import numpy as np
import cv2 as cv
from matplotlib import pyplot as plt

img = cv.imread("lena.jpg")

b, g, r = cv.split(img)
cv.imshow("img", img)
cv.imshow("b", b)
cv.imshow("g", g)
cv.imshow("r", r)

plt.hist(b.ravel(), 256, [0, 256])
plt.hist(g.ravel(), 256, [0, 256])
plt.hist(r.ravel(), 256, [0, 256])

hist = cv.calcHist([img], [0], None, [256], [0, 256])
plt.plot(hist)
plt.show()

cv.waitKey(0)
cv.destroyAllWindows()