Index: trunk/psModules/src/imcombine/pmSubtraction.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtraction.c	(revision 16352)
+++ trunk/psModules/src/imcombine/pmSubtraction.c	(revision 16423)
@@ -4,6 +4,6 @@
  *  @author GLG, MHPCC
  *
- *  @version $Revision: 1.77 $ $Name: not supported by cvs2svn $
- *  @date $Date: 2008-02-07 04:03:23 $
+ *  @version $Revision: 1.78 $ $Name: not supported by cvs2svn $
+ *  @date $Date: 2008-02-14 00:13:09 $
  *
  *  Copyright 2004-2007 Institute for Astronomy, University of Hawaii
@@ -715,4 +715,5 @@
 
     int numCols = ro1->image->numCols, numRows = ro1->image->numRows; // Image dimensions
+    int x0 = ro1->col0, y0 = ro1->row0; // Image offset
 
     psImage *convImage1 = out1->image;   // Convolved image
@@ -771,4 +772,9 @@
         yMax = PS_MIN(region->y1, yMax);
     }
+
+    // Size to use when calculating normalised coordinates (different from actual size when convolving
+    // subimage)
+    int xNormSize = (kernels->numCols > 0 ? kernels->numCols : numCols);
+    int yNormSize = (kernels->numRows > 0 ? kernels->numRows : numRows);
 
     psMaskType maskSource;              // Mask these pixels when convolving
@@ -798,8 +804,10 @@
     for (int j = yMin; j < yMax; j += fullSize) {
         int ySubMax = PS_MIN(j + fullSize, yMax); // Range for subregion of interest
-        float yNorm = 2.0 * (float)(j + size + 1 - numRows/2.0) / (float)numRows; // Normalised coordinate
+        float yNorm = 2.0 * (float)(j + y0 + size + 1 - yNormSize/2.0) /
+            (float)yNormSize; // Normalised coordinate
         for (int i = xMin; i < xMax; i += fullSize) {
             int xSubMax = PS_MIN(i + fullSize, xMax); // Range for subregion of interest
-            float xNorm = 2.0 * (float)(i + size + 1 - numCols/2.0) / (float)numCols; // Normalised coordinate
+            float xNorm = 2.0 * (float)(i + x0 + size + 1 - xNormSize/2.0) /
+                (float)xNormSize; // Normalised coordinate
 
             // Only generate polynomial values every kernel footprint, since we have already assumed