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SPEC_RGB.C
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1993-10-07
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/* Copyright (c) 1990 Regents of the University of California */
#ifndef lint
static char SCCSid[] = "@(#)spec_rgb.c 2.1 11/12/91 LBL";
#endif
/*
* Convert colors and spectral ranges.
*/
#include "color.h"
/*
* The following table contains the CIE tristimulus integrals
* for X, Y, and Z. The table is cumulative, so that
* each color coordinate integrates to 1.
*/
#define STARTWL 380 /* starting wavelength (nanometers) */
#define INCWL 10 /* wavelength increment */
#define NINC 40 /* # of values */
static BYTE chroma[3][NINC] = {
{ /* X */
0, 0, 0, 2, 6, 13, 22, 30, 36, 41,
42, 43, 43, 44, 46, 52, 60, 71, 87, 106,
128, 153, 178, 200, 219, 233, 243, 249, 252, 254,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255
}, { /* Y */
0, 0, 0, 0, 0, 1, 2, 4, 7, 11,
17, 24, 34, 48, 64, 84, 105, 127, 148, 169,
188, 205, 220, 232, 240, 246, 250, 253, 254, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255
}, { /* Z */
0, 0, 2, 10, 32, 66, 118, 153, 191, 220,
237, 246, 251, 253, 254, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
255, 255, 255, 255, 255, 255, 255, 255, 255, 255
}
};
#ifdef NTSC
static float xyz2rgbmat[3][3] = { /* XYZ to RGB (NTSC) */
1.73, -.48, -.26,
-.81, 1.65, -.02,
.08, -.17, 1.28,
};
#else
static float xyz2rgbmat[3][3] = { /* XYZ to RGB (color monitor) */
2.739, -1.145, -.424,
-1.119, 2.029, .033,
.138, -.333, 1.105,
};
#endif
spec_rgb(col, s, e) /* compute RGB color from spectral range */
COLOR col;
int s, e;
{
COLOR ciecolor;
spec_cie(ciecolor, s, e);
cie_rgb(col, ciecolor);
}
spec_cie(col, s, e) /* compute a color from a spectral range */
COLOR col; /* returned color */
int s, e; /* starting and ending wavelengths */
{
register int i, d, r;
s -= STARTWL;
if (s < 0)
s = 0;
e -= STARTWL;
if (e <= s) {
col[RED] = col[GRN] = col[BLU] = 0.0;
return;
}
if (e >= INCWL*(NINC - 1))
e = INCWL*(NINC - 1) - 1;
d = e / INCWL; /* interpolate values */
r = e % INCWL;
for (i = 0; i < 3; i++)
col[i] = chroma[i][d]*(INCWL - r) + chroma[i][d + 1]*r;
d = s / INCWL;
r = s % INCWL;
for (i = 0; i < 3; i++)
col[i] -= chroma[i][d]*(INCWL - r) - chroma[i][d + 1]*r;
col[RED] = (col[RED] + 0.5) / (256*INCWL);
col[GRN] = (col[GRN] + 0.5) / (256*INCWL);
col[BLU] = (col[BLU] + 0.5) / (256*INCWL);
}
cie_rgb(rgbcolor, ciecolor) /* convert CIE to RGB */
register COLOR rgbcolor, ciecolor;
{
register int i;
for (i = 0; i < 3; i++) {
rgbcolor[i] = xyz2rgbmat[i][0]*ciecolor[0] +
xyz2rgbmat[i][1]*ciecolor[1] +
xyz2rgbmat[i][2]*ciecolor[2] ;
if (rgbcolor[i] < 0.0)
rgbcolor[i] = 0.0;
}
}