如何找到轮廓opencv c ++的极端点

Question

我有这张图片：

如何在OpenCv c ++中实现极端点查找器代码，如图所示？

任何人都有任何想法吗？

# determine the most extreme points along the contour

leftmost = tuple(cnt [cnt[:,:,0].argmin()][0]);
rightmost = tuple(cnt [cnt[:,:,0].argmax()][0]);
topmost = tuple(cnt [cnt[:,:,1].argmin()][0]);
bottommost = tuple(cnt [cnt[:,:,1].argmax()][0]);

Answer 1

假设您已经拥有轮廓并且它是一个点矢量，您可以将std::minmax_element函数用于同一端。它支持一种比较方法，如果它遵循签名，它可以是任何你想要的。所以一个类似于你所做的简单代码：

#include <iostream>
#include <vector>
#include <algorithm>

// this is not necessary, just for testing (OpenCV Points should be used instead)
struct Point
{
    int x;
    int y;


    Point():
    x(0), y(0){}
    Point(int xVal, int yVal):
    x(xVal), y(yVal){}
};

int main()
{
    std::vector<Point> cnt = {
        {1,2},{4,5},{1,6}, {7,8}, {9,3}, {2,6}
    };

    // compare x axis
    auto val = std::minmax_element(cnt.begin(), cnt.end(), [](Point const& a, Point const& b){
        return a.x < b.x;
    });

    std::cout << " leftMost [ " << val.first->x << ", " << val.first->y << " ]" << std::endl;
    std::cout << " RightMost [ " << val.second->x << ", " << val.second->y << " ]" << std::endl;

    // compare y axis
    val = std::minmax_element(cnt.begin(), cnt.end(), [](Point const& a, Point const& b){
        return a.y < b.y;
    });

    std::cout << " TopMost [ " << val.first->x << ", " << val.first->y << " ]" << std::endl;
    std::cout << " BottomMost [ " << val.second->x << ", " << val.second->y << " ]" << std::endl;


    return 0;
}

这是运行它的link。

在这个例子中，Point结构只是为了模拟OpenCV，但它的工作方式完全相同。我创建了一个测试向量，运行minmax_element仅比较x轴并打印结果。我对y轴做同样的事情。

此函数向这些对象返回一对迭代器，如果需要返回它们，请确保复制它们：）

Answer 2

void thresh_callback(int, void* )
{
    Mat canny_output;
    vector<vector<Point> > contours;
    vector<Vec4i> hierarchy;

    Canny( src_gray, canny_output, thresh, thresh*2, 3 );
    findContours( canny_output, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(0, 0) );

    Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );

    for( size_t i = 0; i< contours.size(); i++ )
    {
        Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
        drawContours( drawing, contours, (int)i, color, 2, 8, hierarchy, 0, Point() );
    }

    namedWindow( "Contours", WINDOW_AUTOSIZE );
    imshow( "Contours", drawing );
}

使用此代码上面的代码是如何工作的