--- tiff-4.0.6/tools/rgb2ycbcr.c	2015-08-29 00:17:08.195093258 +0200
+++ tiff-4.0.6/tools/rgb2ycbcr.c	2016-09-01 16:23:31.472089246 +0200
@@ -95,9 +95,13 @@
 			break;
 		case 'h':
 			horizSubSampling = atoi(optarg);
+            if( horizSubSampling != 1 && horizSubSampling != 2 && horizSubSampling != 4 )
+                usage(-1);
 			break;
 		case 'v':
 			vertSubSampling = atoi(optarg);
+            if( vertSubSampling != 1 && vertSubSampling != 2 && vertSubSampling != 4 )
+                usage(-1);
 			break;
 		case 'r':
 			rowsperstrip = atoi(optarg);