# file for PS1, Python Task 3
import matplotlib.pyplot as p
import numpy,os
import PS1_tests
from PS1_1 import huffman
from PS1_2 import decode
if __name__ == '__main__':
# read in the image, convert into vector of pixels
img = p.imread('PS1_fax_image.png')
nrows,ncols,pixels = PS1_tests.img2pixels(img)
# convert the image into a sequence of alternating
# white and black runs, with a maximum run length
# of 255 (longer runs are converted into multiple
# runs of 255 followed by a run of 0 of the other
# color). So each element of the list is a number
# between 0 and 255.
runs = PS1_tests.pixels2runs(pixels,maxrun=255)
# now print out number of bits for pixel-by-pixel
# encoding and fixed-length encoding for runs
print "Baseline 0:"
print " bits to encode pixels:",pixels.size
print "\nBaseline 1:"
print " total number of runs:",runs.size
print " bits to encode runs with fixed-length code:",\
8*runs.size
print "\nBaseline 2:"
def compare(a, b) :
if len(a) != len(b) :
return False
for i in range(len(a)) :
if a[i] != b[i] :
return False
return True
if __name__ == '__main__':
# start by building Huffman tree from probabilities
plist = ((0.34,'A'),(0.5,'B'),(0.08,'C'),(0.08,'D'))
cdict = huffman(plist)
# test case 1: decode a simple message
message = ['A', 'B', 'C', 'D']
encoded_message = PS1_tests.encode(cdict,message)
decoded_message = decode(cdict,encoded_message)
assert message == decoded_message, \
"Decoding failed: expected %s, got %s" % \
(message,decoded_message)
# test case 2: construct a random message and encode it
message = [random.choice('ABCD') for i in xrange(100)]
encoded_message = PS1_tests.encode(cdict,message)
decoded_message = decode(cdict,encoded_message)
assert message == decoded_message, \
"Decoding failed: expected %s, got %s" % \
(message,decoded_message)
print "Tests passed!"
if len(a) != len(b):
return False
for i in range(len(a)):
if a[i] != b[i]:
return False
return True
if __name__ == '__main__':
# start by building Huffman tree from probabilities
plist = ((0.34, 'A'), (0.5, 'B'), (0.08, 'C'), (0.08, 'D'))
cdict = huffman(plist)
# test case 1: decode a simple message
message = ['A', 'B', 'C', 'D']
encoded_message = PS1_tests.encode(cdict, message)
decoded_message = decode(cdict, encoded_message)
assert message == decoded_message, \
"Decoding failed: expected %s, got %s" % \
(message,decoded_message)
# test case 2: construct a random message and encode it
message = [random.choice('ABCD') for i in xrange(100)]
encoded_message = PS1_tests.encode(cdict, message)
decoded_message = decode(cdict, encoded_message)
assert message == decoded_message, \
"Decoding failed: expected %s, got %s" % \
(message,decoded_message)
print "Tests passed!"
if type(left) == tuple:
codebook = tree_to_codebook(left, codebook, prefix + [0])
else:
codebook[left] = prefix + [0]
if type(right) == tuple:
codebook = tree_to_codebook(right, codebook, prefix + [1])
else:
codebook[right] = prefix + [1]
return codebook
if __name__ == '__main__':
# test case 1: four symbols with equal probability
PS1_tests.test_huffman(
huffman,
# symbol probabilities
((0.25, 'A'), (0.25, 'B'), (0.25, 'C'), (0.25, 'D')),
# expected encoding lengths
((2, 'A'), (2, 'B'), (2, 'C'), (2, 'D')))
# test case 2: example from section 22.3 in notes
PS1_tests.test_huffman(
huffman,
# symbol probabilities
((0.34, 'A'), (0.5, 'B'), (0.08, 'C'), (0.08, 'D')),
# expected encoding lengths
((2, 'A'), (1, 'B'), (3, 'C'), (3, 'D')))
# test case 3: example from Exercise 5 in notes
PS1_tests.test_huffman(
huffman,
# symbol probabilities
interium[-1][0] = interium[-2][0] + interium[-1][0]
for f in interium[-2][1] :
interium[-1][1].insert(0, f)
interium.pop(-2)
interium.sort(key=lambda x:x[0], reverse=True)
return rlt
if __name__ == '__main__':
# test case 1: four symbols with equal probability
PS1_tests.test_huffman(huffman,
# symbol probabilities
((0.25,'A'),(0.25,'B'),(0.25,'C'),
(0.25,'D')),
# expected encoding lengths
((2,'A'),(2,'B'),(2,'C'),(2,'D')))
# test case 2: example from section 22.3 in notes
PS1_tests.test_huffman(huffman,
# symbol probabilities
((0.34,'A'),(0.5,'B'),(0.08,'C'),
(0.08,'D')),
# expected encoding lengths
((2,'A'),(1,'B'),(3,'C'),(3,'D')))
# test case 3: example from Exercise 5 in notes
PS1_tests.test_huffman(huffman,
# symbol probabilities
((0.07,'I'),(0.23,'II'),(0.07,'III'),
