Image Processing in Java | Set 9 ( Face Detection )

In the introductory set on Image Processing, BufferedImage class of Java was used for processing images the applications of BufferedImage class is limited to some operations only, i.e, we can modify the R, G, B values of given input image and produce the modified image. For complex image processing such as face/object detection OpenCV library is used which we will use in this article.

At first we need to setup OpenCV for Java, we recommend to use eclipse for the same since it is easy to use and setup.

Now lets understand some of the methods required for face detection.

  1. CascadeClassifier() : This class is used to load the trained cascaded set of faces which we will be using to detect face for any input image.
  2. Imcodecs.imread()/Imcodecs.imwrite() : These methods are used to read and write images as Mat objects which are rendered by OpenCV.
  3. Imgproc.rectangle() : Used to generate rectangle box outlining faces detected, it takes four arguments – input_image, top_left_point, bottom_right_point, color_of_border.
// Java program to demonstrate face detection
package ocv;
import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.core.MatOfRect;
import org.opencv.core.Point;
import org.opencv.core.Rect;
import org.opencv.core.Scalar;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;
import org.opencv.objdetect.CascadeClassifier;
public class FaceDetector
    public static void main(String[] args)
        // For proper execution of native libraries
        // Core.NATIVE_LIBRARY_NAME must be loaded before
        // calling any of the opencv methods
        // Face detector creation by loading source cascade xml file
        // using CascadeClassifier.
        // the file can be downloade from
        // haarcascade_frontalface_alt.xml
        // and must be placed in same directory of the source java file
        CascadeClassifier faceDetector = new CascadeClassifier();
        // Input image
        Mat image = Imgcodecs.imread("E:\input.jpg");
        // Detecting faces
        MatOfRect faceDetections = new MatOfRect();
        faceDetector.detectMultiScale(image, faceDetections);
        // Creating a rectangular box showing faces detected
        for (Rect rect : faceDetections.toArray())
            Imgproc.rectangle(image, new Point(rect.x, rect.y),
             new Point(rect.x + rect.width, rect.y + rect.height),
                                           new Scalar(0, 255, 0));
        // Saving the output image
        String filename = "Ouput.jpg";
        Imgcodecs.imwrite("E:\"+filename, image);


    Input.jpg                                         Output.jpg
input                        ouput

Explanation of Code:

  1. It loads the native OpenCV library to use Java API. An instance of CascadeClassifier is created, passing it the name of the file from which the classifier is loaded.
  2. Next, detectMultiScale method is used on the classifier passing it the given image and MatOfRect object.
  3. MatOfRect is responsible to do face detections after processing.
  4. The process is iterated for doing all the face detections and mark the image with rectangles and at the end image is saved as output.png file.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

This article is attributed to GeeksforGeeks.org

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