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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
This commit is contained in:
Nigel Tao
parent
3bac16a6bf
commit
5500f027f7
@ -183,7 +183,6 @@ NOTEST+=\
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hash\
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http/pprof\
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http/httptest\
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image/jpeg\
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net/dict\
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rand\
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runtime/cgo\
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@ -6,8 +6,10 @@ include ../../../Make.inc
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TARG=image/jpeg
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GOFILES=\
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fdct.go\
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huffman.go\
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idct.go\
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reader.go\
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writer.go\
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include ../../../Make.pkg
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190
src/pkg/image/jpeg/fdct.go
Normal file
190
src/pkg/image/jpeg/fdct.go
Normal file
@ -0,0 +1,190 @@
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package jpeg
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// This file implements a Forward Discrete Cosine Transformation.
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/*
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It is based on the code in jfdctint.c from the Independent JPEG Group,
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found at http://www.ijg.org/files/jpegsrc.v8c.tar.gz.
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The "LEGAL ISSUES" section of the README in that archive says:
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In plain English:
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1. We don't promise that this software works. (But if you find any bugs,
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please let us know!)
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2. You can use this software for whatever you want. You don't have to pay us.
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3. You may not pretend that you wrote this software. If you use it in a
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program, you must acknowledge somewhere in your documentation that
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you've used the IJG code.
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In legalese:
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The authors make NO WARRANTY or representation, either express or implied,
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with respect to this software, its quality, accuracy, merchantability, or
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fitness for a particular purpose. This software is provided "AS IS", and you,
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its user, assume the entire risk as to its quality and accuracy.
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This software is copyright (C) 1991-2011, Thomas G. Lane, Guido Vollbeding.
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All Rights Reserved except as specified below.
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Permission is hereby granted to use, copy, modify, and distribute this
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software (or portions thereof) for any purpose, without fee, subject to these
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conditions:
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(1) If any part of the source code for this software is distributed, then this
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README file must be included, with this copyright and no-warranty notice
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unaltered; and any additions, deletions, or changes to the original files
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must be clearly indicated in accompanying documentation.
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(2) If only executable code is distributed, then the accompanying
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documentation must state that "this software is based in part on the work of
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the Independent JPEG Group".
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(3) Permission for use of this software is granted only if the user accepts
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full responsibility for any undesirable consequences; the authors accept
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NO LIABILITY for damages of any kind.
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These conditions apply to any software derived from or based on the IJG code,
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not just to the unmodified library. If you use our work, you ought to
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acknowledge us.
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Permission is NOT granted for the use of any IJG author's name or company name
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in advertising or publicity relating to this software or products derived from
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it. This software may be referred to only as "the Independent JPEG Group's
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software".
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We specifically permit and encourage the use of this software as the basis of
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commercial products, provided that all warranty or liability claims are
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assumed by the product vendor.
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*/
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// Trigonometric constants in 13-bit fixed point format.
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const (
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fix_0_298631336 = 2446
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fix_0_390180644 = 3196
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fix_0_541196100 = 4433
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fix_0_765366865 = 6270
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fix_0_899976223 = 7373
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fix_1_175875602 = 9633
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fix_1_501321110 = 12299
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fix_1_847759065 = 15137
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fix_1_961570560 = 16069
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fix_2_053119869 = 16819
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fix_2_562915447 = 20995
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fix_3_072711026 = 25172
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)
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const (
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constBits = 13
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pass1Bits = 2
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centerJSample = 128
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)
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// fdct performs a forward DCT on an 8x8 block of coefficients, including a
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// level shift.
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func fdct(b *block) {
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// Pass 1: process rows.
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for y := 0; y < 8; y++ {
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x0 := b[y*8+0]
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x1 := b[y*8+1]
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x2 := b[y*8+2]
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x3 := b[y*8+3]
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x4 := b[y*8+4]
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x5 := b[y*8+5]
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x6 := b[y*8+6]
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x7 := b[y*8+7]
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tmp0 := x0 + x7
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tmp1 := x1 + x6
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tmp2 := x2 + x5
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tmp3 := x3 + x4
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tmp10 := tmp0 + tmp3
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tmp12 := tmp0 - tmp3
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tmp11 := tmp1 + tmp2
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tmp13 := tmp1 - tmp2
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tmp0 = x0 - x7
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tmp1 = x1 - x6
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tmp2 = x2 - x5
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tmp3 = x3 - x4
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b[y*8+0] = (tmp10 + tmp11 - 8*centerJSample) << pass1Bits
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b[y*8+4] = (tmp10 - tmp11) << pass1Bits
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z1 := (tmp12 + tmp13) * fix_0_541196100
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z1 += 1 << (constBits - pass1Bits - 1)
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b[y*8+2] = (z1 + tmp12*fix_0_765366865) >> (constBits - pass1Bits)
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b[y*8+6] = (z1 - tmp13*fix_1_847759065) >> (constBits - pass1Bits)
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tmp10 = tmp0 + tmp3
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tmp11 = tmp1 + tmp2
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tmp12 = tmp0 + tmp2
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tmp13 = tmp1 + tmp3
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z1 = (tmp12 + tmp13) * fix_1_175875602
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z1 += 1 << (constBits - pass1Bits - 1)
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tmp0 = tmp0 * fix_1_501321110
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tmp1 = tmp1 * fix_3_072711026
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tmp2 = tmp2 * fix_2_053119869
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tmp3 = tmp3 * fix_0_298631336
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tmp10 = tmp10 * -fix_0_899976223
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tmp11 = tmp11 * -fix_2_562915447
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tmp12 = tmp12 * -fix_0_390180644
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tmp13 = tmp13 * -fix_1_961570560
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tmp12 += z1
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tmp13 += z1
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b[y*8+1] = (tmp0 + tmp10 + tmp12) >> (constBits - pass1Bits)
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b[y*8+3] = (tmp1 + tmp11 + tmp13) >> (constBits - pass1Bits)
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b[y*8+5] = (tmp2 + tmp11 + tmp12) >> (constBits - pass1Bits)
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b[y*8+7] = (tmp3 + tmp10 + tmp13) >> (constBits - pass1Bits)
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}
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// Pass 2: process columns.
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// We remove pass1Bits scaling, but leave results scaled up by an overall factor of 8.
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for x := 0; x < 8; x++ {
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tmp0 := b[0*8+x] + b[7*8+x]
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tmp1 := b[1*8+x] + b[6*8+x]
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tmp2 := b[2*8+x] + b[5*8+x]
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tmp3 := b[3*8+x] + b[4*8+x]
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tmp10 := tmp0 + tmp3 + 1<<(pass1Bits-1)
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tmp12 := tmp0 - tmp3
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tmp11 := tmp1 + tmp2
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tmp13 := tmp1 - tmp2
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tmp0 = b[0*8+x] - b[7*8+x]
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tmp1 = b[1*8+x] - b[6*8+x]
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tmp2 = b[2*8+x] - b[5*8+x]
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tmp3 = b[3*8+x] - b[4*8+x]
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b[0*8+x] = (tmp10 + tmp11) >> pass1Bits
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b[4*8+x] = (tmp10 - tmp11) >> pass1Bits
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z1 := (tmp12 + tmp13) * fix_0_541196100
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z1 += 1 << (constBits + pass1Bits - 1)
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b[2*8+x] = (z1 + tmp12*fix_0_765366865) >> (constBits + pass1Bits)
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b[6*8+x] = (z1 - tmp13*fix_1_847759065) >> (constBits + pass1Bits)
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tmp10 = tmp0 + tmp3
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tmp11 = tmp1 + tmp2
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tmp12 = tmp0 + tmp2
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tmp13 = tmp1 + tmp3
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z1 = (tmp12 + tmp13) * fix_1_175875602
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z1 += 1 << (constBits + pass1Bits - 1)
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tmp0 = tmp0 * fix_1_501321110
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tmp1 = tmp1 * fix_3_072711026
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tmp2 = tmp2 * fix_2_053119869
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tmp3 = tmp3 * fix_0_298631336
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tmp10 = tmp10 * -fix_0_899976223
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tmp11 = tmp11 * -fix_2_562915447
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tmp12 = tmp12 * -fix_0_390180644
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tmp13 = tmp13 * -fix_1_961570560
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tmp12 += z1
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tmp13 += z1
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b[1*8+x] = (tmp0 + tmp10 + tmp12) >> (constBits + pass1Bits)
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b[3*8+x] = (tmp1 + tmp11 + tmp13) >> (constBits + pass1Bits)
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b[5*8+x] = (tmp2 + tmp11 + tmp12) >> (constBits + pass1Bits)
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b[7*8+x] = (tmp3 + tmp10 + tmp13) >> (constBits + pass1Bits)
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}
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}
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@ -63,7 +63,7 @@ const (
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//
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// For more on the actual algorithm, see Z. Wang, "Fast algorithms for the discrete W transform and
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// for the discrete Fourier transform", IEEE Trans. on ASSP, Vol. ASSP- 32, pp. 803-816, Aug. 1984.
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func idct(b *[blockSize]int) {
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func idct(b *block) {
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// Horizontal 1-D IDCT.
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for y := 0; y < 8; y++ {
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// If all the AC components are zero, then the IDCT is trivial.
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@ -2,11 +2,11 @@
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// The jpeg package implements a decoder for JPEG images, as defined in ITU-T T.81.
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// Package jpeg implements a JPEG image decoder and encoder.
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//
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// JPEG is defined in ITU-T T.81: http://www.w3.org/Graphics/JPEG/itu-t81.pdf.
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package jpeg
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// See http://www.w3.org/Graphics/JPEG/itu-t81.pdf
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import (
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"bufio"
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"image"
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@ -32,6 +32,8 @@ type component struct {
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tq uint8 // Quantization table destination selector.
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}
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type block [blockSize]int
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const (
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blockSize = 64 // A DCT block is 8x8.
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@ -88,9 +90,9 @@ type decoder struct {
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ri int // Restart Interval.
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comps [nComponent]component
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huff [maxTc + 1][maxTh + 1]huffman
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quant [maxTq + 1][blockSize]int
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quant [maxTq + 1]block
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b bits
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blocks [nComponent][maxH * maxV][blockSize]int
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blocks [nComponent][maxH * maxV]block
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tmp [1024]byte
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}
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@ -269,7 +271,7 @@ func (d *decoder) processSOS(n int) os.Error {
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myy := (d.height + 8*int(v0) - 1) / (8 * int(v0))
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mcu, expectedRST := 0, uint8(rst0Marker)
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var allZeroes [blockSize]int
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var allZeroes block
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var dc [nComponent]int
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for my := 0; my < myy; my++ {
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for mx := 0; mx < mxx; mx++ {
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523
src/pkg/image/jpeg/writer.go
Normal file
523
src/pkg/image/jpeg/writer.go
Normal file
@ -0,0 +1,523 @@
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package jpeg
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import (
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"bufio"
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"image"
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"image/ycbcr"
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"io"
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"os"
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)
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// min returns the minimum of two integers.
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func min(x, y int) int {
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if x < y {
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return x
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}
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return y
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}
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// div returns a/b rounded to the nearest integer, instead of rounded to zero.
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func div(a int, b int) int {
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if a >= 0 {
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return (a + (b >> 1)) / b
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}
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return -((-a + (b >> 1)) / b)
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}
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// bitCount counts the number of bits needed to hold an integer.
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var bitCount = [256]byte{
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0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
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5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
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6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
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6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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}
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type quantIndex int
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const (
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quantIndexLuminance quantIndex = iota
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quantIndexChrominance
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nQuantIndex
|
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)
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|
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// unscaledQuant are the unscaled quantization tables. Each encoder copies and
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// scales the tables according to its quality parameter.
|
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var unscaledQuant = [nQuantIndex][blockSize]byte{
|
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// Luminance.
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{
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16, 11, 10, 16, 24, 40, 51, 61,
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12, 12, 14, 19, 26, 58, 60, 55,
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14, 13, 16, 24, 40, 57, 69, 56,
|
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14, 17, 22, 29, 51, 87, 80, 62,
|
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18, 22, 37, 56, 68, 109, 103, 77,
|
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24, 35, 55, 64, 81, 104, 113, 92,
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49, 64, 78, 87, 103, 121, 120, 101,
|
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72, 92, 95, 98, 112, 100, 103, 99,
|
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},
|
||||
// Chrominance.
|
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{
|
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17, 18, 24, 47, 99, 99, 99, 99,
|
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18, 21, 26, 66, 99, 99, 99, 99,
|
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24, 26, 56, 99, 99, 99, 99, 99,
|
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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,
|
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99, 99, 99, 99, 99, 99, 99, 99,
|
||||
},
|
||||
}
|
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|
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type huffIndex int
|
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|
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const (
|
||||
huffIndexLuminanceDC huffIndex = iota
|
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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.
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||||
{
|
||||
[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,
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||||
0x17, 0x18, 0x19, 0x1a, 0x25, 0x26, 0x27, 0x28,
|
||||
0x29, 0x2a, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39,
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0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49,
|
||||
0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59,
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||||
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() os.Error
|
||||
Write([]byte) (int, os.Error)
|
||||
WriteByte(byte) os.Error
|
||||
}
|
||||
|
||||
// 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 os.Error
|
||||
// buf is a scratch buffer.
|
||||
buf [16]byte
|
||||
// bits and nBits are accumulated bits to write to w.
|
||||
bits uint32
|
||||
nBits uint8
|
||||
// quant is the scaled quantization tables.
|
||||
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 bitstream.
|
||||
// The precondition is bits < 1<<nBits && nBits <= 16.
|
||||
func (e *encoder) emit(bits uint32, nBits uint8) {
|
||||
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 int) {
|
||||
x := theHuffmanLUT[h][value]
|
||||
e.emit(x&(1<<24-1), uint8(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 int) {
|
||||
a, b := value, value
|
||||
if a < 0 {
|
||||
a, b = -value, value-1
|
||||
}
|
||||
var nBits uint8
|
||||
if a < 0x100 {
|
||||
nBits = bitCount[a]
|
||||
} else {
|
||||
nBits = 8 + bitCount[a>>8]
|
||||
}
|
||||
e.emitHuff(h, runLength<<4|int(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() {
|
||||
markerlen := 2
|
||||
for _, q := range e.quant {
|
||||
markerlen += 1 + len(q)
|
||||
}
|
||||
e.writeMarkerHeader(dqtMarker, markerlen)
|
||||
for i, q := range e.quant {
|
||||
e.writeByte(uint8(i))
|
||||
e.write(q[:])
|
||||
}
|
||||
}
|
||||
|
||||
// writeSOF0 writes the Start Of Frame (Baseline) marker.
|
||||
func (e *encoder) writeSOF0(size image.Point) {
|
||||
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] = nComponent
|
||||
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() {
|
||||
markerlen := 2
|
||||
for _, s := range theHuffmanSpec {
|
||||
markerlen += 1 + 16 + len(s.value)
|
||||
}
|
||||
e.writeMarkerHeader(dhtMarker, markerlen)
|
||||
for i, s := range theHuffmanSpec {
|
||||
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.
|
||||
func (e *encoder) writeBlock(b *block, q quantIndex, prevDC int) int {
|
||||
fdct(b)
|
||||
// Emit the DC delta.
|
||||
dc := div(b[0], (8 * int(e.quant[q][0])))
|
||||
e.emitHuffRLE(huffIndex(2*q+0), 0, dc-prevDC)
|
||||
// Emit the AC components.
|
||||
h, runLength := huffIndex(2*q+1), 0
|
||||
for k := 1; k < blockSize; k++ {
|
||||
ac := div(b[unzig[k]], (8 * int(e.quant[q][k])))
|
||||
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 := ycbcr.RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))
|
||||
yBlock[8*j+i] = int(yy)
|
||||
cbBlock[8*j+i] = int(cb)
|
||||
crBlock[8*j+i] = int(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
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// sosHeader 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",
|
||||
// - padding "\x00\x00\x00".
|
||||
var sosHeader = []byte{
|
||||
0xff, 0xda, 0x00, 0x0c, 0x03, 0x01, 0x00, 0x02,
|
||||
0x11, 0x03, 0x11, 0x00, 0x00, 0x00,
|
||||
}
|
||||
|
||||
// writeSOS writes the StartOfScan marker.
|
||||
func (e *encoder) writeSOS(m image.Image) {
|
||||
e.write(sosHeader)
|
||||
var (
|
||||
// Scratch buffers to hold the YCbCr values.
|
||||
yBlock block
|
||||
cbBlock [4]block
|
||||
crBlock [4]block
|
||||
cBlock block
|
||||
// DC components are delta-encoded.
|
||||
prevDCY, prevDCCb, prevDCCr int
|
||||
)
|
||||
bounds := m.Bounds()
|
||||
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.Point{x + xOff, y + yOff}
|
||||
toYCbCr(m, p, &yBlock, &cbBlock[i], &crBlock[i])
|
||||
prevDCY = e.writeBlock(&yBlock, 0, prevDCY)
|
||||
}
|
||||
scale(&cBlock, &cbBlock)
|
||||
prevDCCb = e.writeBlock(&cBlock, 1, prevDCCb)
|
||||
scale(&cBlock, &crBlock)
|
||||
prevDCCr = e.writeBlock(&cBlock, 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) os.Error {
|
||||
b := m.Bounds()
|
||||
if b.Dx() >= 1<<16 || b.Dy() >= 1<<16 {
|
||||
return os.NewError("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)
|
||||
}
|
||||
}
|
||||
// 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())
|
||||
// Write the Huffman tables.
|
||||
e.writeDHT()
|
||||
// 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
|
||||
}
|
||||
87
src/pkg/image/jpeg/writer_test.go
Normal file
87
src/pkg/image/jpeg/writer_test.go
Normal file
@ -0,0 +1,87 @@
|
||||
// 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
|
||||
}
|
||||
}
|
||||
}
|
||||
Loading…
Reference in New Issue
Block a user