void splitTo3Channel_dan1(const cv::Mat& input, std::vector<cv::Mat>& output)
{
    CV_Assert(!input.empty());
    CV_Assert(input.channels() == 3);

    // (re)allocate outputs
    output.clear();
    for (int i(0); i < input.channels(); ++i) {
        output.push_back(cv::Mat::zeros(input.size(), input.type()));
    }

    // Set up index pairs (input->output);
    int from_to[] = { 0,0, 1,4, 2,8 };
    cv::mixChannels(&input, 1, &output[0], 3, from_to, 3);
}

void splitTo3Channel_dan1b(const cv::Mat& input, std::vector<cv::Mat>& output)
{
    CV_Assert(!input.empty());
    CV_Assert(input.channels() == 3);

    // (re)allocate outputs
    output.clear();
    for (int i(0); i < input.channels(); ++i) {
        output.push_back(cv::Mat::zeros(input.size(), input.type()));
    }

    // Set up index pairs (input->output);
    std::vector<int> from_to{ 0,0, 1,4, 2,8 };
    CV_Assert(from_to.size() == (output.size() * 2));
    cv::mixChannels(&input, 1
        , &output[0], output.size()
        , &from_to[0], output.size());
}

void splitTo3Channel_dan1c(const cv::Mat& input, std::vector<cv::Mat>& output)
{
    CV_Assert(!input.empty());

    // (re)allocate outputs
    output.clear();
    for (int i(0); i < input.channels(); ++i) {
        output.push_back(cv::Mat::zeros(input.size(), input.type()));
    }

    // Set up channel index pairs (input->output);
    std::vector<int> from_to;
    for (int i(0); i < input.channels(); ++i) {
        from_to.push_back(i); // Input
        from_to.push_back(i * input.channels() + i); // Output
    }

    cv::mixChannels(&input, 1
        , &output[0], output.size()
        , &from_to[0], output.size());
}

void splitToNChannel_dan2(const cv::Mat& input
    , std::vector<cv::Mat>& output
    , bool reuse_output = false)
{
    CV_Assert(!input.empty());
    CV_Assert(input.channels() <= 4); // Not tested for more than 4
    CV_Assert(output.empty() || (output.size() == input.channels()));

    // Allocate (or just clear if reusing/possible to reuse) outputs
    if (reuse_output && (output.size() == input.channels())) {
        for (int i(0); i < input.channels(); ++i) {
            if ((output[i].size() == input.size()) && (output[i].type() == input.type())) {
                output[i].setTo(cv::Scalar());
            } else {
                output[i] = cv::Mat::zeros(input.size(), input.type());
            }
        }
    } else {
        output.clear();
        for (int i(0); i < input.channels(); ++i) {
            output.push_back(cv::Mat::zeros(input.size(), input.type()));
        }
    }

    // Set up channel index pairs (input->output);
    std::vector<int> from_to;
    for (int i(0); i < input.channels(); ++i) {
        from_to.push_back(i); // Input
        from_to.push_back(i * input.channels() + i); // Output
    }

    cv::mixChannels(&input, 1
        , &output[0], output.size()
        , &from_to[0], output.size());
}