Re: camera / cvRetrieveFrame problem

Hi Helge,

For the second problem:

motion is not a copy of image. From the documentation:

int  origin;  /* 0 - top-left origin,
                  1 - bottom-left origin (Windows bitmaps style) */

So setting the origin has nothing to do with copying. Use
cvCopy(src, dst, mask) for copying.

For the first problem I cannot help you, sorry. The code looks ok, maybe 
you can try providing the correct videodevice instead of -1. But I'm not 
sure.

Regards,

Marco


helge.stahlmann wrote:
> Hi,
> 
> It seems there is an error in the following code example, but I don't
> know where to start searching. Maybe one of you could be so kind to
> help me finding the bug.
> 
> - - - - - - - - - - - - 
> #include <stdafx.h>
> #include "cv.h"
> #include "highgui.h"
> #include "cvcam.h"
> #include "cxcore.h"
> #include <time.h>
> #include <math.h>
> #include <ctype.h>
> 
> int main(int argc, char* argv[])
> {
>   CvCapture* capture;
>   int cameraSelected = -1;
>   capture = cvCaptureFromCAM(cameraSelected);
>   // capture = cvCaptureFromAVI("office101.avi");
>   cvWaitKey(0);
> 
>   if( capture )
>   {
>     IplImage* motion = 0;
>     cvNamedWindow( "Motion", CV_WINDOW_AUTOSIZE );
>     for(;;)
>     {
>       IplImage* image = 0;
>       if( !cvGrabFrame( capture ))
>       break;
>       image = cvRetrieveFrame( capture );
>       if( image )
>       {
>         if( !motion )
>         {
>           motion = cvCreateImage(cvSize(image->width,image->height), 8, 3 );
>           cvZero( motion );
>           motion->origin = image->origin;
>         }
>       }
> 
>       cvShowImage( "Motion", image );
>       if( cvWaitKey(10) >= 0 )
>       break;
>      }
>       
>      cvReleaseCapture( &capture );
>      cvDestroyWindow( "Motion" );
>   }
> 
>    return 0;
> }
> - - - - - - - - - - - 
> 
> First problem:
> 
> On execution, the camera gets initialized the motion frame opens but
> it doesn't show any images. No exceptions, no error messages. The usb
> webcam works fine using cvcam (cvcamInit(), cvcamStart(),...).
> 
> While stepping through the code, I found out that
> cvRetrieveFrame(capture) doesn't return any image, but I don't
> understand why.
> 
> Second problem:
> 
> I tried the same example with cvCaptureFromAVI instead of
> cvCaptureFormCAM with an example video from openAVCSR which works
> fine, but only if I use cvShowImage( "Motion", image ) instead of
> cvShowImage( "Motion", motion ). That seems strange to me as motion is
> just a copy of the image.
> 
> Any help would be appreciated.
> 
> Helge
> 
> 
> 
> 
> 
> 
> 
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> 
> 
>  
> 
> 
> 



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