// Copyright 2012 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 ( "image" ) // makeImg allocates and initializes the destination image. func (d *decoder) makeImg(mxx, myy int) { if d.nComp == 1 { m := image.NewGray(image.Rect(0, 0, 8*mxx, 8*myy)) d.img1 = m.SubImage(image.Rect(0, 0, d.width, d.height)).(*image.Gray) return } h0 := d.comp[0].h v0 := d.comp[0].v hRatio := h0 / d.comp[1].h vRatio := v0 / d.comp[1].v var subsampleRatio image.YCbCrSubsampleRatio switch hRatio<<4 | vRatio { case 0x11: subsampleRatio = image.YCbCrSubsampleRatio444 case 0x12: subsampleRatio = image.YCbCrSubsampleRatio440 case 0x21: subsampleRatio = image.YCbCrSubsampleRatio422 case 0x22: subsampleRatio = image.YCbCrSubsampleRatio420 case 0x41: subsampleRatio = image.YCbCrSubsampleRatio411 case 0x42: subsampleRatio = image.YCbCrSubsampleRatio410 default: panic("unreachable") } m := image.NewYCbCr(image.Rect(0, 0, 8*h0*mxx, 8*v0*myy), subsampleRatio) d.img3 = m.SubImage(image.Rect(0, 0, d.width, d.height)).(*image.YCbCr) if d.nComp == 4 { h3, v3 := d.comp[3].h, d.comp[3].v d.blackPix = make([]byte, 8*h3*mxx*8*v3*myy) d.blackStride = 8 * h3 * mxx } } // Specified in section B.2.3. func (d *decoder) processSOS(n int) error { if d.nComp == 0 { return FormatError("missing SOF marker") } if n < 6 || 4+2*d.nComp < n || n%2 != 0 { return FormatError("SOS has wrong length") } if err := d.readFull(d.tmp[:n]); err != nil { return err } nComp := int(d.tmp[0]) if n != 4+2*nComp { return FormatError("SOS length inconsistent with number of components") } var scan [maxComponents]struct { compIndex uint8 td uint8 // DC table selector. ta uint8 // AC table selector. } totalHV := 0 for i := 0; i < nComp; i++ { cs := d.tmp[1+2*i] // Component selector. compIndex := -1 for j, comp := range d.comp[:d.nComp] { if cs == comp.c { compIndex = j } } if compIndex < 0 { return FormatError("unknown component selector") } scan[i].compIndex = uint8(compIndex) // Section B.2.3 states that "the value of Cs_j shall be different from // the values of Cs_1 through Cs_(j-1)". Since we have previously // verified that a frame's component identifiers (C_i values in section // B.2.2) are unique, it suffices to check that the implicit indexes // into d.comp are unique. for j := 0; j < i; j++ { if scan[i].compIndex == scan[j].compIndex { return FormatError("repeated component selector") } } totalHV += d.comp[compIndex].h * d.comp[compIndex].v // The baseline t <= 1 restriction is specified in table B.3. scan[i].td = d.tmp[2+2*i] >> 4 if t := scan[i].td; t > maxTh || (d.baseline && t > 1) { return FormatError("bad Td value") } scan[i].ta = d.tmp[2+2*i] & 0x0f if t := scan[i].ta; t > maxTh || (d.baseline && t > 1) { return FormatError("bad Ta value") } } // Section B.2.3 states that if there is more than one component then the // total H*V values in a scan must be <= 10. if d.nComp > 1 && totalHV > 10 { return FormatError("total sampling factors too large") } // zigStart and zigEnd are the spectral selection bounds. // ah and al are the successive approximation high and low values. // The spec calls these values Ss, Se, Ah and Al. // // For progressive JPEGs, these are the two more-or-less independent // aspects of progression. Spectral selection progression is when not // all of a block's 64 DCT coefficients are transmitted in one pass. // For example, three passes could transmit coefficient 0 (the DC // component), coefficients 1-5, and coefficients 6-63, in zig-zag // order. Successive approximation is when not all of the bits of a // band of coefficients are transmitted in one pass. For example, // three passes could transmit the 6 most significant bits, followed // by the second-least significant bit, followed by the least // significant bit. // // For sequential JPEGs, these parameters are hard-coded to 0/63/0/0, as // per table B.3. zigStart, zigEnd, ah, al := int32(0), int32(blockSize-1), uint32(0), uint32(0) if d.progressive { zigStart = int32(d.tmp[1+2*nComp]) zigEnd = int32(d.tmp[2+2*nComp]) ah = uint32(d.tmp[3+2*nComp] >> 4) al = uint32(d.tmp[3+2*nComp] & 0x0f) if (zigStart == 0 && zigEnd != 0) || zigStart > zigEnd || blockSize <= zigEnd { return FormatError("bad spectral selection bounds") } if zigStart != 0 && nComp != 1 { return FormatError("progressive AC coefficients for more than one component") } if ah != 0 && ah != al+1 { return FormatError("bad successive approximation values") } } // mxx and myy are the number of MCUs (Minimum Coded Units) in the image. h0, v0 := d.comp[0].h, d.comp[0].v // The h and v values from the Y components. mxx := (d.width + 8*h0 - 1) / (8 * h0) myy := (d.height + 8*v0 - 1) / (8 * v0) if d.img1 == nil && d.img3 == nil { d.makeImg(mxx, myy) } if d.progressive { for i := 0; i < nComp; i++ { compIndex := scan[i].compIndex if d.progCoeffs[compIndex] == nil { d.progCoeffs[compIndex] = make([]block, mxx*myy*d.comp[compIndex].h*d.comp[compIndex].v) } } } d.bits = bits{} mcu, expectedRST := 0, uint8(rst0Marker) var ( // b is the decoded coefficients, in natural (not zig-zag) order. b block dc [maxComponents]int32 // bx and by are the location of the current block, in units of 8x8 // blocks: the third block in the first row has (bx, by) = (2, 0). bx, by int blockCount int ) for my := 0; my < myy; my++ { for mx := 0; mx < mxx; mx++ { for i := 0; i < nComp; i++ { compIndex := scan[i].compIndex hi := d.comp[compIndex].h vi := d.comp[compIndex].v for j := 0; j < hi*vi; j++ { // The blocks are traversed one MCU at a time. For 4:2:0 chroma // subsampling, there are four Y 8x8 blocks in every 16x16 MCU. // // For a sequential 32x16 pixel image, the Y blocks visiting order is: // 0 1 4 5 // 2 3 6 7 // // For progressive images, the interleaved scans (those with nComp > 1) // are traversed as above, but non-interleaved scans are traversed left // to right, top to bottom: // 0 1 2 3 // 4 5 6 7 // Only DC scans (zigStart == 0) can be interleaved. AC scans must have // only one component. // // To further complicate matters, for non-interleaved scans, there is no // data for any blocks that are inside the image at the MCU level but // outside the image at the pixel level. For example, a 24x16 pixel 4:2:0 // progressive image consists of two 16x16 MCUs. The interleaved scans // will process 8 Y blocks: // 0 1 4 5 // 2 3 6 7 // The non-interleaved scans will process only 6 Y blocks: // 0 1 2 // 3 4 5 if nComp != 1 { bx = hi*mx + j%hi by = vi*my + j/hi } else { q := mxx * hi bx = blockCount % q by = blockCount / q blockCount++ if bx*8 >= d.width || by*8 >= d.height { continue } } // Load the previous partially decoded coefficients, if applicable. if d.progressive { b = d.progCoeffs[compIndex][by*mxx*hi+bx] } else { b = block{} } if ah != 0 { if err := d.refine(&b, &d.huff[acTable][scan[i].ta], zigStart, zigEnd, 1< 16 { return UnsupportedError("excessive DC component") } dcDelta, err := d.receiveExtend(value) if err != nil { return err } dc[compIndex] += dcDelta b[0] = dc[compIndex] << al } if zig <= zigEnd && d.eobRun > 0 { d.eobRun-- } else { // Decode the AC coefficients, as specified in section F.2.2.2. huff := &d.huff[acTable][scan[i].ta] for ; zig <= zigEnd; zig++ { value, err := d.decodeHuffman(huff) if err != nil { return err } val0 := value >> 4 val1 := value & 0x0f if val1 != 0 { zig += int32(val0) if zig > zigEnd { break } ac, err := d.receiveExtend(val1) if err != nil { return err } b[unzig[zig]] = ac << al } else { if val0 != 0x0f { d.eobRun = uint16(1 << val0) if val0 != 0 { bits, err := d.decodeBits(int32(val0)) if err != nil { return err } d.eobRun |= uint16(bits) } d.eobRun-- break } zig += 0x0f } } } } if d.progressive { // Save the coefficients. d.progCoeffs[compIndex][by*mxx*hi+bx] = b // At this point, we could call reconstructBlock to dequantize and perform the // inverse DCT, to save early stages of a progressive image to the *image.YCbCr // buffers (the whole point of progressive encoding), but in Go, the jpeg.Decode // function does not return until the entire image is decoded, so we "continue" // here to avoid wasted computation. Instead, reconstructBlock is called on each // accumulated block by the reconstructProgressiveImage method after all of the // SOS markers are processed. continue } if err := d.reconstructBlock(&b, bx, by, int(compIndex)); err != nil { return err } } // for j } // for i mcu++ if d.ri > 0 && mcu%d.ri == 0 && mcu < mxx*myy { // A more sophisticated decoder could use RST[0-7] markers to resynchronize from corrupt input, // but this one assumes well-formed input, and hence the restart marker follows immediately. if err := d.readFull(d.tmp[:2]); err != nil { return err } // Section F.1.2.3 says that "Byte alignment of markers is // achieved by padding incomplete bytes with 1-bits. If padding // with 1-bits creates a X’FF’ value, a zero byte is stuffed // before adding the marker." // // Seeing "\xff\x00" here is not spec compliant, as we are not // expecting an *incomplete* byte (that needed padding). Still, // some real world encoders (see golang.org/issue/28717) insert // it, so we accept it and re-try the 2 byte read. // // libjpeg issues a warning (but not an error) for this: // https://github.com/LuaDist/libjpeg/blob/6c0fcb8ddee365e7abc4d332662b06900612e923/jdmarker.c#L1041-L1046 if d.tmp[0] == 0xff && d.tmp[1] == 0x00 { if err := d.readFull(d.tmp[:2]); err != nil { return err } } if d.tmp[0] != 0xff || d.tmp[1] != expectedRST { return FormatError("bad RST marker") } expectedRST++ if expectedRST == rst7Marker+1 { expectedRST = rst0Marker } // Reset the Huffman decoder. d.bits = bits{} // Reset the DC components, as per section F.2.1.3.1. dc = [maxComponents]int32{} // Reset the progressive decoder state, as per section G.1.2.2. d.eobRun = 0 } } // for mx } // for my return nil } // refine decodes a successive approximation refinement block, as specified in // section G.1.2. func (d *decoder) refine(b *block, h *huffman, zigStart, zigEnd, delta int32) error { // Refining a DC component is trivial. if zigStart == 0 { if zigEnd != 0 { panic("unreachable") } bit, err := d.decodeBit() if err != nil { return err } if bit { b[0] |= delta } return nil } // Refining AC components is more complicated; see sections G.1.2.2 and G.1.2.3. zig := zigStart if d.eobRun == 0 { loop: for ; zig <= zigEnd; zig++ { z := int32(0) value, err := d.decodeHuffman(h) if err != nil { return err } val0 := value >> 4 val1 := value & 0x0f switch val1 { case 0: if val0 != 0x0f { d.eobRun = uint16(1 << val0) if val0 != 0 { bits, err := d.decodeBits(int32(val0)) if err != nil { return err } d.eobRun |= uint16(bits) } break loop } case 1: z = delta bit, err := d.decodeBit() if err != nil { return err } if !bit { z = -z } default: return FormatError("unexpected Huffman code") } zig, err = d.refineNonZeroes(b, zig, zigEnd, int32(val0), delta) if err != nil { return err } if zig > zigEnd { return FormatError("too many coefficients") } if z != 0 { b[unzig[zig]] = z } } } if d.eobRun > 0 { d.eobRun-- if _, err := d.refineNonZeroes(b, zig, zigEnd, -1, delta); err != nil { return err } } return nil } // refineNonZeroes refines non-zero entries of b in zig-zag order. If nz >= 0, // the first nz zero entries are skipped over. func (d *decoder) refineNonZeroes(b *block, zig, zigEnd, nz, delta int32) (int32, error) { for ; zig <= zigEnd; zig++ { u := unzig[zig] if b[u] == 0 { if nz == 0 { break } nz-- continue } bit, err := d.decodeBit() if err != nil { return 0, err } if !bit { continue } if b[u] >= 0 { b[u] += delta } else { b[u] -= delta } } return zig, nil } func (d *decoder) reconstructProgressiveImage() error { // The h0, mxx, by and bx variables have the same meaning as in the // processSOS method. h0 := d.comp[0].h mxx := (d.width + 8*h0 - 1) / (8 * h0) for i := 0; i < d.nComp; i++ { if d.progCoeffs[i] == nil { continue } v := 8 * d.comp[0].v / d.comp[i].v h := 8 * d.comp[0].h / d.comp[i].h stride := mxx * d.comp[i].h for by := 0; by*v < d.height; by++ { for bx := 0; bx*h < d.width; bx++ { if err := d.reconstructBlock(&d.progCoeffs[i][by*stride+bx], bx, by, i); err != nil { return err } } } } return nil } // reconstructBlock dequantizes, performs the inverse DCT and stores the block // to the image. func (d *decoder) reconstructBlock(b *block, bx, by, compIndex int) error { qt := &d.quant[d.comp[compIndex].tq] for zig := 0; zig < blockSize; zig++ { b[unzig[zig]] *= qt[zig] } idct(b) dst, stride := []byte(nil), 0 if d.nComp == 1 { dst, stride = d.img1.Pix[8*(by*d.img1.Stride+bx):], d.img1.Stride } else { switch compIndex { case 0: dst, stride = d.img3.Y[8*(by*d.img3.YStride+bx):], d.img3.YStride case 1: dst, stride = d.img3.Cb[8*(by*d.img3.CStride+bx):], d.img3.CStride case 2: dst, stride = d.img3.Cr[8*(by*d.img3.CStride+bx):], d.img3.CStride case 3: dst, stride = d.blackPix[8*(by*d.blackStride+bx):], d.blackStride default: return UnsupportedError("too many components") } } // Level shift by +128, clip to [0, 255], and write to dst. for y := 0; y < 8; y++ { y8 := y * 8 yStride := y * stride for x := 0; x < 8; x++ { c := b[y8+x] if c < -128 { c = 0 } else if c > 127 { c = 255 } else { c += 128 } dst[yStride+x] = uint8(c) } } return nil }