Index: /trunk/psphot/src/psphotGrowthCurve.c
===================================================================
--- /trunk/psphot/src/psphotGrowthCurve.c	(revision 9836)
+++ /trunk/psphot/src/psphotGrowthCurve.c	(revision 9837)
@@ -17,7 +17,7 @@
     pmModel *modelRef = pmModelAlloc(psf->type);
 
-    // use center of the image
-    xc = 0.5*readout->image->numCols + readout->image->col0;
-    yc = 0.5*readout->image->numRows + readout->image->row0;
+    // use the center of the center pixel of the image
+    xc = 0.5*readout->image->numCols + readout->image->col0 + 0.5;
+    yc = 0.5*readout->image->numRows + readout->image->row0 + 0.5;
     dx = psf->growth->maxRadius + 1;
     dy = psf->growth->maxRadius + 1;