diff --git a/hexrd/ui/hexrd_config.py b/hexrd/ui/hexrd_config.py
index 381797aee..c296e41aa 100644
--- a/hexrd/ui/hexrd_config.py
+++ b/hexrd/ui/hexrd_config.py
@@ -889,7 +889,7 @@ def masked_images_dict(self):
         for det, mask in self.raw_masks_dict.items():
             for name, img in images_dict.items():
                 if det == name:
-                    img[~mask] = 0
+                    img[~mask] = np.nan
 
         return images_dict
 
diff --git a/hexrd/ui/image_file_manager.py b/hexrd/ui/image_file_manager.py
index b0326948c..0505283c2 100644
--- a/hexrd/ui/image_file_manager.py
+++ b/hexrd/ui/image_file_manager.py
@@ -36,7 +36,7 @@ def load_dummy_images(self, initial=False):
             cols = iconfig['detectors'][det]['pixels']['columns']
             rows = iconfig['detectors'][det]['pixels']['rows']
             shape = (rows, cols)
-            data = np.ones(shape, dtype=np.uint8)
+            data = np.ones(shape, dtype=np.float16)
             ims = imageseries.open(None, 'array', data=data)
 
             # Set a flag on these image series indicating that they are