Index: trunk/psModules/src/imcombine/pmSubtractionKernels.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtractionKernels.c	(revision 14366)
+++ trunk/psModules/src/imcombine/pmSubtractionKernels.c	(revision 14420)
@@ -147,10 +147,13 @@
                 // Set the pre-calculated kernel
                 psKernel *preCalc = psKernelAlloc(-size, size, -size, size);
+                double sum = 0.0;       // Normalisation
                 for (int v = -size; v <= size; v++) {
                     for (int u = -size; u <= size; u++) {
-                        preCalc->kernel[v][u] = power(u, uOrder) * power(v, vOrder) *
+                        sum += preCalc->kernel[v][u] = power(u, uOrder) * power(v, vOrder) *
                             expf(-0.5 * (PS_SQR(u) + PS_SQR(v)) / PS_SQR(sigmas->data.F32[i]));
                     }
                 }
+                // Normalise sum of kernel component to unity
+                psBinaryOp(preCalc->image, preCalc->image, "*", psScalarAlloc(1.0/sum, PS_TYPE_F32));
 
                 // Iterate over spatial order.  This loop creates the terms for
@@ -450,10 +453,13 @@
                 // Set the pre-calculated kernel
                 psKernel *preCalc = psKernelAlloc(-size, size, -size, size);
+                double sum = 0.0;       // Normalisation
                 for (int v = -size; v <= size; v++) {
                     for (int u = -size; u <= size; u++) {
-                        preCalc->kernel[v][u] = power(u, uOrder) * power(v, vOrder) *
+                        sum += preCalc->kernel[v][u] = power(u, uOrder) * power(v, vOrder) *
                             expf(-0.5 * (PS_SQR(u) + PS_SQR(v)) / PS_SQR(sigmas->data.F32[i]));
                     }
                 }
+                // Normalise sum of kernel component to unity
+                psBinaryOp(preCalc->image, preCalc->image, "*", psScalarAlloc(1.0/sum, PS_TYPE_F32));
 
                 // Iterate over spatial order.  This loop creates the terms for