在Mat类出现之前，OpenCV用于处理Image的三大类分别是：
IplImage， CvMat和CvArr其中IplImage及其重要。
但是它是C语言的结构体，同时有C语言的优点和缺点，需要手工管理内存的分配与销毁。
除非平台只支持C语言，否则不是要使用lplImage。
在OpenCV4.0以及更高版本中不要尝试去折腾IplImage。可能会失败。

    enum { MAGIC_VAL = 0x42FF0000, AUTO_STEP = 0, CONTINUOUS_FLAG = CV_MAT_CONT_FLAG, SUBMATRIX_FLAG =   CV_SUBMAT_FLAG  };
    enum { MAGIC_MASK = 0xFFFF0000, TYPE_MASK = 0x00000FFF, DEPTH_MASK = 7 };

    //! 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;

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

    //! custom allocator
    MatAllocator* allocator;
    //! and the standard allocator
    static MatAllocator* getStdAllocator();
    static MatAllocator* getDefaultAllocator();
    static void setDefaultAllocator(MatAllocator* allocator);

    //! internal use method: updates the continuity flag
    void updateContinuityFlag();

    //! interaction with UMat
    UMatData* u;

    MatSize size;
    MatStep step;

#include <iostream>
#include <iomanip>
#include <opencv2/opencv.hpp>
#include <opencv2/core.hpp>
#include <opencv2/imgcodecs.hpp>
using namespace std;
using namespace cv;

struct MatHeader
{
    int nFlags, nStep0, nStep1;
    int nDims, nRows, nCols;
    int nDepth, nType, nChannelIndex;   // 通道索引
    bool bMagic, bContinuous, bSubMatrix;

    void show()
    {
        cout << "flags         = " << nFlags            << "\n"
             << "dim           = " << nDims             << "\n"
             << "step0         = " << nStep0            << "\n"
             << "step1         = " << nStep1            << "\n"
             << "rows          = " << nRows             << "\n"
             << "cols          = " << nCols             << "\n"
             << "depth         = " << nDepth            << "\n"
             << "type          = " << nType             << "\n"
             << "channels      = " << nChannelIndex + 1 << "\n"
             << "is magic      = " << bMagic            << "\n"
             << "is continuous = " << bContinuous       << "\n"
             << "is sub matrix = " << bSubMatrix        << "\n"
             << endl;
    }
};

int main()
{
    Mat img = cv::imread("test.jpg", cv::IMREAD_COLOR);
    if (img.empty())
    {
        cout << "failed to read image" << endl;
        return -1;
    }

    MatHeader header;
    header.nFlags        =  img.flags;   
    header.nStep0        =  img.step[0];    
    header.nStep1        =  img.step[1];
    header.nDims         =  img.dims;
    header.nRows         =  img.rows;
    header.nCols         =  img.cols;
    header.nDepth        =  img.flags & Mat::DEPTH_MASK;
    header.nType         =  img.flags & Mat::TYPE_MASK;
    header.nChannelIndex = (img.flags & Mat::TYPE_MASK) >> 3;
    header.bMagic        = (img.flags & Mat::MAGIC_MASK) == Mat::MAGIC_VAL;
    header.bContinuous   = (img.flags & Mat::CONTINUOUS_FLAG) >> 14;
    header.bSubMatrix    = (img.flags & Mat::SUBMATRIX_FLAG) >> 15;
    header.show();

    cout << "channels()     = " << img.channels()     << endl;
    cout << "depth()        = " << img.depth()        << endl;
    cout << "isContinuous() = " << img.isContinuous() << endl;
    cout << "isSubmatrix()  = " << img.isSubmatrix()  << endl;
    cout << "type()         = " << img.type()         << endl;
    cout << "elemSize()     = " << img.elemSize()     << endl;
    cout << "elemSize1()    = " << img.elemSize1()    << endl;

    return 0;
}