--- CV/CV.xs	2006/02/17 08:48:06	1.33
+++ CV/CV.xs	2006/03/07 16:26:25	1.34
@@ -357,20 +357,21 @@
         double diff = 0.;
         int peak = 0;
 
-        for (y = 0; y < h; y++)
-          {
-            guchar *pa_ = pa + y * sa;
-            guchar *pb_ = pb + y * sb;
+        if (x && y)
+          for (y = 0; y < h; y++)
+            {
+              guchar *pa_ = pa + y * sa;
+              guchar *pb_ = pb + y * sb;
 
-            for (x = 0; x < w; x ++)
-              {
-                int d;
+              for (x = 0; x < w; x++)
+                {
+                  int d;
 
-                d = ((int)*pa_++) - ((int)*pb_++); diff += d*d; peak = MAX (peak, abs (d));
-                d = ((int)*pa_++) - ((int)*pb_++); diff += d*d; peak = MAX (peak, abs (d));
-                d = ((int)*pa_++) - ((int)*pb_++); diff += d*d; peak = MAX (peak, abs (d));
-              }
-          }
+                  d = ((int)*pa_++) - ((int)*pb_++); diff += d*d; peak = MAX (peak, abs (d));
+                  d = ((int)*pa_++) - ((int)*pb_++); diff += d*d; peak = MAX (peak, abs (d));
+                  d = ((int)*pa_++) - ((int)*pb_++); diff += d*d; peak = MAX (peak, abs (d));
+                }
+            }
 
         EXTEND (SP, 2);
         PUSHs (sv_2mortal (newSVnv (sqrt (diff / (w * h * 3. * 255. * 255.)))));