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
     3  // license that can be found in the LICENSE file.
     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) {
    72  	bad := false
    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)
    79  				bad = true
    80  			}
    81  		}
    82  	}
    83  	if bad {
    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 {
   132  		// Read the image.
   133  		m0, err := readPng(tc.filename)
   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++ {
   264  		Encode(io.Discard, img, options)
   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++ {
   286  		Encode(io.Discard, img, options)
   287  	}
   288  }
   289
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