使用OpenCV搜索字符轮廓

Question

我正在尝试查找符号的轮廓。我几乎可以正常工作，这是第一个测试图像：

但是，在第二张测试图像中，我只能找到一个轮廓：

这是我的代码：

import org.opencv.core.*;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;
import javax.swing.*;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;
import java.util.ArrayList;


public class FilteOpenCV {
    public static final Scalar COLOR_WHITE = colorRGB(255, 255, 255);
    public static final Scalar COLOR_BLUE = colorRGB(0, 0, 255);
    public static Scalar colorRGB(double red, double green, double blue) {
        return new Scalar(blue, green, red);
    }
    //получаем BufferedImage
    public static BufferedImage MatToBufferedImage(Mat m) {
        if (m == null || m.empty()) return null;
        if (m.depth() == CvType.CV_8U) {
        } else if (m.depth() == CvType.CV_16U) { // CV_16U => CV_8U
            Mat m_16 = new Mat();
            m.convertTo(m_16, CvType.CV_8U, 255.0 / 65535);
            m = m_16;
        } else if (m.depth() == CvType.CV_32F) { // CV_32F => CV_8U
            Mat m_32 = new Mat();
            m.convertTo(m_32, CvType.CV_8U, 255);
            m = m_32;
        } else
            return null;
        int type = 0;
        if (m.channels() == 1)
            type = BufferedImage.TYPE_BYTE_GRAY;
        else if (m.channels() == 3)
            type = BufferedImage.TYPE_3BYTE_BGR;
        else if (m.channels() == 4)
            type = BufferedImage.TYPE_4BYTE_ABGR;
        else
            return null;
        byte[] buf = new byte[m.channels() * m.cols() * m.rows()];
        m.get(0, 0, buf);
        byte tmp = 0;
        if (m.channels() == 4) { // BGRA => ABGR
            for (int i = 0; i < buf.length; i += 4) {
                tmp = buf[i + 3];
                buf[i + 3] = buf[i + 2];
                buf[i + 2] = buf[i + 1];
                buf[i + 1] = buf[i];
                buf[i] = tmp;
            }
        }
        BufferedImage image = new BufferedImage(m.cols(), m.rows(), type);
        byte[] data =
                ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
        System.arraycopy(buf, 0, data, 0, buf.length);
        return image;
    }
    //показываем изображение
    public static void showImage(Mat img, String title) {
        BufferedImage im = MatToBufferedImage(img);
        if (im == null) return;
        int w = 1000, h = 600;
        JFrame window = new JFrame(title);
        window.setSize(w, h);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        ImageIcon imageIcon = new ImageIcon(im);
        JLabel label = new JLabel(imageIcon);
        JScrollPane pane = new JScrollPane(label);
        window.setContentPane(pane);
        if (im.getWidth() < w && im.getHeight() < h) {
            window.pack();
        }
        window.setLocationRelativeTo(null);
        window.setVisible(true);
    }

    public static void main(String[] args) {
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
        Mat img = Imgcodecs.imread("C:\\Users\\dennn\\PycharmProjects\\untitled2\\imag\\output11.jpg"); //считываем
        if (img.empty()) {
            System.out.println("Не удалось загрузить изображение");
            return;
        }
        showImage(img, "Оригинал");
        Mat imgGray = new Mat();
        Imgproc.cvtColor(img, imgGray, Imgproc.COLOR_BGR2GRAY);
        Mat edges = new Mat();
        Imgproc.Canny(imgGray, edges, 80, 200);
        Mat edgesCopy = edges.clone(); // Создаем копию
        ArrayList<MatOfPoint> contours = new ArrayList<MatOfPoint>();
        Imgproc.findContours(edgesCopy, contours, new Mat(),
                Imgproc.RETR_EXTERNAL,
                Imgproc.CHAIN_APPROX_SIMPLE);
        for (int i = 0, j = contours.size(); i < j; i++) {
            System.out.println(Imgproc.contourArea(contours.get(i)));
            Rect r = Imgproc.boundingRect(contours.get(i));
            System.out.println("boundingRect = " + r);
            double len = Imgproc.arcLength(
                    new MatOfPoint2f(contours.get(i).toArray()), true);
            System.out.println("arcLength = " + len);
            Imgproc.rectangle(img, new Point(r.x, r.y),
                    new Point(r.x + r.width - 1, r.y + r.height - 1),
                    COLOR_BLUE);
        }
        showImage(img, "boundingRect");
        img.release(); imgGray.release();
        edges.release(); edgesCopy.release();
    }
}

我不明白为什么我只能在第二张图像中找到一个轮廓。我怎么解决这个问题？任何帮助表示赞赏。