gray_multiple.py

import cv2
import os,glob
from os import listdir,makedirs
from os.path import isfile,join

path = 'resized/' # Source Folder
dstpath = 'gray/' # Destination Folder

try:
    makedirs(dstpath)
except:
    print ("The directory already exists, and the images will be written in the same folder")

files = [f for f in listdir(path) if isfile(join(path,f))]

for image in files:
    try:
        img = cv2.imread(os.path.join(path,image))
        gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
        dstPath = join(dstpath,image)
        cv2.imwrite(dstPath,gray)
    except:
        print ("{} is not converted".format(image))

for fil in glob.glob("*.png"):
    try:
        image = cv2.imread(fil)
        gray_image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
        cv2.imwrite(os.path.join(dstpath,fil),gray_image)
    except:
        print('{} is not converted')