Webcam picture only gray

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Hello,

i try this Code to make a picture with my Webcam But the Picture i get is only gray . it´s only a Problem in C++ with Opencv. In VB Code ist works well. Have somewone an idea ? Thanks System: Win 10 / StudioCommunity 2015

// Webcam

#include "opencv2\highgui\highgui.hpp"
#include "opencv2\imgproc\imgproc.hpp"
#include "opencv\cv.h"
#include <stdio.h>

#define XRES 1280
#define YRES 720
#define WINDOWNAME "openCV USB-camera"

    int main(int argc, char **argv) {
    // open camera:
    CvCapture* capture = 0;
    capture = cvCaptureFromCAM(-1);
    if (!capture) {
        fprintf(stderr, "couldn't open Camera device");
        return -1;
    }
    // set resolution
    cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_WIDTH, XRES);
    cvSetCaptureProperty(capture, CV_CAP_PROP_FRAME_HEIGHT, YRES);
    // grab and show frames:
    IplImage *frame = cvQueryFrame(capture);
    cvNamedWindow(WINDOWNAME, CV_WINDOW_AUTOSIZE);
    while (frame != NULL) {
        int key = cvWaitKey(10);
        if (key == 27) break; // stop when ESC is pressed
        cvShowImage(WINDOWNAME, frame);
        frame = cvQueryFrame(capture);
    }
    // close camera:
    cvReleaseCapture(&capture);
    cvDestroyWindow(WINDOWNAME);

    return 0;
}