cv::Mat serialization to binary file

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Let me answer you with the question: are you completely sure you need to serialize Mat object? You can simply store it in one of commonly used formats that does not perform data compresion. For example 'pgm' for gray images or 'ppm' for color images. Your task will be complete and this way you will have no need to write functions of your own.

I know this is an old question, but I had to do this recently... There's a great/easy answer on stackoverflow, which I make use of in the below snippet. serializeMat() saves to a binary file and deserializeMat() loads from the same file.

Note that, by default (using binary_xarchive), the files are not platform-independant. Use the equivalent text_xarchive instead if you require multi-platform-compatibility of the saved files.

#include <boost/archive/binary_oarchive.hpp>
#include <boost/archive/binary_iarchive.hpp>


void serializeMat(const string& filename, Mat& mat) {
    ofstream ofs(filename.c_str());
    boost::archive::binary_oarchive oa(ofs);
    serialize(oa, mat, 0);
}

void deserializeMat(Mat& mat, const string& filename) {
    std::ifstream ifs(filename.c_str());
    boost::archive::binary_iarchive ia(ifs);
    serialize(ia, mat, 0);
}


// http://stackoverflow.com/a/21444792/1072039
template<class Archive>
void serialize(Archive &ar, cv::Mat& mat, const unsigned int)
{
    int cols, rows, type;
    bool continuous;

    if (Archive::is_saving::value) {
        cols = mat.cols; rows = mat.rows; type = mat.type();
        continuous = mat.isContinuous();
    }

    ar & cols & rows & type & continuous;

    if (Archive::is_loading::value)
        mat.create(rows, cols, type);

    if (continuous) {
        const unsigned int data_size = rows * cols * mat.elemSize();
        ar & boost::serialization::make_array(mat.ptr(), data_size);
    } else {
        const unsigned int row_size = cols*mat.elemSize();
        for (int i = 0; i < rows; i++) {
            ar & boost::serialization::make_array(mat.ptr(i), row_size);
        }
    }
}

You can save it to the file with fwrite(..) function. It is sample for 16U one-channel Mat:

FILE *imageFile = fopen(imageName, "wb");
fwrite(image.data, camFrameWidth*camFrameHeight, sizeof(u_int16_t), imageFile);

For reading(but you should know rows and cols count):

 FILE * pFile;
    long lSize;
    char * buffer;
    size_t result;

    pFile = fopen ( imagePath.c_str() , "rb" );
    if (pFile==NULL) {fputs ("File error",stderr); exit (1);}

    // obtain file size:
    fseek (pFile , 0 , SEEK_END);
    lSize = ftell (pFile);
    rewind (pFile);

    // allocate memory to contain the whole file:
    buffer = (char*) malloc (sizeof(char)*lSize);

    if (buffer == NULL) {fputs ("Memory error",stderr); exit (2);}

    // copy the file into the buffer:
    result = fread (buffer,1,lSize,pFile);
    if (result != lSize) {fputs ("Reading error",stderr); exit (3);}

    // clean up
    fclose (pFile);

    Mat image;
    uint16_t *imageMap = (uint16_t*)buffer;
    image.create( rows, cols, CV_16UC1 );
    memcpy( image.data, imageMap, rows*cols*sizeof(uint16_t) );

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 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;
}

I wrote this short code:

/* Will save in the file: cols\n rows\n elemSize\n type\n DATA */ void serializeMatbin(Mat& mat, std::string filename){ if (!mat.isContinuous()) { cout << "Not implemented yet" << endl; exit(1); } int elemSizeInBytes = (int)mat.elemSize(); int elemType = (int)mat.type(); int dataSize = (int)(mat.cols * mat.rows * mat.elemSize());

FILE* FP = fopen(filename.c_str(), "wb");
int sizeImg[4] = {mat.cols, mat.rows, elemSizeInBytes, elemType };
fwrite(/*buffer*/ sizeImg, /*howmanyelements*/ 4, /* size of each element */ sizeof(int), /*file*/ FP);
fwrite(mat.data, mat.cols * mat.rows, elemSizeInBytes, FP);
fclose(FP);

}

Mat deserializeMatbin(std::string filename){ FILE* fp = fopen(filename.c_str(), "r"); int header[4]; fread(header, sizeof(int), 4, fp); int cols = header[0]; int rows = header[1]; int elemSizeInBytes = header[2]; int elemType = header[3];

Mat outputMat = Mat(rows, cols, elemType);

fread(outputMat.data, elemSizeInBytes, cols * rows, fp);
fclose(fp);
return outputMat;

}

void testSerializeMatbin(){ Mat a = Mat::ones(/cols/ 10, /* rows */ 5, CV_8U) * 2; std::string filename = "test.matbin"; serializeMatbin(a, filename); Mat b = deserializeMatbin(filename); cout << "Rows: " << b.rows << " Cols: " << b.cols << " type: " << b.type()<< endl; }