text: #!/usr/bin/env python
  
  '''
  Video histogram sample to show live histogram of video
  
  Keys:
      ESC    - exit
  
  '''
  
  # Python 2/3 compatibility
  from __future__ import print_function
  
  import numpy as np
  import cv2 as cv
  
  # built-in modules
  import sys
  
  # local modules
  import video
  
  class App():
  
      def set_scale(self, val):
          self.hist_scale = val
  
      def run(self):
          hsv_map = np.zeros((180, 256, 3), np.uint8)
          h, s = np.indices(hsv_map.shape[:2])
          hsv_map[:,:,0] = h
          hsv_map[:,:,1] = s
          hsv_map[:,:,2] = 255
          hsv_map = cv.cvtColor(hsv_map, cv.COLOR_HSV2BGR)
          cv.imshow('hsv_map', hsv_map)
  
          cv.namedWindow('hist', 0)
          self.hist_scale = 10
  
          cv.createTrackbar('scale', 'hist', self.hist_scale, 32, self.set_scale)
  
          try:
              fn = sys.argv[1]
          except:
              fn = 0
          cam = video.create_capture(fn, fallback='synth:bg=baboon.jpg:class=chess:noise=0.05')
  
          while True:
              _flag, frame = cam.read()
              cv.imshow('camera', frame)
  
              small = cv.pyrDown(frame)
  
              hsv = cv.cvtColor(small, cv.COLOR_BGR2HSV)
              dark = hsv[...,2] < 32
              hsv[dark] = 0
              h = cv.calcHist([hsv], [0, 1], None, [180, 256], [0, 180, 0, 256])
  
              h = np.clip(h*0.005*self.hist_scale, 0, 1)
              vis = hsv_map*h[:,:,np.newaxis] / 255.0
              cv.imshow('hist', vis)
  
              ch = cv.waitKey(1)
              if ch == 27:
                  break
  
          print('Done')
  
  
  if __name__ == '__main__':
      print(__doc__)
      App().run()
      cv.destroyAllWindows()
  