work on optical flow sample

samples/python2/opt_flow.py

+import numpy as np
+import cv2, cv
+import video
+import sys
+
+try: fn = sys.argv[1]
+except: fn = video.presets['chess']
+
+cam = video.create_capture(fn)
+ret, prev = cam.read()
+#prev = cv2.pyrDown(prev)
+prevgray = cv2.cvtColor(prev, cv.CV_BGR2GRAY)
+
+def draw_flow(img, flow, step):
+    h, w = img.shape[:2]
+    y, x = map(np.ravel, np.mgrid[step/2:h:step, step/2:w:step])
+    f = flow[y,x]
+    x1 = x + f[:,0]
+    y1 = y + f[:,1]
+    #lines = np.int32( np.vstack([x, y, x1, y1]).T )
+    vis = cv2.cvtColor(img, cv.CV_GRAY2BGR)
+    #print lines
+    #cv2.polylines(vis, lines, 0, (0, 255, 0))
+    for x_, y_, x1_, y1_ in np.int32(zip(x, y, x1, y1)):
+        cv2.line(vis, (x_, y_), (x1_, y1_), (0, 255, 0))
+    return vis
+
+while True:
+    ret, img = cam.read()
+    #img = cv2.pyrDown(img)
+    gray = cv2.cvtColor(img, cv.CV_BGR2GRAY)
+    flow = cv2.calcOpticalFlowFarneback(prevgray, gray, 0.5, 3, 15, 3, 5, 1.2, 0)
+    prevgray = gray
+
+    cv2.imshow('flow', draw_flow(gray, flow, 16))
+    if cv2.waitKey(5) == 27:
+        break
+