img = cv2.imread('test.jpg')
hsv = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
h, s, v = cv2.split(hsv)
v += 255
final_hsv = cv2.merge((h, s, v))
img = cv2.cvtColor(final_hsv, cv2.COLOR_HSV2BGR)
cv2.imwrite('image_processed.jpg', img)
How to fast change image brightness with python + OpenCV?