perf(observation_processor): add CUDA support for image processing

src/lerobot/processor/observation_processor.py

@@ -52,6 +52,8 @@ class VanillaObservationProcessorStep(ObservationProcessorStep):
     -   Adds a batch dimension if one is not already present.
     """
 
+    device: str | None = None
+
     def _process_single_image(self, img: np.ndarray) -> Tensor:
         """
         Processes a single NumPy image array into a channel-first, normalized tensor.
@@ -71,6 +73,9 @@ class VanillaObservationProcessorStep(ObservationProcessorStep):
         # Convert to tensor
         img_tensor = torch.from_numpy(img)
 
+        if self.device is not None:
+            img_tensor = img_tensor.to(device=self.device)
+
         # Add batch dimension if needed
         if img_tensor.ndim == 3:
             img_tensor = img_tensor.unsqueeze(0)

tests/processor/test_observation_processor.py

@@ -52,6 +52,34 @@ def test_process_single_image():
     assert processed_img.max() <= 1.0
 
 
+@pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA not available")
+def test_process_single_image_cuda():
+    """Test processing a single image with CUDA device."""
+    processor = VanillaObservationProcessorStep(device="cuda")
+
+    # Create a mock image (H, W, C) format, uint8
+    image = np.random.randint(0, 256, size=(64, 64, 3), dtype=np.uint8)
+
+    observation = {"pixels": image}
+    transition = create_transition(observation=observation)
+
+    result = processor(transition)
+    processed_obs = result[TransitionKey.OBSERVATION]
+
+    # Check that the image was processed correctly
+    assert OBS_IMAGE in processed_obs
+    processed_img = processed_obs[OBS_IMAGE]
+
+    # Check shape: should be (1, 3, 64, 64) - batch, channels, height, width
+    assert processed_img.shape == (1, 3, 64, 64)
+
+    # Check dtype and range
+    assert processed_img.dtype == torch.float32
+    assert processed_img.device.type == "cuda"
+    assert processed_img.min() >= 0.0
+    assert processed_img.max() <= 1.0
+
+
 def test_process_image_dict():
     """Test processing multiple images in a dictionary."""
     processor = VanillaObservationProcessorStep()