fast-reid/fastreid/modeling/backbones/resnet.py

# encoding: utf-8
"""
@author:  liaoxingyu
@contact: sherlockliao01@gmail.com
"""

import logging
import math

import torch
from torch import nn
from torch.utils import model_zoo

from .build import BACKBONE_REGISTRY

model_urls = {
    18: 'https://download.pytorch.org/models/resnet18-5c106cde.pth',
    34: 'https://download.pytorch.org/models/resnet34-333f7ec4.pth',
    50: 'https://download.pytorch.org/models/resnet50-19c8e357.pth',
    101: 'https://download.pytorch.org/models/resnet101-5d3b4d8f.pth',
    152: 'https://download.pytorch.org/models/resnet152-b121ed2d.pth',
    # 'resnext50_32x4d': 'https://download.pytorch.org/models/resnext50_32x4d-7cdf4587.pth',
    # 'resnext101_32x8d': 'https://download.pytorch.org/models/resnext101_32x8d-8ba56ff5.pth',
    # 'wide_resnet50_2': 'https://download.pytorch.org/models/wide_resnet50_2-95faca4d.pth',
    # 'wide_resnet101_2': 'https://download.pytorch.org/models/wide_resnet101_2-32ee1156.pth',
}

__all__ = ['ResNet', 'Bottleneck']


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, with_ibn=False, stride=1, downsample=None):
        super(Bottleneck, self).__init__()
        self.conv1 = nn.Conv2d(inplanes, planes, kernel_size=1, bias=False)
        if with_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 * 4, kernel_size=1, bias=False)
        self.bn3 = nn.BatchNorm2d(planes * 4)
        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):
    def __init__(self, last_stride, with_ibn, with_se, block, layers):
        scale = 64
        self.inplanes = scale
        super().__init__()
        self.conv1 = nn.Conv2d(3, 64, kernel_size=7, stride=2, padding=3,
                               bias=False)
        self.bn1 = nn.BatchNorm2d(64)
        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], with_ibn=with_ibn)
        self.layer2 = self._make_layer(block, scale * 2, layers[1], stride=2, with_ibn=with_ibn)
        self.layer3 = self._make_layer(block, scale * 4, layers[2], stride=2, with_ibn=with_ibn)
        self.layer4 = self._make_layer(block, scale * 8, layers[3], stride=last_stride)

        self.random_init()

    def _make_layer(self, block, planes, blocks, stride=1, with_ibn=False):
        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 = []
        if planes == 512:
            with_ibn = False
        layers.append(block(self.inplanes, planes, with_ibn, stride, downsample))
        self.inplanes = planes * block.expansion
        for i in range(1, blocks):
            layers.append(block(self.inplanes, planes, with_ibn))

        return nn.Sequential(*layers)

    def forward(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 random_init(self):
        for m in self.modules():
            if isinstance(m, nn.Conv2d):
                n = m.kernel_size[0] * m.kernel_size[1] * m.out_channels
                nn.init.normal_(m.weight, 0, math.sqrt(2. / n))
            elif isinstance(m, nn.BatchNorm2d):
                nn.init.constant_(m.weight, 1)
                nn.init.constant_(m.bias, 0)


@BACKBONE_REGISTRY.register()
def build_resnet_backbone(cfg):
    """
    Create a ResNet instance from config.
    Returns:
        ResNet: a :class:`ResNet` instance.
    """

    # fmt: off
    pretrain = cfg.MODEL.BACKBONE.PRETRAIN
    pretrain_path = cfg.MODEL.BACKBONE.PRETRAIN_PATH
    last_stride = cfg.MODEL.BACKBONE.LAST_STRIDE
    with_ibn = cfg.MODEL.BACKBONE.WITH_IBN
    with_se = cfg.MODEL.BACKBONE.WITH_SE
    depth = cfg.MODEL.BACKBONE.DEPTH

    num_blocks_per_stage = {50: [3, 4, 6, 3], 101: [3, 4, 23, 3], 152: [3, 8, 36, 3]}[depth]
    model = ResNet(last_stride, with_ibn, with_se, Bottleneck, num_blocks_per_stage)
    if pretrain:
        if not with_ibn:
            # original resnet
            state_dict = model_zoo.load_url(model_urls[depth])
            # remove fully-connected-layers
            state_dict.pop('fc.weight')
            state_dict.pop('fc.bias')
        else:
            # ibn resnet
            state_dict = torch.load(pretrain_path)['state_dict']
            # remove fully-connected-layers
            state_dict.pop('module.fc.weight')
            state_dict.pop('module.fc.bias')
            # remove module in name
            new_state_dict = {}
            for k in state_dict:
                new_k = '.'.join(k.split('.')[1:])
                if model.state_dict()[new_k].shape == state_dict[k].shape:
                    new_state_dict[new_k] = state_dict[k]
            state_dict = new_state_dict
        res = model.load_state_dict(state_dict, strict=False)
        logger = logging.getLogger(__name__)
        logger.info('missing keys is {}'.format(res.missing_keys))
        logger.info('unexpected keys is {}'.format(res.unexpected_keys))
    return model