diff --git a/README.md b/README.md index 3be2dc0..ea188a1 100644 --- a/README.md +++ b/README.md @@ -19,6 +19,7 @@ - [CrossFormer](#crossformer) - [RegionViT](#regionvit) - [ScalableViT](#scalablevit) +- [SepViT](#sepvit) - [NesT](#nest) - [MobileViT](#mobilevit) - [Masked Autoencoder](#masked-autoencoder) @@ -559,13 +560,42 @@ model = ScalableViT( reduction_factor = (8, 4, 2, 1), # downsampling of the key / values in SSA. in the paper, this was represented as (reduction_factor ** -2) window_size = (64, 32, None, None), # window size of the IWSA at each stage. None means no windowing needed dropout = 0.1, # attention and feedforward dropout -).cuda() +) -img = torch.randn(1, 3, 256, 256).cuda() +img = torch.randn(1, 3, 256, 256) preds = model(img) # (1, 1000) ``` +## SepViT + + + +Another Bytedance AI paper, it proposes a depthwise-pointwise self-attention layer that seems largely inspired by mobilenet's depthwise-separable convolution. The most interesting aspect is the reuse of the feature map from the depthwise self-attention stage as the values for the pointwise self-attention, as shown in the diagram above. + +I have decided to include only the version of `SepViT` with this specific self-attention layer, as the grouped attention layers are not remarkable nor novel, and the authors were not clear on how they treated the window tokens for the group self-attention layer. Besides, it seems like with `DSSA` layer alone, they were able to beat Swin. + +ex. SepViT-Lite + +```python +import torch +from vit_pytorch.sep_vit import SepViT + +v = SepViT( + num_classes = 1000, + dim = 32, # dimensions of first stage, which doubles every stage (32, 64, 128, 256) for SepViT-Lite + dim_head = 32, # attention head dimension + heads = (1, 2, 4, 8), # number of heads per stage + depth = (1, 2, 6, 2), # number of transformer blocks per stage + window_size = 7, # window size of DSS Attention block + dropout = 0.1 # dropout +) + +img = torch.randn(1, 3, 224, 224) + +preds = v(img) # (1, 1000) +``` + ## NesT @@ -1506,6 +1536,14 @@ Coming from computer vision and new to transformers? Here are some resources tha } ``` +```bibtex +@inproceedings{Li2022SepViTSV, + title = {SepViT: Separable Vision Transformer}, + author = {Wei Li and Xing Wang and Xin Xia and Jie Wu and Xuefeng Xiao and Minghang Zheng and Shiping Wen}, + year = {2022} +} +``` + ```bibtex @misc{vaswani2017attention, title = {Attention Is All You Need}, diff --git a/images/sep-vit.png b/images/sep-vit.png new file mode 100644 index 0000000..eaff45d Binary files /dev/null and b/images/sep-vit.png differ diff --git a/setup.py b/setup.py index 5b7e043..c18cac1 100644 --- a/setup.py +++ b/setup.py @@ -3,7 +3,7 @@ from setuptools import setup, find_packages setup( name = 'vit-pytorch', packages = find_packages(exclude=['examples']), - version = '0.31.1', + version = '0.32.0', license='MIT', description = 'Vision Transformer (ViT) - Pytorch', author = 'Phil Wang', diff --git a/vit_pytorch/sep_vit.py b/vit_pytorch/sep_vit.py new file mode 100644 index 0000000..69e5fc1 --- /dev/null +++ b/vit_pytorch/sep_vit.py @@ -0,0 +1,296 @@ +from functools import partial + +import torch +from torch import nn, einsum + +from einops import rearrange, repeat +from einops.layers.torch import Rearrange, Reduce + +# helpers + +def cast_tuple(val, length = 1): + return val if isinstance(val, tuple) else ((val,) * length) + +# helper classes + +class ChanLayerNorm(nn.Module): + def __init__(self, dim, eps = 1e-5): + super().__init__() + self.eps = eps + self.g = nn.Parameter(torch.ones(1, dim, 1, 1)) + self.b = nn.Parameter(torch.zeros(1, dim, 1, 1)) + + def forward(self, x): + var = torch.var(x, dim = 1, unbiased = False, keepdim = True) + mean = torch.mean(x, dim = 1, keepdim = True) + return (x - mean) / (var + self.eps).sqrt() * self.g + self.b + +class PreNorm(nn.Module): + def __init__(self, dim, fn): + super().__init__() + self.norm = ChanLayerNorm(dim) + self.fn = fn + + def forward(self, x): + return self.fn(self.norm(x)) + +class OverlappingPatchEmbed(nn.Module): + def __init__(self, dim_in, dim_out, stride = 2): + super().__init__() + kernel_size = stride * 2 - 1 + padding = kernel_size // 2 + self.conv = nn.Conv2d(dim_in, dim_out, kernel_size, stride = stride, padding = padding) + + def forward(self, x): + return self.conv(x) + +class PEG(nn.Module): + def __init__(self, dim, kernel_size = 3): + super().__init__() + self.proj = nn.Conv2d(dim, dim, kernel_size = kernel_size, padding = kernel_size // 2, groups = dim, stride = 1) + + def forward(self, x): + return self.proj(x) + x + +# feedforward + +class FeedForward(nn.Module): + def __init__(self, dim, mult = 4, dropout = 0.): + super().__init__() + inner_dim = int(dim * mult) + self.net = nn.Sequential( + nn.Conv2d(dim, inner_dim, 1), + nn.GELU(), + nn.Dropout(dropout), + nn.Conv2d(inner_dim, dim, 1), + nn.Dropout(dropout) + ) + def forward(self, x): + return self.net(x) + +# attention + +class DSSA(nn.Module): + def __init__( + self, + dim, + heads = 8, + dim_head = 32, + dropout = 0., + window_size = 7 + ): + super().__init__() + self.heads = heads + self.scale = dim_head ** -0.5 + self.window_size = window_size + inner_dim = dim_head * heads + + self.attend = nn.Sequential( + nn.Softmax(dim = -1), + nn.Dropout(dropout) + ) + + self.to_qkv = nn.Conv1d(dim, inner_dim * 3, 1, bias = False) + + # window tokens + + self.window_tokens = nn.Parameter(torch.randn(dim)) + + # prenorm and non-linearity for window tokens + # then projection to queries and keys for window tokens + + self.window_tokens_to_qk = nn.Sequential( + nn.LayerNorm(dim_head), + nn.GELU(), + Rearrange('b h n c -> b (h c) n'), + nn.Conv1d(inner_dim, inner_dim * 2, 1, groups = heads), + Rearrange('b (h c) n -> b h n c', h = heads), + ) + + # window attention + + self.window_attend = nn.Sequential( + nn.Softmax(dim = -1), + nn.Dropout(dropout) + ) + + self.to_out = nn.Sequential( + nn.Conv2d(inner_dim, dim, 1), + nn.Dropout(dropout) + ) + + def forward(self, x): + """ + einstein notation + + b - batch + c - channels + w1 - window size (height) + w2 - also window size (width) + i - sequence dimension (source) + j - sequence dimension (target dimension to be reduced) + h - heads + x - height of feature map divided by window size + y - width of feature map divided by window size + """ + + batch, height, width, heads, wsz = x.shape[0], *x.shape[-2:], self.heads, self.window_size + assert (height % wsz) == 0 and (width % wsz) == 0, f'height {height} and width {width} must be divisible by window size {wsz}' + num_windows = (height // wsz) * (width // wsz) + + # fold in windows for "depthwise" attention - not sure why it is named depthwise when it is just "windowed" attention + + x = rearrange(x, 'b c (h w1) (w w2) -> (b h w) c (w1 w2)', w1 = wsz, w2 = wsz) + + # add windowing tokens + + w = repeat(self.window_tokens, 'c -> b c 1', b = x.shape[0]) + x = torch.cat((w, x), dim = -1) + + # project for queries, keys, value + + q, k, v = self.to_qkv(x).chunk(3, dim = 1) + + # split out heads + + q, k, v = map(lambda t: rearrange(t, 'b (h d) ... -> b h (...) d', h = heads), (q, k, v)) + + # scale + + q = q * self.scale + + # similarity + + dots = einsum('b h i d, b h j d -> b h i j', q, k) + + # attention + + attn = self.attend(dots) + + # aggregate values + + out = torch.matmul(attn, v) + + # split out windowed tokens + + window_tokens, windowed_fmaps = out[:, :, 0], out[:, :, 1:] + + # early return if there is only 1 window + + if num_windows == 1: + fmap = rearrange(windowed_fmaps, '(b x y) h (w1 w2) d -> b (h d) (x w1) (y w2)', x = height // wsz, y = width // wsz, w1 = wsz, w2 = wsz) + return self.to_out(fmap) + + # carry out the pointwise attention, the main novelty in the paper + + window_tokens = rearrange(window_tokens, '(b x y) h d -> b h (x y) d', x = height // wsz, y = width // wsz) + windowed_fmaps = rearrange(windowed_fmaps, '(b x y) h n d -> b h (x y) n d', x = height // wsz, y = width // wsz) + + # windowed queries and keys (preceded by prenorm activation) + + w_q, w_k = self.window_tokens_to_qk(window_tokens).chunk(2, dim = -1) + + # scale + + w_q = w_q * self.scale + + # similarities + + w_dots = einsum('b h i d, b h j d -> b h i j', w_q, w_k) + + w_attn = self.window_attend(w_dots) + + # aggregate the feature maps from the "depthwise" attention step (the most interesting part of the paper, one i haven't seen before) + + aggregated_windowed_fmap = einsum('b h i j, b h j w d -> b h i w d', w_attn, windowed_fmaps) + + # fold back the windows and then combine heads for aggregation + + fmap = rearrange(aggregated_windowed_fmap, 'b h (x y) (w1 w2) d -> b (h d) (x w1) (y w2)', x = height // wsz, y = width // wsz, w1 = wsz, w2 = wsz) + return self.to_out(fmap) + +class Transformer(nn.Module): + def __init__( + self, + dim, + depth, + dim_head = 32, + heads = 8, + ff_mult = 4, + dropout = 0., + norm_output = True + ): + super().__init__() + self.layers = nn.ModuleList([]) + + for ind in range(depth): + self.layers.append(nn.ModuleList([ + PreNorm(dim, DSSA(dim, heads = heads, dim_head = dim_head, dropout = dropout)), + PreNorm(dim, FeedForward(dim, mult = ff_mult, dropout = dropout)), + ])) + + self.norm = ChanLayerNorm(dim) if norm_output else nn.Identity() + + def forward(self, x): + for attn, ff in self.layers: + x = attn(x) + x + x = ff(x) + x + + return self.norm(x) + +class SepViT(nn.Module): + def __init__( + self, + *, + num_classes, + dim, + depth, + heads, + window_size = 7, + dim_head = 32, + ff_mult = 4, + channels = 3, + dropout = 0. + ): + super().__init__() + self.to_patches = nn.Conv2d(channels, dim, 7, stride = 4, padding = 3) + + assert isinstance(depth, tuple), 'depth needs to be tuple if integers indicating number of transformer blocks at that stage' + + num_stages = len(depth) + + dims = tuple(map(lambda i: (2 ** i) * dim, range(num_stages))) + dims = (channels, *dims) + dim_pairs = tuple(zip(dims[:-1], dims[1:])) + + strides = (4, *((2,) * (num_stages - 1))) + + hyperparams_per_stage = [heads, window_size] + hyperparams_per_stage = list(map(partial(cast_tuple, length = num_stages), hyperparams_per_stage)) + assert all(tuple(map(lambda arr: len(arr) == num_stages, hyperparams_per_stage))) + + self.layers = nn.ModuleList([]) + + for ind, ((layer_dim_in, layer_dim), layer_depth, layer_stride, layer_heads, layer_window_size) in enumerate(zip(dim_pairs, depth, strides, *hyperparams_per_stage)): + is_last = ind == (num_stages - 1) + + self.layers.append(nn.ModuleList([ + OverlappingPatchEmbed(layer_dim_in, layer_dim, stride = layer_stride), + PEG(layer_dim), + Transformer(dim = layer_dim, depth = layer_depth, heads = layer_heads, ff_mult = ff_mult, dropout = dropout, norm_output = not is_last), + ])) + + self.mlp_head = nn.Sequential( + Reduce('b d h w -> b d', 'mean'), + nn.LayerNorm(dims[-1]), + nn.Linear(dims[-1], num_classes) + ) + + def forward(self, x): + + for ope, peg, transformer in self.layers: + x = ope(x) + x = peg(x) + x = transformer(x) + + return self.mlp_head(x)