OpenCV load/save histogram data
// save
cv::Mat my_histogram;
cv::FileStorage fs("my_histogram_file.yml", cv::FileStorage::WRITE);
if (!fs.IsOpen()) {std::cout << "unable to open file storage!" << std::endl; return;}
fs << "my_histogram" << my_histogram;
fs.release();

// load
cv::Mat my_histogram;
cv::FileStorage fs("my_histogram_file.yml", cv::FileStorage::READ);
if (!fs.IsOpen()) {std::cout << "unable to open file storage!" << std::endl; return;}
fs >> "my_histogram" >> my_histogram;
fs.release();