--- ray/src/px/mt160r.c	1990/01/26 08:17:31	1.6
+++ ray/src/px/mt160r.c	1991/11/12 16:04:57	2.1
@@ -1,4 +1,4 @@
-/* Copyright (c) 1986 Regents of the University of California */
+/* Copyright (c) 1991 Regents of the University of California */
 
 #ifndef lint
 static char SCCSid[] = "$SunId$ LBL";
@@ -13,6 +13,7 @@ static char SCCSid[] = "$SunId$ LBL";
 #include  <stdio.h>
 
 #include  "color.h"
+#include  "resolu.h"
 
 #define  NCOLS		880		/* for wide carriage */
 
@@ -49,9 +50,12 @@ char  *fname;
 		return(-1);
 	}
 				/* discard header */
-	getheader(input, NULL);
+	if (checkheader(input, COLRFMT, NULL) < 0) {
+		fprintf(stderr, "%s: not a Radiance picture\n", fname);
+		return(-1);
+	}
 				/* get picture dimensions */
-	if (fgetresolu(&xres, &yres, input) != (YMAJOR|YDECR)) {
+	if (fgetresolu(&xres, &yres, input) < 0) {
 		fprintf(stderr, "%s: bad picture size\n", fname);
 		return(-1);
 	}
@@ -115,14 +119,16 @@ COLR  clr;
 register int  x;
 {
 	static int  cerr[NCOLS];
-	static int  err;
+	static int  err, errp;
 	int  b;
 	register int  isblack;
 
 	b = normbright(clr);
+	errp = err;
 	err += b + cerr[x];
 	isblack = err < 128;
 	if (!isblack) err -= 256;
-	cerr[x] = err /= 2;
+	err /= 3;
+	cerr[x] = err + errp;
 	return(isblack);
 }