Error matching with ORB in Android

Question

My code is working good but when it extracts keypoints, it matches poorly the two images. Here you can find my code, but I don\'t know how to draw good matched in JAVA

Answer 1

Your code should be like this:

 FeatureDetector detector = FeatureDetector.create(FeatureDetector.ORB);
 DescriptorExtractor descriptor = DescriptorExtractor.create(DescriptorExtractor.ORB);;
 DescriptorMatcher matcher = DescriptorMatcher.create(DescriptorMatcher.BRUTEFORCE_HAMMING);

 //first image
 Mat img1 = Highgui.imread("<image1 path>");
 Mat descriptors1 = new Mat();
 MatOfKeyPoint keypoints1 = new MatOfKeyPoint();

 detector.detect(img1, keypoints1);
 descriptor.compute(img1, keypoints1, descriptors1);

 //second image
 Mat img2 = Highgui.imread("<image2 path>");
 Mat descriptors2 = new Mat();
 MatOfKeyPoint keypoints2 = new MatOfKeyPoint();

 detector.detect(img2, keypoints2);
 descriptor.compute(img2, keypoints2, descriptors2);

 //matcher should include 2 different image's descriptors
 MatOfDMatch  matches = new MatOfDMatch();             
 matcher.match(descriptors1,descriptors2,matches);
 //feature and connection colors
 Scalar RED = new Scalar(255,0,0);
 Scalar GREEN = new Scalar(0,255,0);
 //output image
 Mat outputImg = new Mat();
 MatOfByte drawnMatches = new MatOfByte();
 //this will draw all matches, works fine
 Features2d.drawMatches(img1, keypoints1, img2, keypoints2, matches, 
 outputImg, GREEN, RED,  drawnMatches, Features2d.NOT_DRAW_SINGLE_POINTS);

Also if you want to display just features, you can add this code:

 Mat featuredImg = new Mat();
 Scalar kpColor = new Scalar(255,159,10);//this will be color of keypoints
 //featuredImg will be the output of first image
 Features2d.drawKeypoints(img1, keypoints1, featuredImg , kpColor, 0);
 //featuredImg will be the output of first image
 Features2d.drawKeypoints(img1, keypoints1, featuredImg , kpColor, 0);

Then you can show matched points like this:

  Bitmap imageMatched = Bitmap.createBitmap(outputImg.cols(), outputImg.rows(), Bitmap.Config.RGB_565);//need to save bitmap
  Utils.matToBitmap(outputImg, imageMatched);
  ImageView.setImageBitmap(imageMatched);

Eventually you can implement good matches. I hope this thread will be helpful.

Answer 2

Good Matches method is basing on removing from your MatOfDMatch matches = new MatOfDMatch(); list matched points that has different descriptors or spacial location. What I suggest to do is to loop over matches list and put to the new list matches that are satisfy conditions like:

int DIST_LIMIT = 80;
List<DMatch> matchesList = matches.toList();
List<DMatch> matches_final= new ArrayList<DMatch>();
for(int i=0; i<matchesList.size(); i++)
   if(matchesList .get(i).distance <= DIST_LIMIT){
       matches_final.add(matches.toList().get(i));
   }
}

MatOfDMatch matches_final_mat = new MatOfDMatch();
matches_final_mat.fromList(matches_final);

Same thing you can do with matched points coordinates. Here is the useful link.