556 lines
15 KiB
Go
556 lines
15 KiB
Go
// 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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"errors"
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"image"
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"image/color"
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"io"
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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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// unscaledQuant are the unscaled quantization tables in zig-zag order. Each
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// encoder copies and scales the tables according to its quality parameter.
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// The values are derived from section K.1 after converting from natural to
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// zig-zag order.
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var unscaledQuant = [nQuantIndex][blockSize]byte{
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// Luminance.
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{
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16, 11, 12, 14, 12, 10, 16, 14,
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13, 14, 18, 17, 16, 19, 24, 40,
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26, 24, 22, 22, 24, 49, 35, 37,
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29, 40, 58, 51, 61, 60, 57, 51,
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56, 55, 64, 72, 92, 78, 64, 68,
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87, 69, 55, 56, 80, 109, 81, 87,
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95, 98, 103, 104, 103, 62, 77, 113,
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121, 112, 100, 120, 92, 101, 103, 99,
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},
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// Chrominance.
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{
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17, 18, 18, 24, 21, 24, 47, 26,
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26, 47, 99, 66, 56, 66, 99, 99,
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99, 99, 99, 99, 99, 99, 99, 99,
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99, 99, 99, 99, 99, 99, 99, 99,
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99, 99, 99, 99, 99, 99, 99, 99,
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99, 99, 99, 99, 99, 99, 99, 99,
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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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}
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type huffIndex int
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const (
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huffIndexLuminanceDC huffIndex = iota
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huffIndexLuminanceAC
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huffIndexChrominanceDC
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huffIndexChrominanceAC
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nHuffIndex
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)
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// huffmanSpec specifies a Huffman encoding.
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type huffmanSpec struct {
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// count[i] is the number of codes of length i bits.
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count [16]byte
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// value[i] is the decoded value of the i'th codeword.
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value []byte
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}
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// theHuffmanSpec is the Huffman encoding specifications.
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// This encoder uses the same Huffman encoding for all images.
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var theHuffmanSpec = [nHuffIndex]huffmanSpec{
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// Luminance DC.
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{
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[16]byte{0, 1, 5, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0},
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[]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
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},
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// Luminance AC.
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{
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[16]byte{0, 2, 1, 3, 3, 2, 4, 3, 5, 5, 4, 4, 0, 0, 1, 125},
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[]byte{
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0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12,
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0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07,
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0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xa1, 0x08,
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0x23, 0x42, 0xb1, 0xc1, 0x15, 0x52, 0xd1, 0xf0,
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0x24, 0x33, 0x62, 0x72, 0x82, 0x09, 0x0a, 0x16,
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0x17, 0x18, 0x19, 0x1a, 0x25, 0x26, 0x27, 0x28,
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0x29, 0x2a, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39,
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0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49,
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0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59,
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0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
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0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79,
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0x7a, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89,
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0x8a, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98,
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0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
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0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6,
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0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3, 0xc4, 0xc5,
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0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4,
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0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe1, 0xe2,
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0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea,
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0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,
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0xf9, 0xfa,
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},
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},
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// Chrominance DC.
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{
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[16]byte{0, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0},
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[]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},
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},
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// Chrominance AC.
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{
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[16]byte{0, 2, 1, 2, 4, 4, 3, 4, 7, 5, 4, 4, 0, 1, 2, 119},
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[]byte{
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0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21,
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0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71,
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0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91,
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0xa1, 0xb1, 0xc1, 0x09, 0x23, 0x33, 0x52, 0xf0,
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0x15, 0x62, 0x72, 0xd1, 0x0a, 0x16, 0x24, 0x34,
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0xe1, 0x25, 0xf1, 0x17, 0x18, 0x19, 0x1a, 0x26,
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0x27, 0x28, 0x29, 0x2a, 0x35, 0x36, 0x37, 0x38,
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0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,
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0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
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0x59, 0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,
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0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,
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0x79, 0x7a, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
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0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95, 0x96,
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0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5,
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0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4,
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0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3,
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0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2,
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0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda,
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0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9,
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0xea, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,
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0xf9, 0xfa,
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},
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},
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}
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// huffmanLUT is a compiled look-up table representation of a huffmanSpec.
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// Each value maps to a uint32 of which the 8 most significant bits hold the
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// codeword size in bits and the 24 least significant bits hold the codeword.
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// The maximum codeword size is 16 bits.
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type huffmanLUT []uint32
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func (h *huffmanLUT) init(s huffmanSpec) {
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maxValue := 0
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for _, v := range s.value {
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if int(v) > maxValue {
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maxValue = int(v)
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}
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}
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*h = make([]uint32, maxValue+1)
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code, k := uint32(0), 0
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for i := 0; i < len(s.count); i++ {
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nBits := uint32(i+1) << 24
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for j := uint8(0); j < s.count[i]; j++ {
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(*h)[s.value[k]] = nBits | code
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code++
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k++
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}
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code <<= 1
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}
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}
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// theHuffmanLUT are compiled representations of theHuffmanSpec.
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var theHuffmanLUT [4]huffmanLUT
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func init() {
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for i, s := range theHuffmanSpec {
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theHuffmanLUT[i].init(s)
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}
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}
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// writer is a buffered writer.
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type writer interface {
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Flush() error
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Write([]byte) (int, error)
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WriteByte(byte) error
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}
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// encoder encodes an image to the JPEG format.
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type encoder struct {
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// w is the writer to write to. err is the first error encountered during
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// writing. All attempted writes after the first error become no-ops.
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w writer
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err error
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// buf is a scratch buffer.
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buf [16]byte
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// bits and nBits are accumulated bits to write to w.
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bits, nBits uint32
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// quant is the scaled quantization tables, in zig-zag order.
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quant [nQuantIndex][blockSize]byte
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}
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func (e *encoder) flush() {
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if e.err != nil {
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return
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}
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e.err = e.w.Flush()
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}
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func (e *encoder) write(p []byte) {
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if e.err != nil {
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return
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}
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_, e.err = e.w.Write(p)
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}
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func (e *encoder) writeByte(b byte) {
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if e.err != nil {
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return
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}
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e.err = e.w.WriteByte(b)
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}
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// emit emits the least significant nBits bits of bits to the bitstream.
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// The precondition is bits < 1<<nBits && nBits <= 16.
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func (e *encoder) emit(bits, nBits uint32) {
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nBits += e.nBits
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bits <<= 32 - nBits
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bits |= e.bits
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for nBits >= 8 {
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b := uint8(bits >> 24)
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e.writeByte(b)
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if b == 0xff {
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e.writeByte(0x00)
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}
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bits <<= 8
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nBits -= 8
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}
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e.bits, e.nBits = bits, nBits
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}
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// emitHuff emits the given value with the given Huffman encoder.
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func (e *encoder) emitHuff(h huffIndex, value int) {
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x := theHuffmanLUT[h][value]
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e.emit(x&(1<<24-1), x>>24)
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}
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// emitHuffRLE emits a run of runLength copies of value encoded with the given
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// Huffman encoder.
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func (e *encoder) emitHuffRLE(h huffIndex, runLength, value int) {
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a, b := value, value
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if a < 0 {
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a, b = -value, value-1
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}
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var nBits uint32
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if a < 0x100 {
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nBits = uint32(bitCount[a])
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} else {
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nBits = 8 + uint32(bitCount[a>>8])
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}
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e.emitHuff(h, runLength<<4|int(nBits))
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if nBits > 0 {
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e.emit(uint32(b)&(1<<nBits-1), nBits)
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}
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}
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// writeMarkerHeader writes the header for a marker with the given length.
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func (e *encoder) writeMarkerHeader(marker uint8, markerlen int) {
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e.buf[0] = 0xff
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e.buf[1] = marker
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e.buf[2] = uint8(markerlen >> 8)
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e.buf[3] = uint8(markerlen & 0xff)
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e.write(e.buf[:4])
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}
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// writeDQT writes the Define Quantization Table marker.
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func (e *encoder) writeDQT() {
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const markerlen = 2 + int(nQuantIndex)*(1+blockSize)
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e.writeMarkerHeader(dqtMarker, markerlen)
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for i := range e.quant {
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e.writeByte(uint8(i))
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e.write(e.quant[i][:])
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}
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}
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// writeSOF0 writes the Start Of Frame (Baseline) marker.
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func (e *encoder) writeSOF0(size image.Point) {
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const markerlen = 8 + 3*nColorComponent
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e.writeMarkerHeader(sof0Marker, markerlen)
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e.buf[0] = 8 // 8-bit color.
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e.buf[1] = uint8(size.Y >> 8)
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e.buf[2] = uint8(size.Y & 0xff)
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e.buf[3] = uint8(size.X >> 8)
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e.buf[4] = uint8(size.X & 0xff)
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e.buf[5] = nColorComponent
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for i := 0; i < nColorComponent; i++ {
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e.buf[3*i+6] = uint8(i + 1)
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// We use 4:2:0 chroma subsampling.
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e.buf[3*i+7] = "\x22\x11\x11"[i]
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e.buf[3*i+8] = "\x00\x01\x01"[i]
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}
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e.write(e.buf[:3*(nColorComponent-1)+9])
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}
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// writeDHT writes the Define Huffman Table marker.
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func (e *encoder) writeDHT() {
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markerlen := 2
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for _, s := range theHuffmanSpec {
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markerlen += 1 + 16 + len(s.value)
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}
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e.writeMarkerHeader(dhtMarker, markerlen)
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for i, s := range theHuffmanSpec {
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e.writeByte("\x00\x10\x01\x11"[i])
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e.write(s.count[:])
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e.write(s.value)
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}
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}
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// writeBlock writes a block of pixel data using the given quantization table,
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// returning the post-quantized DC value of the DCT-transformed block.
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// b is in natural (not zig-zag) order.
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func (e *encoder) writeBlock(b *block, q quantIndex, prevDC int) int {
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fdct(b)
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// Emit the DC delta.
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dc := div(b[0], (8 * int(e.quant[q][0])))
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e.emitHuffRLE(huffIndex(2*q+0), 0, dc-prevDC)
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// Emit the AC components.
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h, runLength := huffIndex(2*q+1), 0
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for zig := 1; zig < blockSize; zig++ {
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ac := div(b[unzig[zig]], (8 * int(e.quant[q][zig])))
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if ac == 0 {
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runLength++
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} else {
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for runLength > 15 {
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e.emitHuff(h, 0xf0)
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runLength -= 16
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}
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e.emitHuffRLE(h, runLength, ac)
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runLength = 0
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}
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}
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if runLength > 0 {
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e.emitHuff(h, 0x00)
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}
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return dc
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}
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// toYCbCr converts the 8x8 region of m whose top-left corner is p to its
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// YCbCr values.
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func toYCbCr(m image.Image, p image.Point, yBlock, cbBlock, crBlock *block) {
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b := m.Bounds()
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xmax := b.Max.X - 1
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ymax := b.Max.Y - 1
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for j := 0; j < 8; j++ {
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for i := 0; i < 8; i++ {
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r, g, b, _ := m.At(min(p.X+i, xmax), min(p.Y+j, ymax)).RGBA()
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yy, cb, cr := color.RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))
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yBlock[8*j+i] = int(yy)
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cbBlock[8*j+i] = int(cb)
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crBlock[8*j+i] = int(cr)
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}
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}
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}
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// rgbaToYCbCr is a specialized version of toYCbCr for image.RGBA images.
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func rgbaToYCbCr(m *image.RGBA, p image.Point, yBlock, cbBlock, crBlock *block) {
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b := m.Bounds()
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xmax := b.Max.X - 1
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ymax := b.Max.Y - 1
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for j := 0; j < 8; j++ {
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sj := p.Y + j
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if sj > ymax {
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sj = ymax
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}
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offset := (sj-b.Min.Y)*m.Stride - b.Min.X*4
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for i := 0; i < 8; i++ {
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sx := p.X + i
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if sx > xmax {
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sx = xmax
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}
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pix := m.Pix[offset+sx*4:]
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yy, cb, cr := color.RGBToYCbCr(pix[0], pix[1], pix[2])
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yBlock[8*j+i] = int(yy)
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cbBlock[8*j+i] = int(cb)
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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",
|
|
// - 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 sosHeader = []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) {
|
|
e.write(sosHeader)
|
|
var (
|
|
// Scratch buffers to hold the YCbCr values.
|
|
// The blocks are in natural (not zig-zag) order.
|
|
yBlock block
|
|
cbBlock [4]block
|
|
crBlock [4]block
|
|
cBlock block
|
|
// DC components are delta-encoded.
|
|
prevDCY, prevDCCb, prevDCCr int
|
|
)
|
|
bounds := m.Bounds()
|
|
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, &yBlock, &cbBlock[i], &crBlock[i])
|
|
} else {
|
|
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) 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)
|
|
}
|
|
}
|
|
// 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
|
|
}
|