...
Run Format

Source file src/image/jpeg/writer_test.go

Documentation: image/jpeg

  // 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 jpeg
  
  import (
  	"bytes"
  	"fmt"
  	"image"
  	"image/color"
  	"image/png"
  	"io/ioutil"
  	"math/rand"
  	"os"
  	"testing"
  )
  
  // zigzag maps from the natural ordering to the zig-zag ordering. For example,
  // zigzag[0*8 + 3] is the zig-zag sequence number of the element in the fourth
  // column and first row.
  var zigzag = [blockSize]int{
  	0, 1, 5, 6, 14, 15, 27, 28,
  	2, 4, 7, 13, 16, 26, 29, 42,
  	3, 8, 12, 17, 25, 30, 41, 43,
  	9, 11, 18, 24, 31, 40, 44, 53,
  	10, 19, 23, 32, 39, 45, 52, 54,
  	20, 22, 33, 38, 46, 51, 55, 60,
  	21, 34, 37, 47, 50, 56, 59, 61,
  	35, 36, 48, 49, 57, 58, 62, 63,
  }
  
  func TestZigUnzig(t *testing.T) {
  	for i := 0; i < blockSize; i++ {
  		if unzig[zigzag[i]] != i {
  			t.Errorf("unzig[zigzag[%d]] == %d", i, unzig[zigzag[i]])
  		}
  		if zigzag[unzig[i]] != i {
  			t.Errorf("zigzag[unzig[%d]] == %d", i, zigzag[unzig[i]])
  		}
  	}
  }
  
  // unscaledQuantInNaturalOrder are the unscaled quantization tables in
  // natural (not zig-zag) order, as specified in section K.1.
  var unscaledQuantInNaturalOrder = [nQuantIndex][blockSize]byte{
  	// Luminance.
  	{
  		16, 11, 10, 16, 24, 40, 51, 61,
  		12, 12, 14, 19, 26, 58, 60, 55,
  		14, 13, 16, 24, 40, 57, 69, 56,
  		14, 17, 22, 29, 51, 87, 80, 62,
  		18, 22, 37, 56, 68, 109, 103, 77,
  		24, 35, 55, 64, 81, 104, 113, 92,
  		49, 64, 78, 87, 103, 121, 120, 101,
  		72, 92, 95, 98, 112, 100, 103, 99,
  	},
  	// Chrominance.
  	{
  		17, 18, 24, 47, 99, 99, 99, 99,
  		18, 21, 26, 66, 99, 99, 99, 99,
  		24, 26, 56, 99, 99, 99, 99, 99,
  		47, 66, 99, 99, 99, 99, 99, 99,
  		99, 99, 99, 99, 99, 99, 99, 99,
  		99, 99, 99, 99, 99, 99, 99, 99,
  		99, 99, 99, 99, 99, 99, 99, 99,
  		99, 99, 99, 99, 99, 99, 99, 99,
  	},
  }
  
  func TestUnscaledQuant(t *testing.T) {
  	bad := false
  	for i := quantIndex(0); i < nQuantIndex; i++ {
  		for zig := 0; zig < blockSize; zig++ {
  			got := unscaledQuant[i][zig]
  			want := unscaledQuantInNaturalOrder[i][unzig[zig]]
  			if got != want {
  				t.Errorf("i=%d, zig=%d: got %d, want %d", i, zig, got, want)
  				bad = true
  			}
  		}
  	}
  	if bad {
  		names := [nQuantIndex]string{"Luminance", "Chrominance"}
  		buf := &bytes.Buffer{}
  		for i, name := range names {
  			fmt.Fprintf(buf, "// %s.\n{\n", name)
  			for zig := 0; zig < blockSize; zig++ {
  				fmt.Fprintf(buf, "%d, ", unscaledQuantInNaturalOrder[i][unzig[zig]])
  				if zig%8 == 7 {
  					buf.WriteString("\n")
  				}
  			}
  			buf.WriteString("},\n")
  		}
  		t.Logf("expected unscaledQuant values:\n%s", buf.String())
  	}
  }
  
  var testCase = []struct {
  	filename  string
  	quality   int
  	tolerance int64
  }{
  	{"../testdata/video-001.png", 1, 24 << 8},
  	{"../testdata/video-001.png", 20, 12 << 8},
  	{"../testdata/video-001.png", 60, 8 << 8},
  	{"../testdata/video-001.png", 80, 6 << 8},
  	{"../testdata/video-001.png", 90, 4 << 8},
  	{"../testdata/video-001.png", 100, 2 << 8},
  }
  
  func delta(u0, u1 uint32) int64 {
  	d := int64(u0) - int64(u1)
  	if d < 0 {
  		return -d
  	}
  	return d
  }
  
  func readPng(filename string) (image.Image, error) {
  	f, err := os.Open(filename)
  	if err != nil {
  		return nil, err
  	}
  	defer f.Close()
  	return png.Decode(f)
  }
  
  func TestWriter(t *testing.T) {
  	for _, tc := range testCase {
  		// Read the image.
  		m0, err := readPng(tc.filename)
  		if err != nil {
  			t.Error(tc.filename, err)
  			continue
  		}
  		// Encode that image as JPEG.
  		var buf bytes.Buffer
  		err = Encode(&buf, m0, &Options{Quality: tc.quality})
  		if err != nil {
  			t.Error(tc.filename, err)
  			continue
  		}
  		// Decode that JPEG.
  		m1, err := Decode(&buf)
  		if err != nil {
  			t.Error(tc.filename, err)
  			continue
  		}
  		if m0.Bounds() != m1.Bounds() {
  			t.Errorf("%s, bounds differ: %v and %v", tc.filename, m0.Bounds(), m1.Bounds())
  			continue
  		}
  		// Compare the average delta to the tolerance level.
  		if averageDelta(m0, m1) > tc.tolerance {
  			t.Errorf("%s, quality=%d: average delta is too high", tc.filename, tc.quality)
  			continue
  		}
  	}
  }
  
  // TestWriteGrayscale tests that a grayscale images survives a round-trip
  // through encode/decode cycle.
  func TestWriteGrayscale(t *testing.T) {
  	m0 := image.NewGray(image.Rect(0, 0, 32, 32))
  	for i := range m0.Pix {
  		m0.Pix[i] = uint8(i)
  	}
  	var buf bytes.Buffer
  	if err := Encode(&buf, m0, nil); err != nil {
  		t.Fatal(err)
  	}
  	m1, err := Decode(&buf)
  	if err != nil {
  		t.Fatal(err)
  	}
  	if m0.Bounds() != m1.Bounds() {
  		t.Fatalf("bounds differ: %v and %v", m0.Bounds(), m1.Bounds())
  	}
  	if _, ok := m1.(*image.Gray); !ok {
  		t.Errorf("got %T, want *image.Gray", m1)
  	}
  	// Compare the average delta to the tolerance level.
  	want := int64(2 << 8)
  	if got := averageDelta(m0, m1); got > want {
  		t.Errorf("average delta too high; got %d, want <= %d", got, want)
  	}
  }
  
  // averageDelta returns the average delta in RGB space. The two images must
  // have the same bounds.
  func averageDelta(m0, m1 image.Image) int64 {
  	b := m0.Bounds()
  	var sum, n int64
  	for y := b.Min.Y; y < b.Max.Y; y++ {
  		for x := b.Min.X; x < b.Max.X; x++ {
  			c0 := m0.At(x, y)
  			c1 := m1.At(x, y)
  			r0, g0, b0, _ := c0.RGBA()
  			r1, g1, b1, _ := c1.RGBA()
  			sum += delta(r0, r1)
  			sum += delta(g0, g1)
  			sum += delta(b0, b1)
  			n += 3
  		}
  	}
  	return sum / n
  }
  
  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)),
  				uint8(rnd.Intn(256)),
  				uint8(rnd.Intn(256)),
  				255,
  			}
  			imgRGBA.SetRGBA(x, y, col)
  			yo := imgYCbCr.YOffset(x, y)
  			co := imgYCbCr.COffset(x, y)
  			cy, ccr, ccb := color.RGBToYCbCr(col.R, col.G, col.B)
  			imgYCbCr.Y[yo] = cy
  			imgYCbCr.Cb[co] = ccr
  			imgYCbCr.Cr[co] = ccb
  		}
  	}
  
  	// Now check that both images are identical after an encode.
  	var bufRGBA, bufYCbCr bytes.Buffer
  	Encode(&bufRGBA, imgRGBA, nil)
  	Encode(&bufYCbCr, imgYCbCr, nil)
  	if !bytes.Equal(bufRGBA.Bytes(), bufYCbCr.Bytes()) {
  		t.Errorf("RGBA and YCbCr encoded bytes differ")
  	}
  }
  
  func BenchmarkEncodeRGBA(b *testing.B) {
  	b.StopTimer()
  	img := image.NewRGBA(image.Rect(0, 0, 640, 480))
  	bo := img.Bounds()
  	rnd := rand.New(rand.NewSource(123))
  	for y := bo.Min.Y; y < bo.Max.Y; y++ {
  		for x := bo.Min.X; x < bo.Max.X; x++ {
  			img.SetRGBA(x, y, color.RGBA{
  				uint8(rnd.Intn(256)),
  				uint8(rnd.Intn(256)),
  				uint8(rnd.Intn(256)),
  				255,
  			})
  		}
  	}
  	b.SetBytes(640 * 480 * 4)
  	b.StartTimer()
  	options := &Options{Quality: 90}
  	for i := 0; i < b.N; i++ {
  		Encode(ioutil.Discard, img, options)
  	}
  }
  
  func BenchmarkEncodeYCbCr(b *testing.B) {
  	b.StopTimer()
  	img := image.NewYCbCr(image.Rect(0, 0, 640, 480), image.YCbCrSubsampleRatio420)
  	bo := img.Bounds()
  	rnd := rand.New(rand.NewSource(123))
  	for y := bo.Min.Y; y < bo.Max.Y; y++ {
  		for x := bo.Min.X; x < bo.Max.X; x++ {
  			cy := img.YOffset(x, y)
  			ci := img.COffset(x, y)
  			img.Y[cy] = uint8(rnd.Intn(256))
  			img.Cb[ci] = uint8(rnd.Intn(256))
  			img.Cr[ci] = uint8(rnd.Intn(256))
  		}
  	}
  	b.SetBytes(640 * 480 * 3)
  	b.StartTimer()
  	options := &Options{Quality: 90}
  	for i := 0; i < b.N; i++ {
  		Encode(ioutil.Discard, img, options)
  	}
  }
  

View as plain text