image/ycbcr: move the Y'CbCr types into image and image/color.

R=r, rsc
CC=golang-dev
https://golang.org/cl/5493084

src/cmd/gofix/Makefile

@@ -20,6 +20,7 @@ GOFILES=\
 	httputil.go\
 	imagecolor.go\
 	imagenew.go\
+	imageycbcr.go\
 	iocopyn.go\
 	main.go\
 	mapdelete.go\

src/cmd/gofix/imageycbcr.go

+// Copyright 2011 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 main
+
+import (
+	"go/ast"
+)
+
+func init() {
+	register(imageycbcrFix)
+}
+
+var imageycbcrFix = fix{
+	"imageycbcr",
+	"2011-12-20",
+	imageycbcr,
+	`Adapt code to types moved from image/ycbcr to image and image/color.
+
+http://codereview.appspot.com/5493084
+`,
+}
+
+func imageycbcr(f *ast.File) (fixed bool) {
+	if !imports(f, "image/ycbcr") {
+		return
+	}
+
+	walk(f, func(n interface{}) {
+		s, ok := n.(*ast.SelectorExpr)
+
+		if !ok || !isTopName(s.X, "ycbcr") {
+			return
+		}
+
+		switch s.Sel.String() {
+		case "RGBToYCbCr", "YCbCrToRGB":
+			addImport(f, "image/color")
+			s.X.(*ast.Ident).Name = "color"
+		case "YCbCrColor":
+			addImport(f, "image/color")
+			s.X.(*ast.Ident).Name = "color"
+			s.Sel.Name = "YCbCr"
+		case "YCbCrColorModel":
+			addImport(f, "image/color")
+			s.X.(*ast.Ident).Name = "color"
+			s.Sel.Name = "YCbCrModel"
+		case "SubsampleRatio", "SubsampleRatio444", "SubsampleRatio422", "SubsampleRatio420":
+			addImport(f, "image")
+			s.X.(*ast.Ident).Name = "image"
+			s.Sel.Name = "YCbCr" + s.Sel.Name
+		case "YCbCr":
+			addImport(f, "image")
+			s.X.(*ast.Ident).Name = "image"
+		default:
+			return
+		}
+		fixed = true
+	})
+
+	deleteImport(f, "image/ycbcr")
+	return
+}

src/cmd/gofix/imageycbcr_test.go

+// Copyright 2011 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 main
+
+func init() {
+	addTestCases(ycbcrTests, imageycbcr)
+}
+
+var ycbcrTests = []testCase{
+	{
+		Name: "ycbcr.0",
+		In: `package main
+
+import (
+	"image/ycbcr"
+)
+
+func f() {
+	_ = ycbcr.RGBToYCbCr
+	_ = ycbcr.YCbCrToRGB
+	_ = ycbcr.YCbCrColorModel
+	var _ ycbcr.YCbCrColor
+	var _ ycbcr.YCbCr
+	var (
+		_ ycbcr.SubsampleRatio = ycbcr.SubsampleRatio444
+		_ ycbcr.SubsampleRatio = ycbcr.SubsampleRatio422
+		_ ycbcr.SubsampleRatio = ycbcr.SubsampleRatio420
+	)
+}
+`,
+		Out: `package main
+
+import (
+	"image"
+	"image/color"
+)
+
+func f() {
+	_ = color.RGBToYCbCr
+	_ = color.YCbCrToRGB
+	_ = color.YCbCrModel
+	var _ color.YCbCr
+	var _ image.YCbCr
+	var (
+		_ image.YCbCrSubsampleRatio = image.YCbCrSubsampleRatio444
+		_ image.YCbCrSubsampleRatio = image.YCbCrSubsampleRatio422
+		_ image.YCbCrSubsampleRatio = image.YCbCrSubsampleRatio420
+	)
+}
+`,
+	},
+}

src/pkg/Makefile

@@ -111,7 +111,6 @@ DIRS=\
 	image/jpeg\
 	image/png\
 	image/tiff\
-	image/ycbcr\
 	index/suffixarray\
 	io\
 	io/ioutil\
@@ -205,7 +204,6 @@ NOTEST+=\
 	go/doc\
 	hash\
 	image/bmp\
-	image/color\
 	image/gif\
 	net/dict\
 	net/http/pprof\

src/pkg/image/Makefile

@@ -10,5 +10,6 @@ GOFILES=\
 	geom.go\
 	image.go\
 	names.go\
+	ycbcr.go\
 
 include ../../Make.pkg

src/pkg/image/color/Makefile

@@ -7,5 +7,6 @@ include ../../../Make.inc
 TARG=image/color
 GOFILES=\
 	color.go\
+	ycbcr.go\
 
 include ../../../Make.pkg

src/pkg/image/ycbcr/ycbcr.go → src/pkg/image/color/ycbcr.go

@@ -2,23 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package ycbcr provides images from the Y'CbCr color model.
-//
-// JPEG, VP8, the MPEG family and other codecs use this color model. Such
-// codecs often use the terms YUV and Y'CbCr interchangeably, but strictly
-// speaking, the term YUV applies only to analog video signals.
-//
-// Conversion between RGB and Y'CbCr is lossy and there are multiple, slightly
-// different formulae for converting between the two. This package follows
-// the JFIF specification at http://www.w3.org/Graphics/JPEG/jfif3.pdf.
-package ycbcr
+package color
 
-import (
-	"image"
-	"image/color"
-)
-
-// RGBToYCbCr converts an RGB triple to a YCbCr triple. All components lie
+// RGBToYCbCr converts an RGB triple to a Y'CbCr triple. All components lie
 // within the range [0, 255].
 func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8) {
 	// The JFIF specification says:
@@ -50,7 +36,7 @@ func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8) {
 	return uint8(yy), uint8(cb), uint8(cr)
 }
 
-// YCbCrToRGB converts a YCbCr triple to an RGB triple. All components lie
+// YCbCrToRGB converts a Y'CbCr triple to an RGB triple. All components lie
 // within the range [0, 255].
 func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8) {
 	// The JFIF specification says:
@@ -82,103 +68,32 @@ func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8) {
 	return uint8(r), uint8(g), uint8(b)
 }
 
-// YCbCrColor represents a fully opaque 24-bit Y'CbCr color, having 8 bits for
-// each of one luma and two chroma components.
-type YCbCrColor struct {
+// YCbCr represents a fully opaque 24-bit Y'CbCr color, having 8 bits each for
+// one luma and two chroma components.
+//
+// JPEG, VP8, the MPEG family and other codecs use this color model. Such
+// codecs often use the terms YUV and Y'CbCr interchangeably, but strictly
+// speaking, the term YUV applies only to analog video signals, and Y' (luma)
+// is Y (luminance) after applying gamma correction.
+//
+// Conversion between RGB and Y'CbCr is lossy and there are multiple, slightly
+// different formulae for converting between the two. This package follows
+// the JFIF specification at http://www.w3.org/Graphics/JPEG/jfif3.pdf.
+type YCbCr struct {
 	Y, Cb, Cr uint8
 }
 
-func (c YCbCrColor) RGBA() (uint32, uint32, uint32, uint32) {
+func (c YCbCr) RGBA() (uint32, uint32, uint32, uint32) {
 	r, g, b := YCbCrToRGB(c.Y, c.Cb, c.Cr)
 	return uint32(r) * 0x101, uint32(g) * 0x101, uint32(b) * 0x101, 0xffff
 }
 
-func toYCbCrColor(c color.Color) color.Color {
-	if _, ok := c.(YCbCrColor); ok {
+// YCbCrModel is the Model for Y'CbCr colors.
+var YCbCrModel Model = ModelFunc(func(c Color) Color {
+	if _, ok := c.(YCbCr); ok {
 		return c
 	}
 	r, g, b, _ := c.RGBA()
 	y, u, v := RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))
-	return YCbCrColor{y, u, v}
-}
-
-// YCbCrColorModel is the color model for YCbCrColor.
-var YCbCrColorModel color.Model = color.ModelFunc(toYCbCrColor)
-
-// SubsampleRatio is the chroma subsample ratio used in a YCbCr image.
-type SubsampleRatio int
-
-const (
-	SubsampleRatio444 SubsampleRatio = iota
-	SubsampleRatio422
-	SubsampleRatio420
-)
-
-// YCbCr is an in-memory image of YCbCr colors. There is one Y sample per pixel,
-// but each Cb and Cr sample can span one or more pixels.
-// YStride is the Y slice index delta between vertically adjacent pixels.
-// CStride is the Cb and Cr slice index delta between vertically adjacent pixels
-// that map to separate chroma samples.
-// It is not an absolute requirement, but YStride and len(Y) are typically
-// multiples of 8, and:
-//	For 4:4:4, CStride == YStride/1 && len(Cb) == len(Cr) == len(Y)/1.
-//	For 4:2:2, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/2.
-//	For 4:2:0, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/4.
-type YCbCr struct {
-	Y              []uint8
-	Cb             []uint8
-	Cr             []uint8
-	YStride        int
-	CStride        int
-	SubsampleRatio SubsampleRatio
-	Rect           image.Rectangle
-}
-
-func (p *YCbCr) ColorModel() color.Model {
-	return YCbCrColorModel
-}
-
-func (p *YCbCr) Bounds() image.Rectangle {
-	return p.Rect
-}
-
-func (p *YCbCr) At(x, y int) color.Color {
-	if !(image.Point{x, y}.In(p.Rect)) {
-		return YCbCrColor{}
-	}
-	switch p.SubsampleRatio {
-	case SubsampleRatio422:
-		i := x / 2
-		return YCbCrColor{
-			p.Y[y*p.YStride+x],
-			p.Cb[y*p.CStride+i],
-			p.Cr[y*p.CStride+i],
-		}
-	case SubsampleRatio420:
-		i, j := x/2, y/2
-		return YCbCrColor{
-			p.Y[y*p.YStride+x],
-			p.Cb[j*p.CStride+i],
-			p.Cr[j*p.CStride+i],
-		}
-	}
-	// Default to 4:4:4 subsampling.
-	return YCbCrColor{
-		p.Y[y*p.YStride+x],
-		p.Cb[y*p.CStride+x],
-		p.Cr[y*p.CStride+x],
-	}
-}
-
-// 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 *YCbCr) SubImage(r image.Rectangle) image.Image {
-	q := new(YCbCr)
-	*q = *p
-	q.Rect = q.Rect.Intersect(r)
-	return q
-}
-
-func (p *YCbCr) Opaque() bool {
-	return true
-}
+	return YCbCr{y, u, v}
+})

src/pkg/image/ycbcr/ycbcr_test.go → src/pkg/image/color/ycbcr_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package ycbcr
+package color
 
 import (
 	"testing"

src/pkg/image/draw/bench_test.go

@@ -7,7 +7,6 @@ package draw
 import (
 	"image"
 	"image/color"
-	"image/ycbcr"
 	"testing"
 )
 
@@ -97,7 +96,7 @@ func bench(b *testing.B, dcm, scm, mcm color.Model, op Op) {
 			}
 		}
 		src = src1
-	case ycbcr.YCbCrColorModel:
+	case color.YCbCrModel:
 		yy := make([]uint8, srcw*srch)
 		cb := make([]uint8, srcw*srch)
 		cr := make([]uint8, srcw*srch)
@@ -106,13 +105,13 @@ func bench(b *testing.B, dcm, scm, mcm color.Model, op Op) {
 			cb[i] = uint8(5 * i % 0x100)
 			cr[i] = uint8(7 * i % 0x100)
 		}
-		src = &ycbcr.YCbCr{
+		src = &image.YCbCr{
 			Y:              yy,
 			Cb:             cb,
 			Cr:             cr,
 			YStride:        srcw,
 			CStride:        srcw,
-			SubsampleRatio: ycbcr.SubsampleRatio444,
+			SubsampleRatio: image.YCbCrSubsampleRatio444,
 			Rect:           image.Rect(0, 0, srcw, srch),
 		}
 	default:
@@ -177,7 +176,7 @@ func BenchmarkNRGBASrc(b *testing.B) {
 }
 
 func BenchmarkYCbCr(b *testing.B) {
-	bench(b, color.RGBAModel, ycbcr.YCbCrColorModel, nil, Over)
+	bench(b, color.RGBAModel, color.YCbCrModel, nil, Over)
 }
 
 func BenchmarkGlyphOver(b *testing.B) {

src/pkg/image/draw/draw.go

@@ -11,7 +11,6 @@ package draw
 import (
 	"image"
 	"image/color"
-	"image/ycbcr"
 )
 
 // m is the maximum color value returned by image.Color.RGBA.
@@ -81,7 +80,7 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
 				case *image.NRGBA:
 					drawNRGBAOver(dst0, r, src0, sp)
 					return
-				case *ycbcr.YCbCr:
+				case *image.YCbCr:
 					drawYCbCr(dst0, r, src0, sp)
 					return
 				}
@@ -104,7 +103,7 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
 				case *image.NRGBA:
 					drawNRGBASrc(dst0, r, src0, sp)
 					return
-				case *ycbcr.YCbCr:
+				case *image.YCbCr:
 					drawYCbCr(dst0, r, src0, sp)
 					return
 				}
@@ -346,8 +345,8 @@ func drawNRGBASrc(dst *image.RGBA, r image.Rectangle, src *image.NRGBA, sp image
 	}
 }
 
-func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *ycbcr.YCbCr, sp image.Point) {
-	// A YCbCr image is always fully opaque, and so if the mask is implicitly nil
+func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Point) {
+	// An image.YCbCr is always fully opaque, and so if the mask is implicitly nil
 	// (i.e. fully opaque) then the op is effectively always Src.
 	var (
 		yy, cb, cr uint8
@@ -357,7 +356,7 @@ func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *ycbcr.YCbCr, sp image.Po
 	y0 := r.Min.Y - dst.Rect.Min.Y
 	y1 := r.Max.Y - dst.Rect.Min.Y
 	switch src.SubsampleRatio {
-	case ycbcr.SubsampleRatio422:
+	case image.YCbCrSubsampleRatio422:
 		for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
 			dpix := dst.Pix[y*dst.Stride:]
 			for x, sx := x0, sp.X; x != x1; x, sx = x+4, sx+1 {
@@ -365,14 +364,14 @@ func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *ycbcr.YCbCr, sp image.Po
 				yy = src.Y[sy*src.YStride+sx]
 				cb = src.Cb[sy*src.CStride+i]
 				cr = src.Cr[sy*src.CStride+i]
-				rr, gg, bb := ycbcr.YCbCrToRGB(yy, cb, cr)
+				rr, gg, bb := color.YCbCrToRGB(yy, cb, cr)
 				dpix[x+0] = rr
 				dpix[x+1] = gg
 				dpix[x+2] = bb
 				dpix[x+3] = 255
 			}
 		}
-	case ycbcr.SubsampleRatio420:
+	case image.YCbCrSubsampleRatio420:
 		for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
 			dpix := dst.Pix[y*dst.Stride:]
 			for x, sx := x0, sp.X; x != x1; x, sx = x+4, sx+1 {
@@ -380,7 +379,7 @@ func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *ycbcr.YCbCr, sp image.Po
 				yy = src.Y[sy*src.YStride+sx]
 				cb = src.Cb[j*src.CStride+i]
 				cr = src.Cr[j*src.CStride+i]
-				rr, gg, bb := ycbcr.YCbCrToRGB(yy, cb, cr)
+				rr, gg, bb := color.YCbCrToRGB(yy, cb, cr)
 				dpix[x+0] = rr
 				dpix[x+1] = gg
 				dpix[x+2] = bb
@@ -395,7 +394,7 @@ func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *ycbcr.YCbCr, sp image.Po
 				yy = src.Y[sy*src.YStride+sx]
 				cb = src.Cb[sy*src.CStride+sx]
 				cr = src.Cr[sy*src.CStride+sx]
-				rr, gg, bb := ycbcr.YCbCrToRGB(yy, cb, cr)
+				rr, gg, bb := color.YCbCrToRGB(yy, cb, cr)
 				dpix[x+0] = rr
 				dpix[x+1] = gg
 				dpix[x+2] = bb

src/pkg/image/draw/draw_test.go

@@ -7,7 +7,6 @@ package draw
 import (
 	"image"
 	"image/color"
-	"image/ycbcr"
 	"testing"
 )
 
@@ -56,13 +55,13 @@ func vgradGreenNRGBA(alpha int) image.Image {
 }
 
 func vgradCr() image.Image {
-	m := &ycbcr.YCbCr{
+	m := &image.YCbCr{
 		Y:              make([]byte, 16*16),
 		Cb:             make([]byte, 16*16),
 		Cr:             make([]byte, 16*16),
 		YStride:        16,
 		CStride:        16,
-		SubsampleRatio: ycbcr.SubsampleRatio444,
+		SubsampleRatio: image.YCbCrSubsampleRatio444,
 		Rect:           image.Rect(0, 0, 16, 16),
 	}
 	for y := 0; y < 16; y++ {

src/pkg/image/jpeg/reader.go

@@ -11,7 +11,6 @@ import (
 	"bufio"
 	"image"
 	"image/color"
-	"image/ycbcr"
 	"io"
 )
 
@@ -97,7 +96,7 @@ type decoder struct {
 	r             Reader
 	width, height int
 	img1          *image.Gray
-	img3          *ycbcr.YCbCr
+	img3          *image.YCbCr
 	ri            int // Restart Interval.
 	nComp         int
 	comp          [nColorComponent]component
@@ -203,20 +202,20 @@ func (d *decoder) makeImg(h0, v0, mxx, myy int) {
 		d.img1 = m.SubImage(image.Rect(0, 0, d.width, d.height)).(*image.Gray)
 		return
 	}
-	var subsampleRatio ycbcr.SubsampleRatio
+	var subsampleRatio image.YCbCrSubsampleRatio
 	n := h0 * v0
 	switch n {
 	case 1:
-		subsampleRatio = ycbcr.SubsampleRatio444
+		subsampleRatio = image.YCbCrSubsampleRatio444
 	case 2:
-		subsampleRatio = ycbcr.SubsampleRatio422
+		subsampleRatio = image.YCbCrSubsampleRatio422
 	case 4:
-		subsampleRatio = ycbcr.SubsampleRatio420
+		subsampleRatio = image.YCbCrSubsampleRatio420
 	default:
 		panic("unreachable")
 	}
 	b := make([]byte, mxx*myy*(1*8*8*n+2*8*8))
-	d.img3 = &ycbcr.YCbCr{
+	d.img3 = &image.YCbCr{
 		Y:              b[mxx*myy*(0*8*8*n+0*8*8) : mxx*myy*(1*8*8*n+0*8*8)],
 		Cb:             b[mxx*myy*(1*8*8*n+0*8*8) : mxx*myy*(1*8*8*n+1*8*8)],
 		Cr:             b[mxx*myy*(1*8*8*n+1*8*8) : mxx*myy*(1*8*8*n+2*8*8)],
@@ -466,7 +465,7 @@ func DecodeConfig(r io.Reader) (image.Config, error) {
 	case nGrayComponent:
 		return image.Config{color.GrayModel, d.width, d.height}, nil
 	case nColorComponent:
-		return image.Config{ycbcr.YCbCrColorModel, d.width, d.height}, nil
+		return image.Config{color.YCbCrModel, d.width, d.height}, nil
 	}
 	return image.Config{}, FormatError("missing SOF marker")
 }

src/pkg/image/jpeg/writer.go

@@ -8,7 +8,7 @@ import (
 	"bufio"
 	"errors"
 	"image"
-	"image/ycbcr"
+	"image/color"
 	"io"
 )
 
@@ -379,7 +379,7 @@ func toYCbCr(m image.Image, p image.Point, yBlock, cbBlock, crBlock *block) {
 	for j := 0; j < 8; j++ {
 		for i := 0; i < 8; i++ {
 			r, g, b, _ := m.At(min(p.X+i, xmax), min(p.Y+j, ymax)).RGBA()
-			yy, cb, cr := ycbcr.RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))
+			yy, cb, cr := color.RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))
 			yBlock[8*j+i] = int(yy)
 			cbBlock[8*j+i] = int(cb)
 			crBlock[8*j+i] = int(cr)
@@ -404,7 +404,7 @@ func rgbaToYCbCr(m *image.RGBA, p image.Point, yBlock, cbBlock, crBlock *block)
 				sx = xmax
 			}
 			pix := m.Pix[offset+sx*4:]
-			yy, cb, cr := ycbcr.RGBToYCbCr(pix[0], pix[1], pix[2])
+			yy, cb, cr := color.RGBToYCbCr(pix[0], pix[1], pix[2])
 			yBlock[8*j+i] = int(yy)
 			cbBlock[8*j+i] = int(cb)
 			crBlock[8*j+i] = int(cr)

src/pkg/image/ycbcr.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package image
+
+import (
+	"image/color"
+)
+
+// YCbCrSubsampleRatio is the chroma subsample ratio used in a YCbCr image.
+type YCbCrSubsampleRatio int
+
+const (
+	YCbCrSubsampleRatio444 YCbCrSubsampleRatio = iota
+	YCbCrSubsampleRatio422
+	YCbCrSubsampleRatio420
+)
+
+// YCbCr is an in-memory image of Y'CbCr colors. There is one Y sample per
+// pixel, but each Cb and Cr sample can span one or more pixels.
+// YStride is the Y slice index delta between vertically adjacent pixels.
+// CStride is the Cb and Cr slice index delta between vertically adjacent pixels
+// that map to separate chroma samples.
+// It is not an absolute requirement, but YStride and len(Y) are typically
+// multiples of 8, and:
+//	For 4:4:4, CStride == YStride/1 && len(Cb) == len(Cr) == len(Y)/1.
+//	For 4:2:2, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/2.
+//	For 4:2:0, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/4.
+type YCbCr struct {
+	Y              []uint8
+	Cb             []uint8
+	Cr             []uint8
+	YStride        int
+	CStride        int
+	SubsampleRatio YCbCrSubsampleRatio
+	Rect           Rectangle
+}
+
+func (p *YCbCr) ColorModel() color.Model {
+	return color.YCbCrModel
+}
+
+func (p *YCbCr) Bounds() Rectangle {
+	return p.Rect
+}
+
+func (p *YCbCr) At(x, y int) color.Color {
+	if !(Point{x, y}.In(p.Rect)) {
+		return color.YCbCr{}
+	}
+	switch p.SubsampleRatio {
+	case YCbCrSubsampleRatio422:
+		i := x / 2
+		return color.YCbCr{
+			p.Y[y*p.YStride+x],
+			p.Cb[y*p.CStride+i],
+			p.Cr[y*p.CStride+i],
+		}
+	case YCbCrSubsampleRatio420:
+		i, j := x/2, y/2
+		return color.YCbCr{
+			p.Y[y*p.YStride+x],
+			p.Cb[j*p.CStride+i],
+			p.Cr[j*p.CStride+i],
+		}
+	}
+	// Default to 4:4:4 subsampling.
+	return color.YCbCr{
+		p.Y[y*p.YStride+x],
+		p.Cb[y*p.CStride+x],
+		p.Cr[y*p.CStride+x],
+	}
+}
+
+// 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 *YCbCr) SubImage(r Rectangle) Image {
+	q := new(YCbCr)
+	*q = *p
+	q.Rect = q.Rect.Intersect(r)
+	return q
+}
+
+func (p *YCbCr) Opaque() bool {
+	return true
+}

src/pkg/image/ycbcr/Makefile

-# Copyright 2011 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.
-
-include ../../../Make.inc
-
-TARG=image/ycbcr
-GOFILES=\
-	ycbcr.go\
-
-include ../../../Make.pkg