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341 lines
12 KiB
341 lines
12 KiB
# Copyright (c) OpenMMLab. All rights reserved.
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import math
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import torch
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from functools import partial
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import torch.nn as nn
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import torch.nn.functional as F
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import torch.utils.checkpoint as checkpoint
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from timm.models.layers import drop_path, to_2tuple, trunc_normal_
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from ..builder import BACKBONES
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from .base_backbone import BaseBackbone
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def get_abs_pos(abs_pos, h, w, ori_h, ori_w, has_cls_token=True):
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"""
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Calculate absolute positional embeddings. If needed, resize embeddings and remove cls_token
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dimension for the original embeddings.
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Args:
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abs_pos (Tensor): absolute positional embeddings with (1, num_position, C).
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has_cls_token (bool): If true, has 1 embedding in abs_pos for cls token.
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hw (Tuple): size of input image tokens.
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Returns:
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Absolute positional embeddings after processing with shape (1, H, W, C)
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"""
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cls_token = None
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B, L, C = abs_pos.shape
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if has_cls_token:
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cls_token = abs_pos[:, 0:1]
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abs_pos = abs_pos[:, 1:]
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if ori_h != h or ori_w != w:
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new_abs_pos = F.interpolate(
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abs_pos.reshape(1, ori_h, ori_w, -1).permute(0, 3, 1, 2),
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size=(h, w),
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mode="bicubic",
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align_corners=False,
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).permute(0, 2, 3, 1).reshape(B, -1, C)
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else:
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new_abs_pos = abs_pos
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if cls_token is not None:
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new_abs_pos = torch.cat([cls_token, new_abs_pos], dim=1)
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return new_abs_pos
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class DropPath(nn.Module):
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"""Drop paths (Stochastic Depth) per sample (when applied in main path of residual blocks).
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"""
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def __init__(self, drop_prob=None):
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super(DropPath, self).__init__()
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self.drop_prob = drop_prob
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def forward(self, x):
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return drop_path(x, self.drop_prob, self.training)
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def extra_repr(self):
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return 'p={}'.format(self.drop_prob)
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class Mlp(nn.Module):
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def __init__(self, in_features, hidden_features=None, out_features=None, act_layer=nn.GELU, drop=0.):
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super().__init__()
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out_features = out_features or in_features
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hidden_features = hidden_features or in_features
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self.fc1 = nn.Linear(in_features, hidden_features)
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self.act = act_layer()
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self.fc2 = nn.Linear(hidden_features, out_features)
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self.drop = nn.Dropout(drop)
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def forward(self, x):
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x = self.fc1(x)
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x = self.act(x)
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x = self.fc2(x)
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x = self.drop(x)
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return x
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class Attention(nn.Module):
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def __init__(
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self, dim, num_heads=8, qkv_bias=False, qk_scale=None, attn_drop=0.,
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proj_drop=0., attn_head_dim=None,):
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super().__init__()
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self.num_heads = num_heads
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head_dim = dim // num_heads
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self.dim = dim
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if attn_head_dim is not None:
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head_dim = attn_head_dim
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all_head_dim = head_dim * self.num_heads
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self.scale = qk_scale or head_dim ** -0.5
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self.qkv = nn.Linear(dim, all_head_dim * 3, bias=qkv_bias)
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self.attn_drop = nn.Dropout(attn_drop)
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self.proj = nn.Linear(all_head_dim, dim)
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self.proj_drop = nn.Dropout(proj_drop)
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def forward(self, x):
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B, N, C = x.shape
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qkv = self.qkv(x)
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qkv = qkv.reshape(B, N, 3, self.num_heads, -1).permute(2, 0, 3, 1, 4)
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q, k, v = qkv[0], qkv[1], qkv[2] # make torchscript happy (cannot use tensor as tuple)
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q = q * self.scale
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attn = (q @ k.transpose(-2, -1))
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attn = attn.softmax(dim=-1)
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attn = self.attn_drop(attn)
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x = (attn @ v).transpose(1, 2).reshape(B, N, -1)
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x = self.proj(x)
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x = self.proj_drop(x)
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return x
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class Block(nn.Module):
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def __init__(self, dim, num_heads, mlp_ratio=4., qkv_bias=False, qk_scale=None,
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drop=0., attn_drop=0., drop_path=0., act_layer=nn.GELU,
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norm_layer=nn.LayerNorm, attn_head_dim=None
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):
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super().__init__()
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self.norm1 = norm_layer(dim)
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self.attn = Attention(
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dim, num_heads=num_heads, qkv_bias=qkv_bias, qk_scale=qk_scale,
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attn_drop=attn_drop, proj_drop=drop, attn_head_dim=attn_head_dim
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)
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# NOTE: drop path for stochastic depth, we shall see if this is better than dropout here
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self.drop_path = DropPath(drop_path) if drop_path > 0. else nn.Identity()
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self.norm2 = norm_layer(dim)
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mlp_hidden_dim = int(dim * mlp_ratio)
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self.mlp = Mlp(in_features=dim, hidden_features=mlp_hidden_dim, act_layer=act_layer, drop=drop)
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def forward(self, x):
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x = x + self.drop_path(self.attn(self.norm1(x)))
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x = x + self.drop_path(self.mlp(self.norm2(x)))
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return x
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class PatchEmbed(nn.Module):
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""" Image to Patch Embedding
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"""
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def __init__(self, img_size=224, patch_size=16, in_chans=3, embed_dim=768, ratio=1):
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super().__init__()
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img_size = to_2tuple(img_size)
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patch_size = to_2tuple(patch_size)
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num_patches = (img_size[1] // patch_size[1]) * (img_size[0] // patch_size[0]) * (ratio ** 2)
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self.patch_shape = (int(img_size[0] // patch_size[0] * ratio), int(img_size[1] // patch_size[1] * ratio))
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self.origin_patch_shape = (int(img_size[0] // patch_size[0]), int(img_size[1] // patch_size[1]))
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self.img_size = img_size
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self.patch_size = patch_size
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self.num_patches = num_patches
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self.proj = nn.Conv2d(in_chans, embed_dim, kernel_size=patch_size, stride=(patch_size[0] // ratio), padding=4 + 2 * (ratio//2-1))
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def forward(self, x, **kwargs):
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B, C, H, W = x.shape
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x = self.proj(x)
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Hp, Wp = x.shape[2], x.shape[3]
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x = x.flatten(2).transpose(1, 2)
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return x, (Hp, Wp)
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class HybridEmbed(nn.Module):
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""" CNN Feature Map Embedding
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Extract feature map from CNN, flatten, project to embedding dim.
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"""
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def __init__(self, backbone, img_size=224, feature_size=None, in_chans=3, embed_dim=768):
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super().__init__()
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assert isinstance(backbone, nn.Module)
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img_size = to_2tuple(img_size)
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self.img_size = img_size
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self.backbone = backbone
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if feature_size is None:
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with torch.no_grad():
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training = backbone.training
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if training:
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backbone.eval()
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o = self.backbone(torch.zeros(1, in_chans, img_size[0], img_size[1]))[-1]
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feature_size = o.shape[-2:]
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feature_dim = o.shape[1]
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backbone.train(training)
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else:
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feature_size = to_2tuple(feature_size)
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feature_dim = self.backbone.feature_info.channels()[-1]
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self.num_patches = feature_size[0] * feature_size[1]
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self.proj = nn.Linear(feature_dim, embed_dim)
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def forward(self, x):
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x = self.backbone(x)[-1]
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x = x.flatten(2).transpose(1, 2)
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x = self.proj(x)
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return x
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@BACKBONES.register_module()
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class ViT(BaseBackbone):
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def __init__(self,
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img_size=224, patch_size=16, in_chans=3, num_classes=80, embed_dim=768, depth=12,
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num_heads=12, mlp_ratio=4., qkv_bias=False, qk_scale=None, drop_rate=0., attn_drop_rate=0.,
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drop_path_rate=0., hybrid_backbone=None, norm_layer=None, use_checkpoint=False,
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frozen_stages=-1, ratio=1, last_norm=True,
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patch_padding='pad', freeze_attn=False, freeze_ffn=False,
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):
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# Protect mutable default arguments
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super(ViT, self).__init__()
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norm_layer = norm_layer or partial(nn.LayerNorm, eps=1e-6)
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self.num_classes = num_classes
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self.num_features = self.embed_dim = embed_dim # num_features for consistency with other models
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self.frozen_stages = frozen_stages
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self.use_checkpoint = use_checkpoint
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self.patch_padding = patch_padding
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self.freeze_attn = freeze_attn
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self.freeze_ffn = freeze_ffn
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self.depth = depth
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if hybrid_backbone is not None:
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self.patch_embed = HybridEmbed(
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hybrid_backbone, img_size=img_size, in_chans=in_chans, embed_dim=embed_dim)
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else:
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self.patch_embed = PatchEmbed(
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img_size=img_size, patch_size=patch_size, in_chans=in_chans, embed_dim=embed_dim, ratio=ratio)
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num_patches = self.patch_embed.num_patches
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# since the pretraining model has class token
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self.pos_embed = nn.Parameter(torch.zeros(1, num_patches + 1, embed_dim))
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dpr = [x.item() for x in torch.linspace(0, drop_path_rate, depth)] # stochastic depth decay rule
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self.blocks = nn.ModuleList([
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Block(
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dim=embed_dim, num_heads=num_heads, mlp_ratio=mlp_ratio, qkv_bias=qkv_bias, qk_scale=qk_scale,
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drop=drop_rate, attn_drop=attn_drop_rate, drop_path=dpr[i], norm_layer=norm_layer,
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)
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for i in range(depth)])
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self.last_norm = norm_layer(embed_dim) if last_norm else nn.Identity()
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if self.pos_embed is not None:
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trunc_normal_(self.pos_embed, std=.02)
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self._freeze_stages()
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def _freeze_stages(self):
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"""Freeze parameters."""
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if self.frozen_stages >= 0:
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self.patch_embed.eval()
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for param in self.patch_embed.parameters():
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param.requires_grad = False
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for i in range(1, self.frozen_stages + 1):
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m = self.blocks[i]
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m.eval()
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for param in m.parameters():
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param.requires_grad = False
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if self.freeze_attn:
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for i in range(0, self.depth):
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m = self.blocks[i]
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m.attn.eval()
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m.norm1.eval()
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for param in m.attn.parameters():
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param.requires_grad = False
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for param in m.norm1.parameters():
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param.requires_grad = False
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if self.freeze_ffn:
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self.pos_embed.requires_grad = False
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self.patch_embed.eval()
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for param in self.patch_embed.parameters():
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param.requires_grad = False
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for i in range(0, self.depth):
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m = self.blocks[i]
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m.mlp.eval()
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m.norm2.eval()
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for param in m.mlp.parameters():
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param.requires_grad = False
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for param in m.norm2.parameters():
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param.requires_grad = False
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def init_weights(self, pretrained=None):
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"""Initialize the weights in backbone.
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Args:
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pretrained (str, optional): Path to pre-trained weights.
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Defaults to None.
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"""
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super().init_weights(pretrained, patch_padding=self.patch_padding)
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if pretrained is None:
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def _init_weights(m):
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if isinstance(m, nn.Linear):
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trunc_normal_(m.weight, std=.02)
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if isinstance(m, nn.Linear) and m.bias is not None:
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nn.init.constant_(m.bias, 0)
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elif isinstance(m, nn.LayerNorm):
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nn.init.constant_(m.bias, 0)
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nn.init.constant_(m.weight, 1.0)
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self.apply(_init_weights)
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def get_num_layers(self):
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return len(self.blocks)
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@torch.jit.ignore
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def no_weight_decay(self):
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return {'pos_embed', 'cls_token'}
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def forward_features(self, x):
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B, C, H, W = x.shape
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x, (Hp, Wp) = self.patch_embed(x)
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if self.pos_embed is not None:
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# fit for multiple GPU training
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# since the first element for pos embed (sin-cos manner) is zero, it will cause no difference
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x = x + self.pos_embed[:, 1:] + self.pos_embed[:, :1]
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for blk in self.blocks:
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if self.use_checkpoint:
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x = checkpoint.checkpoint(blk, x)
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else:
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x = blk(x)
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x = self.last_norm(x)
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xp = x.permute(0, 2, 1).reshape(B, -1, Hp, Wp).contiguous()
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return xp
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def forward(self, x):
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x = self.forward_features(x)
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return x
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def train(self, mode=True):
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"""Convert the model into training mode."""
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super().train(mode)
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self._freeze_stages()
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