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!

Exact duplicate of : stackoverflow.com/questions/16992370/… — Aurelius
– Aurelius, Commented Jun 25, 2013 at 15:00
Thanks! I searched a few minutes but did not find any related question so I posted. It was a problem of different choices of keywords. — PaulYang
– PaulYang, Commented Jun 25, 2013 at 15:59
Possible duplicate of cv::Mat matrix, HOW TO Reduce digits to the right of the decimal point in cv::Mat? — Alessandro Jacopson
– Alessandro Jacopson, Commented Feb 28, 2018 at 10:08

abyesilyurt · Accepted Answer · 2019-09-26 16:03:41Z

5

new versions of OpenCV make it easy!

see cv::Formatter

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

edited Sep 26, 2019 at 16:03

abyesilyurt

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answered Feb 6, 2019 at 7:42

ma.mehralian

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Dmoonleo · Accepted Answer · 2013-06-25 15:47:37Z

#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;
}

Marius · Accepted Answer · 2013-06-25 08:14:48Z

0

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 );

answered Jun 25, 2013 at 8:14

Marius

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3 Comments

PaulYang Over a year ago

Thank you! I added this setf command first, and then precision command second. The format did changed (now -7.7898273846583732e-15 becomes 0.00000000000000). But it is still too long.

Marius Over a year ago

Then the implementation of the printing-method of the matrix overwrites the precision.

Alessandro Jacopson Over a year ago

@Marius To set the precision with the builtin opencv mat::operator<< see stackoverflow.com/a/40672924/15485

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