How does python convert an RGB image to a pytho grayscale image?

I'm trying to use the matplotlib read RGB image and convert it to grayscale.
In MATLAB, I use this:

1	img =rgb2gray(imread(‘image.png‘));

In the Matplotlib tutorial they did not cover it. They just read in the image

12	importmatplotlib.image as mpimgimg =mpimg.imread(‘image.png‘)

Then they slice the array, but this is not from what I know to convert RGB to grayscale.

1	lum_img =img[:,:,0]

Edit:
I find it hard to believe that numpy or matplotlib does not have built-in functions to convert from RGB to gray. Is this not a common operation in image processing?
I have written a very simple function that can use imported images within 5 minutes imread . This is very inefficient, but that's why I want a built-in professional implementation.
Sebastian has improved my functionality, but I still want to find a built-in one.
MATLAB (Ntsc/pal) Implementation:

12345678

importnumpy as npdefrgb2gray(rgb):    r, g, b =rgb[:,:,0], rgb[:,:,1], rgb[:,:,2]    gray =0.2989*r +0.5870*g +0.1140* b    returngray

Reply:

How to use PiL

123	fromPIL import Imageimg =Image.open(‘image.png‘).convert(‘LA‘)img.save(‘greyscale.png‘)

Using Matplotlib and the formula

1	Y‘ =0.299 R + 0.587 G + 0.114B

You can do this:

1234567891011

importnumpy as npimportmatplotlib.pyplot as pltimport matplotlib.image as mpimgdefrgb2gray(rgb):    returnnp.dot(rgb[...,:3], [0.299, 0.587, 0.114])img = mpimg.imread(‘image.png‘)     gray =rgb2gray(img)    plt.imshow(gray, cmap =plt.get_cmap(‘gray‘))plt.show()

How does python convert an RGB image to a pytho grayscale image?