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# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
import math
import fvcore.nn.weight_init as weight_init
import torch.nn.functional as F
from torch import nn
from detectron2.layers import Conv2d, ShapeSpec, get_norm
from detectron2.modeling.backbone import Backbone
from detectron2.modeling.backbone.fpn import FPN
from detectron2.modeling.backbone.build import BACKBONE_REGISTRY
from detectron2.modeling.backbone.resnet import build_resnet_backbone
class LastLevelP6P7_P5(nn.Module):
"""
This module is used in RetinaNet to generate extra layers, P6 and P7 from
C5 feature.
"""
def __init__(self, in_channels, out_channels):
super().__init__()
self.num_levels = 2
self.in_feature = "p5"
self.p6 = nn.Conv2d(in_channels, out_channels, 3, 2, 1)
self.p7 = nn.Conv2d(out_channels, out_channels, 3, 2, 1)
for module in [self.p6, self.p7]:
weight_init.c2_xavier_fill(module)
def forward(self, c5):
p6 = self.p6(c5)
p7 = self.p7(F.relu(p6))
return [p6, p7]
@BACKBONE_REGISTRY.register()
def build_p67_resnet_fpn_backbone(cfg, input_shape: ShapeSpec):
"""
Args:
cfg: a detectron2 CfgNode
Returns:
backbone (Backbone): backbone module, must be a subclass of :class:`Backbone`.
"""
bottom_up = build_resnet_backbone(cfg, input_shape)
in_features = cfg.MODEL.FPN.IN_FEATURES
out_channels = cfg.MODEL.FPN.OUT_CHANNELS
backbone = FPN(
bottom_up=bottom_up,
in_features=in_features,
out_channels=out_channels,
norm=cfg.MODEL.FPN.NORM,
top_block=LastLevelP6P7_P5(out_channels, out_channels),
fuse_type=cfg.MODEL.FPN.FUSE_TYPE,
)
return backbone
@BACKBONE_REGISTRY.register()
def build_p35_resnet_fpn_backbone(cfg, input_shape: ShapeSpec):
"""
Args:
cfg: a detectron2 CfgNode
Returns:
backbone (Backbone): backbone module, must be a subclass of :class:`Backbone`.
"""
bottom_up = build_resnet_backbone(cfg, input_shape)
in_features = cfg.MODEL.FPN.IN_FEATURES
out_channels = cfg.MODEL.FPN.OUT_CHANNELS
backbone = FPN(
bottom_up=bottom_up,
in_features=in_features,
out_channels=out_channels,
norm=cfg.MODEL.FPN.NORM,
top_block=None,
fuse_type=cfg.MODEL.FPN.FUSE_TYPE,
)
return backbone |