Finding Area of Convex Hull Gives an Assertion Error

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I'm very new to image processing.I'm trying to calculate the solidity in opencv on contours of an image. But contourArea() method in my code gives an assertion error that is:

"OpenCV Error: Assertion failed (contour.checkVector(2) >= 0 && (contour.depth() == CV_32F || contour.depth() == CV_32S)) in cv::contourArea").

How can I fix it. Thank You.

import static com.googlecode.javacv.cpp.opencv_imgproc.CV_THRESH_BINARY; import java.util.ArrayList; import java.util.List; import org.opencv.core.Core; import org.opencv.core.Mat; import org.opencv.core.MatOfInt; import org.opencv.core.MatOfPoint; import org.opencv.core.Scalar; import org.opencv.highgui.Highgui; import org.opencv.imgproc.Imgproc; import static org.opencv.imgproc.Imgproc.contourArea; import static org.opencv.imgproc.Imgproc.findContours;

public class Solidity { public static void main(String[] args) { System.loadLibrary(Core.NATIVE_LIBRARY_NAME); Mat image = Highgui.imread("D:\MyImage.bmp");

    if (image.empty() == true) {
        System.out.println("Error: no image found!");
    } else {

        List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
        Mat image_2 = new Mat();


        Imgproc.cvtColor(image, image_2, Imgproc.COLOR_BGR2GRAY);
        Imgproc.threshold(image_2, image_2, 150, 255, CV_THRESH_BINARY);

        findContours(image_2, contours, new Mat(), Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);           


        for (int i = 0; i < contours.size(); i++) {
            Imgproc.drawContours(image, contours, -1, new Scalar(240, 0, 0), 2);

            double area=contourArea(contours.get(i));

            MatOfInt matOfInt=new MatOfInt();

            Imgproc.convexHull(contours.get(i),matOfInt);

            //Mat conMat=new Mat(contours.get(i).size(),CV_32FC1);
            //Error comes from here
            double hullArea=contourArea(matOfInt);

            double solidity=area/hullArea;

            System.out.println(solidity);
        }

    }

}

}