图像对比度减弱变换

import cv2
import numpy as np
import matplotlib.pyplot as plt
img=cv2.imread("C:/Users/xpp/Desktop/Lena.png")
grayImage=cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
height,width=grayImage.shape[:2]
result=np.zeros((height,width),np.uint8)
#图像灰度上移变换
for i in range(height):
    for j in range(width):
        if int(grayImage[i,j]*0.8+50)>255:
            gray=255
        else:
            gray=grayImage[i,j]*0.8+50
        result[i,j]=np.uint8(gray)
cv2.imshow("original",grayImage)
cv2.imshow("result",result)
if cv2.waitKey()==27:
    cv2.destroyAllWindows()