alpha channel webcam capture opencv c++

Question

I read a logitech c200 webcam on usb-port with this code in c++ with opencv:

Mat result;
IplImage* frame;
int hell=0;
int dunkel=0;
CvCapture* capture;
capture = 0;
capture = cvCaptureFromCAM( CV_CAP_ANY );
cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH, 320);
cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_HEIGHT, 240);

frame = cvQueryFrame( capture );

if( !frame ) break;
result = frame;
flip(result , result ,-1);

cvReleaseCapture( &capture );

for(int i = 0; i < 240; ++i){
    for(int j = 0; j < 320; ++j){ 

    if((result.at<Vec3b>(i,j)[1] > 230) && (result.at<Vec3b>(i,j)[0] > 230))
        { hell++;}
    else
        {dunkel++;}
    }
}

How can I get the alpha channel, in this case the [4] fourth element of one element in the Mat-Matrix in OpenCV?

Thanks for Help

Answer 1

there is no alpha channel in images from a webcam.

also, please use opencv's c++ api, the venerable c one is a dead end.

Answer 2

is there a possibility to read the alpha channel from a webcam? like the hsv-color model:

http://en.wikipedia.org/wiki/HSL_and_HSV

it's the hue(Farbton)