release MobileViT, from @murufeng

Author: lucidrains

README.md

@@ -554,17 +554,17 @@ pred = nest(img) # (1, 1000)
 
 <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
+This <a href="https://arxiv.org/abs/2110.02178">paper</a> introduce MobileViT, a light-weight and general purpose 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)
 
-```
+```python
 import torch
 from vit_pytorch.mobile_vit import MobileViT
 
 mbvit_xs = MobileViT(
-    image_size=(256, 256),
+    image_size = (256, 256),
     dims = [96, 120, 144],
     channels = [16, 32, 48, 48, 64, 64, 80, 80, 96, 96, 384],
     num_classes = 1000
@@ -1190,6 +1190,17 @@ Coming from computer vision and new to transformers? Here are some resources tha
 }
 ```
 
+```bibtex
+@misc{mehta2021mobilevit,
+    title   = {MobileViT: Light-weight, General-purpose, and Mobile-friendly Vision Transformer},
+    author  = {Sachin Mehta and Mohammad Rastegari},
+    year    = {2021},
+    eprint  = {2110.02178},
+    archivePrefix = {arXiv},
+    primaryClass = {cs.CV}
+}
+```
+
 ```bibtex
 @misc{vaswani2017attention,
     title   = {Attention Is All You Need},

setup.py

@@ -3,7 +3,7 @@
 setup(
   name = 'vit-pytorch',
   packages = find_packages(exclude=['examples']),
-  version = '0.24.3',
+  version = '0.25.0',
   license='MIT',
   description = 'Vision Transformer (ViT) - Pytorch',
   author = 'Phil Wang',

vit_pytorch/mobile_vit.py

@@ -9,9 +9,9 @@
 import torch.nn as nn
 
 from einops import rearrange
+from einops.layers.torch import Reduce
 
 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)
@@ -20,7 +20,7 @@ def _make_divisible(v, divisor, min_value=None):
     return new_v
 
 
-def Conv_BN_ReLU(inp, oup, kernel, stride=1):
+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),
@@ -63,8 +63,6 @@ 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
 
@@ -74,7 +72,7 @@ def __init__(self, dim, heads=8, dim_head=64, dropout=0.):
         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)
@@ -96,6 +94,7 @@ def __init__(self, dim, depth, heads, dim_head, mlp_dim, dropout = 0.):
                 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
@@ -136,23 +135,24 @@ def __init__(self, inp, oup, stride=1, expand_ratio=4):
             )
 
     def forward(self, x):
+        out = self.conv(x)
+
         if self.identity:
-            return x + self.conv(x)
-        else:
-            return self.conv(x)
+            out = out + x
+        return out
 
 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.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)
+        self.conv4 = conv_bn_relu(2 * channel, channel, kernel_size)
 
     def forward(self, x):
         y = x.clone()
@@ -165,8 +165,7 @@ def forward(self, x):
         _, _, 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)
+        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)
@@ -176,54 +175,65 @@ def forward(self, x):
 
 
 class MobileViT(nn.Module):
-    def __init__(self, image_size, dims, channels, num_classes, expansion=4, kernel_size=3, patch_size=(2, 2)):
+    def __init__(
+        self,
+        image_size,
+        dims,
+        channels,
+        num_classes,
+        expansion = 4,
+        kernel_size = 3,
+        patch_size = (2, 2),
+        depths = (2, 4, 3)
+    ):
         super().__init__()
+        assert len(dims) == 3, 'dims must be a tuple of 3'
+        assert len(depths) == 3, 'depths must be a tuple of 3'
+
         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)
+        init_dim, *_, last_dim = channels
+
+        self.conv1 = conv_bn_relu(3, init_dim, kernel=3, stride=2)
+
+        self.stem = nn.ModuleList([])
+        self.stem.append(MV2Block(channels[0], channels[1], 1, expansion))
+        self.stem.append(MV2Block(channels[1], channels[2], 2, expansion))
+        self.stem.append(MV2Block(channels[2], channels[3], 1, expansion))
+        self.stem.append(MV2Block(channels[2], channels[3], 1, expansion))
+    
+        self.trunk = nn.ModuleList([])
+        self.trunk.append(nn.ModuleList([
+            MV2Block(channels[3], channels[4], 2, expansion),
+            MobileViTBlock(dims[0], depths[0], channels[5], kernel_size, patch_size, int(dims[0] * 2))
+        ]))
+
+        self.trunk.append(nn.ModuleList([
+            MV2Block(channels[5], channels[6], 2, expansion),
+            MobileViTBlock(dims[1], depths[1], channels[7], kernel_size, patch_size, int(dims[1] * 4))
+        ]))
+
+        self.trunk.append(nn.ModuleList([
+            MV2Block(channels[7], channels[8], 2, expansion),
+            MobileViTBlock(dims[2], depths[2], channels[9], kernel_size, patch_size, int(dims[2] * 4))
+        ]))
+
+        self.to_logits = nn.Sequential(
+            conv_1x1_bn(channels[-2], last_dim),
+            Reduce('b c h w -> b c', 'mean'),
+            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)
+        for conv in self.stem:
+            x = conv(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
+        for conv, attn in self.trunk:
+            x = conv(x)
+            x = attn(x)
 
+        return self.to_logits(x)