CODEWITHSUNDEEP
androidopencvjavacvorb
Julia
Julia

Reputation: 358

OpenCV 2.4.5 android, FeatureDetector, DescriptorExtractor

Using OpenCV-2.4.5-android-sdk, I try to match two images with feature detection (ORB detector and hamming matcher). Unfortunateley, I'm always getting a NullPointerException when computing the descriptors. What am I doing wrong? 

        FeatureDetector detector = FeatureDetector.create("ORB");
        DescriptorExtractor descriptor = DescriptorExtractor.create("ORB");
        BFMatcher matcher = new BFMatcher(Hamming.normType, true);

        KeyPoint keypoints1 = new KeyPoint();
        KeyPoint keypoints2 = new KeyPoint();
        CvMat[] descriptors = new CvMat[2];

        //ORB orb = new ORB();

        //orb.detect(image1, null, keypoints1);
        detector.detect(image1, keypoints1, null);
        descriptor.compute(image1, keypoints1, descriptors[0]);

        detector.detect(image2, keypoints2, null);
        //orb.detect(image2, null, keypoints2);
        descriptor.compute(image2, keypoints2, descriptors[1]);

        // matcher should include 2 different image's descriptors
        DMatch matches = new DMatch();
        matcher.match(descriptors[0], descriptors[1], matches, null);

I wonder, if I have a change to perform feature detection with openCV on Android without android-ndk. Would you suggest trying to write and integrate native c++ code?

Update: After restructureing the project's setup, following this: http://docs.opencv.org/trunk/doc/tutorials/introduction/android_binary_package/dev_with_OCV_on_Android.html#dev-with-ocv-on-android description, the code looks like this:

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

    MatOfKeyPoint keypoints1 = new MatOfKeyPoint();
    MatOfKeyPoint keypoints2 = new MatOfKeyPoint();
    Mat[] descriptors = new Mat[2];

    //ORB orb = new ORB();
    //orb.detect(image1, null, keypoints1);
    detector.detect(image1, keypoints1, null);
    descriptor.compute(image1, keypoints1, descriptors[0]);

    detector.detect(image2, keypoints2, null);
    //orb.detect(image2, null, keypoints2);
    descriptor.compute(image2, keypoints2, descriptors[1]);

    // matcher should include 2 different image's descriptors
    MatOfDMatch matches = new MatOfDMatch();
    matcher.match(descriptors[0], descriptors[1], matches);

The NPE still occurs.

Upvotes: 2

Views: 3374

Answers (3)

Isaac
Isaac

Reputation: 1536

Try to initializate thouse matrix. Instead of saying Mat[] descriptors = new Mat[2];

try: Mat descriptors1= new Mat(); Mat descriptors2= new Mat();

Upvotes: 0

user2420371
user2420371

Reputation: 1

Allocate objects eg. 

Mat descriptortwo = new Mat();

and then remove the null argument from the optional mask parameter, like so: 

detector.detect(image1,keypoints1);

Think it should do the trick :)

Upvotes: 0

Shirish Kamath
Shirish Kamath

Reputation: 376

You seem to have missed allocating objects to the descriptors[] array.

    descriptors[0] = new CvMat();
    descriptors[1] = new CvMat();

Upvotes: 1

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