from skimage import filters, color

img = io.imread('./bridge.jpg')

grey_img = color.rgb2gray(img)
geay_converted_img = filters.sobel(filters.median(grey_img, selem=np.ones((1,1))))
rgb_converted_img = color.gray2rgb(geay_converted_img)

img[rgb_converted_img < 0.15] = img[rgb_converted_img < 0.15] / 9