433 lines
12 KiB
Go
433 lines
12 KiB
Go
// 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
|
|
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 DC data blocks (zigStart == 0) are traversed
|
|
// as above, but AC data blocks are traversed left to right, top to bottom:
|
|
// 0 1 2 3
|
|
// 4 5 6 7
|
|
//
|
|
// To further complicate matters, there is no AC 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 earlier scans will process 8 Y blocks:
|
|
// 0 1 4 5
|
|
// 2 3 6 7
|
|
// The later scans will process only 6 Y blocks:
|
|
// 0 1 2
|
|
// 3 4 5
|
|
if zigStart == 0 {
|
|
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
|
|
}
|