523 lines
15 KiB
Go
523 lines
15 KiB
Go
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package jpeg
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import (
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"image"
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)
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// makeImg allocates and initializes the destination image.
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func (d *decoder) makeImg(mxx, myy int) {
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if d.nComp == 1 {
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m := image.NewGray(image.Rect(0, 0, 8*mxx, 8*myy))
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d.img1 = m.SubImage(image.Rect(0, 0, d.width, d.height)).(*image.Gray)
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return
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}
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h0 := d.comp[0].h
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v0 := d.comp[0].v
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hRatio := h0 / d.comp[1].h
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vRatio := v0 / d.comp[1].v
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var subsampleRatio image.YCbCrSubsampleRatio
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switch hRatio<<4 | vRatio {
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case 0x11:
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subsampleRatio = image.YCbCrSubsampleRatio444
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case 0x12:
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subsampleRatio = image.YCbCrSubsampleRatio440
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case 0x21:
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subsampleRatio = image.YCbCrSubsampleRatio422
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case 0x22:
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subsampleRatio = image.YCbCrSubsampleRatio420
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case 0x41:
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subsampleRatio = image.YCbCrSubsampleRatio411
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case 0x42:
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subsampleRatio = image.YCbCrSubsampleRatio410
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default:
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panic("unreachable")
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}
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m := image.NewYCbCr(image.Rect(0, 0, 8*h0*mxx, 8*v0*myy), subsampleRatio)
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d.img3 = m.SubImage(image.Rect(0, 0, d.width, d.height)).(*image.YCbCr)
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if d.nComp == 4 {
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h3, v3 := d.comp[3].h, d.comp[3].v
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d.blackPix = make([]byte, 8*h3*mxx*8*v3*myy)
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d.blackStride = 8 * h3 * mxx
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}
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}
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// Specified in section B.2.3.
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func (d *decoder) processSOS(n int) error {
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if d.nComp == 0 {
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return FormatError("missing SOF marker")
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}
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if n < 6 || 4+2*d.nComp < n || n%2 != 0 {
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return FormatError("SOS has wrong length")
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}
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if err := d.readFull(d.tmp[:n]); err != nil {
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return err
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}
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nComp := int(d.tmp[0])
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if n != 4+2*nComp {
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return FormatError("SOS length inconsistent with number of components")
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}
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var scan [maxComponents]struct {
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compIndex uint8
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td uint8 // DC table selector.
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ta uint8 // AC table selector.
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}
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totalHV := 0
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for i := 0; i < nComp; i++ {
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cs := d.tmp[1+2*i] // Component selector.
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compIndex := -1
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for j, comp := range d.comp[:d.nComp] {
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if cs == comp.c {
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compIndex = j
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}
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}
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if compIndex < 0 {
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return FormatError("unknown component selector")
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}
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scan[i].compIndex = uint8(compIndex)
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// Section B.2.3 states that "the value of Cs_j shall be different from
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// the values of Cs_1 through Cs_(j-1)". Since we have previously
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// verified that a frame's component identifiers (C_i values in section
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// B.2.2) are unique, it suffices to check that the implicit indexes
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// into d.comp are unique.
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for j := 0; j < i; j++ {
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if scan[i].compIndex == scan[j].compIndex {
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return FormatError("repeated component selector")
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}
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}
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totalHV += d.comp[compIndex].h * d.comp[compIndex].v
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// The baseline t <= 1 restriction is specified in table B.3.
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scan[i].td = d.tmp[2+2*i] >> 4
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if t := scan[i].td; t > maxTh || (d.baseline && t > 1) {
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return FormatError("bad Td value")
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}
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scan[i].ta = d.tmp[2+2*i] & 0x0f
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if t := scan[i].ta; t > maxTh || (d.baseline && t > 1) {
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return FormatError("bad Ta value")
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}
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}
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// Section B.2.3 states that if there is more than one component then the
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// total H*V values in a scan must be <= 10.
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if d.nComp > 1 && totalHV > 10 {
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return FormatError("total sampling factors too large")
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}
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// zigStart and zigEnd are the spectral selection bounds.
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// ah and al are the successive approximation high and low values.
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// The spec calls these values Ss, Se, Ah and Al.
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//
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// For progressive JPEGs, these are the two more-or-less independent
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// aspects of progression. Spectral selection progression is when not
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// all of a block's 64 DCT coefficients are transmitted in one pass.
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// For example, three passes could transmit coefficient 0 (the DC
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// component), coefficients 1-5, and coefficients 6-63, in zig-zag
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// order. Successive approximation is when not all of the bits of a
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// band of coefficients are transmitted in one pass. For example,
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// three passes could transmit the 6 most significant bits, followed
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// by the second-least significant bit, followed by the least
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// significant bit.
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//
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// For sequential JPEGs, these parameters are hard-coded to 0/63/0/0, as
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// per table B.3.
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zigStart, zigEnd, ah, al := int32(0), int32(blockSize-1), uint32(0), uint32(0)
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if d.progressive {
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zigStart = int32(d.tmp[1+2*nComp])
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zigEnd = int32(d.tmp[2+2*nComp])
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ah = uint32(d.tmp[3+2*nComp] >> 4)
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al = uint32(d.tmp[3+2*nComp] & 0x0f)
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if (zigStart == 0 && zigEnd != 0) || zigStart > zigEnd || blockSize <= zigEnd {
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return FormatError("bad spectral selection bounds")
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}
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if zigStart != 0 && nComp != 1 {
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return FormatError("progressive AC coefficients for more than one component")
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}
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if ah != 0 && ah != al+1 {
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return FormatError("bad successive approximation values")
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}
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}
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// mxx and myy are the number of MCUs (Minimum Coded Units) in the image.
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h0, v0 := d.comp[0].h, d.comp[0].v // The h and v values from the Y components.
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mxx := (d.width + 8*h0 - 1) / (8 * h0)
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myy := (d.height + 8*v0 - 1) / (8 * v0)
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if d.img1 == nil && d.img3 == nil {
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d.makeImg(mxx, myy)
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}
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if d.progressive {
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for i := 0; i < nComp; i++ {
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compIndex := scan[i].compIndex
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if d.progCoeffs[compIndex] == nil {
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d.progCoeffs[compIndex] = make([]block, mxx*myy*d.comp[compIndex].h*d.comp[compIndex].v)
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}
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}
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}
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d.bits = bits{}
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mcu, expectedRST := 0, uint8(rst0Marker)
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var (
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// b is the decoded coefficients, in natural (not zig-zag) order.
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b block
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dc [maxComponents]int32
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// bx and by are the location of the current block, in units of 8x8
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// blocks: the third block in the first row has (bx, by) = (2, 0).
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bx, by int
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blockCount int
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)
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for my := 0; my < myy; my++ {
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for mx := 0; mx < mxx; mx++ {
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for i := 0; i < nComp; i++ {
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compIndex := scan[i].compIndex
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hi := d.comp[compIndex].h
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vi := d.comp[compIndex].v
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for j := 0; j < hi*vi; j++ {
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// The blocks are traversed one MCU at a time. For 4:2:0 chroma
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// subsampling, there are four Y 8x8 blocks in every 16x16 MCU.
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//
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// For a sequential 32x16 pixel image, the Y blocks visiting order is:
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// 0 1 4 5
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// 2 3 6 7
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//
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// For progressive images, the interleaved scans (those with nComp > 1)
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// are traversed as above, but non-interleaved scans are traversed left
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// to right, top to bottom:
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// 0 1 2 3
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// 4 5 6 7
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// Only DC scans (zigStart == 0) can be interleaved. AC scans must have
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// only one component.
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//
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// To further complicate matters, for non-interleaved scans, there is no
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// data for any blocks that are inside the image at the MCU level but
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// outside the image at the pixel level. For example, a 24x16 pixel 4:2:0
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// progressive image consists of two 16x16 MCUs. The interleaved scans
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// will process 8 Y blocks:
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// 0 1 4 5
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// 2 3 6 7
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// The non-interleaved scans will process only 6 Y blocks:
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// 0 1 2
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// 3 4 5
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if nComp != 1 {
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bx = hi*mx + j%hi
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by = vi*my + j/hi
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} else {
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q := mxx * hi
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bx = blockCount % q
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by = blockCount / q
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blockCount++
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if bx*8 >= d.width || by*8 >= d.height {
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continue
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}
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}
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// Load the previous partially decoded coefficients, if applicable.
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if d.progressive {
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b = d.progCoeffs[compIndex][by*mxx*hi+bx]
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} else {
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b = block{}
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}
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if ah != 0 {
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if err := d.refine(&b, &d.huff[acTable][scan[i].ta], zigStart, zigEnd, 1<<al); err != nil {
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return err
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}
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} else {
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zig := zigStart
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if zig == 0 {
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zig++
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// Decode the DC coefficient, as specified in section F.2.2.1.
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value, err := d.decodeHuffman(&d.huff[dcTable][scan[i].td])
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if err != nil {
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return err
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}
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if value > 16 {
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return UnsupportedError("excessive DC component")
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}
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dcDelta, err := d.receiveExtend(value)
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if err != nil {
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return err
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}
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dc[compIndex] += dcDelta
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b[0] = dc[compIndex] << al
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}
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if zig <= zigEnd && d.eobRun > 0 {
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d.eobRun--
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} else {
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// Decode the AC coefficients, as specified in section F.2.2.2.
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huff := &d.huff[acTable][scan[i].ta]
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for ; zig <= zigEnd; zig++ {
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value, err := d.decodeHuffman(huff)
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if err != nil {
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return err
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}
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val0 := value >> 4
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val1 := value & 0x0f
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if val1 != 0 {
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zig += int32(val0)
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if zig > zigEnd {
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break
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}
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ac, err := d.receiveExtend(val1)
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if err != nil {
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return err
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}
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b[unzig[zig]] = ac << al
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} else {
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if val0 != 0x0f {
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d.eobRun = uint16(1 << val0)
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if val0 != 0 {
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bits, err := d.decodeBits(int32(val0))
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if err != nil {
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return err
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}
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d.eobRun |= uint16(bits)
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}
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d.eobRun--
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break
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}
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zig += 0x0f
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}
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}
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}
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}
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if d.progressive {
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// Save the coefficients.
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d.progCoeffs[compIndex][by*mxx*hi+bx] = b
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// At this point, we could call reconstructBlock to dequantize and perform the
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// inverse DCT, to save early stages of a progressive image to the *image.YCbCr
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// buffers (the whole point of progressive encoding), but in Go, the jpeg.Decode
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// function does not return until the entire image is decoded, so we "continue"
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// here to avoid wasted computation. Instead, reconstructBlock is called on each
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// accumulated block by the reconstructProgressiveImage method after all of the
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// SOS markers are processed.
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continue
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}
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if err := d.reconstructBlock(&b, bx, by, int(compIndex)); err != nil {
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return err
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}
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} // for j
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} // for i
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mcu++
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if d.ri > 0 && mcu%d.ri == 0 && mcu < mxx*myy {
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// A more sophisticated decoder could use RST[0-7] markers to resynchronize from corrupt input,
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// but this one assumes well-formed input, and hence the restart marker follows immediately.
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if err := d.readFull(d.tmp[:2]); err != nil {
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return err
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}
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// Section F.1.2.3 says that "Byte alignment of markers is
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// achieved by padding incomplete bytes with 1-bits. If padding
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// with 1-bits creates a X’FF’ value, a zero byte is stuffed
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// before adding the marker."
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//
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// Seeing "\xff\x00" here is not spec compliant, as we are not
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// expecting an *incomplete* byte (that needed padding). Still,
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// some real world encoders (see golang.org/issue/28717) insert
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// it, so we accept it and re-try the 2 byte read.
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//
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// libjpeg issues a warning (but not an error) for this:
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// https://github.com/LuaDist/libjpeg/blob/6c0fcb8ddee365e7abc4d332662b06900612e923/jdmarker.c#L1041-L1046
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if d.tmp[0] == 0xff && d.tmp[1] == 0x00 {
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if err := d.readFull(d.tmp[:2]); err != nil {
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return err
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}
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}
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if d.tmp[0] != 0xff || d.tmp[1] != expectedRST {
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return FormatError("bad RST marker")
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}
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expectedRST++
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if expectedRST == rst7Marker+1 {
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expectedRST = rst0Marker
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}
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// Reset the Huffman decoder.
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d.bits = bits{}
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// Reset the DC components, as per section F.2.1.3.1.
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dc = [maxComponents]int32{}
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// Reset the progressive decoder state, as per section G.1.2.2.
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d.eobRun = 0
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}
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} // for mx
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} // for my
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return nil
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}
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// refine decodes a successive approximation refinement block, as specified in
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// section G.1.2.
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func (d *decoder) refine(b *block, h *huffman, zigStart, zigEnd, delta int32) error {
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// Refining a DC component is trivial.
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if zigStart == 0 {
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if zigEnd != 0 {
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panic("unreachable")
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}
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bit, err := d.decodeBit()
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if err != nil {
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return err
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}
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if bit {
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b[0] |= delta
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}
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return nil
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}
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// Refining AC components is more complicated; see sections G.1.2.2 and G.1.2.3.
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zig := zigStart
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if d.eobRun == 0 {
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loop:
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for ; zig <= zigEnd; zig++ {
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z := int32(0)
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value, err := d.decodeHuffman(h)
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if err != nil {
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return err
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}
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val0 := value >> 4
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val1 := value & 0x0f
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switch val1 {
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case 0:
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if val0 != 0x0f {
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d.eobRun = uint16(1 << val0)
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if val0 != 0 {
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bits, err := d.decodeBits(int32(val0))
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if err != nil {
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return err
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}
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d.eobRun |= uint16(bits)
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}
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break loop
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}
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case 1:
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z = delta
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bit, err := d.decodeBit()
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if err != nil {
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return err
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}
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if !bit {
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z = -z
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}
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default:
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return FormatError("unexpected Huffman code")
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}
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zig, err = d.refineNonZeroes(b, zig, zigEnd, int32(val0), delta)
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if err != nil {
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return err
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}
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if zig > zigEnd {
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return FormatError("too many coefficients")
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}
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if z != 0 {
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b[unzig[zig]] = z
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}
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}
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}
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if d.eobRun > 0 {
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d.eobRun--
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if _, err := d.refineNonZeroes(b, zig, zigEnd, -1, delta); err != nil {
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return err
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}
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}
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return nil
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}
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// refineNonZeroes refines non-zero entries of b in zig-zag order. If nz >= 0,
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// the first nz zero entries are skipped over.
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func (d *decoder) refineNonZeroes(b *block, zig, zigEnd, nz, delta int32) (int32, error) {
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for ; zig <= zigEnd; zig++ {
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u := unzig[zig]
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if b[u] == 0 {
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if nz == 0 {
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break
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}
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nz--
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continue
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}
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bit, err := d.decodeBit()
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if err != nil {
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return 0, err
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}
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if !bit {
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continue
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}
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if b[u] >= 0 {
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b[u] += delta
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} else {
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b[u] -= delta
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}
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}
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return zig, nil
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}
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func (d *decoder) reconstructProgressiveImage() error {
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// The h0, mxx, by and bx variables have the same meaning as in the
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// processSOS method.
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h0 := d.comp[0].h
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mxx := (d.width + 8*h0 - 1) / (8 * h0)
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for i := 0; i < d.nComp; i++ {
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if d.progCoeffs[i] == nil {
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continue
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}
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v := 8 * d.comp[0].v / d.comp[i].v
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h := 8 * d.comp[0].h / d.comp[i].h
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stride := mxx * d.comp[i].h
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for by := 0; by*v < d.height; by++ {
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for bx := 0; bx*h < d.width; bx++ {
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if err := d.reconstructBlock(&d.progCoeffs[i][by*stride+bx], bx, by, i); err != nil {
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return err
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}
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}
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}
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}
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return nil
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}
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// reconstructBlock dequantizes, performs the inverse DCT and stores the block
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// to the image.
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func (d *decoder) reconstructBlock(b *block, bx, by, compIndex int) error {
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qt := &d.quant[d.comp[compIndex].tq]
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for zig := 0; zig < blockSize; zig++ {
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b[unzig[zig]] *= qt[zig]
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}
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idct(b)
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dst, stride := []byte(nil), 0
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if d.nComp == 1 {
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dst, stride = d.img1.Pix[8*(by*d.img1.Stride+bx):], d.img1.Stride
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} else {
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switch compIndex {
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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
|
||
}
|