OpenCv案例（二）：基于OpenCVSharp计算图像中的圆的周长和面积

需求：求下图中圆形的面积和周长；

原图如下：

处理后图像： 

 

 计算结果：

代码如下：

 public Mat GetObjectByImg(Mat src,out double retArea, out double length)
        {
            retArea = 0;
            length = 0;
            //二值化
            Mat binaryMat = new Mat();
            Cv2.Threshold(src, binaryMat, 0, 255, ThresholdTypes.Binary | ThresholdTypes.Otsu);
            Cv2.ImShow("binaryImg", binaryMat);

            //形态学操作
            Mat kernel = Cv2.GetStructuringElement(MorphShapes.Rect, new Size(9, 9), new Point(-1, -1));
            Mat dst = new Mat();
            //闭操作
            Cv2.MorphologyEx(binaryMat, dst, MorphTypes.Close, kernel, new Point(-1, -1));
            Cv2.ImShow("closeImg", dst);

            //开操作
            kernel = Cv2.GetStructuringElement(MorphShapes.Rect, new Size(9, 9), new Point(-1, -1));
            Cv2.MorphologyEx(dst, dst, MorphTypes.Open, kernel, new Point(-1, -1));
            Cv2.ImShow("openImg", dst);

            //轮廓查找
            Point[][] contours;
            HierarchyIndex[] hierarchies;
            Cv2.FindContours(dst, out contours, out hierarchies, RetrievalModes.Tree, ContourApproximationModes.ApproxSimple, new Point());

            Mat retImg = Mat.Zeros(src.Size(), MatType.CV_8UC1);
            int x = 0, y = 0;
            Mat circleImage = new Mat();
            for (int i = 0; i < contours.Length; i++)
            {
                //面积过滤
                double area = Cv2.ContourArea(contours[i]);
                if (area < 100)
                {
                    continue;
                }
                //横纵比例 当横纵比例为1:1时
                Rect rect = Cv2.BoundingRect(contours[i]);
                double ratio = Convert.ToDouble(rect.Width) / Convert.ToDouble(rect.Height);
                if (ratio > 0.9 && ratio < 1.1)
                {
                    Cv2.DrawContours(retImg, contours, i, new Scalar(255, 255, 0), 1, LineTypes.Link8);
                    retArea = area;
                    length = Cv2.ArcLength(contours[i], true);
                    x = rect.X + rect.Width / 2;
                    y = rect.Y + rect.Height / 2;

                    Cv2.Circle(retImg, x, y, 2, new Scalar(128, 128, 128), 2, LineTypes.Link8, 0);
                }
            }
            Cv2.ImShow("retImg", retImg);

            circleImage = src.Clone();
            Cv2.CvtColor(circleImage, circleImage, ColorConversionCodes.GRAY2BGR);
            Cv2.Circle(circleImage, x, y, 2, new Scalar(0, 0, 255), 2, LineTypes.Link8, 0);
            Cv2.ImShow("circleImage", circleImage);
            return circleImage;
        }

该案例基本操作步骤如上，针对于类似案例以及适当调节以上使用的算法参数；