Index: trunk/ppSub/src/ppSubDefineOutput.c
===================================================================
--- trunk/ppSub/src/ppSubDefineOutput.c	(revision 21524)
+++ trunk/ppSub/src/ppSubDefineOutput.c	(revision 23403)
@@ -26,11 +26,15 @@
     psAssert(view, "Require view");
 
-    // generate an output readout
     pmCell *outCell = pmFPAfileThisCell(config->files, view, "PPSUB.OUTPUT"); // Output cell
-    pmReadout *outRO = pmReadoutAlloc(outCell); // Output readout: subtraction
     pmFPA *outFPA = outCell->parent->parent; // Output FPA
     pmHDU *outHDU = outFPA->hdu; // Output HDU
     if (!outHDU->header) {
         outHDU->header = psMetadataAlloc();
+    }
+
+    // generate an output readout (first check if it's already there by virtue of kernels)
+    pmReadout *outRO = pmFPAfileThisReadout(config->files, view, "PPSUB.OUTPUT.KERNELS"); // RO with kernel
+    if (!outRO) {
+        outRO = pmReadoutAlloc(outCell); // Output readout: subtraction
     }