gaussian.im

#include "imager.h"
#include <math.h>

static double
gauss(int x, double std) {
  return 1.0/(sqrt(2.0*PI)*std)*exp(-(double)(x)*(float)(x)/(2*std*std));
}

/* Counters are as follows
 l:  lines
 i:  columns
 c:  filter coeffs
 ch: channels
 pc: coeff equalization
*/



int
i_gaussian(i_img *im, double stddev) {
  int i,l,c,ch;
  double pc;
  double *coeff;
  double res[MAXCHANNELS];
  i_img *timg;
  int radius, diameter;

  mm_log((1,"i_gaussian(im %p, stdev %.2f)\n",im,stddev));
  i_clear_error();

  if (stddev <= 0) {
    i_push_error(0, "stddev must be positive");
    return 0;
  }
  /* totally silly cutoff */
  if (stddev > 1000) {
    stddev = 1000;
  }
 
  timg = i_sametype(im, im->xsize, im->ysize);

  if (im->bits <= 8)
    radius = ceil(2 * stddev);
  else
    radius = ceil(3 * stddev);

  diameter = 1 + radius * 2;

  coeff = mymalloc(sizeof(double) * diameter);

  for(i=0;i <= radius;i++) 
    coeff[radius + i]=coeff[radius - i]=gauss(i, stddev);
  pc=0;
  for(i=0; i < diameter; i++)
    pc+=coeff[i];
  for(i=0;i < diameter;i++)
    coeff[i] /= pc;


#code im->bits <= 8
  IM_COLOR rcolor;
  for(l=0;l<im->ysize;l++) {
    for(i=0;i<im->xsize;i++) {
      pc=0.0;
      for(ch=0;ch<im->channels;ch++) 
	res[ch]=0; 
      for(c = 0;c < diameter; c++)
	if (IM_GPIX(im,i+c-radius,l,&rcolor)!=-1) {
	  for(ch=0;ch<im->channels;ch++) 
	    res[ch]+= rcolor.channel[ch] * coeff[c];
	  pc+=coeff[c];
	}
      for(ch=0;ch<im->channels;ch++) {
	double value = res[ch] / pc;
	rcolor.channel[ch] = value > IM_SAMPLE_MAX ? IM_SAMPLE_MAX : IM_ROUND(value);
      }
      IM_PPIX(timg,i,l,&rcolor);
    }
  }
  
  for(l=0;l<im->xsize;l++) {
    for(i=0;i<im->ysize;i++) {
      pc=0.0;
      for(ch=0; ch<im->channels; ch++)
	res[ch]=0; 
      for(c=0; c < diameter; c++)
	if (IM_GPIX(timg,l,i+c-radius,&rcolor)!=-1) {
	  for(ch=0;ch<im->channels;ch++) 
	    res[ch]+= rcolor.channel[ch] * coeff[c];
	  pc+=coeff[c];
	}
      for(ch=0;ch<im->channels;ch++) {
	double value = res[ch]/pc;
	rcolor.channel[ch] = value > IM_SAMPLE_MAX ? IM_SAMPLE_MAX : IM_ROUND(value);
      }
      IM_PPIX(im,l,i,&rcolor);
    }
  }
#/code
  myfree(coeff);
  i_img_destroy(timg);
  
  return 1;
}