创建Mat 对象

教程 读取、修改、保存图像 已经讲解了如何使用函数 imwrite() 将一个矩阵写入图像文件中。但是为了debug，更加方便的方式是看实际值。为此，你可以通过 Mat 的运算符 << 来实现，但要记住这只对二维矩阵有效。

Mat 不但是一个很赞的图像容器类，它同时也是一个通用的矩阵类，所以可以用来创建和操作多维矩阵。创建一个Mat对象有多种方法：

矩阵。创建一个Mat对象有多种方法：

• Mat() 构造函数

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

对于二维多通道图像，首先要定义其尺寸，即行数和列数。

然后，需要指定存储元素的数据类型以及每个矩阵点的通道数。为此，依据下面的规则有多种定义

CV_[The number of bits per item][Signed or Unsigned][Type Prefix]C[The channel number]

比如 CV_8UC3 表示使用8位的 unsigned char 型，每个像素由三个元素组成三通道。预先定义的通道数可以多达四个。 Scalar 是个short型vector。指定这个能够使用指定的定制化值来初始化矩阵。当然，如果你需要更多通道数，你可以使用大写的宏并把通道数放在小括号中。

• 在 C\C++ 中通过构造函数进行初始化

      int sz[3] = {2,2,2};     Mat L(3,sz, CV_8UC(1), Scalar::all(0));

  上面的例子演示了如何创建一个超过两维的矩阵：指定维数，然后传递一个指向一个数组的指针，这个数组包含每个维度的尺寸；其余的相同

• 为已存在IplImage指针创建信息头:

  IplImage* img = cvLoadImage("greatwave.png", 1);Mat mtx(img); // convert IplImage* -> Mat

• Create() function: 函数

      M.create(4,4, CV_8UC(2));    cout << "M = "<< endl << " "  << M << endl << endl;

• Create() function: 函数

      M.create(4,4, CV_8UC(2));    cout << "M = "<< endl << " "  << M << endl << endl;

• MATLAB形式的初始化方式： zeros(), ones(), :eyes() 。使用以下方式指定尺寸和数据类型：

      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;

• 对于小矩阵你可以用逗号分隔的初始化函数:

      Mat C = (Mat_<double>(3,3) << 0, -1, 0, -1, 5, -1, 0, -1, 0);     cout << "C = " << endl << " " << C << endl << endl;

使用 clone() 或者 copyTo() 为一个存在的 Mat 对象创建一个新的信息头。

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

Note

调用函数 randu() 来对一个矩阵使用随机数填充，需要指定随机数的上界和下界：

    Mat R = Mat(3, 2, CV_8UC3);    randu(R, Scalar::all(0), Scalar::all(255));

从上面的例子中可以看到默认格式，除此之外，OpenCV还支持以下的输出习惯

默认方式

    cout << "R (default) = " << endl <<        R           << endl << endl;

Python

    cout << "R (python)  = " << endl << format(R,"python") << endl << endl;

以逗号分隔的数值 (CSV)

    cout << "R (csv)     = " << endl << format(R,"csv"   ) << endl << endl;

Numpy

    cout << "R (numpy)   = " << endl << format(R,"numpy" ) << endl << endl;

C语言

    cout << "R (c)       = " << endl << format(R,"C"     ) << endl << endl;

打印其它常用项目

OpenCV支持使用运算符<<来打印其它常用OpenCV数据结构。

2维点

    Point2f P(5, 1);    cout << "Point (2D) = " << P << endl << endl;

3维点

    Point3f P3f(2, 6, 7);    cout << "Point (3D) = " << P3f << endl << endl;

基于cv::Mat的std::vector

    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;

std::vector点

    vector<Point2f> vPoints(20);    for (size_t E = 0; E < vPoints.size(); ++E)        vPoints[E] = Point2f((float)(E * 5), (float)(E % 7));    cout << "A vector of 2D Points = " << vPoints << endl << endl;

测试代码：

#include "stdafx.h"#include "opencv2\core\core.hpp"#include <iostream>using namespace std;using namespace cv;void help(){    cout<< "\n--------------------------------------------------------------------------" << endl    << "This program shows how to create matrices(cv::Mat) in OpenCV and its serial"  << endl    << "out capabilities"                                                            << endl    << "That is, cv::Mat M(...); M.create and cout << M. "                            << endl    << "Shows how output can be formated to OpenCV, python, numpy, csv and C styles." << endl    << "Usage:"                                                                       << endl    << "./cvout_sample"                                                               << endl    << "--------------------------------------------------------------------------"   << endl     << endl;}int _tmain(int argc, _TCHAR* argv[]){    help();        // create by using the constructorMat M1(2,2, CV_8UC1, Scalar(255,200,122));     cout<< "CV8UC1_M1 = " << endl << " " << M1 << endl << endl;Mat M2(2,2, CV_8UC2, Scalar(255,200,122));     cout<< "CV8UC2_M2 = " << endl << " " << M2 << endl << endl;Mat M(2,2, CV_8UC3, Scalar(255,200,122));     cout<< "CV8UC3_M3 = " << endl << " " << M << endl << endl;    // create by using the create function()    M.create(4,4, CV_8UC(2));    cout << "M = "<< endl << " "  << M << endl << endl;    // create multidimensional matrices    int sz[3] = {2,2,2};     Mat L(3,sz, CV_8UC(1), Scalar::all(0));    // Cannot print via operator <<    // Create using MATLAB style eye, ones or zero matrix    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;        // create a 3x3 double-precision identity matrix    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 a matrix with random values    Mat R = Mat(3, 2, CV_8UC3);    randu(R, Scalar::all(0), Scalar::all(255));    // Demonstrate the output formating options    cout << "R (default) = " << endl <<        R           << endl << endl;    cout << "R (python)  = " << endl << format(R,"python") << endl << endl;    cout << "R (numpy)   = " << endl << format(R,"numpy" ) << endl << endl;    cout << "R (csv)     = " << endl << format(R,"csv"   ) << endl << endl;    cout << "R (c)       = " << endl << format(R,"C"     ) << endl << endl;    Point2f P(5, 1);    cout << "Point (2D) = " << P << endl << endl;    Point3f P3f(2, 6, 7);    cout << "Point (3D) = " << P3f << endl << endl;    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;            vector<Point2f> vPoints(20);    for (size_t E = 0; E < vPoints.size(); ++E)        vPoints[E] = Point2f((float)(E * 5), (float)(E % 7));    cout<< "A vector of 2D Points = " << vPoints << endl << endl;    return 0;}

输出结果:

关于Image Engineering & Computer Vision的更多讨论与交流，敬请关注本博客和新浪微博songzi_tea.