Index: trunk/ppArith/src/ppArithArguments.c
===================================================================
--- trunk/ppArith/src/ppArithArguments.c	(revision 15574)
+++ trunk/ppArith/src/ppArithArguments.c	(revision 15597)
@@ -72,4 +72,5 @@
 
     bool isMask = psMetadataLookupBool(NULL, arguments, "-mask"); // Are we dealing with masks?
+    psMetadataAddBool(config->arguments, PS_LIST_TAIL, "MASK", 0, "Produce a mask image?", true);
     const char *inFilerule = isMask ? "PPARITH.INPUT.MASK" : "PPARITH.INPUT.IMAGE"; // Input file rule
     const char *outFilerule = isMask ? "PPARITH.OUTPUT.MASK" : "PPARITH.OUTPUT.IMAGE"; // Output file rule