Add semantic segmentation post-processing method to MobileViT (#19105)

* add post-processing method for semantic segmentation
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

docs/source/en/model_doc/mobilevit.mdx

@@ -66,6 +66,7 @@ This model was contributed by [matthijs](https://huggingface.co/Matthijs). The T
 
 [[autodoc]] MobileViTFeatureExtractor
     - __call__
+    - post_process_semantic_segmentation
 
 ## MobileViTModel
 

src/transformers/models/mobilevit/feature_extraction_mobilevit.py

@@ -14,16 +14,19 @@
 # limitations under the License.
 """Feature extractor class for MobileViT."""
 
-from typing import Optional, Union
+from typing import List, Optional, Tuple, Union
 
 import numpy as np
 from PIL import Image
 
 from ...feature_extraction_utils import BatchFeature, FeatureExtractionMixin
 from ...image_utils import ImageFeatureExtractionMixin, ImageInput, is_torch_tensor
-from ...utils import TensorType, logging
+from ...utils import TensorType, is_torch_available, logging
 
 
+if is_torch_available():
+    import torch
+
 logger = logging.get_logger(__name__)
 
 
@@ -151,3 +154,46 @@ class MobileViTFeatureExtractor(FeatureExtractionMixin, ImageFeatureExtractionMi
         encoded_inputs = BatchFeature(data=data, tensor_type=return_tensors)
 
         return encoded_inputs
+
+    def post_process_semantic_segmentation(self, outputs, target_sizes: List[Tuple] = None):
+        """
+        Converts the output of [`MobileViTForSemanticSegmentation`] into semantic segmentation maps. Only supports
+        PyTorch.
+
+        Args:
+            outputs ([`MobileViTForSemanticSegmentation`]):
+                Raw outputs of the model.
+            target_sizes (`List[Tuple]`, *optional*):
+                A list of length `batch_size`, where each item is a `Tuple[int, int]` corresponding to the requested
+                final size (height, width) of each prediction. If left to None, predictions will not be resized.
+        Returns:
+            `List[torch.Tensor]`:
+                A list of length `batch_size`, where each item is a semantic segmentation map of shape (height, width)
+                corresponding to the target_sizes entry (if `target_sizes` is specified). Each entry of each
+                `torch.Tensor` correspond to a semantic class id.
+        """
+        logits = outputs.logits
+
+        # Resize logits and compute semantic segmentation maps
+        if target_sizes is not None:
+            if len(logits) != len(target_sizes):
+                raise ValueError(
+                    "Make sure that you pass in as many target sizes as the batch dimension of the logits"
+                )
+
+            if is_torch_tensor(target_sizes):
+                target_sizes = target_sizes.numpy()
+
+            semantic_segmentation = []
+
+            for idx in range(len(logits)):
+                resized_logits = torch.nn.functional.interpolate(
+                    logits[idx].unsqueeze(dim=0), size=target_sizes[idx], mode="bilinear", align_corners=False
+                )
+                semantic_map = resized_logits[0].argmax(dim=0)
+                semantic_segmentation.append(semantic_map)
+        else:
+            semantic_segmentation = logits.argmax(dim=1)
+            semantic_segmentation = [semantic_segmentation[i] for i in range(semantic_segmentation.shape[0])]
+
+        return semantic_segmentation

tests/models/mobilevit/test_modeling_mobilevit.py

@@ -340,3 +340,27 @@ class MobileViTModelIntegrationTest(unittest.TestCase):
         )
 
         self.assertTrue(torch.allclose(logits[0, :3, :3, :3], expected_slice, atol=1e-4))
+
+    @slow
+    def test_post_processing_semantic_segmentation(self):
+        model = MobileViTForSemanticSegmentation.from_pretrained("apple/deeplabv3-mobilevit-xx-small")
+        model = model.to(torch_device)
+
+        feature_extractor = MobileViTFeatureExtractor.from_pretrained("apple/deeplabv3-mobilevit-xx-small")
+
+        image = prepare_img()
+        inputs = feature_extractor(images=image, return_tensors="pt").to(torch_device)
+
+        # forward pass
+        with torch.no_grad():
+            outputs = model(**inputs)
+
+        outputs.logits = outputs.logits.detach().cpu()
+
+        segmentation = feature_extractor.post_process_semantic_segmentation(outputs=outputs, target_sizes=[(50, 60)])
+        expected_shape = torch.Size((50, 60))
+        self.assertEqual(segmentation[0].shape, expected_shape)
+
+        segmentation = feature_extractor.post_process_semantic_segmentation(outputs=outputs)
+        expected_shape = torch.Size((32, 32))
+        self.assertEqual(segmentation[0].shape, expected_shape)