fsaddles.c

image processing including fourier,wavelet,segmentation etc.

/*----------------------------- MegaWave Module -----------------------------*/
/* mwcommand 
  name = {fsaddles}; 
  version = {"1.0"}; 
  author = {"Pascal Monasse"}; 
  function = {"Position and value of saddle points in bilinear interpolation"};
  usage = { 
    image-> pImage  "Input fimage",
    saddles <- pSaddlesImage "Output fimage of saddle points",
    nb <- fsaddles "Number of saddle points"
    }; 
*/ 

#include <float.h>
#include "mw.h"

/* The value set at a pixel that is not a saddle point. The most appropriate
value would be NAN ('Not A Number'); unfortunately, this constant is not
systematically defined in 'math.h'. */
#define NOT_A_SADDLE FLT_MAX

/* Compute the saddle values and return the number of saddle points */
int fsaddles(pImage, pSaddlesImage)
Fimage pImage, pSaddlesImage;
{
  int i, j, iNumber;
  double minDiag1, maxDiag1, minDiag2, maxDiag2, temp;
  float **tabtabPixels, **tabtabSaddleValues;

  if(mw_change_fimage(pSaddlesImage, pImage->nrow-1, pImage->ncol-1) == NULL)
    mwerror(FATAL, 1, "Image allocation error");
  tabtabPixels = mw_newtab_gray_fimage(pImage);
  tabtabSaddleValues = mw_newtab_gray_fimage(pSaddlesImage);
  if(tabtabPixels == NULL || tabtabSaddleValues == NULL)
    mwerror(FATAL, 1, "Array of lines: allocation error");

  iNumber = 0;
  for(i = pImage->nrow -2; i >= 0; i--)
    for(j = pImage->ncol -2; j >= 0; j--) {
      if((minDiag1=tabtabPixels[i][j]) > (maxDiag1=tabtabPixels[i+1][j+1])) {
	temp = minDiag1; minDiag1 = maxDiag1; maxDiag1 = temp;
      }
      if((minDiag2=tabtabPixels[i+1][j]) > (maxDiag2=tabtabPixels[i][j+1])) {
	temp = minDiag2; minDiag2 = maxDiag2; maxDiag2 = temp;
      }
      if(minDiag1 > maxDiag2 || maxDiag1 < minDiag2) {
	temp = minDiag1+maxDiag1 - (minDiag2+maxDiag2);
	tabtabSaddleValues[i][j]= (minDiag1*maxDiag1 - minDiag2*maxDiag2)/temp;
	++ iNumber;
      } else
	tabtabSaddleValues[i][j] = NOT_A_SADDLE;
    }
  free(tabtabPixels);
  free(tabtabSaddleValues);

  return iNumber;
}