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LJ92.py
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LJ92.py
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# Parse lossless JPEG (1992 version)
import array,struct
class lj92(object):
def __init__(self):
pass
def parse(self,data):
self.ix = 0
self.data = array.array('B',data)
"""
for cn,c in enumerate(self.data):
if cn%16==0:
print
print "%04x\t"%cn,
print "%02x"%c,
print
"""
self.findSoI()
def find(self):
#print "ix",self.ix
ix = self.ix
while 1:
while self.data[ix] != 0xFF:
ix += 1
ix += 2
self.ix = ix
return self.data[self.ix-1]
return 0
def findSoI(self):
if self.find()==0xd8:
return self.parseImage()
def parseImage(self):
print "Parsing image"
while 1:
nextMarker = self.find()
#print "%x"%nextMarker
if nextMarker == 0xc4:
self.parseHuff()
elif nextMarker == 0xc3:
self.parseSof3()
elif nextMarker == 0xfe: # Comment
self.parseBlock(nextMarker)
elif nextMarker == 0xd9: # End of image
break
elif nextMarker == 0xda:
self.parseScan()
else:
self.parseBlock(nextMarker)
print "Parsing image complete"
def nextbit(self):
if self.cnt == 0:
self.b = self.data[self.ix]
#print "b:%x "%self.b,
self.ix = self.ix + 1
self.cnt = 8
if self.b == 0xff:
self.b2 = self.data[self.ix]
self.ix = self.ix + 1
#if self.b2 == 0:
# Should handle DNL here
bit = self.b >> 7
self.cnt = self.cnt - 1
self.b = (self.b << 1)&0xFF
return bit
def decode(self):
i = 1
code = self.nextbit()
while code > self.maxcode[i]:
i = i+1
code = (code << 1) + self.nextbit()
j = self.valptr[i]
j = j + code - self.mincode[i]
value = self.huffval[j]
return value
def receive(self,ssss):
i = 0
v = 0
while i != ssss:
i = i+1
v = (v<<1) + self.nextbit()
return v
def extend(self,v,t):
vt = 2 ** (t-1)
if v < vt:
vt = (-1 << t) + 1
v = v + vt
return v
def parseScan(self):
scanhead = struct.unpack('>HB',self.data[self.ix:self.ix+3])
comp = struct.unpack('>'+'BB'*scanhead[1],self.data[self.ix+3:self.ix+3+2*scanhead[1]])
sehl = struct.unpack('>BBB',self.data[self.ix+3+2*scanhead[1]:self.ix+scanhead[0]])
#print "scan",scanhead,comp,sehl
pred = sehl[0]
self.ix += scanhead[0]
self.cnt = 0
# Now need to decode huffman coded values
c = 0
pixels = self.y * self.x
out = array.array('H','\0\0'*pixels)
# First pixel predicted from base value
t = self.decode()
diff = self.receive(t)
diff = self.extend(diff,t)
Px = 1 << (self.bits-1)
left = Px + diff
out[0] = left
#print out[c]
c = c + 1
# Rest of first row predicted from left pixel (not great for bayer)
while c<self.x:
t = self.decode()
diff = self.receive(t)
diff = self.extend(diff,t)
Px = left
left = Px + diff
out[c] = left
#print out[c]
c = c + 1
# Rest predicted based on scan chosen predictor
# (Usually using hue change of adjacent colour)
while c<pixels:
t = self.decode()
diff = self.receive(t)
diff = self.extend(diff,t)
if pred==0:
# No prediction... should not be used
pass
elif pred==1:
#Px = Ra
pass
elif pred==2:
#Px = Rb
pass
elif pred==3:
#Px = Rc
pass
elif pred==4:
#Px=Ra + Rb - Rc
pass
elif pred==5:
#Px = Ra + ((Rb - Rc)/2) a)
pass
elif pred==6:
Px = out[c-self.x] + ((left - out[c-self.x-1])>>1)
elif pred==7:
#Px = (Ra + Rb)/2
pass
left = Px + diff
out[c] = left
#print c,pixels,out[c]
c = c + 1
#for i in range(len(out)):
# out[i] = (out[i]>>8)|((out[i]&0xFF)<<8)
self.image = out
def parseBlock(self,marker):
blockhead = struct.unpack('>H',self.data[self.ix:self.ix+2])
#print "block %x"%marker,blockhead[0]
self.ix += blockhead[0]
def parseHuff(self):
huffhead = struct.unpack('>HB16B',self.data[self.ix:self.ix+19])
bits = array.array('i',huffhead[-17:])
bits[0] = 0
huffval = self.data[self.ix+19:self.ix+huffhead[0]]
self.ix += huffhead[0]
# Generate huffman table
k = 0
i = 1
j = 1
huffsize = array.array('i')
while i<=16:
while j<=bits[i]:
huffsize.append(i)
k = k+1
j = j+1
i = i+1
j = 1
huffsize.append(0)
lastk = k
huffcode = array.array('i')
k = 0
code = 0
si = huffsize[0]
while 1:
while huffsize[k] == si:
huffcode.append(code)
code = code+1
k = k+1
if huffsize[k] == 0:
break
while huffsize[k] != si:
code = code << 1
si = si + 1
ehufco = array.array('i',[0]*lastk)
ehufsi = array.array('i',[0]*lastk)
k = 0
while k < lastk:
i = huffval[k]
ehufco[i] = huffcode[k]
ehufsi[i] = huffsize[k]
k = k+1
i = 0
j = 0
maxcode = array.array('i',[0]*17)
mincode = array.array('i',[0]*17)
valptr = array.array('i',[0]*17)
while 1:
while 1:
i = i+1
if i>16:
break
if bits[i]!=0:
break
maxcode[i] = -1
if i>16:
break
valptr[i] = j
mincode[i] = huffcode[j]
j = j+bits[i]-1
maxcode[i] = huffcode[j]
j = j+1
self.maxcode = maxcode
self.mincode = mincode
self.valptr = valptr
self.huffval = huffval
#print "huffman table",huffhead,huffval,huffsize,huffcode,ehufco,ehufsi,mincode,maxcode,valptr
def parseSof3(self):
#print "Lossless sequential huffman coded"
header = struct.unpack('>HBHHBBBB',self.data[self.ix:self.ix+11])
Lf,P,Y,X,Nf,Ci,HV,Tqi = header
self.y = Y
self.x = X
self.bits = P
#print header,"%x"%HV
self.ix += Lf