Convert an image array to a binarized image with a specific threshehold

So, i am extracting pixel values of the three channels R, G, and B of an JPG image, and then I’m calculating some index using the three channels. Which gives me a numpy array : Indice

Here is my code:

import matplotlib.pyplot as plt
import numpy as np
import numpy

Image = plt.imread("/home/stagiaire/Bureau/image_mais_rgb.JPG")

blue = Image[:,:,0]
green = Image[:,:,1]
red= Image[:,:,2]

with np.errstate(divide='ignore'):
    r = red / red + green + blue 
    g = green / red + green + blue 
    b = blue / red + green + blue 

ExGRE = 2*g-r-b
ExRED = 1.4*r-b
Indice = ExGRE - ExRED
Indice_Image = Indice.astype(numpy.uint8)

Now I want to convert this image array to binarized image and to choose a threshehold near 0 (0.1 or 0.2). How can I do it in Python36 ?