Converting TIF from RGB to Grayscale - python

So I am trying to convert RGB TIF file to grayscale. This is the Python code
%matplotlib inline
import numpy as np
import matplotlib.pyplot as plt
import tifffile as tfl
def rgb2gray(rgb):
return np.dot(rgb[...,:3], [0.2989, 0.587, 0.114])
imName = 'three_band/6120_2_0.tif'
im_rgb=tfl.imread(imName).transpose([1,2,0])
gray = rgb2gray(im_rgb)
plt.imshow(gray)
But when I try to view it using pyplot, I get a blue image like this
Can anyone point to what's wrong with my code?
Thanks.

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My intention is to use matplotlib to convert a coloured image into a grayscale image and use colormap to display it in the Viridis scale.
The code for that is as follows:
import numpy as np
import matplotlib.pyplot as plt
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The output displayed is proper and as follows:
Output Image
Now, I want to save the output image in a variable as a numpy array to carry out further processing. Can I do it in any way?

plt.imread() returns a 3-dimensional numpy array with RGB layers. Your rgb2gray() function returns a 2-dimensional numpy array with a grayscale image. There is no need to extract a numpy array from the object returned by plt.imshow() when you have two numpy arrays with the image data already. However, if you insist in doing it, you can try the following:
import numpy as np
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I'm trying to convert a grayscale image's pixels into a numpy array.
Working on google colab.
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enter code here
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import numpy as np
import matplotlib.pyplot as plt
import matplotlib.image as mpimg
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from scipy import misc #to see image
from sklearn.model_selection import train_test_split
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The conversion to grayscale code comes from https://stackoverflow.com/a/12201744/1092820
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import matplotlib.pyplot as plt
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