opencv/samples/python/color_histogram.py

#!/usr/bin/env python

'''
Video histogram sample to show live histogram of video

Keys:
    ESC    - exit

'''

import numpy as np
import cv2

# built-in modules
import sys

# local modules
import video

if __name__ == '__main__':

    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 = cv2.cvtColor(hsv_map, cv2.COLOR_HSV2BGR)
    cv2.imshow('hsv_map', hsv_map)

    cv2.namedWindow('hist', 0)
    hist_scale = 10

    def set_scale(val):
        global hist_scale
        hist_scale = val
    cv2.createTrackbar('scale', 'hist', hist_scale, 32, set_scale)

    try:
        fn = sys.argv[1]
    except:
        fn = 0
    cam = video.create_capture(fn, fallback='synth:bg=../data/baboon.jpg:class=chess:noise=0.05')

    while True:
        flag, frame = cam.read()
        cv2.imshow('camera', frame)

        small = cv2.pyrDown(frame)

        hsv = cv2.cvtColor(small, cv2.COLOR_BGR2HSV)
        dark = hsv[...,2] < 32
        hsv[dark] = 0
        h = cv2.calcHist([hsv], [0, 1], None, [180, 256], [0, 180, 0, 256])

        h = np.clip(h*0.005*hist_scale, 0, 1)
        vis = hsv_map*h[:,:,np.newaxis] / 255.0
        cv2.imshow('hist', vis)

        ch = 0xFF & cv2.waitKey(1)
        if ch == 27:
            break
    cv2.destroyAllWindows()