Hi everyone, I'm new to Python and OpenCV, using versions 3.4 and 3.0 respectively. I'm trying to use two USB webcams to grab 2 sets of frames each and then retrieve the frames. In this code the first two frames are taken with LEDs off, then the second two frames are taken with LEDs on. It is in a loop which runs 'nframes' number of times to produce 'nframes' final images 'framer' and 'framel'. 'nframes' is specified earlier in my code which I haven't included.

However when I use grab it seems to use a frame from before I call the command, so I think it has some buffer saved in its memory. I was getting around this by calling grab twice for each frame, however I'm sure there must be a more efficient way of clearing the memory. I've looked in the documentation and can't find anything about clearing the camera memory.

Here is my relevant code:

Define camera names

    cap1 = cv2.VideoCapture(0) # define right side as cap1
    cap2 = cv2.VideoCapture(1) # define left side as cap2

Background frame

           # turn LEDS off
        print('Get in position!')   
        print('Capture in progress...')
        myoutput.WriteAnalogScalarF64(True,timeout,0,None) # LEDs off
        time.sleep(1)
        #ret, framer1 = cap1.grab() # to throw
        #ret, framel1 = cap2.grab()
        retr1 = cap1.grab() # take background frame 
        retl1 = cap2.grab() 
        time.sleep(.5)

Waveguide frame

        # turn LEDS on
        myoutput.WriteAnalogScalarF64(True,timeout,5,None)
        time.sleep(.5)
        #ret, framer2 = cap1.grab() # to throw
        #ret, framel2 = cap2.grab()
        retr2 = cap1.grab()         # take a waveguide frame
        retl2 = cap2.grab()

        if retr1 == True and retl1 ==  True:
            pass
        else:
            print('Background frame error')
        if retr2 == True and retl2 ==  True:
            pass
        else:
            print('LED-on frame error')

Remove background light & write to file

        # Right
        retr1, framer1 = cap1.retrieve(retr1)
        retl1, framel1 = cap2.retrieve(retl1)
        retr2, framer2 = cap1.retrieve(retr2)
        retl2, framel2 = cap2.retrieve(retl2)
        framer = cv2.subtract(framer2,framer1)
        # Left
        framel = cv2.subtract(framel2,framel1)