Histogram - Python(OpenCV)

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

img = cv.imread("lena.jpg")
#img = np.zeros((200, 200), np.uint8)
#cv.rectangle(img, (0, 100), (200, 200), (255), -1)
#cv.rectangle(img, (0, 50), (100, 100), (127), -1)

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

#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, 250])
#plt.hist(g.ravel(), 256, [0, 256])
#plt.hist(r.ravel(), 256, [0, 256])
plt.show()

cv.waitKey(0)
cv.destroyAllWindows()