我无法在 Opencv 上更改分辨率实时视频

Question

Hi I want to Change live video frame in shape before while loop my webcam default resolution 640x480. When i run it say "(480, 640, 3)" it still default resolution

......
ret, frame1 = cap.read()
cropped1 = frame1[0:240, 0:320]
ret, cropped1 = cap.read()
ret, frame2 = cap.read()
print(cropped1.shape)
while cap.isOpened():

    diff = cv2.absdiff(cropped1, frame2)
    gray = cv2.cvtColor(diff, cv2.COLOR_BGR2GRAY)
    blur = cv2.GaussianBlur(gray, (5,5), 0)
    _, thresh = cv2.threshold(blur, 20, 255, cv2.THRESH_BINARY)
    dilated = cv2.dilate(thresh, None, iterations=3)
    contours, _ = cv2.findContours(dilated, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
    ......

Answer 1

Finally i did it!!!

...
ret, frame1 = cap.read()
ret, frame2 = cap.read()
print(frame1.shape)
while cap.isOpened():

    diff = cv2.absdiff(frame1, frame2) # 640x480 frame
    diff2 = diff[0:240, 0:320]         # Top Left
    diff3 = diff[0:240, 320:640]       # Top Right
    diff4 = diff[240:640, 0:320]       # Down Left
    diff5 = diff[240:480, 320:640]     # Down Right
    gray2 = cv2.cvtColor(diff2, cv2.COLOR_BGR2GRAY)
    blur2 = cv2.GaussianBlur(gray2, (5,5), 0)
    _, thresh2 = cv2.threshold(blur2, 20, 255, cv2.THRESH_BINARY)
    dilated2 = cv2.dilate(thresh2, None, iterations=3)
    contours2, _ = cv2.findContours(dilated2, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

    gray3 = cv2.cvtColor(diff3, cv2.COLOR_BGR2GRAY)
    blur3 = cv2.GaussianBlur(gray3, (5,5), 0)
    _, thresh3 = cv2.threshold(blur3, 20, 255, cv2.THRESH_BINARY)
    dilated3 = cv2.dilate(thresh3, None, iterations=3)
    contours3, _ = cv2.findContours(dilated3, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
    .
    .
    .
    gray5 ...