Here is my code for finding contours in Java using OpenCV. I first used the image to detect the edges in the image, then I passed that image's location to contour function, but it is not showing any contours. Please take look at it. I also attached the images of input and output to code.
package test;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.core.*;
import org.opencv.imgproc.Imgproc;
import org.opencv.highgui.Highgui;
import java.util.*;
import javax.swing.*;
public class DMImageFactory {
public void contours(String location) {
System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
Mat image =Imgcodecs.imread(location);
Mat dst=new Mat();
Core.inRange(image, new Scalar(0,0,0), new Scalar(255,255,255),dst);
if(dst.empty())
System.out.print("empty matrix");
Imshow im = new Imshow("Box1");
im.showImage(image);
List<MatOfPoint> contours = new ArrayList<>();
Mat countour_result = Mat.zeros(image.size(), CvType.CV_8UC3);
Imgproc.findContours(dst, contours, new Mat(),[enter image description here][1]Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_SIMPLE);
Imgproc.drawContours(countour_result, contours, -1,new
Scalar(255,255,255));
Imgcodecs.imwrite("/Users/pranay/Desktop/test/counterdetection_intermidiate.png",countour_result);
System.out.print(contours+" ");
for (MatOfPoint contour: contours)
Imgproc.fillPoly(countour_result, Arrays.asList(contour), new Scalar(255,255,255));
Scalar green = new Scalar(81, 190, 0);
for (MatOfPoint contour: contours) {
RotatedRect rotatedRect = Imgproc.minAreaRect(new
MatOfPoint2f(contour.toArray()));
drawRotatedRect(countour_result, rotatedRect, green, 4);
}
Imgcodecs.imwrite("/Users/pranay/Desktop/test/counterdetection.png",countour_result);
}
public static void drawRotatedRect(Mat image, RotatedRect rotatedRect,
Scalar color, int thickness) {
Point[] vertices = new Point[4];
rotatedRect.points(vertices);
MatOfPoint points = new MatOfPoint(vertices);
Imgproc.drawContours(image, Arrays.asList(points), -1, color,
thickness);
}
}
Probably you are drawing all contours on top of each other and the biggest one is drawn last and it covers all other contours.
Try to draw each contour in a new image.