/* * adaptive contrast enhancement -- a 7 by 7 neighbourhood around each pixel * is examined  for its minimum and maximum values.  The center pixel is * remapped linearly in a way that would send the neighbourhood's maximum to * 255 and its minimum to 0.  cen=255*(cen-min)/(max-min). */#define	NWIN	7	/* size of window */#include "map.cc"int filter(unsigned char *b){	register unsigned char min, max;	register unsigned char *eb=b+NWIN*NWIN;	register unsigned char cen=b[NWIN/2*(NWIN+1)];	for(min=max=*b++;b!=eb;b++) if(*b<min) min=*b; else if(max<*b) max=*b;	if(min==max) return cen;	return 255*(cen-min)/(max-min);}