summaryrefslogtreecommitdiff
path: root/src/image/jpeg/scan.go
diff options
context:
space:
mode:
Diffstat (limited to 'src/image/jpeg/scan.go')
-rw-r--r--src/image/jpeg/scan.go442
1 files changed, 442 insertions, 0 deletions
diff --git a/src/image/jpeg/scan.go b/src/image/jpeg/scan.go
new file mode 100644
index 000000000..2bd1d9d53
--- /dev/null
+++ b/src/image/jpeg/scan.go
@@ -0,0 +1,442 @@
+// 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(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")
+ }
+ 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 [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
+ if scan[i].td > maxTh {
+ return FormatError("bad Td value")
+ }
+ scan[i].ta = d.tmp[2+2*i] & 0x0f
+ if scan[i].ta > maxTh {
+ return FormatError("bad Ta value")
+ }
+ }
+
+ // 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.bits = bits{}
+ mcu, expectedRST := 0, uint8(rst0Marker)
+ var (
+ // b is the decoded coefficients, in natural (not zig-zag) order.
+ b block
+ dc [nColorComponent]int32
+ // bx and by 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:
+ // bx is 2 and by is 0, even though the pixel is in the second MCU.
+ 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
+ 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 {
+ bx, by = d.comp[compIndex].h*mx, d.comp[compIndex].v*my
+ if h0 == 1 {
+ by += j
+ } else {
+ bx += j % 2
+ by += j / 2
+ }
+ } else {
+ q := mxx * d.comp[compIndex].h
+ 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*d.comp[compIndex].h+bx]
+ } 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.
+ 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 {
+ if zigEnd != blockSize-1 || al != 0 {
+ // We haven't completely decoded this 8x8 block. Save the coefficients.
+ d.progCoeffs[compIndex][by*mxx*d.comp[compIndex].h+bx] = 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*(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
+ 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.
+ 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 = [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(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
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-05-21 04:43:10 +0000