title: How to find inflection point in python?
body: <p>I have a histogram of an image in RGB which represents the three curves of the three components R, G and B. I want to find the inflection points of each curve. I used the second derivative to find them but I can't, the second derivative does not cancel its returns null. So how can I find the inflection point? Is there any other method to find them?</p>
  <p><a href="https://i.stack.imgur.com/GF6zo.png" rel="noreferrer"><img src="https://i.stack.imgur.com/GF6zo.png" alt="enter image description here" /></a></p>
  <pre><code>import os, cv2, random
  import numpy as np
  import matplotlib.pyplot as plt
  import math
  from sympy import *
  
  image = cv2.imread('C:/Users/Xers/Desktop/img.jpg')
  
  CHANNELS = ['r', 'g', 'b']
  
  for i, channel in enumerate( CHANNELS ):
      
  
    histogram = cv2.calcHist([image], [i], None, [256], [0,256])
  
    histogram = cv2.GaussianBlur( histogram, (5,5), 0)
  
    plt.plot(histogram, color = channel)
  
       
    x= plt.xlim([0,256])
    y = plt.ylim([0, 24000])
  
  
    derivative1= np.diff(histogram, axis=0)
    derivative2= np.diff(derivative1, axis=0)
  
    inf_point = np.where ( derivative2 == 0)[0]
    print(inf_point)
  plt.show()
  </code></pre>