Can't capture Video from Cam in OpenCV 2.4.7 - c++

Question

This is my code which I copy/paste from here:
#include "opencv2/opencv.hpp"
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
Mat edges;
namedWindow("edges",1);
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
cvtColor(frame, edges, CV_BGR2GRAY);
GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
Canny(edges, edges, 0, 30, 3);
imshow("edges", edges);
if(waitKey(30) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
But I get this error:
OpenCV error: Assertion failed (scn==3 || scn==4)
in unknown function, file ..\..\..\..\opencv\modules\imgproc\src\color.cpp, line 3737
I am using Windows 7 x64, Visual Studio 2008, OpenCV 2.4.7
What can be the problem?
EDIT:
It is sometimes it works, sometimes it does not.
EDIT 2:
I edited VideoCapture cap(0); to cv::VideoCapture cap(0); then, I rebuild my solution and run it. It worked for the first time, I tried to run for the second time, it gave me the same error.
EDIT 3:
I have even edited for(;;):
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
imshow("edges", frame);
if(waitKey(30) >= 0) break;
}
This time I receive another error:
OpenCV error: Assertion failed (size.width>0 && size.height>0)
in unknown function, file ..\..\..\..\opencv\modules\highgui\src\window.cpp, line 261
I guess the problem is with imshow.

Answer 1

I get similar problem. I solve it by putting everything after cap >> frame into an if-statement:
for(;;)
{
Mat frame;
cap >> frame; // get a new frame from camera
if (!frame.empty()) {
cvtColor(frame, edges, CV_BGR2GRAY);
GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
Canny(edges, edges, 0, 30, 3);
imshow("edges", edges);
}
if(waitKey(30) >= 0) break;
}

Answer 2

I tested your code in my environment (Win XP 32 bit OS, VS2008, OpenCV2.4.7). It works normally every time. And you can also do it like this:
IplImage* frame,*edges;
CvCapture* pcapture = cvCreateCameraCapture(0);
cvNamedWindow("edges",CV_WINDOW_AUTOSIZE);
while (1)
{
frame = cvQueryFrame(pcapture);
if (!frame) break;
edges = cvCreateImage(cvGetSize(frame),8,1);
cvCvtColor(frame, edges, CV_BGR2GRAY);
cvSmooth(edges,edges,CV_GAUSSIAN,7,7,1.5,1.5);
cvCanny(edges,edges,0,30,3);
cvShowImage("edges",edges);
cvReleaseImage(&edges);
if (cvWaitKey(30)>=0) break;
}
cvReleaseCapture(&pcapture);
cvDestroyWindow("edges");
You can have a try whether its also have some problems in your environment or not.
Hope a little help to you!