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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# Copyright (c) Facebook, Inc. and its affiliates.
import torch.nn as nn
from detectron2.modeling import ShapeSpec
# from ..layers import ShapeSpec
__all__ = ["Backbone"]
class Backbone(nn.Module):
"""
Abstract base class for network backbones.
"""
def __init__(self):
"""
The `__init__` method of any subclass can specify its own set of arguments.
"""
super().__init__()
def forward(self):
"""
Subclasses must override this method, but adhere to the same return type.
Returns:
dict[str->Tensor]: mapping from feature name (e.g., "res2") to tensor
"""
pass
@property
def size_divisibility(self) -> int:
"""
Some backbones require the input height and width to be divisible by a
specific integer. This is typically true for encoder / decoder type networks
with lateral connection (e.g., FPN) for which feature maps need to match
dimension in the "bottom up" and "top down" paths. Set to 0 if no specific
input size divisibility is required.
"""
return 0
def output_shape(self):
"""
Returns:
dict[str->ShapeSpec]
"""
# this is a backward-compatible default
return {
name: ShapeSpec(
channels=self._out_feature_channels[name], stride=self._out_feature_strides[name]
)
for name in self._out_features
}
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