def convex_hull_resid(prop, **kwargs):
    """Return the ratio of the difference between convex area and area to convex area

    Args:
        prop (skimage.measure.regionprops):
            The property information for a cell returned by regionprops
        **kwargs:
            Arbitrary keyword arguments

    Returns:
        float:
            (convex area - area) / convex area
    """

    return (prop.convex_area - prop.area) / prop.convex_area