c++ - Serializing OpenCV Mat_<Vec3f>

Question

I'm working on a robotics research project where I need to serialize 2D matrices of 3D points: basically each pixel is a 3-vector of floats. These pixels are saved in an OpenCV matrix, and they need to be sent over inter-process communication and saved into files to be processed on multiple computers. I'd like to serialize them in an endian/architecture-independent, space-efficient way, as quickly as possible. cv::imencode here would be perfect, except that it only works on 8-bit and 16-bit elements, and we don't want to lose any precision. The files don't need to be human-readable (although we do that now to ensure data portability, and it's incredibly slow). Are there best practices for this, or elegant ways to do it?

Thanks!

Answer 1

The earlier answers are good, but they won't work for non-continuous matrices which arise when you want to serialize regions of interest (among other things). Also, it is unnecessary to serialize elemSize() because this is derived from the type value.

Here's some code that will work regardless of continuity (with includes/namespace)

#pragma once

#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/serialization/utility.hpp>
#include <opencv2/opencv.hpp>

namespace boost {
namespace serialization {

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);
        }
    }

}

} // namespace serialization
} // namespace boost