CvMat, Mat, IplImage, Cvarr类型

CvMat, Mat, IplImage, Cvarr 元素的获取和类型转换。

参考 http://blog.csdn.net/abcjennifer/article/details/17640195

1、四者关系：

1）.CvMat(CvMat is now obsolete, consider using Mat instead)不建议用；

2）. 派生关系：CvArr -> CvMat -> IplImage

3）. Mat是C++接口，和IplImage有所不同。

2. 相互转换

1). Mat与IplImage相互转换

IplImage* src;

某文章说，转换应该是Mat m(src); 而这不会复制内容，真正能复制内容的是：

Mat -> IplImage:

 Mat m;
 IplImage* transIplimage = cvCloneImage(&(IplImage) m);

IplImage -> Mat

 IplImage* transIplImage;
 Mat m = cvarrToMat(transIplImage,true);

2). CvMat与IplImage相互转换

 IplImage* transIplImage;
 CvMat* cvmat;
 cvGetMat(transIplImage,cvmat);
 cvGetImage(cvmat,transIplImage);

3. (多通道)Mat, IplImage, CvMat的元素获取

单通道的网上很多，这里只写多通道：

1). IplImage

 //i is the index of rows
 //j is the index of cols
 //c is the index of channel
 ((uchar*)pImg->imageData+i*pImg->widthStep)[j*3+c]
 CV_IMAGE_ELEM(pImg,uchar,i,3*j+c)

2 ).Mat

 Mat m;
 int h = m.rows; int w = m.cols;
 int nc = m.channels();
 for (int i = 0;i<h;i++)
 {
     for(int j = 0;j<w;j++)
     {
         Vec3b& elem = m.at<Vec3b>(i,j);
         for (int c = 0; c<nc; c++)
         {
             uchar uc = elem[c] ;//Mat(i,j) of channel c
         }
     }
 }

3). CvMat

CV_MAT_ELEM(cvmat,uchar,i,3*j+c) 

4. 验证获取元素代码（Mat转IplImage）

此代码只用于验证多通道元素获取没有错误，具体用的时候最好还是用opencv直接给的吧（见第3小节）

 IplImage* cvcvt_mat2IplImage(Mat m)
 {
     int h = m.rows; int w = m.cols;
     int nc = m.channels();
     IplImage* pImg = cvCreateImage(cvSize(w,h),8,nc);

     for (int i = 0;i<h;i++)
     {
         for(int j = 0;j<w;j++)
         {
             Vec3b& elem = m.at<Vec3b>(i,j);
             for (int c = 0; c<nc; c++)
             {
                 //以下两种都可以
                 //((uchar*)pImg->imageData+i*pImg->widthStep)[j*3+c] =  elem[c];
                 CV_IMAGE_ELEM(pImg,uchar,i,3*j+c) = elem[c];
             }
         }
     }
     return pImg;
 }