compare_pixels.py

import sys
from PIL import Image


def compare_pixels(png1, png2):
  pixels1 = list(png1.getdata())
  pixels2 = list(png2.getdata())
  if len(pixels1) != len(pixels2):
    return -1 # different pixel count
  match = 0
  mismatch = 0
  for i in range(0, len(pixels1)):
    if pixels1[i] == pixels2[i]:
      match = match + 1
    else:
      mismatch = mismatch + 1
  return match/(match+mismatch)


png1 = Image.open(sys.argv[1])
png2 = Image.open(sys.argv[2])
print(compare_pixels(png1,png2))