["python","matplotlib"]
How can I convert an RGB image into grayscale in Python?

I'm trying to use matplotlib to read in an RGB image and convert it to grayscale. In matlab I use this: img = rgb2gray(imread('image.png')); In the matplotlib tutorial they don't cover it. They just read in the image import matplotlib.image as mpimg img = mpimg.imread('image.png') and then they slice the array, but that's not the same thing as converting RGB to grayscale from what I understand. lum_img = img[:,:,0] I find it hard to believe that numpy or matplotlib doesn't have a built-in function to convert from rgb to gray. Isn't this a common operation in image processing? I wrote a very simple function that works with the image imported using imread in 5 minutes. It's horribly inefficient, but that's why I was hoping for a professional implementation built-in. Sebastian has improved my function, but I'm still hoping to find the built-in one. matlab's (NTSC/PAL) implementation: import numpy as np def rgb2gray(rgb): r, g, b = rgb[:,:,0], rgb[:,:,1], rgb[:,:,2] gray = 0.2989 * r + 0.5870 * g + 0.1140 * b return gray
How about doing it with Pillow: from PIL import Image img = Image.open('image.png').convert('L') img.save('greyscale.png') If an alpha (transparency) channel is present in the input image and should be preserved, use mode LA: img = Image.open('image.png').convert('LA') Using matplotlib and the formula Y' = 0.2989 R + 0.5870 G + 0.1140 B you could do: import numpy as np import matplotlib.pyplot as plt import matplotlib.image as mpimg def rgb2gray(rgb): return np.dot(rgb[...,:3], [0.2989, 0.5870, 0.1140]) img = mpimg.imread('image.png') gray = rgb2gray(img) plt.imshow(gray, cmap=plt.get_cmap('gray'), vmin=0, vmax=1) plt.show()