chore: import upstream snapshot with attribution

samples/python/color_histogram.py

@@ -0,0 +1,73 @@
+#!/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()