imgthbcv.c File Reference

Calculate between-class variance from PET image based on one threshold value, or estimate threshold that gives highest between-class variance. More...

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Functions
double	imgBetween2ClassesVariance (IMG *img, const int fi, float threshold, int verbose)

Detailed Description

Calculate between-class variance from PET image based on one threshold value, or estimate threshold that gives highest between-class variance.

Only for testing purposes.

Copyright

(c) Turku PET Centre

Author

Vesa Oikonen

Definition in file imgthbcv.c.

Function Documentation

imgBetween2ClassesVariance()

double imgBetween2ClassesVariance	(	IMG *	img,
		const int	fi,
		float	threshold,
		int	verbose )

Calculate between-class variance from one frame of a PET image, based on one absolute threshold value.

Between-class variance is calculated using formula by Cao et al. 2018 doi: 10.1109/ACCESS.2018.2889013

Returns

Returns the between-class variance, or NaN in case of an error.

Parameters

img	Pointer to IMG data structure; not modified.
fi	Time frame of image data to use (1..dimt). Dynamic images should be summed before calling this function.
threshold	Absolute threshold value.
verbose	Verbose level

Definition at line 71 of file imgthbcv.c.

  {
  if(verbose>0) {printf("%s(IMG, %d, %f, ...)\n", __func__, fi, threshold); fflush(stdout);}
  double bcv=nan("");
  if(img==NULL || img->dimz<1 || img->dimy<1 || img->dimx<1 || img->dimt<1) return(bcv);
  if(fi<1 || fi>img->dimt) return(bcv);
 
  if(verbose>1) fprintf(stdout, "thresholding\n");
  unsigned int p0=0, p1=0;
  double s0=0.0, s1=0.0;
  for(int zi=0; zi<img->dimz; zi++) {
    for(int yi=0; yi<img->dimy; yi++) {
      for(int xi=0; xi<img->dimx; xi++) {
        if(img->m[zi][yi][xi][fi-1]<threshold) {
          p0++; s0+=img->m[zi][yi][xi][fi-1];
        } else if(img->m[zi][yi][xi][fi-1]>=threshold) {
          p1++; s1+=img->m[zi][yi][xi][fi-1];
        } // NaNs are left out with if else if
      }
    }
  }
  if(verbose>1) {
    printf("p0=%u\n", p0);
    printf("p1=%u\n", p1);
  }
  /* If no pixels in either of classes, between-class variance is 0 */
  if(p0==0 || p1==0) {
    bcv=0.0;
  } else { // otherwise calculate means, and the between-class variance
 
    /* Calculate means */
    double mu0, mu1, mu;
    mu0=s0/(double)p0;
    mu1=s1/(double)p1;
    mu=(s0+s1)/(double)(p0+p1);
    if(verbose>1) {
      printf("mu0=%g\n", mu0);
      printf("mu1=%g\n", mu1);
      printf("mu=%g\n", mu);
    }
 
    /* Calculate between-class variance */
    bcv=(double)p0*(double)p1*( (mu0-mu1)*(mu0-mu1) + (mu0-mu)*(mu0-mu) + (mu1-mu)*(mu1-mu) );
  }
 
  if(verbose>1) {printf("BCV := %g\n", bcv); fflush(stdout);}
  return(bcv);
}