image/jpeg: add an encoder.

It is based on changeset 4186064 by Raph Levien <raph@google.com>.

R=r, nigeltao_gnome
CC=golang-dev
https://golang.org/cl/4435051

src/pkg/Makefile

@@ -183,7 +183,6 @@ NOTEST+=\
 	hash\
 	http/pprof\
 	http/httptest\
-	image/jpeg\
 	net/dict\
 	rand\
 	runtime/cgo\

src/pkg/image/jpeg/Makefile

@@ -6,8 +6,10 @@ include ../../../Make.inc
 
 TARG=image/jpeg
 GOFILES=\
+	fdct.go\
 	huffman.go\
 	idct.go\
 	reader.go\
+	writer.go\
 
 include ../../../Make.pkg

src/pkg/image/jpeg/fdct.go

+// 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
+
+// This file implements a Forward Discrete Cosine Transformation.
+
+/*
+It is based on the code in jfdctint.c from the Independent JPEG Group,
+found at http://www.ijg.org/files/jpegsrc.v8c.tar.gz.
+
+The "LEGAL ISSUES" section of the README in that archive says:
+
+In plain English:
+
+1. We don't promise that this software works.  (But if you find any bugs,
+   please let us know!)
+2. You can use this software for whatever you want.  You don't have to pay us.
+3. You may not pretend that you wrote this software.  If you use it in a
+   program, you must acknowledge somewhere in your documentation that
+   you've used the IJG code.
+
+In legalese:
+
+The authors make NO WARRANTY or representation, either express or implied,
+with respect to this software, its quality, accuracy, merchantability, or
+fitness for a particular purpose.  This software is provided "AS IS", and you,
+its user, assume the entire risk as to its quality and accuracy.
+
+This software is copyright (C) 1991-2011, Thomas G. Lane, Guido Vollbeding.
+All Rights Reserved except as specified below.
+
+Permission is hereby granted to use, copy, modify, and distribute this
+software (or portions thereof) for any purpose, without fee, subject to these
+conditions:
+(1) If any part of the source code for this software is distributed, then this
+README file must be included, with this copyright and no-warranty notice
+unaltered; and any additions, deletions, or changes to the original files
+must be clearly indicated in accompanying documentation.
+(2) If only executable code is distributed, then the accompanying
+documentation must state that "this software is based in part on the work of
+the Independent JPEG Group".
+(3) Permission for use of this software is granted only if the user accepts
+full responsibility for any undesirable consequences; the authors accept
+NO LIABILITY for damages of any kind.
+
+These conditions apply to any software derived from or based on the IJG code,
+not just to the unmodified library.  If you use our work, you ought to
+acknowledge us.
+
+Permission is NOT granted for the use of any IJG author's name or company name
+in advertising or publicity relating to this software or products derived from
+it.  This software may be referred to only as "the Independent JPEG Group's
+software".
+
+We specifically permit and encourage the use of this software as the basis of
+commercial products, provided that all warranty or liability claims are
+assumed by the product vendor.
+*/
+
+// Trigonometric constants in 13-bit fixed point format.
+const (
+	fix_0_298631336 = 2446
+	fix_0_390180644 = 3196
+	fix_0_541196100 = 4433
+	fix_0_765366865 = 6270
+	fix_0_899976223 = 7373
+	fix_1_175875602 = 9633
+	fix_1_501321110 = 12299
+	fix_1_847759065 = 15137
+	fix_1_961570560 = 16069
+	fix_2_053119869 = 16819
+	fix_2_562915447 = 20995
+	fix_3_072711026 = 25172
+)
+
+const (
+	constBits     = 13
+	pass1Bits     = 2
+	centerJSample = 128
+)
+
+// fdct performs a forward DCT on an 8x8 block of coefficients, including a
+// level shift.
+func fdct(b *block) {
+	// Pass 1: process rows.
+	for y := 0; y < 8; y++ {
+		x0 := b[y*8+0]
+		x1 := b[y*8+1]
+		x2 := b[y*8+2]
+		x3 := b[y*8+3]
+		x4 := b[y*8+4]
+		x5 := b[y*8+5]
+		x6 := b[y*8+6]
+		x7 := b[y*8+7]
+
+		tmp0 := x0 + x7
+		tmp1 := x1 + x6
+		tmp2 := x2 + x5
+		tmp3 := x3 + x4
+
+		tmp10 := tmp0 + tmp3
+		tmp12 := tmp0 - tmp3
+		tmp11 := tmp1 + tmp2
+		tmp13 := tmp1 - tmp2
+
+		tmp0 = x0 - x7
+		tmp1 = x1 - x6
+		tmp2 = x2 - x5
+		tmp3 = x3 - x4
+
+		b[y*8+0] = (tmp10 + tmp11 - 8*centerJSample) << pass1Bits
+		b[y*8+4] = (tmp10 - tmp11) << pass1Bits
+		z1 := (tmp12 + tmp13) * fix_0_541196100
+		z1 += 1 << (constBits - pass1Bits - 1)
+		b[y*8+2] = (z1 + tmp12*fix_0_765366865) >> (constBits - pass1Bits)
+		b[y*8+6] = (z1 - tmp13*fix_1_847759065) >> (constBits - pass1Bits)
+
+		tmp10 = tmp0 + tmp3
+		tmp11 = tmp1 + tmp2
+		tmp12 = tmp0 + tmp2
+		tmp13 = tmp1 + tmp3
+		z1 = (tmp12 + tmp13) * fix_1_175875602
+		z1 += 1 << (constBits - pass1Bits - 1)
+		tmp0 = tmp0 * fix_1_501321110
+		tmp1 = tmp1 * fix_3_072711026
+		tmp2 = tmp2 * fix_2_053119869
+		tmp3 = tmp3 * fix_0_298631336
+		tmp10 = tmp10 * -fix_0_899976223
+		tmp11 = tmp11 * -fix_2_562915447
+		tmp12 = tmp12 * -fix_0_390180644
+		tmp13 = tmp13 * -fix_1_961570560
+
+		tmp12 += z1
+		tmp13 += z1
+		b[y*8+1] = (tmp0 + tmp10 + tmp12) >> (constBits - pass1Bits)
+		b[y*8+3] = (tmp1 + tmp11 + tmp13) >> (constBits - pass1Bits)
+		b[y*8+5] = (tmp2 + tmp11 + tmp12) >> (constBits - pass1Bits)
+		b[y*8+7] = (tmp3 + tmp10 + tmp13) >> (constBits - pass1Bits)
+	}
+	// Pass 2: process columns.
+	// We remove pass1Bits scaling, but leave results scaled up by an overall factor of 8.
+	for x := 0; x < 8; x++ {
+		tmp0 := b[0*8+x] + b[7*8+x]
+		tmp1 := b[1*8+x] + b[6*8+x]
+		tmp2 := b[2*8+x] + b[5*8+x]
+		tmp3 := b[3*8+x] + b[4*8+x]
+
+		tmp10 := tmp0 + tmp3 + 1<<(pass1Bits-1)
+		tmp12 := tmp0 - tmp3
+		tmp11 := tmp1 + tmp2
+		tmp13 := tmp1 - tmp2
+
+		tmp0 = b[0*8+x] - b[7*8+x]
+		tmp1 = b[1*8+x] - b[6*8+x]
+		tmp2 = b[2*8+x] - b[5*8+x]
+		tmp3 = b[3*8+x] - b[4*8+x]
+
+		b[0*8+x] = (tmp10 + tmp11) >> pass1Bits
+		b[4*8+x] = (tmp10 - tmp11) >> pass1Bits
+
+		z1 := (tmp12 + tmp13) * fix_0_541196100
+		z1 += 1 << (constBits + pass1Bits - 1)
+		b[2*8+x] = (z1 + tmp12*fix_0_765366865) >> (constBits + pass1Bits)
+		b[6*8+x] = (z1 - tmp13*fix_1_847759065) >> (constBits + pass1Bits)
+
+		tmp10 = tmp0 + tmp3
+		tmp11 = tmp1 + tmp2
+		tmp12 = tmp0 + tmp2
+		tmp13 = tmp1 + tmp3
+		z1 = (tmp12 + tmp13) * fix_1_175875602
+		z1 += 1 << (constBits + pass1Bits - 1)
+		tmp0 = tmp0 * fix_1_501321110
+		tmp1 = tmp1 * fix_3_072711026
+		tmp2 = tmp2 * fix_2_053119869
+		tmp3 = tmp3 * fix_0_298631336
+		tmp10 = tmp10 * -fix_0_899976223
+		tmp11 = tmp11 * -fix_2_562915447
+		tmp12 = tmp12 * -fix_0_390180644
+		tmp13 = tmp13 * -fix_1_961570560
+
+		tmp12 += z1
+		tmp13 += z1
+		b[1*8+x] = (tmp0 + tmp10 + tmp12) >> (constBits + pass1Bits)
+		b[3*8+x] = (tmp1 + tmp11 + tmp13) >> (constBits + pass1Bits)
+		b[5*8+x] = (tmp2 + tmp11 + tmp12) >> (constBits + pass1Bits)
+		b[7*8+x] = (tmp3 + tmp10 + tmp13) >> (constBits + pass1Bits)
+	}
+}

src/pkg/image/jpeg/idct.go

@@ -63,7 +63,7 @@ const (
 //
 // For more on the actual algorithm, see Z. Wang, "Fast algorithms for the discrete W transform and
 // for the discrete Fourier transform", IEEE Trans. on ASSP, Vol. ASSP- 32, pp. 803-816, Aug. 1984.
-func idct(b *[blockSize]int) {
+func idct(b *block) {
 	// Horizontal 1-D IDCT.
 	for y := 0; y < 8; y++ {
 		// If all the AC components are zero, then the IDCT is trivial.

src/pkg/image/jpeg/reader.go

@@ -2,11 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// The jpeg package implements a decoder for JPEG images, as defined in ITU-T T.81.
+// Package jpeg implements a JPEG image decoder and encoder.
+//
+// JPEG is defined in ITU-T T.81: http://www.w3.org/Graphics/JPEG/itu-t81.pdf.
 package jpeg
 
-// See http://www.w3.org/Graphics/JPEG/itu-t81.pdf
-
 import (
 	"bufio"
 	"image"
@@ -32,6 +32,8 @@ type component struct {
 	tq uint8 // Quantization table destination selector.
 }
 
+type block [blockSize]int
+
 const (
 	blockSize = 64 // A DCT block is 8x8.
 
@@ -88,9 +90,9 @@ type decoder struct {
 	ri            int // Restart Interval.
 	comps         [nComponent]component
 	huff          [maxTc + 1][maxTh + 1]huffman
-	quant         [maxTq + 1][blockSize]int
+	quant         [maxTq + 1]block
 	b             bits
-	blocks        [nComponent][maxH * maxV][blockSize]int
+	blocks        [nComponent][maxH * maxV]block
 	tmp           [1024]byte
 }
 
@@ -269,7 +271,7 @@ func (d *decoder) processSOS(n int) os.Error {
 	myy := (d.height + 8*int(v0) - 1) / (8 * int(v0))
 
 	mcu, expectedRST := 0, uint8(rst0Marker)
-	var allZeroes [blockSize]int
+	var allZeroes block
 	var dc [nComponent]int
 	for my := 0; my < myy; my++ {
 		for mx := 0; mx < mxx; mx++ {

src/pkg/image/jpeg/writer_test.go

+// 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"
+	"image"
+	"image/png"
+	"os"
+	"testing"
+)
+
+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, os.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.
+		buf := bytes.NewBuffer(nil)
+		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
+		}
+		// Compute the average delta in RGB space.
+		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
+			}
+		}
+		// Compare the average delta to the tolerance level.
+		if sum/n > tc.tolerance {
+			t.Errorf("%s, quality=%d: average delta is too high", tc.filename, tc.quality)
+			continue
+		}
+	}
+}