Python改变图片类型

import PIL.Image
import os
i=0
path = "./dice2/"
savepath = "./dice2/"
filelist = os.listdir(path)
for file in filelist:
    im = PIL.Image.open(path+filelist[i])
    filename = os.path.splitext(file)[0]
    im.save(savepath+filename+'.png') # or 'test.tif'
    i = i+1