Java OpenCV Webcam

Camera is a very important piece of equipment in computer vision. My first tutorial will be a webcam program based on OpenCV. 1. We need an efficient piece of code that convert OpenCV image, a Mat, to a BufferedImage.

import java.awt.image.BufferedImage;
import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.highgui.Highgui;
import org.opencv.imgproc.Imgproc;

public class Mat2Image {
    Mat mat = new Mat();
    BufferedImage img;
    byte[] dat;
    public Mat2Image() {
    }
    public Mat2Image(Mat mat) {
        getSpace(mat);
    }
    public void getSpace(Mat mat) {
        this.mat = mat;
        int w = mat.cols(), h = mat.rows();
        if (dat == null || dat.length != w * h * 3)
            dat = new byte[w * h * 3];
        if (img == null || img.getWidth() != w || img.getHeight() != h
            || img.getType() != BufferedImage.TYPE_3BYTE_BGR)
                img = new BufferedImage(w, h, 
                            BufferedImage.TYPE_3BYTE_BGR);
        }
        BufferedImage getImage(Mat mat){
            getSpace(mat);
            mat.get(0, 0, dat);
            img.getRaster().setDataElements(0, 0, 
                               mat.cols(), mat.rows(), dat);
        return img;
    }
    static{
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    }
}

2. Here is a simple class that captures video:

import java.awt.image.BufferedImage;
import org.opencv.core.Core;
import org.opencv.highgui.VideoCapture;

public class VideoCap {
    static{
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    }

    VideoCapture cap;
    Mat2Image mat2Img = new Mat2Image();

    VideoCap(){
        cap = new VideoCapture();
        cap.open(0);
    } 
 
    BufferedImage getOneFrame() {
        cap.read(mat2Img.mat);
        return mat2Img.getImage(mat2Img.mat);
    }
}

3. Now we need a JFrame to display the video:

package org.ski;
import java.awt.EventQueue;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

public class MyFrame extends JFrame {
    private JPanel contentPane;

  /**
  * Launch the application.
  */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    MyFrame frame = new MyFrame();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

  /**
  * Create the frame.
  */
    public MyFrame() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 650, 490);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);
  
        new MyThread().start();
    }
 
    VideoCap videoCap = new VideoCap();
 
    public void paint(Graphics g){
        g = contentPane.getGraphics();
        g.drawImage(videoCap.getOneFrame(), 0, 0, this);
    }
 
    class MyThread extends Thread{
        @Override
        public void run() {
            for (;;){
                repaint();
                try { Thread.sleep(30);
                } catch (InterruptedException e) {    }
            }  
        } 
    }
}