tracking.py 文件源码

def _cam_setup(self, source, w, h, fps, exposure):
        cap = cv2.VideoCapture(source)
        if not cap.isOpened():
            return None

        atexit.register(cap.release)

        # Set width/height (note: this fails in OpenCV 2.4.x but works with 3.2)
        cap.set(cv2.CAP_PROP_FRAME_WIDTH, w)
        cap.set(cv2.CAP_PROP_FRAME_HEIGHT, h)

        # Read a frame, just in case it's needed before setting params
        rval, _ = cap.read()
        if not rval:
            cap.release()
            return None

        # Hacks using v4l2-ctl to set capture parameters we can't control through OpenCV
        v4l2args = []

        # Change AWB setting once to make sure new settings are actually used
        # Not sure why this is required, but it appears to work.
        # Without this, white balance is still somehow automatic even
        # after setting it to manual below.
        self._v4l2_call("--set-ctrl=white_balance_auto_preset=1")

        # Set FPS (OpenCV requests 30, hardcoded)
        v4l2args.append("-p %d" % fps)

        # Set exposure (shutter speed/ISO)
        # exposure_time_absolute is given in multiples of 0.1ms.
        # Make sure fps above is not set too high (exposure time
        # will be adjusted automatically to allow higher frame rate)
        v4l2args.append("--set-ctrl=auto_exposure=1")  # 0=auto, 1=manual
        v4l2args.append("--set-ctrl=exposure_time_absolute=%d" % exposure)

        v4l2args.append("--set-ctrl=white_balance_auto_preset=0")
        v4l2args.append("--set-ctrl=red_balance=1000")
        v4l2args.append("--set-ctrl=blue_balance=1000")

        self._v4l2_call(" ".join(v4l2args))

        logging.info("Set exposure via v4l2-ctl.  Capturing/dumping frames so settings take effect before tracking starts.")
        for _ in range(5):
            cap.read()

        return cap