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""" | |
Credit to https://github.com/XingangPan/IBN-Net. | |
""" | |
from __future__ import division, absolute_import | |
import math | |
import torch | |
import torch.nn as nn | |
import torch.utils.model_zoo as model_zoo | |
__all__ = ['resnet50_ibn_a'] | |
model_urls = { | |
'resnet50': 'https://download.pytorch.org/models/resnet50-19c8e357.pth', | |
'resnet101': 'https://download.pytorch.org/models/resnet101-5d3b4d8f.pth', | |
'resnet152': 'https://download.pytorch.org/models/resnet152-b121ed2d.pth', | |
} | |
def conv3x3(in_planes, out_planes, stride=1): | |
"3x3 convolution with padding" | |
return nn.Conv2d( | |
in_planes, | |
out_planes, | |
kernel_size=3, | |
stride=stride, | |
padding=1, | |
bias=False | |
) | |
class BasicBlock(nn.Module): | |
expansion = 1 | |
def __init__(self, inplanes, planes, stride=1, downsample=None): | |
super(BasicBlock, self).__init__() | |
self.conv1 = conv3x3(inplanes, planes, stride) | |
self.bn1 = nn.BatchNorm2d(planes) | |
self.relu = nn.ReLU(inplace=True) | |
self.conv2 = conv3x3(planes, planes) | |
self.bn2 = nn.BatchNorm2d(planes) | |
self.downsample = downsample | |
self.stride = stride | |
def forward(self, x): | |
residual = x | |
out = self.conv1(x) | |
out = self.bn1(out) | |
out = self.relu(out) | |
out = self.conv2(out) | |
out = self.bn2(out) | |
if self.downsample is not None: | |
residual = self.downsample(x) | |
out += residual | |
out = self.relu(out) | |
return out | |
class IBN(nn.Module): | |
def __init__(self, planes): | |
super(IBN, self).__init__() | |
half1 = int(planes / 2) | |
self.half = half1 | |
half2 = planes - half1 | |
self.IN = nn.InstanceNorm2d(half1, affine=True) | |
self.BN = nn.BatchNorm2d(half2) | |
def forward(self, x): | |
split = torch.split(x, self.half, 1) | |
out1 = self.IN(split[0].contiguous()) | |
out2 = self.BN(split[1].contiguous()) | |
out = torch.cat((out1, out2), 1) | |
return out | |
class Bottleneck(nn.Module): | |
expansion = 4 | |
def __init__(self, inplanes, planes, ibn=False, stride=1, downsample=None): | |
super(Bottleneck, self).__init__() | |
self.conv1 = nn.Conv2d(inplanes, planes, kernel_size=1, bias=False) | |
if ibn: | |
self.bn1 = IBN(planes) | |
else: | |
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, planes * self.expansion, kernel_size=1, bias=False | |
) | |
self.bn3 = nn.BatchNorm2d(planes * self.expansion) | |
self.relu = nn.ReLU(inplace=True) | |
self.downsample = downsample | |
self.stride = stride | |
def forward(self, x): | |
residual = x | |
out = self.conv1(x) | |
out = self.bn1(out) | |
out = self.relu(out) | |
out = self.conv2(out) | |
out = self.bn2(out) | |
out = self.relu(out) | |
out = self.conv3(out) | |
out = self.bn3(out) | |
if self.downsample is not None: | |
residual = self.downsample(x) | |
out += residual | |
out = self.relu(out) | |
return out | |
class ResNet(nn.Module): | |
"""Residual network + IBN layer. | |
Reference: | |
- He et al. Deep Residual Learning for Image Recognition. CVPR 2016. | |
- Pan et al. Two at Once: Enhancing Learning and Generalization | |
Capacities via IBN-Net. ECCV 2018. | |
""" | |
def __init__( | |
self, | |
block, | |
layers, | |
num_classes=1000, | |
loss='softmax', | |
fc_dims=None, | |
dropout_p=None, | |
**kwargs | |
): | |
scale = 64 | |
self.inplanes = scale | |
super(ResNet, self).__init__() | |
self.loss = loss | |
self.feature_dim = scale * 8 * block.expansion | |
self.conv1 = nn.Conv2d( | |
3, scale, kernel_size=7, stride=2, padding=3, bias=False | |
) | |
self.bn1 = nn.BatchNorm2d(scale) | |
self.relu = nn.ReLU(inplace=True) | |
self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1) | |
self.layer1 = self._make_layer(block, scale, layers[0]) | |
self.layer2 = self._make_layer(block, scale * 2, layers[1], stride=2) | |
self.layer3 = self._make_layer(block, scale * 4, layers[2], stride=2) | |
self.layer4 = self._make_layer(block, scale * 8, layers[3], stride=2) | |
self.avgpool = nn.AdaptiveAvgPool2d((1, 1)) | |
self.fc = self._construct_fc_layer( | |
fc_dims, scale * 8 * block.expansion, dropout_p | |
) | |
self.classifier = nn.Linear(self.feature_dim, num_classes) | |
for m in self.modules(): | |
if isinstance(m, nn.Conv2d): | |
n = m.kernel_size[0] * m.kernel_size[1] * m.out_channels | |
m.weight.data.normal_(0, math.sqrt(2. / n)) | |
elif isinstance(m, nn.BatchNorm2d): | |
m.weight.data.fill_(1) | |
m.bias.data.zero_() | |
elif isinstance(m, nn.InstanceNorm2d): | |
m.weight.data.fill_(1) | |
m.bias.data.zero_() | |
def _make_layer(self, block, planes, blocks, stride=1): | |
downsample = None | |
if stride != 1 or self.inplanes != planes * block.expansion: | |
downsample = nn.Sequential( | |
nn.Conv2d( | |
self.inplanes, | |
planes * block.expansion, | |
kernel_size=1, | |
stride=stride, | |
bias=False | |
), | |
nn.BatchNorm2d(planes * block.expansion), | |
) | |
layers = [] | |
ibn = True | |
if planes == 512: | |
ibn = False | |
layers.append(block(self.inplanes, planes, ibn, stride, downsample)) | |
self.inplanes = planes * block.expansion | |
for i in range(1, blocks): | |
layers.append(block(self.inplanes, planes, ibn)) | |
return nn.Sequential(*layers) | |
def _construct_fc_layer(self, fc_dims, input_dim, dropout_p=None): | |
"""Constructs fully connected layer | |
Args: | |
fc_dims (list or tuple): dimensions of fc layers, if None, no fc layers are constructed | |
input_dim (int): input dimension | |
dropout_p (float): dropout probability, if None, dropout is unused | |
""" | |
if fc_dims is None: | |
self.feature_dim = input_dim | |
return None | |
assert isinstance( | |
fc_dims, (list, tuple) | |
), 'fc_dims must be either list or tuple, but got {}'.format( | |
type(fc_dims) | |
) | |
layers = [] | |
for dim in fc_dims: | |
layers.append(nn.Linear(input_dim, dim)) | |
layers.append(nn.BatchNorm1d(dim)) | |
layers.append(nn.ReLU(inplace=True)) | |
if dropout_p is not None: | |
layers.append(nn.Dropout(p=dropout_p)) | |
input_dim = dim | |
self.feature_dim = fc_dims[-1] | |
return nn.Sequential(*layers) | |
def featuremaps(self, x): | |
x = self.conv1(x) | |
x = self.bn1(x) | |
x = self.relu(x) | |
x = self.maxpool(x) | |
x = self.layer1(x) | |
x = self.layer2(x) | |
x = self.layer3(x) | |
x = self.layer4(x) | |
return x | |
def forward(self, x): | |
f = self.featuremaps(x) | |
v = self.avgpool(f) | |
v = v.view(v.size(0), -1) | |
if self.fc is not None: | |
v = self.fc(v) | |
if not self.training: | |
return v | |
y = self.classifier(v) | |
if self.loss == 'softmax': | |
return y | |
elif self.loss == 'triplet': | |
return y, v | |
else: | |
raise KeyError("Unsupported loss: {}".format(self.loss)) | |
def init_pretrained_weights(model, model_url): | |
"""Initializes model with pretrained weights. | |
Layers that don't match with pretrained layers in name or size are kept unchanged. | |
""" | |
pretrain_dict = model_zoo.load_url(model_url) | |
model_dict = model.state_dict() | |
pretrain_dict = { | |
k: v | |
for k, v in pretrain_dict.items() | |
if k in model_dict and model_dict[k].size() == v.size() | |
} | |
model_dict.update(pretrain_dict) | |
model.load_state_dict(model_dict) | |
def resnet50_ibn_a(num_classes, loss='softmax', pretrained=False, **kwargs): | |
model = ResNet( | |
Bottleneck, [3, 4, 6, 3], num_classes=num_classes, loss=loss, **kwargs | |
) | |
if pretrained: | |
init_pretrained_weights(model, model_urls['resnet50']) | |
return model | |