"""ResNet in PyTorch.
ImageNet-Style ResNet
[1] Kaiming He, Xiangyu Zhang, Shaoqing Ren, Jian Sun
Deep Residual Learning for Image Recognition. arXiv:1512.03385
Adapted from: https://github.com/bearpaw/pytorch-classification
"""
import torch
import torch.nn as nn
import torch.nn.functional as F
class BasicBlock(nn.Module):
expansion = 1
def __init__(self, in_planes, planes, stride=1, is_last=False):
super(BasicBlock, self).__init__()
self.is_last = is_last
self.conv1 = nn.Conv2d(in_planes, planes, kernel_size=3, stride=stride, padding=1, bias=False)
self.bn1 = nn.BatchNorm2d(planes)
self.conv2 = nn.Conv2d(planes, planes, kernel_size=3, stride=1, padding=1, bias=False)
self.bn2 = nn.BatchNorm2d(planes)
self.shortcut = nn.Sequential()
if stride != 1 or in_planes != self.expansion * planes:
self.shortcut = nn.Sequential(
nn.Conv2d(in_planes, self.expansion * planes, kernel_size=1, stride=stride, bias=False),
nn.BatchNorm2d(self.expansion * planes)
)
def forward(self, x):
out = F.relu(self.bn1(self.conv1(x)))
out = self.bn2(self.conv2(out))
out += self.shortcut(x)
preact = out
out = F.relu(out)
if self.is_last:
return out, preact
else:
return out
class Bottleneck(nn.Module):
expansion = 4
def __init__(self, in_planes, planes, stride=1, is_last=False):
super(Bottleneck, self).__init__()
self.is_last = is_last
self.conv1 = nn.Conv2d(in_planes, planes, kernel_size=1, bias=False)
self.bn1 = nn.BatchNorm2d(planes)
self.conv2 = nn.Conv2d(planes, planes, kernel_size=3, stride=stride, padding=1, bias=False)
self.bn2 = nn.BatchNorm2d(planes)
self.conv3 = nn.Conv2d(planes, self.expansion * planes, kernel_size=1, bias=False)
self.bn3 = nn.BatchNorm2d(self.expansion * planes)
self.shortcut = nn.Sequential()
if stride != 1 or in_planes != self.expansion * planes:
self.shortcut = nn.Sequential(
nn.Conv2d(in_planes, self.expansion * planes, kernel_size=1, stride=stride, bias=False),
nn.BatchNorm2d(self.expansion * planes)
)
def forward(self, x):
out = F.relu(self.bn1(self.conv1(x)))
out = F.relu(self.bn2(self.conv2(out)))
out = self.bn3(self.conv3(out))
out += self.shortcut(x)
preact = out
out = F.relu(out)
if self.is_last:
return out, preact
else:
return out
class ResNet(nn.Module):
def __init__(self, block, num_blocks, in_channel=3, zero_init_residual=False):
super(ResNet, self).__init__()
self.in_planes = 64
self.conv1 = nn.Conv2d(in_channel, 64, kernel_size=3, stride=1, padding=1,
bias=False)
self.bn1 = nn.BatchNorm2d(64)
self.layer1 = self._make_layer(block, 64, num_blocks[0], stride=1)
self.layer2 = self._make_layer(block, 128, num_blocks[1], stride=2)
self.layer3 = self._make_layer(block, 256, num_blocks[2], stride=2)
self.layer4 = self._make_layer(block, 512, num_blocks[3], stride=2)
self.avgpool = nn.AdaptiveAvgPool2d((1, 1))
for m in self.modules():
if isinstance(m, nn.Conv2d):
nn.init.kaiming_normal_(m.weight, mode='fan_out', nonlinearity='relu')
elif isinstance(m, (nn.BatchNorm2d, nn.GroupNorm)):
nn.init.constant_(m.weight, 1)
nn.init.constant_(m.bias, 0)
# Zero-initialize the last BN in each residual branch,
# so that the residual branch starts with zeros, and each residual block behaves
# like an identity. This improves the model by 0.2~0.3% according to:
# https://arxiv.org/abs/1706.02677
if zero_init_residual:
for m in self.modules():
if isinstance(m, Bottleneck):
nn.init.constant_(m.bn3.weight, 0)
elif isinstance(m, BasicBlock):
nn.init.constant_(m.bn2.weight, 0)
def _make_layer(self, block, planes, num_blocks, stride):
strides = [stride] + [1] * (num_blocks - 1)
layers = []
for i in range(num_blocks):
stride = strides[i]
layers.append(block(self.in_planes, planes, stride))
self.in_planes = planes * block.expansion
return nn.Sequential(*layers)
def forward(self, x, layer=100):
out = F.relu(self.bn1(self.conv1(x)))
out = self.layer1(out)
out = self.layer2(out)
out = self.layer3(out)
out = self.layer4(out)
out = self.avgpool(out)
out = torch.flatten(out, 1)
return out
def resnet18(**kwargs):
return ResNet(BasicBlock, [2, 2, 2, 2], **kwargs)
def resnet34(**kwargs):
return ResNet(BasicBlock, [3, 4, 6, 3], **kwargs)
def resnet50(**kwargs):
return ResNet(Bottleneck, [3, 4, 6, 3], **kwargs)
def resnet101(**kwargs):
return ResNet(Bottleneck, [3, 4, 23, 3], **kwargs)
model_dict = {
'resnet18': [resnet18, 512],
'resnet34': [resnet34, 512],
'resnet50': [resnet50, 2048],
'resnet101': [resnet101, 2048],
}
class LinearBatchNorm(nn.Module):
"""Implements BatchNorm1d by BatchNorm2d, for SyncBN purpose"""
def __init__(self, dim, affine=True):
super(LinearBatchNorm, self).__init__()
self.dim = dim
self.bn = nn.BatchNorm2d(dim, affine=affine)
def forward(self, x):
x = x.view(-1, self.dim, 1, 1)
x = self.bn(x)
x = x.view(-1, self.dim)
return x
[docs]
class SupConResNet(nn.Module):
"""backbone + projection head"""
def __init__(self, name='resnet50', head='mlp', feat_dim=128):
super(SupConResNet, self).__init__()
model_fun, dim_in = model_dict[name]
self.encoder = model_fun()
if head == 'linear':
self.head = nn.Linear(dim_in, feat_dim)
elif head == 'mlp':
self.head = nn.Sequential(
nn.Linear(dim_in, dim_in),
nn.ReLU(inplace=True),
nn.Linear(dim_in, feat_dim)
)
else:
raise NotImplementedError(
'head not supported: {}'.format(head))
[docs]
def forward(self, x):
feat = self.encoder(x)
feat = F.normalize(self.head(feat), dim=1)
return feat
[docs]
class SupCEResNet(nn.Module):
"""encoder + classifier"""
def __init__(self, name='resnet50', num_classes=10):
super(SupCEResNet, self).__init__()
model_fun, dim_in = model_dict[name]
self.encoder = model_fun()
self.fc = nn.Linear(dim_in, num_classes)
[docs]
def forward(self, x):
return self.fc(self.encoder(x))
class LinearClassifier(nn.Module):
"""Linear classifier"""
def __init__(self, name='resnet50', num_classes=10):
super(LinearClassifier, self).__init__()
_, feat_dim = model_dict[name]
self.fc = nn.Linear(feat_dim, num_classes)
def forward(self, features):
return self.fc(features)