Motion Detection

Robotics 2
Motion Detection

To complete this lab activity, make a video that includes the following in one video:

(1) You saying your name
(2) Your Python figure output showing just the motion as you wave your hand past the screen.

In this video, we are learning about an approach to motion detection known as 'motion by difference'. In this method, we capture two images spaced in time by an amount 'delta t' and take the difference of the two images to find only what has changed between the two images. We also learn about 'Optical Flow', a method that uses masking to find the velocity of motion in an image.

import numpy as np
import cv2

cap=cv2.VideoCapture(0)

# params for ShiTomasi corner detection
feature_params = dict(maxCorners = 100,qualityLevel = 0.3,minDistance = 7,blockSize = 7)
   
# Parameters for lucas kanade optical flow
ak_params = dict(winSize  = (15,15),maxLevel = 2,criteria = (cv2.TERM_CRITERIA_EPS | cv2.TERM_CRITERIA_COUNT, 10, 0.03))
 
# Create some random colors
color = np.random.randint(0,255,(100,3))

# Take first frame and find corners in it
ret, old_frame = cap.read()
old_gray = cv2.cvtColor(old_frame, cv2.COLOR_BGR2GRAY)
p0 = cv2.goodFeaturesToTrack(old_gray, mask = None, **feature_params)

# Create a mask image for drawing purposes
mask = np.zeros_like(old_frame)

while(1):
    ret,frame = cap.read()
    frame_gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
   
    # calculate optical flow
    p1, st, err = cv2.calcOpticalFlowPyrLK(old_gray, frame_gray, p0, None, **ak_params)
 
    # Select good points
    good_new = p1[st==1]
    good_old = p0[st==1]

# draw the tracks
    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('frame',img)
    k = cv2.waitKey(30) & 0xff
    if k == 27:
        break
    # Now update the previous frame and previous points
    old_gray = frame_gray.copy()
    p0 = good_new.reshape(-1,1,2)
 
cv2.destroyAllWindows()
cap.release()