Index: /trunk/pswarp/src/pswarpTransformReadout_Opt.c
===================================================================
--- /trunk/pswarp/src/pswarpTransformReadout_Opt.c	(revision 15333)
+++ /trunk/pswarp/src/pswarpTransformReadout_Opt.c	(revision 15334)
@@ -179,5 +179,5 @@
             pswarpMap *map = sourceGrid->maps[xGrid][yGrid]; // Locally linear transformation
             double xOut, yOut;          // Output coordinates
-            if (!pswarpMapApply(&xOut, &yOut, map, xIn, yIn)) {
+            if (!pswarpMapApply(&xOut, &yOut, map, xIn + 0.5, yIn + 0.5)) {
                 psError(PS_ERR_UNKNOWN, false, "Unable to transform coordinates for source at %f,%f\n",
                         xIn, yIn);
@@ -186,6 +186,6 @@
                 return false;
             }
-            xOut += outCol0;
-            yOut += outRow0;
+            xOut += outCol0 - 0.5;
+            yOut += outRow0 - 0.5;
             if (xOut < minX || xOut > maxX || yOut < minY || yOut > maxY) {
                 // It's not in the output image