Creating matrix in different ways

Example:

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#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "iostream"

using namespace cv;
using namespace std;

int main( )
{

    Mat src1;
    src1 = imread("lena.jpg", CV_LOAD_IMAGE_COLOR); 
    namedWindow( "Original image", CV_WINDOW_AUTOSIZE ); 
    imshow( "Original image", src1 ); 

    Mat gray;
    cvtColor(src1, gray, CV_BGR2GRAY);
    namedWindow( "Result window", CV_WINDOW_AUTOSIZE ); 
    imshow( "Result window", gray );

    // Use the copy constructor
    Mat src2(src1);
    namedWindow( "window2", CV_WINDOW_AUTOSIZE ); 
    imshow( "window2", src2 ); 

    // Assignment operator
    Mat src3;
    src3 = src2; 
    namedWindow( "window3", CV_WINDOW_AUTOSIZE ); 
    imshow( "window3", src3 ); 

    // Selecting a region of interest using a rectangle 
    Mat src4 (src1, Rect(50, 50, 150, 150) ); 
    namedWindow( "window4", CV_WINDOW_AUTOSIZE ); 
    imshow( "window4", src4 ); 
    // Another way of doing same
    Rect r(10, 10, 100, 100);
    Mat src41 = src1(r);
    namedWindow( "window4.1", CV_WINDOW_AUTOSIZE ); 
    imshow( "window4.1", src41 ); 

    // clone() function
    Mat src5 = src1.clone();
    namedWindow( "window5", CV_WINDOW_AUTOSIZE ); 
    imshow( "window5", src5 ); 

    // copyTo() function
    Mat src6;
    src1.copyTo(src6);
    namedWindow( "window6", CV_WINDOW_AUTOSIZE ); 
    imshow( "window6", src6 ); 

    // Using Range()
    Mat P;
    src6.rowRange(1,2).copyTo(P);
    cout << "P = " << endl << " " << P(Range::all(),Range::all()) << endl << endl ;

    // Range::all() - “the whole sequence”
    // Range(a,b) - "[start , end]
    // Copy {row : 0 to 4} and {col : 5 to 9} to matrix Q
    Mat Q; Q = gray(Range(0,5),Range(5,10));
    cout<< Q << endl << endl;

    //make a black image from an existing image
    src1 = Scalar(0);
    namedWindow( "window7", CV_WINDOW_AUTOSIZE ); 
    imshow( "window7", src1 ); 

    // Create a header for an already existing IplImage pointer
    IplImage* img = cvLoadImage("lena.jpg", 1);
    Mat mtx(img); // convert IplImage* -> Mat
    namedWindow( "window8", CV_WINDOW_AUTOSIZE ); 
    imshow( "window8", mtx );

    // Mat() Constructor
    Mat M(2,2, CV_8UC3, Scalar(0,0,255));
    cout << "M = " << endl << " " << M << endl << endl;

    // Use C\C++ arrays and initialize via constructor
    // Create a matrix with more than two dimensions
    int sz[3] = {4,2,3};
    Mat L(3,sz, CV_8UC(1), Scalar::all(0));

    // Create() function
    Mat N;
    N.create(4,4, CV_8UC(2));
    cout << "N = "<< endl << " " << N << endl << endl;

    // initializer: zeros(), ones(), :eyes(). Specify size and data type to use
    Mat E = Mat::eye(4, 4, CV_64F);
    cout << "E = " << endl << " " << E << endl << endl;

    Mat O = Mat::ones(2, 2, CV_32F);
    cout << "O = " << endl << " " << O << endl << endl;

    Mat Z = Mat::zeros(3,3, CV_8UC1);
    cout << "Z = " << endl << " " << Z << endl << endl;

    // For small matrices you may use comma separated initializers:
    Mat C = (Mat_<double>(3,3) << 0, -1, 0, -1, 5, -1, 0, -1, 0);
    cout << "C = " << endl << " " << C << endl << endl;

    Mat RowClone = C.row(1).clone();
    cout << "RowClone = " << endl << " " << RowClone << endl << endl;

    // Fill out a matrix with random values using the randu() function. 
    // You need to give the lower and upper value for the random values:
    Mat R = Mat(3, 2, CV_8UC3);
    randu(R, Scalar::all(0), Scalar::all(255));
    cout << "R = " << endl << " " << R << endl << endl; 

    // allocates a 30x40 floating-point matrix
    Mat A(30, 40, DataType<float>::type);

    Mat B = Mat_<std::complex<double> >(3, 3);
    // the statement below will print 6, 2 /*, that is depth == CV_64F, channels == 2 */
    cout << B.depth() << ", " << B.channels() << endl;
    
    waitKey(0);
    return 0;
}

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