refreshing/reloading image in a Java Application (Swing)

Question

I have made a programm to take a snapshot from the WebCam (via OpenCV) and safes it to the Project:

Colordetection
|__src
|    |
|   main.java
|
| Snapshot.png

Now I would like to refresh the taken snapshot, everytime I re-take one and repaint it.

String imgText = "Snapshot.png";

JPanel panelScreenshot = new JPanel();
panelScreenshot.setBorder(new TitledBorder(null, "Screenshot", TitledBorder.LEADING, TitledBorder.TOP, null, null));
panelScreenshot.setBounds(10, 11, 667, 543);
panelDisplay.add(panelScreenshot);
panelScreenshot.setLayout(null);

JLabel lblScreenshot = new JLabel();
lblScreenshot.setIcon(new ImageIcon(imgText));
lblScreenshot.setBounds(10, 21, 640, 480);
panelScreenshot.add(lblScreenshot);

JButton btnScreenshot = new JButton("Screenshot");
btnScreenshot.addActionListener(new ActionListener() {
  public void actionPerformed(ActionEvent e) {              


    VideoCapture cap = new VideoCapture(0);

    if(!cap.isOpened()){
      System.out.println("Webcam not Found");

      } 
      else 
      {
      System.out.println("Found Webcam:" + cap.toString());

      Mat frame = new Mat();
      cap.retrieve(frame);

      try {
          Thread.sleep(500);
          Highgui.imwrite("Snapshot.png", frame);

          lblScreenshot.repaint();                  

          } 
          catch (Exception e1) {
            e1.printStackTrace();

      }
      cap.release();                    
    }       
  }
});

The Problem is, it doesn't repaint/refresh as I want to, only if I restart the programm, the new screenshot is there.

I also tryied it with:

ImageIcon icon = new ImageIcon(main.class.getResource("Snapshot.png"));

and changed the paths etc. but it didnt help.

does anyone has a clue?

thanks.

Answer 1

The image is cached by the ImageIcon so you can either:

1. flush the image, to force the reload
2. use ImageIO to reread the image

Simple example:

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.io.*;
import java.util.*;
import javax.imageio.*;
import javax.swing.*;
import java.net.*;

public class ImageReload extends JPanel implements ActionListener
{
    JLabel timeLabel;
    JLabel imageLabel;
    ImageIcon icon = new ImageIcon("timeLabel.jpg");

    public ImageReload()
    {
        setLayout( new BorderLayout() );

        timeLabel = new JLabel( new Date().toString() );
        imageLabel = new JLabel( timeLabel.getText() );

        add(timeLabel, BorderLayout.NORTH);
        add(imageLabel, BorderLayout.SOUTH);

        javax.swing.Timer timer = new javax.swing.Timer(1000, this);
        timer.start();
    }

    public void actionPerformed(ActionEvent e)
    {
        timeLabel.setText( new Date().toString() );

        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                try
                {
                    String imageName = "timeLabel.jpg";
                    BufferedImage image = ScreenImage.createImage(timeLabel);
                    ScreenImage.writeImage(image, imageName);

                    //  This works using ImageIO

//                  imageLabel.setIcon( new ImageIcon(ImageIO.read( new File(imageName) ) ) );

                    //  Or you can flush the image

                    ImageIcon icon = new ImageIcon(imageName);
                    icon.getImage().flush();
                    imageLabel.setIcon( icon );
                }
                catch(Exception e)
                {
                    System.out.println( e );
                }
            }
        });
    }

    private static void createAndShowUI()
    {
        JFrame frame = new JFrame("SSCCE");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add( new ImageReload() );
        frame.setLocationByPlatform( true );
        frame.pack();
        frame.setVisible( true );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowUI();
            }
        });
    }
}

This example also requires the Screen Image class to dynamically regenerated the image.