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import torch
import torch.nn as nn
from mmcv.cnn import (ConvModule, DepthwiseSeparableConvModule, constant_init,
kaiming_init)
from torch.nn.modules.batchnorm import _BatchNorm
from mmseg.models.decode_heads.psp_head import PPM
from mmseg.ops import resize
from ..builder import BACKBONES
from ..utils.inverted_residual import InvertedResidual
class LearningToDownsample(nn.Module):
"""Learning to downsample module.
Args:
in_channels (int): Number of input channels.
dw_channels (tuple[int]): Number of output channels of the first and
the second depthwise conv (dwconv) layers.
out_channels (int): Number of output channels of the whole
'learning to downsample' module.
conv_cfg (dict | None): Config of conv layers. Default: None
norm_cfg (dict | None): Config of norm layers. Default:
dict(type='BN')
act_cfg (dict): Config of activation layers. Default:
dict(type='ReLU')
"""
def __init__(self,
in_channels,
dw_channels,
out_channels,
conv_cfg=None,
norm_cfg=dict(type='BN'),
act_cfg=dict(type='ReLU')):
super(LearningToDownsample, self).__init__()
self.conv_cfg = conv_cfg
self.norm_cfg = norm_cfg
self.act_cfg = act_cfg
dw_channels1 = dw_channels[0]
dw_channels2 = dw_channels[1]
self.conv = ConvModule(
in_channels,
dw_channels1,
3,
stride=2,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg)
self.dsconv1 = DepthwiseSeparableConvModule(
dw_channels1,
dw_channels2,
kernel_size=3,
stride=2,
padding=1,
norm_cfg=self.norm_cfg)
self.dsconv2 = DepthwiseSeparableConvModule(
dw_channels2,
out_channels,
kernel_size=3,
stride=2,
padding=1,
norm_cfg=self.norm_cfg)
def forward(self, x):
x = self.conv(x)
x = self.dsconv1(x)
x = self.dsconv2(x)
return x
class GlobalFeatureExtractor(nn.Module):
"""Global feature extractor module.
Args:
in_channels (int): Number of input channels of the GFE module.
Default: 64
block_channels (tuple[int]): Tuple of ints. Each int specifies the
number of output channels of each Inverted Residual module.
Default: (64, 96, 128)
out_channels(int): Number of output channels of the GFE module.
Default: 128
expand_ratio (int): Adjusts number of channels of the hidden layer
in InvertedResidual by this amount.
Default: 6
num_blocks (tuple[int]): Tuple of ints. Each int specifies the
number of times each Inverted Residual module is repeated.
The repeated Inverted Residual modules are called a 'group'.
Default: (3, 3, 3)
strides (tuple[int]): Tuple of ints. Each int specifies
the downsampling factor of each 'group'.
Default: (2, 2, 1)
pool_scales (tuple[int]): Tuple of ints. Each int specifies
the parameter required in 'global average pooling' within PPM.
Default: (1, 2, 3, 6)
conv_cfg (dict | None): Config of conv layers. Default: None
norm_cfg (dict | None): Config of norm layers. Default:
dict(type='BN')
act_cfg (dict): Config of activation layers. Default:
dict(type='ReLU')
align_corners (bool): align_corners argument of F.interpolate.
Default: False
"""
def __init__(self,
in_channels=64,
block_channels=(64, 96, 128),
out_channels=128,
expand_ratio=6,
num_blocks=(3, 3, 3),
strides=(2, 2, 1),
pool_scales=(1, 2, 3, 6),
conv_cfg=None,
norm_cfg=dict(type='BN'),
act_cfg=dict(type='ReLU'),
align_corners=False):
super(GlobalFeatureExtractor, self).__init__()
self.conv_cfg = conv_cfg
self.norm_cfg = norm_cfg
self.act_cfg = act_cfg
assert len(block_channels) == len(num_blocks) == 3
self.bottleneck1 = self._make_layer(in_channels, block_channels[0],
num_blocks[0], strides[0],
expand_ratio)
self.bottleneck2 = self._make_layer(block_channels[0],
block_channels[1], num_blocks[1],
strides[1], expand_ratio)
self.bottleneck3 = self._make_layer(block_channels[1],
block_channels[2], num_blocks[2],
strides[2], expand_ratio)
self.ppm = PPM(
pool_scales,
block_channels[2],
block_channels[2] // 4,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg,
align_corners=align_corners)
self.out = ConvModule(
block_channels[2] * 2,
out_channels,
1,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg)
def _make_layer(self,
in_channels,
out_channels,
blocks,
stride=1,
expand_ratio=6):
layers = [
InvertedResidual(
in_channels,
out_channels,
stride,
expand_ratio,
norm_cfg=self.norm_cfg)
]
for i in range(1, blocks):
layers.append(
InvertedResidual(
out_channels,
out_channels,
1,
expand_ratio,
norm_cfg=self.norm_cfg))
return nn.Sequential(*layers)
def forward(self, x):
x = self.bottleneck1(x)
x = self.bottleneck2(x)
x = self.bottleneck3(x)
x = torch.cat([x, *self.ppm(x)], dim=1)
x = self.out(x)
return x
class FeatureFusionModule(nn.Module):
"""Feature fusion module.
Args:
higher_in_channels (int): Number of input channels of the
higher-resolution branch.
lower_in_channels (int): Number of input channels of the
lower-resolution branch.
out_channels (int): Number of output channels.
conv_cfg (dict | None): Config of conv layers. Default: None
norm_cfg (dict | None): Config of norm layers. Default:
dict(type='BN')
act_cfg (dict): Config of activation layers. Default:
dict(type='ReLU')
align_corners (bool): align_corners argument of F.interpolate.
Default: False
"""
def __init__(self,
higher_in_channels,
lower_in_channels,
out_channels,
conv_cfg=None,
norm_cfg=dict(type='BN'),
act_cfg=dict(type='ReLU'),
align_corners=False):
super(FeatureFusionModule, self).__init__()
self.conv_cfg = conv_cfg
self.norm_cfg = norm_cfg
self.act_cfg = act_cfg
self.align_corners = align_corners
self.dwconv = ConvModule(
lower_in_channels,
out_channels,
1,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg)
self.conv_lower_res = ConvModule(
out_channels,
out_channels,
1,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=None)
self.conv_higher_res = ConvModule(
higher_in_channels,
out_channels,
1,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=None)
self.relu = nn.ReLU(True)
def forward(self, higher_res_feature, lower_res_feature):
lower_res_feature = resize(
lower_res_feature,
size=higher_res_feature.size()[2:],
mode='bilinear',
align_corners=self.align_corners)
lower_res_feature = self.dwconv(lower_res_feature)
lower_res_feature = self.conv_lower_res(lower_res_feature)
higher_res_feature = self.conv_higher_res(higher_res_feature)
out = higher_res_feature + lower_res_feature
return self.relu(out)
@BACKBONES.register_module()
class FastSCNN(nn.Module):
"""Fast-SCNN Backbone.
Args:
in_channels (int): Number of input image channels. Default: 3.
downsample_dw_channels (tuple[int]): Number of output channels after
the first conv layer & the second conv layer in
Learning-To-Downsample (LTD) module.
Default: (32, 48).
global_in_channels (int): Number of input channels of
Global Feature Extractor(GFE).
Equal to number of output channels of LTD.
Default: 64.
global_block_channels (tuple[int]): Tuple of integers that describe
the output channels for each of the MobileNet-v2 bottleneck
residual blocks in GFE.
Default: (64, 96, 128).
global_block_strides (tuple[int]): Tuple of integers
that describe the strides (downsampling factors) for each of the
MobileNet-v2 bottleneck residual blocks in GFE.
Default: (2, 2, 1).
global_out_channels (int): Number of output channels of GFE.
Default: 128.
higher_in_channels (int): Number of input channels of the higher
resolution branch in FFM.
Equal to global_in_channels.
Default: 64.
lower_in_channels (int): Number of input channels of the lower
resolution branch in FFM.
Equal to global_out_channels.
Default: 128.
fusion_out_channels (int): Number of output channels of FFM.
Default: 128.
out_indices (tuple): Tuple of indices of list
[higher_res_features, lower_res_features, fusion_output].
Often set to (0,1,2) to enable aux. heads.
Default: (0, 1, 2).
conv_cfg (dict | None): Config of conv layers. Default: None
norm_cfg (dict | None): Config of norm layers. Default:
dict(type='BN')
act_cfg (dict): Config of activation layers. Default:
dict(type='ReLU')
align_corners (bool): align_corners argument of F.interpolate.
Default: False
"""
def __init__(self,
in_channels=3,
downsample_dw_channels=(32, 48),
global_in_channels=64,
global_block_channels=(64, 96, 128),
global_block_strides=(2, 2, 1),
global_out_channels=128,
higher_in_channels=64,
lower_in_channels=128,
fusion_out_channels=128,
out_indices=(0, 1, 2),
conv_cfg=None,
norm_cfg=dict(type='BN'),
act_cfg=dict(type='ReLU'),
align_corners=False):
super(FastSCNN, self).__init__()
if global_in_channels != higher_in_channels:
raise AssertionError('Global Input Channels must be the same \
with Higher Input Channels!')
elif global_out_channels != lower_in_channels:
raise AssertionError('Global Output Channels must be the same \
with Lower Input Channels!')
self.in_channels = in_channels
self.downsample_dw_channels1 = downsample_dw_channels[0]
self.downsample_dw_channels2 = downsample_dw_channels[1]
self.global_in_channels = global_in_channels
self.global_block_channels = global_block_channels
self.global_block_strides = global_block_strides
self.global_out_channels = global_out_channels
self.higher_in_channels = higher_in_channels
self.lower_in_channels = lower_in_channels
self.fusion_out_channels = fusion_out_channels
self.out_indices = out_indices
self.conv_cfg = conv_cfg
self.norm_cfg = norm_cfg
self.act_cfg = act_cfg
self.align_corners = align_corners
self.learning_to_downsample = LearningToDownsample(
in_channels,
downsample_dw_channels,
global_in_channels,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg)
self.global_feature_extractor = GlobalFeatureExtractor(
global_in_channels,
global_block_channels,
global_out_channels,
strides=self.global_block_strides,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg,
align_corners=self.align_corners)
self.feature_fusion = FeatureFusionModule(
higher_in_channels,
lower_in_channels,
fusion_out_channels,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg,
align_corners=self.align_corners)
def init_weights(self, pretrained=None):
for m in self.modules():
if isinstance(m, nn.Conv2d):
kaiming_init(m)
elif isinstance(m, (_BatchNorm, nn.GroupNorm)):
constant_init(m, 1)
def forward(self, x):
higher_res_features = self.learning_to_downsample(x)
lower_res_features = self.global_feature_extractor(higher_res_features)
fusion_output = self.feature_fusion(higher_res_features,
lower_res_features)
outs = [higher_res_features, lower_res_features, fusion_output]
outs = [outs[i] for i in self.out_indices]
return tuple(outs)
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