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# Source file src/image/jpeg/writer_test.go

## Documentation: image/jpeg

```     1  // Copyright 2011 The Go Authors. All rights reserved.
2  // Use of this source code is governed by a BSD-style
4
5  package jpeg
6
7  import (
8  	"bytes"
9  	"fmt"
10  	"image"
11  	"image/color"
12  	"image/png"
13  	"io"
14  	"math/rand"
15  	"os"
16  	"testing"
17  )
18
19  // zigzag maps from the natural ordering to the zig-zag ordering. For example,
20  // zigzag[0*8 + 3] is the zig-zag sequence number of the element in the fourth
21  // column and first row.
22  var zigzag = [blockSize]int{
23  	0, 1, 5, 6, 14, 15, 27, 28,
24  	2, 4, 7, 13, 16, 26, 29, 42,
25  	3, 8, 12, 17, 25, 30, 41, 43,
26  	9, 11, 18, 24, 31, 40, 44, 53,
27  	10, 19, 23, 32, 39, 45, 52, 54,
28  	20, 22, 33, 38, 46, 51, 55, 60,
29  	21, 34, 37, 47, 50, 56, 59, 61,
30  	35, 36, 48, 49, 57, 58, 62, 63,
31  }
32
33  func TestZigUnzig(t *testing.T) {
34  	for i := 0; i < blockSize; i++ {
35  		if unzig[zigzag[i]] != i {
36  			t.Errorf("unzig[zigzag[%d]] == %d", i, unzig[zigzag[i]])
37  		}
38  		if zigzag[unzig[i]] != i {
39  			t.Errorf("zigzag[unzig[%d]] == %d", i, zigzag[unzig[i]])
40  		}
41  	}
42  }
43
44  // unscaledQuantInNaturalOrder are the unscaled quantization tables in
45  // natural (not zig-zag) order, as specified in section K.1.
46  var unscaledQuantInNaturalOrder = [nQuantIndex][blockSize]byte{
47  	// Luminance.
48  	{
49  		16, 11, 10, 16, 24, 40, 51, 61,
50  		12, 12, 14, 19, 26, 58, 60, 55,
51  		14, 13, 16, 24, 40, 57, 69, 56,
52  		14, 17, 22, 29, 51, 87, 80, 62,
53  		18, 22, 37, 56, 68, 109, 103, 77,
54  		24, 35, 55, 64, 81, 104, 113, 92,
55  		49, 64, 78, 87, 103, 121, 120, 101,
56  		72, 92, 95, 98, 112, 100, 103, 99,
57  	},
58  	// Chrominance.
59  	{
60  		17, 18, 24, 47, 99, 99, 99, 99,
61  		18, 21, 26, 66, 99, 99, 99, 99,
62  		24, 26, 56, 99, 99, 99, 99, 99,
63  		47, 66, 99, 99, 99, 99, 99, 99,
64  		99, 99, 99, 99, 99, 99, 99, 99,
65  		99, 99, 99, 99, 99, 99, 99, 99,
66  		99, 99, 99, 99, 99, 99, 99, 99,
67  		99, 99, 99, 99, 99, 99, 99, 99,
68  	},
69  }
70
71  func TestUnscaledQuant(t *testing.T) {
73  	for i := quantIndex(0); i < nQuantIndex; i++ {
74  		for zig := 0; zig < blockSize; zig++ {
75  			got := unscaledQuant[i][zig]
76  			want := unscaledQuantInNaturalOrder[i][unzig[zig]]
77  			if got != want {
78  				t.Errorf("i=%d, zig=%d: got %d, want %d", i, zig, got, want)
80  			}
81  		}
82  	}
84  		names := [nQuantIndex]string{"Luminance", "Chrominance"}
85  		buf := &bytes.Buffer{}
86  		for i, name := range names {
87  			fmt.Fprintf(buf, "// %s.\n{\n", name)
88  			for zig := 0; zig < blockSize; zig++ {
89  				fmt.Fprintf(buf, "%d, ", unscaledQuantInNaturalOrder[i][unzig[zig]])
90  				if zig%8 == 7 {
91  					buf.WriteString("\n")
92  				}
93  			}
94  			buf.WriteString("},\n")
95  		}
96  		t.Logf("expected unscaledQuant values:\n%s", buf.String())
97  	}
98  }
99
100  var testCase = []struct {
101  	filename  string
102  	quality   int
103  	tolerance int64
104  }{
105  	{"../testdata/video-001.png", 1, 24 << 8},
106  	{"../testdata/video-001.png", 20, 12 << 8},
107  	{"../testdata/video-001.png", 60, 8 << 8},
108  	{"../testdata/video-001.png", 80, 6 << 8},
109  	{"../testdata/video-001.png", 90, 4 << 8},
110  	{"../testdata/video-001.png", 100, 2 << 8},
111  }
112
113  func delta(u0, u1 uint32) int64 {
114  	d := int64(u0) - int64(u1)
115  	if d < 0 {
116  		return -d
117  	}
118  	return d
119  }
120
121  func readPng(filename string) (image.Image, error) {
122  	f, err := os.Open(filename)
123  	if err != nil {
124  		return nil, err
125  	}
126  	defer f.Close()
127  	return png.Decode(f)
128  }
129
130  func TestWriter(t *testing.T) {
131  	for _, tc := range testCase {
134  		if err != nil {
135  			t.Error(tc.filename, err)
136  			continue
137  		}
138  		// Encode that image as JPEG.
139  		var buf bytes.Buffer
140  		err = Encode(&buf, m0, &Options{Quality: tc.quality})
141  		if err != nil {
142  			t.Error(tc.filename, err)
143  			continue
144  		}
145  		// Decode that JPEG.
146  		m1, err := Decode(&buf)
147  		if err != nil {
148  			t.Error(tc.filename, err)
149  			continue
150  		}
151  		if m0.Bounds() != m1.Bounds() {
152  			t.Errorf("%s, bounds differ: %v and %v", tc.filename, m0.Bounds(), m1.Bounds())
153  			continue
154  		}
155  		// Compare the average delta to the tolerance level.
156  		if averageDelta(m0, m1) > tc.tolerance {
157  			t.Errorf("%s, quality=%d: average delta is too high", tc.filename, tc.quality)
158  			continue
159  		}
160  	}
161  }
162
163  // TestWriteGrayscale tests that a grayscale images survives a round-trip
164  // through encode/decode cycle.
165  func TestWriteGrayscale(t *testing.T) {
166  	m0 := image.NewGray(image.Rect(0, 0, 32, 32))
167  	for i := range m0.Pix {
168  		m0.Pix[i] = uint8(i)
169  	}
170  	var buf bytes.Buffer
171  	if err := Encode(&buf, m0, nil); err != nil {
172  		t.Fatal(err)
173  	}
174  	m1, err := Decode(&buf)
175  	if err != nil {
176  		t.Fatal(err)
177  	}
178  	if m0.Bounds() != m1.Bounds() {
179  		t.Fatalf("bounds differ: %v and %v", m0.Bounds(), m1.Bounds())
180  	}
181  	if _, ok := m1.(*image.Gray); !ok {
182  		t.Errorf("got %T, want *image.Gray", m1)
183  	}
184  	// Compare the average delta to the tolerance level.
185  	want := int64(2 << 8)
186  	if got := averageDelta(m0, m1); got > want {
187  		t.Errorf("average delta too high; got %d, want <= %d", got, want)
188  	}
189  }
190
191  // averageDelta returns the average delta in RGB space. The two images must
192  // have the same bounds.
193  func averageDelta(m0, m1 image.Image) int64 {
194  	b := m0.Bounds()
195  	var sum, n int64
196  	for y := b.Min.Y; y < b.Max.Y; y++ {
197  		for x := b.Min.X; x < b.Max.X; x++ {
198  			c0 := m0.At(x, y)
199  			c1 := m1.At(x, y)
200  			r0, g0, b0, _ := c0.RGBA()
201  			r1, g1, b1, _ := c1.RGBA()
202  			sum += delta(r0, r1)
203  			sum += delta(g0, g1)
204  			sum += delta(b0, b1)
205  			n += 3
206  		}
207  	}
208  	return sum / n
209  }
210
211  func TestEncodeYCbCr(t *testing.T) {
212  	bo := image.Rect(0, 0, 640, 480)
213  	imgRGBA := image.NewRGBA(bo)
214  	// Must use 444 subsampling to avoid lossy RGBA to YCbCr conversion.
215  	imgYCbCr := image.NewYCbCr(bo, image.YCbCrSubsampleRatio444)
216  	rnd := rand.New(rand.NewSource(123))
217  	// Create identical rgba and ycbcr images.
218  	for y := bo.Min.Y; y < bo.Max.Y; y++ {
219  		for x := bo.Min.X; x < bo.Max.X; x++ {
220  			col := color.RGBA{
221  				uint8(rnd.Intn(256)),
222  				uint8(rnd.Intn(256)),
223  				uint8(rnd.Intn(256)),
224  				255,
225  			}
226  			imgRGBA.SetRGBA(x, y, col)
227  			yo := imgYCbCr.YOffset(x, y)
228  			co := imgYCbCr.COffset(x, y)
229  			cy, ccr, ccb := color.RGBToYCbCr(col.R, col.G, col.B)
230  			imgYCbCr.Y[yo] = cy
231  			imgYCbCr.Cb[co] = ccr
232  			imgYCbCr.Cr[co] = ccb
233  		}
234  	}
235
236  	// Now check that both images are identical after an encode.
237  	var bufRGBA, bufYCbCr bytes.Buffer
238  	Encode(&bufRGBA, imgRGBA, nil)
239  	Encode(&bufYCbCr, imgYCbCr, nil)
240  	if !bytes.Equal(bufRGBA.Bytes(), bufYCbCr.Bytes()) {
241  		t.Errorf("RGBA and YCbCr encoded bytes differ")
242  	}
243  }
244
245  func BenchmarkEncodeRGBA(b *testing.B) {
246  	img := image.NewRGBA(image.Rect(0, 0, 640, 480))
247  	bo := img.Bounds()
248  	rnd := rand.New(rand.NewSource(123))
249  	for y := bo.Min.Y; y < bo.Max.Y; y++ {
250  		for x := bo.Min.X; x < bo.Max.X; x++ {
251  			img.SetRGBA(x, y, color.RGBA{
252  				uint8(rnd.Intn(256)),
253  				uint8(rnd.Intn(256)),
254  				uint8(rnd.Intn(256)),
255  				255,
256  			})
257  		}
258  	}
259  	b.SetBytes(640 * 480 * 4)
260  	b.ReportAllocs()
261  	b.ResetTimer()
262  	options := &Options{Quality: 90}
263  	for i := 0; i < b.N; i++ {
265  	}
266  }
267
268  func BenchmarkEncodeYCbCr(b *testing.B) {
269  	img := image.NewYCbCr(image.Rect(0, 0, 640, 480), image.YCbCrSubsampleRatio420)
270  	bo := img.Bounds()
271  	rnd := rand.New(rand.NewSource(123))
272  	for y := bo.Min.Y; y < bo.Max.Y; y++ {
273  		for x := bo.Min.X; x < bo.Max.X; x++ {
274  			cy := img.YOffset(x, y)
275  			ci := img.COffset(x, y)
276  			img.Y[cy] = uint8(rnd.Intn(256))
277  			img.Cb[ci] = uint8(rnd.Intn(256))
278  			img.Cr[ci] = uint8(rnd.Intn(256))
279  		}
280  	}
281  	b.SetBytes(640 * 480 * 3)
282  	b.ReportAllocs()
283  	b.ResetTimer()
284  	options := &Options{Quality: 90}
285  	for i := 0; i < b.N; i++ {