Print openCV Mat content with certain format in C++

Question

I would like to ask how to format a OpenCV Mat in C++ and print it out?

For example, a Mat with double content M, when I wrote

cout<<M<<endl;

I will get

[-7.7898273846583732e-15, -0.03749374753019832; -0.0374787251930463, -7.7893623846343843e-15]

But I want a neat output, for example

[0.0000, -0.0374; -0.0374, 0.0000]

Is there any built-in way to do so?

I know we can use

cout<<format(M,"C")<<endl;

to set the output styple. So I am looking for something similar to this.

Thank you very much!

Answer 1

#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>

#include <iostream>
#include <iomanip>

using namespace cv;
using namespace std;

void print(Mat mat, int prec)
{      
    for(int i=0; i<mat.size().height; i++)
    {
        cout << "[";
        for(int j=0; j<mat.size().width; j++)
        {
            cout << setprecision(prec) << mat.at<double>(i,j);
            if(j != mat.size().width-1)
                cout << ", ";
            else
                cout << "]" << endl; 
        }
    }
}

int main(int argc, char** argv)
{
    double data[2][4];
    for(int i=0; i<2; i++)
    {
        for(int j=0; j<4; j++)
        {
            data[i][j] = 0.123456789;
        }
    }
    Mat src = Mat(2, 4, CV_64F, &data);
    print(src, 3);

    return 0;
}

Answer 2

This should do the trick:

cout.precision(5);
cout << M << endl;

You may also want to set the format to fixed before:

cout.setf( std::ios::fixed, std::ios::floatfield );

Answer 3

new versions of OpenCV make it easy!

see cv::Formatter

Mat src;
...
cv::Ptr<cv::Formatter> fmt=Formatter::get(cv::Formatter::FMT_DEFAULT);
fmt->set64fPrecision(4);
fmt->set32fPrecision(4);
std::cout << fmt->format(src) << std::endl;