OpenCV Mat的实现
由于Mat在OpneCV里的地位非常重要，这篇文章打算好好研究一番...估计时间跨度会非常长...慢慢更新...
关于Mat的定义，参看我的这篇博客 http://blog.csdn.net/gauss_acm/article/details/50808753
先上常用的函数，因为很多函数内部都可能用到这些函数，所以这样方便看下面的复杂函数
看这些前，建议先看看我上面的博客，对Mat有一个更好的理解，这样下面看起来就轻松了
//! 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;inline bool Mat::isContinuous() const { return (flags & CONTINUOUS_FLAG) != 0; }inline bool Mat::isSubmatrix() const { return (flags & SUBMATRIX_FLAG) != 0; }inline size_t Mat::elemSize() const { return dims > 0 ? step.p[dims-1] : 0; }inline size_t Mat::elemSize1() const { return CV_ELEM_SIZE1(flags); }/* Size of each channel item,
0x124489 = 1000 0100 0100 0010 0010 0001 0001 ~ array of sizeof(arr_type_elem) */
#define CV_ELEM_SIZE1(type) \
((((sizeof(size_t)<<28)|0x8442211) >> CV_MAT_DEPTH(type)*4) & 15)
/* 0x3a50 = 11 10 10 01 01 00 00 ~ array of log2(sizeof(arr_type_elem)) */
#define CV_ELEM_SIZE(type) \
(CV_MAT_CN(type) << ((((sizeof(size_t)/4+1)*16384|0x3a50) >> CV_MAT_DEPTH(type)*2) & 3))inline int Mat::type() const { return CV_MAT_TYPE(flags); }
inline int Mat::depth() const { return CV_MAT_DEPTH(flags); }
inline int Mat::channels() const { return CV_MAT_CN(flags); }inline size_t Mat::step1(int i) const { return step.p[i]/elemSize1(); }inline size_t Mat::total() const
{
if( dims <= 2 )
return rows*cols;
size_t p = 1;
for( int i = 0; i < dims; i++ )
p *= size[i];
return p;
}inline bool Mat::empty() const { return data == 0 || total() == 0; }先来看一个重要的函数
//! sets every matrix element to s
Mat& operator = (const Scalar& s);具体实现
Mat& Mat::operator = (const Scalar& s)
{
const Mat* arrays[] = { this };
uchar* ptr;
NAryMatIterator it(arrays, &ptr, 1);
size_t size = it.size*elemSize(); //获得超平面字节数
if( s[0] == 0 && s[1] == 0 && s[2] == 0 && s[3] == 0 )
{
//全0的情况直接按字节填充0
for( size_t i = 0; i < it.nplanes; i++, ++it )
memset( ptr, 0, size );
}
else
{
if( it.nplanes > 0 ) //先填充第一个超平面
{
double scalar[12];
scalarToRawData(s, scalar, type(), 12);
size_t blockSize = 12*elemSize1();
for( size_t j = 0; j < size; j += blockSize )
{
size_t sz = MIN(blockSize, size - j);
memcpy( ptr + j, scalar, sz );
}
}
for( size_t i = 1; i < it.nplanes; i++ )
{
//填充完第一个超平面后data已经有数据了,因为ptr是指针
++it;
memcpy( ptr, data, size ); //用第一个超平面拷贝到其他超平面
}
}
return *this;
}里面有NAryMatIterator这个类，实际上这个是一个迭代器，推荐看一下我的另一篇 http://blog.csdn.net/gauss_acm/article/details/51195572 ，看完之后，你会发现在opencv里考虑了矩阵不连续存储的情况，所以这个迭代器将会以超平面的形式遍历矩阵
我们看看scalarToRawData这个函数
void scalarToRawData(const Scalar& s, void* _buf, int type, int unroll_to)
{
int i, depth = CV_MAT_DEPTH(type), cn = CV_MAT_CN(type);
CV_Assert(cn <= 4);
switch(depth)
{
case CV_8U:
{
uchar* buf = (uchar*)_buf;
for(i = 0; i < cn; i++)
buf[i] = saturate_cast(s.val[i]);
for(; i < unroll_to; i++)
buf[i] = buf[i-cn];
}
break;
case CV_8S:
{
schar* buf = (schar*)_buf;
for(i = 0; i < cn; i++)
buf[i] = saturate_cast(s.val[i]);
for(; i < unroll_to; i++)
buf[i] = buf[i-cn];
}
break;
case CV_16U:
{
ushort* buf = (ushort*)_buf;
for(i = 0; i < cn; i++)
buf[i] = saturate_cast(s.val[i]);
for(; i < unroll_to; i++)
buf[i] = buf[i-cn];
}
break;
case CV_16S:
{
short* buf = (short*)_buf;
for(i = 0; i < cn; i++)
buf[i] = saturate_cast(s.val[i]);
for(; i < unroll_to; i++)
buf[i] = buf[i-cn];
}
break;
case CV_32S:
{
int* buf = (int*)_buf;
for(i = 0; i < cn; i++)
buf[i] = saturate_cast(s.val[i]);
for(; i < unroll_to; i++)
buf[i] = buf[i-cn];
}
break;
case CV_32F:
{
float* buf = (float*)_buf;
for(i = 0; i < cn; i++)
buf[i] = saturate_cast(s.val[i]);
for(; i < unroll_to; i++)
buf[i] = buf[i-cn];
}
break;
case CV_64F:
{
double* buf = (double*)_buf;
for(i = 0; i < cn; i++)
buf[i] = saturate_cast(s.val[i]);
for(; i < unroll_to; i++)
buf[i] = buf[i-cn];
break;
}
default:
CV_Error(CV_StsUnsupportedFormat,"");
}
} 这个复制语句我们将在很多Mat的构造函数看到...
最重要的3个create函数
//! 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);具体实现
inline void Mat::create(int _rows, int _cols, int _type)
{
_type &= TYPE_MASK;
//如果矩阵参数相同并且数据区域!=null不创建矩阵
if( dims <= 2 && rows == _rows && cols == _cols && type() == _type && data )
return;
int sz[] = {_rows, _cols};
create(2, sz, _type);
}
inline void Mat::create(Size _sz, int _type)
{
create(_sz.height, _sz.width, _type);
}
void Mat::create(int d, const int* _sizes, int _type)
{
int i;
CV_Assert(0 <= d && _sizes && d <= CV_MAX_DIM && _sizes);
_type = CV_MAT_TYPE(_type);
if( data && (d == dims || (d == 1 && dims <= 2)) && _type == type() )
{
if( d == 2 && rows == _sizes[0] && cols == _sizes[1] )
return;
for( i = 0; i < d; i++ )
if( size[i] != _sizes[i] )
break;
if( i == d && (d > 1 || size[1] == 1))
return;
}
release();
if( d == 0 )
return;
flags = (_type & CV_MAT_TYPE_MASK) | MAGIC_VAL;
setSize(*this, d, _sizes, 0, allocator == 0);
if( total() > 0 )
{
if( !allocator )
{
size_t total = alignSize(step.p[0]*size.p[0], (int)sizeof(*refcount));
data = datastart = (uchar*)fastMalloc(total + (int)sizeof(*refcount));
refcount = (int*)(data + total);
*refcount = 1;
}
else
{
allocator->allocate(dims, size, _type, refcount, datastart, data, step.p);
CV_Assert( step[dims-1] == (size_t)CV_ELEM_SIZE(flags) );
}
}
finalizeHdr(*this);
}其实前两个都会调用第3个，所以看第3个就可以了...
当allocator==NULL,则会分配data空间，datastart=data，引用计数设置为1... 其他函数详见下面分析
CV_MAX_DIM=32，也就是说最多创建32维的矩阵，上来先判断需要创建的矩阵是否已存在，否则release
inline void Mat::release()
{
if( refcount && CV_XADD(refcount, -1) == 1 )
deallocate();
data = datastart = dataend = datalimit = 0;
size.p[0] = 0;
refcount = 0;
}void Mat::deallocate()
{
if( allocator )
allocator->deallocate(refcount, datastart, data);
else
{
CV_DbgAssert(refcount != 0);
fastFree(datastart);
}
}CV_XADD可以看成后置自增运算.,可以参考我的博客 http://blog.csdn.net/gauss_acm/article/details/50971503
也就是当refcount为1，马上减为0，就需要释放掉，调用dellocate
先看一下setSize
static inline void setSize( Mat& m, int _dims, const int* _sz,
const size_t* _steps, bool autoSteps=false )
{
CV_Assert( 0 <= _dims && _dims <= CV_MAX_DIM );
if( m.dims != _dims )
{
if( m.step.p != m.step.buf )
{
fastFree(m.step.p);
m.step.p = m.step.buf;
m.size.p = &m.rows;
}
if( _dims > 2 )
{
m.step.p = (size_t*)fastMalloc(_dims*sizeof(m.step.p[0]) + (_dims+1)*sizeof(m.size.p[0]));
m.size.p = (int*)(m.step.p + _dims) + 1;
m.size.p[-1] = _dims;
m.rows = m.cols = -1;
}
}
m.dims = _dims;
if( !_sz )
return;
size_t esz = CV_ELEM_SIZE(m.flags), total = esz;
int i;
for( i = _dims-1; i >= 0; i-- )
{
int s = _sz[i];
CV_Assert( s >= 0 );
m.size.p[i] = s;
if( _steps )
m.step.p[i] = i < _dims-1 ? _steps[i] : esz;
else if( autoSteps )
{
m.step.p[i] = total;
int64 total1 = (int64)total*s;
if( (uint64)total1 != (size_t)total1 )
CV_Error( CV_StsOutOfRange, "The total matrix size does not fit to \"size_t\" type" );
total = (size_t)total1;
}
}
if( _dims == 1 )
{
m.dims = 2;
m.cols = 1;
m.step[1] = esz;
}
}里面还有fastMalloc和fastFree两个函数，这是opencv库分配和释放内存的函数，其中使用了指针对齐的技术，
详见我的博客 http://blog.csdn.net/gauss_acm/article/details/50971503
create里的alignSize
/*!
Aligns buffer size by the certain number of bytes
This small inline function aligns a buffer size by the certian number of bytes by enlarging it.
*/
static inline size_t alignSize(size_t sz, int n)
{
return (sz + n-1) & -n;
}static void finalizeHdr(Mat& m)
{
updateContinuityFlag(m);
int d = m.dims;
if( d > 2 )
m.rows = m.cols = -1;
if( m.data )
{
m.datalimit = m.datastart + m.size[0]*m.step[0];
if( m.size[0] > 0 )
{
m.dataend = m.data + m.size[d-1]*m.step[d-1];
for( int i = 0; i < d-1; i++ )
m.dataend += (m.size[i] - 1)*m.step[i];
}
else
m.dataend = m.datalimit;
}
else
m.dataend = m.datalimit = 0;
}static void updateContinuityFlag(Mat& m)
{
int i, j;
for( i = 0; i < m.dims; i++ )
{
if( m.size[i] > 1 )
break;
}
for( j = m.dims-1; j > i; j-- )
{
if( m.step[j]*m.size[j] < m.step[j-1] )
break;
}
int64 t = (int64)m.step[0]*m.size[0];
if( j <= i && t == (int)t )
m.flags |= Mat::CONTINUOUS_FLAG;
else
m.flags &= ~Mat::CONTINUOUS_FLAG;
}接下来是Mat一些构造函数
//! 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);没什么好说的，基本上都是在内部调用create函数，Scalar则使用我上面讲的Mat = Scalar函数
inline Mat::Mat()
: flags(0), dims(0), rows(0), cols(0), data(0), refcount(0),
datastart(0), dataend(0), datalimit(0), allocator(0), size(&rows)
{
}
inline Mat::Mat(int _rows, int _cols, int _type)
: flags(0), dims(0), rows(0), cols(0), data(0), refcount(0),
datastart(0), dataend(0), datalimit(0), allocator(0), size(&rows)
{
create(_rows, _cols, _type);
}
inline Mat::Mat(int _rows, int _cols, int _type, const Scalar& _s)
: flags(0), dims(0), rows(0), cols(0), data(0), refcount(0),
datastart(0), dataend(0), datalimit(0), allocator(0), size(&rows)
{
create(_rows, _cols, _type);
*this = _s;
}
inline Mat::Mat(Size _sz, int _type)
: flags(0), dims(0), rows(0), cols(0), data(0), refcount(0),
datastart(0), dataend(0), datalimit(0), allocator(0), size(&rows)
{
create( _sz.height, _sz.width, _type );
}
inline Mat::Mat(Size _sz, int _type, const Scalar& _s)
: flags(0), dims(0), rows(0), cols(0), data(0), refcount(0),
datastart(0), dataend(0), datalimit(0), allocator(0), size(&rows)
{
create(_sz.height, _sz.width, _type);
*this = _s;
}
inline Mat::Mat(int _dims, const int* _sz, int _type)
: flags(0), dims(0), rows(0), cols(0), data(0), refcount(0),
datastart(0), dataend(0), datalimit(0), allocator(0), size(&rows)
{
create(_dims, _sz, _type);
}
inline Mat::Mat(int _dims, const int* _sz, int _type, const Scalar& _s)
: flags(0), dims(0), rows(0), cols(0), data(0), refcount(0),
datastart(0), dataend(0), datalimit(0), allocator(0), size(&rows)
{
create(_dims, _sz, _type);
*this = _s;
} 拷贝构造
//! copy constructor
Mat(const Mat& m);inline Mat::Mat(const Mat& m)
: flags(m.flags), dims(m.dims), rows(m.rows), cols(m.cols), data(m.data),
refcount(m.refcount), datastart(m.datastart), dataend(m.dataend),
datalimit(m.datalimit), allocator(m.allocator), size(&rows)
{
if( refcount )
CV_XADD(refcount, 1);
if( m.dims <= 2 )
{
step[0] = m.step[0]; step[1] = m.step[1];
}
else
{
dims = 0;
copySize(m);
}
}注意：拷贝构造函数值拷贝了一个矩阵头...数据区域是公用的...所以当改变拷贝矩阵的数据时，原矩阵也跟着改变...要小心使用...
当维数小于等于2的情况，step复制一下就可以了，因为size在冒号语法里已初始化，否则调用copySize
void Mat::copySize(const Mat& m)
{
setSize(*this, m.dims, 0, 0);
for( int i = 0; i < dims; i++ )
{
size[i] = m.size[i];
step[i] = m.step[i];
}
}在copySize里调用了setSize，注意调用前dims清0，这样在setSize里step和size会申请空间...最后复制一下数据就可以了
利用用户自己构造的数据来创建Mat
//! 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);inline Mat::Mat(int _rows, int _cols, int _type, void* _data, size_t _step)
: flags(MAGIC_VAL + (_type & TYPE_MASK)), dims(2), rows(_rows), cols(_cols),
data((uchar*)_data), refcount(0), datastart((uchar*)_data), dataend(0),
datalimit(0), allocator(0), size(&rows)
{
size_t esz = CV_ELEM_SIZE(_type), minstep = cols*esz;
if( _step == AUTO_STEP )
{
_step = minstep;
flags |= CONTINUOUS_FLAG;
}
else
{
if( rows == 1 ) _step = minstep;
CV_DbgAssert( _step >= minstep );
flags |= _step == minstep ? CONTINUOUS_FLAG : 0;
}
step[0] = _step; step[1] = esz;
datalimit = datastart + _step*rows;
dataend = datalimit - _step + minstep;
}这个函数创建的是二维矩阵,1~4通道，函数参数里data是用户创建的数据区域首地址，_step是每一行元素所占的字节数，_step默认是0，此时函数会自动根据cols*elemSize来计算...但也可以传入一个具体的值，这个值可以大于cols*elemSize，也就是用户自己分配的数据区域同样可以不连续，那么更新flag的连续性标志就可以根据这个大于来做...dataend是数据结束的地址，不包括填充的空白字节，所以减去_step，最后一行单独算，于是加上cols *elemSize，由于这块 数据区域是用户自己分配的，所以refcount不需要设置为1，也就是这块区域无需Mat自己释放...
inline Mat::Mat(Size _sz, int _type, void* _data, size_t _step)
: flags(MAGIC_VAL + (_type & TYPE_MASK)), dims(2), rows(_sz.height), cols(_sz.width),
data((uchar*)_data), refcount(0), datastart((uchar*)_data), dataend(0),
datalimit(0), allocator(0), size(&rows)
{
size_t esz = CV_ELEM_SIZE(_type), minstep = cols*esz;
if( _step == AUTO_STEP )
{
_step = minstep;
flags |= CONTINUOUS_FLAG;
}
else
{
if( rows == 1 ) _step = minstep;
CV_DbgAssert( _step >= minstep );
flags |= _step == minstep ? CONTINUOUS_FLAG : 0;
}
step[0] = _step; step[1] = esz;
datalimit = datastart + _step*rows;
dataend = datalimit - _step + minstep;
}Mat::Mat(int _dims, const int* _sizes, int _type, void* _data, const size_t* _steps)
: flags(MAGIC_VAL|CV_MAT_TYPE(_type)), dims(0),
rows(0), cols(0), data((uchar*)_data), refcount(0),
datastart((uchar*)_data), dataend((uchar*)_data), datalimit((uchar*)_data),
allocator(0), size(&rows)
{
setSize(*this, _dims, _sizes, _steps, true);
finalizeHdr(*this);
}inline Mat& Mat::operator = (const Mat& m)
{
if( this != &m )
{
if( m.refcount )
CV_XADD(m.refcount, 1);
release();
flags = m.flags;
if( dims <= 2 && m.dims <= 2 )
{
dims = m.dims;
rows = m.rows;
cols = m.cols;
step[0] = m.step[0];
step[1] = m.step[1];
}
else
copySize(m);
data = m.data;
datastart = m.datastart;
dataend = m.dataend;
datalimit = m.datalimit;
refcount = m.refcount;
allocator = m.allocator;
}
return *this;
}复制构造函数，如果两个对象指针相同，直接返回，否则先维护引用数，再维护其他域，如果小于等2维，直接拷贝，大于2为需要copySize，这个函数上面已分析...
接下来我们考虑如何截取子矩阵，同时更新flags|=SUBMATRIX_FLAG,我们不需要重新复制数据区域，只需要增加引用计数，并且我们需要修改data的首地址为子矩阵的第一个元素的地址，同时需要更新每一维的size，但是我们不需要更新step，为什么呢？因为我们引用的是之前的矩阵的数据区域，这个数据区域可能比子矩阵大，所以子矩阵不一定连续存储，所以我们计算子矩阵某个元素的地址，还是需要按照之前的矩阵的step来计算，同时我们考虑更新CONTINUOUS_FLAG标志...
//! 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);还有三个括号运算符
//! 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;因为这之间调用关系复杂，所以我还是按照调用关系来吧
Mat::Mat(const Mat& m, const Range* ranges)
: flags(m.flags), dims(0), rows(0), cols(0), data(0), refcount(0),
datastart(0), dataend(0), datalimit(0), allocator(0), size(&rows)
{
int i, d = m.dims;
CV_Assert(ranges);
for( i = 0; i < d; i++ )
{
//检查Range的范围是否正确
Range r = ranges[i];
CV_Assert( r == Range::all() || (0 <= r.start && r.start < r.end && r.end <= m.size[i]) );
}
*this = m; //在复制构造函数里,引用数自动增加1
for( i = 0; i < d; i++ )
{
Range r = ranges[i];
if( r != Range::all() && r != Range(0, size.p[i]))
{
size.p[i] = r.end - r.start; //更新size的每一维
data += r.start*step.p[i]; //计算data为子矩阵的数据起始地址
flags |= SUBMATRIX_FLAG; //更新SUBMATRIX_FLAG标志
}
}
//更新连续性标志
updateContinuityFlag(*this);
}inline Mat Mat::operator()(const Range* ranges) const
{
return Mat(*this, ranges); //注意这里会有一个临时对象返回，但之后会被析构，因此引用数不会变多
}Mat::Mat(const Mat& m, const Range& rowRange, const Range& colRange)
: flags(0), dims(0), rows(0), cols(0), data(0), refcount(0),
datastart(0), dataend(0), datalimit(0), allocator(0), size(&rows)
{
CV_Assert( m.dims >= 2 );
if( m.dims > 2 )
{
//大于2维,从第3维开始默认全部是Range::all()
AutoBuffer rs(m.dims);
rs[0] = rowRange;
rs[1] = colRange;
for( int i = 2; i < m.dims; i++ )
rs[i] = Range::all();
*this = m(rs); //从处rs会隐式调用转换函数变成Range*
//然后就是调用m的(Range*)运算符
return;
}
//二维情况
*this = m;
if( rowRange != Range::all() && rowRange != Range(0,rows) )
{
CV_Assert( 0 <= rowRange.start && rowRange.start <= rowRange.end && rowRange.end <= m.rows );
rows = rowRange.size();
data += step*rowRange.start; //step隐式调用转换函数,返回buf[0]
flags |= SUBMATRIX_FLAG; //更新子矩阵标记
}
if( colRange != Range::all() && colRange != Range(0,cols) )
{
CV_Assert( 0 <= colRange.start && colRange.start <= colRange.end && colRange.end <= m.cols );
cols = colRange.size();
data += colRange.start*elemSize();
//如果列数小于原矩阵,则不连续
flags &= cols < m.cols ? ~CONTINUOUS_FLAG : -1;
flags |= SUBMATRIX_FLAG; //更新子矩阵标记
}
if( rows == 1 ) //一行必然是连续的
flags |= CONTINUOUS_FLAG;
if( rows <= 0 || cols <= 0 )
{
release();
rows = cols = 0;
}
} inline Mat Mat::operator()( Range rowRange, Range colRange ) const
{
return Mat(*this, rowRange, colRange);
} //相当于Range(roi.x,roi.x+roi.width),Range(roi.y,roi.y+roi.height)
Mat::Mat(const Mat& m, const Rect& roi)
: flags(m.flags), dims(2), rows(roi.height), cols(roi.width),
data(m.data + roi.y*m.step[0]), refcount(m.refcount),
datastart(m.datastart), dataend(m.dataend), datalimit(m.datalimit),
allocator(m.allocator), size(&rows)
{
CV_Assert( m.dims <= 2 );
//子矩阵的cols小于原矩阵,不连续
flags &= roi.width < m.cols ? ~CONTINUOUS_FLAG : -1;
//一行必定连续
flags |= roi.height == 1 ? CONTINUOUS_FLAG : 0;
size_t esz = CV_ELEM_SIZE(flags);
data += roi.x*esz;
CV_Assert( 0 <= roi.x && 0 <= roi.width && roi.x + roi.width <= m.cols &&
0 <= roi.y && 0 <= roi.height && roi.y + roi.height <= m.rows );
if( refcount )
CV_XADD(refcount, 1);
if( roi.width < m.cols || roi.height < m.rows )
flags |= SUBMATRIX_FLAG;
step[0] = m.step[0]; step[1] = esz;
if( rows <= 0 || cols <= 0 )
{
release();
rows = cols = 0;
}
}inline Mat Mat::operator()( const Rect& roi ) const
{ return Mat(*this, roi); }然后关于子矩阵寻址做一下严格的说明，以二维矩阵为例，设原矩阵的step信息：step[0]和step[1]，子矩阵为[x0,y0]->[x1,y1],那么对于x0<=x<=x1,y0<=y<=y1,我们可以使用y*step[0]+x*step[1]定位，但这样每一维需要记录两个端点，于是我们来做一个平移变换，以子矩阵的左上角为参考系，那么左上角地址为D=y0*step[0]+x0*step[1],于是对于[x,y],我们可以用D+(y-y0)*step[0]+(x-x0)*step[1],于是我们只需要将[x0,x1]区间映射到[0,x1-x0],[y0,y1]映射到[0,y1-y0],这样[x,y]对应了[x-x0,y-y0],这样我们每一维我们只需要记录右端点x1-x0,y1-y0,再把子矩阵左上角地址赋值给data，这样就可以正确寻址了...大概是这么一个思想...
持续更新中...