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/* Copyright (c) 1996 Regents of the University of California */
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#ifndef lint
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static char SCCSid[] = "$SunId$ LBL";
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#endif
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/*
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* Routines for computing and applying brightness mapping.
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*/
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#include "pcond.h"
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#define CVRATIO 0.025 /* fraction of samples allowed > env. */
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#define exp10(x) exp(2.302585093*(x))
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float modhist[HISTRES]; /* modified histogram */
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double mhistot; /* modified histogram total */
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float cumf[HISTRES+1]; /* cumulative distribution function */
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mkcumf() /* make cumulative distribution function */
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{
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register int i;
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register double sum;
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mhistot = 0.; /* compute modified total */
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for (i = 0; i < HISTRES; i++)
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mhistot += modhist[i];
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sum = 0.; /* compute cumulative function */
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for (i = 0; i < HISTRES; i++) {
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cumf[i] = sum/mhistot;
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sum += modhist[i];
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}
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cumf[HISTRES] = 1.;
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}
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double
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cf(b) /* return cumulative function at b */
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double b;
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{
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double x;
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register int i;
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i = x = HISTRES*(b - bwmin)/(bwmax - bwmin);
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x -= (double)i;
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return(cumf[i]*(1.-x) + cumf[i+1]*x);
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}
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double
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BLw(Lw) /* map world luminance to display brightness */
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double Lw;
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{
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double b;
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if (Lw <= LMIN || (b = Bl(Lw)) <= bwmin+FTINY)
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return(Bldmin);
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if (b >= bwmax-FTINY)
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return(Bldmax);
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return(Bldmin + cf(b)*(Bldmax-Bldmin));
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}
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double
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htcontrs(La) /* human threshold contrast sensitivity, dL(La) */
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double La;
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{
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double l10La, l10dL;
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/* formula taken from Ferwerda et al. [SG96] */
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if (La < 1.148e-4)
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return(1.38e-3);
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l10La = log10(La);
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if (l10La < -1.44) /* rod response regime */
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l10dL = pow(.405*l10La + 1.6, 2.18) - 2.86;
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else if (l10La < -.0184)
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l10dL = l10La - .395;
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else if (l10La < 1.9) /* cone response regime */
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l10dL = pow(.249*l10La + .65, 2.7) - .72;
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else
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l10dL = l10La - 1.255;
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return(exp10(l10dL));
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}
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double
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clampf(Lw) /* derivative clamping function */
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double Lw;
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{
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double bLw, ratio;
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bLw = BLw(Lw); /* apply current brightness map */
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ratio = what2do&DO_HSENS ? htcontrs(Lb(bLw))/htcontrs(Lw) : Lb(bLw)/Lw;
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return(ratio/(Lb1(bLw)*(Bldmax-Bldmin)*Bl1(Lw)));
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}
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int
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mkbrmap() /* make dynamic range map */
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{
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double T, b, s;
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double ceiling, trimmings;
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register int i;
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/* copy initial histogram */
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bcopy((char *)bwhist, (char *)modhist, sizeof(modhist));
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s = (bwmax - bwmin)/HISTRES;
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/* loop until satisfactory */
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do {
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mkcumf(); /* sync brightness mapping */
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if (mhistot <= histot*CVRATIO)
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return(-1); /* no compression needed! */
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T = mhistot * (bwmax - bwmin) / HISTRES;
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trimmings = 0.; /* clip to envelope */
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for (i = 0, b = bwmin + .5*s; i < HISTRES; i++, b += s) {
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ceiling = T*clampf(Lb(b));
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if (modhist[i] > ceiling) {
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trimmings += modhist[i] - ceiling;
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modhist[i] = ceiling;
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}
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}
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} while (trimmings > histot*CVRATIO);
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return(0); /* we got it */
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}
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scotscan(scan, xres) /* apply scotopic color sensitivity loss */
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COLOR *scan;
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int xres;
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{
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COLOR ctmp;
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double incolor, b, Lw;
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register int i;
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for (i = 0; i < xres; i++) {
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Lw = plum(scan[i]);
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if (Lw >= TopMesopic)
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incolor = 1.;
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else if (Lw <= BotMesopic)
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incolor = 0.;
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else
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incolor = (Lw - BotMesopic) /
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(TopMesopic - BotMesopic);
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if (incolor < 1.-FTINY) {
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b = (1.-incolor)*slum(scan[i])*inpexp/SWNORM;
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if (lumf == rgblum) b /= WHTEFFICACY;
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setcolor(ctmp, b, b, b);
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if (incolor <= FTINY)
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setcolor(scan[i], 0., 0., 0.);
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else
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scalecolor(scan[i], incolor);
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addcolor(scan[i], ctmp);
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}
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}
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}
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mapscan(scan, xres) /* apply tone mapping operator to scanline */
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COLOR *scan;
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int xres;
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{
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double mult, Lw, b;
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register int i;
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for (i = 0; i < xres; i++) {
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Lw = plum(scan[i]);
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if (Lw < LMIN) {
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setcolor(scan[i], 0., 0., 0.);
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continue;
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}
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b = BLw(Lw);
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mult = (Lb(b) - ldmin)/(ldmax - ldmin) / (Lw*inpexp);
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if (lumf == rgblum) mult *= WHTEFFICACY;
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scalecolor(scan[i], mult);
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}
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}
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putmapping(fp) /* put out mapping function */
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FILE *fp;
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{
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double b, s;
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register int i;
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double wlum, sf;
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sf = scalef*inpexp;
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if (lumf == cielum) sf *= WHTEFFICACY;
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s = (bwmax - bwmin)/HISTRES;
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for (i = 0, b = bwmin + .5*s; i < HISTRES; i++, b += s) {
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wlum = Lb(b);
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if (what2do&DO_LINEAR)
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fprintf(fp, "%e %e\n", wlum, sf*wlum);
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else
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fprintf(fp, "%e %e\n", wlum, Lb(BLw(wlum)));
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}
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}
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