Android Opencv: Save ORB features using Json

问题:

i want to save orb features to database that i get from this code:

bmp=BitmapFactory.decodeResource(getResources(),R.drawable.t1);
Utils.bitmapToMat(bmp, mat);
FeatureDetector detector = FeatureDetector.create(FeatureDetector.ORB);
detector.detect(mat, keypoints);
DescriptorExtractor extractor = DescriptorExtractor.create(DescriptorExtractor.ORB);
extractor.compute(mat, keypoints, features);

i using json code to save the data from Mat of feature with the code i get from here: http://answers.opencv.org/question/8873/best-way-to-store-a-mat-object-in-android/?answer=28608#post-id-28608

but when i show the json string, that show like this:

i don't understand about that data, how can that be calculated by DescriptorMatcher.BRUTEFORCE_HAMMING ?