--- ray/src/px/panim.c	1990/04/05 13:58:45	1.6
+++ ray/src/px/panim.c	1991/11/12 16:05:34	2.1
@@ -103,6 +103,11 @@ char	*file;
 	}
 						/* get dimensions */
 	getheader(fp, NULL);
+	if (checkheader(fp, COLRFMT, NULL) < 0) {
+		fputs(file, stderr);
+		fputs(": not a Radiance picture\n", stderr);
+		exit(1);
+	}
 	if (fgetresolu(&xres, &yres, fp) != (YMAJOR|YDECR) ||
 			xres > SCANLINE || yres > NUMSCANS) {
 		fputs(file, stderr);
@@ -144,7 +149,7 @@ compgamma()				/* compute gamma correction map */
 	register int  i, val;
 
 	for (i = 0; i < 256; i++) {
-		val = pow(i/256.0, 1.0/GAMMA) * 256.0;
+		val = pow((i+0.5)/256.0, 1.0/GAMMA) * 256.0;
 		if (val > 248) val = 248;
 		gammamap[i] = val;
 	}