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I am running the code faceDetect.cpp , i need to count how many people are beign detected , i can detect how many people are in in the same frame by incrementing a variable for each face detected but in the case for example if the person appear , disapear and re-appear i couldn't find a way to count it as just one person the complete code can be found here

https://github.com/Itseez/opencv/blob/master/samples/cpp/facedetect.cpp

we are interrested in this part of the code (the function detectAndDraw) where the face and the eye are beign detected

void detectAndDraw( Mat& img, CascadeClassifier& cascade,
                CascadeClassifier& nestedCascade,
                double scale, bool tryflip )
{
    int i = 0;
    double t = 0;
    vector<Rect> faces, faces2;
    const static Scalar colors[] =  { CV_RGB(0,0,255),
        CV_RGB(0,128,255),
        CV_RGB(0,255,255),
        CV_RGB(0,255,0),
        CV_RGB(255,128,0),
        CV_RGB(255,255,0),
        CV_RGB(255,0,0),
        CV_RGB(255,0,255)} ;
    Mat gray, smallImg( cvRound (img.rows/scale), cvRound(img.cols/scale), CV_8UC1 );

cvtColor( img, gray, COLOR_BGR2GRAY );
resize( gray, smallImg, smallImg.size(), 0, 0, INTER_LINEAR );
equalizeHist( smallImg, smallImg );

t = (double)cvGetTickCount();
cascade.detectMultiScale( smallImg, faces,
    1.1, 2, 0
    //|CASCADE_FIND_BIGGEST_OBJECT
    //|CASCADE_DO_ROUGH_SEARCH
    |CASCADE_SCALE_IMAGE
    ,
    Size(30, 30) );
if( tryflip )
{
    flip(smallImg, smallImg, 1);
    cascade.detectMultiScale( smallImg, faces2,
                             1.1, 2, 0
                             //|CASCADE_FIND_BIGGEST_OBJECT
                             //|CASCADE_DO_ROUGH_SEARCH
                             |CASCADE_SCALE_IMAGE
                             ,
                             Size(30, 30) );
    for( vector<Rect>::const_iterator r = faces2.begin(); r != faces2.end(); r++ )
    {
        faces.push_back(Rect(smallImg.cols - r->x - r->width, r->y, r->width, r->height));
    }
}
t = (double)cvGetTickCount() - t;
printf( "detection time = %g ms\n", t/((double)cvGetTickFrequency()*1000.) );
for( vector<Rect>::const_iterator r = faces.begin(); r != faces.end(); r++, i++ )
{
    Mat smallImgROI;
    vector<Rect> nestedObjects;
    Point center;
    Scalar color = colors[i%8];
    int radius;

    double aspect_ratio = (double)r->width/r->height;
    if( 0.75 < aspect_ratio && aspect_ratio < 1.3 )
    {
        center.x = cvRound((r->x + r->width*0.5)*scale);
        center.y = cvRound((r->y + r->height*0.5)*scale);
        radius = cvRound((r->width + r->height)*0.25*scale);
        circle( img, center, radius, color, 3, 8, 0 );
    }
    else
        rectangle( img, cvPoint(cvRound(r->x*scale), cvRound(r->y*scale)),
                   cvPoint(cvRound((r->x + r->width-1)*scale), cvRound((r->y + r->height-1)*scale)),
                   color, 3, 8, 0);
    if( nestedCascade.empty() )
        continue;
    smallImgROI = smallImg(*r);
    nestedCascade.detectMultiScale( smallImgROI, nestedObjects,
        1.1, 2, 0
        //|CASCADE_FIND_BIGGEST_OBJECT
        //|CASCADE_DO_ROUGH_SEARCH
        //|CASCADE_DO_CANNY_PRUNING
        |CASCADE_SCALE_IMAGE
        ,
        Size(30, 30) );
    for( vector<Rect>::const_iterator nr = nestedObjects.begin(); nr != nestedObjects.end(); nr++ )
    {
        center.x = cvRound((r->x + nr->x + nr->width*0.5)*scale);
        center.y = cvRound((r->y + nr->y + nr->height*0.5)*scale);
        radius = cvRound((nr->width + nr->height)*0.25*scale);
        circle( img, center, radius, color, 3, 8, 0 );
    }
}
cv::imshow( "result", img );

}

note that the color is changed every time a new face is detected , that is the case when multiple image are detected in the same frame , but i am interrested in one person where the color normally doesn't change

any hints ?