how expand rectangle after detected faces opencv

Question

I write code and i want How to expand the rectangle after the detection of the faces to up to the head and neck of human

    #include <opencv2/imgproc/imgproc.hpp>  //this code detetced faces ///
    #include <opencv2/objdetect/objdetect.hpp>///////////
    #include <opencv2/highgui/highgui.hpp>
     ////////////////////
    using namespace cv;
    using namespace std;

    int main()
    {

        CascadeClassifier cascade;

        if (!cascade.load("haarcascade_frontalface_alt2.xml"))  //load harcascade xml
            return -1;

         Mat src = imread("11.jpg");  //read image 

        if (src.empty())
            return -1;
    cv::resize(src,src,cv::Size(600,600));  resize image 
        Mat gray;
        cvtColor(src, gray, CV_BGR2GRAY);
        equalizeHist(gray, gray);

        vector<Rect> faces;
        cascade.detectMultiScale(gray, faces, 1.2, 3,0,Size(30,30));

        for (size_t i = 0; i < faces.size(); i++)
        {
     /////////////////////////////
            Rect r = faces[i];
    //////////////////////////////       

              Mat faceROI = gray( faces[i] );
          int x = faces[i].x;
          int y = faces[i].y;
          int h =0.3*y+faces[i].height;
          int w = faces[i].width;
          printf("Orig dimensions after h * w crop 1: %dx%d\n",h,w);
            printf("Orig dimensions after  x* y crop 2: %dx%d\n",x,y);

           rectangle(src,Point (x,y),Point(x + w,y +h),Scalar(255,0,255),1,4,0);
             imshow("mmmmmmmmmmm.jpg",src );  //show image in windows 
        }
    ///////////////////////////////

        waitKey(0);

        return 0;
    }

Answer 1

To expand the OpenCV faces rectangle, you can also use below operators(1) to cv::Rect class

//expanding or shrinking a rectangle by a certain amount
cv::Rect += cv::Size
//shifting a rectangle by a certain offset
cv::Rect -= cv::Point

Example for expanding face rectangle by 10% would be

cv::Size deltaSize( faces[i].width * 0.1f, faces[i].height * 0.1f ); // 0.1f = 10/100
cv::Point offset( deltaSize.width/2, deltaSize.height/2);
faces[i] += deltaSize;
faces[i] -= offset;

Answer 2

You need to adjust the height and starting y coordinate appropriately.

On a short look, I felt height of box should be increases by a factor of 0.3 on both the sides (top and bottom). So I subtracted 0.3*h from y and added 0.3*2*h (i.e. 0.6*h) to h.

It is just my rough calculation. For fine adjustment, you analyze it for different faces and come up with a measurement that best suits your purpose.

Here is the changed code:

int x = faces[i].x;
int h_temp = faces[i].height;    // storing original height
int y = faces[i].y - h_temp*0.3; // y is reduced by 0.3*h
int w = faces[i].width;
int h = h_temp*1.6;              // height is increases by 60%

And below is the result I got for example. Green shows original I got. Blue is the modified:

Remember, how much you want to select, depends on you. Make adjustments to above values to get your required result.