diff --git a/mmp/a1/tensors.py b/mmp/a1/tensors.py
index 0c7c329..4669751 100644
--- a/mmp/a1/tensors.py
+++ b/mmp/a1/tensors.py
@@ -1,6 +1,4 @@
 import torch
-from PIL import Image
-from torchvision.transforms import ToTensor
 
 
 def avg_color(img: torch.Tensor):
@@ -9,9 +7,9 @@ def avg_color(img: torch.Tensor):
 
 
 def mask(foreground: torch.Tensor, background: torch.Tensor, mask_tensor: torch.Tensor, threshold: float):
-    raise NotImplementedError()
+    mask = mask_tensor > threshold
+    return torch.where(mask, foreground, background)
 
 
 def add_matrix_vector(matrix: torch.Tensor, vector: torch.Tensor):
     return matrix.add(vector)
-