calculo_entropia.py

   1 import math
   2 import sys
   3
   4 def calcular_entropia(bitstream):
   5     n = len(bitstream)
   6     if n == 0: return 0
   7
   8     p0 = bitstream.count('0') / n
   9     p1 = bitstream.count('1') / n
  10
  11     entropia = 0
  12     for p in [p0, p1]:
  13         if p > 0:
  14             entropia -= p * math.log2(p)
  15     return entropia
  16
  17 def calcular_entropia_condicional(bitstream):
  18     transicoes = {'00': 0, '01': 0, '10': 0, '11': 0}
  19     contagem_base = {'0': 0, '1': 0}
  20
  21     for i in range(len(bitstream) - 1):
  22         par = bitstream[i:i+2]
  23         transicoes[par] += 1
  24         contagem_base[bitstream[i]] += 1
  25
  26     h_condicional = 0
  27     for base in ['0', '1']:
  28         p_base = contagem_base[base] / (len(bitstream) - 1)
  29         if p_base > 0:
  30             h_local = 0
  31             for prox in ['0', '1']:
  32                 p_transicao = transicoes[base + prox] / contagem_base[base]
  33                 if p_transicao > 0:
  34                     h_local -= p_transicao * math.log2(p_transicao)
  35             h_condicional += p_base * h_local
  36
  37     return h_condicional
  38
  39 def clean_image_data(image_data):
  40
  41     clean_text = ""
  42
  43     for line in image_data:
  44         line = line.strip()
  45         line = line.replace(" ", "")
  46         if not line or line.startswith('#'):
  47             continue
  48         clean_text += line
  49
  50     return clean_text
  51
  52 with open(sys.argv[1], "r") as image:
  53         lines = image.readlines()
  54         image_data = clean_image_data(lines[2:])
  55
  56         h_x = calcular_entropia(image_data)
  57         h_condicional = calcular_entropia_condicional(image_data)
  58
  59         print(f"Entropia: {h_x:.4f} bits/pixel")
  60         print(f"Entropia Condicional: {h_condicional:.4f} bits/pixel")