How to convert an image to grayscale using python ?

To convert an image to grayscale using python, a solution is to use PIL example:

from PIL import Image

img = Image.open('lena.png').convert('LA')
img.save('greyscale.png')

Note: the conversion to grayscale is not unique see l'article de wikipedia's article). It is also possible to convert an image to grayscale and change the relative weights on RGB colors, example:

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('lena.png')

gray = rgb2gray(img)

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

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

References