Helper method which loads dataset and determines clipping range.

    Args:
      dataset_dir: location of the dataset.
      epsilon: maximum allowed size of adversarial perturbation.

def _load_dataset_clipping(self, dataset_dir, epsilon):
    """Helper method which loads dataset and determines clipping range.

    Args:
      dataset_dir: location of the dataset.
      epsilon: maximum allowed size of adversarial perturbation.
    """
    self.dataset_max_clip = {}
    self.dataset_min_clip = {}
    self._dataset_image_count = 0
    for fname in os.listdir(dataset_dir):
      if not fname.endswith('.png'):
        continue
      image_id = fname[:-4]
      image = np.array(
          Image.open(os.path.join(dataset_dir, fname)).convert('RGB'))
      image = image.astype('int32')
      self._dataset_image_count += 1
      self.dataset_max_clip[image_id] = np.clip(image + epsilon,
                                                0,
                                                255).astype('uint8')
      self.dataset_min_clip[image_id] = np.clip(image - epsilon,
                                                0,
                                                255).astype('uint8')