How to change contrast/brightness of a CAM using OpenCV 2.4.2

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Hey,

Please let me know how to change the brightness and contrast of a cam using OpenCV 2.4.2. I wrote a code, but there is no impact of using this code. Please let me know how to write the code.

I used like this.

    CvCapture *capture = cvCaptureFromCAM(CV_CAP_DSHOW);
if(!cvSetCaptureProperty(capture,CV_CAP_PROP_CONTRAST,0.7))
    AfxMessageBox("Not done.");
    while ( 1 ) 
{
         IplImage* frame = cvQueryFrame( capture );
         int c;
     cvNamedWindow("Image Display", CV_WINDOW_AUTOSIZE);
     while(1)
     {
    frame=cvQueryFrame(capture);
    cvShowImage("Image Display", frame );
         }
    }

Thanks