func (p *YCbCr) RGBA64At(x, y int) color.RGBA64 {
	r, g, b, a := p.YCbCrAt(x, y).RGBA()
	return color.RGBA64{uint16(r), uint16(g), uint16(b), uint16(a)}
}

func (p *YCbCr) YCbCrAt(x, y int) color.YCbCr {
	if !(Point{x, y}.In(p.Rect)) {
		return color.YCbCr{}
	}
	yi := p.YOffset(x, y)
	ci := p.COffset(x, y)
	return color.YCbCr{
		p.Y[yi],
		p.Cb[ci],
		p.Cr[ci],
	}
}

	for i := 0; i < 256; i++ {
		c0 := NYCbCrA{YCbCr{0xff, 0x80, 0x80}, uint8(i)}
		c1 := Alpha{uint8(i)}
		if err := eq(c0, c1); err != nil {
			t.Errorf("i=0x%02x:\n%v", i, err)
		}
	}
}

// TestNYCbCrAYCbCr tests that NYCbCrA colors are a superset of YCbCr colors.
func TestNYCbCrAYCbCr(t *testing.T) {
	for i := 0; i < 256; i++ {
		c0 := NYCbCrA{YCbCr{uint8(i), 0x40, 0xc0}, 0xff}
		c1 := YCbCr{uint8(i), 0x40, 0xc0}

		log.Fatal(err)
	}
}

const pre = `// Code generated by go run gen.go; DO NOT EDIT.

package imageutil

import (
	"image"
)

// DrawYCbCr draws the YCbCr source image on the RGBA destination image with
// r.Min in dst aligned with sp in src. It reports whether the draw was
// successful. If it returns false, no dst pixels were changed.
//

	for _, c := range colors {
		var dst any
		switch c.Space {
		case "RGB":
			dst = new(RGB)
		case "YCbCr":
			dst = new(YCbCr)
		}
		err := json.Unmarshal(c.Point, dst)
		if err != nil {
			log.Fatalln("error:", err)
		}
		fmt.Println(c.Space, dst)
	}
	// Output:
	// YCbCr &{255 0 -10}
	// RGB &{98 218 255}
}

// This example uses RawMessage to use a precomputed JSON during marshal.

					subRect := Rect(x0, y0, x1, y1)
					sub := m.SubImage(subRect).(*YCbCr)

					// For each point in the sub-image's bounds, check that m.At(x, y) equals sub.At(x, y).
					for y := sub.Rect.Min.Y; y < sub.Rect.Max.Y; y++ {
						for x := sub.Rect.Min.X; x < sub.Rect.Max.X; x++ {
							color0 := m.At(x, y).(color.YCbCr)
							color1 := sub.At(x, y).(color.YCbCr)
							if color0 != color1 {

// Code generated by go run gen.go; DO NOT EDIT.

package imageutil

import (
	"image"
)

// DrawYCbCr draws the YCbCr source image on the RGBA destination image with
// r.Min in dst aligned with sp in src. It reports whether the draw was
// successful. If it returns false, no dst pixels were changed.
//
// This function assumes that r is entirely within dst's bounds and the
// translation of r from dst coordinate space to src coordinate space is

	"image/color.Gray":    true,
	"image/color.NRGBA64": true,
	"image/color.NRGBA":   true,
	"image/color.NYCbCrA": true,
	"image/color.RGBA64":  true,
	"image/color.RGBA":    true,
	"image/color.YCbCr":   true,
	"image.Point":         true,
	"image.Rectangle":     true,
	"image.Uniform":       true,

	"unicode.Range16": true,
	"unicode.Range32": true,

func TestEncodeYCbCr(t *testing.T) {
	bo := image.Rect(0, 0, 640, 480)
	imgRGBA := image.NewRGBA(bo)
	// Must use 444 subsampling to avoid lossy RGBA to YCbCr conversion.
	imgYCbCr := image.NewYCbCr(bo, image.YCbCrSubsampleRatio444)
	rnd := rand.New(rand.NewSource(123))
	// Create identical rgba and ycbcr images.
	for y := bo.Min.Y; y < bo.Max.Y; y++ {
		for x := bo.Min.X; x < bo.Max.X; x++ {
			col := color.RGBA{
				uint8(rnd.Intn(256)),

		return c
	}
	r, g, b, _ := c.RGBA()

	// These coefficients (the fractions 0.299, 0.587 and 0.114) are the same
	// as those given by the JFIF specification and used by func RGBToYCbCr in
	// ycbcr.go.
	//
	// Note that 19595 + 38470 + 7471 equals 65536.
	//
	// The 24 is 16 + 8. The 16 is the same as used in RGBToYCbCr. The 8 is
	// because the return value is 8 bit color, not 16 bit color.

		cb := make([]uint8, srcw*srch)
		cr := make([]uint8, srcw*srch)
		for i := range yy {
			yy[i] = uint8(3 * i % 0x100)
			cb[i] = uint8(5 * i % 0x100)
			cr[i] = uint8(7 * i % 0x100)
		}
		src = &image.YCbCr{
			Y:              yy,
			Cb:             cb,
			Cr:             cr,
			YStride:        srcw,
			CStride:        srcw,
			SubsampleRatio: image.YCbCrSubsampleRatio444,