#include <opencv2/opencv.hpp>

int main()
{
    uint8_t data[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
    cv::Mat bgr(2, 2, CV_8UC3, data);

    cv::Mat result = cv::Mat1b(bgr.rows * 3, bgr.cols);

    std::vector<cv::Mat> views = {
        result.rowRange(0, bgr.rows)
        , result.rowRange(bgr.rows, bgr.rows * 2)
        , result.rowRange(bgr.rows * 2, bgr.rows * 3)
    };
    cv::split(bgr, views);

    std::cout << bgr << '\n';

    std::cout << result << '\n';

    return 0;
}