How to do it...

Perform the following steps:

1. Import the packages:

import cv2
import numpy as np
import matplotlib.pyplot as plt

2. Read the image as grayscale:

image = cv2.imread('../data/Lena.png', 0)

3. Compute the gradient approximations using the Sobel operator:

dx = cv2.Sobel(image, cv2.CV_32F, 1, 0)
dy = cv2.Sobel(image, cv2.CV_32F, 0, 1)

4. Visualize the results:

plt.figure(figsize=(8,3))
plt.subplot(131)
plt.axis('off')
plt.title('image')
plt.imshow(image, cmap='gray')
plt.subplot(132)
plt.axis('off')
plt.imshow(dx, cmap='gray')
plt.title(r'$\frac{dI}{dx}$')
plt.subplot(133)
plt.axis('off')
plt.title(r'$\frac{dI}{dy}$')
plt.imshow(dy, cmap='gray')
plt.tight_layout()
plt.show()