Detection of multiple objects for further processing. [closed]

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I am new to this, but have written code to detect an object from an image and then apply background and foreground masks, It works great if there is only one object. I have some images where there are up to 4 different objects. If there are multiple objects my code just selects one and processes that. My code is as follows:

 string imgPath = defTempPath + "\\" + "picTemp.jpg";// main image to process
                sketchImg = Cv2.ImRead(imgPath, ImreadModes.AnyColor);
                if (sketchImg != null)
                {
                    Mat img = new Mat(sketchImg.Rows, sketchImg.Cols, MatType.CV_8UC1);
                    Cv2.CvtColor(sketchImg, img, ColorConversionCodes.BGR2GRAY);
                    Mat I = new Mat();
                    Cv2.Threshold(img, I, 50, 255, ThresholdTypes.BinaryInv);
                    //Cv2.Dilate(I, I, Cv2.GetStructuringElement(MorphShapes.Rect, new OpenCvSharp.Size(3, 3)));
                    OpenCvSharp.Point[][] contours;
                    HierarchyIndex[] hierarchyIndexes;
                    Cv2.FindContours(I, out contours, out hierarchyIndexes, RetrievalModes.CComp, ContourApproximationModes.ApproxSimple, null);

                    int mind = -1;
                    double marea = 0;
                    int i = 0;
                    while (i >= 0)
                    {
                        double area = Cv2.ContourArea(contours[i]);
                        if (area > marea)
                        {
                            marea = area;
                            mind = i;
                        }
                        i = hierarchyIndexes[i].Next;
                    }

                    if (mind != -1)
                    {
                        Mat mask1 = new Mat(img.Rows, img.Cols, sketchImg.Type());
                        mask1.SetTo(new Scalar(0, 0, 0));
                        Mat mask2 = new Mat(img.Rows, img.Cols, sketchImg.Type());
                        mask2.SetTo(new Scalar(0, 0, 0));
                        var contour = contours[mind];
                        List<OpenCvSharp.Point> points = contour.ToList();
                        List<List<OpenCvSharp.Point>> cnt = new List<List<OpenCvSharp.Point>>();
                        cnt.Add(points);

                        Cv2.FillPoly(mask1, cnt, new Scalar(255, 255, 255));

                        i = 0;
                        while (i >= 0)
                        {
                            cnt.Clear();
                            if (i == mind)
                            {
                                i = hierarchyIndexes[i].Next;
                            }
                            else
                            {
                                contour = contours[i];
                                points = contour.ToList();
                                cnt.Add(points);
                                Cv2.FillPoly(mask2, cnt, new Scalar(255, 255, 255));

                                i = hierarchyIndexes[i].Next;
                            }
                        }

                        Mat mask = new Mat();
                        Cv2.Subtract(mask1, mask2, mask);

                        if (bgImg == null)
                        {
                            bgImg = new Mat(sketchImg.Rows, sketchImg.Cols, sketchImg.Type());
                            bgImg.SetTo(new Scalar(0));
                        }
                        if (fgImg == null)
                        {
                            fgImg = new Mat(sketchImg.Rows, sketchImg.Cols, sketchImg.Type());
                            fgImg.SetTo(new Scalar(255));
                        }

                        bgImg = bgImg.Resize(sketchImg.Size());
                        fgImg = fgImg.Resize(sketchImg.Size());
                        Mat res1 = new Mat(sketchImg.Rows, sketchImg.Cols, sketchImg.Type());
                        Mat res2 = new Mat(sketchImg.Rows, sketchImg.Cols, sketchImg.Type());
                        res = new Mat(sketchImg.Rows, sketchImg.Cols, sketchImg.Type());


                        Cv2.BitwiseAnd(fgImg, mask, res1);
                        Cv2.BitwiseNot(mask, mask);
                        Cv2.BitwiseAnd(bgImg, mask, res2);
                        Cv2.Add(res1, res2, res);

                   //     pictureBox2.SizeMode = PictureBoxSizeMode.Zoom;
                        pictureBox2.BackgroundImage = new Bitmap(res.ToMemoryStream(), false);
                        Cv2.ImWrite(defaultOutputPath + "\\op.jpg", res);

here is a sample picture of an image with multiple objects - can not figure out how to add image to post. These are basically line drawings Vector drawings converted to an image.