@classmethod
def make_mask_outside(cls, mask, size, buffer=0):
    """Return labeled mask of area around bead."""
    if buffer > 0:
        mask_min = cls._morph_mask_step(buffer, mask)
    else:
        mask_min = mask
    mask_outside = cls._morph_mask_step(size, mask)
    mask_outside[mask_min > 0] = 0
    return mask_outside
