Python opencv(4) 调节图像亮度

import cv2
import numpy as np
fn = "baboon.jpg"
if __name__ == '__main__':
print 'loading %s ...' % fn
print 'processing...'
img = cv2.imread(fn)
w = img.shape[1]
h = img.shape[0]
ii = 0
#let image get darker
for xi in xrange(0,w):
for xj in xrange(0,h):
#set the pixel value decrease to 20%
img[xj,xi,0] = int(img[xj,xi,0]*0.2)
img[xj,xi,1] = int(img[xj,xi,0]*0.2)
img[xj,xi,2] = int(img[xj,xi,0]*0.2)
#show the process
if xi%10==0 :print '.',
cv2.namedWindow('img')
cv2.imshow('img',img)
cv2.waitKey()
cv2.destroyAllWindows()
print'.'
print 'processing'
for xi in xrange(0,w):
for xj in xrange(0,h):
##set the pixel value increase to 1020%
img[xj,xi,0] = int(img[xj,xi,0]*10.2)
img[xj,xi,1] = int(img[xj,xi,1]*10.2)
img[xj,xi,2] = int(img[xj,xi,2]*10.2)
#show the process
if xi%10==0 :print '.',
cv2.namedWindow('img')
cv2.imshow('img',img)
cv2.waitKey()
cv2.destroyAllWindows()