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# ------------------------------------------------------------------------------
# Copyright and License Information
# Adapted from
# https://github.com/microsoft/voxelpose-pytorch/blob/main/lib/models/v2v_net.py
# Original Licence: MIT License
# ------------------------------------------------------------------------------
import torch.nn as nn
import torch.nn.functional as F
from mmcv.cnn import ConvModule
from ..builder import BACKBONES
from .base_backbone import BaseBackbone
class Basic3DBlock(nn.Module):
"""A basic 3D convolutional block.
Args:
in_channels (int): Input channels of this block.
out_channels (int): Output channels of this block.
kernel_size (int): Kernel size of the convolution operation
conv_cfg (dict): Dictionary to construct and config conv layer.
Default: dict(type='Conv3d')
norm_cfg (dict): Dictionary to construct and config norm layer.
Default: dict(type='BN3d')
"""
def __init__(self,
in_channels,
out_channels,
kernel_size,
conv_cfg=dict(type='Conv3d'),
norm_cfg=dict(type='BN3d')):
super(Basic3DBlock, self).__init__()
self.block = ConvModule(
in_channels,
out_channels,
kernel_size,
stride=1,
padding=((kernel_size - 1) // 2),
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
bias=True)
def forward(self, x):
"""Forward function."""
return self.block(x)
class Res3DBlock(nn.Module):
"""A residual 3D convolutional block.
Args:
in_channels (int): Input channels of this block.
out_channels (int): Output channels of this block.
kernel_size (int): Kernel size of the convolution operation
Default: 3
conv_cfg (dict): Dictionary to construct and config conv layer.
Default: dict(type='Conv3d')
norm_cfg (dict): Dictionary to construct and config norm layer.
Default: dict(type='BN3d')
"""
def __init__(self,
in_channels,
out_channels,
kernel_size=3,
conv_cfg=dict(type='Conv3d'),
norm_cfg=dict(type='BN3d')):
super(Res3DBlock, self).__init__()
self.res_branch = nn.Sequential(
ConvModule(
in_channels,
out_channels,
kernel_size,
stride=1,
padding=((kernel_size - 1) // 2),
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
bias=True),
ConvModule(
out_channels,
out_channels,
kernel_size,
stride=1,
padding=((kernel_size - 1) // 2),
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=None,
bias=True))
if in_channels == out_channels:
self.skip_con = nn.Sequential()
else:
self.skip_con = ConvModule(
in_channels,
out_channels,
1,
stride=1,
padding=0,
conv_cfg=conv_cfg,
norm_cfg=norm_cfg,
act_cfg=None,
bias=True)
def forward(self, x):
"""Forward function."""
res = self.res_branch(x)
skip = self.skip_con(x)
return F.relu(res + skip, True)
class Pool3DBlock(nn.Module):
"""A 3D max-pool block.
Args:
pool_size (int): Pool size of the 3D max-pool layer
"""
def __init__(self, pool_size):
super(Pool3DBlock, self).__init__()
self.pool_size = pool_size
def forward(self, x):
"""Forward function."""
return F.max_pool3d(
x, kernel_size=self.pool_size, stride=self.pool_size)
class Upsample3DBlock(nn.Module):
"""A 3D upsample block.
Args:
in_channels (int): Input channels of this block.
out_channels (int): Output channels of this block.
kernel_size (int): Kernel size of the transposed convolution operation.
Default: 2
stride (int): Kernel size of the transposed convolution operation.
Default: 2
"""
def __init__(self, in_channels, out_channels, kernel_size=2, stride=2):
super(Upsample3DBlock, self).__init__()
assert kernel_size == 2
assert stride == 2
self.block = nn.Sequential(
nn.ConvTranspose3d(
in_channels,
out_channels,
kernel_size=kernel_size,
stride=stride,
padding=0,
output_padding=0), nn.BatchNorm3d(out_channels), nn.ReLU(True))
def forward(self, x):
"""Forward function."""
return self.block(x)
class EncoderDecorder(nn.Module):
"""An encoder-decoder block.
Args:
in_channels (int): Input channels of this block
"""
def __init__(self, in_channels=32):
super(EncoderDecorder, self).__init__()
self.encoder_pool1 = Pool3DBlock(2)
self.encoder_res1 = Res3DBlock(in_channels, in_channels * 2)
self.encoder_pool2 = Pool3DBlock(2)
self.encoder_res2 = Res3DBlock(in_channels * 2, in_channels * 4)
self.mid_res = Res3DBlock(in_channels * 4, in_channels * 4)
self.decoder_res2 = Res3DBlock(in_channels * 4, in_channels * 4)
self.decoder_upsample2 = Upsample3DBlock(in_channels * 4,
in_channels * 2, 2, 2)
self.decoder_res1 = Res3DBlock(in_channels * 2, in_channels * 2)
self.decoder_upsample1 = Upsample3DBlock(in_channels * 2, in_channels,
2, 2)
self.skip_res1 = Res3DBlock(in_channels, in_channels)
self.skip_res2 = Res3DBlock(in_channels * 2, in_channels * 2)
def forward(self, x):
"""Forward function."""
skip_x1 = self.skip_res1(x)
x = self.encoder_pool1(x)
x = self.encoder_res1(x)
skip_x2 = self.skip_res2(x)
x = self.encoder_pool2(x)
x = self.encoder_res2(x)
x = self.mid_res(x)
x = self.decoder_res2(x)
x = self.decoder_upsample2(x)
x = x + skip_x2
x = self.decoder_res1(x)
x = self.decoder_upsample1(x)
x = x + skip_x1
return x
@BACKBONES.register_module()
class V2VNet(BaseBackbone):
"""V2VNet.
Please refer to the `paper <https://arxiv.org/abs/1711.07399>`
for details.
Args:
input_channels (int):
Number of channels of the input feature volume.
output_channels (int):
Number of channels of the output volume.
mid_channels (int):
Input and output channels of the encoder-decoder block.
"""
def __init__(self, input_channels, output_channels, mid_channels=32):
super(V2VNet, self).__init__()
self.front_layers = nn.Sequential(
Basic3DBlock(input_channels, mid_channels // 2, 7),
Res3DBlock(mid_channels // 2, mid_channels),
)
self.encoder_decoder = EncoderDecorder(in_channels=mid_channels)
self.output_layer = nn.Conv3d(
mid_channels, output_channels, kernel_size=1, stride=1, padding=0)
self._initialize_weights()
def forward(self, x):
"""Forward function."""
x = self.front_layers(x)
x = self.encoder_decoder(x)
x = self.output_layer(x)
return x
def _initialize_weights(self):
for m in self.modules():
if isinstance(m, nn.Conv3d):
nn.init.normal_(m.weight, 0, 0.001)
nn.init.constant_(m.bias, 0)
elif isinstance(m, nn.ConvTranspose3d):
nn.init.normal_(m.weight, 0, 0.001)
nn.init.constant_(m.bias, 0)