--- ray/src/util/cmatrix.c	2021/01/15 18:31:38	2.31
+++ ray/src/util/cmatrix.c	2022/12/04 16:58:08	2.36
@@ -1,5 +1,5 @@
 #ifndef lint
-static const char RCSid[] = "$Id: cmatrix.c,v 2.31 2021/01/15 18:31:38 greg Exp $";
+static const char RCSid[] = "$Id: cmatrix.c,v 2.36 2022/12/04 16:58:08 greg Exp $";
 #endif
 /*
  * Color matrix routines.
@@ -15,6 +15,8 @@ static const char RCSid[] = "$Id: cmatrix.c,v 2.31 202
 #include "paths.h"
 #include "resolu.h"
 
+const char	stdin_name[] = "<stdin>";
+
 const char	*cm_fmt_id[] = {
 			"unknown", COLRFMT, CIEFMT,
 			"float", "ascii", "double"
@@ -212,14 +214,19 @@ CMATRIX *
 cm_load(const char *inspec, int nrows, int ncols, int dtype)
 {
 	const int	ROWINC = 2048;
-	FILE		*fp = stdin;
+	int		dimsOK = (dtype == DTascii) | (nrows > 0) && ncols;
 	int		swap = 0;
+	FILE		*fp;
 	COLOR		scale;
 	CMATRIX		*cm;
 
 	if (!inspec)
-		inspec = "<stdin>";
-	else if (inspec[0] == '!') {
+		inspec = stdin_name;
+	else if (!*inspec)
+		return(NULL);
+	if (inspec == stdin_name) {		/* reading from stdin? */
+		fp = stdin;
+	} else if (inspec[0] == '!') {
 		fp = popen(inspec+1, "r");
 		if (!fp) {
 			sprintf(errmsg, "cannot start command '%s'", inspec);
@@ -234,13 +241,15 @@ cm_load(const char *inspec, int nrows, int ncols, int 
 #endif
 	if (dtype != DTascii)
 		SET_FILE_BINARY(fp);		/* doesn't really work */
-	if (!dtype | !ncols) {			/* expecting header? */
+	if (!dtype | !dimsOK) {			/* expecting header? */
 		char	*err = cm_getheader(&dtype, &nrows, &ncols, &swap, scale, fp);
 		if (err)
 			error(USER, err);
+		dimsOK = ncols > 0 && ( nrows > 0 ||
+				(dtype != DTrgbe) & (dtype != DTxyze) );
 	}
-	if (ncols <= 0 && !fscnresolu(&ncols, &nrows, fp))
-		error(USER, "unspecified number of columns");
+	if (!dimsOK && !fscnresolu(&ncols, &nrows, fp))
+		error(USER, "unspecified matrix size");
 	switch (dtype) {
 	case DTascii:
 	case DTfloat: