Mat myDFT(const Mat & src)
{
    Mat result(src.size(), CV_32FC2, Scalar::all(0));
    //calc DFT for each row
    vector<vector<complex<double>>> fourierImageForRows;
    for (int row = 0; row < src.rows; row++)
    {

        vector<complex<double>> rowFourier;
        for (int u = 0; u < src.cols; u++)//u - частотная переменная
        {
            double coeff = -2 * PI * u / src.cols;
            double a = cos(coeff);
            double b = sin(coeff);

            complex<double> W(a, b);
            complex<double> W_0(a, b);

            double real = src.at<float>(row, 0);
            double imag = 0;

            for (int n = 1; n < src.cols; n++)
            {
                double magn = src.at<float>(row, n);

                real += magn * W.real();
                imag += magn * W.imag();
                W *= W_0;//ЗАЧЕМ
            }
            complex<double>res(real, -imag);
            rowFourier.emplace_back(res);
        }
        fourierImageForRows.emplace_back(rowFourier);
    }

    //calc DFT for cols
    vector<vector<complex<double>>> resultFourier;
    for (int col = 0; col < src.cols; col++)
    {
        vector<complex<double>> rowFourier;
        for (int w = 0; w < src.rows; w++)
        {
            double coeff = -2 * PI * w / src.rows;
            double a = cos(coeff);
            double b = sin(coeff);
            complex<double> W(a, b);
            complex<double> W_0(a, b);

            double real = fourierImageForRows[0][col].real() * 1;
            double imag = -fourierImageForRows[0][col].imag();

            for (int n = 1; n < src.rows; n++)
            {
                complex<double> value = fourierImageForRows[n][col];
                complex<double> res = W * conj(value);

                real += res.real();
                imag += res.imag();

                W *= W_0;
            }
            complex<double>res(real, imag);
            rowFourier.emplace_back(res);
            result.at<Vec2f>(w, col) = Vec2f(real, imag);
        }
    }

    return result;//получаем изображение в частотном представлении

}