--- ray/src/common/ccyrgb.c	2011/02/18 00:40:25	3.1
+++ ray/src/common/ccyrgb.c	2023/11/15 18:02:52	3.5
@@ -1,8 +1,8 @@
 #ifndef lint
-static const char	RCSid[] = "$Id: ccyrgb.c,v 3.1 2011/02/18 00:40:25 greg Exp $";
+static const char	RCSid[] = "$Id: ccyrgb.c,v 3.5 2023/11/15 18:02:52 greg Exp $";
 #endif
 /*
- * Convert MGF color to RGB representation
+ * Convert MGF color to Radiance RGB and spectral representations
  */
 
 #include <stdio.h>
@@ -38,11 +38,54 @@ rgb2ccy(COLOR cin, C_COLOR *cout)
 	*cout = c_dfcolor;
 	df = xyz[CIEX] + xyz[CIEY] + xyz[CIEZ];
 	if (df <= .0)
-		return;
+		return(.0);
 	df = 1./df;
 	cout->cx = xyz[CIEX]*df;
 	cout->cy = xyz[CIEZ]*df;
 	cout->flags = (C_CSXY|C_CDXY);
 
 	return(xyz[CIEY]);
+}
+
+void
+ccy2scolor(			/* convert MGF color, Y to spectral color */
+	C_COLOR	*cin,	/* input MGF color or spectrum */
+	double	cieY,	/* input luminance or reflectance */
+	SCOLOR	sco	/* output spectral color */
+)
+{
+	COLORV	nf, sorig[C_CNSS];
+	int	i;
+
+	if (cin->flags & C_CDXY || NCSAMP <= 3) {
+		COLOR	col;		/* tristimulus in or out, so... */
+		ccy2rgb(cin, cieY, col);
+		setscolor(sco, colval(col,RED), colval(col,GRN), colval(col,BLU));
+		return;
+	}
+	c_ccvt(cin, C_CSXY);
+	nf = cieY*C_CNSS/(cin->ssum*3*cin->cy);
+	for (i = C_CNSS; i--; )		/* may as well reverse order */
+		sorig[C_CNSS-1-i] = nf*(COLORV)cin->ssamp[i];
+
+	convertscolor(sco, NCSAMP, WLPART[0], WLPART[3],
+			sorig, C_CNSS, C_CMAXWL+.5*C_CWLI, C_CMINWL-.5*C_CWLI);
+}
+
+/* Convert spectral color to MGF color and Y value */
+double
+scolor2ccy(SCOLOR sci, C_COLOR *cout)
+{
+	float		hinc, cspec[MAXCSAMP];
+	int		i = NCSAMP;
+
+	if (i <= 3)		/* defined as RGB, so... */
+		return(rgb2ccy(sci, cout));
+
+	while (i-- > 0)		/* need to reverse array */
+		cspec[i] = sci[NCSAMP-1-i];
+
+	hinc = (WLPART[0]-WLPART[3])/(float)(2*NCSAMP);
+
+	return(c_sset(cout, WLPART[3]+hinc, WLPART[0]-hinc, cspec, NCSAMP));
 }