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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
 
package jpeg
 
import (
        "bufio"
        "errors"
        "image"
        "image/color"
        "io"
)
 
// min returns the minimum of two integers.
func min(x, y int) int {
        if x < y {
                return x
        }
        return y
}
 
// div returns a/b rounded to the nearest integer, instead of rounded to zero.
func div(a int, b int) int {
        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. Each encoder copies and
// scales the tables according to its quality parameter.
var unscaledQuant = [nQuantIndex][blockSize]byte{
        // Luminance.
        {
                16, 11, 10, 16, 24, 40, 51, 61,
                12, 12, 14, 19, 26, 58, 60, 55,
                14, 13, 16, 24, 40, 57, 69, 56,
                14, 17, 22, 29, 51, 87, 80, 62,
                18, 22, 37, 56, 68, 109, 103, 77,
                24, 35, 55, 64, 81, 104, 113, 92,
                49, 64, 78, 87, 103, 121, 120, 101,
                72, 92, 95, 98, 112, 100, 103, 99,
        },
        // Chrominance.
        {
                17, 18, 24, 47, 99, 99, 99, 99,
                18, 21, 26, 66, 99, 99, 99, 99,
                24, 26, 56, 99, 99, 99, 99, 99,
                47, 66, 99, 99, 99, 99, 99, 99,
                99, 99, 99, 99, 99, 99, 99, 99,
                99, 99, 99, 99, 99, 99, 99, 99,
                99, 99, 99, 99, 99, 99, 99, 99,
                99, 99, 99, 99, 99, 99, 99, 99,
        },
}
 
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
        Write([]byte) (int, error)
        WriteByte(byte) 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 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.
        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<
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 int) {
        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 int) {
        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|int(nBits))
        if nBits > 0 {
                e.emit(uint32(b)&(1<
        }
}
 
// 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 + int(nQuantIndex)*(1+blockSize)
        e.writeMarkerHeader(dqtMarker, markerlen)
        for i := range e.quant {
                e.writeByte(uint8(i))
                e.write(e.quant[i][:])
        }
}
 
// writeSOF0 writes the Start Of Frame (Baseline) marker.
func (e *encoder) writeSOF0(size image.Point) {
        markerlen := 8 + 3*nColorComponent
        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] = nColorComponent
        for i := 0; i < nColorComponent; 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*(nColorComponent-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 := color.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)
                }
        }
}
 
// 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] = 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()
        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
}

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[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [libgo/] [go/] [image/] [jpeg/] [writer.go] - Blame information for rev 760

Line No.	Rev	Author	Line
1	747	jeremybenn	`// Copyright 2011 The Go Authors. All rights reserved.`
2			`// Use of this source code is governed by a BSD-style`
3			`// license that can be found in the LICENSE file.`
4
5			`package jpeg`
6
7			`import (`
8			`"bufio"`
9			`"errors"`
10			`"image"`
11			`"image/color"`
12			`"io"`
13			`)`
14
15			`// min returns the minimum of two integers.`
16			`func min(x, y int) int {`
17			`if x < y {`
18			`return x`
19			`}`
20			`return y`
21			`}`
22
23			`// div returns a/b rounded to the nearest integer, instead of rounded to zero.`
24			`func div(a int, b int) int {`
25			`if a >= 0 {`
26			`return (a + (b >> 1)) / b`
27			`}`
28			`return -((-a + (b >> 1)) / b)`
29			`}`
30
31			`// bitCount counts the number of bits needed to hold an integer.`
32			`var bitCount = [256]byte{`
33			`0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,`
34			`5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,`
35			`6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,`
36			`6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,`
37			`7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,`
38			`7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,`
39			`7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,`
40			`7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,`
41			`8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,`
42			`8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,`
43			`8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,`
44			`8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,`
45			`8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,`
46			`8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,`
47			`8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,`
48			`8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,`
49			`}`
50
51			`type quantIndex int`
52
53			`const (`
54			`quantIndexLuminance quantIndex = iota`
55			`quantIndexChrominance`
56			`nQuantIndex`
57			`)`
58
59			`// unscaledQuant are the unscaled quantization tables. Each encoder copies and`
60			`// scales the tables according to its quality parameter.`
61			`var unscaledQuant = [nQuantIndex][blockSize]byte{`
62			`// Luminance.`
63			`{`
64			`16, 11, 10, 16, 24, 40, 51, 61,`
65			`12, 12, 14, 19, 26, 58, 60, 55,`
66			`14, 13, 16, 24, 40, 57, 69, 56,`
67			`14, 17, 22, 29, 51, 87, 80, 62,`
68			`18, 22, 37, 56, 68, 109, 103, 77,`
69			`24, 35, 55, 64, 81, 104, 113, 92,`
70			`49, 64, 78, 87, 103, 121, 120, 101,`
71			`72, 92, 95, 98, 112, 100, 103, 99,`
72			`},`
73			`// Chrominance.`
74			`{`
75			`17, 18, 24, 47, 99, 99, 99, 99,`
76			`18, 21, 26, 66, 99, 99, 99, 99,`
77			`24, 26, 56, 99, 99, 99, 99, 99,`
78			`47, 66, 99, 99, 99, 99, 99, 99,`
79			`99, 99, 99, 99, 99, 99, 99, 99,`
80			`99, 99, 99, 99, 99, 99, 99, 99,`
81			`99, 99, 99, 99, 99, 99, 99, 99,`
82			`99, 99, 99, 99, 99, 99, 99, 99,`
83			`},`
84			`}`
85
86			`type huffIndex int`
87
88			`const (`
89			`huffIndexLuminanceDC huffIndex = iota`
90			`huffIndexLuminanceAC`
91			`huffIndexChrominanceDC`
92			`huffIndexChrominanceAC`
93			`nHuffIndex`
94			`)`
95
96			`// huffmanSpec specifies a Huffman encoding.`
97			`type huffmanSpec struct {`
98			`// count[i] is the number of codes of length i bits.`
99			`count [16]byte`
100			`// value[i] is the decoded value of the i'th codeword.`
101			`value []byte`
102			`}`
103
104			`// theHuffmanSpec is the Huffman encoding specifications.`
105			`// This encoder uses the same Huffman encoding for all images.`
106			`var theHuffmanSpec = [nHuffIndex]huffmanSpec{`
107			`// Luminance DC.`
108			`{`
109			`[16]byte{0, 1, 5, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0},`
110			`[]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},`
111			`},`
112			`// Luminance AC.`
113			`{`
114			`[16]byte{0, 2, 1, 3, 3, 2, 4, 3, 5, 5, 4, 4, 0, 0, 1, 125},`
115			`[]byte{`
116			`0x01, 0x02, 0x03, 0x00, 0x04, 0x11, 0x05, 0x12,`
117			`0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07,`
118			`0x22, 0x71, 0x14, 0x32, 0x81, 0x91, 0xa1, 0x08,`
119			`0x23, 0x42, 0xb1, 0xc1, 0x15, 0x52, 0xd1, 0xf0,`
120			`0x24, 0x33, 0x62, 0x72, 0x82, 0x09, 0x0a, 0x16,`
121			`0x17, 0x18, 0x19, 0x1a, 0x25, 0x26, 0x27, 0x28,`
122			`0x29, 0x2a, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39,`
123			`0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49,`
124			`0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59,`
125			`0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,`
126			`0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79,`
127			`0x7a, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89,`
128			`0x8a, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98,`
129			`0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,`
130			`0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6,`
131			`0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3, 0xc4, 0xc5,`
132			`0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4,`
133			`0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe1, 0xe2,`
134			`0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea,`
135			`0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,`
136			`0xf9, 0xfa,`
137			`},`
138			`},`
139			`// Chrominance DC.`
140			`{`
141			`[16]byte{0, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0},`
142			`[]byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11},`
143			`},`
144			`// Chrominance AC.`
145			`{`
146			`[16]byte{0, 2, 1, 2, 4, 4, 3, 4, 7, 5, 4, 4, 0, 1, 2, 119},`
147			`[]byte{`
148			`0x00, 0x01, 0x02, 0x03, 0x11, 0x04, 0x05, 0x21,`
149			`0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71,`
150			`0x13, 0x22, 0x32, 0x81, 0x08, 0x14, 0x42, 0x91,`
151			`0xa1, 0xb1, 0xc1, 0x09, 0x23, 0x33, 0x52, 0xf0,`
152			`0x15, 0x62, 0x72, 0xd1, 0x0a, 0x16, 0x24, 0x34,`
153			`0xe1, 0x25, 0xf1, 0x17, 0x18, 0x19, 0x1a, 0x26,`
154			`0x27, 0x28, 0x29, 0x2a, 0x35, 0x36, 0x37, 0x38,`
155			`0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48,`
156			`0x49, 0x4a, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,`
157			`0x59, 0x5a, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,`
158			`0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,`
159			`0x79, 0x7a, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,`
160			`0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95, 0x96,`
161			`0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5,`
162			`0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4,`
163			`0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2, 0xc3,`
164			`0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2,`
165			`0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda,`
166			`0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9,`
167			`0xea, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,`
168			`0xf9, 0xfa,`
169			`},`
170			`},`
171			`}`
172
173			`// huffmanLUT is a compiled look-up table representation of a huffmanSpec.`
174			`// Each value maps to a uint32 of which the 8 most significant bits hold the`
175			`// codeword size in bits and the 24 least significant bits hold the codeword.`
176			`// The maximum codeword size is 16 bits.`
177			`type huffmanLUT []uint32`
178
179			`func (h *huffmanLUT) init(s huffmanSpec) {`
180			`maxValue := 0`
181			`for _, v := range s.value {`
182			`if int(v) > maxValue {`
183			`maxValue = int(v)`
184			`}`
185			`}`
186			`*h = make([]uint32, maxValue+1)`
187			`code, k := uint32(0), 0`
188			`for i := 0; i < len(s.count); i++ {`
189			`nBits := uint32(i+1) << 24`
190			`for j := uint8(0); j < s.count[i]; j++ {`
191			`(*h)[s.value[k]] = nBits \| code`
192			`code++`
193			`k++`
194			`}`
195			`code <<= 1`
196			`}`
197			`}`
198
199			`// theHuffmanLUT are compiled representations of theHuffmanSpec.`
200			`var theHuffmanLUT [4]huffmanLUT`
201
202			`func init() {`
203			`for i, s := range theHuffmanSpec {`
204			`theHuffmanLUT[i].init(s)`
205			`}`
206			`}`
207
208			`// writer is a buffered writer.`
209			`type writer interface {`
210			`Flush() error`
211			`Write([]byte) (int, error)`
212			`WriteByte(byte) error`
213			`}`
214
215			`// encoder encodes an image to the JPEG format.`
216			`type encoder struct {`
217			`// w is the writer to write to. err is the first error encountered during`
218			`// writing. All attempted writes after the first error become no-ops.`
219			`w writer`
220			`err error`
221			`// buf is a scratch buffer.`
222			`buf [16]byte`
223			`// bits and nBits are accumulated bits to write to w.`
224			`bits, nBits uint32`
225			`// quant is the scaled quantization tables.`
226			`quant [nQuantIndex][blockSize]byte`
227			`}`
228
229			`func (e *encoder) flush() {`
230			`if e.err != nil {`
231			`return`
232			`}`
233			`e.err = e.w.Flush()`
234			`}`
235
236			`func (e *encoder) write(p []byte) {`
237			`if e.err != nil {`
238			`return`
239			`}`
240			`_, e.err = e.w.Write(p)`
241			`}`
242
243			`func (e *encoder) writeByte(b byte) {`
244			`if e.err != nil {`
245			`return`
246			`}`
247			`e.err = e.w.WriteByte(b)`
248			`}`
249
250			`// emit emits the least significant nBits bits of bits to the bitstream.`
251			`// The precondition is bits < 1<`
252			`func (e *encoder) emit(bits, nBits uint32) {`
253			`nBits += e.nBits`
254			`bits <<= 32 - nBits`
255			`bits \|= e.bits`
256			`for nBits >= 8 {`
257			`b := uint8(bits >> 24)`
258			`e.writeByte(b)`
259			`if b == 0xff {`
260			`e.writeByte(0x00)`
261			`}`
262			`bits <<= 8`
263			`nBits -= 8`
264			`}`
265			`e.bits, e.nBits = bits, nBits`
266			`}`
267
268			`// emitHuff emits the given value with the given Huffman encoder.`
269			`func (e *encoder) emitHuff(h huffIndex, value int) {`
270			`x := theHuffmanLUT[h][value]`
271			`e.emit(x&(1<<24-1), x>>24)`
272			`}`
273
274			`// emitHuffRLE emits a run of runLength copies of value encoded with the given`
275			`// Huffman encoder.`
276			`func (e *encoder) emitHuffRLE(h huffIndex, runLength, value int) {`
277			`a, b := value, value`
278			`if a < 0 {`
279			`a, b = -value, value-1`
280			`}`
281			`var nBits uint32`
282			`if a < 0x100 {`
283			`nBits = uint32(bitCount[a])`
284			`} else {`
285			`nBits = 8 + uint32(bitCount[a>>8])`
286			`}`
287			`e.emitHuff(h, runLength<<4\|int(nBits))`
288			`if nBits > 0 {`
289			`e.emit(uint32(b)&(1<`
290			`}`
291			`}`
292
293			`// writeMarkerHeader writes the header for a marker with the given length.`
294			`func (e *encoder) writeMarkerHeader(marker uint8, markerlen int) {`
295			`e.buf[0] = 0xff`
296			`e.buf[1] = marker`
297			`e.buf[2] = uint8(markerlen >> 8)`
298			`e.buf[3] = uint8(markerlen & 0xff)`
299			`e.write(e.buf[:4])`
300			`}`
301
302			`// writeDQT writes the Define Quantization Table marker.`
303			`func (e *encoder) writeDQT() {`
304			`markerlen := 2 + int(nQuantIndex)*(1+blockSize)`
305			`e.writeMarkerHeader(dqtMarker, markerlen)`
306			`for i := range e.quant {`
307			`e.writeByte(uint8(i))`
308			`e.write(e.quant[i][:])`
309			`}`
310			`}`
311
312			`// writeSOF0 writes the Start Of Frame (Baseline) marker.`
313			`func (e *encoder) writeSOF0(size image.Point) {`
314			`markerlen := 8 + 3*nColorComponent`
315			`e.writeMarkerHeader(sof0Marker, markerlen)`
316			`e.buf[0] = 8 // 8-bit color.`
317			`e.buf[1] = uint8(size.Y >> 8)`
318			`e.buf[2] = uint8(size.Y & 0xff)`
319			`e.buf[3] = uint8(size.X >> 8)`
320			`e.buf[4] = uint8(size.X & 0xff)`
321			`e.buf[5] = nColorComponent`
322			`for i := 0; i < nColorComponent; i++ {`
323			`e.buf[3*i+6] = uint8(i + 1)`
324			`// We use 4:2:0 chroma subsampling.`
325			`e.buf[3*i+7] = "\x22\x11\x11"[i]`
326			`e.buf[3*i+8] = "\x00\x01\x01"[i]`
327			`}`
328			`e.write(e.buf[:3*(nColorComponent-1)+9])`
329			`}`
330
331			`// writeDHT writes the Define Huffman Table marker.`
332			`func (e *encoder) writeDHT() {`
333			`markerlen := 2`
334			`for _, s := range theHuffmanSpec {`
335			`markerlen += 1 + 16 + len(s.value)`
336			`}`
337			`e.writeMarkerHeader(dhtMarker, markerlen)`
338			`for i, s := range theHuffmanSpec {`
339			`e.writeByte("\x00\x10\x01\x11"[i])`
340			`e.write(s.count[:])`
341			`e.write(s.value)`
342			`}`
343			`}`
344
345			`// writeBlock writes a block of pixel data using the given quantization table,`
346			`// returning the post-quantized DC value of the DCT-transformed block.`
347			`func (e encoder) writeBlock(b block, q quantIndex, prevDC int) int {`
348			`fdct(b)`
349			`// Emit the DC delta.`
350			`dc := div(b[0], (8 * int(e.quant[q][0])))`
351			`e.emitHuffRLE(huffIndex(2*q+0), 0, dc-prevDC)`
352			`// Emit the AC components.`
353			`h, runLength := huffIndex(2*q+1), 0`
354			`for k := 1; k < blockSize; k++ {`
355			`ac := div(b[unzig[k]], (8 * int(e.quant[q][k])))`
356			`if ac == 0 {`
357			`runLength++`
358			`} else {`
359			`for runLength > 15 {`
360			`e.emitHuff(h, 0xf0)`
361			`runLength -= 16`
362			`}`
363			`e.emitHuffRLE(h, runLength, ac)`
364			`runLength = 0`
365			`}`
366			`}`
367			`if runLength > 0 {`
368			`e.emitHuff(h, 0x00)`
369			`}`
370			`return dc`
371			`}`
372
373			`// toYCbCr converts the 8x8 region of m whose top-left corner is p to its`
374			`// YCbCr values.`
375			`func toYCbCr(m image.Image, p image.Point, yBlock, cbBlock, crBlock *block) {`
376			`b := m.Bounds()`
377			`xmax := b.Max.X - 1`
378			`ymax := b.Max.Y - 1`
379			`for j := 0; j < 8; j++ {`
380			`for i := 0; i < 8; i++ {`
381			`r, g, b, _ := m.At(min(p.X+i, xmax), min(p.Y+j, ymax)).RGBA()`
382			`yy, cb, cr := color.RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))`
383			`yBlock[8*j+i] = int(yy)`
384			`cbBlock[8*j+i] = int(cb)`
385			`crBlock[8*j+i] = int(cr)`
386			`}`
387			`}`
388			`}`
389
390			`// rgbaToYCbCr is a specialized version of toYCbCr for image.RGBA images.`
391			`func rgbaToYCbCr(m image.RGBA, p image.Point, yBlock, cbBlock, crBlock block) {`
392			`b := m.Bounds()`
393			`xmax := b.Max.X - 1`
394			`ymax := b.Max.Y - 1`
395			`for j := 0; j < 8; j++ {`
396			`sj := p.Y + j`
397			`if sj > ymax {`
398			`sj = ymax`
399			`}`
400			`offset := (sj-b.Min.Y)m.Stride - b.Min.X4`
401			`for i := 0; i < 8; i++ {`
402			`sx := p.X + i`
403			`if sx > xmax {`
404			`sx = xmax`
405			`}`
406			`pix := m.Pix[offset+sx*4:]`
407			`yy, cb, cr := color.RGBToYCbCr(pix[0], pix[1], pix[2])`
408			`yBlock[8*j+i] = int(yy)`
409			`cbBlock[8*j+i] = int(cb)`
410			`crBlock[8*j+i] = int(cr)`
411			`}`
412			`}`
413			`}`
414
415			`// scale scales the 16x16 region represented by the 4 src blocks to the 8x8`
416			`// dst block.`
417			`func scale(dst block, src [4]block) {`
418			`for i := 0; i < 4; i++ {`
419			`dstOff := (i&2)<<4 \| (i&1)<<2`
420			`for y := 0; y < 4; y++ {`
421			`for x := 0; x < 4; x++ {`
422			`j := 16y + 2x`
423			`sum := src[i][j] + src[i][j+1] + src[i][j+8] + src[i][j+9]`
424			`dst[8*y+x+dstOff] = (sum + 2) >> 2`
425			`}`
426			`}`
427			`}`
428			`}`
429
430			`// sosHeader is the SOS marker "\xff\xda" followed by 12 bytes:`
431			`// - the marker length "\x00\x0c",`
432			`// - the number of components "\x03",`
433			`// - component 1 uses DC table 0 and AC table 0 "\x01\x00",`
434			`// - component 2 uses DC table 1 and AC table 1 "\x02\x11",`
435			`// - component 3 uses DC table 1 and AC table 1 "\x03\x11",`
436			`// - padding "\x00\x00\x00".`
437			`var sosHeader = []byte{`
438			`0xff, 0xda, 0x00, 0x0c, 0x03, 0x01, 0x00, 0x02,`
439			`0x11, 0x03, 0x11, 0x00, 0x00, 0x00,`
440			`}`
441
442			`// writeSOS writes the StartOfScan marker.`
443			`func (e *encoder) writeSOS(m image.Image) {`
444			`e.write(sosHeader)`
445			`var (`
446			`// Scratch buffers to hold the YCbCr values.`
447			`yBlock block`
448			`cbBlock [4]block`
449			`crBlock [4]block`
450			`cBlock block`
451			`// DC components are delta-encoded.`
452			`prevDCY, prevDCCb, prevDCCr int`
453			`)`
454			`bounds := m.Bounds()`
455			`rgba, _ := m.(*image.RGBA)`
456			`for y := bounds.Min.Y; y < bounds.Max.Y; y += 16 {`
457			`for x := bounds.Min.X; x < bounds.Max.X; x += 16 {`
458			`for i := 0; i < 4; i++ {`
459			`xOff := (i & 1) * 8`
460			`yOff := (i & 2) * 4`
461			`p := image.Pt(x+xOff, y+yOff)`
462			`if rgba != nil {`
463			`rgbaToYCbCr(rgba, p, &yBlock, &cbBlock[i], &crBlock[i])`
464			`} else {`
465			`toYCbCr(m, p, &yBlock, &cbBlock[i], &crBlock[i])`
466			`}`
467			`prevDCY = e.writeBlock(&yBlock, 0, prevDCY)`
468			`}`
469			`scale(&cBlock, &cbBlock)`
470			`prevDCCb = e.writeBlock(&cBlock, 1, prevDCCb)`
471			`scale(&cBlock, &crBlock)`
472			`prevDCCr = e.writeBlock(&cBlock, 1, prevDCCr)`
473			`}`
474			`}`
475			`// Pad the last byte with 1's.`
476			`e.emit(0x7f, 7)`
477			`}`
478
479			`// DefaultQuality is the default quality encoding parameter.`
480			`const DefaultQuality = 75`
481
482			`// Options are the encoding parameters.`
483			`// Quality ranges from 1 to 100 inclusive, higher is better.`
484			`type Options struct {`
485			`Quality int`
486			`}`
487
488			`// Encode writes the Image m to w in JPEG 4:2:0 baseline format with the given`
489			`// options. Default parameters are used if a nil *Options is passed.`
490			`func Encode(w io.Writer, m image.Image, o *Options) error {`
491			`b := m.Bounds()`
492			`if b.Dx() >= 1<<16 \|\| b.Dy() >= 1<<16 {`
493			`return errors.New("jpeg: image is too large to encode")`
494			`}`
495			`var e encoder`
496			`if ww, ok := w.(writer); ok {`
497			`e.w = ww`
498			`} else {`
499			`e.w = bufio.NewWriter(w)`
500			`}`
501			`// Clip quality to [1, 100].`
502			`quality := DefaultQuality`
503			`if o != nil {`
504			`quality = o.Quality`
505			`if quality < 1 {`
506			`quality = 1`
507			`} else if quality > 100 {`
508			`quality = 100`
509			`}`
510			`}`
511			`// Convert from a quality rating to a scaling factor.`
512			`var scale int`
513			`if quality < 50 {`
514			`scale = 5000 / quality`
515			`} else {`
516			`scale = 200 - quality*2`
517			`}`
518			`// Initialize the quantization tables.`
519			`for i := range e.quant {`
520			`for j := range e.quant[i] {`
521			`x := int(unscaledQuant[i][j])`
522			`x = (x*scale + 50) / 100`
523			`if x < 1 {`
524			`x = 1`
525			`} else if x > 255 {`
526			`x = 255`
527			`}`
528			`e.quant[i][j] = uint8(x)`
529			`}`
530			`}`
531			`// Write the Start Of Image marker.`
532			`e.buf[0] = 0xff`
533			`e.buf[1] = 0xd8`
534			`e.write(e.buf[:2])`
535			`// Write the quantization tables.`
536			`e.writeDQT()`
537			`// Write the image dimensions.`
538			`e.writeSOF0(b.Size())`
539			`// Write the Huffman tables.`
540			`e.writeDHT()`
541			`// Write the image data.`
542			`e.writeSOS(m)`
543			`// Write the End Of Image marker.`
544			`e.buf[0] = 0xff`
545			`e.buf[1] = 0xd9`
546			`e.write(e.buf[:2])`
547			`e.flush()`
548			`return e.err`
549			`}`