improvise a max vit with register tokens

setup.py

@@ -3,7 +3,7 @@
 setup(
   name = 'vit-pytorch',
   packages = find_packages(exclude=['examples']),
-  version = '1.5.0',
+  version = '1.5.2',
   license='MIT',
   description = 'Vision Transformer (ViT) - Pytorch',
   long_description_content_type = 'text/markdown',
@@ -16,7 +16,7 @@
     'image recognition'
   ],
   install_requires=[
-    'einops>=0.6.1',
+    'einops>=0.7.0',
     'torch>=1.10',
     'torchvision'
   ],

vit_pytorch/max_vit.py

@@ -173,7 +173,7 @@ def forward(self, x):
 
         # split heads
 
-        q, k, v = map(lambda t: rearrange(t, 'b n (h d ) -> b h n d', h = h), (q, k, v))
+        q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> b h n d', h = h), (q, k, v))
 
         # scale
 

vit_pytorch/max_vit_with_registers.py

@@ -0,0 +1,339 @@
+from functools import partial
+
+import torch
+from torch import nn, einsum
+import torch.nn.functional as F
+from torch.nn import Module, ModuleList, Sequential
+
+from einops import rearrange, repeat, reduce, pack, unpack
+from einops.layers.torch import Rearrange, Reduce
+
+# helpers
+
+def exists(val):
+    return val is not None
+
+def default(val, d):
+    return val if exists(val) else d
+
+def pack_one(x, pattern):
+    return pack([x], pattern)
+
+def unpack_one(x, ps, pattern):
+    return unpack(x, ps, pattern)[0]
+
+def cast_tuple(val, length = 1):
+    return val if isinstance(val, tuple) else ((val,) * length)
+
+# helper classes
+
+def FeedForward(dim, mult = 4, dropout = 0.):
+    inner_dim = int(dim * mult)
+    return Sequential(
+        nn.LayerNorm(dim),
+        nn.Linear(dim, inner_dim),
+        nn.GELU(),
+        nn.Dropout(dropout),
+        nn.Linear(inner_dim, dim),
+        nn.Dropout(dropout)
+    )
+
+# MBConv
+
+class SqueezeExcitation(Module):
+    def __init__(self, dim, shrinkage_rate = 0.25):
+        super().__init__()
+        hidden_dim = int(dim * shrinkage_rate)
+
+        self.gate = Sequential(
+            Reduce('b c h w -> b c', 'mean'),
+            nn.Linear(dim, hidden_dim, bias = False),
+            nn.SiLU(),
+            nn.Linear(hidden_dim, dim, bias = False),
+            nn.Sigmoid(),
+            Rearrange('b c -> b c 1 1')
+        )
+
+    def forward(self, x):
+        return x * self.gate(x)
+
+class MBConvResidual(Module):
+    def __init__(self, fn, dropout = 0.):
+        super().__init__()
+        self.fn = fn
+        self.dropsample = Dropsample(dropout)
+
+    def forward(self, x):
+        out = self.fn(x)
+        out = self.dropsample(out)
+        return out + x
+
+class Dropsample(Module):
+    def __init__(self, prob = 0):
+        super().__init__()
+        self.prob = prob
+
+    def forward(self, x):
+        device = x.device
+
+        if self.prob == 0. or (not self.training):
+            return x
+
+        keep_mask = torch.FloatTensor((x.shape[0], 1, 1, 1), device = device).uniform_() > self.prob
+        return x * keep_mask / (1 - self.prob)
+
+def MBConv(
+    dim_in,
+    dim_out,
+    *,
+    downsample,
+    expansion_rate = 4,
+    shrinkage_rate = 0.25,
+    dropout = 0.
+):
+    hidden_dim = int(expansion_rate * dim_out)
+    stride = 2 if downsample else 1
+
+    net = Sequential(
+        nn.Conv2d(dim_in, hidden_dim, 1),
+        nn.BatchNorm2d(hidden_dim),
+        nn.GELU(),
+        nn.Conv2d(hidden_dim, hidden_dim, 3, stride = stride, padding = 1, groups = hidden_dim),
+        nn.BatchNorm2d(hidden_dim),
+        nn.GELU(),
+        SqueezeExcitation(hidden_dim, shrinkage_rate = shrinkage_rate),
+        nn.Conv2d(hidden_dim, dim_out, 1),
+        nn.BatchNorm2d(dim_out)
+    )
+
+    if dim_in == dim_out and not downsample:
+        net = MBConvResidual(net, dropout = dropout)
+
+    return net
+
+# attention related classes
+
+class Attention(Module):
+    def __init__(
+        self,
+        dim,
+        dim_head = 32,
+        dropout = 0.,
+        window_size = 7
+    ):
+        super().__init__()
+        assert (dim % dim_head) == 0, 'dimension should be divisible by dimension per head'
+
+        self.heads = dim // dim_head
+        self.scale = dim_head ** -0.5
+
+        self.norm = nn.LayerNorm(dim)
+        self.to_qkv = nn.Linear(dim, dim * 3, bias = False)
+
+        self.attend = nn.Sequential(
+            nn.Softmax(dim = -1),
+            nn.Dropout(dropout)
+        )
+
+        self.to_out = nn.Sequential(
+            nn.Linear(dim, dim, bias = False),
+            nn.Dropout(dropout)
+        )
+
+        # relative positional bias
+
+        self.rel_pos_bias = nn.Embedding((2 * window_size - 1) ** 2, self.heads)
+
+        pos = torch.arange(window_size)
+        grid = torch.stack(torch.meshgrid(pos, pos, indexing = 'ij'))
+        grid = rearrange(grid, 'c i j -> (i j) c')
+        rel_pos = rearrange(grid, 'i ... -> i 1 ...') - rearrange(grid, 'j ... -> 1 j ...')
+        rel_pos += window_size - 1
+        rel_pos_indices = (rel_pos * torch.tensor([2 * window_size - 1, 1])).sum(dim = -1)
+
+        self.register_buffer('rel_pos_indices', rel_pos_indices, persistent = False)
+
+    def forward(self, x):
+        device, h = x.device, self.heads
+
+        x = self.norm(x)
+
+        # project for queries, keys, values
+
+        q, k, v = self.to_qkv(x).chunk(3, dim = -1)
+
+        # split heads
+
+        q, k, v = map(lambda t: rearrange(t, 'b n (h d) -> b h n d', h = h), (q, k, v))
+
+        # scale
+
+        q = q * self.scale
+
+        # sim
+
+        sim = einsum('b h i d, b h j d -> b h i j', q, k)
+
+        # add positional bias
+
+        bias = self.rel_pos_bias(self.rel_pos_indices)
+        bias = rearrange(bias, 'i j h -> h i j')
+
+        num_registers = sim.shape[-1] - bias.shape[-1]
+        bias = F.pad(bias, (num_registers, 0, num_registers, 0), value = 0.)
+
+        sim = sim + bias
+
+        # attention
+
+        attn = self.attend(sim)
+
+        # aggregate
+
+        out = einsum('b h i j, b h j d -> b h i d', attn, v)
+
+        # combine heads out
+
+        out = rearrange(out, 'b h n d -> b n (h d)')
+        return self.to_out(out)
+
+class MaxViT(Module):
+    def __init__(
+        self,
+        *,
+        num_classes,
+        dim,
+        depth,
+        dim_head = 32,
+        dim_conv_stem = None,
+        window_size = 7,
+        mbconv_expansion_rate = 4,
+        mbconv_shrinkage_rate = 0.25,
+        dropout = 0.1,
+        channels = 3,
+        num_register_tokens = 4
+    ):
+        super().__init__()
+        assert isinstance(depth, tuple), 'depth needs to be tuple if integers indicating number of transformer blocks at that stage'
+
+        # convolutional stem
+
+        dim_conv_stem = default(dim_conv_stem, dim)
+
+        self.conv_stem = Sequential(
+            nn.Conv2d(channels, dim_conv_stem, 3, stride = 2, padding = 1),
+            nn.Conv2d(dim_conv_stem, dim_conv_stem, 3, padding = 1)
+        )
+
+        # variables
+
+        num_stages = len(depth)
+
+        dims = tuple(map(lambda i: (2 ** i) * dim, range(num_stages)))
+        dims = (dim_conv_stem, *dims)
+        dim_pairs = tuple(zip(dims[:-1], dims[1:]))
+
+        self.layers = nn.ModuleList([])
+
+        # window size
+
+        self.window_size = window_size
+
+        self.register_tokens = nn.ParameterList([])
+
+        # iterate through stages
+
+        for ind, ((layer_dim_in, layer_dim), layer_depth) in enumerate(zip(dim_pairs, depth)):
+            for stage_ind in range(layer_depth):
+                is_first = stage_ind == 0
+                stage_dim_in = layer_dim_in if is_first else layer_dim
+
+                conv = MBConv(
+                    stage_dim_in,
+                    layer_dim,
+                    downsample = is_first,
+                    expansion_rate = mbconv_expansion_rate,
+                    shrinkage_rate = mbconv_shrinkage_rate
+                )
+
+                block_attn = Attention(dim = layer_dim, dim_head = dim_head, dropout = dropout, window_size = window_size)
+                block_ff = FeedForward(dim = layer_dim, dropout = dropout)
+
+                grid_attn = Attention(dim = layer_dim, dim_head = dim_head, dropout = dropout, window_size = window_size)
+                grid_ff = FeedForward(dim = layer_dim, dropout = dropout)
+
+                register_tokens = nn.Parameter(torch.randn(num_register_tokens, layer_dim))
+
+                self.layers.append(ModuleList([
+                    conv,
+                    ModuleList([block_attn, block_ff]),
+                    ModuleList([grid_attn, grid_ff])
+                ]))
+
+                self.register_tokens.append(register_tokens)
+
+        # mlp head out
+
+        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):
+        b, w = x.shape[0], self.window_size
+
+        x = self.conv_stem(x)
+
+        for (conv, (block_attn, block_ff), (grid_attn, grid_ff)), register_tokens in zip(self.layers, self.register_tokens):
+            x = conv(x)
+
+            # block-like attention
+
+            x = rearrange(x, 'b d (x w1) (y w2) -> b x y w1 w2 d', w1 = w, w2 = w)
+
+            # prepare register tokens
+
+            r = repeat(register_tokens, 'n d -> b x y n d', b = b, x = x.shape[1],y = x.shape[2])
+            r, register_batch_ps = pack_one(r, '* n d')
+
+            x, window_ps = pack_one(x, 'b x y * d')
+            x, batch_ps  = pack_one(x, '* n d')
+            x, register_ps = pack([r, x], 'b * d')
+
+            x = block_attn(x) + x
+            x = block_ff(x) + x
+
+            r, x = unpack(x, register_ps, 'b * d')
+
+            x = unpack_one(x, batch_ps, '* n d')
+            x = unpack_one(x, window_ps, 'b x y * d')
+            x = rearrange(x, 'b x y w1 w2 d -> b d (x w1) (y w2)')
+
+            r = unpack_one(r, register_batch_ps, '* n d')
+
+            # grid-like attention
+
+            x = rearrange(x, 'b d (w1 x) (w2 y) -> b x y w1 w2 d', w1 = w, w2 = w)
+
+            # prepare register tokens
+
+            r = reduce(r, 'b x y n d -> b n d', 'mean')
+            r = repeat(r, 'b n d -> b x y n d', x = x.shape[1], y = x.shape[2])
+            r, register_batch_ps = pack_one(r, '* n d')
+
+            x, window_ps = pack_one(x, 'b x y * d')
+            x, batch_ps  = pack_one(x, '* n d')
+            x, register_ps = pack([r, x], 'b * d')
+
+            x = grid_attn(x) + x
+
+            r, x = unpack(x, register_ps, 'b * d')
+
+            x = grid_ff(x) + x
+
+            x = unpack_one(x, batch_ps, '* n d')
+            x = unpack_one(x, window_ps, 'b x y * d')
+            x = rearrange(x, 'b x y w1 w2 d -> b d (w1 x) (w2 y)')
+
+        return self.mlp_head(x)