// 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
}