motion vector opencv python

1import numpy as np
2import cv2
3
4cap = cv2.VideoCapture('slow.flv')
5
6# params for ShiTomasi corner detection
7feature_params = dict( maxCorners = 100,
8                       qualityLevel = 0.3,
9                       minDistance = 7,
10                       blockSize = 7 )
11
12# Parameters for lucas kanade optical flow
13lk_params = dict( winSize  = (15,15),
14                  maxLevel = 2,
15                  criteria = (cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 10, 0.03))
16
17# Create some random colors
18color = np.random.randint(0,255,(100,3))
19
20# Take first frame and find corners in it
21ret, old_frame = cap.read()
22old_gray = cv2.cvtColor(old_frame, cv2.COLOR_BGR2GRAY)
23p0 = cv2.goodFeaturesToTrack(old_gray, mask = None, **feature_params)
24
25# Create a mask image for drawing purposes
26mask = np.zeros_like(old_frame)
27
28while(1):
29    ret,frame = cap.read()
30    frame_gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
31
32    # calculate optical flow
33    p1, st, err = cv2.calcOpticalFlowPyrLK(old_gray, frame_gray, p0, None, **lk_params)
34
35    # Select good points
36    good_new = p1[st==1]
37    good_old = p0[st==1]
38
39    # draw the tracks
40    for i,(new,old) in enumerate(zip(good_new,good_old)):
41        a,b = new.ravel()
42        c,d = old.ravel()
43        mask = cv2.line(mask, (a,b),(c,d), color[i].tolist(), 2)
44        frame = cv2.circle(frame,(a,b),5,color[i].tolist(),-1)
45    img = cv2.add(frame,mask)
46
47    cv2.imshow('frame',img)
48    k = cv2.waitKey(30) & 0xff
49    if k == 27:
50        break
51
52    # Now update the previous frame and previous points
53    old_gray = frame_gray.copy()
54    p0 = good_new.reshape(-1,1,2)
55
56cv2.destroyAllWindows()
57cap.release()
58