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models/classifier.py

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+"""
+调度分类器模型
+
+轻量 CNN 分类器，用于判断验证码类型 (normal / math / 3d)。
+不同类型验证码视觉差异大，分类任务简单。
+
+架构: 4 层卷积 + GAP + FC
+输入: 灰度图 1×64×128
+输出: softmax 概率分布 (num_types 个类别)
+体积目标: < 500KB
+"""
+
+import torch
+import torch.nn as nn
+
+
+class CaptchaClassifier(nn.Module):
+    """
+    轻量分类器。
+
+    4 层卷积 (每层 Conv + BN + ReLU + MaxPool)
+    → 全局平均池化 → 全连接 → 输出类别数。
+    """
+
+    def __init__(self, num_types: int = 3):
+        super().__init__()
+        self.num_types = num_types
+
+        self.features = nn.Sequential(
+            # block 1: 1 -> 16, 64x128 -> 32x64
+            nn.Conv2d(1, 16, kernel_size=3, padding=1),
+            nn.BatchNorm2d(16),
+            nn.ReLU(inplace=True),
+            nn.MaxPool2d(2, 2),
+
+            # block 2: 16 -> 32, 32x64 -> 16x32
+            nn.Conv2d(16, 32, kernel_size=3, padding=1),
+            nn.BatchNorm2d(32),
+            nn.ReLU(inplace=True),
+            nn.MaxPool2d(2, 2),
+
+            # block 3: 32 -> 64, 16x32 -> 8x16
+            nn.Conv2d(32, 64, kernel_size=3, padding=1),
+            nn.BatchNorm2d(64),
+            nn.ReLU(inplace=True),
+            nn.MaxPool2d(2, 2),
+
+            # block 4: 64 -> 64, 8x16 -> 4x8
+            nn.Conv2d(64, 64, kernel_size=3, padding=1),
+            nn.BatchNorm2d(64),
+            nn.ReLU(inplace=True),
+            nn.MaxPool2d(2, 2),
+        )
+
+        # 全局平均池化 → 输出 (batch, 64, 1, 1)
+        self.gap = nn.AdaptiveAvgPool2d(1)
+
+        self.classifier = nn.Linear(64, num_types)
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        """
+        Args:
+            x: (batch, 1, 64, 128) 灰度图
+
+        Returns:
+            logits: (batch, num_types)  未经 softmax 的原始输出
+        """
+        x = self.features(x)
+        x = self.gap(x)              # (B, 64, 1, 1)
+        x = x.view(x.size(0), -1)    # (B, 64)
+        x = self.classifier(x)       # (B, num_types)
+        return x