28、【opencv入门】轮廓查找与绘制（6）——外接圆、椭圆拟合、逼近多边形曲线、计算轮廓面积及长度、提取不规则轮廓

一、轮廓最小外接圆---minEnclosingCircle()

CV_EXPORTS_W void minEnclosingCircle(InputArray points, CV_OUT Point2f& center, CV_OUT float& radius);

　　points: 输入的二维点集, 可以填Mat类型或std::vector

　　center: Point2f&类型的center, 圆的输出圆心

　　radius: float&类型, 表示圆的输出半径

//最小外接圆
#include "opencv2/opencv.hpp"
#include<iostream>

using namespace std;
using namespace cv;

int main() 
{
    Mat srcImg = imread("1.png");
    imshow("src", srcImg);
    Mat dstImg = srcImg.clone();
    GaussianBlur(srcImg, srcImg, Size(3, 3), 0, 0);
    cvtColor(srcImg, srcImg, CV_BGR2GRAY);
    Canny(srcImg, srcImg, 100, 200);
    imshow("Canny", srcImg);

    //查找轮廓
    vector<vector<Point>> contours;
    vector<Vec4i> hierarcy;
    findContours(srcImg, contours, hierarcy, CV_RETR_TREE, CV_CHAIN_APPROX_NONE);
    cout << "num=" << contours.size() << endl;

    Point2f center;  //定义圆中心坐标
    float radius;  //定义圆半径
    for (int i = 0; i<contours.size(); i++)  //依次遍历每个轮廓
    {
        minEnclosingCircle(Mat(contours[i]), center, radius);
        drawContours(dstImg, contours, i, Scalar(0, 0, 255), 2, 8);
        circle(dstImg, center, radius, Scalar(0, 255, 0), 2, 8);  //绘制第i个轮廓的最小外接圆
    }
    imshow("dst", dstImg);

    waitKey(0);
    return 0;
}

二、轮廓椭圆拟合---fitEllipse()

CV_EXPORTS_W RotatedRect fitElipse(InputArray points);

　　points: 输入的二维点集, 可以填Mat类型或std::vector

　　返回值: RotatedRect类旋转矩形对象

//轮廓椭圆拟合
#include "opencv2/opencv.hpp"

using namespace cv;

int main() 
{
    Mat srcImg = imread("1.png");
    imshow("src", srcImg);
    Mat dstImg = srcImg.clone();
    GaussianBlur(srcImg, srcImg, Size(3, 3), 0, 0);
    cvtColor(srcImg, srcImg, CV_BGR2GRAY);
    Canny(srcImg, srcImg, 100, 200);
    imshow("Canny", srcImg);

    //查找轮廓
    vector<vector<Point>> contours;
    vector<Vec4i> hierarcy;
    findContours(srcImg, contours, hierarcy, CV_RETR_TREE, CV_CHAIN_APPROX_NONE);

    vector<RotatedRect> box(contours.size());
    Point2f rect[4];
    for (int i = 0; i<contours.size(); i++)
    {
        box[i] = fitEllipse(Mat(contours[i]));
        //ellipse(dstImg, box[i].center, Size(box[i].size.width/2, box[i].size.height/2), box[i].angle, 0, 360, Scalar(0, 255, 0), 2, 8);
        ellipse(dstImg, box[i], Scalar(0, 255, 0), 2, 8);
    }
    imshow("dst", dstImg);

    waitKey(0);
    return 0;
}

三、逼近多边形曲线---approxPolyDP()

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

　　curve: 输入的二维点集, 可以填Mat类型或std::vector

　　approxCurve: 多边形逼近的结果, 其类型和输入二维点集类型一致

　　epsilon: 逼近的精度, 为原始曲线和近似曲线间的最大值

　　closed: 如果其为真, 则近似的曲线为封闭曲线, 否则近似的曲线不封闭

//逼近多边形曲线
#include "opencv2/opencv.hpp"
using namespace cv;

int main() 
{
    Mat srcImg = imread("2.jpg");
    imshow("src", srcImg);
    Mat dstImg = srcImg.clone();
    Mat dstImg2(srcImg.size(), CV_8UC3, Scalar::all(0));//全黑图像

    GaussianBlur(srcImg, srcImg, Size(3, 3), 0, 0);
    cvtColor(srcImg, srcImg, CV_BGR2GRAY);
    //Canny(srcImg, srcImg, 100, 200);
    threshold(srcImg, srcImg, 200, 255, CV_THRESH_BINARY_INV);
    imshow("threshold", srcImg);

    vector<vector<Point>> contours;
    vector<Vec4i> hierarcy;
    findContours(srcImg, contours, hierarcy, CV_RETR_TREE, CV_CHAIN_APPROX_NONE);
    vector<vector<Point>> contours_poly(contours.size());

    for (int i = 0; i<contours.size(); i++)
    {
        approxPolyDP(Mat(contours[i]), contours_poly[i],15, true);//true曲线封闭，反之不封闭
        drawContours(dstImg, contours, i, Scalar(0, 255, 0), 2, 8);//绘制轮廓
        drawContours(dstImg2, contours_poly, i, Scalar(0, 255, 255), 2, 8);  //绘制多边形逼近
    }
    imshow("dst", dstImg);
    imshow("approx", dstImg2);

    waitKey(0);
    return 0;
}

 四、计算轮廓面积---contourArea()

CV_EXPORTS_W double contourArea(InputArray contour, bool oriented=false);

　　contour: 输入的二维点集或轮廓, 可以填Mat类型或std::vector

　　oriented: 默认值false, 表示返回面积为绝对值, 负责带符号

　　返回值: double类型返回轮廓面积

 五、计算轮廓长度---arcLength()

CV_EXPORTS_W double arcLength(InputArray curve, bool closed);

　　curve: 输入的二维点集, 可以填Mat类型或std::vector

　　colsed: 用于指示曲线是否封闭的标识符, 默认值true, 表示曲线封闭 

　　返回值: double类型返回轮廓长度

注:contourArea()&& arcLength()可用于轮廓删选 

//计算轮廓面积和轮廓长度
#include "opencv2/opencv.hpp"
#include<iostream>

using namespace std;
using namespace cv;

int main() 
{
    Mat srcImg = imread("3.jpg");
    imshow("src", srcImg);
    Mat dstImg = srcImg.clone();
    Mat dstImg2(srcImg.size(), CV_8UC3, Scalar::all(0));

    GaussianBlur(srcImg, srcImg, Size(3, 3), 0, 0);
    cvtColor(srcImg, srcImg, CV_BGR2GRAY);
    //Canny(srcImg, srcImg, 100, 200);
    threshold(srcImg, srcImg, 200, 255, CV_THRESH_BINARY);
    imshow("threshold", srcImg);

    vector<vector<Point>> contours;
    vector<Vec4i> hierarcy;
    findContours(srcImg, contours, hierarcy, CV_RETR_TREE, CV_CHAIN_APPROX_NONE);
    cout << "num=" << contours.size() << endl;

    for (int i = 0; i<contours.size(); i++)
    {
        double area = contourArea(contours[i]);//计算第i个轮廓的面积
        cout<<"area--"<<i<<"---"<<area<<endl;

        double length = arcLength(contours[i], true);
        cout << "length--" << i << "---" << length << endl;
        //if(area>10000)  //面积大约1W
        //if(area> 100 && area<300)

        if (length<300 && area>300)  
            drawContours(dstImg, contours, i, Scalar(0, 0, 255), 2, 8);
    }
    imshow("dst", dstImg);
    waitKey(0);
    return 0;
}

六、提取不规则轮廓

//提取不规则轮廓
#include "opencv2/opencv.hpp"

using namespace cv;

int main() 
{
    Mat srcImg = imread("2.jpg");
    imshow("src", srcImg);
    Mat dstImg = srcImg.clone();  //原图备份
    Mat tempImg = srcImg.clone();  //原图备份
    Mat tempImg2(srcImg.size(), CV_8UC3, Scalar::all(0));  //定义全黑的和原图一样大小的图像
    Mat draw(srcImg.size(), CV_8UC3, Scalar::all(0)); 
    Mat tempImg3(srcImg.size(), CV_8UC3, Scalar::all(0)); 

    GaussianBlur(srcImg, srcImg, Size(3, 3), 0, 0);
    cvtColor(srcImg, srcImg, CV_BGR2GRAY);
    threshold(srcImg, srcImg, 100, 255, CV_THRESH_BINARY); //二值化
    imshow("threshold", srcImg);

    vector<vector<Point>> contours;
    vector<Vec4i> hierarcy;
    findContours(srcImg, contours, hierarcy, CV_RETR_TREE, CV_CHAIN_APPROX_NONE);
    while (1)
    {
        for (int i = 0; i<contours.size(); i++)
        {
            tempImg2.copyTo(draw);  //每次进入将draw清空为全黑
            tempImg2.copyTo(tempImg3); 
            //drawContours(dstImg, contours, i, Scalar(0, 255, 0), 5, 8);    
            drawContours(draw, contours, i, Scalar(255, 255, 255), -1, 8);
            Mat mask;  //定义掩码
            cvtColor(draw, mask, CV_BGR2GRAY);
            tempImg.copyTo(tempImg3, mask);  //将tempImg 复制到tempImg3(只有mask部分被复制)
            imshow("draw", draw);
            imshow("result", tempImg3);
            char key = waitKey();
            if (key == 27)  //按下Esc键跳出for循环
                break;
        }
        break;
    }
    return 0;
}