// Matrix of doubles (64-bit floats) with 480 rows and 640 column
// CV_64F= 1 chanel, gretscake wiht 64 bits float

 Mat grayscaleImage(480, 640, CV_64F);

 // Matrix of 8-bit unsigned integers with 480 rows and 640 columns.
// CV_8UC3= 3 chanels - color of 8 bits each

 Mat rgbImage(480, 640, CV_8UC3);

// matrix_1 allocates a new block of memory.
Mat matrix_1(1024, 1024, CV_64F);

// matrix_2 and matrix_2 share the same data.
Mat matrix_2 = matrix_1;

// matrix_1 and matrix_2 are both affected.
matrix_2.at<double>(5, 7) = 42.0;

// row_10 also shares the same data.
Mat row_10 = matrix_1.row(10);

// matrix_3 creates a copy of the data.
Mat matrix_3 = matrix_1.clone();