Index: trunk/psModules/src/imcombine/pmSubtractionStamps.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtractionStamps.c	(revision 14519)
+++ trunk/psModules/src/imcombine/pmSubtractionStamps.c	(revision 14533)
@@ -303,5 +303,5 @@
 
 
-bool pmSubtractionGenerateStamps(psArray *stamps, float sigma, int footprint,
+bool pmSubtractionGenerateStamps(psArray *stamps, float fwhm, int footprint,
                                  const pmSubtractionKernels *kernels)
 {
@@ -312,4 +312,5 @@
     int size = kernels->size + footprint; // Size of postage stamps
     int num = stamps->n;                // Number of stamps
+    float sigma = fwhm / (2.0 * sqrtf(2.0 * ln(2.0))); // Gaussian sigma
 
     for (int i = 0; i < num; i++) {
@@ -337,5 +338,5 @@
             for (int u = -size; u <= size; u++) {
                 input->kernel[v][u] = flux / sigma * 0.5 * M_2_SQRTPI * M_SQRT1_2 *
-                    expf(0.5 * (PS_SQR(u + xStamp) + PS_SQR(v + yStamp)) / PS_SQR(sigma));
+                    expf(-0.5 * (PS_SQR(u + xStamp) + PS_SQR(v + yStamp)) / PS_SQR(sigma));
             }
         }