How to track the position of the face in OpenCV using C++?

When we want to track the position of the face, it is better to enclose the face with ellipse because an ellipse has a center. This center is also the center point of the detected face. As result, tracking the position of detected face becomes more accurate.

The following program tracks the center of detected face and show the position in console window −


//This header includes definition of 'rectangle()' function//
//This header includes the definition of Cascade Classifier//
using namespace std;
using namespace cv;
int main(int argc, char** argv){
   Mat image_with_humanface;//Declaring a matrix to load image with human faces//
   image_with_humanface = imread("person.jpg");//loading an image that contains human face in it//
   namedWindow("Face Detection");//Declaring an window to show the result//
   string trained_classifier_location = "C:/opencv/sources/data/haarcascades/haarcascade_frontalface_alt.xml";//Defining the location our XML Trained Classifier in a string//
   CascadeClassifier faceDetector;//Declaring an object named 'face detector' of CascadeClassifier class//
   faceDetector.load(trained_classifier_location);//loading the XML trained classifier in the object//
   vector<Rect>faces;//Declaring a rectangular vector named faces//
   faceDetector.detectMultiScale(image_with_humanface, faces, 1.1, 4, CASCADE_SCALE_IMAGE,Size(20,20));//Detecting the faces in 'image_with_humanfaces' matrix//
   for (int i = 0; i < faces.size(); i++){ //Initiating for loop to detect the largest face//
      Point center(faces[i].x + faces[i].width * 0.5, faces[i].y + faces[i].height * 0.5);//getting the center of the face//
      ellipse(image_with_humanface, center, Size(faces[i].width * 0.5, faces[i].height * 0.5), 0, 0, 360, Scalar(255, 0, 255), 4, 8, 0);//draw an ellipse on the face//
      int horizontal = (faces[i].x + faces[i].width * 0.5);//Getting the horizontal value of coordinate//
      int vertical = (faces[i].y + faces[i].width * 0.5);//Getting the vertical value of coordinate//
   cout << "Position of the face is at(x,y)=" << " ("<<CAP_PROP_XI_DECIMATION_HORIZONTAL<<","<<CAP_PROP_XI_DECIMATION_VERTICAL<<")"<< endl;//
   imshow("Face Detection", image_with_humanface);//Showing the largest face face//
   waitKey(0);//To wait for keystroke to terminate the program
   return 0;