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Source code for mmdet.models.backbones.mobilenet_v2

# Copyright (c) OpenMMLab. All rights reserved.
import warnings

import torch.nn as nn
from mmcv.cnn import ConvModule
from mmcv.runner import BaseModule
from torch.nn.modules.batchnorm import _BatchNorm

from ..builder import BACKBONES
from ..utils import InvertedResidual, make_divisible


[docs]@BACKBONES.register_module() class MobileNetV2(BaseModule): """MobileNetV2 backbone. Args: widen_factor (float): Width multiplier, multiply number of channels in each layer by this amount. Default: 1.0. out_indices (Sequence[int], optional): Output from which stages. Default: (1, 2, 4, 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. pretrained (str, optional): model pretrained path. Default: None init_cfg (dict or list[dict], optional): Initialization config dict. Default: None """ # 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=(1, 2, 4, 7), frozen_stages=-1, conv_cfg=None, norm_cfg=dict(type='BN'), act_cfg=dict(type='ReLU6'), norm_eval=False, with_cp=False, pretrained=None, init_cfg=None): super(MobileNetV2, self).__init__(init_cfg) self.pretrained = pretrained assert not (init_cfg and pretrained), \ 'init_cfg and pretrained cannot be specified at the same time' if isinstance(pretrained, str): warnings.warn('DeprecationWarning: pretrained is deprecated, ' 'please use "init_cfg" instead') self.init_cfg = dict(type='Pretrained', checkpoint=pretrained) elif pretrained is None: if init_cfg is None: self.init_cfg = [ dict(type='Kaiming', layer='Conv2d'), dict( type='Constant', val=1, layer=['_BatchNorm', 'GroupNorm']) ] else: raise TypeError('pretrained must be a str or None') self.widen_factor = widen_factor self.out_indices = out_indices if not set(out_indices).issubset(set(range(0, 8))): raise ValueError('out_indices must be a subset of range' f'(0, 8). But received {out_indices}') 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')
[docs] 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, mid_channels=int(round(self.in_channels * expand_ratio)), stride=stride, with_expand_conv=expand_ratio != 1, 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 _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
[docs] def forward(self, x): """Forward function.""" 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)
[docs] def train(self, mode=True): """Convert the model into training mode while keep normalization layer frozen.""" super(MobileNetV2, self).train(mode) self._freeze_stages() if mode and self.norm_eval: for m in self.modules(): # trick: eval have effect on BatchNorm only if isinstance(m, _BatchNorm): m.eval()
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