// 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" ) // 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<= 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<> 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 }