Index: trunk/psLib/src/imageops/psImageMaskOps.c
===================================================================
--- trunk/psLib/src/imageops/psImageMaskOps.c	(revision 25753)
+++ trunk/psLib/src/imageops/psImageMaskOps.c	(revision 31446)
@@ -146,6 +146,6 @@
     for (int iy = 0; iy < image->numRows; iy++) { \
         for (int ix = 0; ix < image->numCols; ix++) { \
-            dx = ix + image->col0 - x; \
-            dy = iy + image->row0 - y; \
+            dx = ix + 0.5 + image->col0 - x; \
+            dy = iy + 0.5 + image->row0 - y; \
             r2 = PS_SQR(dx) + PS_SQR(dy); \
             if (r2 <= R2) { \
@@ -197,6 +197,6 @@
     for (int iy = 0; iy < image->numRows; iy++) { \
         for (int ix = 0; ix < image->numCols; ix++) { \
-            dx = ix + image->col0 - x; \
-            dy = iy + image->row0 - y; \
+            dx = ix + 0.5 + image->col0 - x; \
+            dy = iy + 0.5 + image->row0 - y; \
             r2 = PS_SQR(dx) + PS_SQR(dy); \
             if (r2 > R2) { \