document pixel mean

lib/fast_rcnn/config.py

@@ -114,7 +114,8 @@ __C.TEST.BBOX_REG = True
 __C.DEDUP_BOXES = 1./16.
 
 # Pixel mean values (BGR order) as a (1, 1, 3) array
-# These are the values originally used for training VGG16
+# We use the same pixel mean for all networks even though it's not exactly what
+# they were trained with
 __C.PIXEL_MEANS = np.array([[[102.9801, 115.9465, 122.7717]]])
 
 # For reproducibility