OpenCV Java Harris Corner Detection

Question

I am developing an Android application and I want to make use of Harris corner detection. I want to draw the corners detected but I cannot seem to find the documentation for the Java code.

My code so far:

Mat inputImage = inputFrame.rgba();
Imgproc.cornerHarris(inputImage, inputImage, 7, 5, 0.05, Imgproc.BORDER_DEFAULT);

How can I detect and display the corners?

Answer 1

For Java you can try this piece of code.

private void Harris(Mat Scene, Mat Object, int thresh) {

    // This function implements the Harris Corner detection. The corners at intensity > thresh
    // are drawn.
    Mat Harris_scene = new Mat();
    Mat Harris_object = new Mat();

    Mat harris_scene_norm = new Mat(), harris_object_norm = new Mat(), harris_scene_scaled = new Mat(), harris_object_scaled = new Mat();
    int blockSize = 9;
    int apertureSize = 5;
    double k = 0.1;
    Imgproc.cornerHarris(Scene, Harris_scene,blockSize, apertureSize,k);
    Imgproc.cornerHarris(Object, Harris_object, blockSize,apertureSize,k);

    Core.normalize(Harris_scene, harris_scene_norm, 0, 255, Core.NORM_MINMAX, CvType.CV_32FC1, new Mat());
    Core.normalize(Harris_object, harris_object_norm, 0, 255, Core.NORM_MINMAX, CvType.CV_32FC1, new Mat());

    Core.convertScaleAbs(harris_scene_norm, harris_scene_scaled);
    Core.convertScaleAbs(harris_object_norm, harris_object_scaled);

    for( int j = 0; j < harris_scene_norm.rows() ; j++){
        for( int i = 0; i < harris_scene_norm.cols(); i++){
            if ((int) harris_scene_norm.get(j,i)[0] > thresh){
                Imgproc.circle(harris_scene_scaled, new Point(i,j), 5 , new Scalar(0), 2 ,8 , 0);
            }
        }
    }

    for( int j = 0; j < harris_object_norm.rows() ; j++){
        for( int i = 0; i < harris_object_norm.cols(); i++){
            if ((int) harris_object_norm.get(j,i)[0] > thresh){
                Imgproc.circle(harris_object_scaled, new Point(i,j), 5 , new Scalar(0), 2 ,8 , 0);
            }
        }
    }
 }

I just wrote this following code here

Answer 2

I know this is not ideal, but it is also not so bad - you can look at the c++ documentation and examples, the translation to Java is usually straight forward: One example: Harris corner detector . (you did not mention your version, this is from v2.4).

Answer 3

If anyone is still looking for OpenCV Java Samples, you can find it here in the following links.

Complete Java Samples

https://github.com/opencv/opencv/tree/master/samples/java/tutorial_code

Motion Tracking

https://github.com/opencv/opencv/tree/master/samples/java/tutorial_code/TrackingMotion

Harris Corner Detection

https://github.com/opencv/opencv/blob/master/samples/java/tutorial_code/TrackingMotion/harris_detector/CornerHarrisDemo.java