old_contents: # coding=utf-8
  import cv2
  import numpy as np
  import random
  import os
  from argparse import ArgumentParser
  ALPHA = 5
  
  
  def build_parser():
      parser = ArgumentParser()
      parser.add_argument('--original', dest='ori', required=True)
      parser.add_argument('--image', dest='img', required=True)
      parser.add_argument('--result', dest='res', required=True)
      parser.add_argument('--alpha', dest='alpha', default=ALPHA)
      return parser
  
  
  def main():
      parser = build_parser()
      options = parser.parse_args()
      ori = options.ori
      img = options.img
      res = options.res
      alpha = options.alpha
      if not os.path.isfile(ori):
          parser.error("original image %s does not exist." % ori)
      if not os.path.isfile(img):
          parser.error("image %s does not exist." % img)
      decode(ori, img, res, alpha)
  
  
  def decode(ori_path, img_path, res_path, alpha):
      ori = cv2.imread(ori_path)
      img = cv2.imread(img_path)
      ori_f = np.fft.fft2(ori)
      img_f = np.fft.fft2(img)
      height, width = ori.shape[0], ori.shape[1]
      watermark = (ori_f - img_f) / alpha
      watermark = np.real(watermark)
      res = np.zeros(watermark.shape)
      random.seed(height + width)
      x = range(height / 2)
      y = range(width)
      random.shuffle(x)
      random.shuffle(y)
      for i in range(height / 2):
          for j in range(width):
              res[x[i]][y[j]] = watermark[i][j]
      cv2.imwrite(res_path, res, [int(cv2.IMWRITE_JPEG_QUALITY), 100])
  
  
  if __name__ == '__main__':
      main()
new_contents: # coding=utf-8
  import cv2
  import numpy as np
  import random
  import os
  from argparse import ArgumentParser
  ALPHA = 5
  
  
  def build_parser():
      parser = ArgumentParser()
      parser.add_argument('--original', dest='ori', required=True)
      parser.add_argument('--image', dest='img', required=True)
      parser.add_argument('--result', dest='res', required=True)
      parser.add_argument('--alpha', dest='alpha', default=ALPHA)
      return parser
  
  
  def main():
      parser = build_parser()
      options = parser.parse_args()
      ori = options.ori
      img = options.img
      res = options.res
      alpha = float(options.alpha)
      if not os.path.isfile(ori):
          parser.error("original image %s does not exist." % ori)
      if not os.path.isfile(img):
          parser.error("image %s does not exist." % img)
      decode(ori, img, res, alpha)
  
  
  def decode(ori_path, img_path, res_path, alpha):
      ori = cv2.imread(ori_path)
      img = cv2.imread(img_path)
      ori_f = np.fft.fft2(ori)
      img_f = np.fft.fft2(img)
      height, width = ori.shape[0], ori.shape[1]
      watermark = (ori_f - img_f) / alpha
      watermark = np.real(watermark)
      res = np.zeros(watermark.shape)
      random.seed(height + width)
      x = range(height / 2)
      y = range(width)
      random.shuffle(x)
      random.shuffle(y)
      for i in range(height / 2):
          for j in range(width):
              res[x[i]][y[j]] = watermark[i][j]
      cv2.imwrite(res_path, res, [int(cv2.IMWRITE_JPEG_QUALITY), 100])
  
  
  if __name__ == '__main__':
      main()
  
subject: fix alpha