# Non-local block using embedded gaussian
# Code from
# https://github.com/AlexHex7/Non-local_pytorch/blob/master/Non-Local_pytorch_0.3.1/lib/non_local_embedded_gaussian.py
# modified by Zilliz.
import torch
from torch import nn
from torch.nn import functional as F
import torchvision
class _NonLocalBlockND(nn.Module):
"""
Args:
"""
def __init__(self, in_channels, inter_channels=None, dimension=3, sub_sample=True, bn_layer=True):
super().__init__()
assert dimension in [1, 2, 3]
self.dimension = dimension
self.sub_sample = sub_sample
self.in_channels = in_channels
self.inter_channels = inter_channels
if self.inter_channels is None:
self.inter_channels = in_channels // 2
if self.inter_channels == 0:
self.inter_channels = 1
if dimension == 3:
conv_nd = nn.Conv3d
max_pool_layer = nn.MaxPool3d(kernel_size=(1, 2, 2))
bn = nn.BatchNorm3d
elif dimension == 2:
conv_nd = nn.Conv2d
max_pool_layer = nn.MaxPool2d(kernel_size=(2, 2))
bn = nn.BatchNorm2d
else:
conv_nd = nn.Conv1d
max_pool_layer = nn.MaxPool1d(kernel_size=(2))
bn = nn.BatchNorm1d
self.g = conv_nd(in_channels=self.in_channels, out_channels=self.inter_channels,
kernel_size=1, stride=1, padding=0)
if bn_layer:
self.w = nn.Sequential(
conv_nd(in_channels=self.inter_channels, out_channels=self.in_channels,
kernel_size=1, stride=1, padding=0),
bn(self.in_channels)
)
nn.init.constant_(self.w[1].weight, 0)
nn.init.constant_(self.w[1].bias, 0)
else:
self.w = conv_nd(in_channels=self.inter_channels, out_channels=self.in_channels,
kernel_size=1, stride=1, padding=0)
nn.init.constant_(self.w.weight, 0)
nn.init.constant_(self.w.bias, 0)
self.theta = conv_nd(in_channels=self.in_channels, out_channels=self.inter_channels,
kernel_size=1, stride=1, padding=0)
self.phi = conv_nd(in_channels=self.in_channels, out_channels=self.inter_channels,
kernel_size=1, stride=1, padding=0)
if sub_sample:
self.g = nn.Sequential(self.g, max_pool_layer)
self.phi = nn.Sequential(self.phi, max_pool_layer)
def forward(self, x):
'''
:param x: (b, c, t, h, w)
:return:
'''
batch_size = x.size(0)
g_x = self.g(x).view(batch_size, self.inter_channels, -1)
g_x = g_x.permute(0, 2, 1)
theta_x = self.theta(x).view(batch_size, self.inter_channels, -1)
theta_x = theta_x.permute(0, 2, 1)
phi_x = self.phi(x).view(batch_size, self.inter_channels, -1)
f = torch.matmul(theta_x, phi_x)
f_div_c = F.softmax(f, dim=-1)
y = torch.matmul(f_div_c, g_x)
y = y.permute(0, 2, 1).contiguous()
y = y.view(batch_size, self.inter_channels, *x.size()[2:])
w_y = self.w(y)
z = w_y + x
return z
[docs]class NONLocalBlock1D(_NonLocalBlockND):
"""
Args:
"""
[docs] def __init__(self, in_channels, inter_channels=None, sub_sample=True, bn_layer=True):
super().__init__(in_channels,
inter_channels=inter_channels,
dimension=1, sub_sample=sub_sample,
bn_layer=bn_layer)
[docs]class NONLocalBlock2D(_NonLocalBlockND):
"""
Args:
"""
[docs] def __init__(self, in_channels, inter_channels=None, sub_sample=True, bn_layer=True):
super().__init__(in_channels,
inter_channels=inter_channels,
dimension=2, sub_sample=sub_sample,
bn_layer=bn_layer)
[docs]class NONLocalBlock3D(_NonLocalBlockND):
"""
Args:
"""
[docs] def __init__(self, in_channels, inter_channels=None, sub_sample=True, bn_layer=True):
super().__init__(in_channels,
inter_channels=inter_channels,
dimension=3, sub_sample=sub_sample,
bn_layer=bn_layer)
[docs]class NL3DWrapper(nn.Module):
"""
Args:
"""
[docs] def __init__(self, block, n_segment):
super().__init__()
self.block = block
self.nl = NONLocalBlock3D(block.bn3.num_features)
self.n_segment = n_segment
[docs] def forward(self, x):
x = self.block(x)
nt, c, h, w = x.size()
x = x.view(nt // self.n_segment, self.n_segment, c, h, w).transpose(1, 2) # n, c, t, h, w
x = self.nl(x)
x = x.transpose(1, 2).contiguous().view(nt, c, h, w)
return x
[docs]def make_non_local(net, n_segment):
if isinstance(net, torchvision.models.ResNet):
net.layer2 = nn.Sequential(
NL3DWrapper(net.layer2[0], n_segment),
net.layer2[1],
NL3DWrapper(net.layer2[2], n_segment),
net.layer2[3],
)
net.layer3 = nn.Sequential(
NL3DWrapper(net.layer3[0], n_segment),
net.layer3[1],
NL3DWrapper(net.layer3[2], n_segment),
net.layer3[3],
NL3DWrapper(net.layer3[4], n_segment),
net.layer3[5],
)
else:
raise NotImplementedError
