OpenCV (C++) 几何形状识别（面积过滤、横纵比过滤等等）

 #include <opencv2/opencv.hpp>
 #include <iostream>
 #include <math.h>

 using namespace cv;
 using namespace std;

 int main(int argc, char** argv)
 {
     Mat src = imread("3 input.bmp", IMREAD_GRAYSCALE);
     Mat binary, dst = Mat::zeros(src.size(), CV_8UC3);
     Mat Triangle = dst.clone(), Rect1 = dst.clone(), BigCircle = dst.clone(), SmallCircle = dst.clone();

     if (src.empty()) {
         printf("Could not load image...");
         return -;
     }
     src = ~src;//取反
     imshow("原图", src);
     //二值化
     threshold(src, binary, , , THRESH_BINARY | THRESH_OTSU);

     //发现轮廓
     vector<vector<Point>> contours;
     vector<Vec4i> hireachy;
     findContours(binary, contours, hireachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point());

     //面积删选
     for (size_t t = ; t < contours.size(); t++)
     {
         double area = contourArea(contours[t]);
         if (area < ) continue;//将面积小于40000的去掉
         drawContours(Triangle, contours, t, Scalar(, , ), , , Mat(), , Point());
     }

     for (size_t t = ; t < contours.size(); t++)
     {
         double area = contourArea(contours[t]);
         if (area >  || area<) continue;//将面积小于40000的去掉
         drawContours(BigCircle, contours, t, Scalar(, , ), , , Mat(), , Point());
     }

     for (size_t t = ; t < contours.size(); t++)
     {
         double area = contourArea(contours[t]);
         if (area >  || area<) continue;//将面积小于40000的去掉
         drawContours(Rect, contours, t, Scalar(, , ), , , Mat(), , Point());
     }

     for (size_t t = ; t < contours.size(); t++)
     {
         double area = contourArea(contours[t]);
         if (area > ) continue;//将面积小于40000的去掉
         //其他过滤方法

         /*//横纵比过滤
         Rect rect= boundingRect(contours[t]);//返回最小外接矩形
         float ratio = float(rect.width) / float(rect.height);//计算横纵比
         if (ratio<1.1&&ratio>0.9) {}

         //周长过滤
         float length = arcLength(contours[t], true);//计算轮廓长度

         */

         drawContours(SmallCircle, contours, t, Scalar(, , ), , , Mat(), , Point());
     }
     imshow("Triangle", Triangle);
     imshow("BigCircle", BigCircle);
     imshow("Rect", Rect1);
     imshow("SmallCircle", SmallCircle);

     waitKey();
     return ;
 }

方法二：多边形逼近：

void approxPolyDP(InputArray curve, OutputArray approxCurve, double epsilon, bool closed)；

参数说明：

InputArray curve：输入的点集
OutputArray approxCurve：输出的点集，当前点集是能最小包容指定点集的。draw出来即是一个多边形；
double epsilon：指定的精度，也即是原始曲线与近似曲线之间的最大距离。
bool closed：若为true,则说明近似曲线是闭合的，它的首位都是相连，反之，若为false，则断开。

 #include <opencv2/opencv.hpp>
 #include <iostream>

 #define MATCHMETHOD TM_SQDIFF_NORMED//宏定义匹配模式
 using namespace cv;
 using namespace std;

 int main(int argc, char** argv)
 {
     Mat src = imread("F:/2019视觉培训内容/2019视觉培训内容/3 input.bmp");
     Mat src_gray,binary ;
     Mat Triangle = src.clone(), Rect = src.clone(), BigCircle = src.clone(), SmallCircle = src.clone();
     if (src.empty()) {
         printf("Could not load image...");
         return -;
     }
     imshow("Input Image",src);

     //二值化
     cvtColor(src, src_gray, COLOR_BGR2GRAY);
     threshold(src_gray, binary, , , THRESH_BINARY | THRESH_OTSU);
     binary = ~binary;
     imshow("binary", binary);

     //发现轮廓
     vector<vector<Point>> contours;
     vector<Point> point;
     vector<Vec4i> hireachy;
     findContours(binary, contours, hireachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point());

     //绘制出所有轮廓
     for (size_t t = ; t < contours.size(); t++)
     {

         int epsilon = 0.01*arcLength(contours[t], true);
         approxPolyDP(contours[t], point, epsilon, true);
         if(point.size()==)
         {
             drawContours(Triangle, contours, t, Scalar(, , ), , , Mat(), , Point());//dst必须先初始化
         }
         else if (point.size() == )
         {
             drawContours(Rect, contours, t, Scalar(, , ), , , Mat(), , Point());//dst必须先初始化
         }

         else
         {
             double area = contourArea(contours[t]);
             if (area < )
             {
                 drawContours(SmallCircle, contours, t, Scalar(, , ), , , Mat(), , Point());//dst必须先初始化
             }
             else
             {
                 drawContours(BigCircle, contours, t, Scalar(, , ), , , Mat(), , Point());//dst必须先初始化
             }
         }

         cout << "边的数目：" << point.size() << endl;
     }

     imshow("Triangle", Triangle);
     imshow("BigCircle", BigCircle);
     imshow("Rect", Rect);
     imshow("SmallCircle", SmallCircle);

     waitKey();

     return ;
 }