Find X and Y coordinates of point in relation to the whole image

Question

I trying to find nose tip landmark inside 2D image. It's not working 100% correct, but as first approach it fully satisfy me.

vector<Rect> noses;
vector<Rect> faces;
vector<Rect> eyes;
Mat frame_gray;
Mat matched_frame; //frame with matched face
Mat gray;
Rect region_of_interest;

cvtColor(frame, frame_gray, COLOR_BGR2GRAY);

face_cascade.detectMultiScale(frame_gray, faces, 1.1, 2, 0 | CASCADE_SCALE_IMAGE, Size(30, 30));

for (int i = 0; i < faces.size(); i++)
{
        Point pt1(faces[i].x, faces[i].y); // Display detected faces on main window - live stream from camera
        Point pt2((faces[i].x + faces[i].height), (faces[i].y + faces[i].width));
        rectangle(frame, pt1, pt2, Scalar(255,0 , 0), 2, 8, 0);

        cvtColor(frame, frame_gray, COLOR_BGR2GRAY);
        equalizeHist( frame_gray, frame_gray );

        //NOSE TIP DETECTION
        Rect noseROI1;
        noseROI1.x = (faces[i].x);
        noseROI1.y = faces[i].y + (faces[i].height/2.5);
        noseROI1.width = (faces[i].width);
        noseROI1.height = (faces[i].height/2.8);

        Point ptNoseX(noseROI1.x, noseROI1.y);
        Point ptNoseY(noseROI1.x+noseROI1.width, noseROI1.y+noseROI1.height);
        //Rectangle around region of interest concentrated on nose
        rectangle(frame, ptNoseX,ptNoseY, Scalar(0,255,255), 2, 2, 0);

        Mat image_roi_nose = frame(noseROI1);

        nose_cascade.detectMultiScale(image_roi_nose, noses, 1.1, 2, 0 | CASCADE_SCALE_IMAGE, Size(40, 30));

        for (int i = 0; i < noses.size(); i++)
        {
            region_of_interest.x = noses[i].x;
            region_of_interest.y = noses[i].y;
            region_of_interest.width = (noses[i].width);
            region_of_interest.height = (noses[i].height);

            matched_frame = frame(region_of_interest);

            cvtColor(matched_frame, gray, CV_BGR2GRAY);

            Point pt1(noses[i].x, noses[i].y);
            Point pt2((noses[i].x + noses[i].height), (noses[i].y + noses[i].width));
            rectangle(image_roi_nose, pt1, pt2, Scalar(0, 255, 0), 2, 8, 0);

            int x1 = noses[i].x + (noses[i].height/2);
            int y1 = noses[i].y + (noses[i].width/2);


            circle(image_roi_nose, Point(x1, y1), 2, CV_RGB(255,0,0),2, 8, 0);
        }

This code finds nose tip, but it returns me x1 and y1 in relation to Mat image_roi_nose, how can I calculate coordinates of this point in relation to whole image?? If my question is unclear, please let me know I will try to explain it with more details.

Thank You all for help!

Answer 1

x = x1 + noseROI1.x;
y = y1 + noseROI1.y;