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decoder.go
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decoder.go
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package jpegsl
import (
"bytes"
"io"
)
type Decoder struct {
bitstream *Bitstream
dataStream *bytes.Reader
huffmanTrees map[byte]*HuffmanNode
huffmanTreesSelected map[int]*HuffmanNode
precision byte
predictor byte
lines uint16
samples uint16
components int
componentIndex map[byte]int
samplingFactorH []byte
samplingFactorV []byte
}
var MARKER_SOF3 uint16 = 0xffc3
var MARKER_DHT uint16 = 0xffc4
var MARKER_SOI uint16 = 0xffd8
var MARKER_SOS uint16 = 0xffda
func NewDecoder(data []byte) *Decoder {
decoder := new(Decoder)
decoder.bitstream = NewBitstream(data)
decoder.dataStream = decoder.bitstream.dataStream
return decoder
}
func (decoder *Decoder) buildTree() int {
tableLength := 0
tableId := read1Byte(decoder.dataStream)
if decoder.huffmanTrees == nil {
decoder.huffmanTrees = make(map[byte]*HuffmanNode)
}
decoder.huffmanTrees[tableId] = NewHuffmanNode(decoder.bitstream)
codeLengthArray := make([]byte, 16)
vals := make([]byte, 16)
for i := 0; i < 16; i++ {
codeLengthArray[i] = read1Byte(decoder.dataStream)
tableLength += int(codeLengthArray[i])
}
k := 0
for i := 0; i < 16; i++ {
for j := 0; j < int(codeLengthArray[i]); j++ {
vals[k] = read1Byte(decoder.dataStream)
decoder.huffmanTrees[tableId].mostLeft(i + 1).value = int(vals[k])
k++
}
}
h := decoder.huffmanTrees[tableId]
var x, code uint32
for i := uint32(0); i < lutSize; i++ {
code <<= 1
for j := 0; j < int(codeLengthArray[i]); j++ {
// The codeLength is 1+i, so shift code by 8-(1+i) to
// calculate the high bits for every 8-bit sequence
// whose codeLength's high bits matches code.
// The high 8 bits of lutValue are the encoded value.
// The low 8 bits are 1 plus the codeLength.
base := uint8(code << (7 - i))
lutValue := uint16(vals[x])<<8 | uint16(2+i)
for k := uint8(0); k < 1<<(7-i); k++ {
h.lut[base|k] = lutValue
}
code++
x++
}
}
//fmt.Print(h.lut)
return tableLength + 17
}
func (decoder *Decoder) decodeDHT(length int64) {
for length > 0 {
length -= int64(decoder.buildTree())
}
}
func (decoder *Decoder) decodeSOF3(length int64) {
decoder.precision = read1Byte(decoder.dataStream)
decoder.lines = read2Bytes(decoder.dataStream)
decoder.samples = read2Bytes(decoder.dataStream)
decoder.components = int(read1Byte(decoder.dataStream))
decoder.componentIndex = make(map[byte]int, decoder.components)
decoder.samplingFactorH = make([]byte, decoder.components)
decoder.samplingFactorV = make([]byte, decoder.components)
for i := 0; i < decoder.components; i++ {
component := read1Byte(decoder.dataStream)
samplingFactor := read1Byte(decoder.dataStream)
read1Byte(decoder.dataStream)
decoder.componentIndex[component] = i
decoder.samplingFactorH[i] = samplingFactor >> 4
decoder.samplingFactorV[i] = samplingFactor & 0xf
}
decoder.dataStream.Seek(length-int64(6+decoder.components*3), io.SeekCurrent)
}
func (decoder *Decoder) decodeSOS(length int64) {
components := read1Byte(decoder.dataStream)
if decoder.huffmanTreesSelected == nil {
decoder.huffmanTreesSelected = make(map[int]*HuffmanNode)
}
for i := 0; i < int(components); i++ {
component := read1Byte(decoder.dataStream)
treeSelection := read1Byte(decoder.dataStream)
decoder.huffmanTreesSelected[decoder.componentIndex[component]] = decoder.huffmanTrees[treeSelection>>4]
}
decoder.predictor = read1Byte(decoder.dataStream)
decoder.dataStream.Seek(length-int64(2+components*2), io.SeekCurrent)
}
func (decoder *Decoder) decodeHeader() {
marker := read2Bytes(decoder.dataStream)
if marker != MARKER_SOI {
return
}
done := false
for !done {
marker := read2Bytes(decoder.dataStream)
length := read2Bytes(decoder.dataStream) - 2
switch marker {
case MARKER_SOF3:
decoder.decodeSOF3(int64(length))
case MARKER_DHT:
decoder.decodeDHT(int64(length))
case MARKER_SOS:
decoder.decodeSOS(int64(length))
done = true
default:
decoder.dataStream.Seek(int64(length), io.SeekCurrent)
}
}
}
func (decoder *Decoder) decodeDiff(node *HuffmanNode) int {
length := node.decode(true)
if length == 0 {
return 0
}
if length == 16 {
return -32768
}
diff := int(decoder.bitstream.bits(length))
//V(ariable) L(ength) I(nteger) encoding: for positive number, encode as itself start with highbit 1
//for negative number x, encoded as 2's compliment of -x
if (diff & (1 << (length - 1))) == 0 {
diff -= (1 << length) - 1
}
return diff
}
// Decode bytes to int array. pass signed as true if the pixel value are signed and false otherwise
// For dicom pixel data parsing, get the value of tag PixelRepresentation. 1 means signed and 0 means unsigned
// Also check the tag PixelPaddingValue, which can be used to pad the image. Those pixels should be treated correctly
func Decode(data []byte, signed bool) []int {
decoder := NewDecoder(data)
decoder.decodeHeader()
width := int(decoder.samples) * decoder.components
imageArray := make([]int, int(decoder.lines)*width)
stripeSize := width
for i := 0; i < decoder.components; i++ {
imageArray[i] = decoder.decodeDiff(decoder.huffmanTreesSelected[i])
if !signed {
imageArray[i] += (1 << (decoder.precision - 1))
} else {
imageArray[i] -= (1 << (decoder.precision - 1))
}
}
for x := decoder.components; x < int(decoder.samples)*decoder.components; x += decoder.components {
for i := 0; i < decoder.components; i++ {
imageArray[x+i] = decoder.decodeDiff(decoder.huffmanTreesSelected[i]) + imageArray[x+i-decoder.components]
}
}
offset := stripeSize
for y := 1; y < int(decoder.lines); y++ {
for i := 0; i < decoder.components; i++ {
imageArray[offset+i] = decoder.decodeDiff(decoder.huffmanTreesSelected[i]) + imageArray[offset+i-stripeSize]
}
for x := decoder.components; x < int(decoder.samples)*decoder.components; x += decoder.components {
for i := 0; i < decoder.components; i++ {
predictor := 0
switch decoder.predictor {
case 1:
predictor = imageArray[offset+x+i-decoder.components]
case 6:
predictor = imageArray[offset+x+i-stripeSize] + ((imageArray[offset+x+i-decoder.components] -
imageArray[offset+x+i-decoder.components-stripeSize]) >> 1)
}
imageArray[offset+x+i] = predictor + decoder.decodeDiff(decoder.huffmanTreesSelected[i])
}
}
offset += stripeSize
}
return imageArray
}