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# Copyright (c) Meta Platforms, Inc. and affiliates.
# All rights reserved.
#
# This source code is licensed under the license found in the
# LICENSE file in the root directory of this source tree.
from typing import Optional, Tuple
import torch.nn.functional as F
from torch import Tensor
from mmdet.registry import MODELS
from .fpn import FPN
@MODELS.register_module()
class FPN_DropBlock(FPN):
def __init__(self,
*args,
plugin: Optional[dict] = dict(
type='DropBlock',
drop_prob=0.3,
block_size=3,
warmup_iters=0),
**kwargs) -> None:
super().__init__(*args, **kwargs)
self.plugin = None
if plugin is not None:
self.plugin = MODELS.build(plugin)
def forward(self, inputs: Tuple[Tensor]) -> tuple:
"""Forward function.
Args:
inputs (tuple[Tensor]): Features from the upstream network, each
is a 4D-tensor.
Returns:
tuple: Feature maps, each is a 4D-tensor.
"""
assert len(inputs) == len(self.in_channels)
# build laterals
laterals = [
lateral_conv(inputs[i + self.start_level])
for i, lateral_conv in enumerate(self.lateral_convs)
]
# build top-down path
used_backbone_levels = len(laterals)
for i in range(used_backbone_levels - 1, 0, -1):
# In some cases, fixing `scale factor` (e.g. 2) is preferred, but
# it cannot co-exist with `size` in `F.interpolate`.
if 'scale_factor' in self.upsample_cfg:
# fix runtime error of "+=" inplace operation in PyTorch 1.10
laterals[i - 1] = laterals[i - 1] + F.interpolate(
laterals[i], **self.upsample_cfg)
else:
prev_shape = laterals[i - 1].shape[2:]
laterals[i - 1] = laterals[i - 1] + F.interpolate(
laterals[i], size=prev_shape, **self.upsample_cfg)
if self.plugin is not None:
laterals[i - 1] = self.plugin(laterals[i - 1])
# build outputs
# part 1: from original levels
outs = [
self.fpn_convs[i](laterals[i]) for i in range(used_backbone_levels)
]
# part 2: add extra levels
if self.num_outs > len(outs):
# use max pool to get more levels on top of outputs
# (e.g., Faster R-CNN, Mask R-CNN)
if not self.add_extra_convs:
for i in range(self.num_outs - used_backbone_levels):
outs.append(F.max_pool2d(outs[-1], 1, stride=2))
# add conv layers on top of original feature maps (RetinaNet)
else:
if self.add_extra_convs == 'on_input':
extra_source = inputs[self.backbone_end_level - 1]
elif self.add_extra_convs == 'on_lateral':
extra_source = laterals[-1]
elif self.add_extra_convs == 'on_output':
extra_source = outs[-1]
else:
raise NotImplementedError
outs.append(self.fpn_convs[used_backbone_levels](extra_source))
for i in range(used_backbone_levels + 1, self.num_outs):
if self.relu_before_extra_convs:
outs.append(self.fpn_convs[i](F.relu(outs[-1])))
else:
outs.append(self.fpn_convs[i](outs[-1]))
return tuple(outs)
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