def show_all_circles(image, cx, cy, rad, color='r'):
    """
    image: numpy array representing the grayscale image
    cx, cy: numpy arrays or lists, centers of the circles
    rad: numpy array or list radius of the circle
    """
    import matplotlib.pyplot as plt
    from matplotlib.patches import Circle

    fig, ax=plt.subplots()
    ax.set_aspect('equal')
    ax.imshow(image, cmap='gray')
    for x, y, r in zip(cx, cy, rad):
        circ=Circle((x, y), r, color=color, fill=False)
        ax.add_patch(circ)

    plt.title('%i circles' %len(cx))
    plt.show()