Adjust Gain/Exposure in opencv on Jetson Nano

Autonomous Machines Jetson & Embedded Systems Jetson Nano
,
4

Note that ArgusCamera is not a real camera device, it is an application that manages a camera.
So by default it tries to auto-tune gains, exposure, whitebalance.
The real camera in case of RPi v2 Cam is a bayer RG10 device.

So if you turn off auto-tuning and set exposure to real device, it may work:

import cv2
import subprocess
import time

def gstreamer_pipeline(
    sensor_id=0,
    capture_width=1280,
    capture_height=720,
    display_width=640,
    display_height=480,
    framerate=30,
    flip_method=2,
):
    return (
        "nvarguscamerasrc sensor-id=%d gainrange=\"16 16\" ispdigitalgainrange=\"1 1\"  aelock=1 awblock=1 ! "
        "video/x-raw(memory:NVMM), width=(int)%d, height=(int)%d, framerate=(fraction)%d/1 ! "
        "nvvidconv flip-method=%d ! "
        "video/x-raw, width=(int)%d, height=(int)%d, format=(string)BGRx ! "
        "videoconvert ! "
        "video/x-raw, format=(string)BGR ! appsink max-buffers=1 drop=True"
        % (
            sensor_id,
            capture_width,
            capture_height,
            framerate,
            flip_method,
            display_width,
            display_height,
        )
    )

min_exposure = 13
max_exposure = 29999
exposure_step = 500
exposure = min_exposure


# Open Pi Camera
cap = cv2.VideoCapture(gstreamer_pipeline(sensor_id=0), cv2.CAP_GSTREAMER)

while cap.isOpened():
    # Grab frame
    ret, frame = cap.read()
    
    # Display if there is a frame
    if ret:
        cv2.imshow('Frame', frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
            
    start = time.time()
    subprocess.check_output(['v4l2-ctl', '--set-ctrl', 'exposure='+str(exposure)]).decode("utf-8")
    end = time.time()
    print('time to set exposure %f seconds' %(end - start))
    print(subprocess.check_output(['v4l2-ctl', '--get-ctrl', 'exposure']).decode("utf-8"))
    print(subprocess.check_output(['v4l2-ctl', '--get-ctrl', 'gain']).decode("utf-8"))
    
    exposure += exposure_step
    if exposure > max_exposure :
    	exposure = min_exposure

# Close everything
cap.release()
cv2.destroyAllWindows()

However, you’ll see that it takes more than one frame (~ 40 ms on Xavier-NX without boosting clocks), so it may not be suitable for changing exposure on each frame.

It may be possible to do that using v4l2 interface from python. I remember this post:

You may also try to see what is under the hood with strace:

sudo apt install strace
strace v4l2-ctl --set-ctrl exposure=55
....
ioctl(3, VIDIOC_S_EXT_CTRLS, {ctrl_class=V4L2_CTRL_CLASS_CAMERA, count=1, controls=[{id=0x9a200a /* V4L2_CID_??? */, size=0, value=55, value64=55}] => controls=[{id=0x9a200a /* V4L2_CID_??? */, size=0, value=55, value64=55}]}) = 0
....

Someone better skilled may further help.