实现代码如下：

import os
import glob
from PIL import Image

root_dir = './image_net_mini'
dirs = os.listdir(root_dir)
for path in dirs:
    JPEG_list = glob.glob(root_dir + '/' + path + '/*.jpg')
    for jpeg in JPEG_list:
        img = Image.open(jpeg)
        if img.mode != 'RGB':
            img = img.convert('RGB')
            print(jpeg)
            os.remove(jpeg)
            img.save(jpeg)