def create_anim(img_arr):
    img = []
    for i in range(img_arr.shape[2]):
        im = plt.imshow(img_arr[:,:,i], animated=True, cmap='gray')
        img.append([im])
    return img


img = create_anim(img_arr) # img_arr is 3d array containing all the frames
fig = plt.figure()
ani = animation.ArtistAnimation(fig, img, interval=50, blit=False,
                                repeat_delay=None, repeat=False)

ani.save("movie.gif", fps=80, writer='imagemagick')