Index: trunk/ppStack/src/ppStackThread.c
===================================================================
--- trunk/ppStack/src/ppStackThread.c	(revision 31158)
+++ trunk/ppStack/src/ppStackThread.c	(revision 34800)
@@ -40,4 +40,5 @@
     psFree(stack->maskFits);
     psFree(stack->varianceFits);
+    psFree(stack->bkgFits);
     return;
 }
@@ -67,5 +68,5 @@
         PS_ASSERT_ARRAYS_SIZE_EQUAL(cells, covariances, NULL);
     }
-
+    
     ppStackThreadData *stack = psAlloc(sizeof(ppStackThreadData)); // Thread data, to return
     psMemSetDeallocator(stack, (psFreeFunc)stackThreadDataFree);
@@ -77,4 +78,5 @@
     stack->maskFits   = psArrayAlloc(numInputs);
     stack->varianceFits = psArrayAlloc(numInputs);
+    stack->bkgFits    = psArrayAlloc(numInputs);
     for (int i = 0; i < numInputs; i++) {
         if (!cells->data[i]) {
@@ -95,8 +97,12 @@
             psFree(resolved); \
         }
-
+		
         IMAGE_OPEN(imageNames, stack->imageFits, i);
-        IMAGE_OPEN(maskNames, stack->maskFits, i);
-        IMAGE_OPEN(varianceNames, stack->varianceFits, i);
+	if (maskNames) {
+	  IMAGE_OPEN(maskNames, stack->maskFits, i);
+	}
+	if (varianceNames) {
+	  IMAGE_OPEN(varianceNames, stack->varianceFits, i);
+	}
     }