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Diffstat (limited to 'src/image/jpeg/writer.go')
| -rw-r--r-- | src/image/jpeg/writer.go | 614 |
1 files changed, 614 insertions, 0 deletions
diff --git a/src/image/jpeg/writer.go b/src/image/jpeg/writer.go new file mode 100644 index 000000000..91bbde3bf --- /dev/null +++ b/src/image/jpeg/writer.go @@ -0,0 +1,614 @@ +// 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) 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) + } + } +} + +// 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) + 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 { + 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 +} |