Question

I’m new to opencv, and write an very simple program to display the images captured from camera.

The code is:

#include "cv.h"
#include "highgui.h"

int main(int argc, char** argv) {
    cvNamedWindow("win");

    CvCapture* capture = cvCreateCameraCapture(0);
    IplImage* frame = cvQueryFrame(capture);
    IplImage* out = cvCreateImage(cvGetSize(frame), frame->depth, 1);
    while(1) {
        frame = cvQueryFrame(capture);
        if(!frame) break;
        cvCanny(frame, out, 10, 100, 30);
        cvShowImage("win", out);  // !!!!! this line thrown exception

        char c = cvWaitKey(20);
        if(c==27) break;
    }

    cvReleaseImage(&out);
    cvReleaseCapture(&capture);
    cvDestroyWindow("win");
    return 0;
}

But when I run it, it throws exception:

Unhandled exception at at 0x000007FEFDD0CACD in Project2.exe: Microsoft C++ exception: cv::Exception at memory location 0x000000000024DA50.

Where is wrong, and how to fix it?

---

Update

At last, I found the reason:

cvCanny(frame, out, 10, 100, 30);

The last argument is too big, if I change it to 3, everything works fine.

Answer 1

Never used opencv before, but I’m going to take a guess here that one of the following:

 CvCapture* capture = cvCreateCameraCapture(0);
 IplImage* frame = cvQueryFrame(capture);
 IplImage* out = cvCreateImage(cvGetSize(frame), frame->depth, 1);

is NULL or invalid, and since you are then passing them onto other functions you are getting crashes further on.