}

    N = keypoints->total;

    if( _descriptors )

    {

        descriptors = cvCreateSeq( 0, sizeof(CvSeq),

    MemStorage storage(cvCreateMemStorage(0));

    Seq<CvSURFPoint> kp;

    cvExtractSURF(&_img, pmask, &kp.seq, 0, storage, *(const CvSURFParams*)this, 0);

    Seq<CvSURFPoint>::iterator it = kp.begin();

    size_t i, n = kp.size();

    keypoints.resize(n);

    cvExtractSURF(&_img, pmask, &kp.seq, &d, storage,

        *(const CvSURFParams*)this, useProvidedKeypoints);

    if( !useProvidedKeypoints )

    {

        Seq<CvSURFPoint>::iterator it = kp.begin();