content: import java.awt.BorderLayout;
  import java.awt.Container;
  import java.awt.Image;
  
  import javax.swing.BoxLayout;
  import javax.swing.ImageIcon;
  import javax.swing.JFrame;
  import javax.swing.JLabel;
  import javax.swing.JPanel;
  import javax.swing.JSlider;
  import javax.swing.event.ChangeEvent;
  import javax.swing.event.ChangeListener;
  
  import org.opencv.core.Core;
  import org.opencv.core.Mat;
  import org.opencv.highgui.HighGui;
  import org.opencv.imgcodecs.Imgcodecs;
  
  public class AddingImagesTrackbar {
      private static final int ALPHA_SLIDER_MAX = 100;
      private int alphaVal = 0;
      private Mat matImgSrc1;
      private Mat matImgSrc2;
      private Mat matImgDst = new Mat();
      private JFrame frame;
      private JLabel imgLabel;
  
      public AddingImagesTrackbar(String[] args) {
          //! [load]
          String imagePath1 = "../data/LinuxLogo.jpg";
          String imagePath2 = "../data/WindowsLogo.jpg";
          if (args.length > 1) {
              imagePath1 = args[0];
              imagePath2 = args[1];
          }
          matImgSrc1 = Imgcodecs.imread(imagePath1);
          matImgSrc2 = Imgcodecs.imread(imagePath2);
          //! [load]
          if (matImgSrc1.empty()) {
              System.out.println("Empty image: " + imagePath1);
              System.exit(0);
          }
          if (matImgSrc2.empty()) {
              System.out.println("Empty image: " + imagePath2);
              System.exit(0);
          }
  
          //! [window]
          // Create and set up the window.
          frame = new JFrame("Linear Blend");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          // Set up the content pane.
          Image img = HighGui.toBufferedImage(matImgSrc2);
          addComponentsToPane(frame.getContentPane(), img);
          // Use the content pane's default BorderLayout. No need for
          // setLayout(new BorderLayout());
          // Display the window.
          frame.pack();
          frame.setVisible(true);
          //! [window]
      }
  
      private void addComponentsToPane(Container pane, Image img) {
          if (!(pane.getLayout() instanceof BorderLayout)) {
              pane.add(new JLabel("Container doesn't use BorderLayout!"));
              return;
          }
  
          JPanel sliderPanel = new JPanel();
          sliderPanel.setLayout(new BoxLayout(sliderPanel, BoxLayout.PAGE_AXIS));
  
          //! [create_trackbar]
          sliderPanel.add(new JLabel(String.format("Alpha x %d", ALPHA_SLIDER_MAX)));
          JSlider slider = new JSlider(0, ALPHA_SLIDER_MAX, 0);
          slider.setMajorTickSpacing(20);
          slider.setMinorTickSpacing(5);
          slider.setPaintTicks(true);
          slider.setPaintLabels(true);
          //! [create_trackbar]
          //! [on_trackbar]
          slider.addChangeListener(new ChangeListener() {
              @Override
              public void stateChanged(ChangeEvent e) {
                  JSlider source = (JSlider) e.getSource();
                  alphaVal = source.getValue();
                  update();
              }
          });
          //! [on_trackbar]
          sliderPanel.add(slider);
  
          pane.add(sliderPanel, BorderLayout.PAGE_START);
          imgLabel = new JLabel(new ImageIcon(img));
          pane.add(imgLabel, BorderLayout.CENTER);
      }
  
      private void update() {
          double alpha = alphaVal / (double) ALPHA_SLIDER_MAX;
          double beta = 1.0 - alpha;
          Core.addWeighted(matImgSrc1, alpha, matImgSrc2, beta, 0, matImgDst);
          Image img = HighGui.toBufferedImage(matImgDst);
          imgLabel.setIcon(new ImageIcon(img));
          frame.repaint();
      }
  
      public static void main(String[] args) {
          // Load the native OpenCV library
          System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
  
          // Schedule a job for the event dispatch thread:
          // creating and showing this application's GUI.
          javax.swing.SwingUtilities.invokeLater(new Runnable() {
              @Override
              public void run() {
                  new AddingImagesTrackbar(args);
              }
          });
      }
  }
  