OpenCV : Mat class method

You can get your mat object information (dimmension, rows, cols, size ....) and resize, reshape, copy Mat object by using Mat class method.


1. Get Information of Mat object

cout << "dimmension : "<< mat7.dims << endl;
cout << "rows : "<< mat7.rows << endl;
cout << "columns : "<< mat7.cols << endl;
cout << "size : "<< mat7.size() << endl << endl;
cout << "number of total elements: " << mat7.total() << endl;
cout << "type :" << mat7.type() << endl;
cout << "depth :" << mat7.depth() << endl;
cout << "channels :" << mat7.channels() << endl;

2. Resize Mat object

Mat_ <int> mat10(2, 4);
mat10 << 1,2,3,4,5,6,7,8;
mat10.resize(1); // resize to one rowmat10.resize(2); // resize to two rowsmat10.resize(3, Scalar(9)); // resize to three rows and fill blanks to 9

3. Reshape Mat object
Reshape method just change channels and rows without change number of total elements.

Mat mm1(2, 6, CV_8U);
print_matInfo("mm1 ", mm1);
Mat mm2 = mm1.reshape(2); // change to 2 channels

print_matInfo("mm1.reshape(2) ", mm2);
Mat mm3 = mm1.reshape(3, 2); // change to 3 channels 2 rows

print_matInfo("mm1.reshape(3, 2) ", mm3);

print_matInfo is method for check change

void print_matInfo(String m_name, Mat mat){
    cout << "[" << m_name << " Matrix]" << endl;
    cout << "channels = " << mat.channels() << endl;
    cout << "rows X columns = " << mat.rows << " X " << mat.cols << endl << endl;
}

As result :
[mm1  Matrix]
channels = 1
rows X columns = 2 X 6

[mm1.reshape(2)  Matrix]
channels = 2
rows X columns = 2 X 3

[mm1.reshape(3, 2)  Matrix]
channels = 3
rows X columns = 2 X 2


 4. Copy Mat object
It is safe to use "copyTo()", "clone()", "convertTo()" method for copy.

double mData2[] = {
        1.1, 2.2, 3.3, 4.4,
        5.5, 6.6, 7.7, 8.8,
        9.9, 10, 11, 12};

Mat mmm4(3, 4, CV_64F, mData2);
Mat mmm5 = mmm4.clone(); // clone to mmm5 from mmm4 

Mat mmm6, mmm7;
mmm4.copyTo(mmm6); // copy to mmm6 from mmm4

mmm4.convertTo(mmm6, CV_8U); // copy to mmm6 and convert data type double to unsign_int

Warning : If you used '=' for copy,  it is not copy to but refer to.

Mat mmm3 = mmm4;
mData2[0] = 3.2; // it change not only mmm4 but also mmm3.

cout << "mm3 = \n" << mmm3 << endl << endl;

5. Mat Operation

cout << oneMat + douMat << endl<< endl; // addition 

cout << oneMat * douMat << endl<< endl; // matrix multiple 

cout << oneMat / douMat << endl<< endl; // devide 

cout << douMat - oneMat << endl<< endl; // subtraction

cout << oneMat.mul(2) << endl << endl;  // multiple 

cout << douMat.inv() << endl << endl; // Inverse matrix 

cout << douMat.t() << endl << endl; // Replace rows and columns