built-in webcam, opencv: sometimes works, sometimes not - c++

Question

I am working on visual studio 2010 C++ and Opencv 2.3.1. Using HP laptop windows 7 32 bit. I really have tried many times to solve this problem but it still happening. My built-in webcam with some codes (some times works and some times not ) and with some other codes it always displays a gray window instead of camera feed?
could anyone help?
Thanks in advance.
For Example The first code sometimes display cam feed and the second one always display gray window
#include "opencv2/opencv.hpp"
using namespace cv;
using namespace std;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
if (!cap.isOpened()) // check if we succeeded
return -1;
Ptr<BackgroundSubtractor> pMOG = new BackgroundSubtractorMOG2();
Mat fg_mask;
Mat frame;
int count = -1;
for (;;)
{
// Get frame
cap >> frame; // get a new frame from camera
// Update counter
++count;
// Background subtraction
pMOG->operator()(frame, fg_mask);
imshow("frame", frame);
imshow("fg_mask", fg_mask);
// Save foreground mask
string name = "mask_" + std::to_string(static_cast<long long>(count)) + ".png";
imwrite("D:\\SO\\temp\\" + name, fg_mask);
if (waitKey(1) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
////////////////////////
second code:
// WriteVideo.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
using namespace cv;
using namespace std;
int main(int argc, char* argv[])
{
VideoCapture cap(0); // open the video camera no. 0
if (!cap.isOpened()) // if not success, exit program
{
cout << "ERROR: Cannot open the video file" << endl;
return -1;
}
namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the video
cout << "Frame Size = " << dWidth << "x" << dHeight << endl;
Size frameSize(static_cast<int>(dWidth), static_cast<int>(dHeight));
VideoWriter oVideoWriter ("D:/visual outs/mix/WriteVideo.avi", CV_FOURCC('P','I','M','1'), 20, frameSize, true); //initialize the VideoWriter object
if ( !oVideoWriter.isOpened() ) //if not initialize the VideoWriter successfully, exit the program
{
cout << "ERROR: Failed to write the video" << endl;
return -1;
}
while (1)
{
Mat frame;
bool bSuccess = cap.read(frame); // read a new frame from video
if (!bSuccess) //if not success, break loop
{
cout << "ERROR: Cannot read a frame from video file" << endl;
break;
}
oVideoWriter.write(frame); //writer the frame into the file
imshow("MyVideo", frame); //show the frame in "MyVideo" window
if (waitKey(10) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
{
cout << "esc key is pressed by user" << endl;
break;
}
}
return 0;
}

Answer 1

Without the actual code, there's nothing we can really do in order to pinpoint the issue. Could you reformulate your question please? Anyway, in order to instantiate a VideoCapture object in OpenCV, the C++ code would be pretty much something like this
#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; // Wait 30 ms for a key feed, then break out of the code if a keypress is found in the message queue
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
As for the standard C version, you'd have to leverage the old yet still reliable CvCapture struct which is contained in the old OpenCV API. In this case, you'd act upon the cvCreateCameraCapture(0) which simply returns a pointer to the newly created camera instance (CvCapture). In the latter case, the code would evaluate to the snipper hereunder.
# include "highgui.h"
# include "cv.h"
int main( int argc, char** argv )
{
CvCapture* capture;
capture = cvCreateCameraCapture(0);
if (!capture)
return -1;
IplImage* bgr_frame = cvQueryFrame(capture); // Query the next frame
CvSize size = cvSize(
(int)cvGetCaptureProperty(capture,
CV_CAP_PROP_FRAME_WIDTH),
(int)cvGetCaptureProperty(capture,
CV_CAP_PROP_FRAME_HEIGHT)
);
cvNamedWindow("OpenCV via CvCapture", CV_WINDOW_AUTOSIZE); // Create a window and assign it a title
/* Open a CvVideoWriter to save the video to a file. Think of it as a stream */
CvVideoWriter *writer = cvCreateVideoWriter(argv[1],
CV_FOURCC('D','I','V','X'),
30,
size
);
while((bgr_frame = cvQueryFrame(capture)) != NULL)
{
cvWriteFrame(writer, bgr_frame);
cvShowImage("OpenCV via CvCapture", bgr_frame);
char c = cvWaitKey(30); // Same as the snippet above. Wait for 30 ms
if(c == 27) break; // If the key code is 0x27 (ESC), break
}
cvReleaseVideoWriter(&writer); // Dispose the CvVideoWriter instance
cvReleaseCapture(&capture); // Dispose the CvCapture instance
cvDestroyWindow("OpenCV via CvCapture"); // Destroy the window
return 0;
}