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""" Vision Transformer (ViT) in PyTorch
Hacked together by / Copyright 2020 Ross Wightman
"""
from functools import partial
import torch
import torch.nn as nn
from baselines.ViT.helpers import load_pretrained
from baselines.ViT.layer_helpers import to_2tuple
from baselines.ViT.weight_init import trunc_normal_
from einops import rearrange
def _cfg(url="", **kwargs):
return {
"url": url,
"num_classes": 1000,
"input_size": (3, 224, 224),
"pool_size": None,
"crop_pct": 0.9,
"interpolation": "bicubic",
"first_conv": "patch_embed.proj",
"classifier": "head",
**kwargs,
}
default_cfgs = {
# patch models
"vit_small_patch16_224": _cfg(
url="https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-weights/vit_small_p16_224-15ec54c9.pth",
),
"vit_base_patch16_224": _cfg(
url="https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-vitjx/jx_vit_base_p16_224-80ecf9dd.pth",
mean=(0.5, 0.5, 0.5),
std=(0.5, 0.5, 0.5),
),
"vit_large_patch16_224": _cfg(
url="https://github.com/rwightman/pytorch-image-models/releases/download/v0.1-vitjx/jx_vit_large_p16_224-4ee7a4dc.pth",
mean=(0.5, 0.5, 0.5),
std=(0.5, 0.5, 0.5),
),
}
class Mlp(nn.Module):
def __init__(
self,
in_features,
hidden_features=None,
out_features=None,
act_layer=nn.GELU,
drop=0.0,
):
super().__init__()
out_features = out_features or in_features
hidden_features = hidden_features or in_features
self.fc1 = nn.Linear(in_features, hidden_features)
self.act = act_layer()
self.fc2 = nn.Linear(hidden_features, out_features)
self.drop = nn.Dropout(drop)
def forward(self, x):
x = self.fc1(x)
x = self.act(x)
x = self.drop(x)
x = self.fc2(x)
x = self.drop(x)
return x
class Attention(nn.Module):
def __init__(self, dim, num_heads=8, qkv_bias=False, attn_drop=0.0, proj_drop=0.0):
super().__init__()
self.num_heads = num_heads
head_dim = dim // num_heads
# NOTE scale factor was wrong in my original version, can set manually to be compat with prev weights
self.scale = head_dim**-0.5
self.qkv = nn.Linear(dim, dim * 3, bias=qkv_bias)
self.attn_drop = nn.Dropout(attn_drop)
self.proj = nn.Linear(dim, dim)
self.proj_drop = nn.Dropout(proj_drop)
self.attn_gradients = None
self.attention_map = None
def save_attn_gradients(self, attn_gradients):
self.attn_gradients = attn_gradients
def get_attn_gradients(self):
return self.attn_gradients
def save_attention_map(self, attention_map):
self.attention_map = attention_map
def get_attention_map(self):
return self.attention_map
def forward(self, x, register_hook=False):
b, n, _, h = *x.shape, self.num_heads
# self.save_output(x)
# x.register_hook(self.save_output_grad)
qkv = self.qkv(x)
q, k, v = rearrange(qkv, "b n (qkv h d) -> qkv b h n d", qkv=3, h=h)
dots = torch.einsum("bhid,bhjd->bhij", q, k) * self.scale
attn = dots.softmax(dim=-1)
attn = self.attn_drop(attn)
out = torch.einsum("bhij,bhjd->bhid", attn, v)
self.save_attention_map(attn)
if register_hook:
attn.register_hook(self.save_attn_gradients)
out = rearrange(out, "b h n d -> b n (h d)")
out = self.proj(out)
out = self.proj_drop(out)
return out
class Block(nn.Module):
def __init__(
self,
dim,
num_heads,
mlp_ratio=4.0,
qkv_bias=False,
drop=0.0,
attn_drop=0.0,
act_layer=nn.GELU,
norm_layer=nn.LayerNorm,
):
super().__init__()
self.norm1 = norm_layer(dim)
self.attn = Attention(
dim,
num_heads=num_heads,
qkv_bias=qkv_bias,
attn_drop=attn_drop,
proj_drop=drop,
)
self.norm2 = norm_layer(dim)
mlp_hidden_dim = int(dim * mlp_ratio)
self.mlp = Mlp(
in_features=dim,
hidden_features=mlp_hidden_dim,
act_layer=act_layer,
drop=drop,
)
def forward(self, x, register_hook=False):
x = x + self.attn(self.norm1(x), register_hook=register_hook)
x = x + self.mlp(self.norm2(x))
return x
class PatchEmbed(nn.Module):
"""Image to Patch Embedding"""
def __init__(self, img_size=224, patch_size=16, in_chans=3, embed_dim=768):
super().__init__()
img_size = to_2tuple(img_size)
patch_size = to_2tuple(patch_size)
num_patches = (img_size[1] // patch_size[1]) * (img_size[0] // patch_size[0])
self.img_size = img_size
self.patch_size = patch_size
self.num_patches = num_patches
self.proj = nn.Conv2d(
in_chans, embed_dim, kernel_size=patch_size, stride=patch_size
)
def forward(self, x):
B, C, H, W = x.shape
# FIXME look at relaxing size constraints
assert (
H == self.img_size[0] and W == self.img_size[1]
), f"Input image size ({H}*{W}) doesn't match model ({self.img_size[0]}*{self.img_size[1]})."
x = self.proj(x).flatten(2).transpose(1, 2)
return x
class VisionTransformer(nn.Module):
"""Vision Transformer"""
def __init__(
self,
img_size=224,
patch_size=16,
in_chans=3,
num_classes=1000,
embed_dim=768,
depth=12,
num_heads=12,
mlp_ratio=4.0,
qkv_bias=False,
drop_rate=0.0,
attn_drop_rate=0.0,
norm_layer=nn.LayerNorm,
):
super().__init__()
self.num_classes = num_classes
self.num_features = (
self.embed_dim
) = embed_dim # num_features for consistency with other models
self.patch_embed = PatchEmbed(
img_size=img_size,
patch_size=patch_size,
in_chans=in_chans,
embed_dim=embed_dim,
)
num_patches = self.patch_embed.num_patches
self.cls_token = nn.Parameter(torch.zeros(1, 1, embed_dim))
self.pos_embed = nn.Parameter(torch.zeros(1, num_patches + 1, embed_dim))
self.pos_drop = nn.Dropout(p=drop_rate)
self.blocks = nn.ModuleList(
[
Block(
dim=embed_dim,
num_heads=num_heads,
mlp_ratio=mlp_ratio,
qkv_bias=qkv_bias,
drop=drop_rate,
attn_drop=attn_drop_rate,
norm_layer=norm_layer,
)
for i in range(depth)
]
)
self.norm = norm_layer(embed_dim)
# Classifier head
self.head = (
nn.Linear(embed_dim, num_classes) if num_classes > 0 else nn.Identity()
)
trunc_normal_(self.pos_embed, std=0.02)
trunc_normal_(self.cls_token, std=0.02)
self.apply(self._init_weights)
def _init_weights(self, m):
if isinstance(m, nn.Linear):
trunc_normal_(m.weight, std=0.02)
if isinstance(m, nn.Linear) and m.bias is not None:
nn.init.constant_(m.bias, 0)
elif isinstance(m, nn.LayerNorm):
nn.init.constant_(m.bias, 0)
nn.init.constant_(m.weight, 1.0)
@torch.jit.ignore
def no_weight_decay(self):
return {"pos_embed", "cls_token"}
def forward(self, x, register_hook=False):
B = x.shape[0]
x = self.patch_embed(x)
cls_tokens = self.cls_token.expand(
B, -1, -1
) # stole cls_tokens impl from Phil Wang, thanks
x = torch.cat((cls_tokens, x), dim=1)
x = x + self.pos_embed
x = self.pos_drop(x)
for blk in self.blocks:
x = blk(x, register_hook=register_hook)
x = self.norm(x)
x = x[:, 0]
x = self.head(x)
return x
def _conv_filter(state_dict, patch_size=16):
"""convert patch embedding weight from manual patchify + linear proj to conv"""
out_dict = {}
for k, v in state_dict.items():
if "patch_embed.proj.weight" in k:
v = v.reshape((v.shape[0], 3, patch_size, patch_size))
out_dict[k] = v
return out_dict
def vit_base_patch16_224(pretrained=False, **kwargs):
model = VisionTransformer(
patch_size=16,
embed_dim=768,
depth=12,
num_heads=12,
mlp_ratio=4,
qkv_bias=True,
norm_layer=partial(nn.LayerNorm, eps=1e-6),
**kwargs,
)
model.default_cfg = default_cfgs["vit_base_patch16_224"]
if pretrained:
load_pretrained(
model,
num_classes=model.num_classes,
in_chans=kwargs.get("in_chans", 3),
filter_fn=_conv_filter,
)
return model
def vit_large_patch16_224(pretrained=False, **kwargs):
model = VisionTransformer(
patch_size=16,
embed_dim=1024,
depth=24,
num_heads=16,
mlp_ratio=4,
qkv_bias=True,
norm_layer=partial(nn.LayerNorm, eps=1e-6),
**kwargs,
)
model.default_cfg = default_cfgs["vit_large_patch16_224"]
if pretrained:
load_pretrained(
model, num_classes=model.num_classes, in_chans=kwargs.get("in_chans", 3)
)
return model
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