Inverting the image colour using OpenCV in Python

import numpy as np
import cv2

img=cv2.imread("C:/Users/ASUS/Desktop/images/google.jpg",0)
height=img.shape[0]
width=img.shape[1]
cv2.imwrite("C:/Users/ASUS/Desktop/images/grayscalegoogle.jpg",img)
maxintensity=255

for i in np.arange(height):
    for j in np.arange(width):
        a=img.item(i,j)     #Getting the pixel value
        b=maxintensity-a
        img.itemset((i,j),b)   #Setting new pixel value to b
       
cv2.imwrite("C:/Users/ASUS/Desktop/images/invertgoogle.jpg",img)
cv2.imshow('Invertedimage',img)     
cv2.waitKey(0)       #waits indefinitely for a keystroke
cv2.destroyAllWindows()

Original Image:

Grayscaled image:

Inverted image: