RGB转化为gray

import os
from PIL import Image

path = "/Users/harry/Downloads/BSD500/gray/val"  # 文件路径
dir = sorted(os.listdir(path))
for file in dir:
    path = os.path.join(path, file)
    img = Image.open(path)
    gray = img.convert('L')
    gray.save(b)
    print(file, "ok")