fasthessian.h

/*********************************************************** 
*  --- OpenSURF ---                                        *
*  This library is distributed under the GNU GPL. Please   *
*  contact chris.evans@irisys.co.uk for more information.  *
*                                                          *
*  C. Evans, Research Into Robust Visual Features,         *
*  MSc University of Bristol, 2008.                        *
*                                                          *
************************************************************/

#ifndef FASTHESSIAN_H
#define FASTHESSIAN_H

#include "cv.h"
#include "ipoint.h"

#include <vector>

static const int OCTAVES = 4;
static const int INTERVALS = 4;
static const float THRES = 0.0004f;
static const int INIT_SAMPLE = 2;


class FastHessian {
  
  public:
    
    //! Destructor
    ~FastHessian();

    //! Constructor without image
    FastHessian(std::vector<Ipoint> &ipts, 
                const int octaves = OCTAVES, 
                const int intervals = INTERVALS, 
                const int init_sample = INIT_SAMPLE, 
                const float thres = THRES);

    //! Constructor with image
    FastHessian(IplImage *img, 
                std::vector<Ipoint> &ipts, 
                const int octaves = OCTAVES, 
                const int intervals = INTERVALS, 
                const int init_sample = INIT_SAMPLE, 
                const float thres = THRES);

    //! Save the parameters
    void saveParameters(const int octaves, 
                        const int intervals,
                        const int init_sample, 
                        const float thres);

    //! Set or re-set the integral image source
    void setIntImage(IplImage *img);

    //! Find the image features and write into vector of features
    void getIpoints();
    
  private:

    //---------------- Private Functions -----------------//

    //! Calculate determinant of hessian responses
    void buildDet();

    //! Non Maximal Suppression function
    int isExtremum(int octave, int interval, int column, int row);    
    
    //! Return the value of the approximated determinant of hessian
    inline float getVal(int octave, int interval, int column, int row);

    //! Return the sign of the laplacian (trace of the hessian)
    inline int getLaplacian(int o, int i, int c, int r);

    //! Interpolation functions - adapted from Lowe's SIFT implementation
    void interpolateExtremum(int octv, int intvl, int r, int c);
    void interpolateStep( int octv, int intvl, int r, int c, double* xi, double* xr, double* xc );
    CvMat* deriv3D( int octv, int intvl, int r, int c );
    CvMat* hessian3D(int octv, int intvl, int r, int c );

    //---------------- Private Variables -----------------//

    //! Pointer to the integral Image, and its attributes 
    IplImage *img;
    int i_width, i_height;

    //! Reference to vector of features passed from outside 
    std::vector<Ipoint> &ipts;

    //! Number of Octaves
    int octaves;

    //! Number of Intervals per octave
    int intervals;

    //! Initial sampling step for Ipoint detection
    int init_sample;

    //! Threshold value for blob resonses
    float thres;

    //! Array stack of determinant of hessian values
    float *m_det;

};


#endif