Index: trunk/psphot/src/psphotFindDetections.c
===================================================================
--- trunk/psphot/src/psphotFindDetections.c	(revision 34418)
+++ trunk/psphot/src/psphotFindDetections.c	(revision 34492)
@@ -71,4 +71,10 @@
     }
 
+    // first pass vs other: if this is the first pass, the code will use PEAKS_NSIGMA_LIMIT and
+    // only attempt to detect PEAKS_NMAX entries.  If 'firstPass' is false, the code will
+    // attempt to replace the subtracted sources in order to measure the footprints.  After
+    // replacement, it is necessary to regenerate the significance image.  If no sources are
+    // available, the code will skip the significance image regeneration step.
+
     bool replaceSourcesForFootprints = false;
     if (firstPass) {
@@ -126,13 +132,16 @@
     if (useFootprints) {
         if (replaceSourcesForFootprints) {
+	    bool modified = false;
 	    // subtract the noise for all sources including satstars
-            psphotAddOrSubNoiseReadout(config, view, filerule, index, recipe, false);
-            psphotReplaceAllSourcesReadout (config, view, filerule, index, recipe, false);
+	    modified |= psphotAddOrSubNoiseReadout(config, view, filerule, index, recipe, false);
+            modified | psphotReplaceAllSourcesReadout (config, view, filerule, index, recipe, false);
 
 	    // add in the satstars
-	    psphotAddOrSubSatstarsReadout (config, view, filerule, index, recipe, true);
+	    modified |= psphotAddOrSubSatstarsReadout (config, view, filerule, index, recipe, true);
 
-            psFree (significance);
-            significance = psphotSignificanceImage (readout, recipe, maskVal);
+	    if (modified) {
+		psFree (significance);
+		significance = psphotSignificanceImage (readout, recipe, maskVal);
+	    }
 
 	    // display the significance image