Initialize GMM by random sampling in GrabCut.

edit

Actually want to remove the initial rectangle selection in GrabCut. For that at the very beginning of the user interaction, a background color model pb(·) (a GMM) is initialized by randomly sampling a number (typically 1,200) of pixels from the background. In each subsequent user interaction, we replace the samples that were labeled as foreground in the previous interaction with the same number of pixels randomly sampled from the background. The background GMM is reestimated using the updated samples.

For this to work I've removed the initMaskWithRect() function. And I want to update the following function in GrabCut to initialize with random sampling

/*
  Initialize GMM background and foreground models using kmeans algorithm.
*/
static void initGMMs( const Mat& img, const Mat& mask, GMM& bgdGMM, GMM& fgdGMM )
{
    const int kMeansItCount = 10;
    const int kMeansType = KMEANS_PP_CENTERS;

    Mat bgdLabels, fgdLabels;
    std::vector<Vec3f> bgdSamples, fgdSamples;
    Point p;
    for( p.y = 0; p.y < img.rows; p.y++ )
    {
        for( p.x = 0; p.x < img.cols; p.x++ )
        {
            if( mask.at<uchar>(p) == GC_BGD || mask.at<uchar>(p) == GC_PR_BGD )
                bgdSamples.push_back( (Vec3f)img.at<Vec3b>(p) );
            else // GC_FGD | GC_PR_FGD
                fgdSamples.push_back( (Vec3f)img.at<Vec3b>(p) );
        }
    }
    CV_Assert( !bgdSamples.empty() && !fgdSamples.empty() );
    Mat _bgdSamples( (int)bgdSamples.size(), 3, CV_32FC1, &bgdSamples[0][0] );
    kmeans( _bgdSamples, GMM::componentsCount, bgdLabels,
            TermCriteria( CV_TERMCRIT_ITER, kMeansItCount, 0.0), 0, kMeansType );
    Mat _fgdSamples( (int)fgdSamples.size(), 3, CV_32FC1, &fgdSamples[0][0] );
    kmeans( _fgdSamples, GMM::componentsCount, fgdLabels,
            TermCriteria( CV_TERMCRIT_ITER, kMeansItCount, 0.0), 0, kMeansType );

    bgdGMM.initLearning();
    for( int i = 0; i < (int)bgdSamples.size(); i++ )
        bgdGMM.addSample( bgdLabels.at<int>(i,0), bgdSamples[i] );
    bgdGMM.endLearning();

    fgdGMM.initLearning();
    for( int i = 0; i < (int)fgdSamples.size(); i++ )
        fgdGMM.addSample( fgdLabels.at<int>(i,0), fgdSamples[i] );
    fgdGMM.endLearning();
}

How to do it ?