CvMat, Mat, IplImage, Cvarr類型

CvMat, Mat, IplImage, Cvarr 元素的獲取和類型轉換。

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

1、四者關係：

1）.CvMat(CvMat is now obsolete, consider using Mat instead)不建議用；

2）. 派生關係：CvArr -> CvMat -> IplImage

3）. Mat是C++接口，和IplImage有所不同。

2. 相互轉換

1). Mat與IplImage相互轉換

IplImage* src;

某文章說，轉換應該是Mat m(src); 而這不會複製內容，真正能複製內容的是：

Mat -> IplImage:

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

IplImage -> Mat

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

2). CvMat與IplImage相互轉換

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

3. (多通道)Mat, IplImage, CvMat的元素獲取

單通道的網上很多，這裏只寫多通道：

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. 驗證獲取元素代碼（Mat轉IplImage）

此代碼只用於驗證多通道元素獲取沒有錯誤，具體用的時候最好還是用opencv直接給的吧（見第3小節）

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++)
            {
                //以下兩種都可以
                //((uchar*)pImg->imageData+i*pImg->widthStep)[j*3+c] =  elem[c];
                CV_IMAGE_ELEM(pImg,uchar,i,3*j+c) = elem[c];
            }
        }
    }
    return pImg;
}