C++opencv获取矩形角点的像素坐标

Question

问题遇到的现象和发生背景

类似这种墙面上的相框，怎么通过C++opencv获取矩形相框角点的像素坐标

我的解答思路和尝试过的方法

ORB::create()存在的问题：在矩形角上选了很多个特征点，另外识别的是整个画面的特征点，找不到哪个坐标是期望矩形的角点

我想要达到的结果

Answer 1

仅供参考：

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/imgproc/imgproc_c.h"
#include "opencv2\highgui\highgui_c.h"
using namespace std;
using namespace cv;
Mat img,smallImg,gray,bw;
vector<Vec4i> hierarchy;
vector<vector<Point> > contours;
int threshval=128;
Rect r;
Rect maxrect,brect;
int idx,n;
const static Scalar colors[15]={
    CV_RGB(  0,  0,128),
    CV_RGB(  0,128,  0),
    CV_RGB(  0,128,128),
    CV_RGB(128,  0,  0),
    CV_RGB(128,  0,128),
    CV_RGB(128,128,  0),
    CV_RGB(128,128,128),
    CV_RGB(160,160,160),
    CV_RGB(  0,  0,255),
    CV_RGB(  0,255,  0),
    CV_RGB(  0,255,255),
    CV_RGB(255,  0,  0),
    CV_RGB(255,  0,255),
    CV_RGB(255,255,  0),
    CV_RGB(255,255,255),
};
Scalar color;
void gamma_correct(Mat& img, Mat& dst, double gamma) {
    Mat tmp;

    img.convertTo(tmp, CV_32FC1, 1.0/255.0, 0.0);
    pow(tmp, gamma, tmp);
    tmp.convertTo(dst , CV_8UC1,     255.0, 0.0);
}
int main() {
    cvNamedWindow("display",1);
    img=imread("image.jpg",1);
    r.x     =img.cols*1/10;
    r.y     =img.rows*1/5;
    r.width =img.cols*8/10;
    r.height=img.rows*3/5;
    smallImg=img(r);
    cvtColor(smallImg,gray,CV_BGR2GRAY);
//  medianBlur(gray,gray,5);
    equalizeHist(gray,gray);
    gamma_correct(gray,gray,4.0);
    imshow("display",gray);
    waitKey(0);

    bw=(gray>threshval);
    imshow("display",bw);
    waitKey(0);

//  Mat Structure1=getStructuringElement(MORPH_RECT   ,Size(6,6));
    Mat Structure1=getStructuringElement(MORPH_ELLIPSE,Size(6,6));
    dilate(bw,bw,Structure1, Point(-1,-1));
    imshow("display",bw);
    waitKey(0);

    Mat Structure0=getStructuringElement(MORPH_RECT   ,Size(3,3));
    Mat Structure0=getStructuringElement(MORPH_ELLIPSE,Size(3,3));
    erode(bw,bw,Structure0,Point(-1,-1));
    imshow("display",bw);
    waitKey(0);

    findContours(bw,contours,hierarchy,RETR_EXTERNAL,CHAIN_APPROX_SIMPLE);
    if (!contours.empty()&&!hierarchy.empty()) {
        idx=0;
        n=0;
        vector<Point> approx;
        for (;idx>=0;idx=hierarchy[idx][0]) {
            color=colors[idx%15];
//          drawContours(smallImg,contours,idx,color,1,8,hierarchy);
            approxPolyDP(Mat(contours[idx]), approx, arcLength(Mat(contours[idx]), true)*0.005, true);//0.005为将毛边拉直的系数
            const Point* p = &approx[0];
            int m=(int)approx.size();
            polylines(smallImg, &p, &m, 1, true, color);
            circle(smallImg,Point(p[0].x,p[0].y),3,color);
            circle(smallImg,Point(p[1].x,p[1].y),2,color);
            for (int i=2;i<m;i++) circle(smallImg,Point(p[i].x,p[i].y),1,color);
            n++;
            if (1==n) {
                maxrect=boundingRect(Mat(contours[idx]));
            } else {
                brect=boundingRect(Mat(contours[idx]));
                CvRect mr;
                mr.x=maxrect.x;
                mr.y=maxrect.y;
                mr.width=maxrect.width;
                mr.height=maxrect.height;
                CvRect br;
                br.x=brect.x;
                br.y=brect.y;
                br.width=brect.width;
                br.height=brect.height;
                maxrect=cvMaxRect(&mr,&br);
            }
        }
        circle(smallImg,Point(maxrect.x+maxrect.width/2,maxrect.y+maxrect.height/2),2,CV_RGB(255,0,0));
    }
    imshow("display",smallImg);
    waitKey(0);
    cvDestroyWindow("display");
    return 0;
}