import numpy as np
import matplotlib.pyplot as plt

imga, imgb = plt.imread('NH A.png'), plt.imread('NH B.png')

if True:
    plt.figure()
    for i, img in enumerate((imga, imgb)):
        plt.subplot(2, 2, i+1)
        plt.imshow(img)

    for i, img in enumerate((imga, imgb)):
        plt.subplot(2, 2, i+1+2)
        imgmono = img[:, :, :3].sum(axis=2)
        plt.imshow(imgmono)

    plt.show()