Bridge light edges

import cv2
import matplotlib as plt
import numpy as np

pic = plt.imread("Unknown.jpg")
sobelx = cv2.Sobel(cv2.cvtColor(pic, cv2.COLOR_RGB2GRAY),cv2.CV_64F,1,0,ksize=11)
sobely = cv2.Sobel(cv2.cvtColor(pic, cv2.COLOR_RGB2GRAY),cv2.CV_64F,0,1,ksize=11)
edges = np.sqrt(sobelx ** 2 + sobely ** 2) > 5000000

pic2 = pic.astype(np.float)
pic2[edges] /= 255
pic2[edges] **= 1/3
pic2[edges] *= 255
pic2 = pic2.astype(np.uint8)

plt.imsave("bridge_light.png", pic2)