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path: root/src/pkg/image/jpeg/scan.go
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Diffstat (limited to 'src/pkg/image/jpeg/scan.go')
-rw-r--r--src/pkg/image/jpeg/scan.go439
1 files changed, 0 insertions, 439 deletions
diff --git a/src/pkg/image/jpeg/scan.go b/src/pkg/image/jpeg/scan.go
deleted file mode 100644
index 559235d51..000000000
--- a/src/pkg/image/jpeg/scan.go
+++ /dev/null
@@ -1,439 +0,0 @@
-// 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"
- "io"
-)
-
-// makeImg allocates and initializes the destination image.
-func (d *decoder) makeImg(h0, v0, mxx, myy int) {
- if d.nComp == nGrayComponent {
- 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
- }
- var subsampleRatio image.YCbCrSubsampleRatio
- switch {
- case h0 == 1 && v0 == 1:
- subsampleRatio = image.YCbCrSubsampleRatio444
- case h0 == 1 && v0 == 2:
- subsampleRatio = image.YCbCrSubsampleRatio440
- case h0 == 2 && v0 == 1:
- subsampleRatio = image.YCbCrSubsampleRatio422
- case h0 == 2 && v0 == 2:
- subsampleRatio = image.YCbCrSubsampleRatio420
- 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)
-}
-
-// 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")
- }
- _, err := io.ReadFull(d.r, d.tmp[:n])
- if 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 [nColorComponent]struct {
- compIndex uint8
- td uint8 // DC table selector.
- ta uint8 // AC table selector.
- }
- for i := 0; i < nComp; i++ {
- cs := d.tmp[1+2*i] // Component selector.
- compIndex := -1
- for j, comp := range d.comp {
- if cs == comp.c {
- compIndex = j
- }
- }
- if compIndex < 0 {
- return FormatError("unknown component selector")
- }
- scan[i].compIndex = uint8(compIndex)
- scan[i].td = d.tmp[2+2*i] >> 4
- scan[i].ta = d.tmp[2+2*i] & 0x0f
- }
-
- // 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 baseline JPEGs, these parameters are hard-coded to 0/63/0/0.
- 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(h0, v0, 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.b = bits{}
- mcu, expectedRST := 0, uint8(rst0Marker)
- var (
- // b is the decoded coefficients, in natural (not zig-zag) order.
- b block
- dc [nColorComponent]int32
- // mx0 and my0 are the location of the current (in terms of 8x8 blocks).
- // For example, with 4:2:0 chroma subsampling, the block whose top left
- // pixel co-ordinates are (16, 8) is the third block in the first row:
- // mx0 is 2 and my0 is 0, even though the pixel is in the second MCU.
- // TODO(nigeltao): rename mx0 and my0 to bx and by?
- mx0, my0 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
- qt := &d.quant[d.comp[compIndex].tq]
- for j := 0; j < d.comp[compIndex].h*d.comp[compIndex].v; 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 baseline 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 {
- mx0, my0 = d.comp[compIndex].h*mx, d.comp[compIndex].v*my
- if h0 == 1 {
- my0 += j
- } else {
- mx0 += j % 2
- my0 += j / 2
- }
- } else {
- q := mxx * d.comp[compIndex].h
- mx0 = blockCount % q
- my0 = blockCount / q
- blockCount++
- if mx0*8 >= d.width || my0*8 >= d.height {
- continue
- }
- }
-
- // Load the previous partially decoded coefficients, if applicable.
- if d.progressive {
- b = d.progCoeffs[compIndex][my0*mxx*d.comp[compIndex].h+mx0]
- } else {
- b = block{}
- }
-
- if ah != 0 {
- if err := d.refine(&b, &d.huff[acTable][scan[i].ta], zigStart, zigEnd, 1<<al); err != nil {
- return err
- }
- } else {
- zig := zigStart
- if zig == 0 {
- zig++
- // Decode the DC coefficient, as specified in section F.2.2.1.
- value, err := d.decodeHuffman(&d.huff[dcTable][scan[i].td])
- if err != nil {
- return err
- }
- if value > 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.
- for ; zig <= zigEnd; zig++ {
- value, err := d.decodeHuffman(&d.huff[acTable][scan[i].ta])
- 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(int(val0))
- if err != nil {
- return err
- }
- d.eobRun |= uint16(bits)
- }
- d.eobRun--
- break
- }
- zig += 0x0f
- }
- }
- }
- }
-
- if d.progressive {
- if zigEnd != blockSize-1 || al != 0 {
- // We haven't completely decoded this 8x8 block. Save the coefficients.
- d.progCoeffs[compIndex][my0*mxx*d.comp[compIndex].h+mx0] = b
- // At this point, we could execute the rest of the loop body 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.
- continue
- }
- }
-
- // Dequantize, perform the inverse DCT and store the block to the image.
- for zig := 0; zig < blockSize; zig++ {
- b[unzig[zig]] *= qt[zig]
- }
- idct(&b)
- dst, stride := []byte(nil), 0
- if d.nComp == nGrayComponent {
- dst, stride = d.img1.Pix[8*(my0*d.img1.Stride+mx0):], d.img1.Stride
- } else {
- switch compIndex {
- case 0:
- dst, stride = d.img3.Y[8*(my0*d.img3.YStride+mx0):], d.img3.YStride
- case 1:
- dst, stride = d.img3.Cb[8*(my0*d.img3.CStride+mx0):], d.img3.CStride
- case 2:
- dst, stride = d.img3.Cr[8*(my0*d.img3.CStride+mx0):], d.img3.CStride
- 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)
- }
- }
- } // 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.
- _, err := io.ReadFull(d.r, d.tmp[0:2])
- if 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.b = bits{}
- // Reset the DC components, as per section F.2.1.3.1.
- dc = [nColorComponent]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(int(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
-}
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