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import torch.nn as nn
from mmcv.cnn import ConvModule
from ..builder import BACKBONES
from ..utils import ResLayer
from .resnet import BasicBlock
class HourglassModule(nn.Module):
"""Hourglass Module for HourglassNet backbone.
Generate module recursively and use BasicBlock as the base unit.
Args:
depth (int): Depth of current HourglassModule.
stage_channels (list[int]): Feature channels of sub-modules in current
and follow-up HourglassModule.
stage_blocks (list[int]): Number of sub-modules stacked in current and
follow-up HourglassModule.
norm_cfg (dict): Dictionary to construct and config norm layer.
"""
def __init__(self,
depth,
stage_channels,
stage_blocks,
norm_cfg=dict(type='BN', requires_grad=True)):
super(HourglassModule, self).__init__()
self.depth = depth
cur_block = stage_blocks[0]
next_block = stage_blocks[1]
cur_channel = stage_channels[0]
next_channel = stage_channels[1]
self.up1 = ResLayer(
BasicBlock, cur_channel, cur_channel, cur_block, norm_cfg=norm_cfg)
self.low1 = ResLayer(
BasicBlock,
cur_channel,
next_channel,
cur_block,
stride=2,
norm_cfg=norm_cfg)
if self.depth > 1:
self.low2 = HourglassModule(depth - 1, stage_channels[1:],
stage_blocks[1:])
else:
self.low2 = ResLayer(
BasicBlock,
next_channel,
next_channel,
next_block,
norm_cfg=norm_cfg)
self.low3 = ResLayer(
BasicBlock,
next_channel,
cur_channel,
cur_block,
norm_cfg=norm_cfg,
downsample_first=False)
self.up2 = nn.Upsample(scale_factor=2)
def forward(self, x):
"""Forward function."""
up1 = self.up1(x)
low1 = self.low1(x)
low2 = self.low2(low1)
low3 = self.low3(low2)
up2 = self.up2(low3)
return up1 + up2
@BACKBONES.register_module()
class HourglassNet(nn.Module):
"""HourglassNet backbone.
Stacked Hourglass Networks for Human Pose Estimation.
More details can be found in the `paper
<https://arxiv.org/abs/1603.06937>`_ .
Args:
downsample_times (int): Downsample times in a HourglassModule.
num_stacks (int): Number of HourglassModule modules stacked,
1 for Hourglass-52, 2 for Hourglass-104.
stage_channels (list[int]): Feature channel of each sub-module in a
HourglassModule.
stage_blocks (list[int]): Number of sub-modules stacked in a
HourglassModule.
feat_channel (int): Feature channel of conv after a HourglassModule.
norm_cfg (dict): Dictionary to construct and config norm layer.
Example:
>>> from mmdet.models import HourglassNet
>>> import torch
>>> self = HourglassNet()
>>> self.eval()
>>> inputs = torch.rand(1, 3, 511, 511)
>>> level_outputs = self.forward(inputs)
>>> for level_output in level_outputs:
... print(tuple(level_output.shape))
(1, 256, 128, 128)
(1, 256, 128, 128)
"""
def __init__(self,
downsample_times=5,
num_stacks=2,
stage_channels=(256, 256, 384, 384, 384, 512),
stage_blocks=(2, 2, 2, 2, 2, 4),
feat_channel=256,
norm_cfg=dict(type='BN', requires_grad=True)):
super(HourglassNet, self).__init__()
self.num_stacks = num_stacks
assert self.num_stacks >= 1
assert len(stage_channels) == len(stage_blocks)
assert len(stage_channels) > downsample_times
cur_channel = stage_channels[0]
self.stem = nn.Sequential(
ConvModule(3, 128, 7, padding=3, stride=2, norm_cfg=norm_cfg),
ResLayer(BasicBlock, 128, 256, 1, stride=2, norm_cfg=norm_cfg))
self.hourglass_modules = nn.ModuleList([
HourglassModule(downsample_times, stage_channels, stage_blocks)
for _ in range(num_stacks)
])
self.inters = ResLayer(
BasicBlock,
cur_channel,
cur_channel,
num_stacks - 1,
norm_cfg=norm_cfg)
self.conv1x1s = nn.ModuleList([
ConvModule(
cur_channel, cur_channel, 1, norm_cfg=norm_cfg, act_cfg=None)
for _ in range(num_stacks - 1)
])
self.out_convs = nn.ModuleList([
ConvModule(
cur_channel, feat_channel, 3, padding=1, norm_cfg=norm_cfg)
for _ in range(num_stacks)
])
self.remap_convs = nn.ModuleList([
ConvModule(
feat_channel, cur_channel, 1, norm_cfg=norm_cfg, act_cfg=None)
for _ in range(num_stacks - 1)
])
self.relu = nn.ReLU(inplace=True)
def init_weights(self, pretrained=None):
"""Init module weights.
We do nothing in this function because all modules we used
(ConvModule, BasicBlock and etc.) have default initialization, and
currently we don't provide pretrained model of HourglassNet.
Detector's __init__() will call backbone's init_weights() with
pretrained as input, so we keep this function.
"""
# Training Centripetal Model needs to reset parameters for Conv2d
for m in self.modules():
if isinstance(m, nn.Conv2d):
m.reset_parameters()
def forward(self, x):
"""Forward function."""
inter_feat = self.stem(x)
out_feats = []
for ind in range(self.num_stacks):
single_hourglass = self.hourglass_modules[ind]
out_conv = self.out_convs[ind]
hourglass_feat = single_hourglass(inter_feat)
out_feat = out_conv(hourglass_feat)
out_feats.append(out_feat)
if ind < self.num_stacks - 1:
inter_feat = self.conv1x1s[ind](
inter_feat) + self.remap_convs[ind](
out_feat)
inter_feat = self.inters[ind](self.relu(inter_feat))
return out_feats
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