segmentation failed (core dumped) working with opencv

Question

I'm running into a problem, trying to perform a template matching using OpenCV on Ubuntu 18.04LTS

#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>

using namespace std;
using namespace cv;

int main( int argc, char** argv )
{
    int match_method =5;
    string image_window = "Source Image";
    string result_window = "Result window";
    Mat img, templ, result;

    /// Load image and template
    img = imread("./RI2.jpg", IMREAD_GRAYSCALE );
    templ = imread("./Pump2.jpg", IMREAD_GRAYSCALE );

    /// Create windows
    //namedWindow( image_window, WINDOW_AUTOSIZE );
    //namedWindow( result_window, WINDOW_AUTOSIZE );

    /// Source image to display
    Mat img_display;
    img.copyTo( img_display );

    /// Create the result matrix
    int result_cols =  img.cols - templ.cols + 1;
    int result_rows = img.rows - templ.rows + 1;
    result.create( result_rows, result_cols, CV_32FC1 );


    /// Do the Matching and Normalize
    matchTemplate( img, templ, result, match_method );
    normalize( result, result, 0, 1, NORM_MINMAX, -1, Mat() );
    Mat resultgrey(result_rows, result_cols, CV_8UC1);

    cout << "resultgrey.size().width: " << resultgrey.size().width << endl;
    cout << "resultgrey.size().height: " << resultgrey.size().height << endl;
    cout << "result.size().width: " << result.size().width << endl;
    cout << "result.size().height: " << result.size().height << endl;

    if( match_method  == 0 || match_method == 1 )
    {
        for (int i=0; i<result.size().width; i++)
        {
            for (int j=0; j<result.size().height; j++)
            {
                if (result.at<float>(i,j)>=0.1)
                {
                    resultgrey.at<int>(i,j)=0;
                }
                else
                {
                    resultgrey.at<int>(i,j)=1;

                }
            }
        }
    }


    else
    {
        for (int i=0; i<result.size().width; i++)
        {
            for (int j=0; j<result.size().height; j++)
            {
                if (result.at<float>(i,j)<=0.98)
                {
                    resultgrey.at<int>(i,j)=0;
                    //cout << "0" << endl;
                }
                else
                {
                    resultgrey.at<int>(i,j)=1;
                    //cout << "1" << endl;
                }
            }
        }
    }

    cout << "3" << endl;

    /// Localizing the objects
    vector<Point> matchLoclist;

    //cout << resultgrey << endl;
    findNonZero(resultgrey, matchLoclist);
    cout << "4" << endl;

    if (matchLoclist.size() == 0)
    {
        cout << "no matches found" << endl;
        return 0;
    }

    ///Draw Rectangles on Pumps found in the scene
    for (int i=0; i<matchLoclist.size(); i++)
    {
        //cout << "matchLoclist[i].x: "<<matchLoclist[i].x  << endl << "matchLoclist[i].y: " << matchLoclist[i].y << endl;
        rectangle( img_display, matchLoclist[i], Point( matchLoclist[i].x + templ.cols, matchLoclist[i].y + templ.rows ), Scalar::all(0), 2, 8, 0 );
        rectangle( result, matchLoclist[i], Point( matchLoclist[i].x + templ.cols, matchLoclist[i].y + templ.rows ), Scalar::all(0), 2, 8, 0 );
    }

    imshow( image_window, img_display );
    imshow( result_window, result );

    waitKey(0);
    return 0;
}

as an output i get:

xxx@ubuntu:~/Projects/Template_matching$ ./template_matching

resultgrey.size().width: 1216

resultgrey.size().height: 723

result.size().width: 1216

result.size().height: 723

Segmentation fault (core dumped)

This happens during the double for-loop where either a 1 or a 0 gets written into "resultrgrey" as I never get the "3" as an output from the cout below

if I take different input pictures (espacially smaller ones) the programm tends to run without this error.

I appreciate any help or suggestions!

Alex

wl2776 · Accepted Answer · 2018-05-30 09:18:39Z

1

You write outside of the allocated buffer because of (1) incorrectly specified data types and (2) swapped arguments to .at, as @rafix07 has noted.

You create 8-bit matrix (8 in CV_8UC1):

Mat resultgrey(result_rows, result_cols, CV_8UC1);

but try to assign 32-bit values to its elements in double-for loop:

resultgrey.at<int>(i,j)=0;

Template method cv::Mat::at calculates address of the (i,j)-th element in memory, based on:

data type, specified in template instantiation,
pointer to data start, stored in the cv::Mat instance,
and data stride (distance in bytes between leftmost pixels of two consecutive lines), also stored in the cv::Mat instance.

Then it returns reference to it. No checks is performed, for speed, therefore it's your responsibility to submit correct arguments.

Size of int is 32 bits on most modern platforms, but can be differrent.

Generally, it is safer to use types from stdint.h header, that have explicit length and sign in their names: uint8_t, int32_t, etc

edited May 30, 2018 at 9:18

answered May 29, 2018 at 9:52

wl2776

4,3794 gold badges39 silver badges94 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Alex Over a year ago

Thank you for your answer! Works like a charm now!

rafix07 · Accepted Answer · 2018-05-29 09:56:46Z

1

Look at reference about Mat::at method

const _Tp& cv::Mat::at    ( int i0, int i1 ) const 
  Parameters  
   i0 Index along the dimension 0
   i1 Index along the dimension 1

the first dimenstion is number of rows, the second dim is number of columns, so you should change all lines in your code with at

resultgrey.at<int>(i,j) // i means col, j means row

to

resultgrey.at<int>(j,i)

answered May 29, 2018 at 9:56

rafix07

21.3k3 gold badges26 silver badges36 bronze badges

1 Comment

Alex Over a year ago

Thank you for your answer! Its these careless mistakes, that sometimes just get me -.-'

Collectives™ on Stack Overflow

segmentation failed (core dumped) working with opencv

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related