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jpeg: import images/jpeg from go tip. 

Imported @ version:

  parent: 20306:04c9a977b540 tip
   runtime: make runtime·usleep and runtime·osyield callable from cgo callback
  branch: default
  commit: (clean)
  update: (current)

Addresses https://camlistore.org/issue/463

Change-Id: I5a38144cb944f6474085d305f86bd2231d7fb0a2
This commit is contained in:
Bill Thiede 2014-07-02 21:10:53 -07:00
parent bafc53703d
commit c919f12cf1
10 changed files with 2959 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
third_party/go/README vendored Normal file
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This directory contains portions of the standard library imported from tip to
take advantage of new features and bug fixes before they're available in the
stable branch.

299
third_party/go/pkg/image/jpeg/dct_test.go vendored Normal file
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// Copyright 2012 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"
"math"
"math/rand"
"testing"
)
func benchmarkDCT(b *testing.B, f func(*block)) {
b.StopTimer()
blocks := make([]block, 0, b.N*len(testBlocks))
for i := 0; i < b.N; i++ {
blocks = append(blocks, testBlocks[:]...)
}
b.StartTimer()
for i := range blocks {
f(&blocks[i])
}
}
func BenchmarkFDCT(b *testing.B) {
benchmarkDCT(b, fdct)
}
func BenchmarkIDCT(b *testing.B) {
benchmarkDCT(b, idct)
}
func TestDCT(t *testing.T) {
blocks := make([]block, len(testBlocks))
copy(blocks, testBlocks[:])
// Append some randomly generated blocks of varying sparseness.
r := rand.New(rand.NewSource(123))
for i := 0; i < 100; i++ {
b := block{}
n := r.Int() % 64
for j := 0; j < n; j++ {
b[r.Int()%len(b)] = r.Int31() % 256
}
blocks = append(blocks, b)
}
// Check that the FDCT and IDCT functions are inverses, after a scale and
// level shift. Scaling reduces the rounding errors in the conversion from
// floats to ints.
for i, b := range blocks {
got, want := b, b
for j := range got {
got[j] = (got[j] - 128) * 8
}
slowFDCT(&got)
slowIDCT(&got)
for j := range got {
got[j] = got[j]/8 + 128
}
if differ(&got, &want) {
t.Errorf("i=%d: IDCT(FDCT)\nsrc\n%s\ngot\n%s\nwant\n%s\n", i, &b, &got, &want)
}
}
// Check that the optimized and slow FDCT implementations agree.
// The fdct function already does a scale and level shift.
for i, b := range blocks {
got, want := b, b
fdct(&got)
for j := range want {
want[j] = (want[j] - 128) * 8
}
slowFDCT(&want)
if differ(&got, &want) {
t.Errorf("i=%d: FDCT\nsrc\n%s\ngot\n%s\nwant\n%s\n", i, &b, &got, &want)
}
}
// Check that the optimized and slow IDCT implementations agree.
for i, b := range blocks {
got, want := b, b
idct(&got)
slowIDCT(&want)
if differ(&got, &want) {
t.Errorf("i=%d: IDCT\nsrc\n%s\ngot\n%s\nwant\n%s\n", i, &b, &got, &want)
}
}
}
// differ reports whether any pair-wise elements in b0 and b1 differ by 2 or
// more. That tolerance is because there isn't a single definitive decoding of
// a given JPEG image, even before the YCbCr to RGB conversion; implementations
// can have different IDCT rounding errors.
func differ(b0, b1 *block) bool {
for i := range b0 {
delta := b0[i] - b1[i]
if delta < -2 || +2 < delta {
return true
}
}
return false
}
// alpha returns 1 if i is 0 and returns √2 otherwise.
func alpha(i int) float64 {
if i == 0 {
return 1
}
return math.Sqrt2
}
var cosines [32]float64 // cosines[k] = cos(π/2 * k/8)
func init() {
for k := range cosines {
cosines[k] = math.Cos(math.Pi * float64(k) / 16)
}
}
// slowFDCT performs the 8*8 2-dimensional forward discrete cosine transform:
//
// dst[u,v] = (1/8) * Σ_x Σ_y alpha(u) * alpha(v) * src[x,y] *
// cos((π/2) * (2*x + 1) * u / 8) *
// cos((π/2) * (2*y + 1) * v / 8)
//
// x and y are in pixel space, and u and v are in transform space.
//
// b acts as both dst and src.
func slowFDCT(b *block) {
var dst [blockSize]float64
for v := 0; v < 8; v++ {
for u := 0; u < 8; u++ {
sum := 0.0
for y := 0; y < 8; y++ {
for x := 0; x < 8; x++ {
sum += alpha(u) * alpha(v) * float64(b[8*y+x]) *
cosines[((2*x+1)*u)%32] *
cosines[((2*y+1)*v)%32]
}
}
dst[8*v+u] = sum / 8
}
}
// Convert from float64 to int32.
for i := range dst {
b[i] = int32(dst[i] + 0.5)
}
}
// slowIDCT performs the 8*8 2-dimensional inverse discrete cosine transform:
//
// dst[x,y] = (1/8) * Σ_u Σ_v alpha(u) * alpha(v) * src[u,v] *
// cos((π/2) * (2*x + 1) * u / 8) *
// cos((π/2) * (2*y + 1) * v / 8)
//
// x and y are in pixel space, and u and v are in transform space.
//
// b acts as both dst and src.
func slowIDCT(b *block) {
var dst [blockSize]float64
for y := 0; y < 8; y++ {
for x := 0; x < 8; x++ {
sum := 0.0
for v := 0; v < 8; v++ {
for u := 0; u < 8; u++ {
sum += alpha(u) * alpha(v) * float64(b[8*v+u]) *
cosines[((2*x+1)*u)%32] *
cosines[((2*y+1)*v)%32]
}
}
dst[8*y+x] = sum / 8
}
}
// Convert from float64 to int32.
for i := range dst {
b[i] = int32(dst[i] + 0.5)
}
}
func (b *block) String() string {
s := bytes.NewBuffer(nil)
fmt.Fprintf(s, "{\n")
for y := 0; y < 8; y++ {
fmt.Fprintf(s, "\t")
for x := 0; x < 8; x++ {
fmt.Fprintf(s, "0x%04x, ", uint16(b[8*y+x]))
}
fmt.Fprintln(s)
}
fmt.Fprintf(s, "}")
return s.String()
}
// testBlocks are the first 10 pre-IDCT blocks from ../testdata/video-001.jpeg.
var testBlocks = [10]block{
{
0x7f, 0xf6, 0x01, 0x07, 0xff, 0x00, 0x00, 0x00,
0xf5, 0x01, 0xfa, 0x01, 0xfe, 0x00, 0x01, 0x00,
0x05, 0x05, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
0x01, 0xff, 0xf8, 0x00, 0x01, 0xff, 0x00, 0x00,
0x00, 0x01, 0x00, 0x01, 0x00, 0xff, 0xff, 0x00,
0xff, 0x0c, 0x00, 0x00, 0x00, 0x00, 0xff, 0x01,
0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
0x01, 0x00, 0x00, 0x01, 0xff, 0x01, 0x00, 0xfe,
},
{
0x29, 0x07, 0x00, 0xfc, 0x01, 0x01, 0x00, 0x00,
0x07, 0x00, 0x03, 0x00, 0x01, 0x00, 0xff, 0xff,
0xff, 0xfd, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x04, 0x00, 0xff, 0x01, 0x00, 0x00,
0x01, 0x00, 0x01, 0xff, 0x00, 0x00, 0x00, 0x00,
0x01, 0xfa, 0x01, 0x00, 0x01, 0x00, 0x01, 0xff,
0x00, 0x00, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0xff, 0x00, 0xff, 0x00, 0x02,
},
{
0xc5, 0xfa, 0x01, 0x00, 0x00, 0x01, 0x00, 0xff,
0x02, 0xff, 0x01, 0x00, 0x01, 0x00, 0xff, 0x00,
0xff, 0xff, 0x00, 0xff, 0x01, 0x00, 0x00, 0x00,
0xff, 0x00, 0x01, 0x00, 0x00, 0x00, 0xff, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff,
0x00, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
},
{
0x86, 0x05, 0x00, 0x02, 0x00, 0x00, 0x01, 0x00,
0xf2, 0x06, 0x00, 0x00, 0x01, 0x02, 0x00, 0x00,
0xf6, 0xfa, 0xf9, 0x00, 0xff, 0x01, 0x00, 0x00,
0xf9, 0x00, 0x00, 0xff, 0x00, 0x00, 0x00, 0x00,
0x00, 0xff, 0x00, 0xff, 0xff, 0xff, 0x00, 0x00,
0xff, 0x00, 0x00, 0x01, 0x00, 0xff, 0x01, 0x00,
0x00, 0x00, 0x00, 0xff, 0x00, 0x00, 0x00, 0x01,
0x00, 0x01, 0xff, 0x01, 0x00, 0xff, 0x00, 0x00,
},
{
0x24, 0xfe, 0x00, 0xff, 0x00, 0xff, 0xff, 0x00,
0x08, 0xfd, 0x00, 0x01, 0x01, 0x00, 0x01, 0x00,
0x06, 0x03, 0x03, 0xff, 0x00, 0x00, 0x00, 0x00,
0x04, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff,
0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x01,
0x01, 0x00, 0x01, 0xff, 0x00, 0x01, 0x00, 0x00,
0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0xff, 0x01,
},
{
0xcd, 0xff, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01,
0x03, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff,
0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00,
0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x01, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x00,
0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
0x00, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0xff,
},
{
0x81, 0xfe, 0x05, 0xff, 0x01, 0xff, 0x01, 0x00,
0xef, 0xf9, 0x00, 0xf9, 0x00, 0xff, 0x00, 0xff,
0x05, 0xf9, 0x00, 0xf8, 0x01, 0xff, 0x01, 0xff,
0x00, 0xff, 0x07, 0x00, 0x01, 0x00, 0x00, 0x00,
0x01, 0x00, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00,
0x01, 0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x01,
0xff, 0x01, 0x01, 0x00, 0xff, 0x00, 0x00, 0x00,
0x01, 0x01, 0x00, 0xff, 0x00, 0x00, 0x00, 0xff,
},
{
0x28, 0x00, 0xfe, 0x00, 0x00, 0x00, 0x00, 0x00,
0x0b, 0x02, 0x01, 0x03, 0x00, 0xff, 0x00, 0x01,
0xfe, 0x02, 0x01, 0x03, 0xff, 0x00, 0x00, 0x00,
0x01, 0x00, 0xfd, 0x00, 0x01, 0x00, 0xff, 0x00,
0x01, 0xff, 0x00, 0xff, 0x01, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0xff, 0x01, 0x01, 0x00, 0xff,
0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0xff, 0xff, 0x00, 0x00, 0x00, 0xff, 0x00, 0x01,
},
{
0xdf, 0xf9, 0xfe, 0x00, 0x03, 0x01, 0xff, 0xff,
0x04, 0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
0xff, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x01,
0x00, 0x00, 0xfe, 0x01, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0xff, 0x01, 0x00, 0x00, 0x00, 0x01,
0xff, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
0x00, 0xff, 0x00, 0xff, 0x01, 0x00, 0x00, 0x01,
0xff, 0xff, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
},
{
0x88, 0xfd, 0x00, 0x00, 0xff, 0x00, 0x01, 0xff,
0xe1, 0x06, 0x06, 0x01, 0xff, 0x00, 0x01, 0x00,
0x08, 0x00, 0xfa, 0x00, 0xff, 0xff, 0xff, 0xff,
0x08, 0x01, 0x00, 0xff, 0x01, 0xff, 0x00, 0x00,
0xf5, 0xff, 0x00, 0x01, 0xff, 0x01, 0x01, 0x00,
0xff, 0xff, 0x01, 0xff, 0x01, 0x00, 0x01, 0x00,
0x00, 0x01, 0x01, 0xff, 0x00, 0xff, 0x00, 0x01,
0x02, 0x00, 0x00, 0xff, 0xff, 0x00, 0xff, 0x00,
},
}

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third_party/go/pkg/image/jpeg/fdct.go vendored Normal file
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// 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)
}
}

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// Copyright 2009 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 (
"io"
)
// maxCodeLength is the maximum (inclusive) number of bits in a Huffman code.
const maxCodeLength = 16
// maxNCodes is the maximum (inclusive) number of codes in a Huffman tree.
const maxNCodes = 256
// lutSize is the log-2 size of the Huffman decoder's look-up table.
const lutSize = 8
// huffman is a Huffman decoder, specified in section C.
type huffman struct {
// length is the number of codes in the tree.
nCodes int32
// lut is the look-up table for the next lutSize bits in the bit-stream.
// The high 8 bits of the uint16 are the encoded value. The low 8 bits
// are 1 plus the code length, or 0 if the value is too large to fit in
// lutSize bits.
lut [1 << lutSize]uint16
// vals are the decoded values, sorted by their encoding.
vals [maxNCodes]uint8
// minCodes[i] is the minimum code of length i, or -1 if there are no
// codes of that length.
minCodes [maxCodeLength]int32
// maxCodes[i] is the maximum code of length i, or -1 if there are no
// codes of that length.
maxCodes [maxCodeLength]int32
// valsIndices[i] is the index into vals of minCodes[i].
valsIndices [maxCodeLength]int32
}
// errShortHuffmanData means that an unexpected EOF occurred while decoding
// Huffman data.
var errShortHuffmanData = FormatError("short Huffman data")
// ensureNBits reads bytes from the byte buffer to ensure that d.bits.n is at
// least n. For best performance (avoiding function calls inside hot loops),
// the caller is the one responsible for first checking that d.bits.n < n.
func (d *decoder) ensureNBits(n int32) error {
for {
c, err := d.readByteStuffedByte()
if err != nil {
if err == io.EOF {
return errShortHuffmanData
}
return err
}
d.bits.a = d.bits.a<<8 | uint32(c)
d.bits.n += 8
if d.bits.m == 0 {
d.bits.m = 1 << 7
} else {
d.bits.m <<= 8
}
if d.bits.n >= n {
break
}
}
return nil
}
// receiveExtend is the composition of RECEIVE and EXTEND, specified in section
// F.2.2.1.
func (d *decoder) receiveExtend(t uint8) (int32, error) {
if d.bits.n < int32(t) {
if err := d.ensureNBits(int32(t)); err != nil {
return 0, err
}
}
d.bits.n -= int32(t)
d.bits.m >>= t
s := int32(1) << t
x := int32(d.bits.a>>uint8(d.bits.n)) & (s - 1)
if x < s>>1 {
x += ((-1) << t) + 1
}
return x, nil
}
// processDHT processes a Define Huffman Table marker, and initializes a huffman
// struct from its contents. Specified in section B.2.4.2.
func (d *decoder) processDHT(n int) error {
for n > 0 {
if n < 17 {
return FormatError("DHT has wrong length")
}
if err := d.readFull(d.tmp[:17]); err != nil {
return err
}
tc := d.tmp[0] >> 4
if tc > maxTc {
return FormatError("bad Tc value")
}
th := d.tmp[0] & 0x0f
if th > maxTh || !d.progressive && th > 1 {
return FormatError("bad Th value")
}
h := &d.huff[tc][th]
// Read nCodes and h.vals (and derive h.nCodes).
// nCodes[i] is the number of codes with code length i.
// h.nCodes is the total number of codes.
h.nCodes = 0
var nCodes [maxCodeLength]int32
for i := range nCodes {
nCodes[i] = int32(d.tmp[i+1])
h.nCodes += nCodes[i]
}
if h.nCodes == 0 {
return FormatError("Huffman table has zero length")
}
if h.nCodes > maxNCodes {
return FormatError("Huffman table has excessive length")
}
n -= int(h.nCodes) + 17
if n < 0 {
return FormatError("DHT has wrong length")
}
if err := d.readFull(h.vals[:h.nCodes]); err != nil {
return err
}
// Derive the look-up table.
for i := range h.lut {
h.lut[i] = 0
}
var x, code uint32
for i := uint32(0); i < lutSize; i++ {
code <<= 1
for j := int32(0); j < nCodes[i]; j++ {
// The codeLength is 1+i, so shift code by 8-(1+i) to
// calculate the high bits for every 8-bit sequence
// whose codeLength's high bits matches code.
// The high 8 bits of lutValue are the encoded value.
// The low 8 bits are 1 plus the codeLength.
base := uint8(code << (7 - i))
lutValue := uint16(h.vals[x])<<8 | uint16(2+i)
for k := uint8(0); k < 1<<(7-i); k++ {
h.lut[base|k] = lutValue
}
code++
x++
}
}
// Derive minCodes, maxCodes, and valsIndices.
var c, index int32
for i, n := range nCodes {
if n == 0 {
h.minCodes[i] = -1
h.maxCodes[i] = -1
h.valsIndices[i] = -1
} else {
h.minCodes[i] = c
h.maxCodes[i] = c + n - 1
h.valsIndices[i] = index
c += n
index += n
}
c <<= 1
}
}
return nil
}
// decodeHuffman returns the next Huffman-coded value from the bit-stream,
// decoded according to h.
func (d *decoder) decodeHuffman(h *huffman) (uint8, error) {
if h.nCodes == 0 {
return 0, FormatError("uninitialized Huffman table")
}
if d.bits.n < 8 {
if err := d.ensureNBits(8); err != nil {
if err != errMissingFF00 && err != errShortHuffmanData {
return 0, err
}
// There are no more bytes of data in this segment, but we may still
// be able to read the next symbol out of the previously read bits.
// First, undo the readByte that the ensureNBits call made.
d.unreadByteStuffedByte()
goto slowPath
}
}
if v := h.lut[(d.bits.a>>uint32(d.bits.n-lutSize))&0xff]; v != 0 {
n := (v & 0xff) - 1
d.bits.n -= int32(n)
d.bits.m >>= n
return uint8(v >> 8), nil
}
slowPath:
for i, code := 0, int32(0); i < maxCodeLength; i++ {
if d.bits.n == 0 {
if err := d.ensureNBits(1); err != nil {
return 0, err
}
}
if d.bits.a&d.bits.m != 0 {
code |= 1
}
d.bits.n--
d.bits.m >>= 1
if code <= h.maxCodes[i] {
return h.vals[h.valsIndices[i]+code-h.minCodes[i]], nil
}
code <<= 1
}
return 0, FormatError("bad Huffman code")
}
func (d *decoder) decodeBit() (bool, error) {
if d.bits.n == 0 {
if err := d.ensureNBits(1); err != nil {
return false, err
}
}
ret := d.bits.a&d.bits.m != 0
d.bits.n--
d.bits.m >>= 1
return ret, nil
}
func (d *decoder) decodeBits(n int32) (uint32, error) {
if d.bits.n < n {
if err := d.ensureNBits(n); err != nil {
return 0, err
}
}
ret := d.bits.a >> uint32(d.bits.n-n)
ret &= (1 << uint32(n)) - 1
d.bits.n -= n
d.bits.m >>= uint32(n)
return ret, nil
}

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// Copyright 2009 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 is a Go translation of idct.c from
//
// http://standards.iso.org/ittf/PubliclyAvailableStandards/ISO_IEC_13818-4_2004_Conformance_Testing/Video/verifier/mpeg2decode_960109.tar.gz
//
// which carries the following notice:
/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */
/*
* Disclaimer of Warranty
*
* These software programs are available to the user without any license fee or
* royalty on an "as is" basis. The MPEG Software Simulation Group disclaims
* any and all warranties, whether express, implied, or statuary, including any
* implied warranties or merchantability or of fitness for a particular
* purpose. In no event shall the copyright-holder be liable for any
* incidental, punitive, or consequential damages of any kind whatsoever
* arising from the use of these programs.
*
* This disclaimer of warranty extends to the user of these programs and user's
* customers, employees, agents, transferees, successors, and assigns.
*
* The MPEG Software Simulation Group does not represent or warrant that the
* programs furnished hereunder are free of infringement of any third-party
* patents.
*
* Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
* are subject to royalty fees to patent holders. Many of these patents are
* general enough such that they are unavoidable regardless of implementation
* design.
*
*/
const blockSize = 64 // A DCT block is 8x8.
type block [blockSize]int32
const (
w1 = 2841 // 2048*sqrt(2)*cos(1*pi/16)
w2 = 2676 // 2048*sqrt(2)*cos(2*pi/16)
w3 = 2408 // 2048*sqrt(2)*cos(3*pi/16)
w5 = 1609 // 2048*sqrt(2)*cos(5*pi/16)
w6 = 1108 // 2048*sqrt(2)*cos(6*pi/16)
w7 = 565 // 2048*sqrt(2)*cos(7*pi/16)
w1pw7 = w1 + w7
w1mw7 = w1 - w7
w2pw6 = w2 + w6
w2mw6 = w2 - w6
w3pw5 = w3 + w5
w3mw5 = w3 - w5
r2 = 181 // 256/sqrt(2)
)
// idct performs a 2-D Inverse Discrete Cosine Transformation.
//
// The input coefficients should already have been multiplied by the
// appropriate quantization table. We use fixed-point computation, with the
// number of bits for the fractional component varying over the intermediate
// stages.
//
// 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(src *block) {
// Horizontal 1-D IDCT.
for y := 0; y < 8; y++ {
y8 := y * 8
// If all the AC components are zero, then the IDCT is trivial.
if src[y8+1] == 0 && src[y8+2] == 0 && src[y8+3] == 0 &&
src[y8+4] == 0 && src[y8+5] == 0 && src[y8+6] == 0 && src[y8+7] == 0 {
dc := src[y8+0] << 3
src[y8+0] = dc
src[y8+1] = dc
src[y8+2] = dc
src[y8+3] = dc
src[y8+4] = dc
src[y8+5] = dc
src[y8+6] = dc
src[y8+7] = dc
continue
}
// Prescale.
x0 := (src[y8+0] << 11) + 128
x1 := src[y8+4] << 11
x2 := src[y8+6]
x3 := src[y8+2]
x4 := src[y8+1]
x5 := src[y8+7]
x6 := src[y8+5]
x7 := src[y8+3]
// Stage 1.
x8 := w7 * (x4 + x5)
x4 = x8 + w1mw7*x4
x5 = x8 - w1pw7*x5
x8 = w3 * (x6 + x7)
x6 = x8 - w3mw5*x6
x7 = x8 - w3pw5*x7
// Stage 2.
x8 = x0 + x1
x0 -= x1
x1 = w6 * (x3 + x2)
x2 = x1 - w2pw6*x2
x3 = x1 + w2mw6*x3
x1 = x4 + x6
x4 -= x6
x6 = x5 + x7
x5 -= x7
// Stage 3.
x7 = x8 + x3
x8 -= x3
x3 = x0 + x2
x0 -= x2
x2 = (r2*(x4+x5) + 128) >> 8
x4 = (r2*(x4-x5) + 128) >> 8
// Stage 4.
src[y8+0] = (x7 + x1) >> 8
src[y8+1] = (x3 + x2) >> 8
src[y8+2] = (x0 + x4) >> 8
src[y8+3] = (x8 + x6) >> 8
src[y8+4] = (x8 - x6) >> 8
src[y8+5] = (x0 - x4) >> 8
src[y8+6] = (x3 - x2) >> 8
src[y8+7] = (x7 - x1) >> 8
}
// Vertical 1-D IDCT.
for x := 0; x < 8; x++ {
// Similar to the horizontal 1-D IDCT case, if all the AC components are zero, then the IDCT is trivial.
// However, after performing the horizontal 1-D IDCT, there are typically non-zero AC components, so
// we do not bother to check for the all-zero case.
// Prescale.
y0 := (src[8*0+x] << 8) + 8192
y1 := src[8*4+x] << 8
y2 := src[8*6+x]
y3 := src[8*2+x]
y4 := src[8*1+x]
y5 := src[8*7+x]
y6 := src[8*5+x]
y7 := src[8*3+x]
// Stage 1.
y8 := w7*(y4+y5) + 4
y4 = (y8 + w1mw7*y4) >> 3
y5 = (y8 - w1pw7*y5) >> 3
y8 = w3*(y6+y7) + 4
y6 = (y8 - w3mw5*y6) >> 3
y7 = (y8 - w3pw5*y7) >> 3
// Stage 2.
y8 = y0 + y1
y0 -= y1
y1 = w6*(y3+y2) + 4
y2 = (y1 - w2pw6*y2) >> 3
y3 = (y1 + w2mw6*y3) >> 3
y1 = y4 + y6
y4 -= y6
y6 = y5 + y7
y5 -= y7
// Stage 3.
y7 = y8 + y3
y8 -= y3
y3 = y0 + y2
y0 -= y2
y2 = (r2*(y4+y5) + 128) >> 8
y4 = (r2*(y4-y5) + 128) >> 8
// Stage 4.
src[8*0+x] = (y7 + y1) >> 14
src[8*1+x] = (y3 + y2) >> 14
src[8*2+x] = (y0 + y4) >> 14
src[8*3+x] = (y8 + y6) >> 14
src[8*4+x] = (y8 - y6) >> 14
src[8*5+x] = (y0 - y4) >> 14
src[8*6+x] = (y3 - y2) >> 14
src[8*7+x] = (y7 - y1) >> 14
}
}

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// Copyright 2009 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 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
import (
"image"
"image/color"
"io"
)
// TODO(nigeltao): fix up the doc comment style so that sentences start with
// the name of the type or function that they annotate.
// A FormatError reports that the input is not a valid JPEG.
type FormatError string
func (e FormatError) Error() string { return "invalid JPEG format: " + string(e) }
// An UnsupportedError reports that the input uses a valid but unimplemented JPEG feature.
type UnsupportedError string
func (e UnsupportedError) Error() string { return "unsupported JPEG feature: " + string(e) }
// Component specification, specified in section B.2.2.
type component struct {
h int // Horizontal sampling factor.
v int // Vertical sampling factor.
c uint8 // Component identifier.
tq uint8 // Quantization table destination selector.
}
const (
dcTable = 0
acTable = 1
maxTc = 1
maxTh = 3
maxTq = 3
// A grayscale JPEG image has only a Y component.
nGrayComponent = 1
// A color JPEG image has Y, Cb and Cr components.
nColorComponent = 3
// We only support 4:4:4, 4:4:0, 4:2:2 and 4:2:0 downsampling, and therefore the
// number of luma samples per chroma sample is at most 2 in the horizontal
// and 2 in the vertical direction.
maxH = 2
maxV = 2
)
const (
soiMarker = 0xd8 // Start Of Image.
eoiMarker = 0xd9 // End Of Image.
sof0Marker = 0xc0 // Start Of Frame (Baseline).
sof2Marker = 0xc2 // Start Of Frame (Progressive).
dhtMarker = 0xc4 // Define Huffman Table.
dqtMarker = 0xdb // Define Quantization Table.
sosMarker = 0xda // Start Of Scan.
driMarker = 0xdd // Define Restart Interval.
rst0Marker = 0xd0 // ReSTart (0).
rst7Marker = 0xd7 // ReSTart (7).
app0Marker = 0xe0 // APPlication specific (0).
app15Marker = 0xef // APPlication specific (15).
comMarker = 0xfe // COMment.
)
// unzig maps from the zig-zag ordering to the natural ordering. For example,
// unzig[3] is the column and row of the fourth element in zig-zag order. The
// value is 16, which means first column (16%8 == 0) and third row (16/8 == 2).
var unzig = [blockSize]int{
0, 1, 8, 16, 9, 2, 3, 10,
17, 24, 32, 25, 18, 11, 4, 5,
12, 19, 26, 33, 40, 48, 41, 34,
27, 20, 13, 6, 7, 14, 21, 28,
35, 42, 49, 56, 57, 50, 43, 36,
29, 22, 15, 23, 30, 37, 44, 51,
58, 59, 52, 45, 38, 31, 39, 46,
53, 60, 61, 54, 47, 55, 62, 63,
}
// Reader is deprecated.
type Reader interface {
io.ByteReader
io.Reader
}
// bits holds the unprocessed bits that have been taken from the byte-stream.
// The n least significant bits of a form the unread bits, to be read in MSB to
// LSB order.
type bits struct {
a uint32 // accumulator.
m uint32 // mask. m==1<<(n-1) when n>0, with m==0 when n==0.
n int32 // the number of unread bits in a.
}
type decoder struct {
r io.Reader
bits bits
// bytes is a byte buffer, similar to a bufio.Reader, except that it
// has to be able to unread more than 1 byte, due to byte stuffing.
// Byte stuffing is specified in section F.1.2.3.
bytes struct {
// buf[i:j] are the buffered bytes read from the underlying
// io.Reader that haven't yet been passed further on.
buf [4096]byte
i, j int
// nUnreadable is the number of bytes to back up i after
// overshooting. It can be 0, 1 or 2.
nUnreadable int
}
width, height int
img1 *image.Gray
img3 *image.YCbCr
ri int // Restart Interval.
nComp int
progressive bool
eobRun uint16 // End-of-Band run, specified in section G.1.2.2.
comp [nColorComponent]component
progCoeffs [nColorComponent][]block // Saved state between progressive-mode scans.
huff [maxTc + 1][maxTh + 1]huffman
quant [maxTq + 1]block // Quantization tables, in zig-zag order.
tmp [blockSize + 1]byte
}
// fill fills up the d.bytes.buf buffer from the underlying io.Reader. It
// should only be called when there are no unread bytes in d.bytes.
func (d *decoder) fill() error {
if d.bytes.i != d.bytes.j {
panic("jpeg: fill called when unread bytes exist")
}
// Move the last 2 bytes to the start of the buffer, in case we need
// to call unreadByteStuffedByte.
if d.bytes.j > 2 {
d.bytes.buf[0] = d.bytes.buf[d.bytes.j-2]
d.bytes.buf[1] = d.bytes.buf[d.bytes.j-1]
d.bytes.i, d.bytes.j = 2, 2
}
// Fill in the rest of the buffer.
n, err := d.r.Read(d.bytes.buf[d.bytes.j:])
d.bytes.j += n
return err
}
// unreadByteStuffedByte undoes the most recent readByteStuffedByte call,
// giving a byte of data back from d.bits to d.bytes. The Huffman look-up table
// requires at least 8 bits for look-up, which means that Huffman decoding can
// sometimes overshoot and read one or two too many bytes. Two-byte overshoot
// can happen when expecting to read a 0xff 0x00 byte-stuffed byte.
func (d *decoder) unreadByteStuffedByte() {
if d.bytes.nUnreadable == 0 {
panic("jpeg: unreadByteStuffedByte call cannot be fulfilled")
}
d.bytes.i -= d.bytes.nUnreadable
d.bytes.nUnreadable = 0
if d.bits.n >= 8 {
d.bits.a >>= 8
d.bits.n -= 8
d.bits.m >>= 8
}
}
// readByte returns the next byte, whether buffered or not buffered. It does
// not care about byte stuffing.
func (d *decoder) readByte() (x byte, err error) {
for d.bytes.i == d.bytes.j {
if err = d.fill(); err != nil {
return 0, err
}
}
x = d.bytes.buf[d.bytes.i]
d.bytes.i++
d.bytes.nUnreadable = 0
return x, nil
}
// errMissingFF00 means that readByteStuffedByte encountered an 0xff byte (a
// marker byte) that wasn't the expected byte-stuffed sequence 0xff, 0x00.
var errMissingFF00 = FormatError("missing 0xff00 sequence")
// readByteStuffedByte is like readByte but is for byte-stuffed Huffman data.
func (d *decoder) readByteStuffedByte() (x byte, err error) {
// Take the fast path if d.bytes.buf contains at least two bytes.
if d.bytes.i+2 <= d.bytes.j {
x = d.bytes.buf[d.bytes.i]
d.bytes.i++
d.bytes.nUnreadable = 1
if x != 0xff {
return x, err
}
if d.bytes.buf[d.bytes.i] != 0x00 {
return 0, errMissingFF00
}
d.bytes.i++
d.bytes.nUnreadable = 2
return 0xff, nil
}
x, err = d.readByte()
if err != nil {
return 0, err
}
if x != 0xff {
d.bytes.nUnreadable = 1
return x, nil
}
x, err = d.readByte()
if err != nil {
d.bytes.nUnreadable = 1
return 0, err
}
d.bytes.nUnreadable = 2
if x != 0x00 {
return 0, errMissingFF00
}
return 0xff, nil
}
// readFull reads exactly len(p) bytes into p. It does not care about byte
// stuffing.
func (d *decoder) readFull(p []byte) error {
// Unread the overshot bytes, if any.
if d.bytes.nUnreadable != 0 {
if d.bits.n >= 8 {
d.unreadByteStuffedByte()
}
d.bytes.nUnreadable = 0
}
for {
n := copy(p, d.bytes.buf[d.bytes.i:d.bytes.j])
p = p[n:]
d.bytes.i += n
if len(p) == 0 {
break
}
if err := d.fill(); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return err
}
}
return nil
}
// ignore ignores the next n bytes.
func (d *decoder) ignore(n int) error {
// Unread the overshot bytes, if any.
if d.bytes.nUnreadable != 0 {
if d.bits.n >= 8 {
d.unreadByteStuffedByte()
}
d.bytes.nUnreadable = 0
}
for {
m := d.bytes.j - d.bytes.i
if m > n {
m = n
}
d.bytes.i += m
n -= m
if n == 0 {
break
}
if err := d.fill(); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return err
}
}
return nil
}
// Specified in section B.2.2.
func (d *decoder) processSOF(n int) error {
switch n {
case 6 + 3*nGrayComponent:
d.nComp = nGrayComponent
case 6 + 3*nColorComponent:
d.nComp = nColorComponent
default:
return UnsupportedError("SOF has wrong length")
}
if err := d.readFull(d.tmp[:n]); err != nil {
return err
}
// We only support 8-bit precision.
if d.tmp[0] != 8 {
return UnsupportedError("precision")
}
d.height = int(d.tmp[1])<<8 + int(d.tmp[2])
d.width = int(d.tmp[3])<<8 + int(d.tmp[4])
if int(d.tmp[5]) != d.nComp {
return UnsupportedError("SOF has wrong number of image components")
}
for i := 0; i < d.nComp; i++ {
d.comp[i].c = d.tmp[6+3*i]
d.comp[i].tq = d.tmp[8+3*i]
if d.nComp == nGrayComponent {
// If a JPEG image has only one component, section A.2 says "this data
// is non-interleaved by definition" and section A.2.2 says "[in this
// case...] the order of data units within a scan shall be left-to-right
// and top-to-bottom... regardless of the values of H_1 and V_1". Section
// 4.8.2 also says "[for non-interleaved data], the MCU is defined to be
// one data unit". Similarly, section A.1.1 explains that it is the ratio
// of H_i to max_j(H_j) that matters, and similarly for V. For grayscale
// images, H_1 is the maximum H_j for all components j, so that ratio is
// always 1. The component's (h, v) is effectively always (1, 1): even if
// the nominal (h, v) is (2, 1), a 20x5 image is encoded in three 8x8
// MCUs, not two 16x8 MCUs.
d.comp[i].h = 1
d.comp[i].v = 1
continue
}
hv := d.tmp[7+3*i]
d.comp[i].h = int(hv >> 4)
d.comp[i].v = int(hv & 0x0f)
// For color images, we only support 4:4:4, 4:4:0, 4:2:2 or 4:2:0 chroma
// downsampling ratios. This implies that the (h, v) values for the Y
// component are either (1, 1), (1, 2), (2, 1) or (2, 2), and the (h, v)
// values for the Cr and Cb components must be (1, 1).
if i == 0 {
if hv != 0x11 && hv != 0x21 && hv != 0x22 && hv != 0x12 {
return UnsupportedError("luma/chroma downsample ratio")
}
} else if hv != 0x11 {
return UnsupportedError("luma/chroma downsample ratio")
}
}
return nil
}
// Specified in section B.2.4.1.
func (d *decoder) processDQT(n int) error {
const qtLength = 1 + blockSize
for ; n >= qtLength; n -= qtLength {
if err := d.readFull(d.tmp[:qtLength]); err != nil {
return err
}
pq := d.tmp[0] >> 4
if pq != 0 {
return UnsupportedError("bad Pq value")
}
tq := d.tmp[0] & 0x0f
if tq > maxTq {
return FormatError("bad Tq value")
}
for i := range d.quant[tq] {
d.quant[tq][i] = int32(d.tmp[i+1])
}
}
if n != 0 {
return FormatError("DQT has wrong length")
}
return nil
}
// Specified in section B.2.4.4.
func (d *decoder) processDRI(n int) error {
if n != 2 {
return FormatError("DRI has wrong length")
}
if err := d.readFull(d.tmp[:2]); err != nil {
return err
}
d.ri = int(d.tmp[0])<<8 + int(d.tmp[1])
return nil
}
// decode reads a JPEG image from r and returns it as an image.Image.
func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, error) {
d.r = r
// Check for the Start Of Image marker.
if err := d.readFull(d.tmp[:2]); err != nil {
return nil, err
}
if d.tmp[0] != 0xff || d.tmp[1] != soiMarker {
return nil, FormatError("missing SOI marker")
}
// Process the remaining segments until the End Of Image marker.
for {
err := d.readFull(d.tmp[:2])
if err != nil {
return nil, err
}
for d.tmp[0] != 0xff {
// Strictly speaking, this is a format error. However, libjpeg is
// liberal in what it accepts. As of version 9, next_marker in
// jdmarker.c treats this as a warning (JWRN_EXTRANEOUS_DATA) and
// continues to decode the stream. Even before next_marker sees
// extraneous data, jpeg_fill_bit_buffer in jdhuff.c reads as many
// bytes as it can, possibly past the end of a scan's data. It
// effectively puts back any markers that it overscanned (e.g. an
// "\xff\xd9" EOI marker), but it does not put back non-marker data,
// and thus it can silently ignore a small number of extraneous
// non-marker bytes before next_marker has a chance to see them (and
// print a warning).
//
// We are therefore also liberal in what we accept. Extraneous data
// is silently ignored.
//
// This is similar to, but not exactly the same as, the restart
// mechanism within a scan (the RST[0-7] markers).
//
// Note that extraneous 0xff bytes in e.g. SOS data are escaped as
// "\xff\x00", and so are detected a little further down below.
d.tmp[0] = d.tmp[1]
d.tmp[1], err = d.readByte()
if err != nil {
return nil, err
}
}
marker := d.tmp[1]
if marker == 0 {
// Treat "\xff\x00" as extraneous data.
continue
}
for marker == 0xff {
// Section B.1.1.2 says, "Any marker may optionally be preceded by any
// number of fill bytes, which are bytes assigned code X'FF'".
marker, err = d.readByte()
if err != nil {
return nil, err
}
}
if marker == eoiMarker { // End Of Image.
break
}
if rst0Marker <= marker && marker <= rst7Marker {
// Figures B.2 and B.16 of the specification suggest that restart markers should
// only occur between Entropy Coded Segments and not after the final ECS.
// However, some encoders may generate incorrect JPEGs with a final restart
// marker. That restart marker will be seen here instead of inside the processSOS
// method, and is ignored as a harmless error. Restart markers have no extra data,
// so we check for this before we read the 16-bit length of the segment.
continue
}
// Read the 16-bit length of the segment. The value includes the 2 bytes for the
// length itself, so we subtract 2 to get the number of remaining bytes.
if err = d.readFull(d.tmp[:2]); err != nil {
return nil, err
}
n := int(d.tmp[0])<<8 + int(d.tmp[1]) - 2
if n < 0 {
return nil, FormatError("short segment length")
}
switch {
case marker == sof0Marker || marker == sof2Marker: // Start Of Frame.
d.progressive = marker == sof2Marker
err = d.processSOF(n)
if configOnly {
return nil, err
}
case marker == dhtMarker: // Define Huffman Table.
err = d.processDHT(n)
case marker == dqtMarker: // Define Quantization Table.
err = d.processDQT(n)
case marker == sosMarker: // Start Of Scan.
err = d.processSOS(n)
case marker == driMarker: // Define Restart Interval.
err = d.processDRI(n)
case app0Marker <= marker && marker <= app15Marker || marker == comMarker: // APPlication specific, or COMment.
err = d.ignore(n)
default:
err = UnsupportedError("unknown marker")
}
if err != nil {
return nil, err
}
}
if d.img1 != nil {
return d.img1, nil
}
if d.img3 != nil {
return d.img3, nil
}
return nil, FormatError("missing SOS marker")
}
// Decode reads a JPEG image from r and returns it as an image.Image.
func Decode(r io.Reader) (image.Image, error) {
var d decoder
return d.decode(r, false)
}
// DecodeConfig returns the color model and dimensions of a JPEG image without
// decoding the entire image.
func DecodeConfig(r io.Reader) (image.Config, error) {
var d decoder
if _, err := d.decode(r, true); err != nil {
return image.Config{}, err
}
switch d.nComp {
case nGrayComponent:
return image.Config{
ColorModel: color.GrayModel,
Width: d.width,
Height: d.height,
}, nil
case nColorComponent:
return image.Config{
ColorModel: color.YCbCrModel,
Width: d.width,
Height: d.height,
}, nil
}
return image.Config{}, FormatError("missing SOF marker")
}
func init() {
image.RegisterFormat("jpeg", "\xff\xd8", Decode, DecodeConfig)
}

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// Copyright 2012 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"
"io/ioutil"
"math/rand"
"os"
"strings"
"testing"
)
// TestDecodeProgressive tests that decoding the baseline and progressive
// versions of the same image result in exactly the same pixel data, in YCbCr
// space for color images, and Y space for grayscale images.
func TestDecodeProgressive(t *testing.T) {
testCases := []string{
"../testdata/video-001",
"../testdata/video-001.q50.420",
"../testdata/video-001.q50.422",
"../testdata/video-001.q50.440",
"../testdata/video-001.q50.444",
"../testdata/video-005.gray.q50",
"../testdata/video-005.gray.q50.2x2",
"../testdata/video-001.separate.dc.progression",
}
for _, tc := range testCases {
m0, err := decodeFile(tc + ".jpeg")
if err != nil {
t.Errorf("%s: %v", tc+".jpeg", err)
continue
}
m1, err := decodeFile(tc + ".progressive.jpeg")
if err != nil {
t.Errorf("%s: %v", tc+".progressive.jpeg", err)
continue
}
if m0.Bounds() != m1.Bounds() {
t.Errorf("%s: bounds differ: %v and %v", tc, m0.Bounds(), m1.Bounds())
continue
}
// All of the video-*.jpeg files are 150x103.
if m0.Bounds() != image.Rect(0, 0, 150, 103) {
t.Errorf("%s: bad bounds: %v", tc, m0.Bounds())
continue
}
switch m0 := m0.(type) {
case *image.YCbCr:
m1 := m1.(*image.YCbCr)
if err := check(m0.Bounds(), m0.Y, m1.Y, m0.YStride, m1.YStride); err != nil {
t.Errorf("%s (Y): %v", tc, err)
continue
}
if err := check(m0.Bounds(), m0.Cb, m1.Cb, m0.CStride, m1.CStride); err != nil {
t.Errorf("%s (Cb): %v", tc, err)
continue
}
if err := check(m0.Bounds(), m0.Cr, m1.Cr, m0.CStride, m1.CStride); err != nil {
t.Errorf("%s (Cr): %v", tc, err)
continue
}
case *image.Gray:
m1 := m1.(*image.Gray)
if err := check(m0.Bounds(), m0.Pix, m1.Pix, m0.Stride, m1.Stride); err != nil {
t.Errorf("%s: %v", tc, err)
continue
}
default:
t.Errorf("%s: unexpected image type %T", tc, m0)
continue
}
}
}
func decodeFile(filename string) (image.Image, error) {
f, err := os.Open(filename)
if err != nil {
return nil, err
}
defer f.Close()
return Decode(f)
}
// check checks that the two pix data are equal, within the given bounds.
func check(bounds image.Rectangle, pix0, pix1 []byte, stride0, stride1 int) error {
if stride0 <= 0 || stride0%8 != 0 {
return fmt.Errorf("bad stride %d", stride0)
}
if stride1 <= 0 || stride1%8 != 0 {
return fmt.Errorf("bad stride %d", stride1)
}
// Compare the two pix data, one 8x8 block at a time.
for y := 0; y < len(pix0)/stride0 && y < len(pix1)/stride1; y += 8 {
for x := 0; x < stride0 && x < stride1; x += 8 {
if x >= bounds.Max.X || y >= bounds.Max.Y {
// We don't care if the two pix data differ if the 8x8 block is
// entirely outside of the image's bounds. For example, this can
// occur with a 4:2:0 chroma subsampling and a 1x1 image. Baseline
// decoding works on the one 16x16 MCU as a whole; progressive
// decoding's first pass works on that 16x16 MCU as a whole but
// refinement passes only process one 8x8 block within the MCU.
continue
}
for j := 0; j < 8; j++ {
for i := 0; i < 8; i++ {
index0 := (y+j)*stride0 + (x + i)
index1 := (y+j)*stride1 + (x + i)
if pix0[index0] != pix1[index1] {
return fmt.Errorf("blocks at (%d, %d) differ:\n%sand\n%s", x, y,
pixString(pix0, stride0, x, y),
pixString(pix1, stride1, x, y),
)
}
}
}
}
}
return nil
}
func pixString(pix []byte, stride, x, y int) string {
s := bytes.NewBuffer(nil)
for j := 0; j < 8; j++ {
fmt.Fprintf(s, "\t")
for i := 0; i < 8; i++ {
fmt.Fprintf(s, "%02x ", pix[(y+j)*stride+(x+i)])
}
fmt.Fprintf(s, "\n")
}
return s.String()
}
func TestExtraneousData(t *testing.T) {
// Encode a 1x1 red image.
src := image.NewRGBA(image.Rect(0, 0, 1, 1))
src.Set(0, 0, color.RGBA{0xff, 0x00, 0x00, 0xff})
buf := new(bytes.Buffer)
if err := Encode(buf, src, nil); err != nil {
t.Fatalf("encode: %v", err)
}
enc := buf.String()
// Sanity check that the encoded JPEG is long enough, that it ends in a
// "\xff\xd9" EOI marker, and that it contains a "\xff\xda" SOS marker
// somewhere in the final 64 bytes.
if len(enc) < 64 {
t.Fatalf("encoded JPEG is too short: %d bytes", len(enc))
}
if got, want := enc[len(enc)-2:], "\xff\xd9"; got != want {
t.Fatalf("encoded JPEG ends with %q, want %q", got, want)
}
if s := enc[len(enc)-64:]; !strings.Contains(s, "\xff\xda") {
t.Fatalf("encoded JPEG does not contain a SOS marker (ff da) near the end: % x", s)
}
// Test that adding some random junk between the SOS marker and the
// EOI marker does not affect the decoding.
rnd := rand.New(rand.NewSource(1))
for i, nerr := 0, 0; i < 1000 && nerr < 10; i++ {
buf.Reset()
// Write all but the trailing "\xff\xd9" EOI marker.
buf.WriteString(enc[:len(enc)-2])
// Write some random extraneous data.
for n := rnd.Intn(10); n > 0; n-- {
if x := byte(rnd.Intn(256)); x != 0xff {
buf.WriteByte(x)
} else {
// The JPEG format escapes a SOS 0xff data byte as "\xff\x00".
buf.WriteString("\xff\x00")
}
}
// Write the "\xff\xd9" EOI marker.
buf.WriteString("\xff\xd9")
// Check that we can still decode the resultant image.
got, err := Decode(buf)
if err != nil {
t.Errorf("could not decode image #%d: %v", i, err)
nerr++
continue
}
if got.Bounds() != src.Bounds() {
t.Errorf("image #%d, bounds differ: %v and %v", i, got.Bounds(), src.Bounds())
nerr++
continue
}
if averageDelta(got, src) > 2<<8 {
t.Errorf("image #%d changed too much after a round trip", i)
nerr++
continue
}
}
}
func benchmarkDecode(b *testing.B, filename string) {
b.StopTimer()
data, err := ioutil.ReadFile(filename)
if err != nil {
b.Fatal(err)
}
cfg, err := DecodeConfig(bytes.NewReader(data))
if err != nil {
b.Fatal(err)
}
b.SetBytes(int64(cfg.Width * cfg.Height * 4))
b.StartTimer()
for i := 0; i < b.N; i++ {
Decode(bytes.NewReader(data))
}
}
func BenchmarkDecodeBaseline(b *testing.B) {
benchmarkDecode(b, "../testdata/video-001.jpeg")
}
func BenchmarkDecodeProgressive(b *testing.B) {
benchmarkDecode(b, "../testdata/video-001.progressive.jpeg")
}

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// Copyright 2012 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 (
"image"
)
// makeImg allocates and initializes the destination image.
func (d *decoder) makeImg(h0, v0, mxx, myy int) {
if d.nComp == nGrayComponent {
m := image.NewGray(image.Rect(0, 0, 8*mxx, 8*myy))
d.img1 = m.SubImage(image.Rect(0, 0, d.width, d.height)).(*image.Gray)
return
}
var subsampleRatio image.YCbCrSubsampleRatio
switch {
case h0 == 1 && v0 == 1:
subsampleRatio = image.YCbCrSubsampleRatio444
case h0 == 1 && v0 == 2:
subsampleRatio = image.YCbCrSubsampleRatio440
case h0 == 2 && v0 == 1:
subsampleRatio = image.YCbCrSubsampleRatio422
case h0 == 2 && v0 == 2:
subsampleRatio = image.YCbCrSubsampleRatio420
default:
panic("unreachable")
}
m := image.NewYCbCr(image.Rect(0, 0, 8*h0*mxx, 8*v0*myy), subsampleRatio)
d.img3 = m.SubImage(image.Rect(0, 0, d.width, d.height)).(*image.YCbCr)
}
// Specified in section B.2.3.
func (d *decoder) processSOS(n int) error {
if d.nComp == 0 {
return FormatError("missing SOF marker")
}
if n < 6 || 4+2*d.nComp < n || n%2 != 0 {
return FormatError("SOS has wrong length")
}
if err := d.readFull(d.tmp[:n]); err != nil {
return err
}
nComp := int(d.tmp[0])
if n != 4+2*nComp {
return FormatError("SOS length inconsistent with number of components")
}
var scan [nColorComponent]struct {
compIndex uint8
td uint8 // DC table selector.
ta uint8 // AC table selector.
}
for i := 0; i < nComp; i++ {
cs := d.tmp[1+2*i] // Component selector.
compIndex := -1
for j, comp := range d.comp {
if cs == comp.c {
compIndex = j
}
}
if compIndex < 0 {
return FormatError("unknown component selector")
}
scan[i].compIndex = uint8(compIndex)
scan[i].td = d.tmp[2+2*i] >> 4
scan[i].ta = d.tmp[2+2*i] & 0x0f
}
// zigStart and zigEnd are the spectral selection bounds.
// ah and al are the successive approximation high and low values.
// The spec calls these values Ss, Se, Ah and Al.
//
// For progressive JPEGs, these are the two more-or-less independent
// aspects of progression. Spectral selection progression is when not
// all of a block's 64 DCT coefficients are transmitted in one pass.
// For example, three passes could transmit coefficient 0 (the DC
// component), coefficients 1-5, and coefficients 6-63, in zig-zag
// order. Successive approximation is when not all of the bits of a
// band of coefficients are transmitted in one pass. For example,
// three passes could transmit the 6 most significant bits, followed
// by the second-least significant bit, followed by the least
// significant bit.
//
// For baseline JPEGs, these parameters are hard-coded to 0/63/0/0.
zigStart, zigEnd, ah, al := int32(0), int32(blockSize-1), uint32(0), uint32(0)
if d.progressive {
zigStart = int32(d.tmp[1+2*nComp])
zigEnd = int32(d.tmp[2+2*nComp])
ah = uint32(d.tmp[3+2*nComp] >> 4)
al = uint32(d.tmp[3+2*nComp] & 0x0f)
if (zigStart == 0 && zigEnd != 0) || zigStart > zigEnd || blockSize <= zigEnd {
return FormatError("bad spectral selection bounds")
}
if zigStart != 0 && nComp != 1 {
return FormatError("progressive AC coefficients for more than one component")
}
if ah != 0 && ah != al+1 {
return FormatError("bad successive approximation values")
}
}
// mxx and myy are the number of MCUs (Minimum Coded Units) in the image.
h0, v0 := d.comp[0].h, d.comp[0].v // The h and v values from the Y components.
mxx := (d.width + 8*h0 - 1) / (8 * h0)
myy := (d.height + 8*v0 - 1) / (8 * v0)
if d.img1 == nil && d.img3 == nil {
d.makeImg(h0, v0, mxx, myy)
}
if d.progressive {
for i := 0; i < nComp; i++ {
compIndex := scan[i].compIndex
if d.progCoeffs[compIndex] == nil {
d.progCoeffs[compIndex] = make([]block, mxx*myy*d.comp[compIndex].h*d.comp[compIndex].v)
}
}
}
d.bits = bits{}
mcu, expectedRST := 0, uint8(rst0Marker)
var (
// b is the decoded coefficients, in natural (not zig-zag) order.
b block
dc [nColorComponent]int32
// mx0 and my0 are the location of the current (in terms of 8x8 blocks).
// For example, with 4:2:0 chroma subsampling, the block whose top left
// pixel co-ordinates are (16, 8) is the third block in the first row:
// mx0 is 2 and my0 is 0, even though the pixel is in the second MCU.
// TODO(nigeltao): rename mx0 and my0 to bx and by?
mx0, my0 int
blockCount int
)
for my := 0; my < myy; my++ {
for mx := 0; mx < mxx; mx++ {
for i := 0; i < nComp; i++ {
compIndex := scan[i].compIndex
qt := &d.quant[d.comp[compIndex].tq]
for j := 0; j < d.comp[compIndex].h*d.comp[compIndex].v; j++ {
// The blocks are traversed one MCU at a time. For 4:2:0 chroma
// subsampling, there are four Y 8x8 blocks in every 16x16 MCU.
//
// For a baseline 32x16 pixel image, the Y blocks visiting order is:
// 0 1 4 5
// 2 3 6 7
//
// For progressive images, the interleaved scans (those with nComp > 1)
// are traversed as above, but non-interleaved scans are traversed left
// to right, top to bottom:
// 0 1 2 3
// 4 5 6 7
// Only DC scans (zigStart == 0) can be interleaved. AC scans must have
// only one component.
//
// To further complicate matters, for non-interleaved scans, there is no
// data for any blocks that are inside the image at the MCU level but
// outside the image at the pixel level. For example, a 24x16 pixel 4:2:0
// progressive image consists of two 16x16 MCUs. The interleaved scans
// will process 8 Y blocks:
// 0 1 4 5
// 2 3 6 7
// The non-interleaved scans will process only 6 Y blocks:
// 0 1 2
// 3 4 5
if nComp != 1 {
mx0, my0 = d.comp[compIndex].h*mx, d.comp[compIndex].v*my
if h0 == 1 {
my0 += j
} else {
mx0 += j % 2
my0 += j / 2
}
} else {
q := mxx * d.comp[compIndex].h
mx0 = blockCount % q
my0 = blockCount / q
blockCount++
if mx0*8 >= d.width || my0*8 >= d.height {
continue
}
}
// Load the previous partially decoded coefficients, if applicable.
if d.progressive {
b = d.progCoeffs[compIndex][my0*mxx*d.comp[compIndex].h+mx0]
} else {
b = block{}
}
if ah != 0 {
if err := d.refine(&b, &d.huff[acTable][scan[i].ta], zigStart, zigEnd, 1<<al); err != nil {
return err
}
} else {
zig := zigStart
if zig == 0 {
zig++
// Decode the DC coefficient, as specified in section F.2.2.1.
value, err := d.decodeHuffman(&d.huff[dcTable][scan[i].td])
if err != nil {
return err
}
if value > 16 {
return UnsupportedError("excessive DC component")
}
dcDelta, err := d.receiveExtend(value)
if err != nil {
return err
}
dc[compIndex] += dcDelta
b[0] = dc[compIndex] << al
}
if zig <= zigEnd && d.eobRun > 0 {
d.eobRun--
} else {
// Decode the AC coefficients, as specified in section F.2.2.2.
huff := &d.huff[acTable][scan[i].ta]
for ; zig <= zigEnd; zig++ {
value, err := d.decodeHuffman(huff)
if err != nil {
return err
}
val0 := value >> 4
val1 := value & 0x0f
if val1 != 0 {
zig += int32(val0)
if zig > zigEnd {
break
}
ac, err := d.receiveExtend(val1)
if err != nil {
return err
}
b[unzig[zig]] = ac << al
} else {
if val0 != 0x0f {
d.eobRun = uint16(1 << val0)
if val0 != 0 {
bits, err := d.decodeBits(int32(val0))
if err != nil {
return err
}
d.eobRun |= uint16(bits)
}
d.eobRun--
break
}
zig += 0x0f
}
}
}
}
if d.progressive {
if zigEnd != blockSize-1 || al != 0 {
// We haven't completely decoded this 8x8 block. Save the coefficients.
d.progCoeffs[compIndex][my0*mxx*d.comp[compIndex].h+mx0] = b
// At this point, we could execute the rest of the loop body to dequantize and
// perform the inverse DCT, to save early stages of a progressive image to the
// *image.YCbCr buffers (the whole point of progressive encoding), but in Go,
// the jpeg.Decode function does not return until the entire image is decoded,
// so we "continue" here to avoid wasted computation.
continue
}
}
// Dequantize, perform the inverse DCT and store the block to the image.
for zig := 0; zig < blockSize; zig++ {
b[unzig[zig]] *= qt[zig]
}
idct(&b)
dst, stride := []byte(nil), 0
if d.nComp == nGrayComponent {
dst, stride = d.img1.Pix[8*(my0*d.img1.Stride+mx0):], d.img1.Stride
} else {
switch compIndex {
case 0:
dst, stride = d.img3.Y[8*(my0*d.img3.YStride+mx0):], d.img3.YStride
case 1:
dst, stride = d.img3.Cb[8*(my0*d.img3.CStride+mx0):], d.img3.CStride
case 2:
dst, stride = d.img3.Cr[8*(my0*d.img3.CStride+mx0):], d.img3.CStride
default:
return UnsupportedError("too many components")
}
}
// Level shift by +128, clip to [0, 255], and write to dst.
for y := 0; y < 8; y++ {
y8 := y * 8
yStride := y * stride
for x := 0; x < 8; x++ {
c := b[y8+x]
if c < -128 {
c = 0
} else if c > 127 {
c = 255
} else {
c += 128
}
dst[yStride+x] = uint8(c)
}
}
} // for j
} // for i
mcu++
if d.ri > 0 && mcu%d.ri == 0 && mcu < mxx*myy {
// A more sophisticated decoder could use RST[0-7] markers to resynchronize from corrupt input,
// but this one assumes well-formed input, and hence the restart marker follows immediately.
if err := d.readFull(d.tmp[:2]); err != nil {
return err
}
if d.tmp[0] != 0xff || d.tmp[1] != expectedRST {
return FormatError("bad RST marker")
}
expectedRST++
if expectedRST == rst7Marker+1 {
expectedRST = rst0Marker
}
// Reset the Huffman decoder.
d.bits = bits{}
// Reset the DC components, as per section F.2.1.3.1.
dc = [nColorComponent]int32{}
// Reset the progressive decoder state, as per section G.1.2.2.
d.eobRun = 0
}
} // for mx
} // for my
return nil
}
// refine decodes a successive approximation refinement block, as specified in
// section G.1.2.
func (d *decoder) refine(b *block, h *huffman, zigStart, zigEnd, delta int32) error {
// Refining a DC component is trivial.
if zigStart == 0 {
if zigEnd != 0 {
panic("unreachable")
}
bit, err := d.decodeBit()
if err != nil {
return err
}
if bit {
b[0] |= delta
}
return nil
}
// Refining AC components is more complicated; see sections G.1.2.2 and G.1.2.3.
zig := zigStart
if d.eobRun == 0 {
loop:
for ; zig <= zigEnd; zig++ {
z := int32(0)
value, err := d.decodeHuffman(h)
if err != nil {
return err
}
val0 := value >> 4
val1 := value & 0x0f
switch val1 {
case 0:
if val0 != 0x0f {
d.eobRun = uint16(1 << val0)
if val0 != 0 {
bits, err := d.decodeBits(int32(val0))
if err != nil {
return err
}
d.eobRun |= uint16(bits)
}
break loop
}
case 1:
z = delta
bit, err := d.decodeBit()
if err != nil {
return err
}
if !bit {
z = -z
}
default:
return FormatError("unexpected Huffman code")
}
zig, err = d.refineNonZeroes(b, zig, zigEnd, int32(val0), delta)
if err != nil {
return err
}
if zig > zigEnd {
return FormatError("too many coefficients")
}
if z != 0 {
b[unzig[zig]] = z
}
}
}
if d.eobRun > 0 {
d.eobRun--
if _, err := d.refineNonZeroes(b, zig, zigEnd, -1, delta); err != nil {
return err
}
}
return nil
}
// refineNonZeroes refines non-zero entries of b in zig-zag order. If nz >= 0,
// the first nz zero entries are skipped over.
func (d *decoder) refineNonZeroes(b *block, zig, zigEnd, nz, delta int32) (int32, error) {
for ; zig <= zigEnd; zig++ {
u := unzig[zig]
if b[u] == 0 {
if nz == 0 {
break
}
nz--
continue
}
bit, err := d.decodeBit()
if err != nil {
return 0, err
}
if !bit {
continue
}
if b[u] >= 0 {
b[u] += delta
} else {
b[u] -= delta
}
}
return zig, nil
}

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// 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 (
"bufio"
"errors"
"image"
"image/color"
"io"
)
// min returns the minimum of two integers.
func min(x, y int) int {
if x < y {
return x
}
return y
}
// div returns a/b rounded to the nearest integer, instead of rounded to zero.
func div(a, b int32) int32 {
if a >= 0 {
return (a + (b >> 1)) / b
}
return -((-a + (b >> 1)) / b)
}
// bitCount counts the number of bits needed to hold an integer.
var bitCount = [256]byte{
0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
}
type quantIndex int
const (
quantIndexLuminance quantIndex = iota
quantIndexChrominance
nQuantIndex
)
// unscaledQuant are the unscaled quantization tables in zig-zag order. Each
// encoder copies and scales the tables according to its quality parameter.
// The values are derived from section K.1 after converting from natural to
// zig-zag order.
var unscaledQuant = [nQuantIndex][blockSize]byte{
// Luminance.
{
16, 11, 12, 14, 12, 10, 16, 14,
13, 14, 18, 17, 16, 19, 24, 40,
26, 24, 22, 22, 24, 49, 35, 37,
29, 40, 58, 51, 61, 60, 57, 51,
56, 55, 64, 72, 92, 78, 64, 68,
87, 69, 55, 56, 80, 109, 81, 87,
95, 98, 103, 104, 103, 62, 77, 113,
121, 112, 100, 120, 92, 101, 103, 99,
},
// Chrominance.
{
17, 18, 18, 24, 21, 24, 47, 26,
26, 47, 99, 66, 56, 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, 99, 99, 99, 99,
99, 99, 99, 99, 99, 99, 99, 99,
},
}
type huffIndex int
const (
huffIndexLuminanceDC huffIndex = iota
huffIndexLuminanceAC
huffIndexChrominanceDC
huffIndexChrominanceAC
nHuffIndex
)
// huffmanSpec specifies a Huffman encoding.
type huffmanSpec struct {
// count[i] is the number of codes of length i bits.
count [16]byte
// value[i] is the decoded value of the i'th codeword.
value []byte
}
// theHuffmanSpec is the Huffman encoding specifications.
// This encoder uses the same Huffman encoding for all images.
var theHuffmanSpec = [nHuffIndex]huffmanSpec{
// Luminance DC.
{
[16]byte{0, 1, 5, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0},
[]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
},
// Luminance AC.
{
[16]byte{0, 2, 1, 3, 3, 2, 4, 3, 5, 5, 4, 4, 0, 0, 1, 125},
[]byte{
0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12,
0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07,
0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xa1, 0x08,
0x23, 0x42, 0xb1, 0xc1, 0x15, 0x52, 0xd1, 0xf0,
0x24, 0x33, 0x62, 0x72, 0x82, 0x09, 0x0a, 0x16,
0x17, 0x18, 0x19, 0x1a, 0x25, 0x26, 0x27, 0x28,
0x29, 0x2a, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39,
0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49,
0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59,
0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79,
0x7a, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89,
0x8a, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98,
0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6,
0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3, 0xc4, 0xc5,
0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4,
0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe1, 0xe2,
0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea,
0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,
0xf9, 0xfa,
},
},
// Chrominance DC.
{
[16]byte{0, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0},
[]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
},
// Chrominance AC.
{
[16]byte{0, 2, 1, 2, 4, 4, 3, 4, 7, 5, 4, 4, 0, 1, 2, 119},
[]byte{
0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21,
0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71,
0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91,
0xa1, 0xb1, 0xc1, 0x09, 0x23, 0x33, 0x52, 0xf0,
0x15, 0x62, 0x72, 0xd1, 0x0a, 0x16, 0x24, 0x34,
0xe1, 0x25, 0xf1, 0x17, 0x18, 0x19, 0x1a, 0x26,
0x27, 0x28, 0x29, 0x2a, 0x35, 0x36, 0x37, 0x38,
0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
0x59, 0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,
0x79, 0x7a, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95, 0x96,
0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5,
0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4,
0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3,
0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2,
0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda,
0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9,
0xea, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,
0xf9, 0xfa,
},
},
}
// huffmanLUT is a compiled look-up table representation of a huffmanSpec.
// Each value maps to a uint32 of which the 8 most significant bits hold the
// codeword size in bits and the 24 least significant bits hold the codeword.
// The maximum codeword size is 16 bits.
type huffmanLUT []uint32
func (h *huffmanLUT) init(s huffmanSpec) {
maxValue := 0
for _, v := range s.value {
if int(v) > maxValue {
maxValue = int(v)
}
}
*h = make([]uint32, maxValue+1)
code, k := uint32(0), 0
for i := 0; i < len(s.count); i++ {
nBits := uint32(i+1) << 24
for j := uint8(0); j < s.count[i]; j++ {
(*h)[s.value[k]] = nBits | code
code++
k++
}
code <<= 1
}
}
// theHuffmanLUT are compiled representations of theHuffmanSpec.
var theHuffmanLUT [4]huffmanLUT
func init() {
for i, s := range theHuffmanSpec {
theHuffmanLUT[i].init(s)
}
}
// writer is a buffered writer.
type writer interface {
Flush() error
io.Writer
io.ByteWriter
}
// encoder encodes an image to the JPEG format.
type encoder struct {
// w is the writer to write to. err is the first error encountered during
// writing. All attempted writes after the first error become no-ops.
w writer
err error
// buf is a scratch buffer.
buf [16]byte
// bits and nBits are accumulated bits to write to w.
bits, nBits uint32
// quant is the scaled quantization tables, in zig-zag order.
quant [nQuantIndex][blockSize]byte
}
func (e *encoder) flush() {
if e.err != nil {
return
}
e.err = e.w.Flush()
}
func (e *encoder) write(p []byte) {
if e.err != nil {
return
}
_, e.err = e.w.Write(p)
}
func (e *encoder) writeByte(b byte) {
if e.err != nil {
return
}
e.err = e.w.WriteByte(b)
}
// emit emits the least significant nBits bits of bits to the bit-stream.
// The precondition is bits < 1<<nBits && nBits <= 16.
func (e *encoder) emit(bits, nBits uint32) {
nBits += e.nBits
bits <<= 32 - nBits
bits |= e.bits
for nBits >= 8 {
b := uint8(bits >> 24)
e.writeByte(b)
if b == 0xff {
e.writeByte(0x00)
}
bits <<= 8
nBits -= 8
}
e.bits, e.nBits = bits, nBits
}
// emitHuff emits the given value with the given Huffman encoder.
func (e *encoder) emitHuff(h huffIndex, value int32) {
x := theHuffmanLUT[h][value]
e.emit(x&(1<<24-1), x>>24)
}
// emitHuffRLE emits a run of runLength copies of value encoded with the given
// Huffman encoder.
func (e *encoder) emitHuffRLE(h huffIndex, runLength, value int32) {
a, b := value, value
if a < 0 {
a, b = -value, value-1
}
var nBits uint32
if a < 0x100 {
nBits = uint32(bitCount[a])
} else {
nBits = 8 + uint32(bitCount[a>>8])
}
e.emitHuff(h, runLength<<4|int32(nBits))
if nBits > 0 {
e.emit(uint32(b)&(1<<nBits-1), nBits)
}
}
// writeMarkerHeader writes the header for a marker with the given length.
func (e *encoder) writeMarkerHeader(marker uint8, markerlen int) {
e.buf[0] = 0xff
e.buf[1] = marker
e.buf[2] = uint8(markerlen >> 8)
e.buf[3] = uint8(markerlen & 0xff)
e.write(e.buf[:4])
}
// writeDQT writes the Define Quantization Table marker.
func (e *encoder) writeDQT() {
const markerlen = 2 + int(nQuantIndex)*(1+blockSize)
e.writeMarkerHeader(dqtMarker, markerlen)
for i := range e.quant {
e.writeByte(uint8(i))
e.write(e.quant[i][:])
}
}
// writeSOF0 writes the Start Of Frame (Baseline) marker.
func (e *encoder) writeSOF0(size image.Point, nComponent int) {
markerlen := 8 + 3*nComponent
e.writeMarkerHeader(sof0Marker, markerlen)
e.buf[0] = 8 // 8-bit color.
e.buf[1] = uint8(size.Y >> 8)
e.buf[2] = uint8(size.Y & 0xff)
e.buf[3] = uint8(size.X >> 8)
e.buf[4] = uint8(size.X & 0xff)
e.buf[5] = uint8(nComponent)
if nComponent == 1 {
e.buf[6] = 1
// No subsampling for grayscale image.
e.buf[7] = 0x11
e.buf[8] = 0x00
} else {
for i := 0; i < nComponent; i++ {
e.buf[3*i+6] = uint8(i + 1)
// We use 4:2:0 chroma subsampling.
e.buf[3*i+7] = "\x22\x11\x11"[i]
e.buf[3*i+8] = "\x00\x01\x01"[i]
}
}
e.write(e.buf[:3*(nComponent-1)+9])
}
// writeDHT writes the Define Huffman Table marker.
func (e *encoder) writeDHT(nComponent int) {
markerlen := 2
specs := theHuffmanSpec[:]
if nComponent == 1 {
// Drop the Chrominance tables.
specs = specs[:2]
}
for _, s := range specs {
markerlen += 1 + 16 + len(s.value)
}
e.writeMarkerHeader(dhtMarker, markerlen)
for i, s := range specs {
e.writeByte("\x00\x10\x01\x11"[i])
e.write(s.count[:])
e.write(s.value)
}
}
// writeBlock writes a block of pixel data using the given quantization table,
// returning the post-quantized DC value of the DCT-transformed block. b is in
// natural (not zig-zag) order.
func (e *encoder) writeBlock(b *block, q quantIndex, prevDC int32) int32 {
fdct(b)
// Emit the DC delta.
dc := div(b[0], 8*int32(e.quant[q][0]))
e.emitHuffRLE(huffIndex(2*q+0), 0, dc-prevDC)
// Emit the AC components.
h, runLength := huffIndex(2*q+1), int32(0)
for zig := 1; zig < blockSize; zig++ {
ac := div(b[unzig[zig]], 8*int32(e.quant[q][zig]))
if ac == 0 {
runLength++
} else {
for runLength > 15 {
e.emitHuff(h, 0xf0)
runLength -= 16
}
e.emitHuffRLE(h, runLength, ac)
runLength = 0
}
}
if runLength > 0 {
e.emitHuff(h, 0x00)
}
return dc
}
// toYCbCr converts the 8x8 region of m whose top-left corner is p to its
// YCbCr values.
func toYCbCr(m image.Image, p image.Point, yBlock, cbBlock, crBlock *block) {
b := m.Bounds()
xmax := b.Max.X - 1
ymax := b.Max.Y - 1
for j := 0; j < 8; j++ {
for i := 0; i < 8; i++ {
r, g, b, _ := m.At(min(p.X+i, xmax), min(p.Y+j, ymax)).RGBA()
yy, cb, cr := color.RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))
yBlock[8*j+i] = int32(yy)
cbBlock[8*j+i] = int32(cb)
crBlock[8*j+i] = int32(cr)
}
}
}
// grayToY stores the 8x8 region of m whose top-left corner is p in yBlock.
func grayToY(m *image.Gray, p image.Point, yBlock *block) {
b := m.Bounds()
xmax := b.Max.X - 1
ymax := b.Max.Y - 1
pix := m.Pix
for j := 0; j < 8; j++ {
for i := 0; i < 8; i++ {
idx := m.PixOffset(min(p.X+i, xmax), min(p.Y+j, ymax))
yBlock[8*j+i] = int32(pix[idx])
}
}
}
// rgbaToYCbCr is a specialized version of toYCbCr for image.RGBA images.
func rgbaToYCbCr(m *image.RGBA, p image.Point, yBlock, cbBlock, crBlock *block) {
b := m.Bounds()
xmax := b.Max.X - 1
ymax := b.Max.Y - 1
for j := 0; j < 8; j++ {
sj := p.Y + j
if sj > ymax {
sj = ymax
}
offset := (sj-b.Min.Y)*m.Stride - b.Min.X*4
for i := 0; i < 8; i++ {
sx := p.X + i
if sx > xmax {
sx = xmax
}
pix := m.Pix[offset+sx*4:]
yy, cb, cr := color.RGBToYCbCr(pix[0], pix[1], pix[2])
yBlock[8*j+i] = int32(yy)
cbBlock[8*j+i] = int32(cb)
crBlock[8*j+i] = int32(cr)
}
}
}
// scale scales the 16x16 region represented by the 4 src blocks to the 8x8
// dst block.
func scale(dst *block, src *[4]block) {
for i := 0; i < 4; i++ {
dstOff := (i&2)<<4 | (i&1)<<2
for y := 0; y < 4; y++ {
for x := 0; x < 4; x++ {
j := 16*y + 2*x
sum := src[i][j] + src[i][j+1] + src[i][j+8] + src[i][j+9]
dst[8*y+x+dstOff] = (sum + 2) >> 2
}
}
}
}
// sosHeaderY is the SOS marker "\xff\xda" followed by 8 bytes:
// - the marker length "\x00\x08",
// - the number of components "\x01",
// - component 1 uses DC table 0 and AC table 0 "\x01\x00",
// - the bytes "\x00\x3f\x00". Section B.2.3 of the spec says that for
// sequential DCTs, those bytes (8-bit Ss, 8-bit Se, 4-bit Ah, 4-bit Al)
// should be 0x00, 0x3f, 0x00<<4 | 0x00.
var sosHeaderY = []byte{
0xff, 0xda, 0x00, 0x08, 0x01, 0x01, 0x00, 0x00, 0x3f, 0x00,
}
// sosHeaderYCbCr is the SOS marker "\xff\xda" followed by 12 bytes:
// - the marker length "\x00\x0c",
// - the number of components "\x03",
// - component 1 uses DC table 0 and AC table 0 "\x01\x00",
// - component 2 uses DC table 1 and AC table 1 "\x02\x11",
// - component 3 uses DC table 1 and AC table 1 "\x03\x11",
// - the bytes "\x00\x3f\x00". Section B.2.3 of the spec says that for
// sequential DCTs, those bytes (8-bit Ss, 8-bit Se, 4-bit Ah, 4-bit Al)
// should be 0x00, 0x3f, 0x00<<4 | 0x00.
var sosHeaderYCbCr = []byte{
0xff, 0xda, 0x00, 0x0c, 0x03, 0x01, 0x00, 0x02,
0x11, 0x03, 0x11, 0x00, 0x3f, 0x00,
}
// writeSOS writes the StartOfScan marker.
func (e *encoder) writeSOS(m image.Image) {
switch m.(type) {
case *image.Gray:
e.write(sosHeaderY)
default:
e.write(sosHeaderYCbCr)
}
var (
// Scratch buffers to hold the YCbCr values.
// The blocks are in natural (not zig-zag) order.
b block
cb, cr [4]block
// DC components are delta-encoded.
prevDCY, prevDCCb, prevDCCr int32
)
bounds := m.Bounds()
switch m := m.(type) {
// TODO(wathiede): switch on m.ColorModel() instead of type.
case *image.Gray:
for y := bounds.Min.Y; y < bounds.Max.Y; y += 8 {
for x := bounds.Min.X; x < bounds.Max.X; x += 8 {
p := image.Pt(x, y)
grayToY(m, p, &b)
prevDCY = e.writeBlock(&b, 0, prevDCY)
}
}
default:
rgba, _ := m.(*image.RGBA)
for y := bounds.Min.Y; y < bounds.Max.Y; y += 16 {
for x := bounds.Min.X; x < bounds.Max.X; x += 16 {
for i := 0; i < 4; i++ {
xOff := (i & 1) * 8
yOff := (i & 2) * 4
p := image.Pt(x+xOff, y+yOff)
if rgba != nil {
rgbaToYCbCr(rgba, p, &b, &cb[i], &cr[i])
} else {
toYCbCr(m, p, &b, &cb[i], &cr[i])
}
prevDCY = e.writeBlock(&b, 0, prevDCY)
}
scale(&b, &cb)
prevDCCb = e.writeBlock(&b, 1, prevDCCb)
scale(&b, &cr)
prevDCCr = e.writeBlock(&b, 1, prevDCCr)
}
}
}
// Pad the last byte with 1's.
e.emit(0x7f, 7)
}
// DefaultQuality is the default quality encoding parameter.
const DefaultQuality = 75
// Options are the encoding parameters.
// Quality ranges from 1 to 100 inclusive, higher is better.
type Options struct {
Quality int
}
// Encode writes the Image m to w in JPEG 4:2:0 baseline format with the given
// options. Default parameters are used if a nil *Options is passed.
func Encode(w io.Writer, m image.Image, o *Options) error {
b := m.Bounds()
if b.Dx() >= 1<<16 || b.Dy() >= 1<<16 {
return errors.New("jpeg: image is too large to encode")
}
var e encoder
if ww, ok := w.(writer); ok {
e.w = ww
} else {
e.w = bufio.NewWriter(w)
}
// Clip quality to [1, 100].
quality := DefaultQuality
if o != nil {
quality = o.Quality
if quality < 1 {
quality = 1
} else if quality > 100 {
quality = 100
}
}
// Convert from a quality rating to a scaling factor.
var scale int
if quality < 50 {
scale = 5000 / quality
} else {
scale = 200 - quality*2
}
// Initialize the quantization tables.
for i := range e.quant {
for j := range e.quant[i] {
x := int(unscaledQuant[i][j])
x = (x*scale + 50) / 100
if x < 1 {
x = 1
} else if x > 255 {
x = 255
}
e.quant[i][j] = uint8(x)
}
}
// Compute number of components based on input image type.
nComponent := 3
switch m.(type) {
// TODO(wathiede): switch on m.ColorModel() instead of type.
case *image.Gray:
nComponent = 1
}
// Write the Start Of Image marker.
e.buf[0] = 0xff
e.buf[1] = 0xd8
e.write(e.buf[:2])
// Write the quantization tables.
e.writeDQT()
// Write the image dimensions.
e.writeSOF0(b.Size(), nComponent)
// Write the Huffman tables.
e.writeDHT(nComponent)
// Write the image data.
e.writeSOS(m)
// Write the End Of Image marker.
e.buf[0] = 0xff
e.buf[1] = 0xd9
e.write(e.buf[:2])
e.flush()
return e.err
}

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// 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 BenchmarkEncode(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)
}
}