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How to count the number of faces in OpenCV using C++?
Counting the number of faces located in an image is easy. The program we wrote in the previous section already have the information of number of faces in 'faces.size()'. This code-'faces.size()' gives an integer value.
For example, if we write 'int x = faces.size()', the 'x' will contain the number of faces.
The following program calculates the number of faces from a given image and shows it in console window.
Example
#include<iostream>
#include<opencv2/highgui/highgui.hpp>
#include<opencv2/objdetect/objdetect.hpp>
//This header includes the definition of Cascade Classifier//
#include<string>
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("friends.jpg");//loading an image that contains human face in it//
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//
int x = faces.size();//Calculating the number of faces and storing the integer value in x//
cout << "Number of face(s)in the image=" << x << endl;//Displaying the value of x in the console window//
system("pause");//Pausing the system to visualize the result//
return 0;
}Output
Updated on: 10-Mar-2021
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