Set camera paramter without reset of it

1

I need to change the cap_prop_auto_exposure by some condition of my app. The problem is when i call camera.set(cap_prop_auto_exposure), it does not work if i dont call camera.release and camera.open before.
In other words, i can change cameram’s parameters only once when i turn it on.
Is it true? Is there any to change parameters without reset of the camera?

2

what OS, or rather, what CAP backend?

3

windows 10 here.

DSHOW doesn’t do anything, cap.get returning -1.
MSMF does something, cap.get always returning 0.

range is 0 … 3 in case of V4L2 API. other backends treat it as a boolean.

import cv2 as cv
if True:
    cap = cv.VideoCapture(0) # apiPreference=cv.CAP_...
    assert cap.isOpened()
    def set_auto_exposure(value):
        cap.set(cv.CAP_PROP_AUTO_EXPOSURE, value)
        print("new value", cap.get(cv.CAP_PROP_AUTO_EXPOSURE))
    cv.namedWindow("cap")
    cv.createTrackbar("AUTO_EXPOSURE", "cap", 0, 3, set_auto_exposure)
    while True:
        ret, frame = cap.read()
        if not ret: break
        cv2.imshow("cap", frame)
        if cv2.waitKey(1) in (13, 27): # esc/enter
            break
    cap.release()
    cv.destroyAllWindows()
4

Thank for reply.
It is ubuntu 20.04 on jetson nvidia.

Cap.set is done on c++
I dont understand the “backend” you mentioned, what are dshow and msmf?