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import math
import torch
import torch.nn as nn
import torch.utils.checkpoint as cp
from mmcv.cnn import (build_conv_layer, build_norm_layer, constant_init,
kaiming_init)
from mmcv.runner import load_checkpoint
from torch.nn.modules.batchnorm import _BatchNorm
from mmdet.utils import get_root_logger
from ..builder import BACKBONES
from .resnet import Bottleneck as _Bottleneck
from .resnet import ResNet
class Bottle2neck(_Bottleneck):
expansion = 4
def __init__(self,
inplanes,
planes,
scales=4,
base_width=26,
base_channels=64,
stage_type='normal',
**kwargs):
"""Bottle2neck block for Res2Net.
If style is "pytorch", the stride-two layer is the 3x3 conv layer, if
it is "caffe", the stride-two layer is the first 1x1 conv layer.
"""
super(Bottle2neck, self).__init__(inplanes, planes, **kwargs)
assert scales > 1, 'Res2Net degenerates to ResNet when scales = 1.'
width = int(math.floor(self.planes * (base_width / base_channels)))
self.norm1_name, norm1 = build_norm_layer(
self.norm_cfg, width * scales, postfix=1)
self.norm3_name, norm3 = build_norm_layer(
self.norm_cfg, self.planes * self.expansion, postfix=3)
self.conv1 = build_conv_layer(
self.conv_cfg,
self.inplanes,
width * scales,
kernel_size=1,
stride=self.conv1_stride,
bias=False)
self.add_module(self.norm1_name, norm1)
if stage_type == 'stage' and self.conv2_stride != 1:
self.pool = nn.AvgPool2d(
kernel_size=3, stride=self.conv2_stride, padding=1)
convs = []
bns = []
fallback_on_stride = False
if self.with_dcn:
fallback_on_stride = self.dcn.pop('fallback_on_stride', False)
if not self.with_dcn or fallback_on_stride:
for i in range(scales - 1):
convs.append(
build_conv_layer(
self.conv_cfg,
width,
width,
kernel_size=3,
stride=self.conv2_stride,
padding=self.dilation,
dilation=self.dilation,
bias=False))
bns.append(
build_norm_layer(self.norm_cfg, width, postfix=i + 1)[1])
self.convs = nn.ModuleList(convs)
self.bns = nn.ModuleList(bns)
else:
assert self.conv_cfg is None, 'conv_cfg must be None for DCN'
for i in range(scales - 1):
convs.append(
build_conv_layer(
self.dcn,
width,
width,
kernel_size=3,
stride=self.conv2_stride,
padding=self.dilation,
dilation=self.dilation,
bias=False))
bns.append(
build_norm_layer(self.norm_cfg, width, postfix=i + 1)[1])
self.convs = nn.ModuleList(convs)
self.bns = nn.ModuleList(bns)
self.conv3 = build_conv_layer(
self.conv_cfg,
width * scales,
self.planes * self.expansion,
kernel_size=1,
bias=False)
self.add_module(self.norm3_name, norm3)
self.stage_type = stage_type
self.scales = scales
self.width = width
delattr(self, 'conv2')
delattr(self, self.norm2_name)
def forward(self, x):
"""Forward function."""
def _inner_forward(x):
identity = x
out = self.conv1(x)
out = self.norm1(out)
out = self.relu(out)
if self.with_plugins:
out = self.forward_plugin(out, self.after_conv1_plugin_names)
spx = torch.split(out, self.width, 1)
sp = self.convs[0](spx[0].contiguous())
sp = self.relu(self.bns[0](sp))
out = sp
for i in range(1, self.scales - 1):
if self.stage_type == 'stage':
sp = spx[i]
else:
sp = sp + spx[i]
sp = self.convs[i](sp.contiguous())
sp = self.relu(self.bns[i](sp))
out = torch.cat((out, sp), 1)
if self.stage_type == 'normal' or self.conv2_stride == 1:
out = torch.cat((out, spx[self.scales - 1]), 1)
elif self.stage_type == 'stage':
out = torch.cat((out, self.pool(spx[self.scales - 1])), 1)
if self.with_plugins:
out = self.forward_plugin(out, self.after_conv2_plugin_names)
out = self.conv3(out)
out = self.norm3(out)
if self.with_plugins:
out = self.forward_plugin(out, self.after_conv3_plugin_names)
if self.downsample is not None:
identity = self.downsample(x)
out += identity
return out
if self.with_cp and x.requires_grad:
out = cp.checkpoint(_inner_forward, x)
else:
out = _inner_forward(x)
out = self.relu(out)
return out
class Res2Layer(nn.Sequential):
"""Res2Layer to build Res2Net style backbone.
Args:
block (nn.Module): block used to build ResLayer.
inplanes (int): inplanes of block.
planes (int): planes of block.
num_blocks (int): number of blocks.
stride (int): stride of the first block. Default: 1
avg_down (bool): Use AvgPool instead of stride conv when
downsampling in the bottle2neck. Default: False
conv_cfg (dict): dictionary to construct and config conv layer.
Default: None
norm_cfg (dict): dictionary to construct and config norm layer.
Default: dict(type='BN')
scales (int): Scales used in Res2Net. Default: 4
base_width (int): Basic width of each scale. Default: 26
"""
def __init__(self,
block,
inplanes,
planes,
num_blocks,
stride=1,
avg_down=True,
conv_cfg=None,
norm_cfg=dict(type='BN'),
scales=4,
base_width=26,
**kwargs):
self.block = block
downsample = None
if stride != 1 or inplanes != planes * block.expansion:
downsample = nn.Sequential(
nn.AvgPool2d(
kernel_size=stride,
stride=stride,
ceil_mode=True,
count_include_pad=False),
build_conv_layer(
conv_cfg,
inplanes,
planes * block.expansion,
kernel_size=1,
stride=1,
bias=False),
build_norm_layer(norm_cfg, planes * block.expansion)[1],
)
layers = []
layers.append(
block(
inplanes=inplanes,
planes=planes,
stride=stride,
downsample=downsample,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
scales=scales,
base_width=base_width,
stage_type='stage',
**kwargs))
inplanes = planes * block.expansion
for i in range(1, num_blocks):
layers.append(
block(
inplanes=inplanes,
planes=planes,
stride=1,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
scales=scales,
base_width=base_width,
**kwargs))
super(Res2Layer, self).__init__(*layers)
@BACKBONES.register_module()
class Res2Net(ResNet):
"""Res2Net backbone.
Args:
scales (int): Scales used in Res2Net. Default: 4
base_width (int): Basic width of each scale. Default: 26
depth (int): Depth of res2net, from {50, 101, 152}.
in_channels (int): Number of input image channels. Default: 3.
num_stages (int): Res2net stages. Default: 4.
strides (Sequence[int]): Strides of the first block of each stage.
dilations (Sequence[int]): Dilation of each stage.
out_indices (Sequence[int]): Output from which stages.
style (str): `pytorch` or `caffe`. If set to "pytorch", the stride-two
layer is the 3x3 conv layer, otherwise the stride-two layer is
the first 1x1 conv layer.
deep_stem (bool): Replace 7x7 conv in input stem with 3 3x3 conv
avg_down (bool): Use AvgPool instead of stride conv when
downsampling in the bottle2neck.
frozen_stages (int): Stages to be frozen (stop grad and set eval mode).
-1 means not freezing any parameters.
norm_cfg (dict): Dictionary to construct and config norm layer.
norm_eval (bool): Whether to set norm layers to eval mode, namely,
freeze running stats (mean and var). Note: Effect on Batch Norm
and its variants only.
plugins (list[dict]): List of plugins for stages, each dict contains:
- cfg (dict, required): Cfg dict to build plugin.
- position (str, required): Position inside block to insert
plugin, options are 'after_conv1', 'after_conv2', 'after_conv3'.
- stages (tuple[bool], optional): Stages to apply plugin, length
should be same as 'num_stages'.
with_cp (bool): Use checkpoint or not. Using checkpoint will save some
memory while slowing down the training speed.
zero_init_residual (bool): Whether to use zero init for last norm layer
in resblocks to let them behave as identity.
Example:
>>> from mmdet.models import Res2Net
>>> import torch
>>> self = Res2Net(depth=50, scales=4, base_width=26)
>>> self.eval()
>>> inputs = torch.rand(1, 3, 32, 32)
>>> level_outputs = self.forward(inputs)
>>> for level_out in level_outputs:
... print(tuple(level_out.shape))
(1, 256, 8, 8)
(1, 512, 4, 4)
(1, 1024, 2, 2)
(1, 2048, 1, 1)
"""
arch_settings = {
50: (Bottle2neck, (3, 4, 6, 3)),
101: (Bottle2neck, (3, 4, 23, 3)),
152: (Bottle2neck, (3, 8, 36, 3))
}
def __init__(self,
scales=4,
base_width=26,
style='pytorch',
deep_stem=True,
avg_down=True,
**kwargs):
self.scales = scales
self.base_width = base_width
super(Res2Net, self).__init__(
style='pytorch', deep_stem=True, avg_down=True, **kwargs)
def make_res_layer(self, **kwargs):
return Res2Layer(
scales=self.scales,
base_width=self.base_width,
base_channels=self.base_channels,
**kwargs)
def init_weights(self, pretrained=None):
"""Initialize the weights in backbone.
Args:
pretrained (str, optional): Path to pre-trained weights.
Defaults to None.
"""
if isinstance(pretrained, str):
logger = get_root_logger()
load_checkpoint(self, pretrained, strict=False, logger=logger)
elif pretrained is None:
for m in self.modules():
if isinstance(m, nn.Conv2d):
kaiming_init(m)
elif isinstance(m, (_BatchNorm, nn.GroupNorm)):
constant_init(m, 1)
if self.dcn is not None:
for m in self.modules():
if isinstance(m, Bottle2neck):
# dcn in Res2Net bottle2neck is in ModuleList
for n in m.convs:
if hasattr(n, 'conv_offset'):
constant_init(n.conv_offset, 0)
if self.zero_init_residual:
for m in self.modules():
if isinstance(m, Bottle2neck):
constant_init(m.norm3, 0)
else:
raise TypeError('pretrained must be a str or None')
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