i+0] = uint8(c.A >> 8)
	 778  	p.Pix[i+1] = uint8(c.A)
	 779  }
	 780  
	 781  // SubImage returns an image representing the portion of the image p visible
	 782  // through r. The returned value shares pixels with the original image.
	 783  func (p *Alpha16) SubImage(r Rectangle) Image {
	 784  	r = r.Intersect(p.Rect)
	 785  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	 786  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	 787  	// this, the Pix[i:] expression below can panic.
	 788  	if r.Empty() {
	 789  		return &Alpha16{}
	 790  	}
	 791  	i := p.PixOffset(r.Min.X, r.Min.Y)
	 792  	return &Alpha16{
	 793  		Pix:		p.Pix[i:],
	 794  		Stride: p.Stride,
	 795  		Rect:	 r,
	 796  	}
	 797  }
	 798  
	 799  // Opaque scans the entire image and reports whether it is fully opaque.
	 800  func (p *Alpha16) Opaque() bool {
	 801  	if p.Rect.Empty() {
	 802  		return true
	 803  	}
	 804  	i0, i1 := 0, p.Rect.Dx()*2
	 805  	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
	 806  		for i := i0; i < i1; i += 2 {
	 807  			if p.Pix[i+0] != 0xff || p.Pix[i+1] != 0xff {
	 808  				return false
	 809  			}
	 810  		}
	 811  		i0 += p.Stride
	 812  		i1 += p.Stride
	 813  	}
	 814  	return true
	 815  }
	 816  
	 817  // NewAlpha16 returns a new Alpha16 image with the given bounds.
	 818  func NewAlpha16(r Rectangle) *Alpha16 {
	 819  	return &Alpha16{
	 820  		Pix:		make([]uint8, pixelBufferLength(2, r, "Alpha16")),
	 821  		Stride: 2 * r.Dx(),
	 822  		Rect:	 r,
	 823  	}
	 824  }
	 825  
	 826  // Gray is an in-memory image whose At method returns color.Gray values.
	 827  type Gray struct {
	 828  	// Pix holds the image's pixels, as gray values. The pixel at
	 829  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*1].
	 830  	Pix []uint8
	 831  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
	 832  	Stride int
	 833  	// Rect is the image's bounds.
	 834  	Rect Rectangle
	 835  }
	 836  
	 837  func (p *Gray) ColorModel() color.Model { return color.GrayModel }
	 838  
	 839  func (p *Gray) Bounds() Rectangle { return p.Rect }
	 840  
	 841  func (p *Gray) At(x, y int) color.Color {
	 842  	return p.GrayAt(x, y)
	 843  }
	 844  
	 845  func (p *Gray) RGBA64At(x, y int) color.RGBA64 {
	 846  	gray := uint16(p.GrayAt(x, y).Y)
	 847  	gray |= gray << 8
	 848  	return color.RGBA64{gray, gray, gray, 0xffff}
	 849  }
	 850  
	 851  func (p *Gray) GrayAt(x, y int) color.Gray {
	 852  	if !(Point{x, y}.In(p.Rect)) {
	 853  		return color.Gray{}
	 854  	}
	 855  	i := p.PixOffset(x, y)
	 856  	return color.Gray{p.Pix[i]}
	 857  }
	 858  
	 859  // PixOffset returns the index of the first element of Pix that corresponds to
	 860  // the pixel at (x, y).
	 861  func (p *Gray) PixOffset(x, y int) int {
	 862  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*1
	 863  }
	 864  
	 865  func (p *Gray) Set(x, y int, c color.Color) {
	 866  	if !(Point{x, y}.In(p.Rect)) {
	 867  		return
	 868  	}
	 869  	i := p.PixOffset(x, y)
	 870  	p.Pix[i] = color.GrayModel.Convert(c).(color.Gray).Y
	 871  }
	 872  
	 873  func (p *Gray) SetRGBA64(x, y int, c color.RGBA64) {
	 874  	if !(Point{x, y}.In(p.Rect)) {
	 875  		return
	 876  	}
	 877  	// This formula is the same as in color.grayModel.
	 878  	gray := (19595*uint32(c.R) + 38470*uint32(c.G) + 7471*uint32(c.B) + 1<<15) >> 24
	 879  	i := p.PixOffset(x, y)
	 880  	p.Pix[i] = uint8(gray)
	 881  }
	 882  
	 883  func (p *Gray) SetGray(x, y int, c color.Gray) {
	 884  	if !(Point{x, y}.In(p.Rect)) {
	 885  		return
	 886  	}
	 887  	i := p.PixOffset(x, y)
	 888  	p.Pix[i] = c.Y
	 889  }
	 890  
	 891  // SubImage returns an image representing the portion of the image p visible
	 892  // through r. The returned value shares pixels with the original image.
	 893  func (p *Gray) SubImage(r Rectangle) Image {
	 894  	r = r.Intersect(p.Rect)
	 895  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	 896  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	 897  	// this, the Pix[i:] expression below can panic.
	 898  	if r.Empty() {
	 899  		return &Gray{}
	 900  	}
	 901  	i := p.PixOffset(r.Min.X, r.Min.Y)
	 902  	return &Gray{
	 903  		Pix:		p.Pix[i:],
	 904  		Stride: p.Stride,
	 905  		Rect:	 r,
	 906  	}
	 907  }
	 908  
	 909  // Opaque scans the entire image and reports whether it is fully opaque.
	 910  func (p *Gray) Opaque() bool {
	 911  	return true
	 912  }
	 913  
	 914  // NewGray returns a new Gray image with the given bounds.
	 915  func NewGray(r Rectangle) *Gray {
	 916  	return &Gray{
	 917  		Pix:		make([]uint8, pixelBufferLength(1, r, "Gray")),
	 918  		Stride: 1 * r.Dx(),
	 919  		Rect:	 r,
	 920  	}
	 921  }
	 922  
	 923  // Gray16 is an in-memory image whose At method returns color.Gray16 values.
	 924  type Gray16 struct {
	 925  	// Pix holds the image's pixels, as gray values in big-endian format. The pixel at
	 926  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*2].
	 927  	Pix []uint8
	 928  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
	 929  	Stride int
	 930  	// Rect is the image's bounds.
	 931  	Rect Rectangle
	 932  }
	 933  
	 934  func (p *Gray16) ColorModel() color.Model { return color.Gray16Model }
	 935  
	 936  func (p *Gray16) Bounds() Rectangle { return p.Rect }
	 937  
	 938  func (p *Gray16) At(x, y int) color.Color {
	 939  	return p.Gray16At(x, y)
	 940  }
	 941  
	 942  func (p *Gray16) RGBA64At(x, y int) color.RGBA64 {
	 943  	gray := p.Gray16At(x, y).Y
	 944  	return color.RGBA64{gray, gray, gray, 0xffff}
	 945  }
	 946  
	 947  func (p *Gray16) Gray16At(x, y int) color.Gray16 {
	 948  	if !(Point{x, y}.In(p.Rect)) {
	 949  		return color.Gray16{}
	 950  	}
	 951  	i := p.PixOffset(x, y)
	 952  	return color.Gray16{uint16(p.Pix[i+0])<<8 | uint16(p.Pix[i+1])}
	 953  }
	 954  
	 955  // PixOffset returns the index of the first element of Pix that corresponds to
	 956  // the pixel at (x, y).
	 957  func (p *Gray16) PixOffset(x, y int) int {
	 958  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*2
	 959  }
	 960  
	 961  func (p *Gray16) Set(x, y int, c color.Color) {
	 962  	if !(Point{x, y}.In(p.Rect)) {
	 963  		return
	 964  	}
	 965  	i := p.PixOffset(x, y)
	 966  	c1 := color.Gray16Model.Convert(c).(color.Gray16)
	 967  	p.Pix[i+0] = uint8(c1.Y >> 8)
	 968  	p.Pix[i+1] = uint8(c1.Y)
	 969  }
	 970  
	 971  func (p *Gray16) SetRGBA64(x, y int, c color.RGBA64) {
	 972  	if !(Point{x, y}.In(p.Rect)) {
	 973  		return
	 974  	}
	 975  	// This formula is the same as in color.gray16Model.
	 976  	gray := (19595*uint32(c.R) + 38470*uint32(c.G) + 7471*uint32(c.B) + 1<<15) >> 16
	 977  	i := p.PixOffset(x, y)
	 978  	p.Pix[i+0] = uint8(gray >> 8)
	 979  	p.Pix[i+1] = uint8(gray)
	 980  }
	 981  
	 982  func (p *Gray16) SetGray16(x, y int, c color.Gray16) {
	 983  	if !(Point{x, y}.In(p.Rect)) {
	 984  		return
	 985  	}
	 986  	i := p.PixOffset(x, y)
	 987  	p.Pix[i+0] = uint8(c.Y >> 8)
	 988  	p.Pix[i+1] = uint8(c.Y)
	 989  }
	 990  
	 991  // SubImage returns an image representing the portion of the image p visible
	 992  // through r. The returned value shares pixels with the original image.
	 993  func (p *Gray16) SubImage(r Rectangle) Image {
	 994  	r = r.Intersect(p.Rect)
	 995  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	 996  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	 997  	// this, the Pix[i:] expression below can panic.
	 998  	if r.Empty() {
	 999  		return &Gray16{}
	1000  	}
	1001  	i := p.PixOffset(r.Min.X, r.Min.Y)
	1002  	return &Gray16{
	1003  		Pix:		p.Pix[i:],
	1004  		Stride: p.Stride,
	1005  		Rect:	 r,
	1006  	}
	1007  }
	1008  
	1009  // Opaque scans the entire image and reports whether it is fully opaque.
	1010  func (p *Gray16) Opaque() bool {
	1011  	return true
	1012  }
	1013  
	1014  // NewGray16 returns a new Gray16 image with the given bounds.
	1015  func NewGray16(r Rectangle) *Gray16 {
	1016  	return &Gray16{
	1017  		Pix:		make([]uint8, pixelBufferLength(2, r, "Gray16")),
	1018  		Stride: 2 * r.Dx(),
	1019  		Rect:	 r,
	1020  	}
	1021  }
	1022  
	1023  // CMYK is an in-memory image whose At method returns color.CMYK values.
	1024  type CMYK struct {
	1025  	// Pix holds the image's pixels, in C, M, Y, K order. The pixel at
	1026  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*4].
	1027  	Pix []uint8
	1028  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
	1029  	Stride int
	1030  	// Rect is the image's bounds.
	1031  	Rect Rectangle
	1032  }
	1033  
	1034  func (p *CMYK) ColorModel() color.Model { return color.CMYKModel }
	1035  
	1036  func (p *CMYK) Bounds() Rectangle { return p.Rect }
	1037  
	1038  func (p *CMYK) At(x, y int) color.Color {
	1039  	return p.CMYKAt(x, y)
	1040  }
	1041  
	1042  func (p *CMYK) RGBA64At(x, y int) color.RGBA64 {
	1043  	r, g, b, a := p.CMYKAt(x, y).RGBA()
	1044  	return color.RGBA64{uint16(r), uint16(g), uint16(b), uint16(a)}
	1045  }
	1046  
	1047  func (p *CMYK) CMYKAt(x, y int) color.CMYK {
	1048  	if !(Point{x, y}.In(p.Rect)) {
	1049  		return color.CMYK{}
	1050  	}
	1051  	i := p.PixOffset(x, y)
	1052  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	1053  	return color.CMYK{s[0], s[1], s[2], s[3]}
	1054  }
	1055  
	1056  // PixOffset returns the index of the first element of Pix that corresponds to
	1057  // the pixel at (x, y).
	1058  func (p *CMYK) PixOffset(x, y int) int {
	1059  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*4
	1060  }
	1061  
	1062  func (p *CMYK) Set(x, y int, c color.Color) {
	1063  	if !(Point{x, y}.In(p.Rect)) {
	1064  		return
	1065  	}
	1066  	i := p.PixOffset(x, y)
	1067  	c1 := color.CMYKModel.Convert(c).(color.CMYK)
	1068  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	1069  	s[0] = c1.C
	1070  	s[1] = c1.M
	1071  	s[2] = c1.Y
	1072  	s[3] = c1.K
	1073  }
	1074  
	1075  func (p *CMYK) SetRGBA64(x, y int, c color.RGBA64) {
	1076  	if !(Point{x, y}.In(p.Rect)) {
	1077  		return
	1078  	}
	1079  	cc, mm, yy, kk := color.RGBToCMYK(uint8(c.R>>8), uint8(c.G>>8), uint8(c.B>>8))
	1080  	i := p.PixOffset(x, y)
	1081  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	1082  	s[0] = cc
	1083  	s[1] = mm
	1084  	s[2] = yy
	1085  	s[3] = kk
	1086  }
	1087  
	1088  func (p *CMYK) SetCMYK(x, y int, c color.CMYK) {
	1089  	if !(Point{x, y}.In(p.Rect)) {
	1090  		return
	1091  	}
	1092  	i := p.PixOffset(x, y)
	1093  	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	1094  	s[0] = c.C
	1095  	s[1] = c.M
	1096  	s[2] = c.Y
	1097  	s[3] = c.K
	1098  }
	1099  
	1100  // SubImage returns an image representing the portion of the image p visible
	1101  // through r. The returned value shares pixels with the original image.
	1102  func (p *CMYK) SubImage(r Rectangle) Image {
	1103  	r = r.Intersect(p.Rect)
	1104  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	1105  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	1106  	// this, the Pix[i:] expression below can panic.
	1107  	if r.Empty() {
	1108  		return &CMYK{}
	1109  	}
	1110  	i := p.PixOffset(r.Min.X, r.Min.Y)
	1111  	return &CMYK{
	1112  		Pix:		p.Pix[i:],
	1113  		Stride: p.Stride,
	1114  		Rect:	 r,
	1115  	}
	1116  }
	1117  
	1118  // Opaque scans the entire image and reports whether it is fully opaque.
	1119  func (p *CMYK) Opaque() bool {
	1120  	return true
	1121  }
	1122  
	1123  // NewCMYK returns a new CMYK image with the given bounds.
	1124  func NewCMYK(r Rectangle) *CMYK {
	1125  	return &CMYK{
	1126  		Pix:		make([]uint8, pixelBufferLength(4, r, "CMYK")),
	1127  		Stride: 4 * r.Dx(),
	1128  		Rect:	 r,
	1129  	}
	1130  }
	1131  
	1132  // Paletted is an in-memory image of uint8 indices into a given palette.
	1133  type Paletted struct {
	1134  	// Pix holds the image's pixels, as palette indices. The pixel at
	1135  	// (x, y) starts at Pix[(y-Rect.Min.Y)*Stride + (x-Rect.Min.X)*1].
	1136  	Pix []uint8
	1137  	// Stride is the Pix stride (in bytes) between vertically adjacent pixels.
	1138  	Stride int
	1139  	// Rect is the image's bounds.
	1140  	Rect Rectangle
	1141  	// Palette is the image's palette.
	1142  	Palette color.Palette
	1143  }
	1144  
	1145  func (p *Paletted) ColorModel() color.Model { return p.Palette }
	1146  
	1147  func (p *Paletted) Bounds() Rectangle { return p.Rect }
	1148  
	1149  func (p *Paletted) At(x, y int) color.Color {
	1150  	if len(p.Palette) == 0 {
	1151  		return nil
	1152  	}
	1153  	if !(Point{x, y}.In(p.Rect)) {
	1154  		return p.Palette[0]
	1155  	}
	1156  	i := p.PixOffset(x, y)
	1157  	return p.Palette[p.Pix[i]]
	1158  }
	1159  
	1160  func (p *Paletted) RGBA64At(x, y int) color.RGBA64 {
	1161  	if len(p.Palette) == 0 {
	1162  		return color.RGBA64{}
	1163  	}
	1164  	c := color.Color(nil)
	1165  	if !(Point{x, y}.In(p.Rect)) {
	1166  		c = p.Palette[0]
	1167  	} else {
	1168  		i := p.PixOffset(x, y)
	1169  		c = p.Palette[p.Pix[i]]
	1170  	}
	1171  	r, g, b, a := c.RGBA()
	1172  	return color.RGBA64{
	1173  		uint16(r),
	1174  		uint16(g),
	1175  		uint16(b),
	1176  		uint16(a),
	1177  	}
	1178  }
	1179  
	1180  // PixOffset returns the index of the first element of Pix that corresponds to
	1181  // the pixel at (x, y).
	1182  func (p *Paletted) PixOffset(x, y int) int {
	1183  	return (y-p.Rect.Min.Y)*p.Stride + (x-p.Rect.Min.X)*1
	1184  }
	1185  
	1186  func (p *Paletted) Set(x, y int, c color.Color) {
	1187  	if !(Point{x, y}.In(p.Rect)) {
	1188  		return
	1189  	}
	1190  	i := p.PixOffset(x, y)
	1191  	p.Pix[i] = uint8(p.Palette.Index(c))
	1192  }
	1193  
	1194  func (p *Paletted) SetRGBA64(x, y int, c color.RGBA64) {
	1195  	if !(Point{x, y}.In(p.Rect)) {
	1196  		return
	1197  	}
	1198  	i := p.PixOffset(x, y)
	1199  	p.Pix[i] = uint8(p.Palette.Index(c))
	1200  }
	1201  
	1202  func (p *Paletted) ColorIndexAt(x, y int) uint8 {
	1203  	if !(Point{x, y}.In(p.Rect)) {
	1204  		return 0
	1205  	}
	1206  	i := p.PixOffset(x, y)
	1207  	return p.Pix[i]
	1208  }
	1209  
	1210  func (p *Paletted) SetColorIndex(x, y int, index uint8) {
	1211  	if !(Point{x, y}.In(p.Rect)) {
	1212  		return
	1213  	}
	1214  	i := p.PixOffset(x, y)
	1215  	p.Pix[i] = index
	1216  }
	1217  
	1218  // SubImage returns an image representing the portion of the image p visible
	1219  // through r. The returned value shares pixels with the original image.
	1220  func (p *Paletted) SubImage(r Rectangle) Image {
	1221  	r = r.Intersect(p.Rect)
	1222  	// If r1 and r2 are Rectangles, r1.Intersect(r2) is not guaranteed to be inside
	1223  	// either r1 or r2 if the intersection is empty. Without explicitly checking for
	1224  	// this, the Pix[i:] expression below can panic.
	1225  	if r.Empty() {
	1226  		return &Paletted{
	1227  			Palette: p.Palette,
	1228  		}
	1229  	}
	1230  	i := p.PixOffset(r.Min.X, r.Min.Y)
	1231  	return &Paletted{
	1232  		Pix:		 p.Pix[i:],
	1233  		Stride:	p.Stride,
	1234  		Rect:		p.Rect.Intersect(r),
	1235  		Palette: p.Palette,
	1236  	}
	1237  }
	1238  
	1239  // Opaque scans the entire image and reports whether it is fully opaque.
	1240  func (p *Paletted) Opaque() bool {
	1241  	var present [256]bool
	1242  	i0, i1 := 0, p.Rect.Dx()
	1243  	for y := p.Rect.Min.Y; y < p.Rect.Max.Y; y++ {
	1244  		for _, c := range p.Pix[i0:i1] {
	1245  			present[c] = true
	1246  		}
	1247  		i0 += p.Stride
	1248  		i1 += p.Stride
	1249  	}
	1250  	for i, c := range p.Palette {
	1251  		if !present[i] {
	1252  			continue
	1253  		}
	1254  		_, _, _, a := c.RGBA()
	1255  		if a != 0xffff {
	1256  			return false
	1257  		}
	1258  	}
	1259  	return true
	1260  }
	1261  
	1262  // NewPaletted returns a new Paletted image with the given width, height and
	1263  // palette.
	1264  func NewPaletted(r Rectangle, p color.Palette) *Paletted {
	1265  	return &Paletted{
	1266  		Pix:		 make([]uint8, pixelBufferLength(1, r, "Paletted")),
	1267  		Stride:	1 * r.Dx(),
	1268  		Rect:		r,
	1269  		Palette: p,
	1270  	}
	1271  }
	1272  

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