code: def split_input(img):
      
      # split the image into left + right pairs
      s = img.shape[0]
      assert img.shape[1] == 2 * s
      input, output = img[:, :s, :], img[:, s:, :]
      if args.mode == 'BtoA':
          input, output = output, input
      if IN_CH == 1:
          input = cv2.cvtColor(input, cv2.COLOR_RGB2GRAY)[:, :, np.newaxis]
      if OUT_CH == 1:
          output = cv2.cvtColor(output, cv2.COLOR_RGB2GRAY)[:, :, np.newaxis]
      return [input, output]
docs: img: an RGB image of shape (s, 2s, 3).
      :return: [input, output]