(This is a duplicate of my question at SO)
An analog framegrabber's image can be read via OpenCV 2.4.2 only after the demo-application has opened the grabber, otherwise a black image results. The following debug code
qDebug() << "Brightness" << cap->get(CV_CAP_PROP_BRIGHTNESS);
qDebug() << "Contrast " << cap->get(CV_CAP_PROP_CONTRAST);
qDebug() << "Saturation" << cap->get(CV_CAP_PROP_SATURATION);
qDebug() << "Hue " << cap->get(CV_CAP_PROP_HUE);
qDebug() << "Gain " << cap->get(CV_CAP_PROP_GAIN);
qDebug() << "Exposure " << cap->get(CV_CAP_PROP_EXPOSURE);
qDebug() << "Width " << cap->get(CV_CAP_PROP_FRAME_WIDTH);
qDebug() << "Height " << cap->get(CV_CAP_PROP_FRAME_HEIGHT);
outputs
Brightness 5000
Contrast 5000
Saturation 4000
Hue 5000
Gain -8.58993e+08
Exposure -1
Width 720
Height 576
Of course these settings seem defective, but they are the same when opening the device successfully after it has been accessed by the grabber's demo application.
I suppose this is a driver issue where certain device settings are required that OpenCV cannot access, including invalid standard settings (gain, exposure). What lower-level methods could be used to find out about / write those settings?