list_of_gifs = ['01','02','03','04','05','06','07','08','21','22','23','24','41']
base_path = 'http://www.vsj.jp/~pivstd/gif/'
base_name = 'image'
base_ext = '.gif'

for gif in list_of_gifs: 
    print('Reading ..')
    print(f'{base_path}{base_name}{gif}{base_ext}')
    im = imageio.get_reader(f'{base_path}{base_name}{gif}{base_ext}')
    # print(im)

    images = []
    for frame in im:
        images.append(frame)

    for I,J in zip(images[:-1],images[1:]):
        simple_piv(I,J)