Retro68/gcc/libgo/go/image/jpeg/reader.go
Wolfgang Thaller aaf905ce07 add gcc 4.70
2012-03-28 01:13:14 +02:00

475 lines
13 KiB
Go

// Copyright 2009 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 implements a JPEG image decoder and encoder.
//
// JPEG is defined in ITU-T T.81: http://www.w3.org/Graphics/JPEG/itu-t81.pdf.
package jpeg
import (
"bufio"
"image"
"image/color"
"io"
)
// TODO(nigeltao): fix up the doc comment style so that sentences start with
// the name of the type or function that they annotate.
// A FormatError reports that the input is not a valid JPEG.
type FormatError string
func (e FormatError) Error() string { return "invalid JPEG format: " + string(e) }
// An UnsupportedError reports that the input uses a valid but unimplemented JPEG feature.
type UnsupportedError string
func (e UnsupportedError) Error() string { return "unsupported JPEG feature: " + string(e) }
// Component specification, specified in section B.2.2.
type component struct {
h int // Horizontal sampling factor.
v int // Vertical sampling factor.
c uint8 // Component identifier.
tq uint8 // Quantization table destination selector.
}
type block [blockSize]int
const (
blockSize = 64 // A DCT block is 8x8.
dcTable = 0
acTable = 1
maxTc = 1
maxTh = 3
maxTq = 3
// A grayscale JPEG image has only a Y component.
nGrayComponent = 1
// A color JPEG image has Y, Cb and Cr components.
nColorComponent = 3
// We only support 4:4:4, 4:2:2 and 4:2:0 downsampling, and therefore the
// number of luma samples per chroma sample is at most 2 in the horizontal
// and 2 in the vertical direction.
maxH = 2
maxV = 2
)
const (
soiMarker = 0xd8 // Start Of Image.
eoiMarker = 0xd9 // End Of Image.
sof0Marker = 0xc0 // Start Of Frame (Baseline).
sof2Marker = 0xc2 // Start Of Frame (Progressive).
dhtMarker = 0xc4 // Define Huffman Table.
dqtMarker = 0xdb // Define Quantization Table.
sosMarker = 0xda // Start Of Scan.
driMarker = 0xdd // Define Restart Interval.
rst0Marker = 0xd0 // ReSTart (0).
rst7Marker = 0xd7 // ReSTart (7).
app0Marker = 0xe0 // APPlication specific (0).
app15Marker = 0xef // APPlication specific (15).
comMarker = 0xfe // COMment.
)
// Maps from the zig-zag ordering to the natural ordering.
var unzig = [blockSize]int{
0, 1, 8, 16, 9, 2, 3, 10,
17, 24, 32, 25, 18, 11, 4, 5,
12, 19, 26, 33, 40, 48, 41, 34,
27, 20, 13, 6, 7, 14, 21, 28,
35, 42, 49, 56, 57, 50, 43, 36,
29, 22, 15, 23, 30, 37, 44, 51,
58, 59, 52, 45, 38, 31, 39, 46,
53, 60, 61, 54, 47, 55, 62, 63,
}
// If the passed in io.Reader does not also have ReadByte, then Decode will introduce its own buffering.
type Reader interface {
io.Reader
ReadByte() (c byte, err error)
}
type decoder struct {
r Reader
width, height int
img1 *image.Gray
img3 *image.YCbCr
ri int // Restart Interval.
nComp int
comp [nColorComponent]component
huff [maxTc + 1][maxTh + 1]huffman
quant [maxTq + 1]block
b bits
tmp [1024]byte
}
// Reads and ignores the next n bytes.
func (d *decoder) ignore(n int) error {
for n > 0 {
m := len(d.tmp)
if m > n {
m = n
}
_, err := io.ReadFull(d.r, d.tmp[0:m])
if err != nil {
return err
}
n -= m
}
return nil
}
// Specified in section B.2.2.
func (d *decoder) processSOF(n int) error {
switch n {
case 6 + 3*nGrayComponent:
d.nComp = nGrayComponent
case 6 + 3*nColorComponent:
d.nComp = nColorComponent
default:
return UnsupportedError("SOF has wrong length")
}
_, err := io.ReadFull(d.r, d.tmp[:n])
if err != nil {
return err
}
// We only support 8-bit precision.
if d.tmp[0] != 8 {
return UnsupportedError("precision")
}
d.height = int(d.tmp[1])<<8 + int(d.tmp[2])
d.width = int(d.tmp[3])<<8 + int(d.tmp[4])
if int(d.tmp[5]) != d.nComp {
return UnsupportedError("SOF has wrong number of image components")
}
for i := 0; i < d.nComp; i++ {
hv := d.tmp[7+3*i]
d.comp[i].h = int(hv >> 4)
d.comp[i].v = int(hv & 0x0f)
d.comp[i].c = d.tmp[6+3*i]
d.comp[i].tq = d.tmp[8+3*i]
if d.nComp == nGrayComponent {
continue
}
// For color images, we only support 4:4:4, 4:2:2 or 4:2:0 chroma
// downsampling ratios. This implies that the (h, v) values for the Y
// component are either (1, 1), (2, 1) or (2, 2), and the (h, v)
// values for the Cr and Cb components must be (1, 1).
if i == 0 {
if hv != 0x11 && hv != 0x21 && hv != 0x22 {
return UnsupportedError("luma downsample ratio")
}
} else if hv != 0x11 {
return UnsupportedError("chroma downsample ratio")
}
}
return nil
}
// Specified in section B.2.4.1.
func (d *decoder) processDQT(n int) error {
const qtLength = 1 + blockSize
for ; n >= qtLength; n -= qtLength {
_, err := io.ReadFull(d.r, d.tmp[0:qtLength])
if err != nil {
return err
}
pq := d.tmp[0] >> 4
if pq != 0 {
return UnsupportedError("bad Pq value")
}
tq := d.tmp[0] & 0x0f
if tq > maxTq {
return FormatError("bad Tq value")
}
for i := range d.quant[tq] {
d.quant[tq][i] = int(d.tmp[i+1])
}
}
if n != 0 {
return FormatError("DQT has wrong length")
}
return nil
}
// 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 h0 * v0 {
case 1:
subsampleRatio = image.YCbCrSubsampleRatio444
case 2:
subsampleRatio = image.YCbCrSubsampleRatio422
case 4:
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 != 4+2*d.nComp {
return UnsupportedError("SOS has wrong length")
}
_, err := io.ReadFull(d.r, d.tmp[0:4+2*d.nComp])
if err != nil {
return err
}
if int(d.tmp[0]) != d.nComp {
return UnsupportedError("SOS has wrong number of image components")
}
var scan [nColorComponent]struct {
td uint8 // DC table selector.
ta uint8 // AC table selector.
}
for i := 0; i < d.nComp; i++ {
cs := d.tmp[1+2*i] // Component selector.
if cs != d.comp[i].c {
return UnsupportedError("scan components out of order")
}
scan[i].td = d.tmp[2+2*i] >> 4
scan[i].ta = d.tmp[2+2*i] & 0x0f
}
// 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)
}
mcu, expectedRST := 0, uint8(rst0Marker)
var (
b block
dc [nColorComponent]int
)
for my := 0; my < myy; my++ {
for mx := 0; mx < mxx; mx++ {
for i := 0; i < d.nComp; i++ {
qt := &d.quant[d.comp[i].tq]
for j := 0; j < d.comp[i].h*d.comp[i].v; j++ {
// TODO(nigeltao): make this a "var b block" once the compiler's escape
// analysis is good enough to allocate it on the stack, not the heap.
b = block{}
// 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[i] += dcDelta
b[0] = dc[i] * qt[0]
// Decode the AC coefficients, as specified in section F.2.2.2.
for k := 1; k < blockSize; k++ {
value, err := d.decodeHuffman(&d.huff[acTable][scan[i].ta])
if err != nil {
return err
}
val0 := value >> 4
val1 := value & 0x0f
if val1 != 0 {
k += int(val0)
if k > blockSize {
return FormatError("bad DCT index")
}
ac, err := d.receiveExtend(val1)
if err != nil {
return err
}
b[unzig[k]] = ac * qt[k]
} else {
if val0 != 0x0f {
break
}
k += 0x0f
}
}
// Perform the inverse DCT and store the MCU component to the image.
if d.nComp == nGrayComponent {
idct(d.img1.Pix[8*(my*d.img1.Stride+mx):], d.img1.Stride, &b)
} else {
switch i {
case 0:
mx0 := h0*mx + (j % 2)
my0 := v0*my + (j / 2)
idct(d.img3.Y[8*(my0*d.img3.YStride+mx0):], d.img3.YStride, &b)
case 1:
idct(d.img3.Cb[8*(my*d.img3.CStride+mx):], d.img3.CStride, &b)
case 2:
idct(d.img3.Cr[8*(my*d.img3.CStride+mx):], d.img3.CStride, &b)
}
}
} // 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]int{}
}
} // for mx
} // for my
return nil
}
// Specified in section B.2.4.4.
func (d *decoder) processDRI(n int) error {
if n != 2 {
return FormatError("DRI has wrong length")
}
_, err := io.ReadFull(d.r, d.tmp[0:2])
if err != nil {
return err
}
d.ri = int(d.tmp[0])<<8 + int(d.tmp[1])
return nil
}
// decode reads a JPEG image from r and returns it as an image.Image.
func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, error) {
if rr, ok := r.(Reader); ok {
d.r = rr
} else {
d.r = bufio.NewReader(r)
}
// Check for the Start Of Image marker.
_, err := io.ReadFull(d.r, d.tmp[0:2])
if err != nil {
return nil, err
}
if d.tmp[0] != 0xff || d.tmp[1] != soiMarker {
return nil, FormatError("missing SOI marker")
}
// Process the remaining segments until the End Of Image marker.
for {
_, err := io.ReadFull(d.r, d.tmp[0:2])
if err != nil {
return nil, err
}
if d.tmp[0] != 0xff {
return nil, FormatError("missing 0xff marker start")
}
marker := d.tmp[1]
if marker == eoiMarker { // End Of Image.
break
}
// Read the 16-bit length of the segment. The value includes the 2 bytes for the
// length itself, so we subtract 2 to get the number of remaining bytes.
_, err = io.ReadFull(d.r, d.tmp[0:2])
if err != nil {
return nil, err
}
n := int(d.tmp[0])<<8 + int(d.tmp[1]) - 2
if n < 0 {
return nil, FormatError("short segment length")
}
switch {
case marker == sof0Marker: // Start Of Frame (Baseline).
err = d.processSOF(n)
if configOnly {
return nil, err
}
case marker == sof2Marker: // Start Of Frame (Progressive).
err = UnsupportedError("progressive mode")
case marker == dhtMarker: // Define Huffman Table.
err = d.processDHT(n)
case marker == dqtMarker: // Define Quantization Table.
err = d.processDQT(n)
case marker == sosMarker: // Start Of Scan.
err = d.processSOS(n)
case marker == driMarker: // Define Restart Interval.
err = d.processDRI(n)
case marker >= app0Marker && marker <= app15Marker || marker == comMarker: // APPlication specific, or COMment.
err = d.ignore(n)
default:
err = UnsupportedError("unknown marker")
}
if err != nil {
return nil, err
}
}
if d.img1 != nil {
return d.img1, nil
}
if d.img3 != nil {
return d.img3, nil
}
return nil, FormatError("missing SOS marker")
}
// Decode reads a JPEG image from r and returns it as an image.Image.
func Decode(r io.Reader) (image.Image, error) {
var d decoder
return d.decode(r, false)
}
// DecodeConfig returns the color model and dimensions of a JPEG image without
// decoding the entire image.
func DecodeConfig(r io.Reader) (image.Config, error) {
var d decoder
if _, err := d.decode(r, true); err != nil {
return image.Config{}, err
}
switch d.nComp {
case nGrayComponent:
return image.Config{
ColorModel: color.GrayModel,
Width: d.width,
Height: d.height,
}, nil
case nColorComponent:
return image.Config{
ColorModel: color.YCbCrModel,
Width: d.width,
Height: d.height,
}, nil
}
return image.Config{}, FormatError("missing SOF marker")
}
func init() {
image.RegisterFormat("jpeg", "\xff\xd8", Decode, DecodeConfig)
}