diff --git a/canny_edge_machine.cpp b/canny_edge_machine.cpp
index ccfbd59..464cf21 100644
--- a/canny_edge_machine.cpp
+++ b/canny_edge_machine.cpp
@@ -72,8 +72,13 @@ class CannyEdgeMachine {
       // build the gauss filter
       int* filter = (int*) malloc(sizeof(int) * filter_width* filter_width);
       int sum_weights = 0;
-      for(int i=0; i<filter_width; i++) {
-	for(int j=0; j<filter_width; j++) {
+      int filter_middle = (filter_width)/2;
+      for(int x=0; x<filter_width; x++) {
+	int i = x;
+	if(x > filter_middle) i = filter_middle - (x - filter_middle);
+	for(int y=0; y<filter_width; y++) {
+	  int j = y;
+  	  if(y > filter_middle) j = filter_middle - (y - filter_middle);
 	  filter[i*filter_width + j] = pow(2, i) * pow(2, j);
 	  sum_weights += filter[i*filter_width + j];
 	}