timm/models/hrnet.py

""" HRNet

Copied from https://github.com/HRNet/HRNet-Image-Classification

Original header:
  Copyright (c) Microsoft
  Licensed under the MIT License.
  Written by Bin Xiao (Bin.Xiao@microsoft.com)
  Modified by Ke Sun (sunk@mail.ustc.edu.cn)
"""
import logging
from typing import List

import torch
import torch.nn as nn
import torch.nn.functional as F

from timm.data import IMAGENET_DEFAULT_MEAN, IMAGENET_DEFAULT_STD
from .features import FeatureInfo
from .helpers import build_model_with_cfg, default_cfg_for_features
from .layers import create_classifier
from .registry import register_model
from .resnet import BasicBlock, Bottleneck  # leveraging ResNet blocks w/ additional features like SE

_BN_MOMENTUM = 0.1
_logger = logging.getLogger(__name__)


def _cfg(url='', **kwargs):
    return {
        'url': url,
        'num_classes': 1000, 'input_size': (3, 224, 224), 'pool_size': (7, 7),
        'crop_pct': 0.875, 'interpolation': 'bilinear',
        'mean': IMAGENET_DEFAULT_MEAN, 'std': IMAGENET_DEFAULT_STD,
        'first_conv': 'conv1', 'classifier': 'classifier',
        **kwargs
    }


default_cfgs = {
    'hrnet_w18_small': _cfg(
        url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-hrnet/hrnet_w18_small_v1-f460c6bc.pth'),
    'hrnet_w18_small_v2': _cfg(
        url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-hrnet/hrnet_w18_small_v2-4c50a8cb.pth'),
    'hrnet_w18': _cfg(
        url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-hrnet/hrnetv2_w18-8cb57bb9.pth'),
    'hrnet_w30': _cfg(
        url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-hrnet/hrnetv2_w30-8d7f8dab.pth'),
    'hrnet_w32': _cfg(
        url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-hrnet/hrnetv2_w32-90d8c5fb.pth'),
    'hrnet_w40': _cfg(
        url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-hrnet/hrnetv2_w40-7cd397a4.pth'),
    'hrnet_w44': _cfg(
        url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-hrnet/hrnetv2_w44-c9ac8c18.pth'),
    'hrnet_w48': _cfg(
        url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-hrnet/hrnetv2_w48-abd2e6ab.pth'),
    'hrnet_w64': _cfg(
        url='https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-hrnet/hrnetv2_w64-b47cc881.pth'),
}

cfg_cls = dict(
    hrnet_w18_small=dict(
        STEM_WIDTH=64,
        STAGE1=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=1,
            BLOCK='BOTTLENECK',
            NUM_BLOCKS=(1,),
            NUM_CHANNELS=(32,),
            FUSE_METHOD='SUM',
        ),
        STAGE2=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=2,
            BLOCK='BASIC',
            NUM_BLOCKS=(2, 2),
            NUM_CHANNELS=(16, 32),
            FUSE_METHOD='SUM'
        ),
        STAGE3=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=3,
            BLOCK='BASIC',
            NUM_BLOCKS=(2, 2, 2),
            NUM_CHANNELS=(16, 32, 64),
            FUSE_METHOD='SUM'
        ),
        STAGE4=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=4,
            BLOCK='BASIC',
            NUM_BLOCKS=(2, 2, 2, 2),
            NUM_CHANNELS=(16, 32, 64, 128),
            FUSE_METHOD='SUM',
        ),
    ),

    hrnet_w18_small_v2=dict(
        STEM_WIDTH=64,
        STAGE1=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=1,
            BLOCK='BOTTLENECK',
            NUM_BLOCKS=(2,),
            NUM_CHANNELS=(64,),
            FUSE_METHOD='SUM',
        ),
        STAGE2=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=2,
            BLOCK='BASIC',
            NUM_BLOCKS=(2, 2),
            NUM_CHANNELS=(18, 36),
            FUSE_METHOD='SUM'
        ),
        STAGE3=dict(
            NUM_MODULES=3,
            NUM_BRANCHES=3,
            BLOCK='BASIC',
            NUM_BLOCKS=(2, 2, 2),
            NUM_CHANNELS=(18, 36, 72),
            FUSE_METHOD='SUM'
        ),
        STAGE4=dict(
            NUM_MODULES=2,
            NUM_BRANCHES=4,
            BLOCK='BASIC',
            NUM_BLOCKS=(2, 2, 2, 2),
            NUM_CHANNELS=(18, 36, 72, 144),
            FUSE_METHOD='SUM',
        ),
    ),

    hrnet_w18=dict(
        STEM_WIDTH=64,
        STAGE1=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=1,
            BLOCK='BOTTLENECK',
            NUM_BLOCKS=(4,),
            NUM_CHANNELS=(64,),
            FUSE_METHOD='SUM',
        ),
        STAGE2=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=2,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4),
            NUM_CHANNELS=(18, 36),
            FUSE_METHOD='SUM'
        ),
        STAGE3=dict(
            NUM_MODULES=4,
            NUM_BRANCHES=3,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4),
            NUM_CHANNELS=(18, 36, 72),
            FUSE_METHOD='SUM'
        ),
        STAGE4=dict(
            NUM_MODULES=3,
            NUM_BRANCHES=4,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4, 4),
            NUM_CHANNELS=(18, 36, 72, 144),
            FUSE_METHOD='SUM',
        ),
    ),

    hrnet_w30=dict(
        STEM_WIDTH=64,
        STAGE1=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=1,
            BLOCK='BOTTLENECK',
            NUM_BLOCKS=(4,),
            NUM_CHANNELS=(64,),
            FUSE_METHOD='SUM',
        ),
        STAGE2=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=2,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4),
            NUM_CHANNELS=(30, 60),
            FUSE_METHOD='SUM'
        ),
        STAGE3=dict(
            NUM_MODULES=4,
            NUM_BRANCHES=3,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4),
            NUM_CHANNELS=(30, 60, 120),
            FUSE_METHOD='SUM'
        ),
        STAGE4=dict(
            NUM_MODULES=3,
            NUM_BRANCHES=4,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4, 4),
            NUM_CHANNELS=(30, 60, 120, 240),
            FUSE_METHOD='SUM',
        ),
    ),

    hrnet_w32=dict(
        STEM_WIDTH=64,
        STAGE1=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=1,
            BLOCK='BOTTLENECK',
            NUM_BLOCKS=(4,),
            NUM_CHANNELS=(64,),
            FUSE_METHOD='SUM',
        ),
        STAGE2=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=2,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4),
            NUM_CHANNELS=(32, 64),
            FUSE_METHOD='SUM'
        ),
        STAGE3=dict(
            NUM_MODULES=4,
            NUM_BRANCHES=3,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4),
            NUM_CHANNELS=(32, 64, 128),
            FUSE_METHOD='SUM'
        ),
        STAGE4=dict(
            NUM_MODULES=3,
            NUM_BRANCHES=4,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4, 4),
            NUM_CHANNELS=(32, 64, 128, 256),
            FUSE_METHOD='SUM',
        ),
    ),

    hrnet_w40=dict(
        STEM_WIDTH=64,
        STAGE1=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=1,
            BLOCK='BOTTLENECK',
            NUM_BLOCKS=(4,),
            NUM_CHANNELS=(64,),
            FUSE_METHOD='SUM',
        ),
        STAGE2=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=2,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4),
            NUM_CHANNELS=(40, 80),
            FUSE_METHOD='SUM'
        ),
        STAGE3=dict(
            NUM_MODULES=4,
            NUM_BRANCHES=3,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4),
            NUM_CHANNELS=(40, 80, 160),
            FUSE_METHOD='SUM'
        ),
        STAGE4=dict(
            NUM_MODULES=3,
            NUM_BRANCHES=4,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4, 4),
            NUM_CHANNELS=(40, 80, 160, 320),
            FUSE_METHOD='SUM',
        ),
    ),

    hrnet_w44=dict(
        STEM_WIDTH=64,
        STAGE1=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=1,
            BLOCK='BOTTLENECK',
            NUM_BLOCKS=(4,),
            NUM_CHANNELS=(64,),
            FUSE_METHOD='SUM',
        ),
        STAGE2=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=2,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4),
            NUM_CHANNELS=(44, 88),
            FUSE_METHOD='SUM'
        ),
        STAGE3=dict(
            NUM_MODULES=4,
            NUM_BRANCHES=3,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4),
            NUM_CHANNELS=(44, 88, 176),
            FUSE_METHOD='SUM'
        ),
        STAGE4=dict(
            NUM_MODULES=3,
            NUM_BRANCHES=4,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4, 4),
            NUM_CHANNELS=(44, 88, 176, 352),
            FUSE_METHOD='SUM',
        ),
    ),

    hrnet_w48=dict(
        STEM_WIDTH=64,
        STAGE1=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=1,
            BLOCK='BOTTLENECK',
            NUM_BLOCKS=(4,),
            NUM_CHANNELS=(64,),
            FUSE_METHOD='SUM',
        ),
        STAGE2=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=2,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4),
            NUM_CHANNELS=(48, 96),
            FUSE_METHOD='SUM'
        ),
        STAGE3=dict(
            NUM_MODULES=4,
            NUM_BRANCHES=3,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4),
            NUM_CHANNELS=(48, 96, 192),
            FUSE_METHOD='SUM'
        ),
        STAGE4=dict(
            NUM_MODULES=3,
            NUM_BRANCHES=4,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4, 4),
            NUM_CHANNELS=(48, 96, 192, 384),
            FUSE_METHOD='SUM',
        ),
    ),

    hrnet_w64=dict(
        STEM_WIDTH=64,
        STAGE1=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=1,
            BLOCK='BOTTLENECK',
            NUM_BLOCKS=(4,),
            NUM_CHANNELS=(64,),
            FUSE_METHOD='SUM',
        ),
        STAGE2=dict(
            NUM_MODULES=1,
            NUM_BRANCHES=2,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4),
            NUM_CHANNELS=(64, 128),
            FUSE_METHOD='SUM'
        ),
        STAGE3=dict(
            NUM_MODULES=4,
            NUM_BRANCHES=3,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4),
            NUM_CHANNELS=(64, 128, 256),
            FUSE_METHOD='SUM'
        ),
        STAGE4=dict(
            NUM_MODULES=3,
            NUM_BRANCHES=4,
            BLOCK='BASIC',
            NUM_BLOCKS=(4, 4, 4, 4),
            NUM_CHANNELS=(64, 128, 256, 512),
            FUSE_METHOD='SUM',
        ),
    )
)


class HighResolutionModule(nn.Module):
    def __init__(self, num_branches, blocks, num_blocks, num_inchannels,
                 num_channels, fuse_method, multi_scale_output=True):
        super(HighResolutionModule, self).__init__()
        self._check_branches(
            num_branches, blocks, num_blocks, num_inchannels, num_channels)

        self.num_inchannels = num_inchannels
        self.fuse_method = fuse_method
        self.num_branches = num_branches

        self.multi_scale_output = multi_scale_output

        self.branches = self._make_branches(
            num_branches, blocks, num_blocks, num_channels)
        self.fuse_layers = self._make_fuse_layers()
        self.fuse_act = nn.ReLU(False)

    def _check_branches(self, num_branches, blocks, num_blocks, num_inchannels, num_channels):
        error_msg = ''
        if num_branches != len(num_blocks):
            error_msg = 'NUM_BRANCHES({}) <> NUM_BLOCKS({})'.format(num_branches, len(num_blocks))
        elif num_branches != len(num_channels):
            error_msg = 'NUM_BRANCHES({}) <> NUM_CHANNELS({})'.format(num_branches, len(num_channels))
        elif num_branches != len(num_inchannels):
            error_msg = 'NUM_BRANCHES({}) <> NUM_INCHANNELS({})'.format(num_branches, len(num_inchannels))
        if error_msg:
            _logger.error(error_msg)
            raise ValueError(error_msg)

    def _make_one_branch(self, branch_index, block, num_blocks, num_channels, stride=1):
        downsample = None
        if stride != 1 or self.num_inchannels[branch_index] != num_channels[branch_index] * block.expansion:
            downsample = nn.Sequential(
                nn.Conv2d(
                    self.num_inchannels[branch_index], num_channels[branch_index] * block.expansion,
                    kernel_size=1, stride=stride, bias=False),
                nn.BatchNorm2d(num_channels[branch_index] * block.expansion, momentum=_BN_MOMENTUM),
            )

        layers = [block(self.num_inchannels[branch_index], num_channels[branch_index], stride, downsample)]
        self.num_inchannels[branch_index] = num_channels[branch_index] * block.expansion
        for i in range(1, num_blocks[branch_index]):
            layers.append(block(self.num_inchannels[branch_index], num_channels[branch_index]))

        return nn.Sequential(*layers)

    def _make_branches(self, num_branches, block, num_blocks, num_channels):
        branches = []
        for i in range(num_branches):
            branches.append(self._make_one_branch(i, block, num_blocks, num_channels))

        return nn.ModuleList(branches)

    def _make_fuse_layers(self):
        if self.num_branches == 1:
            return nn.Identity()

        num_branches = self.num_branches
        num_inchannels = self.num_inchannels
        fuse_layers = []
        for i in range(num_branches if self.multi_scale_output else 1):
            fuse_layer = []
            for j in range(num_branches):
                if j > i:
                    fuse_layer.append(nn.Sequential(
                        nn.Conv2d(num_inchannels[j], num_inchannels[i], 1, 1, 0, bias=False),
                        nn.BatchNorm2d(num_inchannels[i], momentum=_BN_MOMENTUM),
                        nn.Upsample(scale_factor=2 ** (j - i), mode='nearest')))
                elif j == i:
                    fuse_layer.append(nn.Identity())
                else:
                    conv3x3s = []
                    for k in range(i - j):
                        if k == i - j - 1:
                            num_outchannels_conv3x3 = num_inchannels[i]
                            conv3x3s.append(nn.Sequential(
                                nn.Conv2d(num_inchannels[j], num_outchannels_conv3x3, 3, 2, 1, bias=False),
                                nn.BatchNorm2d(num_outchannels_conv3x3, momentum=_BN_MOMENTUM)))
                        else:
                            num_outchannels_conv3x3 = num_inchannels[j]
                            conv3x3s.append(nn.Sequential(
                                nn.Conv2d(num_inchannels[j], num_outchannels_conv3x3, 3, 2, 1, bias=False),
                                nn.BatchNorm2d(num_outchannels_conv3x3, momentum=_BN_MOMENTUM),
                                nn.ReLU(False)))
                    fuse_layer.append(nn.Sequential(*conv3x3s))
            fuse_layers.append(nn.ModuleList(fuse_layer))

        return nn.ModuleList(fuse_layers)

    def get_num_inchannels(self):
        return self.num_inchannels

    def forward(self, x: List[torch.Tensor]):
        if self.num_branches == 1:
            return [self.branches[0](x[0])]

        for i, branch in enumerate(self.branches):
            x[i] = branch(x[i])

        x_fuse = []
        for i, fuse_outer in enumerate(self.fuse_layers):
            y = x[0] if i == 0 else fuse_outer[0](x[0])
            for j in range(1, self.num_branches):
                if i == j:
                    y = y + x[j]
                else:
                    y = y + fuse_outer[j](x[j])
            x_fuse.append(self.fuse_act(y))

        return x_fuse


blocks_dict = {
    'BASIC': BasicBlock,
    'BOTTLENECK': Bottleneck
}


class HighResolutionNet(nn.Module):

    def __init__(self, cfg, in_chans=3, num_classes=1000, global_pool='avg', drop_rate=0.0, head='classification'):
        super(HighResolutionNet, self).__init__()
        self.num_classes = num_classes
        self.drop_rate = drop_rate

        stem_width = cfg['STEM_WIDTH']
        self.conv1 = nn.Conv2d(in_chans, stem_width, kernel_size=3, stride=2, padding=1, bias=False)
        self.bn1 = nn.BatchNorm2d(stem_width, momentum=_BN_MOMENTUM)
        self.act1 = nn.ReLU(inplace=True)
        self.conv2 = nn.Conv2d(stem_width, 64, kernel_size=3, stride=2, padding=1, bias=False)
        self.bn2 = nn.BatchNorm2d(64, momentum=_BN_MOMENTUM)
        self.act2 = nn.ReLU(inplace=True)

        self.stage1_cfg = cfg['STAGE1']
        num_channels = self.stage1_cfg['NUM_CHANNELS'][0]
        block = blocks_dict[self.stage1_cfg['BLOCK']]
        num_blocks = self.stage1_cfg['NUM_BLOCKS'][0]
        self.layer1 = self._make_layer(block, 64, num_channels, num_blocks)
        stage1_out_channel = block.expansion * num_channels

        self.stage2_cfg = cfg['STAGE2']
        num_channels = self.stage2_cfg['NUM_CHANNELS']
        block = blocks_dict[self.stage2_cfg['BLOCK']]
        num_channels = [num_channels[i] * block.expansion for i in range(len(num_channels))]
        self.transition1 = self._make_transition_layer([stage1_out_channel], num_channels)
        self.stage2, pre_stage_channels = self._make_stage(self.stage2_cfg, num_channels)

        self.stage3_cfg = cfg['STAGE3']
        num_channels = self.stage3_cfg['NUM_CHANNELS']
        block = blocks_dict[self.stage3_cfg['BLOCK']]
        num_channels = [num_channels[i] * block.expansion for i in range(len(num_channels))]
        self.transition2 = self._make_transition_layer(pre_stage_channels, num_channels)
        self.stage3, pre_stage_channels = self._make_stage(self.stage3_cfg, num_channels)

        self.stage4_cfg = cfg['STAGE4']
        num_channels = self.stage4_cfg['NUM_CHANNELS']
        block = blocks_dict[self.stage4_cfg['BLOCK']]
        num_channels = [num_channels[i] * block.expansion for i in range(len(num_channels))]
        self.transition3 = self._make_transition_layer(pre_stage_channels, num_channels)
        self.stage4, pre_stage_channels = self._make_stage(self.stage4_cfg, num_channels, multi_scale_output=True)

        self.head = head
        self.head_channels = None  # set if _make_head called
        if head == 'classification':
            # Classification Head
            self.num_features = 2048
            self.incre_modules, self.downsamp_modules, self.final_layer = self._make_head(pre_stage_channels)
            self.global_pool, self.classifier = create_classifier(
                self.num_features, self.num_classes, pool_type=global_pool)
        elif head == 'incre':
            self.num_features = 2048
            self.incre_modules, _, _ = self._make_head(pre_stage_channels, True)
        else:
            self.incre_modules = None
            self.num_features = 256

        curr_stride = 2
        # module names aren't actually valid here, hook or FeatureNet based extraction would not work
        self.feature_info = [dict(num_chs=64, reduction=curr_stride, module='stem')]
        for i, c in enumerate(self.head_channels if self.head_channels else num_channels):
            curr_stride *= 2
            c = c * 4 if self.head_channels else c  # head block expansion factor of 4
            self.feature_info += [dict(num_chs=c, reduction=curr_stride, module=f'stage{i + 1}')]

        self.init_weights()

    def _make_head(self, pre_stage_channels, incre_only=False):
        head_block = Bottleneck
        self.head_channels = [32, 64, 128, 256]

        # Increasing the #channels on each resolution
        # from C, 2C, 4C, 8C to 128, 256, 512, 1024
        incre_modules = []
        for i, channels in enumerate(pre_stage_channels):
            incre_modules.append(self._make_layer(head_block, channels, self.head_channels[i], 1, stride=1))
        incre_modules = nn.ModuleList(incre_modules)
        if incre_only:
            return incre_modules, None, None

        # downsampling modules
        downsamp_modules = []
        for i in range(len(pre_stage_channels) - 1):
            in_channels = self.head_channels[i] * head_block.expansion
            out_channels = self.head_channels[i + 1] * head_block.expansion
            downsamp_module = nn.Sequential(
                nn.Conv2d(
                    in_channels=in_channels, out_channels=out_channels, kernel_size=3, stride=2, padding=1),
                nn.BatchNorm2d(out_channels, momentum=_BN_MOMENTUM),
                nn.ReLU(inplace=True)
            )
            downsamp_modules.append(downsamp_module)
        downsamp_modules = nn.ModuleList(downsamp_modules)

        final_layer = nn.Sequential(
            nn.Conv2d(
                in_channels=self.head_channels[3] * head_block.expansion,
                out_channels=self.num_features, kernel_size=1, stride=1, padding=0
            ),
            nn.BatchNorm2d(self.num_features, momentum=_BN_MOMENTUM),
            nn.ReLU(inplace=True)
        )

        return incre_modules, downsamp_modules, final_layer

    def _make_transition_layer(self, num_channels_pre_layer, num_channels_cur_layer):
        num_branches_cur = len(num_channels_cur_layer)
        num_branches_pre = len(num_channels_pre_layer)

        transition_layers = []
        for i in range(num_branches_cur):
            if i < num_branches_pre:
                if num_channels_cur_layer[i] != num_channels_pre_layer[i]:
                    transition_layers.append(nn.Sequential(
                        nn.Conv2d(num_channels_pre_layer[i], num_channels_cur_layer[i], 3, 1, 1, bias=False),
                        nn.BatchNorm2d(num_channels_cur_layer[i], momentum=_BN_MOMENTUM),
                        nn.ReLU(inplace=True)))
                else:
                    transition_layers.append(nn.Identity())
            else:
                conv3x3s = []
                for j in range(i + 1 - num_branches_pre):
                    inchannels = num_channels_pre_layer[-1]
                    outchannels = num_channels_cur_layer[i] if j == i - num_branches_pre else inchannels
                    conv3x3s.append(nn.Sequential(
                        nn.Conv2d(inchannels, outchannels, 3, 2, 1, bias=False),
                        nn.BatchNorm2d(outchannels, momentum=_BN_MOMENTUM),
                        nn.ReLU(inplace=True)))
                transition_layers.append(nn.Sequential(*conv3x3s))

        return nn.ModuleList(transition_layers)

    def _make_layer(self, block, inplanes, planes, blocks, stride=1):
        downsample = None
        if stride != 1 or inplanes != planes * block.expansion:
            downsample = nn.Sequential(
                nn.Conv2d(inplanes, planes * block.expansion, kernel_size=1, stride=stride, bias=False),
                nn.BatchNorm2d(planes * block.expansion, momentum=_BN_MOMENTUM),
            )

        layers = [block(inplanes, planes, stride, downsample)]
        inplanes = planes * block.expansion
        for i in range(1, blocks):
            layers.append(block(inplanes, planes))

        return nn.Sequential(*layers)

    def _make_stage(self, layer_config, num_inchannels, multi_scale_output=True):
        num_modules = layer_config['NUM_MODULES']
        num_branches = layer_config['NUM_BRANCHES']
        num_blocks = layer_config['NUM_BLOCKS']
        num_channels = layer_config['NUM_CHANNELS']
        block = blocks_dict[layer_config['BLOCK']]
        fuse_method = layer_config['FUSE_METHOD']

        modules = []
        for i in range(num_modules):
            # multi_scale_output is only used last module
            reset_multi_scale_output = multi_scale_output or i < num_modules - 1
            modules.append(HighResolutionModule(
                num_branches, block, num_blocks, num_inchannels, num_channels, fuse_method, reset_multi_scale_output)
            )
            num_inchannels = modules[-1].get_num_inchannels()

        return nn.Sequential(*modules), num_inchannels

    def init_weights(self):
        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.init.constant_(m.weight, 1)
                nn.init.constant_(m.bias, 0)

    def get_classifier(self):
        return self.classifier

    def reset_classifier(self, num_classes, global_pool='avg'):
        self.num_classes = num_classes
        self.global_pool, self.classifier = create_classifier(
            self.num_features, self.num_classes, pool_type=global_pool)

    def stages(self, x) -> List[torch.Tensor]:
        x = self.layer1(x)

        xl = [t(x) for i, t in enumerate(self.transition1)]
        yl = self.stage2(xl)

        xl = [t(yl[-1]) if not isinstance(t, nn.Identity) else yl[i] for i, t in enumerate(self.transition2)]
        yl = self.stage3(xl)

        xl = [t(yl[-1]) if not isinstance(t, nn.Identity) else yl[i] for i, t in enumerate(self.transition3)]
        yl = self.stage4(xl)
        return yl

    def forward_features(self, x):
        # Stem
        x = self.conv1(x)
        x = self.bn1(x)
        x = self.act1(x)
        x = self.conv2(x)
        x = self.bn2(x)
        x = self.act2(x)

        # Stages
        yl = self.stages(x)

        # Classification Head
        y = self.incre_modules[0](yl[0])
        for i, down in enumerate(self.downsamp_modules):
            y = self.incre_modules[i + 1](yl[i + 1]) + down(y)
        y = self.final_layer(y)
        return y

    def forward(self, x):
        x = self.forward_features(x)
        x = self.global_pool(x)
        if self.drop_rate > 0.:
            x = F.dropout(x, p=self.drop_rate, training=self.training)
        x = self.classifier(x)
        return x


class HighResolutionNetFeatures(HighResolutionNet):
    """HighResolutionNet feature extraction

    The design of HRNet makes it easy to grab feature maps, this class provides a simple wrapper to do so.
    It would be more complicated to use the FeatureNet helpers.

    The `feature_location=incre` allows grabbing increased channel count features using part of the
    classification head. If `feature_location=''` the default HRNet features are returned. First stem
    conv is used for stride 2 features.
    """

    def __init__(self, cfg, in_chans=3, num_classes=1000, global_pool='avg', drop_rate=0.0,
                 feature_location='incre', out_indices=(0, 1, 2, 3, 4)):
        assert feature_location in ('incre', '')
        super(HighResolutionNetFeatures, self).__init__(
            cfg, in_chans=in_chans, num_classes=num_classes, global_pool=global_pool,
            drop_rate=drop_rate, head=feature_location)
        self.feature_info = FeatureInfo(self.feature_info, out_indices)
        self._out_idx = {i for i in out_indices}

    def forward_features(self, x):
        assert False, 'Not supported'

    def forward(self, x) -> List[torch.tensor]:
        out = []
        x = self.conv1(x)
        x = self.bn1(x)
        x = self.act1(x)
        if 0 in self._out_idx:
            out.append(x)
        x = self.conv2(x)
        x = self.bn2(x)
        x = self.act2(x)
        x = self.stages(x)
        if self.incre_modules is not None:
            x = [incre(f) for f, incre in zip(x, self.incre_modules)]
        for i, f in enumerate(x):
            if i + 1 in self._out_idx:
                out.append(f)
        return out


def _create_hrnet(variant, pretrained, **model_kwargs):
    model_cls = HighResolutionNet
    features_only = False
    kwargs_filter = None
    if model_kwargs.pop('features_only', False):
        model_cls = HighResolutionNetFeatures
        kwargs_filter = ('num_classes', 'global_pool')
        features_only = True
    model = build_model_with_cfg(
        model_cls, variant, pretrained,
        default_cfg=default_cfgs[variant],
        model_cfg=cfg_cls[variant],
        pretrained_strict=not features_only,
        kwargs_filter=kwargs_filter,
        **model_kwargs)
    if features_only:
        model.default_cfg = default_cfg_for_features(model.default_cfg)
    return model


@register_model
def hrnet_w18_small(pretrained=True, **kwargs):
    return _create_hrnet('hrnet_w18_small', pretrained, **kwargs)


@register_model
def hrnet_w18_small_v2(pretrained=True, **kwargs):
    return _create_hrnet('hrnet_w18_small_v2', pretrained, **kwargs)


@register_model
def hrnet_w18(pretrained=True, **kwargs):
    return _create_hrnet('hrnet_w18', pretrained, **kwargs)


@register_model
def hrnet_w30(pretrained=True, **kwargs):
    return _create_hrnet('hrnet_w30', pretrained, **kwargs)


@register_model
def hrnet_w32(pretrained=True, **kwargs):
    return _create_hrnet('hrnet_w32', pretrained, **kwargs)


@register_model
def hrnet_w40(pretrained=True, **kwargs):
    return _create_hrnet('hrnet_w40', pretrained, **kwargs)


@register_model
def hrnet_w44(pretrained=True, **kwargs):
    return _create_hrnet('hrnet_w44', pretrained, **kwargs)


@register_model
def hrnet_w48(pretrained=True, **kwargs):
    return _create_hrnet('hrnet_w48', pretrained, **kwargs)


@register_model
def hrnet_w64(pretrained=True, **kwargs):
    return _create_hrnet('hrnet_w64', pretrained, **kwargs)