Add AutoBackbone + ResNetBackbone

src/transformers/__init__.py

@@ -920,6 +920,7 @@
             "MODEL_WITH_LM_HEAD_MAPPING",
             "MODEL_FOR_ZERO_SHOT_OBJECT_DETECTION_MAPPING",
             "AutoModel",
+            "AutoBackbone",
             "AutoModelForAudioClassification",
             "AutoModelForAudioFrameClassification",
             "AutoModelForAudioXVector",
@@ -1877,6 +1878,7 @@
             "ResNetForImageClassification",
             "ResNetModel",
             "ResNetPreTrainedModel",
+            "ResNetBackbone",
         ]
     )
     _import_structure["models.retribert"].extend(
@@ -3946,6 +3948,7 @@
             MODEL_FOR_ZERO_SHOT_OBJECT_DETECTION_MAPPING,
             MODEL_MAPPING,
             MODEL_WITH_LM_HEAD_MAPPING,
+            AutoBackbone,
             AutoModel,
             AutoModelForAudioClassification,
             AutoModelForAudioFrameClassification,
@@ -4730,6 +4733,7 @@
         )
         from .models.resnet import (
             RESNET_PRETRAINED_MODEL_ARCHIVE_LIST,
+            ResNetBackbone,
             ResNetForImageClassification,
             ResNetModel,
             ResNetPreTrainedModel,

src/transformers/modeling_outputs.py

@@ -1263,3 +1263,16 @@ class XVectorOutput(ModelOutput):
     embeddings: torch.FloatTensor = None
     hidden_states: Optional[Tuple[torch.FloatTensor]] = None
     attentions: Optional[Tuple[torch.FloatTensor]] = None
+
+
+@dataclass
+class BackboneOutput(ModelOutput):
+    """
+    Base class for outputs of backbones.
+
+    Args:
+        feature_maps (`tuple(torch.FloatTensor)` of shape `(batch_size, num_channels, height, width)`):
+            Feature maps of the stages.
+    """
+
+    feature_maps: Tuple[torch.FloatTensor] = None

src/transformers/models/auto/__init__.py

@@ -73,6 +73,7 @@
         "MODEL_WITH_LM_HEAD_MAPPING",
         "MODEL_FOR_ZERO_SHOT_OBJECT_DETECTION_MAPPING",
         "AutoModel",
+        "AutoBackbone",
         "AutoModelForAudioClassification",
         "AutoModelForAudioFrameClassification",
         "AutoModelForAudioXVector",
@@ -225,6 +226,7 @@
             MODEL_FOR_ZERO_SHOT_OBJECT_DETECTION_MAPPING,
             MODEL_MAPPING,
             MODEL_WITH_LM_HEAD_MAPPING,
+            AutoBackbone,
             AutoModel,
             AutoModelForAudioClassification,
             AutoModelForAudioFrameClassification,

src/transformers/models/auto/modeling_auto.py

@@ -836,6 +836,13 @@
     ]
 )
 
+MODEL_FOR_BACKBONE_MAPPING_NAMES = OrderedDict(
+    [
+        # Backbone mapping
+        ("resnet", "ResNetBackbone"),
+    ]
+)
+
 MODEL_MAPPING = _LazyAutoMapping(CONFIG_MAPPING_NAMES, MODEL_MAPPING_NAMES)
 MODEL_FOR_PRETRAINING_MAPPING = _LazyAutoMapping(CONFIG_MAPPING_NAMES, MODEL_FOR_PRETRAINING_MAPPING_NAMES)
 MODEL_WITH_LM_HEAD_MAPPING = _LazyAutoMapping(CONFIG_MAPPING_NAMES, MODEL_WITH_LM_HEAD_MAPPING_NAMES)
@@ -903,6 +910,8 @@
 )
 MODEL_FOR_AUDIO_XVECTOR_MAPPING = _LazyAutoMapping(CONFIG_MAPPING_NAMES, MODEL_FOR_AUDIO_XVECTOR_MAPPING_NAMES)
 
+MODEL_FOR_BACKBONE_MAPPING = _LazyAutoMapping(CONFIG_MAPPING_NAMES, MODEL_FOR_BACKBONE_MAPPING_NAMES)
+
 
 class AutoModel(_BaseAutoModelClass):
     _model_mapping = MODEL_MAPPING
@@ -1126,6 +1135,10 @@ class AutoModelForAudioXVector(_BaseAutoModelClass):
     _model_mapping = MODEL_FOR_AUDIO_XVECTOR_MAPPING
 
 
+class AutoBackbone(_BaseAutoModelClass):
+    _model_mapping = MODEL_FOR_BACKBONE_MAPPING
+
+
 AutoModelForAudioXVector = auto_class_update(AutoModelForAudioXVector, head_doc="audio retrieval via x-vector")
 
 

src/transformers/models/resnet/__init__.py

@@ -36,6 +36,7 @@
         "ResNetForImageClassification",
         "ResNetModel",
         "ResNetPreTrainedModel",
+        "ResNetBackbone",
     ]
 
 try:
@@ -63,6 +64,7 @@
     else:
         from .modeling_resnet import (
             RESNET_PRETRAINED_MODEL_ARCHIVE_LIST,
+            ResNetBackbone,
             ResNetForImageClassification,
             ResNetModel,
             ResNetPreTrainedModel,

src/transformers/models/resnet/configuration_resnet.py

@@ -58,6 +58,9 @@ class ResNetConfig(PretrainedConfig):
             are supported.
         downsample_in_first_stage (`bool`, *optional*, defaults to `False`):
             If `True`, the first stage will downsample the inputs using a `stride` of 2.
+        out_features (`List[str]`, *optional*):
+            If used as backbone, list of features to output. Can be any of `"stem"`, `"stage1"`, `"stage2"`,
+            `"stage3"`, `"stage4"`.
 
     Example:
     ```python
@@ -85,6 +88,7 @@ def __init__(
         layer_type="bottleneck",
         hidden_act="relu",
         downsample_in_first_stage=False,
+        out_features=None,
         **kwargs
     ):
         super().__init__(**kwargs)
@@ -97,6 +101,16 @@ def __init__(
         self.layer_type = layer_type
         self.hidden_act = hidden_act
         self.downsample_in_first_stage = downsample_in_first_stage
+        self.stage_names = ["stem"] + [f"stage{idx}" for idx in range(1, len(depths) + 1)]
+        if out_features is not None:
+            if not isinstance(out_features, list):
+                raise ValueError("out_features should be a list")
+            for feature in out_features:
+                if feature not in self.stage_names:
+                    raise ValueError(
+                        f"Feature {feature} is not a valid feature name. Valid names are {self.stage_names}"
+                    )
+        self.out_features = out_features
 
 
 class ResNetOnnxConfig(OnnxConfig):

src/transformers/models/resnet/modeling_resnet.py

@@ -23,12 +23,19 @@
 
 from ...activations import ACT2FN
 from ...modeling_outputs import (
+    BackboneOutput,
     BaseModelOutputWithNoAttention,
     BaseModelOutputWithPoolingAndNoAttention,
     ImageClassifierOutputWithNoAttention,
 )
 from ...modeling_utils import PreTrainedModel
-from ...utils import add_code_sample_docstrings, add_start_docstrings, add_start_docstrings_to_model_forward, logging
+from ...utils import (
+    add_code_sample_docstrings,
+    add_start_docstrings,
+    add_start_docstrings_to_model_forward,
+    logging,
+    replace_return_docstrings,
+)
 from .configuration_resnet import ResNetConfig
 
 
@@ -416,3 +423,69 @@ def forward(
             return (loss,) + output if loss is not None else output
 
         return ImageClassifierOutputWithNoAttention(loss=loss, logits=logits, hidden_states=outputs.hidden_states)
+
+
+@add_start_docstrings(
+    """
+    ResNet backbone, to be used with frameworks like DETR and MaskFormer.
+    """,
+    RESNET_START_DOCSTRING,
+)
+class ResNetBackbone(ResNetPreTrainedModel):
+    def __init__(self, config):
+        super().__init__(config)
+
+        self.stage_names = config.stage_names
+        self.resnet = ResNetModel(config)
+
+        self.out_features = config.out_features
+
+        self.out_feature_channels = {
+            "stem": config.embedding_size,
+            "stage1": config.hidden_sizes[0],
+            "stage2": config.hidden_sizes[1],
+            "stage3": config.hidden_sizes[2],
+            "stage4": config.hidden_sizes[3],
+        }
+
+        # initialize weights and apply final processing
+        self.post_init()
+
+    @property
+    def channels(self):
+        return [self.out_feature_channels[name] for name in self.out_features]
+
+    @add_start_docstrings_to_model_forward(RESNET_INPUTS_DOCSTRING)
+    @replace_return_docstrings(output_type=BackboneOutput, config_class=_CONFIG_FOR_DOC)
+    def forward(self, pixel_values: Optional[torch.FloatTensor] = None) -> BackboneOutput:
+        """
+        Returns:
+
+        Examples:
+
+        ```python
+        >>> from transformers import AutoImageProcessor, AutoBackbone
+        >>> import torch
+        >>> from PIL import Image
+        >>> import requests
+
+        >>> url = "http://images.cocodataset.org/val2017/000000039769.jpg"
+        >>> image = Image.open(requests.get(url, stream=True).raw)
+
+        >>> processor = AutoImageProcessor.from_pretrained("microsoft/resnet-50")
+        >>> model = AutoBackbone.from_pretrained("microsoft/resnet-50")
+
+        >>> inputs = processor(image, return_tensors="pt")
+
+        >>> outputs = model(**inputs)
+        ```"""
+        outputs = self.resnet(pixel_values, output_hidden_states=True, return_dict=True)
+
+        hidden_states = outputs.hidden_states
+
+        feature_maps = ()
+        for idx, stage in enumerate(self.stage_names):
+            if stage in self.out_features:
+                feature_maps += (hidden_states[idx],)
+
+        return BackboneOutput(feature_maps=feature_maps)

src/transformers/utils/dummy_pt_objects.py

@@ -437,6 +437,13 @@ def load_tf_weights_in_albert(*args, **kwargs):
 MODEL_WITH_LM_HEAD_MAPPING = None
 
 
+class AutoBackbone(metaclass=DummyObject):
+    _backends = ["torch"]
+
+    def __init__(self, *args, **kwargs):
+        requires_backends(self, ["torch"])
+
+
 class AutoModel(metaclass=DummyObject):
     _backends = ["torch"]
 
@@ -4523,6 +4530,13 @@ def load_tf_weights_in_rembert(*args, **kwargs):
 RESNET_PRETRAINED_MODEL_ARCHIVE_LIST = None
 
 
+class ResNetBackbone(metaclass=DummyObject):
+    _backends = ["torch"]
+
+    def __init__(self, *args, **kwargs):
+        requires_backends(self, ["torch"])
+
+
 class ResNetForImageClassification(metaclass=DummyObject):
     _backends = ["torch"]
 

tests/models/resnet/test_modeling_resnet.py

@@ -30,7 +30,7 @@
     import torch
     from torch import nn
 
-    from transformers import ResNetForImageClassification, ResNetModel
+    from transformers import ResNetBackbone, ResNetForImageClassification, ResNetModel
     from transformers.models.resnet.modeling_resnet import RESNET_PRETRAINED_MODEL_ARCHIVE_LIST
 
 
@@ -55,6 +55,7 @@ def __init__(
         hidden_act="relu",
         num_labels=3,
         scope=None,
+        out_features=["stage1", "stage2", "stage3", "stage4"],
     ):
         self.parent = parent
         self.batch_size = batch_size
@@ -69,6 +70,7 @@ def __init__(
         self.num_labels = num_labels
         self.scope = scope
         self.num_stages = len(hidden_sizes)
+        self.out_features = out_features
 
     def prepare_config_and_inputs(self):
         pixel_values = floats_tensor([self.batch_size, self.num_channels, self.image_size, self.image_size])
@@ -89,6 +91,7 @@ def get_config(self):
             depths=self.depths,
             hidden_act=self.hidden_act,
             num_labels=self.num_labels,
+            out_features=self.out_features,
         )
 
     def create_and_check_model(self, config, pixel_values, labels):
@@ -110,6 +113,19 @@ def create_and_check_for_image_classification(self, config, pixel_values, labels
         result = model(pixel_values, labels=labels)
         self.parent.assertEqual(result.logits.shape, (self.batch_size, self.num_labels))
 
+    def create_and_check_backbone(self, config, pixel_values, labels):
+        model = ResNetBackbone(config=config)
+        model.to(torch_device)
+        model.eval()
+        result = model(pixel_values)
+
+        # verify hidden states
+        self.parent.assertEqual(len(result.feature_maps), len(config.out_features))
+        self.parent.assertListEqual(list(result.feature_maps[0].shape), [3, 10, 8, 8])
+
+        # verify channels
+        self.parent.assertListEqual(model.channels, config.hidden_sizes)
+
     def prepare_config_and_inputs_for_common(self):
         config_and_inputs = self.prepare_config_and_inputs()
         config, pixel_values, labels = config_and_inputs
@@ -176,6 +192,10 @@ def test_model(self):
         config_and_inputs = self.model_tester.prepare_config_and_inputs()
         self.model_tester.create_and_check_model(*config_and_inputs)
 
+    def test_backbone(self):
+        config_and_inputs = self.model_tester.prepare_config_and_inputs()
+        self.model_tester.create_and_check_backbone(*config_and_inputs)
+
     def test_initialization(self):
         config, inputs_dict = self.model_tester.prepare_config_and_inputs_for_common()
 

utils/check_repo.py

@@ -47,6 +47,7 @@
 # Being in this list is an exception and should **not** be the rule.
 IGNORE_NON_TESTED = PRIVATE_MODELS.copy() + [
     # models to ignore for not tested
+    "ResNetBackbone",  # Backbones have their own tests.
     "CLIPSegDecoder",  # Building part of bigger (tested) model.
     "TableTransformerEncoder",  # Building part of bigger (tested) model.
     "TableTransformerDecoder",  # Building part of bigger (tested) model.
@@ -668,6 +669,8 @@ def find_all_documented_objects():
     "PyTorchBenchmarkArguments",
     "TensorFlowBenchmark",
     "TensorFlowBenchmarkArguments",
+    "ResNetBackbone",
+    "AutoBackbone",
 ]