Example translating matlab to Python.

mean_example.py

import cv2
import numpy as np
 
img1 = cv2.imread('NewCuyama.jpg')
img = cv2.cvtColor(img1, cv2.COLOR_BGR2GRAY)

# img is now a numpy array.

# Find the mean of all non-zero pixels.

avg = np.mean( img[img.nonzero()] )
print(img.shape)
print("Average", avg)

cv2.imshow('original',img)
cv2.waitKey(0)

# Set those below average to zero.

img[img <= avg] = 0
cv2.imshow('zero all below mean',img)
cv2.waitKey(0)

# Set pixels under 21% of mean to zero.

img = cv2.cvtColor(img1, cv2.COLOR_BGR2GRAY)
img[img <= 0.21*avg] = 0
cv2.imshow('zero below 21% of mean',img)
cv2.waitKey(0)