Opencv Template Matching Example in Android

OpenCV Template Matching example in Android

I was facing the same problem you did. No source in Java available. Some search in the JavaDoc and some hints for const values later, I wrote this, which is almost the sample code above written in Java:

package opencv;

import org.opencv.core.Core;
import org.opencv.core.Core.MinMaxLocResult;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.core.Point;
import org.opencv.core.Scalar;
import org.opencv.highgui.Highgui;
import org.opencv.imgproc.Imgproc;

class MatchingDemo {
    public void run(String inFile, String templateFile, String outFile, int match_method) {
        System.out.println("\nRunning Template Matching");

        Mat img = Highgui.imread(inFile);
        Mat templ = Highgui.imread(templateFile);

        // / Create the result matrix
        int result_cols = img.cols() - templ.cols() + 1;
        int result_rows = img.rows() - templ.rows() + 1;
        Mat result = new Mat(result_rows, result_cols, CvType.CV_32FC1);

        // / Do the Matching and Normalize
        Imgproc.matchTemplate(img, templ, result, match_method);
        Core.normalize(result, result, 0, 1, Core.NORM_MINMAX, -1, new Mat());

        // / Localizing the best match with minMaxLoc
        MinMaxLocResult mmr = Core.minMaxLoc(result);

        Point matchLoc;
        if (match_method == Imgproc.TM_SQDIFF || match_method == Imgproc.TM_SQDIFF_NORMED) {
            matchLoc = mmr.minLoc;
        } else {
            matchLoc = mmr.maxLoc;
        }

        // / Show me what you got
        Core.rectangle(img, matchLoc, new Point(matchLoc.x + templ.cols(),
                matchLoc.y + templ.rows()), new Scalar(0, 255, 0));

        // Save the visualized detection.
        System.out.println("Writing "+ outFile);
        Highgui.imwrite(outFile, img);

    }
}

public class TemplateMatching {
    public static void main(String[] args) {
        System.loadLibrary("opencv_java246");
        new MatchingDemo().run(args[0], args[1], args[2], Imgproc.TM_CCOEFF);
    }
}

Now, run the program with the following options: lena.png template.png templatematch.png and you should receive the same result I did. Make sure the files are accessible by your runtime and, of course, opencv 2.4.6 library is registered to your classpath.

Android - OpenCV Template Matching with threshold

Core.MinMaxLocResult contains maxLoc, maxVal, minLoc, and minVal values. Just assign match=mmr.maxVal or match=mmr.minVal depending on context.

Alternatively, you could index in the result Mat to get your value and then test if it's over 0.8 as so:

double[] resultVal = result.get(matchLoc.y, matchLoc.x);
if (resultVal[0] >= 0.8) ...

Android - OpenCV Template Matching

googling a little bit , you will found that you've called the template matching before loading the OpenCV library see the same error in openCV forum :

you can only call opencv functions after the BaseLoaderCallback
finished(the opencv dlls were loaded). so, if you put that code into
your onCreate function, you'll get that error.

you could find a complete BaseLoaderCallback documentation in openCV doc

Hope this could help you ^^

Template matching using OpenCV

I might be far off here, but I believe the submat method returns a pointer to the submatrix of mGray. So your template changes from frame to frame since mRgba is always copied to mGray, but mGray is never reallocated. In this case, the solution would be to make a copy of the mGray submatrix. In C++, that would be something like:

mGray.submat(Y-H/2, Y+H/2, X-W/2, X+W/2).copyTo(template);

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