Why Iplimage using char* pointing to raw image data instead of unsigned char* pointer just like Mat did?

edit

Here's the data structure of Iplimage:

typedef struct _IplImage {
  int                  nSize;
  int                  ID;
  int                  nChannels;
  int                  alphaChannel;
  int                  depth;
  char                 colorModel[4];
  char                 channelSeq[4];
  int                  dataOrder;
  int                  origin;
  int                  align;
  int                  width;
  int                  height;
  struct _IplROI*      roi;
  struct _IplImage*    maskROI;
  void*                imageId;
  struct _IplTileInfo* tileInfo;
  int                  imageSize;
  char*                imageData;
  int                  widthStep;
  int                  BorderMode[4];
  int                  BorderConst[4];
  char*                imageDataOrigin;
} IplImage;

As I said, the pointer to imageData is a char*.

class CV_EXPORTS Mat
{
public:
    // ... a lot of methods ...
    ...

    /*! includes several bit-fields:
         - the magic signature
         - continuity flag
         - depth
         - number of channels
     */
    int flags;
    //! the array dimensionality, >= 2
    int dims;
    //! the number of rows and columns or (-1, -1) when the array has more than 2 dimensions
    int rows, cols;
    //! pointer to the data
    uchar* data;

    //! pointer to the reference counter;
    // when array points to user-allocated data, the pointer is NULL
    int* refcount;

    // other members
    ...
};

The pointer to data is uchar* which is unsigned char*.

Here rises a problem that we all know the elements of a color(gray, RGB which are commonly used while loading image) ranges from 0~255, which can be adequately expressed by 8 bits(unsigned char).

Why don't use uchar* in the Iplimage data structure, same as Mat did?