How to do it...

Perform the following steps:

1. Import all necessary modules:

import cv2
import numpy as np

2. Load an image and convert it to one with floating-point elements in range [0,1]:

image = cv2.imread('../data/Lena.png').astype(np.float32) / 255

3. Subtract the mean value from each image pixel to get a zero-mean matrix. Then, divide each pixel value by its standard deviation to have a unit-variance matrix:

image -= image.mean()
image /= image.std()