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Asked: 2026-06-01T01:40:59+00:00

I’m trying to display video from a webcam. I capture the images from the

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I’m trying to display video from a webcam. I capture the images from the webcam using opencv and then I try to display them on a GtkImage.

This is my code, which runs in a seperate thread.

  gpointer View::updateView(gpointer v)
{
    IplImage *image;
    CvCapture *camera;
    GMutex *mutex;
    View *view;

    view=(View*)v;
    camera=view->camera;
    mutex=view->cameraMutex;

    while(1)
    {
        g_mutex_lock(view->cameraMutex);
        image=cvQueryFrame(camera);
        g_mutex_unlock(view->cameraMutex);

        if(image==NULL) continue;

        cvCvtColor(image,image,CV_BGR2RGB);

        GDK_THREADS_ENTER();
        g_object_unref(view->pixbuf);
        view->pixbuf=gdk_pixbuf_new_from_data((guchar*)image->imageData,GDK_COLORSPACE_RGB,FALSE,image->depth,image->width,image->height,image->widthStep,NULL,NULL);

        gtk_image_set_from_pixbuf(GTK_IMAGE(view->image),view->pixbuf);
        gtk_widget_queue_draw(view->image);
        GDK_THREADS_LEAVE();
        usleep(10000);
    }

}

What happens is that one image is taken from the webcam and displayed and then the GtkImage stops updating.

In addition, when I try to use cvReleaseImage, I get a seg fault which says that free has been passed an invalid pointer.

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1 Answer

  1. Editorial Team

    GTK is an event-driven toolkit, like many others. What you’re doing is queuing the new images to draw in an infinite loop, but never give GTK a chance to draw them. This is not how a message pump works. You need to give a hand back to GTK, so it can draw the updated image. The way to do that is explained in gtk_events_pending documentation.

    Moreover, allocating/drawing/deallocating a gdk-pixpuf for each image is sub-optimal. Just allocate the buffer once out of your loop, draw on it in your loop (it will overwrite the previous content), and display it. You only need to reallocate a new buffer if your image size changes.

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