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Image data pointers

Image data is accessed through data pointers (a variable of type DataPtrType). The DataPtrType is defined in the signature of an image (see Image signatures).

Typically, the data pointer type is (a specialization of) a template class with (trivial) inline member functions. The inline functions are eliminated through compiler optimization so there is no loss of efficiency in pixel manipulation. To keep the functions trivial and efficient issues such as border checking should not be done within member functions of the data pointer class.

The requirements for the DataPtrType expressed as a class definition are:

                            DataPtrType(const DataPtrType& rhs);

    DataPtrType&            operator=(const DataPtrType& rhs);

    void                    incX();
    void                    decX();
    void                    incY();
    void                    decY();
    void                    incZ();
    void                    decZ();
    void                    incX(int off);
    void                    decX(int off);
    void                    incY(int off);
    void                    decY(int off);

    void                    incXYZ(int xOff, int yOff, int zOff = 0);
    void                    decXYZ(int xOff, int yOff, int zOff = 0);

    ArithT                  read();
    void                    write(const ArithT& val);
    ArithT                  readIncX();
    void                    writeIncX(const ArithT& val);

    PixelT*                 data();

Horus provides three template classes fullfilling the requirements: HxDataPtr2dScalarTem, HxDataPtr2dTem, and HxDataPtr3dScalarTem. The first two are optimized for 2D images, the last is for 3D images. There are two versions for 2D images (one for scalar pixel values and one for vector values) because of a small technical problem : the scalar values images use native types (short, int, float, and double) and one cannot define a constructor for these types.

Storage and retrieval of individual pixel values is done through the read and write member functions of the data pointer class. Outside the data pointer class pixel values are represented in one of the arithmetic data types (see Arithmetic data types).

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