ValueError not enough values to unpack expected 3 got 1 in below code

Question

import cv2

import numpy as np

img=cv2.imread ("C:\\Users\\20pa1\\Downloads\\pawan_kalyan_teenmar_movie_stills06.jpg" , 0)

img=cv2.resize(img , (1200 , 780))

b,g,r=cv2.split(img)

cv2.imshow("green" , g)

cv2.imshow("red" , r)

cv2.imshow("blue" , b)

cv2.waitKey()

cv2.destroyAllWindows()