I am trying to build Motion Detector using openCV and python but display window is not responding when I terminate program

Question

Here is the code for the same, have a look at it. In this, below code I am creating a Motion Detector and with this I will be recording the timings of when the various objects appeared and disappeared for which I am using dataframe.

The issue with this is that the program executes but when the output is displayed in the form of a Window, it freezes when I try to terminate.

import cv2, pandas
from datetime import datetime

first_frame = None
status_list = [None,None]
times = []
df = pandas.DataFrame(columns=["Start", "End"]) #Dataframe to store the time values during which object detection and movement appears.


video = cv2.VideoCapture(0)#VideoCapture object is used to record video using web cam

while True:
    #check is a bool data type, returns true if VideoCapture object is read
    check,frame = video.read()
    status = 0
    gray = cv2.cvtColor(frame,cv2.COLOR_BGR2GRAY)  # For converting the frame color to gray scale
    gray = cv2.GaussianBlur(gray,(21,21),0)  # For converting the gray scale frame to GaussianBlur

    if first_frame is None:
        first_frame = gray   # used to store the first image/frame of the video
        continue
    delta_frame = cv2.absdiff(first_frame,gray)#calculates the difference between first and other frames
    thresh_delta = cv2.threshold(delta_frame,30,255,cv2.THRESH_BINARY)[1]
    thresh_delta = cv2.dilate(thresh_delta,None,iterations=0) #Provides threshold value, so if the difference is <30 it will turn to black otherwise if >30 pixels will turn to white
    (_,cnts,_) = cv2.findContours(thresh_delta.copy(),cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE) #Define the contour area,i.e. adding borders

    #Removing noises and shadows, any part which is greater than 1000 pixels will be converted to white
    for contour in cnts:
        if cv2.contourArea(contour) < 1000:
            continue
        status = 1 #change in status when the object is detected
        #Creating a rectangular box around the object in frame
        (x,y,w,h) = cv2.boundingRect(contour)
        cv2.rectangle(frame,(x,y),(x+w,y+h),(0,255,0),3)

    #list of status for every frame
    status_list.append(status)

    status_list=status_list[-2:]

    #Record datetime in a list when change occurs
    if status_list[-1]==1 and status_list[-2]==0:
        times.append(datetime.now())
    if status_list[-1]==0 and status_list[-2]==1:
        times.append(datetime.now())

    cv2.imshow('frame',frame)
    #cv2.imshow('Capturing',gray)
    #cv2.imshow('delta',delta_frame)
    #cv2.imshow('thresh',thresh_delta)

    key = cv2.waitKey(1) #changing the frame after 1 millisecond

    #Used for terminating the loop once 'q' is pressed
    if key == ord('q'):
        break

print(status_list)
print(times)

for i in range(0,len(times),2):
    df = df.append({"Start":times[i],"End":times[i+1]},ignore_index=True)

df.to_csv("Times.csv")

video.release()
cv2.destroyAllWindows #will be closing all the windows

welcome to SO. do you run mac, windows, linux? cv2 version? might be helpful. — user1269942, Nov 10 '18 at 06:33

score 0 · Answer 1 · answered Nov 10 '18 at 06:39

0

Try this:

if cv2.waitKey(1) & 0xFF == ord('q'):
    break

For a brief explanation about what "& 0xFF" is, see: What's 0xFF for in cv2.waitKey(1)?

It is basically a bit mask that takes the portion of 'waitKey' value(32 bit) that can be compared to ASCII (8 bit).

answered Nov 10 '18 at 06:39

user1269942

3,772
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I tried this code snippet but it did not work. Now I am not able to terminate the program by pressing 'q'. – Palash Sharma Nov 10 '18 at 19:29

score 0 · Answer 2 · edited Feb 17 '19 at 10:46

You can try this.

k = cv2.waitKey(1) & 0xFF
if k == 27 :        
     break

where k can be any ASCII code on the keyboard ASCII code help

In this case 27 is 'Esc' button.

However, the problem you're having where it is freezing, have you tried continuously pressing any button besides q? I had a similar problem when I was testing out OpenCV's tutorial code here

but i figured it out by playing around and then realizing i needed to hold down any button besides the 'exit' button.

score 0 · Answer 3 · answered Jan 24 '22 at 09:18

I had faced the same issue bcz of this piece of code from geeksforgeeks Please chck the last line of the code:

cv2.destroyAllWindows #will be closing all the windows

Add parenthesis, it shud b:

cv2.destroyAllWindows()

Please try this, rest looks fine Well you can also pass a particular frame that you want to close like:

cv2.destroyAllWindows("frame")

I am trying to build Motion Detector using openCV and python but display window is not responding when I terminate program

3 Answers3