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| """ | |
| LETR Backbone modules. | |
| modified based on https://github.com/facebookresearch/detr/blob/master/models/backbone.py | |
| """ | |
| from collections import OrderedDict | |
| import torch | |
| import torch.nn.functional as F | |
| import torchvision | |
| from torch import nn | |
| from torchvision.models._utils import IntermediateLayerGetter | |
| from typing import Dict, List | |
| from .misc import NestedTensor, is_main_process | |
| from .position_encoding import build_position_encoding | |
| class FrozenBatchNorm2d(torch.nn.Module): | |
| """ | |
| BatchNorm2d where the batch statistics and the affine parameters are fixed. | |
| Copy-paste from torchvision.misc.ops with added eps before rqsrt, | |
| without which any other models than torchvision.models.resnet[18,34,50,101] | |
| produce nans. | |
| """ | |
| def __init__(self, n): | |
| super(FrozenBatchNorm2d, self).__init__() | |
| self.register_buffer("weight", torch.ones(n)) | |
| self.register_buffer("bias", torch.zeros(n)) | |
| self.register_buffer("running_mean", torch.zeros(n)) | |
| self.register_buffer("running_var", torch.ones(n)) | |
| def _load_from_state_dict(self, state_dict, prefix, local_metadata, strict, | |
| missing_keys, unexpected_keys, error_msgs): | |
| num_batches_tracked_key = prefix + 'num_batches_tracked' | |
| if num_batches_tracked_key in state_dict: | |
| del state_dict[num_batches_tracked_key] | |
| super(FrozenBatchNorm2d, self)._load_from_state_dict( | |
| state_dict, prefix, local_metadata, strict, | |
| missing_keys, unexpected_keys, error_msgs) | |
| def forward(self, x): | |
| # move reshapes to the beginning | |
| # to make it fuser-friendly | |
| w = self.weight.reshape(1, -1, 1, 1) | |
| b = self.bias.reshape(1, -1, 1, 1) | |
| rv = self.running_var.reshape(1, -1, 1, 1) | |
| rm = self.running_mean.reshape(1, -1, 1, 1) | |
| eps = 1e-5 | |
| scale = w * (rv + eps).rsqrt() | |
| bias = b - rm * scale | |
| return x * scale + bias | |
| class BackboneBase(nn.Module): | |
| def __init__(self, backbone: nn.Module, train_backbone: bool, num_channels: int, return_interm_layers: bool): | |
| super().__init__() | |
| for name, parameter in backbone.named_parameters(): | |
| if not train_backbone or 'layer2' not in name and 'layer3' not in name and 'layer4' not in name: | |
| parameter.requires_grad_(False) | |
| if return_interm_layers: | |
| return_layers = {"layer1": "0", "layer2": "1", "layer3": "2", "layer4": "3"} | |
| else: | |
| return_layers = {'layer4': "0"} | |
| self.body = IntermediateLayerGetter(backbone, return_layers=return_layers) | |
| self.num_channels = num_channels | |
| def forward(self, tensor_list: NestedTensor): | |
| xs = self.body(tensor_list.tensors) | |
| out: Dict[str, NestedTensor] = {} | |
| for name, x in xs.items(): | |
| m = tensor_list.mask | |
| assert m is not None | |
| mask = F.interpolate(m[None].float(), size=x.shape[-2:]).to(torch.bool)[0] | |
| out[name] = NestedTensor(x, mask) | |
| return out | |
| class Backbone(BackboneBase): | |
| """ResNet backbone with frozen BatchNorm.""" | |
| def __init__(self, name: str, | |
| train_backbone: bool, | |
| return_interm_layers: bool, | |
| dilation: bool): | |
| backbone = getattr(torchvision.models, name)( | |
| replace_stride_with_dilation=[False, False, dilation], | |
| pretrained=is_main_process(), norm_layer=FrozenBatchNorm2d) | |
| num_channels = 512 if name in ('resnet18', 'resnet34') else 2048 | |
| super().__init__(backbone, train_backbone, num_channels, return_interm_layers) | |
| class Joiner(nn.Sequential): | |
| def __init__(self, backbone, position_embedding): | |
| super().__init__(backbone, position_embedding) | |
| def forward(self, tensor_list: NestedTensor): | |
| xs = self[0](tensor_list) | |
| out: List[NestedTensor] = [] | |
| pos = [] | |
| for name, x in xs.items(): | |
| out.append(x) | |
| # position encoding | |
| pos.append(self[1](x).to(x.tensors.dtype)) | |
| return out, pos | |
| def build_backbone(args): | |
| position_embedding = build_position_encoding(args) | |
| train_backbone = args.lr_backbone > 0 | |
| return_interm_layers = True | |
| backbone = Backbone(args.backbone, train_backbone, return_interm_layers, args.dilation) | |
| model = Joiner(backbone, position_embedding) | |
| model.num_channels = backbone.num_channels | |
| return model | |