Index: /trunk/pswarp/src/pswarpTransformReadout_Opt.c
===================================================================
--- /trunk/pswarp/src/pswarpTransformReadout_Opt.c	(revision 18187)
+++ /trunk/pswarp/src/pswarpTransformReadout_Opt.c	(revision 18188)
@@ -148,5 +148,6 @@
     // Store the variance factor and number of good pixels
     if (goodPixels > 0) {
-        float varFactor = psImageInterpolateVarianceFactor(output->image->numCols, output->image->numRows,
+        float varFactor = psImageInterpolateVarianceFactor(inImage->numCols / 2.0 + inCol0,
+                                                           inImage->numRows / 2.0 + inRow0,
                                                            interp); // Variance factor: large --> small scale
         psMetadataItem *vfItem = psMetadataLookup(output->analysis, PSWARP_ANALYSIS_VARFACTOR);