hatching based of maximum of 3 different arrays

[ThomasL]

untested

import numpy as np

A = np.random.randint(0, 255, size=(72,144))
B = np.random.randint(0, 255, size=(72,144))
C = np.random.randint(0, 255, size=(72,144))

colormap = np.zeros((72,144,3), dtype='uint8')
colormap[(A>B) & (A>C),0] = 255 # red
colormap[(B>A) & (B>C),1] = 255 # green
colormap[(C>A) & (C>B),2] = 255 # blue