Reset sigma value while switching between images; Remove unused print

A2/GUI.py

@@ -134,8 +134,8 @@ class GUI(object):
         self._update_label_image(self.original_image_label, image, 1, 0)
 
         self.filter_name.set(FILTER.empty.value)
+        self.sigma_value.set(1.0)
         self._update_label_image(self.filtered_image_label, image, 1, 2)
-        print('Go!')
 
     def change_filter(self, *args) -> None:
         """