1 files changed, 289 insertions, 0 deletions
diff --git a/src/image/jpeg/writer_test.go b/src/image/jpeg/writer_test.go
new file mode 100644
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--- /dev/null
+++ b/src/image/jpeg/writer_test.go
@@ -0,0 +1,289 @@
+// 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"
+	"math/rand"
+	"os"
+	"strings"
+	"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 := &strings.Builder{}
+		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) {
+	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.ReportAllocs()
+	b.ResetTimer()
+	options := &Options{Quality: 90}
+	for i := 0; i < b.N; i++ {
+		Encode(io.Discard, img, options)
+	}
+}
+
+func BenchmarkEncodeYCbCr(b *testing.B) {
+	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.ReportAllocs()
+	b.ResetTimer()
+	options := &Options{Quality: 90}
+	for i := 0; i < b.N; i++ {
+		Encode(io.Discard, img, options)
+	}
+}