CODEWITHSUNDEEP
javaimage-processingopencvtemplate-matching
Eyal
Eyal

Reputation: 1768

Java openCV - after using Imgproc.matchTemplate method, how do i examine the result?

i am calling:

Imgproc.matchTemplate(image, templ, result, 0);

and the result of the match is in a Mat instance. I couldn't find any documentation for this class. If i understand right, the result contains a matrix of probabilities. How can i find the Maximum of the probabilities? I can't even understand how a Mat instance looks like and what it contains.

Thanks Eyal

Upvotes: 6

Views: 6960

Answers (2)

Radim Burget
Radim Burget

Reputation: 1516

lena.png:

enter image description here

pattern.png:

enter image description here

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());
        Highgui.imwrite("out2.png", result);

        // / 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;
            System.out.println(mmr.minVal);
        } else {
            matchLoc = mmr.maxLoc;
            System.out.println(mmr.maxVal);
        }

        // / 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_java249");
        new MatchingDemo().run("lena.png", "pattern.png", "output.png", Imgproc.TM_CCOEFF);
    }
}

Upvotes: 9

Eyal
Eyal

Reputation: 1768

In order to test the results, one should use the function minMaxLoc that is located inside the class Core. The method returns an instance of MinMaxLocResult, and it has many options inside.

Upvotes: 3

Related Questions