content: import org.opencv.core.Core;
  import org.opencv.core.Mat;
  import org.opencv.core.MatOfDMatch;
  import org.opencv.core.MatOfKeyPoint;
  import org.opencv.features2d.DescriptorMatcher;
  import org.opencv.features2d.Features2d;
  import org.opencv.highgui.HighGui;
  import org.opencv.imgcodecs.Imgcodecs;
  import org.opencv.xfeatures2d.SURF;
  
  class SURFMatching {
      public void run(String[] args) {
          String filename1 = args.length > 1 ? args[0] : "../data/box.png";
          String filename2 = args.length > 1 ? args[1] : "../data/box_in_scene.png";
          Mat img1 = Imgcodecs.imread(filename1, Imgcodecs.IMREAD_GRAYSCALE);
          Mat img2 = Imgcodecs.imread(filename2, Imgcodecs.IMREAD_GRAYSCALE);
          if (img1.empty() || img2.empty()) {
              System.err.println("Cannot read images!");
              System.exit(0);
          }
  
          //-- Step 1: Detect the keypoints using SURF Detector, compute the descriptors
          double hessianThreshold = 400;
          int nOctaves = 4, nOctaveLayers = 3;
          boolean extended = false, upright = false;
          SURF detector = SURF.create(hessianThreshold, nOctaves, nOctaveLayers, extended, upright);
          MatOfKeyPoint keypoints1 = new MatOfKeyPoint(), keypoints2 = new MatOfKeyPoint();
          Mat descriptors1 = new Mat(), descriptors2 = new Mat();
          detector.detectAndCompute(img1, new Mat(), keypoints1, descriptors1);
          detector.detectAndCompute(img2, new Mat(), keypoints2, descriptors2);
  
          //-- Step 2: Matching descriptor vectors with a brute force matcher
          // Since SURF is a floating-point descriptor NORM_L2 is used
          DescriptorMatcher matcher = DescriptorMatcher.create(DescriptorMatcher.BRUTEFORCE);
          MatOfDMatch matches = new MatOfDMatch();
          matcher.match(descriptors1, descriptors2, matches);
  
          //-- Draw matches
          Mat imgMatches = new Mat();
          Features2d.drawMatches(img1, keypoints1, img2, keypoints2, matches, imgMatches);
  
          HighGui.imshow("Matches", imgMatches);
          HighGui.waitKey(0);
  
          System.exit(0);
      }
  }
  
  public class SURFMatchingDemo {
      public static void main(String[] args) {
          // Load the native OpenCV library
          System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
  
          new SURFMatching().run(args);
      }
  }
  