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Original file line number | Diff line number | Diff line change |
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import torch | ||
from torch import nn | ||
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from einops import rearrange, repeat | ||
from einops.layers.torch import Rearrange | ||
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# helpers | ||
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def pair(t): | ||
return t if isinstance(t, tuple) else (t, t) | ||
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# classes | ||
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class PreNorm(nn.Module): | ||
def __init__(self, dim, fn): | ||
super().__init__() | ||
self.norm = nn.LayerNorm(dim) | ||
self.fn = fn | ||
def forward(self, x, **kwargs): | ||
return self.fn(self.norm(x), **kwargs) | ||
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class FeedForward(nn.Module): | ||
def __init__(self, dim, hidden_dim, dropout = 0.): | ||
super().__init__() | ||
self.net = nn.Sequential( | ||
nn.Linear(dim, hidden_dim), | ||
nn.GELU(), | ||
nn.Dropout(dropout), | ||
nn.Linear(hidden_dim, dim), | ||
nn.Dropout(dropout) | ||
) | ||
def forward(self, x): | ||
return self.net(x) | ||
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class Attention(nn.Module): | ||
def __init__(self, dim, heads = 8, dim_head = 64, dropout = 0.): | ||
super().__init__() | ||
inner_dim = dim_head * heads | ||
project_out = not (heads == 1 and dim_head == dim) | ||
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self.heads = heads | ||
self.scale = dim_head ** -0.5 | ||
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self.attend = nn.Softmax(dim = -1) | ||
self.dropout = nn.Dropout(dropout) | ||
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self.to_qkv = nn.Linear(dim, inner_dim * 3, bias = False) | ||
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self.to_out = nn.Sequential( | ||
nn.Linear(inner_dim, dim), | ||
nn.Dropout(dropout) | ||
) if project_out else nn.Identity() | ||
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def forward(self, x): | ||
qkv = self.to_qkv(x).chunk(3, dim = -1) | ||
q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> b h n d', h = self.heads), qkv) | ||
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dots = torch.matmul(q, k.transpose(-1, -2)) * self.scale | ||
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attn = self.attend(dots) | ||
attn = self.dropout(attn) | ||
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out = torch.matmul(attn, v) | ||
out = rearrange(out, 'b h n d -> b n (h d)') | ||
return self.to_out(out) | ||
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class Transformer(nn.Module): | ||
def __init__(self, dim, depth, heads, dim_head, mlp_dim, dropout = 0.): | ||
super().__init__() | ||
self.layers = nn.ModuleList([]) | ||
for _ in range(depth): | ||
self.layers.append(nn.ModuleList([ | ||
PreNorm(dim, Attention(dim, heads = heads, dim_head = dim_head, dropout = dropout)), | ||
PreNorm(dim, FeedForward(dim, mlp_dim, dropout = dropout)) | ||
])) | ||
def forward(self, x): | ||
for attn, ff in self.layers: | ||
x = attn(x) + x | ||
x = ff(x) + x | ||
return x | ||
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class ViT(nn.Module): | ||
def __init__( | ||
self, | ||
*, | ||
image_size, | ||
image_patch_size, | ||
frames, | ||
frame_patch_size, | ||
num_classes, | ||
dim, | ||
spatial_depth, | ||
temporal_depth, | ||
heads, | ||
mlp_dim, | ||
pool = 'cls', | ||
channels = 3, | ||
dim_head = 64, | ||
dropout = 0., | ||
emb_dropout = 0. | ||
): | ||
super().__init__() | ||
image_height, image_width = pair(image_size) | ||
patch_height, patch_width = pair(image_patch_size) | ||
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assert image_height % patch_height == 0 and image_width % patch_width == 0, 'Image dimensions must be divisible by the patch size.' | ||
assert frames % frame_patch_size == 0, 'Frames must be divisible by frame patch size' | ||
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num_patches = (image_height // patch_height) * (image_width // patch_width) * (frames // frame_patch_size) | ||
patch_dim = channels * patch_height * patch_width * frame_patch_size | ||
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assert pool in {'cls', 'mean'}, 'pool type must be either cls (cls token) or mean (mean pooling)' | ||
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self.to_patch_embedding = nn.Sequential( | ||
Rearrange('b c (f pf) (h p1) (w p2) -> b f (h w) (p1 p2 pf c)', p1 = patch_height, p2 = patch_width, pf = frame_patch_size), | ||
nn.Linear(patch_dim, dim), | ||
) | ||
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self.pos_embedding = nn.Parameter(torch.randn(1, num_patches + 1, dim)) | ||
self.dropout = nn.Dropout(emb_dropout) | ||
self.spatial_cls_token = nn.Parameter(torch.randn(1, 1, dim)) | ||
self.temporal_cls_token = nn.Parameter(torch.randn(1, 1, dim)) | ||
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self.spatial_transformer = Transformer(dim, spatial_depth, heads, dim_head, mlp_dim, dropout) | ||
self.temporal_transformer = Transformer(dim, temporal_depth, heads, dim_head, mlp_dim, dropout) | ||
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self.pool = pool | ||
self.to_latent = nn.Identity() | ||
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self.mlp_head = nn.Sequential( | ||
nn.LayerNorm(dim), | ||
nn.Linear(dim, num_classes) | ||
) | ||
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def forward(self, img): | ||
x = self.to_patch_embedding(img) | ||
b, f, n, _ = x.shape | ||
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spatial_cls_tokens = repeat(self.spatial_cls_token, '1 1 d -> b f 1 d', b = b, f = f) | ||
x = torch.cat((spatial_cls_tokens, x), dim = 2) | ||
x += self.pos_embedding[:, :(n + 1)] | ||
x = self.dropout(x) | ||
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x = rearrange(x, 'b f n d -> (b f) n d') | ||
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# attend across space | ||
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x = self.spatial_transformer(x) | ||
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x = rearrange(x, '(b f) n d -> b f n d', b = b) | ||
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# excise out the spatial cls tokens for temporal attention | ||
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x = x[:, :, 0] | ||
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# append temporal CLS tokens | ||
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temporal_cls_tokens = repeat(self.temporal_cls_token, '1 1 d-> b 1 d', b = b) | ||
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x = torch.cat((temporal_cls_tokens, x), dim = 1) | ||
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# attend across time | ||
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x = self.temporal_transformer(x) | ||
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x = x.mean(dim = 1) if self.pool == 'mean' else x[:, 0] | ||
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x = self.to_latent(x) | ||
return self.mlp_head(x) |