Add pretrained weights for raft_small from original paper (#5070)

Author: NicolasHug

torchvision/models/optical_flow/raft.py

@@ -20,7 +20,11 @@
 )
 
 
-_MODELS_URLS = {"raft_large": "https://download.pytorch.org/models/raft_large_C_T_V2-1bb1363a.pth"}
+_MODELS_URLS = {
+    "raft_large": "https://download.pytorch.org/models/raft_large_C_T_V2-1bb1363a.pth",
+    # TODO: change to V2 once we upload our own weights
+    "raft_small": "https://download.pytorch.org/models/raft_small_C_T_V1-ad48884c.pth",
+}
 
 
 class ResidualBlock(nn.Module):
@@ -641,8 +645,6 @@ def raft_small(*, pretrained=False, progress=True, **kwargs):
         nn.Module: The model.
 
     """
-    if pretrained:
-        raise ValueError("No checkpoint is available for raft_small")
 
     return _raft(
         arch="raft_small",

torchvision/prototype/models/optical_flow/raft.py

@@ -78,16 +78,19 @@ class Raft_Large_Weights(WeightsEnum):
 
 
 class Raft_Small_Weights(WeightsEnum):
-    pass
-    # C_T_V1 = Weights(
-    #     url="",  # TODO
-    #     transforms=RaftEval,
-    #     meta={
-    #         "recipe": "",
-    #         "epe": -1234,
-    #     },
-    # )
-    # default = C_T_V1
+    C_T_V1 = Weights(
+        # Chairs + Things, ported from original paper repo (raft-small.pth)
+        url="https://download.pytorch.org/models/raft_small_C_T_V1-ad48884c.pth",
+        transforms=RaftEval,
+        meta={
+            **_COMMON_META,
+            "recipe": "https://github.com/princeton-vl/RAFT",
+            "sintel_train_cleanpass_epe": 2.1231,
+            "sintel_train_finalpass_epe": 3.2790,
+        },
+    )
+
+    default = C_T_V1  # TODO: Change to V2 once we upload our own weights
 
 
 @handle_legacy_interface(weights=("pretrained", Raft_Large_Weights.C_T_V2))
@@ -140,7 +143,8 @@ def raft_large(*, weights: Optional[Raft_Large_Weights] = None, progress=True, *
     return model
 
 
-@handle_legacy_interface(weights=("pretrained", None))
+# TODO: change to V2 once we upload our own weights
+@handle_legacy_interface(weights=("pretrained", Raft_Small_Weights.C_T_V1))
 def raft_small(*, weights: Optional[Raft_Small_Weights] = None, progress=True, **kwargs):
     """RAFT "small" model from
     `RAFT: Recurrent All Pairs Field Transforms for Optical Flow <https://arxiv.org/abs/2003.12039>`_.