c++ - 曲线/路径骨架二值图像处理

Question

我正在尝试开发一种可以处理图像骨架的路径/曲线的代码。我想要一个来自两点之间骨架的点 vector 。

这段代码加了点就结束了，没找到解决办法。

 #include "opencv2/highgui/highgui.hpp"
 #include "opencv2/imgproc/imgproc.hpp"
 #include "opencv2/imgproc/imgproc_c.h"
 #include <opencv2/legacy/compat.hpp>
 #include <opencv2/core/core.hpp>
 #include <iostream>
 #include <cmath>
 #include <list>
 using namespace cv;
 using namespace std;

  //this method to find the 8-neighbors of a point from image 
 vector<Point> search8Neighbor(cv::Mat mat,Point startPoint)
 {
  vector<Point> segment;
  Point p;
    //uchar p1 = mat.at<uchar>(startPoint.x, startPoint.y);
    uchar p2 = mat.at<uchar>(startPoint.x-1, startPoint.y);
    uchar p3 = mat.at<uchar>(startPoint.x-1, startPoint.y+1);
    uchar p4 = mat.at<uchar>(startPoint.x, startPoint.y+1);
    uchar p5 = mat.at<uchar>(startPoint.x+1, startPoint.y+1);
    uchar p6 = mat.at<uchar>(startPoint.x+1, startPoint.y);
    uchar p7 = mat.at<uchar>(startPoint.x+1, startPoint.y-1);
    uchar p8 = mat.at<uchar>(startPoint.x, startPoint.y-1);
    uchar p9 = mat.at<uchar>(startPoint.x-1, startPoint.y-1);

    //if(p1==255) segment.push_back(startPoint.x, startPoint.y);
    if (p2 == 255) {
            p.x=startPoint.x-1;
            p.y=startPoint.y;
            segment.push_back(p);
    }
    if(p3==255) {
            p.x=startPoint.x-1;
            p.y=startPoint.y+1;
            segment.push_back(p);
    }

    if(p4==255) {
            p.x=startPoint.x;
            p.y=startPoint.y+1;
            segment.push_back(p);
    }

    if(p5==255) {
            p.x=startPoint.x+1;
            p.y=startPoint.y+1;
            segment.push_back(p);
    }

    if(p6==255) {
            p.x=startPoint.x+1;
            p.y=startPoint.y;
            segment.push_back(p);
    }
    if(p7==255) {
            p.x=startPoint.x+1;
            p.y=startPoint.y-1;
            segment.push_back(p);
    }
    if(p8==255){
            p.x=startPoint.x;
            p.y=startPoint.y-1;
            segment.push_back(p);
    }

    if(p9==255) {
            p.x=startPoint.x-1;
            p.y=startPoint.y-1;
            segment.push_back(p);
    }

    return segment ;

 }
  //this method return a vector of points from a skeleton that contains all the points 
 //  between a start point "peak" and an end point 
 //this method use the idea of Breadth first search 
  vector<Point> traceLine(Mat img , Point peak)
{
    vector<Point> vect1;
    vector<Point> vect2;
    img.at<uchar>(peak.x,peak.y)=0;//
    vect1.push_back(peak);//add peak to vect1
    while(vect1.size() != 0)
        {
        Point p=vect1[0];
        vect1.erase(vect1.begin());
        vect2.push_back(p);
        vector<Point> vectN;
        vectN=search8Neighbor(img,p);
        vector<Point>::iterator it;
        it = vect1.begin();
        //cout<<vectN.size()<<endl;
        for(int i=0;i<vectN.size();i++)
            {
                 img.at<uchar>(vectN[i].x,vectN[i].y)=0;
                vect1.insert(it,vectN[i]);

            }
        }
return vect2;
}

int main( int argc, char** argv )
{
cv::Mat im = cv::imread("aa.jpg",0);
if (im.empty())
return -1;
 cv::Mat img;
cv::threshold(im, img, 155, 255, CV_THRESH_BINARY);
vector<Point> vect1;
Point p;
p.x=20;
p.y=30;
if(mat.at<uchar>(p.x-1, p.y)==255)
vect1=traceLine(img,p);
imshow("image",im);
cv::waitKey();
return 0 ;
}

Answer 1

Mat 以矩阵的正常行/列方式进行索引，因此您需要 mat.at<uchar>(y, x) , 不是 mat.at<uchar>(x, y) , 否则会造成混淆。

你在哪里:

vector<Point>::iterator it;
it = vect1.begin();
...
for(...)
    vect1.insert(it,vectN[i]);

如果插入导致缓冲区被重新分配，这将中断，因为它随后指向一些已被释放的内存，或者可能重新分配给其他东西。而是使用

 vect1.insert(vect1.begin(),vectN[i]);

(这将对您的程序似乎执行的操作给出略微不同的顺序)或使用 push_back()真正获得广度优先行为。

最大的问题在于 search8Neighbor()。你在哪里uchar p2 = mat.at<uchar>(startPoint.x-1, startPoint.y);如果 startPoint 指向图像边缘的像素会怎样？您将引用图像外部的像素，并且程序将徘徊，直到发生异常。在这里，您需要检查您在图像中的位置，并确保附近没有包含来自图像外部的像素。

编辑我不相信如果像我说的那样改变代码就不会工作。我已经实现了修复并且它有效:

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/imgproc/imgproc_c.h"
#include <opencv2/legacy/compat.hpp>
#include <opencv2/core/core.hpp>
#include <iostream>
#include <cmath>
#include <list>
using namespace cv;
using namespace std;

 // Find the 8-neighbors of a point from image.
 vector<Point> search8Neighbor(cv::Mat mat,Point startPoint)
 {
    vector<Point> neighbors;
    vector<Point> offsets;
    offsets.push_back(Point(-1,  0)); // p2
    offsets.push_back(Point(-1,  1)); // p3
    offsets.push_back(Point( 0,  1)); // p4
    offsets.push_back(Point( 1,  1)); // p5
    offsets.push_back(Point( 1,  0)); // p6
    offsets.push_back(Point( 1, -1)); // p7
    offsets.push_back(Point( 0, -1)); // p8
    offsets.push_back(Point(-1, -1)); // p9

    vector<Point>::iterator it;
    for(it = offsets.begin(); it < offsets.end(); ++it)
    {
        if(!((it->x < 0 && startPoint.x == 0)
            || (it->y < 0 && startPoint.y == 0)
            || (it->x > 0 && startPoint.x == mat.cols - 1)
            || (it->y > 0 && startPoint.y == mat.rows - 1)))
        {
            Point p(startPoint + *it);
            if(mat.at<uchar>(p) == 255)
                neighbors.push_back(p);
        }
    }

    return neighbors;
 }

 //this method return a vector of points from a skeleton that contains all the points 
 //  between a start point "peak" and an end point 
 //this method use the idea of Breadth first search 
  vector<Point> traceLine(Mat img , Point peak)
{
    vector<Point> vect1;
    vector<Point> vect2;
    img.at<uchar>(peak.y, peak.x)=0;//
    vect1.push_back(peak);//add peak to vect1
    while(vect1.size() != 0)
        {
        Point p=vect1[0];
        vect1.erase(vect1.begin());
        vect2.push_back(p);
        vector<Point> vectN;
        vectN = search8Neighbor(img, p);

        //cout<< " vectN.size()=" << vectN.size()<<endl;

        for(int i = 0; i < int(vectN.size()); ++i)
            {
                img.at<uchar>(vectN[i].y, vectN[i].x)=0;
                vect1.push_back(vectN[i]);
            }
        }
    return vect2;
}

int main( int argc, char** argv )
{
    cv::Mat im = cv::imread("aa.jpg",0);
    if (im.empty())
        return -1;
    cv::Mat img;
    cv::threshold(im, img, 155, 255, CV_THRESH_BINARY);
    imshow("thresholded image",im);
    vector<Point> vect1;

    Point p(3, 32);
    uchar u = img.at<uchar>(p.x, p.y);
    if(img.at<uchar>(p) == 255)
        vect1 = traceLine(img, p);

    Mat output(im.rows, im.cols, CV_8UC3, Scalar(0, 0, 0));
    vector<Point>::iterator it;

    for(it = vect1.begin(); it < vect1.end(); ++it)
    {
        Vec3b green(0, 255, 0);
        output.at<Vec3b>(*it) = green;
    }
    imshow("output", output);
    cv::waitKey();
    return 0 ;
}