example2_3_medianblur_findcontour.py

import cv2

#Download 'ExampleBGSubtraction.avi' from https://drive.google.com/file/d/1OD_A0wqN2Om2SusCztybu-_hMSUQuRt7/view?usp=sharing

cap = cv2.VideoCapture('ExampleBGSubtraction.avi')

haveFrame,bg = cap.read()

while(cap.isOpened()):
    haveFrame,im = cap.read()

    if (not haveFrame) or (cv2.waitKey(1) & 0xFF == ord('q')):
        break

    diffc = cv2.absdiff(im,bg)
    diffg = cv2.cvtColor(diffc,cv2.COLOR_BGR2GRAY)
    bwmask = cv2.inRange(diffg,50,255)

    bwmask_median = cv2.medianBlur(bwmask,5)

    contours,hierarchy = cv2.findContours(bwmask_median, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE) #for opencv 4.x.x
    #contourmask,contours,hierarchy = cv2.findContours(bwmask_median, cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE) #for opencv 3.2.x 3.4.x
    #contourmask,contours,hierarchy = cv2.findContours(bwmask_median.copy(), cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE) #for opencv 3.1.x

    cv2.drawContours(im, contours, -1, (0, 255, 0), 1)

    cv2.imshow('bwmask', bwmask)
    cv2.moveWindow('bwmask',10,10)
    cv2.imshow('bwmask_median', bwmask_median)
    cv2.moveWindow('bwmask_median', 400, 10)
    cv2.imshow('im', im)
    cv2.moveWindow('im', 800, 10)


cap.release()
cv2.destroyAllWindows()