Fixed the algorithm to convert the features to a json string.

app/src/main/java/com/aluxoft/earrecognition/EarIdentifier.java

 package com.aluxoft.earrecognition;
 
+import com.aluxoft.earrecognition.utils.OpenCvUtils;
 import com.google.gson.Gson;
-import com.google.gson.JsonElement;
-import com.google.gson.JsonSerializationContext;
-import com.google.gson.JsonSerializer;
 
 import org.opencv.core.Mat;
 import org.opencv.core.MatOfKeyPoint;
-import org.opencv.core.Size;
 import org.opencv.features2d.DescriptorExtractor;
 import org.opencv.features2d.FeatureDetector;
 import org.opencv.highgui.Highgui;
-import org.opencv.imgproc.Imgproc;
 
-import java.lang.reflect.Type;
-import java.util.Vector;
+import java.util.ArrayList;
 
 /**
  * Created by josejuliomartinez on 06/10/15.
@@ -50,14 +45,21 @@ public class EarIdentifier {
         keypoints = new MatOfKeyPoint();
 
         image = Highgui.imread(imagePath, Highgui.CV_LOAD_IMAGE_GRAYSCALE);
+
+        OpenCvUtils.resizeMat(image, 160, 120);
+
         FeatureDetector detector = FeatureDetector.create(FeatureDetector.SIFT);
         detector.detect(image, keypoints);
         DescriptorExtractor extractor = DescriptorExtractor.create(DescriptorExtractor.SIFT);
         extractor.compute(image, keypoints, descriptors);
 
-        Vector<Integer> features = new Vector<Integer>();
+        ArrayList<ArrayList<Integer>> features = new ArrayList<>();
         for (int i=0;i<descriptors.rows();++i) {
-            features.add((int)descriptors.get(i, 0)[0]);
+            ArrayList<Integer> feature = new ArrayList<>();
+            for (int j=0;j<descriptors.cols();++j) {
+                feature.add((int)descriptors.get(i, j)[0]);
+            }
+            features.add(feature);
         }
         Gson gson = new Gson();
         return gson.toJson(features);
@@ -68,24 +70,4 @@ public class EarIdentifier {
         System.loadLibrary("nonfree");
     }
 
-    private void resizeMat(Mat image) {
-        final double kMaxWidth = 160;
-        final double kMaxHeight = 120;
-
-        if (image.width() <= kMaxWidth && image.height() <= kMaxHeight) {
-            return;
-        }
-
-        double ratio = (double)image.width() / (double)image.height();
-        double width, height;
-        if (ratio > 1) {
-            width = kMaxWidth;
-            height = kMaxWidth * ((double)image.height()/(double)image.width());
-        } else {
-            height = kMaxHeight;
-            width = kMaxHeight* ratio;
-        }
-        Imgproc.resize(image, image, new Size(width, height));
-    }
-
 }