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# Copyright (c) OpenMMLab. All rights reserved.
import torch.nn as nn
import torch.utils.checkpoint as cp
from mmcv.cnn import ConvModule
from mmengine.model import BaseModule
from torch.nn.modules.batchnorm import _BatchNorm
from mmcls.models.utils import make_divisible
from mmcls.registry import MODELS
from .base_backbone import BaseBackbone
class InvertedResidual(BaseModule):
"""InvertedResidual block for MobileNetV2.
Args:
in_channels (int): The input channels of the InvertedResidual block.
out_channels (int): The output channels of the InvertedResidual block.
stride (int): Stride of the middle (first) 3x3 convolution.
expand_ratio (int): adjusts number of channels of the hidden layer
in InvertedResidual by this amount.
conv_cfg (dict, optional): Config dict for convolution layer.
Default: None, which means using conv2d.
norm_cfg (dict): Config dict for normalization layer.
Default: dict(type='BN').
act_cfg (dict): Config dict for activation layer.
Default: dict(type='ReLU6').
with_cp (bool): Use checkpoint or not. Using checkpoint will save some
memory while slowing down the training speed. Default: False.
Returns:
Tensor: The output tensor
"""
def __init__(self,
in_channels,
out_channels,
stride,
expand_ratio,
conv_cfg=None,
norm_cfg=dict(type='BN'),
act_cfg=dict(type='ReLU6'),
with_cp=False,
init_cfg=None):
super(InvertedResidual, self).__init__(init_cfg)
self.stride = stride
assert stride in [1, 2], f'stride must in [1, 2]. ' \
f'But received {stride}.'
self.with_cp = with_cp
self.use_res_connect = self.stride == 1 and in_channels == out_channels
hidden_dim = int(round(in_channels * expand_ratio))
layers = []
if expand_ratio != 1:
layers.append(
ConvModule(
in_channels=in_channels,
out_channels=hidden_dim,
kernel_size=1,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=act_cfg))
layers.extend([
ConvModule(
in_channels=hidden_dim,
out_channels=hidden_dim,
kernel_size=3,
stride=stride,
padding=1,
groups=hidden_dim,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=act_cfg),
ConvModule(
in_channels=hidden_dim,
out_channels=out_channels,
kernel_size=1,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=None)
])
self.conv = nn.Sequential(*layers)
def forward(self, x):
def _inner_forward(x):
if self.use_res_connect:
return x + self.conv(x)
else:
return self.conv(x)
if self.with_cp and x.requires_grad:
out = cp.checkpoint(_inner_forward, x)
else:
out = _inner_forward(x)
return out
@MODELS.register_module()
class MobileNetV2(BaseBackbone):
"""MobileNetV2 backbone.
Args:
widen_factor (float): Width multiplier, multiply number of
channels in each layer by this amount. Default: 1.0.
out_indices (None or Sequence[int]): Output from which stages.
Default: (7, ).
frozen_stages (int): Stages to be frozen (all param fixed).
Default: -1, which means not freezing any parameters.
conv_cfg (dict, optional): Config dict for convolution layer.
Default: None, which means using conv2d.
norm_cfg (dict): Config dict for normalization layer.
Default: dict(type='BN').
act_cfg (dict): Config dict for activation layer.
Default: dict(type='ReLU6').
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. Default: False.
with_cp (bool): Use checkpoint or not. Using checkpoint will save some
memory while slowing down the training speed. Default: False.
"""
# Parameters to build layers. 4 parameters are needed to construct a
# layer, from left to right: expand_ratio, channel, num_blocks, stride.
arch_settings = [[1, 16, 1, 1], [6, 24, 2, 2], [6, 32, 3, 2],
[6, 64, 4, 2], [6, 96, 3, 1], [6, 160, 3, 2],
[6, 320, 1, 1]]
def __init__(self,
widen_factor=1.,
out_indices=(7, ),
frozen_stages=-1,
conv_cfg=None,
norm_cfg=dict(type='BN'),
act_cfg=dict(type='ReLU6'),
norm_eval=False,
with_cp=False,
init_cfg=[
dict(type='Kaiming', layer=['Conv2d']),
dict(
type='Constant',
val=1,
layer=['_BatchNorm', 'GroupNorm'])
]):
super(MobileNetV2, self).__init__(init_cfg)
self.widen_factor = widen_factor
self.out_indices = out_indices
for index in out_indices:
if index not in range(0, 8):
raise ValueError('the item in out_indices must in '
f'range(0, 8). But received {index}')
if frozen_stages not in range(-1, 8):
raise ValueError('frozen_stages must be in range(-1, 8). '
f'But received {frozen_stages}')
self.out_indices = out_indices
self.frozen_stages = frozen_stages
self.conv_cfg = conv_cfg
self.norm_cfg = norm_cfg
self.act_cfg = act_cfg
self.norm_eval = norm_eval
self.with_cp = with_cp
self.in_channels = make_divisible(32 * widen_factor, 8)
self.conv1 = ConvModule(
in_channels=3,
out_channels=self.in_channels,
kernel_size=3,
stride=2,
padding=1,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg)
self.layers = []
for i, layer_cfg in enumerate(self.arch_settings):
expand_ratio, channel, num_blocks, stride = layer_cfg
out_channels = make_divisible(channel * widen_factor, 8)
inverted_res_layer = self.make_layer(
out_channels=out_channels,
num_blocks=num_blocks,
stride=stride,
expand_ratio=expand_ratio)
layer_name = f'layer{i + 1}'
self.add_module(layer_name, inverted_res_layer)
self.layers.append(layer_name)
if widen_factor > 1.0:
self.out_channel = int(1280 * widen_factor)
else:
self.out_channel = 1280
layer = ConvModule(
in_channels=self.in_channels,
out_channels=self.out_channel,
kernel_size=1,
stride=1,
padding=0,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg)
self.add_module('conv2', layer)
self.layers.append('conv2')
def make_layer(self, out_channels, num_blocks, stride, expand_ratio):
"""Stack InvertedResidual blocks to build a layer for MobileNetV2.
Args:
out_channels (int): out_channels of block.
num_blocks (int): number of blocks.
stride (int): stride of the first block. Default: 1
expand_ratio (int): Expand the number of channels of the
hidden layer in InvertedResidual by this ratio. Default: 6.
"""
layers = []
for i in range(num_blocks):
if i >= 1:
stride = 1
layers.append(
InvertedResidual(
self.in_channels,
out_channels,
stride,
expand_ratio=expand_ratio,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg,
with_cp=self.with_cp))
self.in_channels = out_channels
return nn.Sequential(*layers)
def forward(self, x):
x = self.conv1(x)
outs = []
for i, layer_name in enumerate(self.layers):
layer = getattr(self, layer_name)
x = layer(x)
if i in self.out_indices:
outs.append(x)
return tuple(outs)
def _freeze_stages(self):
if self.frozen_stages >= 0:
for param in self.conv1.parameters():
param.requires_grad = False
for i in range(1, self.frozen_stages + 1):
layer = getattr(self, f'layer{i}')
layer.eval()
for param in layer.parameters():
param.requires_grad = False
def train(self, mode=True):
super(MobileNetV2, self).train(mode)
self._freeze_stages()
if mode and self.norm_eval:
for m in self.modules():
if isinstance(m, _BatchNorm):
m.eval()
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