1 files changed, 145 insertions, 0 deletions
diff --git a/text_recognizer/networks/backbones/efficientnet.py b/text_recognizer/networks/backbones/efficientnet.py
new file mode 100644
index 0000000..61dea77
--- /dev/null
+++ b/text_recognizer/networks/backbones/efficientnet.py
@@ -0,0 +1,145 @@
+"""Efficient net b0 implementation."""
+import torch
+from torch import nn
+from torch import Tensor
+
+
+class ConvNorm(nn.Module):
+    def __init__(
+        self,
+        in_channels: int,
+        out_channels: int,
+        kernel_size: int,
+        stride: int,
+        padding: int,
+        groups: int = 1,
+    ) -> None:
+        super().__init__()
+        self.block = nn.Sequential(
+            nn.Conv2d(
+                in_channels=in_channels,
+                out_channels=out_channels,
+                kernel_size=kernel_size,
+                stride=stride,
+                padding=padding,
+                groups=groups,
+                bias=False,
+            ),
+            nn.BatchNorm2d(num_features=out_channels),
+            nn.SiLU(inplace=True),
+        )
+
+    def forward(self, x: Tensor) -> Tensor:
+        return self.block(x)
+
+
+class SqueezeExcite(nn.Module):
+    def __init__(self, in_channels: int, reduce_dim: int) -> None:
+        super().__init__()
+        self.se = nn.Sequential(
+            nn.AdaptiveAvgPool2d(1),  # [C, H, W] -> [C, 1, 1]
+            nn.Conv2d(in_channels=in_channels, out_channels=reduce_dim, kernel_size=1),
+            nn.SiLU(),
+            nn.Conv2d(in_channels=reduce_dim, out_channels=in_channels, kernel_size=1),
+            nn.Sigmoid(),
+        )
+
+    def forward(self, x: Tensor) -> Tensor:
+        return x * self.se(x)
+
+
+class InvertedResidulaBlock(nn.Module):
+    def __init__(
+        self,
+        in_channels: int,
+        out_channels: int,
+        kernel_size: int,
+        stride: int,
+        padding: int,
+        expand_ratio: float,
+        reduction: int = 4,
+        survival_prob: float = 0.8,
+    ) -> None:
+        super().__init__()
+        self.survival_prob = survival_prob
+        self.use_residual = in_channels == out_channels and stride == 1
+        hidden_dim = in_channels * expand_ratio
+        self.expand = in_channels != hidden_dim
+        reduce_dim = in_channels // reduction
+
+        if self.expand:
+            self.expand_conv = ConvNorm(
+                in_channels, hidden_dim, kernel_size=3, stride=1, padding=1
+            )
+
+        self.conv = nn.Sequential(
+            ConvNorm(
+                hidden_dim, hidden_dim, kernel_size, stride, padding, groups=hidden_dim
+            ),
+            SqueezeExcite(hidden_dim, reduce_dim),
+            nn.Conv2d(
+                in_channels=hidden_dim,
+                out_channels=out_channels,
+                kernel_size=1,
+                bias=False,
+            ),
+            nn.BatchNorm2d(num_features=out_channels),
+        )
+
+    def stochastic_depth(self, x: Tensor) -> Tensor:
+        if not self.training:
+            return x
+
+        binary_tensor = (
+            torch.rand(x.shape[0], 1, 1, 1, device=x.device) < self.survival_prob
+        )
+        return torch.div(x, self.survival_prob) * binary_tensor
+
+    def forward(self, x: Tensor) -> Tensor:
+        out = self.expand_conv(x) if self.expand else x
+        if self.use_residual:
+            return self.stochastic_depth(self.conv(out)) + x
+        return self.conv(out)
+
+
+class EfficientNet(nn.Module):
+    """Efficient net b0 backbone."""
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.base_model = [
+            # expand_ratio, channels, repeats, stride, kernel_size
+            [1, 16, 1, 1, 3],
+            [6, 24, 2, 2, 3],
+            [6, 40, 2, 2, 5],
+            [6, 80, 3, 2, 3],
+            [6, 112, 3, 1, 5],
+            [6, 192, 4, 2, 5],
+            [6, 320, 1, 1, 3],
+        ]
+
+        self.backbone = self._build_b0()
+
+    def _build_b0(self) -> nn.Sequential:
+        in_channels = 32
+        layers = [ConvNorm(1, in_channels, 3, stride=2, padding=1)]
+
+        for expand_ratio, out_channels, repeats, stride, kernel_size in self.base_model:
+            for i in range(repeats):
+                layers.append(
+                    InvertedResidulaBlock(
+                        in_channels,
+                        out_channels,
+                        expand_ratio=expand_ratio,
+                        stride=stride if i == 0 else 1,
+                        kernel_size=kernel_size,
+                        padding=kernel_size // 2,
+                    )
+                )
+                in_channels = out_channels
+        layers.append(ConvNorm(in_channels, 256, kernel_size=1, stride=1, padding=0))
+
+        return nn.Sequential(*layers)
+
+    def forward(self, x: Tensor) -> Tensor:
+        return self.backbone(x)