Python + OpenCV: generate Histograms of images

Python + OpenCv example run on Raspberry Pi 2 to generate Histograms of images, pyHist.py

from PIL import Image
import numpy as np
from matplotlib import pyplot as plt
import cv2

img = Image.open('photo.jpg')
#img = Image.open('b.png')
imgArr = np.asarray(img)

plt.subplot(221), plt.imshow(img)

color = ('r','g','b')
for i,col in enumerate(color):
    histr = cv2.calcHist([imgArr],[i],None,[256],[0,256])
    plt.subplot(222), plt.plot(histr,color = col)
    plt.xlim([0,256])

plt.xlim([0,256])

plt.show()

Reference: http://opencv-python-tutroals.readthedocs.org/en/latest/py_tutorials/py_imgproc/py_histograms/py_histogram_begins/py_histogram_begins.html