integral.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 _OPENSURF_INTEGRALH
#define _OPENSURF_INTEGRALH

#include <algorithm>  // req'd for std::min/max

// undefine VS macros
#ifdef min
#undef min
#endif

#ifdef max
#undef max
#endif

#include "opencv/cv.h"

//! Computes the integral image of image img.  Assumes source image to be a 
//! 32-bit floating point.  Returns IplImage in 32-bit float form.
IplImage *Integral(IplImage *img);


//! Computes the sum of pixels within the rectangle specified by the top-left start
//! co-ordinate and size
inline float BoxIntegral(IplImage *img, int row, int col, int rows, int cols) 
{
	float *data = (float *) img->imageData;
	int step = img->widthStep/sizeof(float);

	// The subtraction by one for row/col is because row/col is inclusive.
	int r1 = std::min(row,          img->height) - 1;
	int c1 = std::min(col,          img->width)  - 1;
	int r2 = std::min(row + rows,   img->height) - 1;
	int c2 = std::min(col + cols,   img->width)  - 1;

	float A(0.0f), B(0.0f), C(0.0f), D(0.0f);
	if (r1 >= 0 && c1 >= 0) A = data[r1 * step + c1];
	if (r1 >= 0 && c2 >= 0) B = data[r1 * step + c2];
	if (r2 >= 0 && c1 >= 0) C = data[r2 * step + c1];
	if (r2 >= 0 && c2 >= 0) D = data[r2 * step + c2];

	return std::max(0.f, A - B - C + D);
}

#endif