//  [python]
def random_crop(images, flow=None, mask=None, crop_height=None, crop_width=None,
                relative_offset=0):
  """Performs a random crop with the given height and width."""
  # early return if crop_height or crop_width is not specified
  if crop_height is None or crop_width is None:
    return images, flow, mask

  orig_height = tf.shape(images)[-3]
  orig_width = tf.shape(images)[-2]

  # check if crop size fits the image size
  scale = 1.0
  ratio = tf.cast(crop_height, tf.float32) / tf.cast(orig_height, tf.float32)
  scale = tf.math.maximum(scale, ratio)
  ratio = tf.cast(crop_width, tf.float32) / tf.cast(orig_width, tf.float32)
  scale = tf.math.maximum(scale, ratio)
  # compute minimum required hight
  new_height = tf.cast(
      tf.math.ceil(tf.cast(orig_height, tf.float32) * scale), tf.int32)
  new_width = tf.cast(
      tf.math.ceil(tf.cast(orig_width, tf.float32) * scale), tf.int32)
  # perform resize (scales with 1 if not required)
  images = uflow_utils.resize(images, new_height, new_width, is_flow=False)

  # compute joint offset
  max_offset_h = new_height - tf.cast(crop_height, dtype=tf.int32)
  max_offset_w = new_width - tf.cast(crop_width, dtype=tf.int32)
  joint_offset_h = tf.random.uniform([], maxval=max_offset_h+1, dtype=tf.int32)
  joint_offset_w = tf.random.uniform([], maxval=max_offset_w+1, dtype=tf.int32)

  # compute relative offset
  min_relative_offset_h = tf.math.maximum(
      joint_offset_h - relative_offset, 0)
  max_relative_offset_h = tf.math.minimum(
      joint_offset_h + relative_offset, max_offset_h)
  min_relative_offset_w = tf.math.maximum(
      joint_offset_w - relative_offset, 0)
  max_relative_offset_w = tf.math.minimum(
      joint_offset_w + relative_offset, max_offset_w)
  relative_offset_h = tf.random.uniform(
      [], minval=min_relative_offset_h, maxval=max_relative_offset_h+1,
      dtype=tf.int32)
  relative_offset_w = tf.random.uniform(
      [], minval=min_relative_offset_w, maxval=max_relative_offset_w+1,
      dtype=tf.int32)

  # crop both images
  image_1, image_2 = tf.unstack(images)
  image_1 = tf.image.crop_to_bounding_box(
      image_1, offset_height=joint_offset_h, offset_width=joint_offset_w,
      target_height=crop_height, target_width=crop_width)
  image_2 = tf.image.crop_to_bounding_box(
      image_2, offset_height=relative_offset_h, offset_width=relative_offset_w,
      target_height=crop_height, target_width=crop_width)
  images = tf.stack([image_1, image_2])

  if flow is not None:
    # perform resize (scales with 1 if not required)
    flow, mask = uflow_utils.resize(
        flow, new_height, new_width, is_flow=True, mask=mask)

    # crop flow and mask
    flow = tf.image.crop_to_bounding_box(
        flow,
        offset_height=joint_offset_h,
        offset_width=joint_offset_w,
        target_height=crop_height,
        target_width=crop_width)
    mask = tf.image.crop_to_bounding_box(
        mask,
        offset_height=joint_offset_h,
        offset_width=joint_offset_w,
        target_height=crop_height,
        target_width=crop_width)

    # correct flow for relative shift (/crop)
    flow_delta = tf.stack(
        [tf.cast(relative_offset_h - joint_offset_h, tf.float32),
         tf.cast(relative_offset_w - joint_offset_w, tf.float32)])
    flow = (flow - flow_delta) * mask
  return images, flow, mask