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/* Copyright (c) 1996 Regents of the University of California */ |
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|
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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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/* |
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* Routines for computing and applying brightness mapping. |
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*/ |
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|
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#include "pcond.h" |
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|
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|
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#define CVRATIO 0.025 /* fraction of samples allowed > env. */ |
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|
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#define exp10(x) exp(2.302585093*(x)) |
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|
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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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|
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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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|
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return(exp10(l10dL)); |
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} |
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|
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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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|
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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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|
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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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|
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return(0); /* we got it */ |
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} |
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|
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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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|
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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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|
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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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|
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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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|
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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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|
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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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} |
