Opencv Mat 类详解以及像素点基本读取方法

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上一节已经介绍了Opnecv的基本构成，下面正式介绍如何使用opencv。

1.Mat类

class CV_EXPORTS Mat{public:    //! default constructor    Mat();    //! constructs 2D matrix of the specified size and type    // (_type is CV_8UC1, CV_64FC3, CV_32SC(12) etc.)    Mat(int rows, int cols, int type);    Mat(Size size, int type);    //! constucts 2D matrix and fills it with the specified value _s.    Mat(int rows, int cols, int type, const Scalar& s);    Mat(Size size, int type, const Scalar& s);    //! constructs n-dimensional matrix    Mat(int ndims, const int* sizes, int type);    Mat(int ndims, const int* sizes, int type, const Scalar& s);    //! copy constructor    Mat(const Mat& m);    //! constructor for matrix headers pointing to user-allocated data    Mat(int rows, int cols, int type, void* data, size_t step=AUTO_STEP);    Mat(Size size, int type, void* data, size_t step=AUTO_STEP);    Mat(int ndims, const int* sizes, int type, void* data, const size_t* steps=0);    //! creates a matrix header for a part of the bigger matrix    Mat(const Mat& m, const Range& rowRange, const Range& colRange=Range::all());    Mat(const Mat& m, const Rect& roi);    Mat(const Mat& m, const Range* ranges);    //! converts old-style CvMat to the new matrix; the data is not copied by default    Mat(const CvMat* m, bool copyData=false);    //! converts old-style CvMatND to the new matrix; the data is not copied by default    Mat(const CvMatND* m, bool copyData=false);    //! converts old-style IplImage to the new matrix; the data is not copied by default    Mat(const IplImage* img, bool copyData=false);    //! builds matrix from std::vector with or without copying the data    template<typename _Tp> explicit Mat(const vector<_Tp>& vec, bool copyData=false);    //! builds matrix from cv::Vec; the data is copied by default    template<typename _Tp, int n> explicit Mat(const Vec<_Tp, n>& vec, bool copyData=true);    //! builds matrix from cv::Matx; the data is copied by default    template<typename _Tp, int m, int n> explicit Mat(const Matx<_Tp, m, n>& mtx, bool copyData=true);    //! builds matrix from a 2D point    template<typename _Tp> explicit Mat(const Point_<_Tp>& pt, bool copyData=true);    //! builds matrix from a 3D point    template<typename _Tp> explicit Mat(const Point3_<_Tp>& pt, bool copyData=true);    //! builds matrix from comma initializer    template<typename _Tp> explicit Mat(const MatCommaInitializer_<_Tp>& commaInitializer);    //! download data from GpuMat    explicit Mat(const gpu::GpuMat& m);    //! destructor - calls release()    ~Mat();    //! assignment operators    Mat& operator = (const Mat& m);    Mat& operator = (const MatExpr& expr);    //! returns a new matrix header for the specified row    Mat row(int y) const;    //! returns a new matrix header for the specified column    Mat col(int x) const;    //! ... for the specified row span    Mat rowRange(int startrow, int endrow) const;    Mat rowRange(const Range& r) const;    //! ... for the specified column span    Mat colRange(int startcol, int endcol) const;    Mat colRange(const Range& r) const;    //! ... for the specified diagonal    // (d=0 - the main diagonal,    //  >0 - a diagonal from the lower half,    //  <0 - a diagonal from the upper half)    Mat diag(int d=0) const;    //! constructs a square diagonal matrix which main diagonal is vector "d"    static Mat diag(const Mat& d);    //! returns deep copy of the matrix, i.e. the data is copied    Mat clone() const;    //! copies the matrix content to "m".    // It calls m.create(this->size(), this->type()).    void copyTo( OutputArray m ) const;    //! copies those matrix elements to "m" that are marked with non-zero mask elements.    void copyTo( OutputArray m, InputArray mask ) const;    //! converts matrix to another datatype with optional scalng. See cvConvertScale.    void convertTo( OutputArray m, int rtype, double alpha=1, double beta=0 ) const;    void assignTo( Mat& m, int type=-1 ) const;    //! sets every matrix element to s    Mat& operator = (const Scalar& s);    //! sets some of the matrix elements to s, according to the mask    Mat& setTo(InputArray value, InputArray mask=noArray());    //! creates alternative matrix header for the same data, with different    // number of channels and/or different number of rows. see cvReshape.    Mat reshape(int cn, int rows=0) const;    Mat reshape(int cn, int newndims, const int* newsz) const;    //! matrix transposition by means of matrix expressions    MatExpr t() const;    //! matrix inversion by means of matrix expressions    MatExpr inv(int method=DECOMP_LU) const;    //! per-element matrix multiplication by means of matrix expressions    MatExpr mul(InputArray m, double scale=1) const;    //! computes cross-product of 2 3D vectors    Mat cross(InputArray m) const;    //! computes dot-product    double dot(InputArray m) const;    //! Matlab-style matrix initialization    static MatExpr zeros(int rows, int cols, int type);    static MatExpr zeros(Size size, int type);    static MatExpr zeros(int ndims, const int* sz, int type);    static MatExpr ones(int rows, int cols, int type);    static MatExpr ones(Size size, int type);    static MatExpr ones(int ndims, const int* sz, int type);    static MatExpr eye(int rows, int cols, int type);    static MatExpr eye(Size size, int type);    //! allocates new matrix data unless the matrix already has specified size and type.    // previous data is unreferenced if needed.    void create(int rows, int cols, int type);    void create(Size size, int type);    void create(int ndims, const int* sizes, int type);    //! increases the reference counter; use with care to avoid memleaks    void addref();    //! decreases reference counter;    // deallocates the data when reference counter reaches 0.    void release();    //! deallocates the matrix data    void deallocate();    //! internal use function; properly re-allocates _size, _step arrays    void copySize(const Mat& m);    //! reserves enough space to fit sz hyper-planes    void reserve(size_t sz);    //! resizes matrix to the specified number of hyper-planes    void resize(size_t sz);    //! resizes matrix to the specified number of hyper-planes; initializes the newly added elements    void resize(size_t sz, const Scalar& s);    //! internal function    void push_back_(const void* elem);    //! adds element to the end of 1d matrix (or possibly multiple elements when _Tp=Mat)    template<typename _Tp> void push_back(const _Tp& elem);    template<typename _Tp> void push_back(const Mat_<_Tp>& elem);    void push_back(const Mat& m);    //! removes several hyper-planes from bottom of the matrix    void pop_back(size_t nelems=1);    //! locates matrix header within a parent matrix. See below    void locateROI( Size& wholeSize, Point& ofs ) const;    //! moves/resizes the current matrix ROI inside the parent matrix.    Mat& adjustROI( int dtop, int dbottom, int dleft, int dright );    //! extracts a rectangular sub-matrix    // (this is a generalized form of row, rowRange etc.)    Mat operator()( Range rowRange, Range colRange ) const;    Mat operator()( const Rect& roi ) const;    Mat operator()( const Range* ranges ) const;    //! converts header to CvMat; no data is copied    operator CvMat() const;    //! converts header to CvMatND; no data is copied    operator CvMatND() const;    //! converts header to IplImage; no data is copied    operator IplImage() const;    template<typename _Tp> operator vector<_Tp>() const;    template<typename _Tp, int n> operator Vec<_Tp, n>() const;    template<typename _Tp, int m, int n> operator Matx<_Tp, m, n>() const;    //! returns true iff the matrix data is continuous    // (i.e. when there are no gaps between successive rows).    // similar to CV_IS_MAT_CONT(cvmat->type)    bool isContinuous() const;    //! returns true if the matrix is a submatrix of another matrix    bool isSubmatrix() const;    //! returns element size in bytes,    // similar to CV_ELEM_SIZE(cvmat->type)    size_t elemSize() const;    //! returns the size of element channel in bytes.    size_t elemSize1() const;    //! returns element type, similar to CV_MAT_TYPE(cvmat->type)    int type() const;    //! returns element type, similar to CV_MAT_DEPTH(cvmat->type)    int depth() const;    //! returns element type, similar to CV_MAT_CN(cvmat->type)    int channels() const;    //! returns step/elemSize1()    size_t step1(int i=0) const;    //! returns true if matrix data is NULL    bool empty() const;    //! returns the total number of matrix elements    size_t total() const;    //! returns N if the matrix is 1-channel (N x ptdim) or ptdim-channel (1 x N) or (N x 1); negative number otherwise    int checkVector(int elemChannels, int depth=-1, bool requireContinuous=true) const;    //! returns pointer to i0-th submatrix along the dimension #0    uchar* ptr(int i0=0);    const uchar* ptr(int i0=0) const;    //! returns pointer to (i0,i1) submatrix along the dimensions #0 and #1    uchar* ptr(int i0, int i1);    const uchar* ptr(int i0, int i1) const;    //! returns pointer to (i0,i1,i3) submatrix along the dimensions #0, #1, #2    uchar* ptr(int i0, int i1, int i2);    const uchar* ptr(int i0, int i1, int i2) const;    //! returns pointer to the matrix element    uchar* ptr(const int* idx);    //! returns read-only pointer to the matrix element    const uchar* ptr(const int* idx) const;    template<int n> uchar* ptr(const Vec<int, n>& idx);    template<int n> const uchar* ptr(const Vec<int, n>& idx) const;    //! template version of the above method    template<typename _Tp> _Tp* ptr(int i0=0);    template<typename _Tp> const _Tp* ptr(int i0=0) const;    template<typename _Tp> _Tp* ptr(int i0, int i1);    template<typename _Tp> const _Tp* ptr(int i0, int i1) const;    template<typename _Tp> _Tp* ptr(int i0, int i1, int i2);    template<typename _Tp> const _Tp* ptr(int i0, int i1, int i2) const;    template<typename _Tp> _Tp* ptr(const int* idx);    template<typename _Tp> const _Tp* ptr(const int* idx) const;    template<typename _Tp, int n> _Tp* ptr(const Vec<int, n>& idx);    template<typename _Tp, int n> const _Tp* ptr(const Vec<int, n>& idx) const;    //! the same as above, with the pointer dereferencing    template<typename _Tp> _Tp& at(int i0=0);    template<typename _Tp> const _Tp& at(int i0=0) const;    template<typename _Tp> _Tp& at(int i0, int i1);    template<typename _Tp> const _Tp& at(int i0, int i1) const;    template<typename _Tp> _Tp& at(int i0, int i1, int i2);    template<typename _Tp> const _Tp& at(int i0, int i1, int i2) const;    template<typename _Tp> _Tp& at(const int* idx);    template<typename _Tp> const _Tp& at(const int* idx) const;    template<typename _Tp, int n> _Tp& at(const Vec<int, n>& idx);    template<typename _Tp, int n> const _Tp& at(const Vec<int, n>& idx) const;    //! special versions for 2D arrays (especially convenient for referencing image pixels)    template<typename _Tp> _Tp& at(Point pt);    template<typename _Tp> const _Tp& at(Point pt) const;    //! template methods for iteration over matrix elements.    // the iterators take care of skipping gaps in the end of rows (if any)    template<typename _Tp> MatIterator_<_Tp> begin();    template<typename _Tp> MatIterator_<_Tp> end();    template<typename _Tp> MatConstIterator_<_Tp> begin() const;    template<typename _Tp> MatConstIterator_<_Tp> end() const;    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;    struct CV_EXPORTS MSize    {        MSize(int* _p);        Size operator()() const;        const int& operator[](int i) const;        int& operator[](int i);        operator const int*() const;        bool operator == (const MSize& sz) const;        bool operator != (const MSize& sz) const;        int* p;    };    struct CV_EXPORTS MStep    {        MStep();        MStep(size_t s);        const size_t& operator[](int i) const;        size_t& operator[](int i);        operator size_t() const;        MStep& operator = (size_t s);        size_t* p;        size_t buf[2];    protected:        MStep& operator = (const MStep&);    };    MSize size;    MStep step;protected:    void initEmpty();};

Mat的构造函数很多，主要的成员变量，这里关注这些 row, col,channel,dim(行、列、通道、纬度，对图像的处理大致都要涉及这些)

  /*! 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;