Athena Athena - 4 months ago 98
C++ Question

findContours does not find the contours in opencv

I've been trying to load an image from camera but I face an error. I believe that

findContours
function has got a problem. Here is the code:

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

using namespace cv;
using namespace std;

Mat src; Mat src_gray;
int max_thresh = 255;
RNG rng(12345);

/// Function header
void thresh_callback(int, void* );

/** @function main */
int main( int argc, char** argv )
{
/// Load source image and convert it to gray
VideoCapture cap(1);
cap>>src;

/// Convert image to gray and blur it
cvtColor( src, src_gray, CV_BGR2GRAY );
blur( src_gray, src_gray, Size(3,3) );

/// Create Window
char* source_window = "Source";
namedWindow( source_window, CV_WINDOW_AUTOSIZE );
imshow( source_window, src );

thresh_callback( 0, 0 );

waitKey(0);
return(0);
}

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

/// Detect edges using canny
Canny( src_gray, canny_output, 100, 100*2, 3 );
/// Find contours
findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );

/// Draw contours
Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );
for( int i = 0; i< contours.size(); i++ )
{
Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() );
}

/// Show in a window
namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
imshow( "Contours", drawing );
}


And here is the error:



  • Critical error detected c0000374
    ConsoleApplication8.exe has triggered a breakpoint.



I would appreciate any help.

Answer

I have had the same problem (or at least a similar one) with that function. I was not able to fix it, so I used the old C style cvFindContours function instead. I have included an example function in wich I used the cvFindContours function to clean up a blob image. This might not be the fastest solution, but at leas it works.

void filtBproject(Mat& Bproject){

    Scalar          color       = CV_RGB(255,255,255); // text color
    IplImage*       BprojectIpl =  &IplImage(Bproject);
    CvMemStorage*   storage     = cvCreateMemStorage(0);
    CvSeq*          contours    = 0;
    int             numCont     = 0;
    int             contAthresh = 45;

    numCont= cvFindContours( BprojectIpl, storage, &contours, sizeof(CvContour),
                    CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0) );

    cvSet(BprojectIpl, cvScalar(0,0,0));
    for( ; contours != 0; contours = contours->h_next )
        {

            if ( (cvContourArea(contours, CV_WHOLE_SEQ) > contAthresh) ){
                cvDrawContours( BprojectIpl, contours, color, color, -1, CV_FILLED, 8 );
            }
        }
}
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