Why does OpenCV give me a black screen?

Question

I\'m currently trying to use OpenCV (using the Processing library). However, when I try to run any examples (either the Processing ones or the C ones included with OpenCV),

Answer 1

I recently had the same problem. The OpenCV library on its own just gave me a blank screen, I had to include the videoInput library:

http://muonics.net/school/spring05/videoInput/

An example I followed was:

#include "stdafx.h"
#include "videoInput.h"
#include "cv.h"
#include "highgui.h"

int main()
{
    videoInput VI;
    int numDevices = VI.listDevices();
    int device1= 0;
    VI.setupDevice(device1);
    int width = VI.getWidth(device1);
    int height = VI.getHeight(device1);
    IplImage* image= cvCreateImage(cvSize(width, height), 8, 3);
    unsigned char* yourBuffer = new unsigned char[VI.getSize(device1)];
    cvNamedWindow("test");
    while(1)
    {
        VI.getPixels(device1, yourBuffer, false, false);
        image->imageData = (char*)yourBuffer;
        cvConvertImage(image, image, CV_CVTIMG_FLIP);
        cvShowImage("test", image);
        if(cvWaitKey(15)==27) break;
    }

    VI.stopDevice(device1);
    cvDestroyWindow("test");
    cvReleaseImage(&image);

    return 0;
}

From this source: http://www.aishack.in/2010/03/capturing-images-with-directx/

Answer 2

OpenCV 2.1 still has a few problems with 64bits OS. You can read this topic on the subject.

If you're looking for working/compilable source code that shows how to use the webcam, check this out.

Let us know if it helped you.

Answer 3

I had somewhat same problem on Ubuntu. I downloaded a code from here: http://www.rainsoft.de/projects/pwc.html It does an extra step before starting to get frames(i think setting FPS). Worth a try, the code is easy to read and works with non-philips cams.

Answer 4

OpenCV only supports a limited number of types of cameras. Most likely your camera is not supported. You can look at either the source code or their web site to see which are supported.