How can I resize an image where the face should be

Question

My webcam takes images. But opencv gender classification needs the images to be of the same size of that of the images used to train. So I need my webcam images to be 300x300 where the face in the webcam images would fit the resolution 300x300.
I have identified the face in the webcam image using opencv face cascade classifiers.
But how can I crop that face to fit in the size of 300x300?
Please help with some code lines as I am new to opencv.

Answer 1

Here a small sample that will help you to crop and resize your faces:

#include <opencv2\opencv.hpp>
using namespace cv;

int main()
{
     Mat3b img = imread("path_to_image");

    // You find the rectFace through face detection
    // Here the values are hardcoded
    Rect rectFace(235, 30, 45, 55);

    Mat3b detection = img.clone();
    rectangle(detection, rectFace, Scalar(0,255,0));

    // Crop the image
    Mat3b face(img(rectFace)); 

    // Resize the face to 300x300
    Mat3b resized;
    resize(face, resized, Size(300,300), 0.0, 0.0, INTER_LANCZOS4);

    // Apply gender classification on resized

    imshow("Detection", detection);
    imshow("Face", face);
    imshow("Resized", resized);
    waitKey();

    return 0;
}

Detected face:

Cropped face:

Resized face: