[ C++: How can I create dynamic template type ]

I have the following piece of code, which I created for changing the intensity of a pixel in an OpenCV image (Cv::Mat class).

As you can see, I'm looping in both cases, but with different template type.

The 'transfer' function can be overloaded.

My question is, therefore, how can I create dynamic template type so that it looks better ..

Mat mat = _mat.clone() ;
int channels = mat.channels();

switch(channels)
{
case 1: 
    for (int i=0; i<mat.rows; i++)
    {
        for (int j=0; j<mat.cols; j++)
        {
            uchar src = mat.at<uchar>(i,j);
            uchar dst = mat.at<uchar>(i,j);

            t.transfer(src, dst);
        }
    }
    break;

case 3: 
    for (int i=0; i<mat.rows; i++)
    {
        for (int j=0; j<mat.cols; j++)
        {
            Vec3b src = mat.at<Vec3b>(i,j);
            Vec3b dst = mat.at<Vec3b>(i,j);

            t.transfer(src, dst);
        }
    }
    break;
}

return mat ;

Answer 1

---

How about something like this:

template <typename U, typename T>
void transfer_mat(Mat & mat, T & t)
{
    for (int i = 0, r = mat.rows; i != r; ++j)
    {
        for (int j = 0, c = mat.cols; j != c; ++j)
        {
            U src = mat.at<U>(i, j);
            U dst = mat.at<U>(i, j);

            t.transfer(src, dst);
        }
    }
}

Then you can say:

switch(channels)
{
case 1:
    transfer_mat<uchar>(mat, t);
    break;
case 2:
    transfer_mat<Vec3b>(mat, t);
    break;
}

Answer 2

---

It's unclear as to the scope of your code (looks like a member function), and what type t is, but this should get you started:

template<typename AtT>
Mat& transfer_impl(Mat& mat, T& t)
{
    for (int i = 0; i < mat.rows; ++i)
        for (int j = 0; j < mat.cols; ++j)
            t.transfer(mat.at<AtT>(i, j), mat.at<AtT>(i, j));
    return mat;
};

Mat transfer(Mat const& _mat, T& t)
{
    Mat mat = _mat.clone();
    switch (mat.channels())
    {
    case 1:  return transfer_impl<uchar>(mat, t);
    case 3:  return transfer_impl<Vec3b>(mat, t);
    default: throw std::runtime_error(/*...*/);
    }
}

Answer 3

---

I'm writing a template function like this :

template<typename T> cv::Mat exercice02_avec_at(const cv::Mat& image, const int BVR[3]) 
{
    // Création d'un clone 
    Mat imageC = image.clone();

    // Recherche du nombre de lignes
    int nl = imageC.rows;

    // Recherche du nombre d'éléments par ligne
    int nc = imageC.cols; 

    // On boucle dans les éléments de la matrice avec méthode .at<Vec3b>()[]
    for(int i = 0 ; i < nl ; i++)
    {

        for(int j = 0; j < nc ; j++)
        {
            imageC.at<T>(i,j)[0] = BVR[0];
            imageC.at<T>(i,j)[1] = BVR[1];
            imageC.at<T>(i,j)[2] = BVR[2];

        }
    }

    return imageC;

}

In my main :

Mat uneImage8bits(10,10, CV_8UC3, Scalar(255,255,255)); // rose Scalar(197,17,217)
int BVR[3] = {197,17,217};

Mat imageModif01 = exercice02_avec_at<Vec3b>(uneImage8bits,BVR);

But I get this error when I build :

main.obj : error LNK2019: unresolved external symbol "class cv::Mat __cdecl exercice02_avec_at >

I need your help

#c++ #templace #OpenCV