Merge pull request #181 from murufeng/main

Add MobileViT

Author: lucidrains

README.md

@@ -19,6 +19,7 @@
 - [CrossFormer](#crossformer)
 - [RegionViT](#regionvit)
 - [NesT](#nest)
+- [MobileViT](#mobilevit)
 - [Masked Autoencoder](#masked-autoencoder)
 - [Simple Masked Image Modeling](#simple-masked-image-modeling)
 - [Masked Patch Prediction](#masked-patch-prediction)
@@ -549,6 +550,31 @@ img = torch.randn(1, 3, 224, 224)
 pred = nest(img) # (1, 1000)
 ```
 
+## MobileViT
+
+<img src="./images/mbvit.png" width="400px"></img>
+
+This <a href="https://arxiv.org/abs/2110.02178">paper</a> introduce MobileViT, a light-weight and generalpurpose vision transformer for mobile devices. MobileViT presents a different
+perspective for the global processing of information with transformers.
+
+You can use it with the following code (ex. mobilevit_xs)
+
+```
+import torch
+from vit_pytorch.mobile_vit import MobileViT
+
+mbvit_xs = MobileViT(
+    image_size=(256, 256),
+    dims = [96, 120, 144],
+    channels = [16, 32, 48, 48, 64, 64, 80, 80, 96, 96, 384],
+    num_classes = 1000
+)
+
+img = torch.randn(1, 3, 256, 256)
+
+pred = mbvit_xs(img) # (1, 1000)
+```
+
 ## Simple Masked Image Modeling
 
 <img src="./images/simmim.png" width="400px"/>

images/mbvit.png

@@ -0,0 +1,229 @@
+"""
+An implementation of MobileViT Model as defined in:
+MobileViT: Light-weight, General-purpose, and Mobile-friendly Vision Transformer
+Arxiv: https://arxiv.org/abs/2110.02178
+Origin Code: https://github.com/murufeng/awesome_lightweight_networks
+"""
+
+import torch
+import torch.nn as nn
+
+from einops import rearrange
+
+def _make_divisible(v, divisor, min_value=None):
+
+    if min_value is None:
+        min_value = divisor
+    new_v = max(min_value, int(v + divisor / 2) // divisor * divisor)
+    if new_v < 0.9 * v:
+        new_v += divisor
+    return new_v
+
+
+def Conv_BN_ReLU(inp, oup, kernel, stride=1):
+    return nn.Sequential(
+        nn.Conv2d(inp, oup, kernel_size=kernel, stride=stride, padding=1, bias=False),
+        nn.BatchNorm2d(oup),
+        nn.ReLU6(inplace=True)
+    )
+
+
+def conv_1x1_bn(inp, oup):
+    return nn.Sequential(
+        nn.Conv2d(inp, oup, 1, 1, 0, bias=False),
+        nn.BatchNorm2d(oup),
+        nn.ReLU6(inplace=True)
+    )
+
+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)
+
+class FeedForward(nn.Module):
+    def __init__(self, dim, hidden_dim, dropout=0.):
+        super().__init__()
+        self.ffn = nn.Sequential(
+            nn.Linear(dim, hidden_dim),
+            nn.SiLU(),
+            nn.Dropout(dropout),
+            nn.Linear(hidden_dim, dim),
+            nn.Dropout(dropout)
+        )
+
+    def forward(self, x):
+        return self.ffn(x)
+
+
+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)
+
+        self.heads = heads
+        self.scale = dim_head ** -0.5
+
+        self.attend = nn.Softmax(dim=-1)
+        self.to_qkv = nn.Linear(dim, inner_dim * 3, bias=False)
+
+        self.to_out = nn.Sequential(
+            nn.Linear(inner_dim, dim),
+            nn.Dropout(dropout)
+        ) if project_out else nn.Identity()
+
+    def forward(self, x):
+        qkv = self.to_qkv(x).chunk(3, dim=-1)
+        q, k, v = map(lambda t: rearrange(t, 'b p n (h d) -> b p h n d', h=self.heads), qkv)
+
+        dots = torch.matmul(q, k.transpose(-1, -2)) * self.scale
+        attn = self.attend(dots)
+        out = torch.matmul(attn, v)
+        out = rearrange(out, 'b p h n d -> b p n (h d)')
+        return self.to_out(out)
+
+
+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
+
+class MV2Block(nn.Module):
+    def __init__(self, inp, oup, stride=1, expand_ratio=4):
+        super(MV2Block, self).__init__()
+        assert stride in [1, 2]
+
+        hidden_dim = round(inp * expand_ratio)
+        self.identity = stride == 1 and inp == oup
+
+        if expand_ratio == 1:
+            self.conv = nn.Sequential(
+                # dw
+                nn.Conv2d(hidden_dim, hidden_dim, 3, stride, 1, groups=hidden_dim, bias=False),
+                nn.BatchNorm2d(hidden_dim),
+                nn.SiLU(),
+                # pw-linear
+                nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False),
+                nn.BatchNorm2d(oup),
+            )
+        else:
+            self.conv = nn.Sequential(
+                # pw
+                nn.Conv2d(inp, hidden_dim, 1, 1, 0, bias=False),
+                nn.BatchNorm2d(hidden_dim),
+                nn.SiLU(),
+                # dw
+                nn.Conv2d(hidden_dim, hidden_dim, 3, stride, 1, groups=hidden_dim, bias=False),
+                nn.BatchNorm2d(hidden_dim),
+                nn.SiLU(),
+                # pw-linear
+                nn.Conv2d(hidden_dim, oup, 1, 1, 0, bias=False),
+                nn.BatchNorm2d(oup),
+            )
+
+    def forward(self, x):
+        if self.identity:
+            return x + self.conv(x)
+        else:
+            return self.conv(x)
+
+class MobileViTBlock(nn.Module):
+    def __init__(self, dim, depth, channel, kernel_size, patch_size, mlp_dim, dropout=0.):
+        super().__init__()
+        self.ph, self.pw = patch_size
+
+        self.conv1 = Conv_BN_ReLU(channel, channel, kernel_size)
+        self.conv2 = conv_1x1_bn(channel, dim)
+
+        self.transformer = Transformer(dim, depth, 1, 32, mlp_dim, dropout)
+
+        self.conv3 = conv_1x1_bn(dim, channel)
+        self.conv4 = Conv_BN_ReLU(2 * channel, channel, kernel_size)
+
+    def forward(self, x):
+        y = x.clone()
+
+        # Local representations
+        x = self.conv1(x)
+        x = self.conv2(x)
+
+        # Global representations
+        _, _, h, w = x.shape
+        x = rearrange(x, 'b d (h ph) (w pw) -> b (ph pw) (h w) d', ph=self.ph, pw=self.pw)
+        x = self.transformer(x)
+        x = rearrange(x, 'b (ph pw) (h w) d -> b d (h ph) (w pw)', h=h // self.ph, w=w // self.pw, ph=self.ph,
+                      pw=self.pw)
+
+        # Fusion
+        x = self.conv3(x)
+        x = torch.cat((x, y), 1)
+        x = self.conv4(x)
+        return x
+
+
+class MobileViT(nn.Module):
+    def __init__(self, image_size, dims, channels, num_classes, expansion=4, kernel_size=3, patch_size=(2, 2)):
+        super().__init__()
+        ih, iw = image_size
+        ph, pw = patch_size
+        assert ih % ph == 0 and iw % pw == 0
+
+        L = [2, 4, 3]
+
+        self.conv1 = Conv_BN_ReLU(3, channels[0], kernel=3, stride=2)
+
+        self.mv2 = nn.ModuleList([])
+        self.mv2.append(MV2Block(channels[0], channels[1], 1, expansion))
+        self.mv2.append(MV2Block(channels[1], channels[2], 2, expansion))
+        self.mv2.append(MV2Block(channels[2], channels[3], 1, expansion))
+        self.mv2.append(MV2Block(channels[2], channels[3], 1, expansion))
+        self.mv2.append(MV2Block(channels[3], channels[4], 2, expansion))
+        self.mv2.append(MV2Block(channels[5], channels[6], 2, expansion))
+        self.mv2.append(MV2Block(channels[7], channels[8], 2, expansion))
+
+        self.mvit = nn.ModuleList([])
+        self.mvit.append(MobileViTBlock(dims[0], L[0], channels[5], kernel_size, patch_size, int(dims[0] * 2)))
+        self.mvit.append(MobileViTBlock(dims[1], L[1], channels[7], kernel_size, patch_size, int(dims[1] * 4)))
+        self.mvit.append(MobileViTBlock(dims[2], L[2], channels[9], kernel_size, patch_size, int(dims[2] * 4)))
+
+        self.conv2 = conv_1x1_bn(channels[-2], channels[-1])
+
+        self.pool = nn.AvgPool2d(ih // 32, 1)
+        self.fc = nn.Linear(channels[-1], num_classes, bias=False)
+
+    def forward(self, x):
+        x = self.conv1(x)
+        x = self.mv2[0](x)
+
+        x = self.mv2[1](x)
+        x = self.mv2[2](x)
+        x = self.mv2[3](x)
+
+        x = self.mv2[4](x)
+        x = self.mvit[0](x)
+
+        x = self.mv2[5](x)
+        x = self.mvit[1](x)
+
+        x = self.mv2[6](x)
+        x = self.mvit[2](x)
+        x = self.conv2(x)
+
+        x = self.pool(x).view(-1, x.shape[1])
+        x = self.fc(x)
+        return x
+