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import torch
import torch.nn as nn
import torch.nn.functional as F
from mmcv.cnn import ConvModule, build_norm_layer
from mmseg.ops import Encoding, resize
from ..builder import HEADS, build_loss
from .decode_head import BaseDecodeHead
class EncModule(nn.Module):
"""Encoding Module used in EncNet.
Args:
in_channels (int): Input channels.
num_codes (int): Number of code words.
conv_cfg (dict|None): Config of conv layers.
norm_cfg (dict|None): Config of norm layers.
act_cfg (dict): Config of activation layers.
"""
def __init__(self, in_channels, num_codes, conv_cfg, norm_cfg, act_cfg):
super(EncModule, self).__init__()
self.encoding_project = ConvModule(
in_channels,
in_channels,
1,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=act_cfg)
# TODO: resolve this hack
# change to 1d
if norm_cfg is not None:
encoding_norm_cfg = norm_cfg.copy()
if encoding_norm_cfg['type'] in ['BN', 'IN']:
encoding_norm_cfg['type'] += '1d'
else:
encoding_norm_cfg['type'] = encoding_norm_cfg['type'].replace(
'2d', '1d')
else:
# fallback to BN1d
encoding_norm_cfg = dict(type='BN1d')
self.encoding = nn.Sequential(
Encoding(channels=in_channels, num_codes=num_codes),
build_norm_layer(encoding_norm_cfg, num_codes)[1],
nn.ReLU(inplace=True))
self.fc = nn.Sequential(
nn.Linear(in_channels, in_channels), nn.Sigmoid())
def forward(self, x):
"""Forward function."""
encoding_projection = self.encoding_project(x)
encoding_feat = self.encoding(encoding_projection).mean(dim=1)
batch_size, channels, _, _ = x.size()
gamma = self.fc(encoding_feat)
y = gamma.view(batch_size, channels, 1, 1)
output = F.relu_(x + x * y)
return encoding_feat, output
@HEADS.register_module()
class EncHead(BaseDecodeHead):
"""Context Encoding for Semantic Segmentation.
This head is the implementation of `EncNet
<https://arxiv.org/abs/1803.08904>`_.
Args:
num_codes (int): Number of code words. Default: 32.
use_se_loss (bool): Whether use Semantic Encoding Loss (SE-loss) to
regularize the training. Default: True.
add_lateral (bool): Whether use lateral connection to fuse features.
Default: False.
loss_se_decode (dict): Config of decode loss.
Default: dict(type='CrossEntropyLoss', use_sigmoid=True).
"""
def __init__(self,
num_codes=32,
use_se_loss=True,
add_lateral=False,
loss_se_decode=dict(
type='CrossEntropyLoss',
use_sigmoid=True,
loss_weight=0.2),
**kwargs):
super(EncHead, self).__init__(
input_transform='multiple_select', **kwargs)
self.use_se_loss = use_se_loss
self.add_lateral = add_lateral
self.num_codes = num_codes
self.bottleneck = ConvModule(
self.in_channels[-1],
self.channels,
3,
padding=1,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg)
if add_lateral:
self.lateral_convs = nn.ModuleList()
for in_channels in self.in_channels[:-1]: # skip the last one
self.lateral_convs.append(
ConvModule(
in_channels,
self.channels,
1,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg))
self.fusion = ConvModule(
len(self.in_channels) * self.channels,
self.channels,
3,
padding=1,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg)
self.enc_module = EncModule(
self.channels,
num_codes=num_codes,
conv_cfg=self.conv_cfg,
norm_cfg=self.norm_cfg,
act_cfg=self.act_cfg)
if self.use_se_loss:
self.loss_se_decode = build_loss(loss_se_decode)
self.se_layer = nn.Linear(self.channels, self.num_classes)
def forward(self, inputs):
"""Forward function."""
inputs = self._transform_inputs(inputs)
feat = self.bottleneck(inputs[-1])
if self.add_lateral:
laterals = [
resize(
lateral_conv(inputs[i]),
size=feat.shape[2:],
mode='bilinear',
align_corners=self.align_corners)
for i, lateral_conv in enumerate(self.lateral_convs)
]
feat = self.fusion(torch.cat([feat, *laterals], 1))
encode_feat, output = self.enc_module(feat)
output = self.cls_seg(output)
if self.use_se_loss:
se_output = self.se_layer(encode_feat)
return output, se_output
else:
return output
def forward_test(self, inputs, img_metas, test_cfg):
"""Forward function for testing, ignore se_loss."""
if self.use_se_loss:
return self.forward(inputs)[0]
else:
return self.forward(inputs)
@staticmethod
def _convert_to_onehot_labels(seg_label, num_classes):
"""Convert segmentation label to onehot.
Args:
seg_label (Tensor): Segmentation label of shape (N, H, W).
num_classes (int): Number of classes.
Returns:
Tensor: Onehot labels of shape (N, num_classes).
"""
batch_size = seg_label.size(0)
onehot_labels = seg_label.new_zeros((batch_size, num_classes))
for i in range(batch_size):
hist = seg_label[i].float().histc(
bins=num_classes, min=0, max=num_classes - 1)
onehot_labels[i] = hist > 0
return onehot_labels
def losses(self, seg_logit, seg_label):
"""Compute segmentation and semantic encoding loss."""
seg_logit, se_seg_logit = seg_logit
loss = dict()
loss.update(super(EncHead, self).losses(seg_logit, seg_label))
se_loss = self.loss_se_decode(
se_seg_logit,
self._convert_to_onehot_labels(seg_label, self.num_classes))
loss['loss_se'] = se_loss
return loss
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