26-最小外接圆、椭圆、轮廓长度、轮廓面积（EmguCv学习）

总结

1、轮廓可以绘制：正外接矩形、最小外接矩形、最小外接圆、最小椭圆：其中最小外接矩形与最小椭圆在绘制时，如果轮廓点少于5个，会导致异常；！！
2、轮廓多边形逼近函数ApproxPolyDp()：输出结果为Point数组，可以使用CvInvoke.Polylines()函数进行绘制；
3、根据轮廓的面积，大小（按比例或绝对值）进行筛选，可以有效的提取出目标轮廓；
4、实验中第二个实例使用颜色识别提取轮廓更好。


epsilon : 单位为像素

Code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;using Emgu.CV;
using Emgu.Util;
using Emgu.CV.Structure;
using Emgu.CV.CvEnum;
using Emgu.CV.Util;
using System.Drawing;namespace lesson26
{class Program{static void Main(string[] args){最小外接圆//Mat src = CvInvoke.Imread("10.png");//Mat dst = src.Clone();//Mat grayImg = new Mat();//CvInvoke.Imshow("input", src);//CvInvoke.CvtColor(src, grayImg, ColorConversion.Bgr2Gray);//CvInvoke.Threshold(grayImg, grayImg, 100, 255, ThresholdType.Binary);//VectorOfVectorOfPoint contours = new VectorOfVectorOfPoint();//VectorOfRect hierarchy = new VectorOfRect();//CvInvoke.FindContours(grayImg, contours, hierarchy, RetrType.External, ChainApproxMethod.ChainApproxNone);//for(int i = 0; i < contours.Size; i++)//{//    CircleF circleF = CvInvoke.MinEnclosingCircle(contours[i]);     //计算最小外接圆//    RotatedRect rotatedRect = CvInvoke.FitEllipse(contours[i]);     //计算外接椭圆//    Point rcenter = new Point((int)rotatedRect.Center.X, (int)rotatedRect.Center.Y);//    Point center = new Point((int)circleF.Center.X,(int)circleF.Center.Y);//    CvInvoke.Circle(dst, center, (int)circleF.Radius, new MCvScalar(255, 0, 0), 2);//    CvInvoke.Ellipse(dst, rcenter, new Size((int)(rotatedRect.Size.Width/2), (int)(rotatedRect.Size.Height/2)), rotatedRect.Angle, 0, 360,//                new MCvScalar(0, 0, 255), 2);//    ///求取面积、周长、多边形逼近//    double length = CvInvoke.ArcLength(contours[i], true);   //计算轮廓周长//    double area = CvInvoke.ContourArea(contours[i], false);  //计算轮廓面积//    Console.WriteLine("contour {0} area: {1:N2}", i, length);//    Console.WriteLine("contour {0} length: {1:N2}", i, area);//    VectorOfPoint approxPoly = new VectorOfPoint();//    CvInvoke.ApproxPolyDP(contours[i], approxPoly, length * 0.02 , true);  //多变形轮廓拟合//    CvInvoke.Polylines(dst, approxPoly, true, new MCvScalar(255, 255, 0), 2); //绘制拟合多边形//}//CvInvoke.Imshow("result", dst);//CvInvoke.WaitKey(0);//利用掩膜不规则轮廓提取Mat src = CvInvoke.Imread("220.jpg");Mat dst = new Mat(src.Size, DepthType.Cv8U, 3);dst.SetTo(new MCvScalar(0, 0, 0));Mat maskImg = dst.Clone();            CvInvoke.Imshow("input", src);Mat grayImg = new Mat();CvInvoke.CvtColor(src, grayImg, ColorConversion.Bgr2Gray);CvInvoke.Threshold(grayImg, grayImg, 100, 255, ThresholdType.BinaryInv);CvInvoke.Imshow("threshold", grayImg);VectorOfVectorOfPoint contours = new VectorOfVectorOfPoint();VectorOfRect hierarchy = new VectorOfRect();CvInvoke.FindContours(grayImg, contours, hierarchy, RetrType.Tree, ChainApproxMethod.ChainApproxNone);for(int i = 0; i < contours.Size; i++){dst.SetTo(new MCvScalar(0, 0, 0));maskImg.SetTo(new MCvScalar(0, 0, 0));CvInvoke.DrawContours(maskImg, contours, i, new MCvScalar(255, 255, 255), -1);double area = CvInvoke.ContourArea(contours[i], false);if (area > 60)          //简单的轮廓面积筛选 {Mat mask = new Mat();CvInvoke.CvtColor(maskImg, mask, ColorConversion.Bgr2Gray);src.CopyTo(dst, mask);CvInvoke.Imshow("mask", mask);CvInvoke.Imshow("result", dst);CvInvoke.WaitKey(0);}}CvInvoke.WaitKey(0);}}
}

效果

1、最小外接圆，最小外接矩形：

2、轮廓提取