Detecting circles in custom shapes

Question

I need help to detect circles in my images , When I run my code the circle is not searched instead the returned shape is an ellipse , sorry bad English

Input image:

Result image:

My code :

public Mat Run(string imgPath , int thresholdValue = 150)
{
        var img=Cv2.ImRead(imgPath);
        Bitmap bitmap = MatToBitmap(img);
        pictureBox1.Image = bitmap;

        Mat gray = img.CvtColor(ColorConversionCodes.BGR2GRAY);

        ThresholdImg = gray.Threshold(thresholdValue, 255, ThresholdTypes.Binary);
        Bitmap threshold = MatToBitmap(ThresholdImg);
        pictureBox2.Image = threshold;

        //Cv2.ImShow("Threshold", ThresholdImg);
        Mat gaussImg = ThresholdImg.GaussianBlur(new OpenCvSharp.Size(5, 5), 0.8);

        //Cv2.ImShow("GaussianBlur", gaussImg);
        Mat medianImg = ThresholdImg.MedianBlur(5);

        //Cv2.ImShow("MedianBlur", medianImg);
        Mat kernel = new Mat(15, 15, MatType.CV_8UC1);
        Mat DilateImg = ThresholdImg.Dilate(kernel);
        Mat binary = DilateImg.Erode(kernel);

        //Cv2.ImShow("Dilate & Erode", binary);
        Mat element = Cv2.GetStructuringElement(MorphShapes.Ellipse, new OpenCvSharp.Size(5, 5));
        Mat openImg = ThresholdImg.MorphologyEx(MorphTypes.Open, element);

        //Cv2.ImShow("Dilate & Erode", openImg);
        Rect roi = new Rect(0, 0, bitmap.Width, bitmap.Height);
        Mat ROIimg = new Mat(openImg, roi);
        Cv2.ImShow("ROI Image", ROIimg);
        OpenCvSharp.Point[][] contours;
        HierarchyIndex[] hierachy;
        Cv2.FindContours(ROIimg, out contours, out hierachy, RetrievalModes.List, ContourApproximationModes.ApproxTC89KCOS);

        //According to the found contour points, fit the ellipse
        for (int i = 0; i < contours.Length; i++)
        {
            //The fitting function must have at least 5 points, if less than it is not fitting
            if (contours[i].Length < 5) continue;
            //Ellipse fitting
            var rrt = Cv2.FitEllipse(contours[i]);
        }
  }

How to accurately detect a circle? , sorry i am new , i cant post my image

Answer 1

I found the solution to the problem , i used Erode and Dilate to separate the circle from the shape

Mat binary = DilateImg.Dilate(kernel, null, 2);
Mat DilateImg = ThresholdImg.Erode(kernel, null, 2);

Erode and Dilate Image

And My result image

Result Image