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 -1;
    }
    src = ~src;//取反
    imshow("原图", src);
    //二值化
    threshold(src, binary, 0, 255, 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 = 0; t < contours.size(); t++)
    {
        double area = contourArea(contours[t]);
        if (area < 40000) continue;//将面积小于40000的去掉
        drawContours(Triangle, contours, t, Scalar(0, 0, 255), 2, 8, Mat(), 0, Point());
    }

    for (size_t t = 0; t < contours.size(); t++)
    {
        double area = contourArea(contours[t]);
        if (area > 40000 || area<20000) continue;//将面积小于40000的去掉
        drawContours(BigCircle, contours, t, Scalar(0, 0, 255), 2, 8, Mat(), 0, Point());
    }

    for (size_t t = 0; t < contours.size(); t++)
    {
        double area = contourArea(contours[t]);
        if (area > 20000 || area<15000) continue;//将面积小于40000的去掉
        drawContours(Rect, contours, t, Scalar(0, 0, 255), 2, 8, Mat(), 0, Point());
    }

    for (size_t t = 0; t < contours.size(); t++)
    {
        double area = contourArea(contours[t]);
        if (area > 15000) 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(0, 0, 255), 2, 8, Mat(), 0, Point());
    }
    imshow("Triangle", Triangle);
    imshow("BigCircle", BigCircle);
    imshow("Rect", Rect1);
    imshow("SmallCircle", SmallCircle);

    waitKey(0);
    return 0;
}

 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 -1;
    }
    imshow("Input Image",src);
      
    //二值化
    cvtColor(src, src_gray, COLOR_BGR2GRAY);
    threshold(src_gray, binary, 0, 255, 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 = 0; t < contours.size(); t++)
    {
                
        int epsilon = 0.01*arcLength(contours[t], true);
        approxPolyDP(contours[t], point, epsilon, true);
        if(point.size()==3)
        {
            drawContours(Triangle, contours, t, Scalar(0, 0, 255), 2, 8, Mat(), 0, Point());//dst必须先初始化 
        }
        else if (point.size() == 4)
        {
            drawContours(Rect, contours, t, Scalar(0, 0, 255), 2, 8, Mat(), 0, Point());//dst必须先初始化
        }

        else 
        {
            double area = contourArea(contours[t]);
            if (area < 15000)
            {
                drawContours(SmallCircle, contours, t, Scalar(0, 0, 255), 2, 8, Mat(), 0, Point());//dst必须先初始化
            }
            else
            {
                drawContours(BigCircle, contours, t, Scalar(0, 0, 255), 2, 8, Mat(), 0, 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(0);

    return 0;
}