c# OpenCvSharp 计算轮廓面积与周长 ContourArea ArcLength

using OpenCvSharp;
using OpenCvSharp.Extensions;
using DlibDotNet;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Threading;

namespace app
{
    public partial class FrmMain : Form
    {
        public FrmMain()
        {
            InitializeComponent();
        }

        /// <summary>
        /// 面积周长
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnCalc_Click(object sender, EventArgs e)
        {
            // 加载图像
            Mat src = Cv2.ImRead(@"img\star.png");
            Cv2.ImShow("原图", src);


            // 如果背景色是白色，则需要进行此操作。即黑色变白色，白色变黑色。
            // 按位运算
            // opencv非运算不是1变0，0变1。而是 !x = 255 - x
            Cv2.BitwiseNot(src, src);
            //Cv2.ImShow("input image1", src);


            // 高斯模糊
            Mat blur = new Mat();
            Cv2.GaussianBlur(src, blur, new OpenCvSharp.Size(15, 15), 0, 0);
            Cv2.ImShow("滤波", blur);

            // 二值化
            Mat grayImg = new Mat();
            Mat binary = new Mat();
            Cv2.CvtColor(blur, grayImg, ColorConversionCodes.BGR2GRAY);
            Cv2.Threshold(grayImg, binary, 0, 255, ThresholdTypes.Binary | ThresholdTypes.Triangle);
            Cv2.ImShow("二值化", binary);

            // 形态学操作
            Mat morphImage = new Mat();
            Mat kernel = Cv2.GetStructuringElement(MorphShapes.Rect, new OpenCvSharp.Size(3, 3), new OpenCvSharp.Point(-1, -1));
            Cv2.MorphologyEx(binary, morphImage, MorphTypes.Close, kernel, new OpenCvSharp.Point(-1, -1), 2);
            Cv2.ImShow("形态学操作", morphImage);

            OpenCvSharp.Point[][] contours;
            HierarchyIndex[] hierarchies;
            // 寻找轮廓
            Cv2.FindContours(morphImage, out contours, out hierarchies, RetrievalModes.External, ContourApproximationModes.ApproxSimple, new OpenCvSharp.Point());
            
            Mat dest = Mat.Zeros(src.Size(), MatType.CV_8UC3);
            for (int i = 0; i < contours.Length; i++)
            {
                double area = Cv2.ContourArea(contours[i]);
                double len = Cv2.ArcLength(contours[i], true);
                Cv2.DrawContours(dest, contours, (int)i, new Scalar(0, 0, 255), 1, LineTypes.Link8, hierarchies);

                Cv2.PutText(dest, "area:" + area.ToString(""), new OpenCvSharp.Point(50, 50), HersheyFonts.HersheySimplex, 1, new Scalar(0, 0, 255), 2, LineTypes.Link4);
                Cv2.PutText(dest, "length:" + len.ToString("0.00"), new OpenCvSharp.Point(50, 150), HersheyFonts.HersheySimplex, 1, new Scalar(0, 0, 255), 2, LineTypes.Link4);
            }


            Cv2.ImShow("最后结果", dest);
            Cv2.WaitKey();

        }
    }
}