因为：

做yolov3-tiny的项目，我的训练数据都是BMP格式的

所以：

import os 
from PIL import Image 
import shutil 
import sys 

output_dirHR = 'jpg_out'

if not os.path.exists(output_dirHR):
    os.makedirs(output_dirHR)

def img2img(dataset_dir,type): 
    files = [] 
    image_list = os.listdir(dataset_dir) 
    files = [os.path.join(dataset_dir, _) for _ in image_list] 
    for index,bmp in enumerate(files):
        if index > 100000: 
            break
        try: 
            sys.stdout.write('\r>>Converting image %d/100000 ' % (index)) 
            sys.stdout.flush() 
            im = Image.open(bmp) 
            img = os.path.splitext(bmp)[0] + "." + type
            im.save(img) 
            shutil.move(img, output_dirHR) 
        except IOError as e: 
            print('could not read:',bmp) 
            print('error:',e) 
            print('skip it\n') 
    sys.stdout.write('Convert Over!\n') 
    sys.stdout.flush()

if __name__ == "__main__": 
    current_dir = os.getcwd() 
    print(current_dir)
    img2img(current_dir,'jpg')