src/image/png/writer_test.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package png

 import (
 	"bytes"
 	"compress/zlib"
 	"encoding/binary"
 	"fmt"
 	"image"
 	"image/color"
 	"image/draw"
 	"io"
 	"testing"
 )

 func diff(m0, m1 image.Image) error {
 	b0, b1 := m0.Bounds(), m1.Bounds()
 	if !b0.Size().Eq(b1.Size()) {
 		return fmt.Errorf("dimensions differ: %v vs %v", b0, b1)
 	}
 	dx := b1.Min.X - b0.Min.X
 	dy := b1.Min.Y - b0.Min.Y
 	for y := b0.Min.Y; y < b0.Max.Y; y++ {
 		for x := b0.Min.X; x < b0.Max.X; x++ {
 			c0 := m0.At(x, y)
 			c1 := m1.At(x+dx, y+dy)
 			r0, g0, b0, a0 := c0.RGBA()
 			r1, g1, b1, a1 := c1.RGBA()
 			if r0 != r1 || g0 != g1 || b0 != b1 || a0 != a1 {
 				return fmt.Errorf("colors differ at (%d, %d): %T%v vs %T%v", x, y, c0, c0, c1, c1)
 			}
 		}
 	}
 	return nil
 }

 func encodeDecode(m image.Image) (image.Image, error) {
 	var b bytes.Buffer
 	err := Encode(&b, m)
 	if err != nil {
 		return nil, err
 	}
 	return Decode(&b)
 }

 func convertToNRGBA(m image.Image) *image.NRGBA {
 	b := m.Bounds()
 	ret := image.NewNRGBA(b)
 	draw.Draw(ret, b, m, b.Min, draw.Src)
 	return ret
 }

 func TestWriter(t *testing.T) {
 	// The filenames variable is declared in reader_test.go.
 	names := filenames
 	if testing.Short() {
 		names = filenamesShort
 	}
 	for _, fn := range names {
 		qfn := "testdata/pngsuite/" + fn + ".png"
 		// Read the image.
 		m0, err := readPNG(qfn)
 		if err != nil {
 			t.Error(fn, err)
 			continue
 		}
 		// Read the image again, encode it, and decode it.
 		m1, err := readPNG(qfn)
 		if err != nil {
 			t.Error(fn, err)
 			continue
 		}
 		m2, err := encodeDecode(m1)
 		if err != nil {
 			t.Error(fn, err)
 			continue
 		}
 		// Compare the two.
 		err = diff(m0, m2)
 		if err != nil {
 			t.Error(fn, err)
 			continue
 		}
 	}
 }

 func TestWriterPaletted(t *testing.T) {
 	const width, height = 32, 16

 	testCases := []struct {
 		plen     int
 		bitdepth uint8
 		datalen  int
 	}{

 		{
 			plen:     256,
 			bitdepth: 8,
 			datalen:  (1 + width) * height,
 		},

 		{
 			plen:     128,
 			bitdepth: 8,
 			datalen:  (1 + width) * height,
 		},

 		{
 			plen:     16,
 			bitdepth: 4,
 			datalen:  (1 + width/2) * height,
 		},

 		{
 			plen:     4,
 			bitdepth: 2,
 			datalen:  (1 + width/4) * height,
 		},

 		{
 			plen:     2,
 			bitdepth: 1,
 			datalen:  (1 + width/8) * height,
 		},
 	}

 	for _, tc := range testCases {
 		t.Run(fmt.Sprintf("plen-%d", tc.plen), func(t *testing.T) {
 			// Create a paletted image with the correct palette length
 			palette := make(color.Palette, tc.plen)
 			for i := range palette {
 				palette[i] = color.NRGBA{
 					R: uint8(i),
 					G: uint8(i),
 					B: uint8(i),
 					A: 255,
 				}
 			}
 			m0 := image.NewPaletted(image.Rect(0, 0, width, height), palette)

 			i := 0
 			for y := 0; y < height; y++ {
 				for x := 0; x < width; x++ {
 					m0.SetColorIndex(x, y, uint8(i%tc.plen))
 					i++
 				}
 			}

 			// Encode the image
 			var b bytes.Buffer
 			if err := Encode(&b, m0); err != nil {
 				t.Error(err)
 				return
 			}
 			const chunkFieldsLength = 12 // 4 bytes for length, name and crc
 			data := b.Bytes()
 			i = len(pngHeader)

 			for i < len(data)-chunkFieldsLength {
 				length := binary.BigEndian.Uint32(data[i : i+4])
 				name := string(data[i+4 : i+8])

 				switch name {
 				case "IHDR":
 					bitdepth := data[i+8+8]
 					if bitdepth != tc.bitdepth {
 						t.Errorf("got bitdepth %d, want %d", bitdepth, tc.bitdepth)
 					}
 				case "IDAT":
 					// Uncompress the image data
 					r, err := zlib.NewReader(bytes.NewReader(data[i+8 : i+8+int(length)]))
 					if err != nil {
 						t.Error(err)
 						return
 					}
 					n, err := io.Copy(io.Discard, r)
 					if err != nil {
 						t.Errorf("got error while reading image data: %v", err)
 					}
 					if n != int64(tc.datalen) {
 						t.Errorf("got uncompressed data length %d, want %d", n, tc.datalen)
 					}
 				}

 				i += chunkFieldsLength + int(length)
 			}
 		})

 	}
 }

 func TestWriterLevels(t *testing.T) {
 	m := image.NewNRGBA(image.Rect(0, 0, 100, 100))

 	var b1, b2 bytes.Buffer
 	if err := (&Encoder{}).Encode(&b1, m); err != nil {
 		t.Fatal(err)
 	}
 	noenc := &Encoder{CompressionLevel: NoCompression}
 	if err := noenc.Encode(&b2, m); err != nil {
 		t.Fatal(err)
 	}

 	if b2.Len() <= b1.Len() {
 		t.Error("DefaultCompression encoding was larger than NoCompression encoding")
 	}
 	if _, err := Decode(&b1); err != nil {
 		t.Error("cannot decode DefaultCompression")
 	}
 	if _, err := Decode(&b2); err != nil {
 		t.Error("cannot decode NoCompression")
 	}
 }

 func TestSubImage(t *testing.T) {
 	m0 := image.NewRGBA(image.Rect(0, 0, 256, 256))
 	for y := 0; y < 256; y++ {
 		for x := 0; x < 256; x++ {
 			m0.Set(x, y, color.RGBA{uint8(x), uint8(y), 0, 255})
 		}
 	}
 	m0 = m0.SubImage(image.Rect(50, 30, 250, 130)).(*image.RGBA)
 	m1, err := encodeDecode(m0)
 	if err != nil {
 		t.Error(err)
 		return
 	}
 	err = diff(m0, m1)
 	if err != nil {
 		t.Error(err)
 		return
 	}
 }

 func TestWriteRGBA(t *testing.T) {
 	const width, height = 640, 480
 	transparentImg := image.NewRGBA(image.Rect(0, 0, width, height))
 	opaqueImg := image.NewRGBA(image.Rect(0, 0, width, height))
 	mixedImg := image.NewRGBA(image.Rect(0, 0, width, height))
 	translucentImg := image.NewRGBA(image.Rect(0, 0, width, height))
 	for y := 0; y < height; y++ {
 		for x := 0; x < width; x++ {
 			opaqueColor := color.RGBA{uint8(x), uint8(y), uint8(y + x), 255}
 			translucentColor := color.RGBA{uint8(x) % 128, uint8(y) % 128, uint8(y+x) % 128, 128}
 			opaqueImg.Set(x, y, opaqueColor)
 			translucentImg.Set(x, y, translucentColor)
 			if y%2 == 0 {
 				mixedImg.Set(x, y, opaqueColor)
 			}
 		}
 	}

 	testCases := []struct {
 		name string
 		img  image.Image
 	}{
 		{"Transparent RGBA", transparentImg},
 		{"Opaque RGBA", opaqueImg},
 		{"50/50 Transparent/Opaque RGBA", mixedImg},
 		{"RGBA with variable alpha", translucentImg},
 	}

 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			m0 := tc.img
 			m1, err := encodeDecode(m0)
 			if err != nil {
 				t.Fatal(err)
 			}
 			err = diff(convertToNRGBA(m0), m1)
 			if err != nil {
 				t.Error(err)
 			}
 		})
 	}
 }

 func BenchmarkEncodeGray(b *testing.B) {
 	img := image.NewGray(image.Rect(0, 0, 640, 480))
 	b.SetBytes(640 * 480 * 1)
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		Encode(io.Discard, img)
 	}
 }

 type pool struct {
 	b *EncoderBuffer
 }

 func (p *pool) Get() *EncoderBuffer {
 	return p.b
 }

 func (p *pool) Put(b *EncoderBuffer) {
 	p.b = b
 }

 func BenchmarkEncodeGrayWithBufferPool(b *testing.B) {
 	img := image.NewGray(image.Rect(0, 0, 640, 480))
 	e := Encoder{
 		BufferPool: &pool{},
 	}
 	b.SetBytes(640 * 480 * 1)
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		e.Encode(io.Discard, img)
 	}
 }

 func BenchmarkEncodeNRGBOpaque(b *testing.B) {
 	img := image.NewNRGBA(image.Rect(0, 0, 640, 480))
 	// Set all pixels to 0xFF alpha to force opaque mode.
 	bo := img.Bounds()
 	for y := bo.Min.Y; y < bo.Max.Y; y++ {
 		for x := bo.Min.X; x < bo.Max.X; x++ {
 			img.Set(x, y, color.NRGBA{0, 0, 0, 255})
 		}
 	}
 	if !img.Opaque() {
 		b.Fatal("expected image to be opaque")
 	}
 	b.SetBytes(640 * 480 * 4)
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		Encode(io.Discard, img)
 	}
 }

 func BenchmarkEncodeNRGBA(b *testing.B) {
 	img := image.NewNRGBA(image.Rect(0, 0, 640, 480))
 	if img.Opaque() {
 		b.Fatal("expected image not to be opaque")
 	}
 	b.SetBytes(640 * 480 * 4)
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		Encode(io.Discard, img)
 	}
 }

 func BenchmarkEncodePaletted(b *testing.B) {
 	img := image.NewPaletted(image.Rect(0, 0, 640, 480), color.Palette{
 		color.RGBA{0, 0, 0, 255},
 		color.RGBA{255, 255, 255, 255},
 	})
 	b.SetBytes(640 * 480 * 1)
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		Encode(io.Discard, img)
 	}
 }

 func BenchmarkEncodeRGBOpaque(b *testing.B) {
 	img := image.NewRGBA(image.Rect(0, 0, 640, 480))
 	// Set all pixels to 0xFF alpha to force opaque mode.
 	bo := img.Bounds()
 	for y := bo.Min.Y; y < bo.Max.Y; y++ {
 		for x := bo.Min.X; x < bo.Max.X; x++ {
 			img.Set(x, y, color.RGBA{0, 0, 0, 255})
 		}
 	}
 	if !img.Opaque() {
 		b.Fatal("expected image to be opaque")
 	}
 	b.SetBytes(640 * 480 * 4)
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		Encode(io.Discard, img)
 	}
 }

 func BenchmarkEncodeRGBA(b *testing.B) {
 	const width, height = 640, 480
 	img := image.NewRGBA(image.Rect(0, 0, width, height))
 	for y := 0; y < height; y++ {
 		for x := 0; x < width; x++ {
 			percent := (x + y) % 100
 			switch {
 			case percent < 10: // 10% of pixels are translucent (have alpha >0 and <255)
 				img.Set(x, y, color.NRGBA{uint8(x), uint8(y), uint8(x * y), uint8(percent)})
 			case percent < 40: // 30% of pixels are transparent (have alpha == 0)
 				img.Set(x, y, color.NRGBA{uint8(x), uint8(y), uint8(x * y), 0})
 			default: // 60% of pixels are opaque (have alpha == 255)
 				img.Set(x, y, color.NRGBA{uint8(x), uint8(y), uint8(x * y), 255})
 			}
 		}
 	}
 	if img.Opaque() {
 		b.Fatal("expected image not to be opaque")
 	}
 	b.SetBytes(width * height * 4)
 	b.ReportAllocs()
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		Encode(io.Discard, img)
 	}
 }
	// 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 png

	import (
	"bytes"
	"compress/zlib"
	"encoding/binary"
	"fmt"
	"image"
	"image/color"
	"image/draw"
	"io"
	"testing"
	)

	func diff(m0, m1 image.Image) error {
	b0, b1 := m0.Bounds(), m1.Bounds()
	if !b0.Size().Eq(b1.Size()) {
	return fmt.Errorf("dimensions differ: %v vs %v", b0, b1)
	}
	dx := b1.Min.X - b0.Min.X
	dy := b1.Min.Y - b0.Min.Y
	for y := b0.Min.Y; y < b0.Max.Y; y++ {
	for x := b0.Min.X; x < b0.Max.X; x++ {
	c0 := m0.At(x, y)
	c1 := m1.At(x+dx, y+dy)
	r0, g0, b0, a0 := c0.RGBA()
	r1, g1, b1, a1 := c1.RGBA()
	if r0 != r1 \|\| g0 != g1 \|\| b0 != b1 \|\| a0 != a1 {
	return fmt.Errorf("colors differ at (%d, %d): %T%v vs %T%v", x, y, c0, c0, c1, c1)
	}
	}
	}
	return nil
	}

	func encodeDecode(m image.Image) (image.Image, error) {
	var b bytes.Buffer
	err := Encode(&b, m)
	if err != nil {
	return nil, err
	}
	return Decode(&b)
	}

	func convertToNRGBA(m image.Image) *image.NRGBA {
	b := m.Bounds()
	ret := image.NewNRGBA(b)
	draw.Draw(ret, b, m, b.Min, draw.Src)
	return ret
	}

	func TestWriter(t *testing.T) {
	// The filenames variable is declared in reader_test.go.
	names := filenames
	if testing.Short() {
	names = filenamesShort
	}
	for _, fn := range names {
	qfn := "testdata/pngsuite/" + fn + ".png"
	// Read the image.
	m0, err := readPNG(qfn)
	if err != nil {
	t.Error(fn, err)
	continue
	}
	// Read the image again, encode it, and decode it.
	m1, err := readPNG(qfn)
	if err != nil {
	t.Error(fn, err)
	continue
	}
	m2, err := encodeDecode(m1)
	if err != nil {
	t.Error(fn, err)
	continue
	}
	// Compare the two.
	err = diff(m0, m2)
	if err != nil {
	t.Error(fn, err)
	continue
	}
	}
	}

	func TestWriterPaletted(t *testing.T) {
	const width, height = 32, 16

	testCases := []struct {
	plen int
	bitdepth uint8
	datalen int
	}{

	{
	plen: 256,
	bitdepth: 8,
	datalen: (1 + width) * height,
	},

	{
	plen: 128,
	bitdepth: 8,
	datalen: (1 + width) * height,
	},

	{
	plen: 16,
	bitdepth: 4,
	datalen: (1 + width/2) * height,
	},

	{
	plen: 4,
	bitdepth: 2,
	datalen: (1 + width/4) * height,
	},

	{
	plen: 2,
	bitdepth: 1,
	datalen: (1 + width/8) * height,
	},
	}

	for _, tc := range testCases {
	t.Run(fmt.Sprintf("plen-%d", tc.plen), func(t *testing.T) {
	// Create a paletted image with the correct palette length
	palette := make(color.Palette, tc.plen)
	for i := range palette {
	palette[i] = color.NRGBA{
	R: uint8(i),
	G: uint8(i),
	B: uint8(i),
	A: 255,
	}
	}
	m0 := image.NewPaletted(image.Rect(0, 0, width, height), palette)

	i := 0
	for y := 0; y < height; y++ {
	for x := 0; x < width; x++ {
	m0.SetColorIndex(x, y, uint8(i%tc.plen))
	i++
	}
	}

	// Encode the image
	var b bytes.Buffer
	if err := Encode(&b, m0); err != nil {
	t.Error(err)
	return
	}
	const chunkFieldsLength = 12 // 4 bytes for length, name and crc
	data := b.Bytes()
	i = len(pngHeader)

	for i < len(data)-chunkFieldsLength {
	length := binary.BigEndian.Uint32(data[i : i+4])
	name := string(data[i+4 : i+8])

	switch name {
	case "IHDR":
	bitdepth := data[i+8+8]
	if bitdepth != tc.bitdepth {
	t.Errorf("got bitdepth %d, want %d", bitdepth, tc.bitdepth)
	}
	case "IDAT":
	// Uncompress the image data
	r, err := zlib.NewReader(bytes.NewReader(data[i+8 : i+8+int(length)]))
	if err != nil {
	t.Error(err)
	return
	}
	n, err := io.Copy(io.Discard, r)
	if err != nil {
	t.Errorf("got error while reading image data: %v", err)
	}
	if n != int64(tc.datalen) {
	t.Errorf("got uncompressed data length %d, want %d", n, tc.datalen)
	}
	}

	i += chunkFieldsLength + int(length)
	}
	})

	}
	}

	func TestWriterLevels(t *testing.T) {
	m := image.NewNRGBA(image.Rect(0, 0, 100, 100))

	var b1, b2 bytes.Buffer
	if err := (&Encoder{}).Encode(&b1, m); err != nil {
	t.Fatal(err)
	}
	noenc := &Encoder{CompressionLevel: NoCompression}
	if err := noenc.Encode(&b2, m); err != nil {
	t.Fatal(err)
	}

	if b2.Len() <= b1.Len() {
	t.Error("DefaultCompression encoding was larger than NoCompression encoding")
	}
	if _, err := Decode(&b1); err != nil {
	t.Error("cannot decode DefaultCompression")
	}
	if _, err := Decode(&b2); err != nil {
	t.Error("cannot decode NoCompression")
	}
	}

	func TestSubImage(t *testing.T) {
	m0 := image.NewRGBA(image.Rect(0, 0, 256, 256))
	for y := 0; y < 256; y++ {
	for x := 0; x < 256; x++ {
	m0.Set(x, y, color.RGBA{uint8(x), uint8(y), 0, 255})
	}
	}
	m0 = m0.SubImage(image.Rect(50, 30, 250, 130)).(*image.RGBA)
	m1, err := encodeDecode(m0)
	if err != nil {
	t.Error(err)
	return
	}
	err = diff(m0, m1)
	if err != nil {
	t.Error(err)
	return
	}
	}

	func TestWriteRGBA(t *testing.T) {
	const width, height = 640, 480
	transparentImg := image.NewRGBA(image.Rect(0, 0, width, height))
	opaqueImg := image.NewRGBA(image.Rect(0, 0, width, height))
	mixedImg := image.NewRGBA(image.Rect(0, 0, width, height))
	translucentImg := image.NewRGBA(image.Rect(0, 0, width, height))
	for y := 0; y < height; y++ {
	for x := 0; x < width; x++ {
	opaqueColor := color.RGBA{uint8(x), uint8(y), uint8(y + x), 255}
	translucentColor := color.RGBA{uint8(x) % 128, uint8(y) % 128, uint8(y+x) % 128, 128}
	opaqueImg.Set(x, y, opaqueColor)
	translucentImg.Set(x, y, translucentColor)
	if y%2 == 0 {
	mixedImg.Set(x, y, opaqueColor)
	}
	}
	}

	testCases := []struct {
	name string
	img image.Image
	}{
	{"Transparent RGBA", transparentImg},
	{"Opaque RGBA", opaqueImg},
	{"50/50 Transparent/Opaque RGBA", mixedImg},
	{"RGBA with variable alpha", translucentImg},
	}

	for _, tc := range testCases {
	t.Run(tc.name, func(t *testing.T) {
	m0 := tc.img
	m1, err := encodeDecode(m0)
	if err != nil {
	t.Fatal(err)
	}
	err = diff(convertToNRGBA(m0), m1)
	if err != nil {
	t.Error(err)
	}
	})
	}
	}

	func BenchmarkEncodeGray(b *testing.B) {
	img := image.NewGray(image.Rect(0, 0, 640, 480))
	b.SetBytes(640 * 480 * 1)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	Encode(io.Discard, img)
	}
	}

	type pool struct {
	b *EncoderBuffer
	}

	func (p pool) Get() EncoderBuffer {
	return p.b
	}

	func (p pool) Put(b EncoderBuffer) {
	p.b = b
	}

	func BenchmarkEncodeGrayWithBufferPool(b *testing.B) {
	img := image.NewGray(image.Rect(0, 0, 640, 480))
	e := Encoder{
	BufferPool: &pool{},
	}
	b.SetBytes(640 * 480 * 1)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	e.Encode(io.Discard, img)
	}
	}

	func BenchmarkEncodeNRGBOpaque(b *testing.B) {
	img := image.NewNRGBA(image.Rect(0, 0, 640, 480))
	// Set all pixels to 0xFF alpha to force opaque mode.
	bo := img.Bounds()
	for y := bo.Min.Y; y < bo.Max.Y; y++ {
	for x := bo.Min.X; x < bo.Max.X; x++ {
	img.Set(x, y, color.NRGBA{0, 0, 0, 255})
	}
	}
	if !img.Opaque() {
	b.Fatal("expected image to be opaque")
	}
	b.SetBytes(640 * 480 * 4)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	Encode(io.Discard, img)
	}
	}

	func BenchmarkEncodeNRGBA(b *testing.B) {
	img := image.NewNRGBA(image.Rect(0, 0, 640, 480))
	if img.Opaque() {
	b.Fatal("expected image not to be opaque")
	}
	b.SetBytes(640 * 480 * 4)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	Encode(io.Discard, img)
	}
	}

	func BenchmarkEncodePaletted(b *testing.B) {
	img := image.NewPaletted(image.Rect(0, 0, 640, 480), color.Palette{
	color.RGBA{0, 0, 0, 255},
	color.RGBA{255, 255, 255, 255},
	})
	b.SetBytes(640 * 480 * 1)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	Encode(io.Discard, img)
	}
	}

	func BenchmarkEncodeRGBOpaque(b *testing.B) {
	img := image.NewRGBA(image.Rect(0, 0, 640, 480))
	// Set all pixels to 0xFF alpha to force opaque mode.
	bo := img.Bounds()
	for y := bo.Min.Y; y < bo.Max.Y; y++ {
	for x := bo.Min.X; x < bo.Max.X; x++ {
	img.Set(x, y, color.RGBA{0, 0, 0, 255})
	}
	}
	if !img.Opaque() {
	b.Fatal("expected image to be opaque")
	}
	b.SetBytes(640 * 480 * 4)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	Encode(io.Discard, img)
	}
	}

	func BenchmarkEncodeRGBA(b *testing.B) {
	const width, height = 640, 480
	img := image.NewRGBA(image.Rect(0, 0, width, height))
	for y := 0; y < height; y++ {
	for x := 0; x < width; x++ {
	percent := (x + y) % 100
	switch {
	case percent < 10: // 10% of pixels are translucent (have alpha >0 and <255)
	img.Set(x, y, color.NRGBA{uint8(x), uint8(y), uint8(x * y), uint8(percent)})
	case percent < 40: // 30% of pixels are transparent (have alpha == 0)
	img.Set(x, y, color.NRGBA{uint8(x), uint8(y), uint8(x * y), 0})
	default: // 60% of pixels are opaque (have alpha == 255)
	img.Set(x, y, color.NRGBA{uint8(x), uint8(y), uint8(x * y), 255})
	}
	}
	}
	if img.Opaque() {
	b.Fatal("expected image not to be opaque")
	}
	b.SetBytes(width * height * 4)
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
	Encode(io.Discard, img)
	}
	}