def square_frame_size(radius):
    """Compute the number of pixels of the external frame of square
    neighbourhoods of the given radii.

    Parameters
    ----------
    radius : list of int
        Radii of the local neighborhoods.

    Returns
    ----------
    points : list of int
        Number of pixels of the local neighborhoods.

    Examples
    --------
    >>> d = RankTransform(radius=[3])
    >>> square_frame_size(d.radius)
    [24]
    >>> square_frame_size([1, 2, 3])
    [8, 16, 24]

    """
    points = [8*r for r in radius]
    return points