import torch.nn as nn import torch.utils.checkpoint as cp from mmcv.cnn import (build_conv_layer, build_norm_layer, constant_init, kaiming_init) from torch.nn.modules.batchnorm import _BatchNorm from ..builder import BACKBONES from .base_backbone import BaseBackbone class BasicBlock(nn.Module): """BasicBlock for ResNet. Args: inplanes (int): inplanes of block. planes (int): planes of block. stride (int): stride of the block. Default: 1 dilation (int): dilation of convolution. Default: 1 downsample (nn.Module): downsample operation on identity branch. Default: None style (str): `pytorch` or `caffe`. If set to "pytorch", the stride-two layer is the 3x3 conv layer, otherwise the stride-two layer is the first 1x1 conv layer. with_cp (bool): Use checkpoint or not. Using checkpoint will save some memory while slowing down the training speed. conv_cfg (dict): dictionary to construct and config conv layer. Default: None norm_cfg (dict): dictionary to construct and config norm layer. Default: dict(type='BN') """ expansion = 1 def __init__(self, inplanes, planes, stride=1, dilation=1, downsample=None, style='pytorch', with_cp=False, conv_cfg=None, norm_cfg=dict(type='BN')): super(BasicBlock, self).__init__() self.norm1_name, norm1 = build_norm_layer(norm_cfg, planes, postfix=1) self.norm2_name, norm2 = build_norm_layer(norm_cfg, planes, postfix=2) self.conv1 = build_conv_layer( conv_cfg, inplanes, planes, 3, stride=stride, padding=dilation, dilation=dilation, bias=False) self.add_module(self.norm1_name, norm1) self.conv2 = build_conv_layer( conv_cfg, planes, planes, 3, padding=1, bias=False) self.add_module(self.norm2_name, norm2) self.relu = nn.ReLU(inplace=True) self.downsample = downsample self.stride = stride self.dilation = dilation self.with_cp = with_cp @property def norm1(self): return getattr(self, self.norm1_name) @property def norm2(self): return getattr(self, self.norm2_name) def forward(self, x): def _inner_forward(x): identity = x out = self.conv1(x) out = self.norm1(out) out = self.relu(out) out = self.conv2(out) out = self.norm2(out) if self.downsample is not None: identity = self.downsample(x) out += identity return out if self.with_cp and x.requires_grad: out = cp.checkpoint(_inner_forward, x) else: out = _inner_forward(x) out = self.relu(out) return out class Bottleneck(nn.Module): """Bottleneck block for ResNet. Args: inplanes (int): inplanes of block. planes (int): planes of block. stride (int): stride of the block. Default: 1 dilation (int): dilation of convolution. Default: 1 downsample (nn.Module): downsample operation on identity branch. Default: None style (str): `pytorch` or `caffe`. If set to "pytorch", the stride-two layer is the 3x3 conv layer, otherwise the stride-two layer is the first 1x1 conv layer. with_cp (bool): Use checkpoint or not. Using checkpoint will save some memory while slowing down the training speed. conv_cfg (dict): dictionary to construct and config conv layer. Default: None norm_cfg (dict): dictionary to construct and config norm layer. Default: dict(type='BN') """ expansion = 4 def __init__(self, inplanes, planes, stride=1, dilation=1, downsample=None, style='pytorch', with_cp=False, conv_cfg=None, norm_cfg=dict(type='BN')): super(Bottleneck, self).__init__() assert style in ['pytorch', 'caffe'] self.inplanes = inplanes self.planes = planes self.stride = stride self.dilation = dilation self.style = style self.with_cp = with_cp self.conv_cfg = conv_cfg self.norm_cfg = norm_cfg if self.style == 'pytorch': self.conv1_stride = 1 self.conv2_stride = stride else: self.conv1_stride = stride self.conv2_stride = 1 self.norm1_name, norm1 = build_norm_layer(norm_cfg, planes, postfix=1) self.norm2_name, norm2 = build_norm_layer(norm_cfg, planes, postfix=2) self.norm3_name, norm3 = build_norm_layer( norm_cfg, planes * self.expansion, postfix=3) self.conv1 = build_conv_layer( conv_cfg, inplanes, planes, kernel_size=1, stride=self.conv1_stride, bias=False) self.add_module(self.norm1_name, norm1) self.conv2 = build_conv_layer( conv_cfg, planes, planes, kernel_size=3, stride=self.conv2_stride, padding=dilation, dilation=dilation, bias=False) self.add_module(self.norm2_name, norm2) self.conv3 = build_conv_layer( conv_cfg, planes, planes * self.expansion, kernel_size=1, bias=False) self.add_module(self.norm3_name, norm3) self.relu = nn.ReLU(inplace=True) self.downsample = downsample @property def norm1(self): return getattr(self, self.norm1_name) @property def norm2(self): return getattr(self, self.norm2_name) @property def norm3(self): return getattr(self, self.norm3_name) def forward(self, x): def _inner_forward(x): identity = x out = self.conv1(x) out = self.norm1(out) out = self.relu(out) out = self.conv2(out) out = self.norm2(out) out = self.relu(out) out = self.conv3(out) out = self.norm3(out) if self.downsample is not None: identity = self.downsample(x) out += identity return out if self.with_cp and x.requires_grad: out = cp.checkpoint(_inner_forward, x) else: out = _inner_forward(x) out = self.relu(out) return out class ResLayer(nn.Sequential): """ResLayer to build ResNet style backbone. Args: block (nn.Module): block used to build ResLayer. inplanes (int): inplanes of block. planes (int): planes of block. num_blocks (int): number of blocks. stride (int): stride of the first block. Default: 1 avg_down (bool): Use AvgPool instead of stride conv when downsampling in the bottleneck. Default: False conv_cfg (dict): dictionary to construct and config conv layer. Default: None norm_cfg (dict): dictionary to construct and config norm layer. Default: dict(type='BN') """ def __init__(self, block, inplanes, planes, num_blocks, stride=1, avg_down=False, conv_cfg=None, norm_cfg=dict(type='BN'), **kwargs): self.block = block downsample = None if stride != 1 or inplanes != planes * block.expansion: downsample = [] conv_stride = stride if avg_down and stride != 1: conv_stride = 1 downsample.append( nn.AvgPool2d( kernel_size=stride, stride=stride, ceil_mode=True, count_include_pad=False)) downsample.extend([ build_conv_layer( conv_cfg, inplanes, planes * block.expansion, kernel_size=1, stride=conv_stride, bias=False), build_norm_layer(norm_cfg, planes * block.expansion)[1] ]) downsample = nn.Sequential(*downsample) layers = [] layers.append( block( inplanes=inplanes, planes=planes, stride=stride, downsample=downsample, conv_cfg=conv_cfg, norm_cfg=norm_cfg, **kwargs)) inplanes = planes * block.expansion for i in range(1, num_blocks): layers.append( block( inplanes=inplanes, planes=planes, stride=1, conv_cfg=conv_cfg, norm_cfg=norm_cfg, **kwargs)) super(ResLayer, self).__init__(*layers) @BACKBONES.register_module() class ResNet(BaseBackbone): """ResNet backbone. Args: depth (int): Depth of resnet, from {18, 34, 50, 101, 152}. in_channels (int): Number of input image channels. Normally 3. base_channels (int): Number of base channels of hidden layer. num_stages (int): Resnet stages, normally 4. strides (Sequence[int]): Strides of the first block of each stage. dilations (Sequence[int]): Dilation of each stage. out_indices (Sequence[int]): Output from which stages. style (str): `pytorch` or `caffe`. If set to "pytorch", the stride-two layer is the 3x3 conv layer, otherwise the stride-two layer is the first 1x1 conv layer. deep_stem (bool): Replace 7x7 conv in input stem with 3 3x3 conv avg_down (bool): Use AvgPool instead of stride conv when downsampling in the bottleneck. frozen_stages (int): Stages to be frozen (stop grad and set eval mode). -1 means not freezing any parameters. norm_cfg (dict): Dictionary to construct and config norm layer. norm_eval (bool): Whether to set norm layers to eval mode, namely, freeze running stats (mean and var). Note: Effect on Batch Norm and its variants only. with_cp (bool): Use checkpoint or not. Using checkpoint will save some memory while slowing down the training speed. zero_init_residual (bool): Whether to use zero init for last norm layer in resblocks to let them behave as identity. Example: >>> from mmcls.models import ResNet >>> import torch >>> self = ResNet(depth=18) >>> self.eval() >>> inputs = torch.rand(1, 3, 32, 32) >>> level_outputs = self.forward(inputs) >>> for level_out in level_outputs: ... print(tuple(level_out.shape)) (1, 64, 8, 8) (1, 128, 4, 4) (1, 256, 2, 2) (1, 512, 1, 1) """ arch_settings = { 18: (BasicBlock, (2, 2, 2, 2)), 34: (BasicBlock, (3, 4, 6, 3)), 50: (Bottleneck, (3, 4, 6, 3)), 101: (Bottleneck, (3, 4, 23, 3)), 152: (Bottleneck, (3, 8, 36, 3)) } def __init__(self, depth, in_channels=3, base_channels=64, num_stages=4, strides=(1, 2, 2, 2), dilations=(1, 1, 1, 1), out_indices=(3, ), style='pytorch', deep_stem=False, avg_down=False, frozen_stages=-1, conv_cfg=None, norm_cfg=dict(type='BN', requires_grad=True), norm_eval=False, with_cp=False, zero_init_residual=False): super(ResNet, self).__init__() if depth not in self.arch_settings: raise KeyError(f'invalid depth {depth} for resnet') self.depth = depth self.base_channels = base_channels self.num_stages = num_stages assert num_stages >= 1 and num_stages <= 4 self.strides = strides self.dilations = dilations assert len(strides) == len(dilations) == num_stages self.out_indices = out_indices assert max(out_indices) < num_stages self.style = style self.deep_stem = deep_stem self.avg_down = avg_down self.frozen_stages = frozen_stages self.conv_cfg = conv_cfg self.norm_cfg = norm_cfg self.with_cp = with_cp self.norm_eval = norm_eval self.zero_init_residual = zero_init_residual self.block, stage_blocks = self.arch_settings[depth] self.stage_blocks = stage_blocks[:num_stages] self.inplanes = base_channels self._make_stem_layer(in_channels, base_channels) self.res_layers = [] for i, num_blocks in enumerate(self.stage_blocks): stride = strides[i] dilation = dilations[i] planes = base_channels * 2**i res_layer = self.make_res_layer( block=self.block, inplanes=self.inplanes, planes=planes, num_blocks=num_blocks, stride=stride, dilation=dilation, style=self.style, avg_down=self.avg_down, with_cp=with_cp, conv_cfg=conv_cfg, norm_cfg=norm_cfg) self.inplanes = planes * self.block.expansion layer_name = f'layer{i + 1}' self.add_module(layer_name, res_layer) self.res_layers.append(layer_name) self._freeze_stages() self.feat_dim = self.block.expansion * base_channels * 2**( len(self.stage_blocks) - 1) def make_res_layer(self, **kwargs): return ResLayer(**kwargs) @property def norm1(self): return getattr(self, self.norm1_name) def _make_stem_layer(self, in_channels, base_channels): if self.deep_stem: self.stem = nn.Sequential( build_conv_layer( self.conv_cfg, in_channels, base_channels // 2, kernel_size=3, stride=2, padding=1, bias=False), build_norm_layer(self.norm_cfg, base_channels // 2)[1], nn.ReLU(inplace=True), build_conv_layer( self.conv_cfg, base_channels // 2, base_channels // 2, kernel_size=3, stride=1, padding=1, bias=False), build_norm_layer(self.norm_cfg, base_channels // 2)[1], nn.ReLU(inplace=True), build_conv_layer( self.conv_cfg, base_channels // 2, base_channels, kernel_size=3, stride=1, padding=1, bias=False), build_norm_layer(self.norm_cfg, base_channels)[1], nn.ReLU(inplace=True)) else: self.conv1 = build_conv_layer( self.conv_cfg, in_channels, base_channels, kernel_size=7, stride=2, padding=3, bias=False) self.norm1_name, norm1 = build_norm_layer( self.norm_cfg, base_channels, postfix=1) self.add_module(self.norm1_name, norm1) self.relu = nn.ReLU(inplace=True) self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1) def _freeze_stages(self): if self.frozen_stages >= 0: if self.deep_stem: self.stem.eval() for param in self.stem.parameters(): param.requires_grad = False else: self.norm1.eval() for m in [self.conv1, self.norm1]: for param in m.parameters(): param.requires_grad = False for i in range(1, self.frozen_stages + 1): m = getattr(self, f'layer{i}') m.eval() for param in m.parameters(): param.requires_grad = False def init_weights(self, pretrained=None): super(ResNet, self).init_weights(pretrained) if pretrained is None: for m in self.modules(): if isinstance(m, nn.Conv2d): kaiming_init(m) elif isinstance(m, (_BatchNorm, nn.GroupNorm)): constant_init(m, 1) if self.zero_init_residual: for m in self.modules(): if isinstance(m, Bottleneck): constant_init(m.norm3, 0) elif isinstance(m, BasicBlock): constant_init(m.norm2, 0) def forward(self, x): if self.deep_stem: x = self.stem(x) else: x = self.conv1(x) x = self.norm1(x) x = self.relu(x) x = self.maxpool(x) outs = [] for i, layer_name in enumerate(self.res_layers): res_layer = getattr(self, layer_name) x = res_layer(x) if i in self.out_indices: outs.append(x) if len(outs) == 1: return outs[0] else: return tuple(outs) def train(self, mode=True): super(ResNet, self).train(mode) self._freeze_stages() if mode and self.norm_eval: for m in self.modules(): # trick: eval have effect on BatchNorm only if isinstance(m, _BatchNorm): m.eval() @BACKBONES.register_module() class ResNetV1d(ResNet): """ResNetV1d variant described in `Bag of Tricks `_. Compared with default ResNet(ResNetV1b), ResNetV1d replaces the 7x7 conv in the input stem with three 3x3 convs. And in the downsampling block, a 2x2 avg_pool with stride 2 is added before conv, whose stride is changed to 1. """ def __init__(self, **kwargs): super(ResNetV1d, self).__init__( deep_stem=True, avg_down=True, **kwargs)