How to read the text file and create Mat object in C++

Question

Hi i have being able to write a Mat object in to a text file. As follows,

std::fstream outputFile;
    outputFile.open( "myFile.txt", std::ios::out ) ;

    outputFile << des_object.rows << std::endl;
    outputFile << des_object.cols << std::endl;

    for(int i=0; i<des_object.rows; i++)
    {
        for(int j=0; j<des_object.cols; j++)
        {
            outputFile << des_object.at<float>(i,j) << std::endl;
        }

    }
    outputFile.close( );

In my code in the first 2 lines im printing the row count and the column count to use when im reading it back. But im unable to read the text file and create the Mat Object again.

The following is the code i tried. Not sure whether my code is correct.

Mat des_object1;
    std::ifstream file("myFile.txt");
    std::string str; 
    int rows;
    int cols;
    int a = 0;
    while (std::getline(file, str))
    {
        int i = 0;
        int j = 0;

        if(a == 0){
            rows = std::stoi( str );
        }else if(a == 1){
            cols = std::stoi( str );
        }else{

            for(i; i< rows; i++)
            {
                for(j; j<cols; j++)
                {
                     des_object1.at<float>(i,j) = ::atof(str.c_str());
                     break;
                }
            }

        }
        ++a;
    }

Answer 1

it's probably far easier, to use the opencv FileStorage:

// write:
Mat m;
FileStorage fs("myfile.txt",FileStorage::WRITE);
fs << "mat1" << m;

// read:
FileStorage fs("myfile.txt",FileStorage::READ);
fs["mat1"] >> m;

Answer 2

You got your inner loops in the wrong location: You'd need to keep the counter around for each iteration reading a line. It can be done a lot simpler, though:

if (in >> rows >> cols) {
    // resize the matrix to its proper size
    for (int r(0); r!= rows; ++r) {
        for (int c(0); c != cols; ++c) {
            if (!(in >> mat[r][c])) {
                throw std:: runtime_error("failed to read matrix");
            }
        }
    }
}

Answer 3

try something like this:

initialize these two outside the while loop

int k=0;
int l=0;

and instead of using the for loop

if(j<cols){
    des_object1.at<float>(k,l) = ::atof(str.c_str());
}else{
    k=0;
    l++;
    des_object1.at<float>(k,l) = ::atof(str.c_str());
}
j++;

Answer 4

I wrote a method for reading a Mat from an .asc that should work for .txt too.

Maybe there are more stylish and efficient ways to do that, but this method works and is easy to understand.

Head

int Load_From_Path_Text(Mat *pMA_Out, string path)

Variables

ifstream        IS_File;
string          ST_Line;
stringstream    SS_Line;
unsigned int    rows        = 0;
unsigned int    cols        = 0;
unsigned int    y           = 0;
unsigned int    x           = 0;
float           F_Value;

Get Size

IS_File.open(path);
while(getline(IS_File, ST_Line))
{
    if(cols == 0)
    {
        SS_Line << ST_Line;
        while(SS_Line >> F_Value)
            cols++;
    }

    rows++;
}
IS_File.close();

Create Image

*pMA_Out = Mat(rows, cols, CV_32FC1);

Read Data

IS_File.open(path);
while(getline(IS_File, ST_Line))
{
    SS_Line.clear();
    SS_Line << ST_Line;
    x = 0;

    while(SS_Line >> F_Value)
    {
        pMA_Out->at<float>(y, x) = F_Value;
        x++;
    }

    y++;
}
IS_File.close();

Example

1 1 1 -2
1 2 1 0.5
1 1 3 2.1
1 1 1 1.5

turns to this (after beeing converted to CV_8UC1 using normalize with CV_MINMAX to be displayed).