Index: trunk/psphot/src/image_stats.c
===================================================================
--- trunk/psphot/src/image_stats.c	(revision 4215)
+++ trunk/psphot/src/image_stats.c	(revision 4216)
@@ -42,4 +42,5 @@
     float GAIN  = psMetadataLookupF32 (&status, config, "GAIN");
 
+    // convert instrumental background to poisson stats
     sky = psStatsAlloc (PS_STAT_SAMPLE_MEAN | PS_STAT_SAMPLE_STDEV);
     sky->sampleMean   = stats->sampleMedian;