docs: def filter_greys_using_image(image, target):
      """Filter out any values in target not in image
  
      :param image: image containing values to appear in filtered image
      :param target: the image to filter
      :rtype: 2d  :class:`numpy.ndarray` containing only value in image
          and with the same dimensions as target
  
      """
      maskbase = numpy.array(range(256), dtype=numpy.uint8)
      mask = numpy.where(numpy.in1d(maskbase, numpy.unique(image)), maskbase, 0)
      return mask[target]