diff --git a/script/Devices/ImageStats.py b/script/Devices/ImageStats.py
index 0747d48..54bbd8e 100644
--- a/script/Devices/ImageStats.py
+++ b/script/Devices/ImageStats.py
@@ -171,7 +171,9 @@ class ImageStats(DeviceBase):
             def __init__(self, obj):
                 self.obj=obj                
             def process(self, image, data):
-                return sub(image, self.obj.background, True) if (self.obj.background is not None) else None                
+                if self.obj.background is None:
+                    return image                
+                return sub(image, self.obj.background, True)        
         self.source.filter = BackgroundSubtractor(self) if (value==True) else None
         
     def captureBackground(self, images):