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JPEG decoder now handles RST (restart) markers.

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R=r
CC=golang-dev
https://golang.org/cl/181075
This commit is contained in:
Nigel Tao 2009-12-29 15:20:53 +11:00
parent e7601e2980
commit 50d3447a36
1 changed files with 42 additions and 0 deletions
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42
src/pkg/image/jpeg/reader.go
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@ -55,6 +55,9 @@ const (
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.
@ -82,6 +85,7 @@ type decoder struct {
r Reader
width, height int
image *image.RGBA
ri int // Restart Interval.
comps [nComponent]component
huff [maxTc + 1][maxTh + 1]huffman
quant [maxTq + 1][blockSize]int
@ -265,6 +269,7 @@ func (d *decoder) processSOS(n int) os.Error {
mxx := (d.width + 8*int(h0) - 1) / (8 * int(h0))
myy := (d.height + 8*int(v0) - 1) / (8 * int(v0))
mcu, expectedRST := 0, uint8(rst0Marker)
var allZeroes [blockSize]int
var dc [nComponent]int
for my := 0; my < myy; my++ {
@ -319,12 +324,47 @@ func (d *decoder) processSOS(n int) os.Error {
} // for j
} // for i
d.convertMCU(mx, my, int(d.comps[0].h), int(d.comps[0].v))
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.
for i := 0; i < nComponent; i++ {
dc[i] = 0
}
}
} // for mx
} // for my
return nil
}
// Specified in section B.2.4.4.
func (d *decoder) processDRI(n int) os.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 formatted image from r and returns it as an image.Image.
func Decode(r io.Reader) (image.Image, os.Error) {
var d decoder
@ -379,6 +419,8 @@ func Decode(r io.Reader) (image.Image, os.Error) {
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: