Sobel filter

import numpy as np
from skimage.io import imread
from skimage.color import rgb2gray
import matplotlib.pyplot as plt
 
input_pixels = np.array(rgb2gray(imread('resources/city.jpg'))*256, dtype=np.uint8)
plt.axis("off")
plt.imshow(input_pixels, cmap="gray")
 
kernel_horizontal = np.array([[-1, 0, 1], 
                              [-2, 0, 2], 
                              [-1, 0, 1]], dtype = np.float)
 
kernel_vertical   = np.array([[1, 2, 1], 
                              [0, 0, 0], 
                              [-1, -2, -1]], dtype = np.float)
 
from scipy import signal
 
Gx = signal.convolve2d(input_pixels, kernel_horizontal, boundary='symm', mode='same')
Gy = signal.convolve2d(input_pixels, kernel_vertical, boundary='symm', mode='same')
 
gradient_magnitude = np.sqrt(Gx * Gx + Gy * Gy)
gradient_magnitude *= 255.0 / np.max(gradient_magnitude)
 
plt.imshow(gradient_magnitude, cmap="gray")