Question

Video capturing with OpenCV

Asked by: ebnhuseyin

I found a simple code on the net about video capturing with opencv functions. However, when i compiled it, it didnt work, cvQueryFrame didnt grab a frame. Actually my camera doesnt a usb camera just connect the pc through DV Capture + Tv Tuner card.
Doesnt OpenCV support Microsoft DV camera VCR driver or do you have any idea about how to correct or change following code?


#include "stdafx.h"
//---------------------------------------------------------
//Open Source Computer Vision Library
//File Name : sample.cpp
//   OS     : WindowsXP
//Library   : OpenCV for MS-Windows ƒÀ4a
// Camera   : USBcamera PMC-30
// Auther   : NAKANO Michiki
//Time-stamp:<November 02, 2004; 22:18>
//---------------------------------------------------------

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


IplImage* src = NULL;      


int _tmain(int argc, _TCHAR* argv[])
{


  int key;      
  CvCapture* capture = NULL;

 
  if(NULL==(capture = cvCaptureFromCAM(-1)))
  {
    printf("\nError on cvCaptureFromCAM");
    return -1;
  }

  //-----
  cvNamedWindow("Capture", CV_WINDOW_AUTOSIZE);
  cvNamedWindow("Capture2", CV_WINDOW_AUTOSIZE);
 
  cvMoveWindow("Capture", 50, 50);
  cvMoveWindow("Capture2", 320, 50);
 
  for(;;){
 
    if(NULL==(src=cvQueryFrame(capture))){
      printf("\nError on cvQueryFrame");
      break;
    }

   
    cvShowImage("Capture", src);

   
    key = cvWaitKey(10);
   
    if(key==0x1b)
      break;
  }
 
  cvReleaseCapture(&capture);
  cvDestroyWindow("Capture");

  return 0;

}

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Asked On
2006-06-15 at 22:57:13ID21888542
Tags

opencv

,

cvcapturefromcam

Topic

C++ Programming Language

Participating Experts
1
Points
250
Comments
4

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Answers

 

by: mrbluePosted on 2006-06-16 at 12:23:50ID: 16922971

I do not know OpenCV but I have found the following description (http://www.cs.bham.ac.uk/resources/courses/robotics/doc/opencvdocs/ref/OpenCVRef_Highgui.htm):

==================================
cvCaptureFromCAM
Allocates CvCapture structure and  binds it to the video camera

CvCapture* cvCaptureFromCAM( int index );index
Index of the camera to be used. If there is only one camera or it does not matter what camera to use,  -1 may be passed.
The function cvCaptureFromCAM allocates and initialized the CvCapture structure for reading a video stream from the camera. Currently two camera interfaces can be used: Video for Windows (VFW) and Matrox Imaging Library (MIL). To connect to VFW camera the parameter "index" should be in range 0-10, to connect to MIL camera the parameter "index" should be in range 100-115. If -1 is passed then the function searches for VFW camera first and then for MIL camera.

After the allocated CvCapture structure is not used any more it should be released by cvReleaseCapture function.
=======================================

It looks like OpenCV recognizes only VFW (this is what I think you should be interested in) or MIL video sources. So you need VFW driver for your camera (TV Tuner or anything else) to be seen by OpenCV.

 

by: mrbluePosted on 2006-06-16 at 12:53:10ID: 16923184

I found info that WDM video sources are mapped to VFW through VFW-to-WDM mapper. This shows as "Microsoft WDM Image Capture" VFW driver as enumerated by capGetDriverDescription() function. If you have more than one such source (WDM) you can switch them with capDlgVideoSource() macro in VFW application.

Theoretically it should work. You can use simple VFW application to select different source for "Microsoft WDM Image Capture" driver - i.e. switch between camera and TV tuner.

 

by: ebnhuseyinPosted on 2006-06-16 at 23:22:13ID: 16925605

At the begining i had two camera system, but i uninstalled to usb one to avoid confusion. Now i have only one camera in my system connected trough DV Capture + Tv Tuner card.  How can i write a VFM application with opencv for it. Is there any simplest way

On the other hand i can watch the preview video using DirectX AMCap program. Is that meaning it has VFW driver?

 

by: ebnhuseyinPosted on 2006-06-16 at 23:36:43ID: 16925649

Moreover,
At that line " capture = cvCaptureFromCAM(-1) ", function doesnt return  NULL value. when the program comes the line "if(NULL==(src=cvQueryFrame(capture)))" error occurs.  Actually its not a error, cvQueryFrame returns NULL value.

20120131-EE-VQP-002

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