mirror of
https://github.com/autc04/Retro68.git
synced 2024-12-01 11:52:47 +00:00
642 lines
17 KiB
Go
642 lines
17 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package jpeg
|
|
|
|
import (
|
|
"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 Sequential) 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)
|
|
}
|
|
}
|
|
}
|
|
|
|
// yCbCrToYCbCr is a specialized version of toYCbCr for image.YCbCr images.
|
|
func yCbCrToYCbCr(m *image.YCbCr, 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++ {
|
|
sy := p.Y + j
|
|
if sy > ymax {
|
|
sy = ymax
|
|
}
|
|
for i := 0; i < 8; i++ {
|
|
sx := p.X + i
|
|
if sx > xmax {
|
|
sx = xmax
|
|
}
|
|
yi := m.YOffset(sx, sy)
|
|
ci := m.COffset(sx, sy)
|
|
yBlock[8*j+i] = int32(m.Y[yi])
|
|
cbBlock[8*j+i] = int32(m.Cb[ci])
|
|
crBlock[8*j+i] = int32(m.Cr[ci])
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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)
|
|
ycbcr, _ := m.(*image.YCbCr)
|
|
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 if ycbcr != nil {
|
|
yCbCrToYCbCr(ycbcr, 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
|
|
}
|