Hello I am currently trying to execute Feature Matching with FLANN from OpenCV in Java.

Here is code of this Tutorial: https://docs.opencv.org/master/d5/d6f/tutorial_feature_flann_matcher.html

My Project was created with "Java with Ant"

I have added the following dependencies

aistcv-4.5.3.jar, opencv-453.jar and opencv_java453.dll to Project folder.

When I try to run this code an error message comes up.

run:
Exception in thread "main" java.lang.UnsatisfiedLinkError: org/opencv/xfeatures2d/SURF.create_0(DIIZZ)J
at org.opencv.xfeatures2d.SURF.create(SURF.java:92)
at surfflannmatchingdemo.SURFFLANNMatching.run(SURFFLANNMatchingDemo.java:43)
at surfflannmatchingdemo.SURFFLANNMatchingDemo.main(SURFFLANNMatchingDemo.java:80)
C:\Users\Juergen\AppData\Local\NetBeans\Cache\12.5\executor-snippets\run.xml:111: The following error occurred while executing this line:
C:\Users\Juergen\AppData\Local\NetBeans\Cache\12.5\executor-snippets\run.xml:68: Java returned: 1
BUILD FAILED (total time: 0 seconds)

What am I doing wrong?

CodePudding user response：

SURF is still patented.

you can only use it IF you build from src with OPENCV_ENABLE_NONFREE=ON.

(you also probably dont have any contrib modules if it is the prebuilt jar file from SF)

try to replace it with SIFT

CodePudding user response：

OpenCV Java Feature Matching with FLANN

If any body have the same trouble like me, here is the Solution.

import java.util.ArrayList;
import java.util.List;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.DMatch;
import org.opencv.core.Mat;
import org.opencv.core.MatOfByte;
import org.opencv.core.MatOfDMatch;
import org.opencv.core.MatOfKeyPoint;
import org.opencv.core.Scalar;
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;

import org.opencv.features2d.SIFT;




class SURFFLANNMatching {
 public void run(String[] args) {
    String filename1 = args.length > 1 ? args[0] : "foto_111.png";
    String filename2 = args.length > 1 ? args[1] : "foto_222.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 contrastThreshold = 0.03, edgeThreshold = 2.0, sigma = 1.0;
    int nOctaveLayers = 3, hessianThreshold = 400;
//        boolean extended = false, upright = false;
            
//      SURF detector = SURF.create(hessianThreshold, nOctaves, nOctaveLayers, extended, upright);
    
    SIFT detector = SIFT.create(hessianThreshold, nOctaveLayers, contrastThreshold, edgeThreshold, sigma);

    
    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 FLANN based matcher
    // Since SURF is a floating-point descriptor NORM_L2 is used
    DescriptorMatcher matcher = DescriptorMatcher.create(DescriptorMatcher.FLANNBASED);
    List<MatOfDMatch> knnMatches = new ArrayList<>();
    matcher.knnMatch(descriptors1, descriptors2, knnMatches, 2);
    
    //-- Filter matches using the Lowe's ratio test
    float ratioThresh = 0.7f;
    List<DMatch> listOfGoodMatches = new ArrayList<>();
    for (int i = 0; i < knnMatches.size(); i  ) {
        if (knnMatches.get(i).rows() > 1) {
            DMatch[] matches = knnMatches.get(i).toArray();
            if (matches[0].distance < ratioThresh * matches[1].distance) {
                listOfGoodMatches.add(matches[0]);
            }
        }
    }
    MatOfDMatch goodMatches = new MatOfDMatch();
    goodMatches.fromList(listOfGoodMatches);
    //-- Draw matches
    Mat imgMatches = new Mat();
    Features2d.drawMatches(img1, keypoints1, img2, keypoints2, goodMatches, imgMatches, Scalar.all(-1),
            Scalar.all(-1), new MatOfByte(), Features2d.DrawMatchesFlags_NOT_DRAW_SINGLE_POINTS);
    //-- Show detected matches
    HighGui.imshow("Good Matches", imgMatches);
    HighGui.waitKey(0);
    System.exit(0);
 }
}

public class SURFFLANNMatchingDemo {
  public static void main(String[] args) {
    // Load the native OpenCV library
    System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    new SURFFLANNMatching().run(args);
  }
}