Search for model metadata with TensorFlow GraphDef (#13389)

Co-authored-by: UltralyticsAssistant <web@ultralytics.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/nn/autobackend.py

@@ -320,6 +320,10 @@ class AutoBackend(nn.Module):
             with open(w, "rb") as f:
                 gd.ParseFromString(f.read())
             frozen_func = wrap_frozen_graph(gd, inputs="x:0", outputs=gd_outputs(gd))
+            try:  # attempt to retrieve metadata from SavedModel file potentially alongside GraphDef file
+                metadata = next(Path(w).resolve().parent.rglob(f"{Path(w).stem}_saved_model*/metadata.yaml"))
+            except StopIteration:
+                pass  # no metadata file found
 
         # TFLite or TFLite Edge TPU
         elif tflite or edgetpu:  # https://www.tensorflow.org/lite/guide/python#install_tensorflow_lite_for_python
@@ -402,7 +406,7 @@ class AutoBackend(nn.Module):
         # Load external metadata YAML
         if isinstance(metadata, (str, Path)) and Path(metadata).exists():
             metadata = yaml_load(metadata)
-        if metadata:
+        if metadata and isinstance(metadata, dict):
             for k, v in metadata.items():
                 if k in {"stride", "batch"}:
                     metadata[k] = int(v)
@@ -563,7 +567,7 @@ class AutoBackend(nn.Module):
                     y = [y]
             elif self.pb:  # GraphDef
                 y = self.frozen_func(x=self.tf.constant(im))
-                if len(y) == 2 and len(self.names) == 999:  # segments and names not defined
+                if (self.task == "segment" or len(y) == 2) and len(self.names) == 999:  # segments and names not defined
                     ip, ib = (0, 1) if len(y[0].shape) == 4 else (1, 0)  # index of protos, boxes
                     nc = y[ib].shape[1] - y[ip].shape[3] - 4  # y = (1, 160, 160, 32), (1, 116, 8400)
                     self.names = {i: f"class{i}" for i in range(nc)}