java - 如何调整openCV(java)中模板匹配的阈值？

Question

我正在使用 openCV 3.4.7 Android SDK (java) 运行模板匹配。代码几乎可以完美运行；当模板匹配时，在匹配区域上绘制一个矩形。问题是，即使没有匹配，它也会绘制一个随机矩形。我认为发生这种情况是因为阈值设置不正确。如果是这样，有人可以帮我吗？

代码如下:

public static void run(String inFile, String templateFile, String outFile,
                    int match_method) {
        Mat img = Imgcodecs.imread(inFile);
        Mat templ = Imgcodecs.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
        Core.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
        Imgproc.rectangle(img, matchLoc, new Point(matchLoc.x + templ.cols(),
                matchLoc.y + templ.rows()), new Scalar(0, 0, 128));

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

Answer 1

您可以使用 Imgproc.TM_CCOEFF_NORMED 或 Imgproc.TM_CCORR_NORMED 且 mmr.maxVal >= 0.8。它应该可以处理大部分误报。

示例代码:

import org.opencv.core.*;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;

import java.io.File;
import java.nio.file.Files;

public class templateMatchingTester {

    private static String str = null;

    static {
        if (str == null) {
            str = "initialised";
            nu.pattern.OpenCV.loadShared();
            System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
        }

    }

    private static Mat createMatrixFromImage(String imagePath) {
        Mat imageMatrix = Imgcodecs.imread(imagePath);
        Mat greyImage = new Mat();
        Imgproc.cvtColor(imageMatrix, greyImage, Imgproc.COLOR_BGR2GRAY);
        return greyImage;
    }

    private static boolean matchTemplate(String pathToInputImage,String pathToTemplate){

        Mat inputImage = createMatrixFromImage(pathToInputImage);
        Mat templateImage = createMatrixFromImage(pathToTemplate);

        // Create the result matrix
        int result_cols = inputImage.cols() - templateImage.cols() + 1;
        int result_rows = inputImage.rows() - templateImage.rows() + 1;
        Mat result = new Mat(result_rows, result_cols, CvType.CV_8UC1);
        int match_method;
        match_method = Imgproc.TM_CCOEFF_NORMED;//Imgproc.TM_CCORR_NORMED;
        Imgproc.matchTemplate(inputImage, templateImage, result, match_method);
        Core.MinMaxLocResult mmr = Core.minMaxLoc(result);
        double minMatchQuality = 0.85; 
        System.out.println(mmr.maxVal);
        if (mmr.maxVal >= minMatchQuality){
            return true;
        } else
        return false;
    }

    public static void main(String args[]) {

        String template = "path/to/your/templateImage";
        final File folder = new File("path/to/your/testImagesFolder/");
        int matchCount = 0;
        for (final File fileEntry : folder.listFiles()){
            if (matchTemplate(fileEntry.getPath(),template)){
                matchCount+=1;
            }else
                System.out.println(fileEntry.getPath());
        }
        System.out.println(matchCount);

    }
}