Merge branch 'dev_1.15.1' into development_issue_2165

Author: beat-buesser

art/attacks/poisoning/perturbations/image_perturbations.py

@@ -21,7 +21,6 @@
 from typing import Optional, Tuple
 
 import numpy as np
-from PIL import Image
 
 
 def add_single_bd(x: np.ndarray, distance: int = 2, pixel_value: int = 1) -> np.ndarray:
@@ -112,6 +111,8 @@ def insert_image(
     :param blend: The blending factor
     :return: Backdoored image.
     """
+    from PIL import Image
+
     n_dim = len(x.shape)
     if n_dim == 4:
         return np.array(

art/estimators/object_detection/pytorch_object_detector.py

@@ -219,7 +219,10 @@ def _preprocess_and_convert_inputs(
 
             # Set gradients
             if not no_grad:
-                x_tensor.requires_grad = True
+                if x_tensor.is_leaf:
+                    x_tensor.requires_grad = True
+                else:
+                    x_tensor.retain_grad()
 
             # Apply framework-specific preprocessing
             x_preprocessed, y_preprocessed = self._apply_preprocessing(x=x_tensor, y=y_tensor, fit=fit, no_grad=no_grad)

art/visualization.py

@@ -25,7 +25,6 @@
 from typing import List, Optional, TYPE_CHECKING
 
 import numpy as np
-from PIL import Image
 
 from art import config
 
@@ -97,6 +96,8 @@ def save_image(image_array: np.ndarray, f_name: str) -> None:
     :param image_array: Image to be saved.
     :param f_name: File name containing extension e.g., my_img.jpg, my_img.png, my_images/my_img.png.
     """
+    from PIL import Image
+
     file_name = os.path.join(config.ART_DATA_PATH, f_name)
     folder = os.path.split(file_name)[0]
     if not os.path.exists(folder):