convert image to grayscale python

How can I convert an RGB image into grayscale in Python?

stackoverflow.com › questions › 12201577 › how-can-i-convert-an-rgb-image-into-grayscale-in-python

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()

Answer from unutbu on Stack Overflow

Stack Overflow

stackoverflow.com › questions › 12201577 › how-can-i-convert-an-rgb-image-into-grayscale-in-python

matplotlib - How can I convert an RGB image into grayscale in Python? - Stack Overflow

Top answer

1 of 16

490

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()

2 of 16

101

You can also use scikit-image, which provides some functions to convert an image in ndarray, like rgb2gray.

from skimage import color
from skimage import io

img = color.rgb2gray(io.imread('image.png'))

Notes: The weights used in this conversion are calibrated for contemporary CRT phosphors: Y = 0.2125 R + 0.7154 G + 0.0721 B

Alternatively, you can read image in grayscale by:

from skimage import io
img = io.imread('image.png', as_gray=True)

GeeksforGeeks

geeksforgeeks.org › python › python-grayscaling-of-images-using-opencv

Python | Grayscaling of Images using OpenCV - GeeksforGeeks

September 23, 2025 - In this method, we can directly load an image in grayscale mode by passing the flag 0 to cv2.imread(). This saves us from having to convert the image separately after loading.

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