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/*
FITSPNG -- eCDF base estimation of intensity scaling parameters
Copyright (C) 2019, 2022 Filip Hroch, Masaryk University, Brno, CZ
Fitspng is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Fitspng is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with Fitspng. If not, see <http://www.gnu.org/licenses/>.
*/
#include "fitspng.h"
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <float.h>
#include <string.h>
#include <assert.h>
#define QSENSE 0.95
#define NMAX 32768
#define MAX(x,y) (x) > (y) ? (x) : (y);
int tone(long npix, const float *pic, float rsense, float *qblack,
float *thresh, float *slope, int colour, int set_rel, int verb)
{
int skip = MAX(npix / NMAX,1);
long nmax = npix / skip;
long nbytes = (nmax+1)*sizeof(float);
int qblack_updated = 0;
float *d, *xcdf, *ycdf;
if( (d = malloc(nbytes)) == NULL ||
(xcdf = malloc(nbytes)) == NULL || (ycdf = malloc(nbytes)) == NULL ) {
perror("There is no room for determination of empirical CDF");
return 0;
}
/* PART I. Estimate of background level */
long m = 0;
for(long i = 0; i < npix - skip && m < nmax; i += skip)
d[m++] = pic[i];
int ncdf = ecdf(m,d,xcdf,ycdf);
/* The low level, black, is estimated as qblack quantile. */
float black = quantile(ncdf,xcdf,ycdf,*qblack);
if( colour && (set_rel == 0 || set_rel == 3) ) {
/* An important exception are colour images in CIE XYZ colour-space.
They have usually intensity with black on zero, qblack should
by set appropriately.
*/
for(int i = 0; i < ncdf; i++)
if( xcdf[i] > 0 ) {
black = xcdf[i];
*qblack = ycdf[i];
qblack_updated = 1;
break;
}
}
float median = quantile(ncdf,xcdf,ycdf,0.5);
float q75 = quantile(ncdf,xcdf,ycdf,0.75);
float q25 = quantile(ncdf,xcdf,ycdf,0.25);
float mad = (q75 - q25) / 2;
float threshold = 3 * mad / 0.6745; /* 3-sigma rule */
/* cherries on the cake */
/*
FILE *file = fopen("b.dat","w");
for(int i = 0; i < ncdf; i++)
fprintf(file,"%f %f\n",xcdf[i],ycdf[i]);
fclose(file);
int nhist = 65536;
int *hist;
hist = malloc(nhist*sizeof(int));
for(int i = 0; i < nhist; i++ ) hist[i] = 0;
for(int i = 0; i < npix; i++) {
int n = pic[i];
if( 0 <= n && n < nhist )
hist[n] = hist[n] + 1;
}
file = fopen("bh.dat","w");
for(int i = 0; i < nhist; i++)
fprintf(file,"%d %d\n",i,hist[i]);
fclose(file);
*/
/* PART II. Estimate of starlight */
long n = 0;
long side = 1;
while( n < (NMAX / 10) && side <= 16 ) {
side = 2*side;
long skip2 = MAX(skip / side,1);
long imax = npix - skip2;
for(long i = 0; n < nmax && i < imax; i += skip2) {
float r = pic[i] - median;
if( r > threshold )
d[n++] = r;
}
}
float q1 = quantile(ncdf,xcdf,ycdf,1-QSENSE);
float q99 = quantile(ncdf,xcdf,ycdf,QSENSE);
float refsense = black > 0 ? sqrt(black) : 1;
if( n > 0 ) {
ncdf = ecdf(n,d,xcdf,ycdf);
refsense = quantile(ncdf,xcdf,ycdf,QSENSE);
}
else if ( median > 100 * FLT_EPSILON )
refsense = 3 * (q99 - q1);
free(d);
free(xcdf);
free(ycdf);
if( verb ) {
fprintf(stderr,"Median=%f MAD=%f Black=%f Qlight=%f n=%ld\n",
median, mad, black, refsense, n);
if( qblack_updated )
fprintf(stderr,"Intensity scaling updated: Qblack=%f\n",*qblack);
}
*thresh = black;
*slope = refsense / rsense;
return 1;
}
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