Adds squeeze and excitation (scSE) modules, resolves mapbox#157

Author: daniel-j-h

robosat/scse.py

@@ -0,0 +1,63 @@
+"""Squeeze and Excitation blocks - attention for classification and segmentation
+
+See:
+- https://arxiv.org/abs/1709.01507 - Squeeze-and-Excitation Networks
+- https://arxiv.org/abs/1803.02579 - Concurrent Spatial and Channel 'Squeeze & Excitation' in Fully Convolutional Networks
+
+"""
+
+import torch
+import torch.nn as nn
+
+
+class SpatialSqChannelEx:
+    """Spatial Squeeze and Channel Excitation (cSE) block
+       See https://arxiv.org/abs/1803.02579 Figure 1 b
+    """
+
+    def __init__(self, num_in, r):
+        super().__init__()
+        self.fc0 = Conv1x1(num_in, num_in // r)
+        self.fc1 = Conv1x1(num_in // r, num_in)
+
+    def forward(self, x):
+        xx = nn.functional.adaptive_avg_pool2d(x, 1)
+        xx = self.fc0(xx)
+        xx = nn.functional.relu(xx, inplace=True)
+        xx = self.fc1(xx)
+        xx = nn.functional.sigmoid(xx)
+        return x * xx
+
+
+class ChannelSqSpatialEx:
+    """Channel Squeeze and Spatial Excitation (sSE) block
+       See https://arxiv.org/abs/1803.02579 Figure 1 c
+    """
+
+    def __init__(self, num_in):
+        super().__init__()
+        self.conv = Conv1x1(num_in, 1)
+
+    def forward(self, x):
+        xx = self.conv(x)
+        xx = nn.functional.sigmoid(xx)
+        return x * xx
+
+
+class SpatialChannelSqChannelEx:
+    """Concurrent Spatial and Channel Squeeze and Channel Excitation (csSE) block
+       See https://arxiv.org/abs/1803.02579 Figure 1 d
+    """
+
+    def __init__(self, num_in, r=16):
+        super().__init__()
+
+        self.cse = SpatialSqChannelEx(num_in, r)
+        self.sse = ChannelSqSpatialEx(num_in)
+
+    def forward(self, x):
+        return self.cse(x) + self.sse(x)
+
+
+def Conv1x1(num_in, num_out):
+    return nn.Conv2d(num_in, num_out, kernel_size=1, bias=False)

robosat/unet.py

@@ -14,6 +14,8 @@
 
 from torchvision.models import resnet50
 
+from robosat.scse import SpatialChannelSqChannelEx
+
 
 class ConvRelu(nn.Module):
     """3x3 convolution followed by ReLU activation building block.