/usr/share/pyshared/libtiff/lzw.py is in python-libtiff 0.3.0~svn78-2.
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This module is obsolete, use tif_lzw extension module instead.
"""
# Author: Pearu Peterson
# Created: May 2010
from __future__ import division
import numpy
default_backend='bittools'
#default_backend='bittools'
if default_backend=='bitarray':
from bitarray import bitarray
if default_backend=='bittools':
from bittools import setword, getword
CODECLEAR = 256
CODEEOI = 257
CODESTART = 258
def encode_bitarray(seq, max_bits=12):
""" Compress sequence using Lempel-Ziv-Welch algorithm for TIFF.
Parameters
----------
seq : {str, numpy.ndarray}
max_bits : int
Specify maximum bits for encoding table.
Returns
-------
bseq : bitarray
See also
--------
decode_bitarray
"""
if isinstance (seq, numpy.ndarray):
seq = seq.tostring()
r = bitarray(0, endian='little')
write = r.fromword
init_table = [(chr(code),code) for code in range (256)]
table = {}
table_get = table.get
table_clear = table.clear
table_update = table.update
sup_code2 = (1<<max_bits) - 2
next_code = CODESTART
bits = 9
max_code = (1<<bits)
s = ''
table_update(init_table)
index = 0
write(CODECLEAR, bits)
for c in seq:
s1 = s + c
if s1 in table:
s = s1
else:
write(table_get(s), bits)
table[s1] = next_code
next_code += 1
s = c
if next_code==sup_code2:
write(table_get(s), bits)
write(CODECLEAR, bits)
s = ''
table_clear()
table_update(init_table)
next_code = CODESTART
bits = 9
max_code = (1<<bits)
elif next_code==max_code:
bits += 1
max_code = (1<<bits)
if s:
write(table_get(s), bits)
write(CODEEOI, bits)
return r
def encode_bittools(seq, max_bits=12):
""" Compress sequence using Lempel-Ziv-Welch algorithm for TIFF.
Parameters
----------
seq : {str, numpy.ndarray}
max_bits : int
Specify maximum bits for encoding table.
Returns
-------
bseq : numpy.ndarray
See also
--------
decode_bittools
"""
if isinstance (seq, numpy.ndarray):
nbytes = seq.nbytes*2
seq = seq.tostring()
else:
nbytes = len(seq)*2
r = numpy.zeros((nbytes,), dtype=numpy.ubyte)
init_table = [(chr(code),code) for code in range (256)]
table = {}
table_get = table.get
table_clear = table.clear
table_update = table.update
sup_code2 = (1<<max_bits) - 2
next_code = CODESTART
bits = 9
max_code = (1<<bits)
s = ''
table_update(init_table)
index = setword(r, 0, bits, CODECLEAR, 1)
for c in seq:
s1 = s + c
if s1 in table:
s = s1
else:
index = setword(r, index, bits, table_get(s), 1)
table[s1] = next_code
next_code += 1
s = c
if next_code==sup_code2:
index = setword(r, index, bits, table_get(s), 1)
index = setword(r, index, bits, CODECLEAR, 1)
s = ''
table_clear()
table_update(init_table)
next_code = CODESTART
bits = 9
max_code = (1<<bits)
elif next_code==max_code:
bits += 1
max_code = (1<<bits)
if s:
index = setword(r, index, bits, table_get(s), 1)
index = setword(r, index, bits, CODEEOI)
bytes = index//8
if 8*bytes < index:
bytes += 1
return r[:bytes]
def decode_bitarray(bseq):
""" Decompress Lempel-Ziv-Welch encoded sequence.
Parameters
----------
bseq : {bitarray, numpy.ndarray}
Returns
-------
seq : str
See also
--------
encode_bitarray
"""
if isinstance(bseq, numpy.ndarray):
bseq = bitarray(bseq, endian='little')
assert bseq.endian ()=='little',`bseq.endian()`
read = bseq.toword
init_invtable = [(code, chr(code)) for code in range (256)]
table = [chr(code) for code in range(256)] + ['CODECLEAR', 'CODEEOI']
table_append = table.append
table_len = table.__len__
bits = 9
max_code2 = (1<<bits) - 2
i = 0
seq = []
seq_append = seq.append
while True:
code = read(i, bits)
i += bits
if code==CODEEOI:
break
elif code==CODECLEAR:
del table[CODESTART:]
bits = 9
max_code2 = (1<<bits) - 2
code = read(i, bits)
i += bits
old_str = table[code]
seq_append(old_str)
old_code = code
else:
l = table_len()
if code < l:
s = table[code]
table_append(old_str + s[0])
old_str = s
else:
old_str = old_str + old_str[0]
table_append(old_str)
seq_append(old_str)
old_code = code
if l==max_code2:
bits += 1
max_code2 = (1<<bits) - 2
return ''.join(seq)
def decode_bittools(bseq):
""" Decompress Lempel-Ziv-Welch encoded sequence.
Parameters
----------
bseq : numpy.ndarray
Returns
-------
seq : str
See also
--------
encode_bittools
"""
init_invtable = [(code, chr(code)) for code in range (256)]
table = [chr(code) for code in range(256)] + ['CODECLEAR', 'CODEEOI']
table_append = table.append
table_len = table.__len__
bits = 9
max_code2 = (1<<bits) - 2
i = 0
seq = []
seq_append = seq.append
while True:
code, i = getword(bseq, i, bits)
if code==CODEEOI:
break
elif code==CODECLEAR:
del table[CODESTART:]
bits = 9
max_code2 = (1<<bits) - 2
code, i = getword(bseq, i, bits)
old_str = table[code]
seq_append(old_str)
old_code = code
else:
l = table_len()
if code < l:
s = table[code]
table_append(old_str + s[0])
old_str = s
else:
old_str = old_str + old_str[0]
table_append(old_str)
seq_append(old_str)
old_code = code
if l==max_code2:
bits += 1
max_code2 = (1<<bits) - 2
return ''.join(seq)
#print 'backend:', default_backend
if default_backend=='bitarray':
encode = encode_bitarray
decode = decode_bitarray
def encode_array(arr):
return encode_bitarray(arr).toarray ()
if default_backend=='bittools':
encode = encode_array = encode_bittools
decode = decode_bittools
def test_lzw():
for s in ['TOBEORNOTTOBEORTOBEORNOT', '/WED/WE/WEE/WEB/WET'][:0]:
r = encode (s)
a = decode (r)
assert a==s,`a,s`
if 1:
f = open(__file__)
s = f.read ()
f.close ()
r = encode (s)
a = decode (r)
assert a==s
print 'ok'
import sys
import os
import time
for fn in sys.argv[1:]:
if not os.path.exists(fn):
continue
t0 = time.time()
f = open(fn, 'rb')
s = f.read()
f.close()
t = time.time()-t0
print 'Reading %s took %.3f seconds, bytes = %s' % (fn, t, len(s))
t0 = time.time()
r = encode(s)
t = time.time()-t0
sz = len(r)
if default_backend=='bitarray':
sz //= 8
print 'Encoding took %.3f seconds, compress ratio = %.3f, Kbytes per second = %.3f' % (t, len (s)/sz, len(s)/t/1024)
t0 = time.time()
s1 = decode(r)
t = time.time()-t0
print 'Decoding took %.3f seconds, Kbytes per second = %.3f' % (t, (sz/t)/1024)
assert s1==s
if __name__=='__main__':
test_lzw()
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