#include <cv.h>

#include <highgui.h>

using namespace cv;

int main(int arg, char** argv)

{

        Mat1b data(23, 42);

        data.setTo(0);

        Rect roi(2, 2, data.cols-4, data.rows-4);

        Mat1b data_roi(data, roi);

        MatIterator_<uchar> it;

        for (it = data_roi.begin(); it != data_roi.end(); ++it)

                *it = 255;

//        *it = 255;

        imshow("data", data);

        waitKey();

        return 0;

}