Cast masks to np.unit8 before converting to PIL.Image.Image (#19616)

* Cast masks to np.unit8 before converting to PIL.Image.Image

* Update tests

* Fixup

src/transformers/pipelines/image_segmentation.py

@@ -172,7 +172,7 @@ class ImageSegmentationPipeline(Pipeline):
 
             for label in labels:
                 mask = (segmentation == label) * 255
-                mask = Image.fromarray(mask, mode="L")
+                mask = Image.fromarray(mask.astype(np.uint8), mode="L")
                 label = self.model.config.id2label[label]
                 annotation.append({"score": None, "label": label, "mask": mask})
         else:

tests/pipelines/test_pipelines_image_segmentation.py

@@ -226,15 +226,11 @@ class ImageSegmentationPipelineTests(unittest.TestCase, metaclass=PipelineTestCa
         self.assertEqual(
             nested_simplify(outputs, decimals=4),
             [
-                {
-                    "score": None,
-                    "label": "LABEL_0",
-                    "mask": "775518a7ed09eea888752176c6ba8f38",
-                },
+                {"score": None, "label": "LABEL_0", "mask": "42d09072282a32da2ac77375a4c1280f"},
                 {
                     "score": None,
                     "label": "LABEL_1",
-                    "mask": "a12da23a46848128af68c63aa8ba7a02",
+                    "mask": "46b8cc3976732873b219f77a1213c1a5",
                 },
             ],
         )