问我正在学习一个Opencv教程，但是我不确定cv2.absdiff(frame1，frame2)的用途，这是什么目的？

EN

    import cv2
import numpy as np

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

ret, frame1 = cap.read()
ret, frame2 = cap.read()


while cap.isOpened():
    diff = cv2.absdiff(frame1, frame2)
    gray = cv2.cvtColor(diff, cv2.COLOR_BGR2GRAY)
    blur = cv2.GaussianBlur(gray, (5,5), 0)
    _, thresh = cv2.threshold(blur, 20, 255, cv2.THRESH_BINARY)
    dilate = cv2.dilate(thresh, None, iterations=3)
    contour, _ = cv2.findContours(dilate, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

    cv2.drawContours(frame1, contour, -1, (0, 255, 0), 2)


    cv2.imshow('feed', frame1)

    frame1 = frame2
    ret, frame2 = cap.read()


    if cv2.waitKey(40) == 27:
        break

cv2.destroyAllWindows()
cap.release()