cv2.calchist python

-images : it is the source image of type uint8 or float32 represented as “[img]”.
-channels : it is the index of channel for which we calculate histogram. For grayscale image, its value is [0] and
-color image, you can pass [0], [1] or [2] to calculate histogram of blue, green or red channel respectively.
-mask : mask image. To find histogram of full image, it is given as “None”.
-histSize : this represents our BIN count. For full scale, we pass [256].
-ranges : this is our RANGE. Normally, it is [0,256].

cv2.calcHist(images, channels, mask, histSize, ranges[, hist[, accumulate]])
################################################################################################
# importing required libraries of opencv 
import cv2 
  
# importing library for plotting 
from matplotlib import pyplot as plt 
  
# reads an input image 
img = cv2.imread('ex.jpg',0) 
  
# find frequency of pixels in range 0-255 
histr = cv2.calcHist([img],[0],None,[256],[0,256]) 
  
# show the plotting graph of an image 
plt.plot(histr) 
plt.show()