Answers for "how to save a grayscale image in python"

save an image in python as grayscale cv2

cv2.imwrite('data/dst/lena_opencv_red.jpg', im)

Image to grayscale using python

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.image as mpimg

def rgb2gray(rgb):
    return np.dot(rgb[...,:3], [0.299, 0.587, 0.144])

img = mpimg.imread('img.png')

gray = rgb2gray(img)

plt.imshow(gray, cmap='gray')

plt.savefig('greyscale.png')
plt.show()