webcam.py

import cv2
import numpy as np

cv2.namedWindow("preview")
vc = cv2.VideoCapture(0)

feature_params = dict(
    maxCorners = 100,
    qualityLevel = 0.01,
    minDistance = 7,
    blockSize = 7,
    useHarrisDetector = True,
)

lk_params = dict(
    winSize  = (15,15),
    maxLevel = 2,
    criteria = (cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 10, 0.03)
)

rval, frame = vc.read()
old_gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
p0 = cv2.goodFeaturesToTrack(old_gray, mask= None, **feature_params)
mask = np.zeros_like(frame)

color = np.random.randint(0,255,(100,3))
while rval:
    rval, frame = vc.read()
    frame_gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    p1, st, err = cv2.calcOpticalFlowPyrLK(old_gray, frame_gray, p0, None, **lk_params)
    print err

    good_new = p1[st==1]        
    good_old = p0[st==1]

    for i,(new,old) in enumerate(zip(good_new,good_old)):
        a,b = new.ravel()
        c,d = old.ravel()
        mask = cv2.line(mask, (a,b),(c,d), color[i].tolist(), 2)
        frame = cv2.circle(frame,(a,b),5,color[i].tolist(),-1)
    img = cv2.add(frame,mask)

    cv2.imshow("preview", frame)
    k = cv2.waitKey(30) & 0xff
    if k == 27:
        break

    old_gray = frame_gray.copy()
    p0 = good_new.reshape(-1,1,2)

cv2.destroyWindow("preview")