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Dear users,

I'm currently investigating the use of the cv::Mat class as a storage basis for a software dedicated to sequences of images.Basically, I have a binary file containing some raw data that I need to access, process and finally display. Up to now, I was using a simple std::vector but I'm currently thinking of replacing this vector by a cv::Mat object to benefit from all the great tools openCV provides. I'm currently facing a performance issue regarding to time needed to read a file and fill the cv::Mat object.

Here are the method I have written to fill the cv::Mat object :

void ImageReader::readData(cv::Mat &mat)
{
    std::ifstream in(m_file, std::ios::in | std::ios::binary);
    in.seekg(10);
    in.read((char*)(mat.data), 2949120*sizeof(std::uint16_t));
    in.close();
}

And here is the one the std::vector

void ImageReader::readDataStd(std::vector<std::uint16_t> &vec)
{
    std::ifstream in(m_file, std::ios::in | std::ios::binary);
    in.seekg(10);
    in.read((char*)(vec.data()), 2949120*sizeof(std::uint16_t));
    in.close();
}

The file I read basically contains one small header then followed by the data (1920 * 1536 pixels, each pixel is a uint16 in this example). Although the pieces of code are basically the same, I do not get the same performance on my machine : the method that fills the cv::Mat is almost twice slower than the one filling the std::vector (8ms versus 4.2ms).

Is this result logical? Do I make something wrong? Why do I get such a difference? Is there any tips that can help me to reduce the filling time?

I'm new to C++, so please be kind if the answer is obvious ;-)

Best regards,

Vincent