Opencv cannot access my webcam

I have trouble with accessing webcam using opencv 2.4.3.

My System:

Hp Probook 4530s - HP Fixed HD Webcam

Ubuntu 12.10

OpenCV 2.4.3

İf I want to capture my built-in camera i get ERROR: capture is NULL

I'm using http://opencv.willowgarage.com/wiki/CameraCapture sample code.

Sample code is:

#include "cv.h" 
#include "highgui.h" 
#include <stdio.h>  
// A Simple Camera Capture Framework 
int main() {
CvCapture* capture = cvCaptureFromCAM( CV_CAP_ANY );
if ( !capture ) {
 fprintf( stderr, "ERROR: capture is NULL \n" );
 getchar();
 return -1;
}
// Create a window in which the captured images will be presented
cvNamedWindow( "mywindow", CV_WINDOW_AUTOSIZE );
// Show the image captured from the camera in the window and repeat
while ( 1 ) {
 // Get one frame
 IplImage* frame = cvQueryFrame( capture );
 if ( !frame ) {
   fprintf( stderr, "ERROR: frame is null...\n" );
   getchar();
   break;
 }
 cvShowImage( "mywindow", frame );
 // Do not release the frame!
 //If ESC key pressed, Key=0x10001B under OpenCV 0.9.7(linux version),
 //remove higher bits using AND operator
 if ( (cvWaitKey(10) & 255) == 27 ) break;
}
// Release the capture device housekeeping
cvReleaseCapture( &capture );
cvDestroyWindow( "mywindow" );
return 0;
}

I also tried with xawtv -hwscan using typing terminal. I get this output:

looking for available devices
port 129-144

type : Xvideo, image scaler
name : Intel(R) Textured Video`


/dev/video0: OK    
             [ -device /dev/video0 ]
type : libv4l

name : HP HD Webcam [Fixed]

flags:  capture

then I can access my webcam typing xawtv video0. I think I have no trouble with my webcam. I have trouble with opencv.

I solved my problem few minutes ago. And I decided share my solution for people who handling similar error.

First I didnt install some of below packets ( I dont remember which of them, so I paste all of them)

libjpeg62-dev

libtiff4-dev

zlib1g-dev

libjasper-dev

libavcodec-dev

libdc1394-22-dev

libgstreamer0.10-dev

libgstreamer-plugins-base0.10-dev

libavformat-dev

libv4l-dev

libswscale-dev

Then You should configure your cmake process with this code

cmake -D CMAKE_BULD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D BUILD_PYTHON_SUPPORT=ON USE_V4L=ON WITH_TBB=ON -D BUILD_NEW_PYTHON_SUPPORT=ON USE_GStreamer=ON ..

Please notice USE_V4L=ON this code..

I hope you solve after reading my solution.

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/imgproc/imgproc.hpp>

using namespace cv;
using namespace std;

int main()
{
  VideoCapture webcam;
  webcam.open(0);

  if(!webcam.isOpened())//**EDITED**
    {
      std::cout<<"CANNOT OPEN CAM"<<std::endl;
      return -1;
    }

  Mat frame;

  while(true)
  {
    webcam >> frame;
    imshow("TEST",frame);
    waitKey(20);
  }
  return 0;
}

Try the above code...

In some cases it is down to the inbuilt cameras response time (as it was in my case). I discovered that the in-built webcam on my HP G62 only "wakes up" after the first opencv cap.read(frame) call. Therefore to get a positive read from the camera (and hence no error later in the code) I made the call several times before proceeding:

if (!cap.read(frame))
{
    if(!cap.read(frame))
    {
        if(!cap.read(frame))
        {
            if(!cap.read(frame))
            {
                 printf("Cam read error");
            }
        }
    }
}

For me the optimum was 4 read calls, which ensured my camera was awake and on before running through the main block of code. It is possible that a simple "waitKey" call would work and only two read calls, although I haven't tried this.

来源：https://stackoverflow.com/questions/14424325/opencv-cannot-access-my-webcam

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webcam