Fix MaskFormer failing postprocess tests (#19354)

Ensures post_process_instance_segmentation and post_process_panoptic_segmentation methods return a tensor of shape (target_height, target_width) filled with -1 values if no segment with score > threshold is found.

src/transformers/models/maskformer/feature_extraction_maskformer.py

@@ -772,8 +772,9 @@ class MaskFormerFeatureExtractor(FeatureExtractionMixin, ImageFeatureExtractionM
 
             # No mask found
             if mask_probs_item.shape[0] <= 0:
-                segmentation = None
-                segments: List[Dict] = []
+                height, width = target_sizes[i] if target_sizes is not None else mask_probs_item.shape[1:]
+                segmentation = torch.zeros((height, width)) - 1
+                results.append({"segmentation": segmentation, "segments_info": []})
                 continue
 
             # Get segmentation map and segment information of batch item
@@ -860,8 +861,9 @@ class MaskFormerFeatureExtractor(FeatureExtractionMixin, ImageFeatureExtractionM
 
             # No mask found
             if mask_probs_item.shape[0] <= 0:
-                segmentation = None
-                segments: List[Dict] = []
+                height, width = target_sizes[i] if target_sizes is not None else mask_probs_item.shape[1:]
+                segmentation = torch.zeros((height, width)) - 1
+                results.append({"segmentation": segmentation, "segments_info": []})
                 continue
 
             # Get segmentation map and segment information of batch item

tests/models/maskformer/test_feature_extraction_maskformer.py

@@ -401,10 +401,11 @@ class MaskFormerFeatureExtractionTest(FeatureExtractionSavingTestMixin, unittest
 
     @unittest.skip("Fix me Alara!")
     def test_post_process_panoptic_segmentation(self):
-        fature_extractor = self.feature_extraction_class(num_labels=self.feature_extract_tester.num_classes)
+        feature_extractor = self.feature_extraction_class(num_labels=self.feature_extract_tester.num_classes)
         outputs = self.feature_extract_tester.get_fake_maskformer_outputs()
-        segmentation = fature_extractor.post_process_panoptic_segmentation(outputs, threshold=0)
-
+        segmentation = feature_extractor.post_process_panoptic_segmentation(outputs, threshold=0)
+        print(len(segmentation))
+        print(self.feature_extract_tester.batch_size)
         self.assertTrue(len(segmentation) == self.feature_extract_tester.batch_size)
         for el in segmentation:
             self.assertTrue("segmentation" in el)