Index: trunk/ppSub/src/ppSubArguments.c
===================================================================
--- trunk/ppSub/src/ppSubArguments.c	(revision 24672)
+++ trunk/ppSub/src/ppSubArguments.c	(revision 24833)
@@ -84,4 +84,5 @@
     psMetadataAddS32(arguments, PS_LIST_TAIL, "-threads", 0, "Number of threads", 0);
     psMetadataAddStr(arguments, PS_LIST_TAIL, "-dumpconfig", 0, "file to dump configuration to", NULL);
+    psMetadataAddS32(arguments, PS_LIST_TAIL, "-convolve", 0, "Image to convolve [1 or 2]", 0);
     psMetadataAddBool(arguments, PS_LIST_TAIL, "-photometry", 0, "Perform photometry?", NULL);
     psMetadataAddBool(arguments, PS_LIST_TAIL, "-inverse", 0, "Generate inverse subtractions?", NULL);
Index: trunk/ppSub/src/ppSubMatchPSFs.c
===================================================================
--- trunk/ppSub/src/ppSubMatchPSFs.c	(revision 24672)
+++ trunk/ppSub/src/ppSubMatchPSFs.c	(revision 24833)
@@ -153,5 +153,24 @@
 
     bool dual = psMetadataLookupBool(&mdok, recipe, "DUAL"); // Dual convolution?
-    pmSubtractionMode subMode = dual ? PM_SUBTRACTION_MODE_DUAL : PM_SUBTRACTION_MODE_UNSURE; // Subtracn mode
+    pmSubtractionMode subMode;          // Subtraction mode
+    if (dual) {
+        subMode = PM_SUBTRACTION_MODE_DUAL;
+    } else {
+        int convolve = psMetadataLookupS32(NULL, config->arguments, "-convolve"); // Image number to convolve
+        switch (convolve) {
+          case 0:
+            subMode = PM_SUBTRACTION_MODE_UNSURE;
+            break;
+          case 1:
+            subMode = PM_SUBTRACTION_MODE_1;
+            break;
+          case 2:
+            subMode = PM_SUBTRACTION_MODE_2;
+            break;
+          default:
+            psErrorStackPrint(stderr, "Invalid value for -convolve");
+            return false;
+        }
+    }
 
     int threads = psMetadataLookupS32(NULL, config->arguments, "-threads"); // Number of threads