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

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]