CascadeClassifier in java does not find face with webcam

Question

I am trying to translate the OpenCV CascadeClassifier tutorial from C++ to Java. Working good in C++. Also this java tutorial is working fine.

But the translation is simply not detecting the face. I don't get explicit errors. I can see the processing of the video input from the webcam (grey/histogram...) and the video display. Cascade load doesn't give error. But the CascadeClassifier call just doesn't return any faces... So, you probably can skip all the code and just go to my CascadeClassifier call, down to public Mat detect(Mat inputframe). As I am new to Java and OpenCV, I paste the rest (I removed anything I felt may not be significant), just in case, but don't mean for you to debug that...

I have also tried this call (and other portions) in many different ways and nothing... running out of ideas...

Thank you!!

import java.awt.*;
import java.awt.image.BufferedImage;
import javax.swing.*;

import org.opencv.core.Mat;
import org.opencv.core.MatOfRect;
import org.opencv.highgui.VideoCapture;
import org.opencv.imgproc.Imgproc;
import org.opencv.objdetect.CascadeClassifier;

class My_Panel extends JPanel{

    private static final long serialVersionUID = 1L;
    private BufferedImage image;
    private CascadeClassifier face_cascade;

    // Create a constructor method
    public My_Panel(){
        super(); 
        String face_cascade_name = "/haarcascade_frontalface_alt.xml";
        //String face_cascade_name = "/lbpcascade_frontalface.xml";
        //-- 1. Load the cascades

        String str;
        str = getClass().getResource(face_cascade_name).getPath();
        str = str.replace("/C:","C:");
        face_cascade_name=str;

        face_cascade=new CascadeClassifier(face_cascade_name);
        if( !face_cascade.empty())
        {
            System.out.println("--(!)Error loading A\n");
            return;
        }
        else
        {
                System.out.println("Face classifier loooaaaaaded up");
        }
    }

    private BufferedImage getimage(){
        return image;
    }

    public void setimage(BufferedImage newimage){
        image=newimage;
        return;
    }

    /**
     * Converts/writes a Mat into a BufferedImage.
     * 
     * @param matrix Mat of type CV_8UC3 or CV_8UC1
     * @return BufferedImage of type TYPE_3BYTE_BGR or TYPE_BYTE_GRAY
     */
    public BufferedImage matToBufferedImage(Mat matrix) {
        int cols = matrix.cols();
        int rows = matrix.rows();
        int elemSize = (int)matrix.elemSize();
        byte[] data = new byte[cols * rows * elemSize];
        int type;

        matrix.get(0, 0, data);

        switch (matrix.channels()) {
            case 1:
                type = BufferedImage.TYPE_BYTE_GRAY;
                break;

            case 3: 
                type = BufferedImage.TYPE_3BYTE_BGR;

                // bgr to rgb
                byte b;
                for(int i=0; i<data.length; i=i+3) {
                    b = data[i];
                    data[i] = data[i+2];
                    data[i+2] = b;
                }
                break;

            default:
                return null;
        }

        BufferedImage image2 = new BufferedImage(cols, rows, type);
        image2.getRaster().setDataElements(0, 0, cols, rows, data);

        return image2;
    }

    public void paintComponent(Graphics g){
         BufferedImage temp=getimage();
         g.drawImage(temp,10,10,temp.getWidth(),temp.getHeight(), this); 
    }

    public Mat detect(Mat inputframe){
        Mat mRgba=new Mat();
        Mat mGrey=new Mat();
        MatOfRect faces = new MatOfRect();
        //MatOfRect eyes = new MatOfRect();

        inputframe.copyTo(mRgba);
        inputframe.copyTo(mGrey);
        Imgproc.cvtColor( mRgba, mGrey, Imgproc.COLOR_BGR2GRAY);
        Imgproc.equalizeHist( mGrey, mGrey );

        face_cascade.detectMultiScale(mGrey, faces);
        //face_cascade.detectMultiScale(mGrey, faces, 1.1, 2, 0|Objdetect.CASCADE_SCALE_IMAGE, new Size(30, 30), new Size(200,200) );
        //face_cascade.detectMultiScale(mGrey, faces, 1.1, 2, 2//CV_HAAR_SCALE_IMAGE,
        //      ,new Size(30, 30), new Size(200,200) );

        System.out.println(String.format("Detected %s faces", faces.toArray().length));

        return mGrey;
        }
}

public class window {
    public static void main(String arg[]){
     // Load the native library.
     System.loadLibrary("opencv_java245");  

     String window_name = "Capture - Face detection";

     JFrame frame = new JFrame(window_name);
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     frame.setSize(400,400);

     My_Panel my_panel = new My_Panel();
     frame.setContentPane(my_panel);          
     frame.setVisible(true);           

     //-- 2. Read the video stream
     BufferedImage temp;
     Mat webcam_image=new Mat();

     VideoCapture capture =new VideoCapture(0); 
     if( capture.isOpened())
        {
          while( true )
          {
              capture.read(webcam_image);
              if( !webcam_image.empty() )
               { 
                   frame.setSize(webcam_image.width()+40,webcam_image.height()+60);

                   //-- 3. Apply the classifier to the captured image
                   // At this point I was wondering where this should be done.
                   // I put it within the panel class, but maybe one could actually
                   // create a processor object...
                   webcam_image=my_panel.detect(webcam_image);

                 //-- 4. Display the image
                   temp=my_panel.matToBufferedImage(webcam_image);
                   my_panel.setimage(temp);
                   my_panel.repaint(); 
               }
               else
               { 
                   System.out.println(" --(!) No captured frame -- Break!"); 
                   break; 
               }
              }
           }
           return;
    }
}

PS.: Other info, just in case:

1. mGrey is: Mat [ 480*640*CV_8UC1, isCont=true, isSubmat=false, nativeObj=0x19d9af48, dataAddr=0x19dc3430 ]
2. face is: Mat [ 0*0*CV_8UC1, isCont=false, isSubmat=false, nativeObj=0x194bb048, dataAddr=0x0 ]

Answer 1

I have tried your code and it works fine! You have only one issue with haarcascade_frontalface_alt.xml file location. Try to use a full path to the file: face_cascade= new CascadeClassifier("D:/HelloCV/src/haarcascade_frontalface_alt.xml");