I am trying to find the keypoints of an image using SURF detector...But the number of key points is always one

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heres my code (i am using javacv):

import org.bytedeco.javacpp.opencv_core;
import org.bytedeco.javacpp.opencv_features2d;
import org.bytedeco.javacpp.opencv_nonfree;

import static org.bytedeco.javacpp.opencv_highgui.imread;
 opencv_core.Mat images[] = new opencv_core.Mat[2];
        images[0] = new opencv_core.Mat();
        images[1] = new opencv_core.Mat();
        images[0] = imread("/storage/emulated/0/DCIM/Camera/p3.jpg");
        images[1] = imread("/storage/emulated/0/DCIM/Camera/p4.jpg");
        System.out.println("images read");
        opencv_nonfree.SURF surf= new opencv_nonfree.SURF(100);
       opencv_features2d.KeyPoint keyPoints1 = new opencv_features2d.KeyPoint();
        opencv_features2d.KeyPoint keyPoints2 = new opencv_features2d.KeyPoint();
        surf.detect(images[0],  keyPoints1);
        surf.detect(images[1],  keyPoints2);
        System.out.println("Number of SURF points (1): " + keyPoints1.capacity());
        System.out.println("Number of SURF points (2): " + keyPoints2.capacity());