code: def _get_output(self, a, image):
          
          sd = np.square(self._input_images - image)
          mses = np.mean(sd, axis=tuple(range(1, sd.ndim)))
          index = np.argmin(mses)
  
          # if we run into numerical problems with this approach, we might
          # need to add a very tiny threshold here
          if mses[index] > 0:
              raise ValueError('No precomputed output image for this image')
          return self._output_images[index]
docs: Looks up the precomputed adversarial image for a given image.