This document discusses facial recognition using OpenCV in C++. It describes using Haar cascades, which is an object detection algorithm, to detect faces in images and video streams. It explains that Haar cascades use Haar-like features such as edges, lines, and changes in intensities to rapidly detect faces. Code examples are provided to load an image, detect faces using a pre-trained cascade model, and draw rectangles around the detected faces. Additional code shows how to perform real-time face detection on video camera streams.

1. www.luxoft.com
Facial Recognition with C++
Pavel Zhdanov

2. www.luxoft.com 2
www.luxoft.com
About Me

3. www.luxoft.com 3
www.luxoft.com
Algorithm
● Face detection
● Train a face recognition model
● Recognize faces in images (video streams) with OpenCV.

4. www.luxoft.com 4
www.luxoft.com
std::string path = "photo.png";
cv::Mat img = cv::imread(path);
cv::imshow("Image", img);
cv::waitKey(0);

5. www.luxoft.com 5
www.luxoft.com

6. www.luxoft.com 6
www.luxoft.com
Haar Cascades
An Object Detection Algorithm used to identify faces
in an image or real time video

7. www.luxoft.com 7
www.luxoft.com
https://github.com/opencv/opencv/tree/master/data/haarcascades
These include models for:
• Face detection
• Eye detection
• Upper body
• Lower body detection
• License plate detection
• Etc.

8. www.luxoft.com 8
www.luxoft.com
How It Works
The Features

9. www.luxoft.com 9
www.luxoft.com
Features
• Edge
• Line
• Any structure in the image where there is a
sudden change of intensities

10. www.luxoft.com 10
www.luxoft.com

11. www.luxoft.com 11
www.luxoft.com
An edge is detected if the Haar value is closer to 1

12. www.luxoft.com 12
www.luxoft.com
Sample Haar Features

13. www.luxoft.com 13
www.luxoft.com
cv::Mat img = cv::imread("photo.png");
cv::CascadeClassifier faceCascade;
faceCascade.load("/haarcascade_frontalface_default.xml"));
std::vector<cv::Rect> faces;
faceCascade.detectMultiScale(img, faces, 1.1, 10);
for (int i = 0; i < faces.size(); ++i) {
cv::rectangle(img, faces[i].tl(), faces[i].br(), cv::Scalar(255, 0, 255), 3);
}
cv::imshow("Image", img);
cv::waitKey(0);

14. www.luxoft.com 14
www.luxoft.com

15. www.luxoft.com 15
www.luxoft.com
void detect_face_on_image_and_draw_circle(
cv::Mat& img,
cv::CascadeClassifier& faceCascade) {
std::vector<cv::Rect> faces;
faceCascade.detectMultiScale(img, faces, 1.1, 10);
for (int i = 0; i < faces.size(); ++i) {
cv::rectangle(img, faces[i].tl(), faces[i].br(), cv::Scalar(255, 0, 255), 3);
}
}

16. www.luxoft.com 16
www.luxoft.com
cv::VideoCapture cap(1);
cv::Mat img;
while (true) {
cap.read(img);
cv::imshow("Image", img);
cv::waitKey(1);
}

17. www.luxoft.com 17
www.luxoft.com
cv::VideoCapture cap(1);
cv::Mat img;
cv::CascadeClassifier faceCascade;
faceCascade.load(“haarcascade_frontalface_default.xml"));
while (true) {
cap.read(img);
detect_face_on_image_and_draw_circle(img, faceCascade);
cv::imshow("Image", img);
cv::waitKey(1);
}

18. www.luxoft.com
Thank you for your attention