|   | 1 |  initial version  | 
i prefer the solution here
|   | 2 |  No.2 Revision  | 
i prefer there is a great code at stackoverflow.com by Miki
#include <opencv2\opencv.hpp>
#include <iostream>
#include <fstream>
using namespace std;
using namespace cv;
void matwrite(const string& filename, const Mat& mat)
{
    ofstream fs(filename, fstream::binary);
    // Header
    int type = mat.type();
    int channels = mat.channels();
    fs.write((char*)&mat.rows, sizeof(int));    // rows
    fs.write((char*)&mat.cols, sizeof(int));    // cols
    fs.write((char*)&type, sizeof(int));        // type
    fs.write((char*)&channels, sizeof(int));    // channels
    // Data
    if (mat.isContinuous())
    {
        fs.write(mat.ptr<char>(0), (mat.dataend - mat.datastart));
    }
    else
    {
        int rowsz = CV_ELEM_SIZE(type) * mat.cols;
        for (int r = 0; r < mat.rows; ++r)
        {
            fs.write(mat.ptr<char>(r), rowsz);
        }
    }
}
Mat matread(const string& filename)
{
    ifstream fs(filename, fstream::binary);
    // Header
    int rows, cols, type, channels;
    fs.read((char*)&rows, sizeof(int));         // rows
    fs.read((char*)&cols, sizeof(int));         // cols
    fs.read((char*)&type, sizeof(int));         // type
    fs.read((char*)&channels, sizeof(int));     // channels
    // Data
    Mat mat(rows, cols, type);
    fs.read((char*)mat.data, CV_ELEM_SIZE(type) * rows * cols);
    return mat;
}
int main()
{
    // Save the solution here random generated data
    {
        Mat m(1024*256, 192, CV_8UC1);
        randu(m, 0, 1000);
        FileStorage fs("fs.yml", FileStorage::WRITE);
        fs << "m" << m;
        matwrite("raw.bin", m);
    }
    // Load the saved matrix
    {
        // Method 1: using FileStorage
        double tic = double(getTickCount());
        FileStorage fs("fs.yml", FileStorage::READ);
        Mat m1;
        fs["m"] >> m1;
        double toc = (double(getTickCount()) - tic) * 1000. / getTickFrequency();
        cout << "Using FileStorage: " << toc << endl; 
    }
    {
        // Method 2: usign raw binary data
        double tic = double(getTickCount());
        Mat m2 = matread("raw.bin");
        double toc = (double(getTickCount()) - tic) * 1000. / getTickFrequency();
        cout << "Using Raw: " << toc << endl;
    }
    int dummy;
    cin >> dummy;
    return 0;
}