code: def _crop_box(self, size):
          
          (left, top) = self.offset
          right = left + min(size[0], self.width)
          bottom = top + min(size[1], self.height)
  
          return (left, top, right, bottom)
docs: Helper that calculates the crop box for the offset within the image.
  
          :param size: The width and height of the image composition.
          :type size: tuple
          :returns: The bounding box of the image, given ``size``.
          :rtype: tuple