OpenCV 学习笔记 -- Mat类 - The Basic Image Container

Mat -- the Basic Image Container

 

Mat 是OpenCV中最基本的数据结构，它包括头部和矩阵数据两个部分。 

    enum { MAGIC_VAL=0x42FF0000, AUTO_STEP=0, CONTINUOUS_FLAG=CV_MAT_CONT_FLAG, SUBMATRIX_FLAG=CV_SUBMAT_FLAG };

    /*! includes several bit-fields:
         - the magic signature
         - continuity flag
         - depth
         - number of channels
     */
    int flags;
    //! the matrix dimensionality, >= 2
    int dims;
    //! the number of rows and columns or (-1, -1) when the matrix has more than 2 dimensions
    int rows, cols;
    //! pointer to the data
    uchar* data;

    //! pointer to the reference counter;
    // when matrix points to user-allocated data, the pointer is NULL
    int* refcount;

    //! helper fields used in locateROI and adjustROI
    uchar* datastart;
    uchar* dataend;
    uchar* datalimit;

    //! custom allocator
    MatAllocator* allocator;

 

Mat 采用引用计数来管理内存，通过‘=’、拷贝构造函数创建新的Mat 对象，只copy头部，而实际的矩阵数据是不copy的，原对象和新的对象的引用计数都会自增1. 

数据存储方法

数据存储方法是关于颜色空间和数据类型选择的问题。

Mat类支持下面5种数据类型和6中颜色：灰度，RGB，RGBA，HSV, YCrCb，CIE Lab

    union
    {
        uchar* ptr;
        short* s;
        int* i;
        float* fl;
        double* db;
    } data;

 

构造函数

// 默认构造函数构造一个对象
// Mat();
Mat mtx;

//构造二维的Mat对象
//Mat(int rows, int cols, int type);
//Mat(Size size, int type);
//Mat(int rows, int cols, int type, const Scalar& s); //specify value _s.
//Mat(Size size, int type, const Scalar& s); //specify value _s.
Mat A(2,2, CV_8UC1);
Size sz(2,2);
Mat B(sz, CV_8UC3);
Mat C(sz, CV_8UC3, Scalar(255,0,0));
Mat M(2,2, CV_8UC3, Scalar(0,0,255));
cout << "M = " << endl << " " << M << endl << endl; 


// 构造一个指定维数(3)的Mat对象
int sz[3] = {2,2,2}; 
Mat L(3,sz, CV_8UC(1), Scalar::all(0));

// 根据给定的IplImage，构造一个Mat头部
IplImage* img = cvLoadImage("greatwave.png", 1);
Mat mtx(img); // convert IplImage* -> Mat

// 用Create函数构造一个Mat对象
M.create(4,4, CV_8UC(2));
cout << "M = "<< endl << " "  << M << endl << endl; 


// 用静态函数eye,ones, zeros初始化一个对角矩阵、单位矩阵、零矩阵
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;


// 构造并初始化一个小型的Mat对象
Mat C = (Mat_<double>(3,3) << 0, -1, 0, -1, 5, -1, 0, -1, 0); 
cout << "C = " << endl << " " << C << endl << endl;


// 用clone()/copyTo() 函数复制一个Mat对象
Mat H1 = C.row(0).clone();
Mat H2; C.row(1).copyTo(H2);//copyTo 函数的参数是一个Mat类型的引用，copyTo(Mat& m);

 

 

对std::cout的支持

可以直接通过cout输出格式化的字符串

vector<float> v;
v.push_back( (float)CV_PI);   v.push_back(2);    v.push_back(3.01f);
    
cout << "Vector of floats via Mat = " << Mat(v) << endl << endl;

 

从这里获得支持std::cout的例子程序.

 

参考文献：

http://opencv.itseez.com/doc/tutorials/core/mat_the_basic_image_container/mat_the_basic_image_container.html#matthebasicimagecontainer

本章结束！