I've been trying to integrate Qt and OpenCV and ran into a strange problem: some OpenCV functions cause access violations, but only when called during a timerEvent. I simplified the code as much as possible as a proof of concept (see below). The two functions that crash are cvCvtColor (when converting from BGR to Gray) and cvCanny when the sobel aperture has a size greater than 3. Both of these functions work when called anywhere else in the program (e.g. constructor or main). But when called from a timerEvent, an access violation crashes the program. Any ideas?

WinXP
Qt 4.6.1 (mingw)
OpenCV 2.0.0a

CvDebug.pro
Qt Code: 
  1. TARGET = QtOpenCV
  2. TEMPLATE = app
  3.  
  4. INCLUDEPATH += C:\OpenCV\include\opencv
  5. LIBS += -L"C:\OpenCV\lib" -lcv200 -lhighgui200 -lcxcore200
  6. SOURCES += main.cpp CvDebug.cpp
  7. HEADERS += CvDebug.h
To copy to clipboard, switch view to plain text mode 

main.cpp
Qt Code: 
  1. #include <QtGui/QApplication>
  2. #include "CvDebug.h"
  3.  
  4. int main(int argc, char **argv)
  5. {
  6.     QApplication a(argc, argv);
  7.     CvDebug w;
  8.     w.show();
  9.     return a.exec();
  10. }
To copy to clipboard, switch view to plain text mode 

CvDebug.h
Qt Code: 
  1. #ifndef CVDEBUG_H
  2. #define CVDEBUG_H
  3.  
  4. #include <QtGui/QMainWindow>
  5. #include <cv.h>
  6. #include <highgui.h>
  7.  
  8. class CvDebug : public QMainWindow
  9. {
  10.     Q_OBJECT
  11.  
  12. public:
  13.     CvDebug(QWidget *parent = 0);
  14.     ~CvDebug();
  15.     CvCapture *camera;
  16.  
  17. protected:
  18.     void timerEvent(QTimerEvent*);
  19. };
  20.  
  21. #endif // CVDEBUG_H
To copy to clipboard, switch view to plain text mode 

CvDebug.cpp
Qt Code: 
  1. #include "CvDebug.h"
  2. #include <cv.h>
  3. #include <highgui.h>
  4. #include <cxcore.h>
  5.  
  6. CvDebug::CvDebug(QWidget *parent) : QMainWindow(parent)
  7. {
  8.     cvNamedWindow( "Color", CV_WINDOW_AUTOSIZE );
  9.     cvNamedWindow( "Gray",  CV_WINDOW_AUTOSIZE );
  10.     camera = cvCreateCameraCapture(0);
  11.  
  12.     startTimer(100);  // msec
  13. }
  14.  
  15. CvDebug::~CvDebug()
  16. {
  17.     cvDestroyWindow( "Color" );
  18.     cvDestroyWindow( "Gray" );
  19.     cvReleaseCapture(&camera);
  20. }
  21.  
  22. void CvDebug::timerEvent(QTimerEvent*)
  23. {
  24.     IplImage* image = cvQueryFrame( camera );
  25.     cvShowImage( "Color", image);
  26.     IplImage* grayImage = cvCreateImage( cvGetSize(image), IPL_DEPTH_8U, 1);
  27.     cvCvtColor( image, grayImage, CV_BGR2GRAY );
  28.     cvShowImage( "Gray", grayImage );
  29. }
To copy to clipboard, switch view to plain text mode