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.CvType;
  import org.opencv.core.Mat;
  import org.opencv.core.Scalar;
  import org.opencv.core.Size;
  import org.opencv.highgui.HighGui;
  import org.opencv.imgcodecs.Imgcodecs;
  import org.opencv.imgproc.Imgproc;
  
  public class CannyDetectorDemo {
      private static final int MAX_LOW_THRESHOLD = 100;
      private static final int RATIO = 3;
      private static final int KERNEL_SIZE = 3;
      private static final Size BLUR_SIZE = new Size(3,3);
      private int lowThresh = 0;
      private Mat src;
      private Mat srcBlur = new Mat();
      private Mat detectedEdges = new Mat();
      private Mat dst = new Mat();
      private JFrame frame;
      private JLabel imgLabel;
  
      public CannyDetectorDemo(String[] args) {
          String imagePath = args.length > 0 ? args[0] : "../data/fruits.jpg";
          src = Imgcodecs.imread(imagePath);
          if (src.empty()) {
              System.out.println("Empty image: " + imagePath);
              System.exit(0);
          }
  
          // Create and set up the window.
          frame = new JFrame("Edge Map (Canny detector demo)");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          // Set up the content pane.
          Image img = HighGui.toBufferedImage(src);
          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);
      }
  
      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));
  
          sliderPanel.add(new JLabel("Min Threshold:"));
          JSlider slider = new JSlider(0, MAX_LOW_THRESHOLD, 0);
          slider.setMajorTickSpacing(10);
          slider.setMinorTickSpacing(5);
          slider.setPaintTicks(true);
          slider.setPaintLabels(true);
          slider.addChangeListener(new ChangeListener() {
              @Override
              public void stateChanged(ChangeEvent e) {
                  JSlider source = (JSlider) e.getSource();
                  lowThresh = source.getValue();
                  update();
              }
          });
          sliderPanel.add(slider);
  
          pane.add(sliderPanel, BorderLayout.PAGE_START);
          imgLabel = new JLabel(new ImageIcon(img));
          pane.add(imgLabel, BorderLayout.CENTER);
      }
  
      private void update() {
          Imgproc.blur(src, srcBlur, BLUR_SIZE);
          Imgproc.Canny(srcBlur, detectedEdges, lowThresh, lowThresh * RATIO, KERNEL_SIZE, false);
          dst = new Mat(src.size(), CvType.CV_8UC3, Scalar.all(0));
          src.copyTo(dst, detectedEdges);
          Image img = HighGui.toBufferedImage(dst);
          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 CannyDetectorDemo(args);
              }
          });
      }
  }
  