Day 51 在预训练 ResNet18 中注入
预训练 ResNet18 模型注入方法
在预训练的 ResNet18 模型中注入自定义模块或修改现有结构时，需确保不破坏原有特征提取能力。以下是常见注入方法：
修改特定层结构通过替换或扩展特定层（如卷积层、全连接层）实现功能注入。例如，在最后一层前插入自定义模块：
import torch.nn as nn from torchvision.models import resnet18 model = resnet18(pretrained=True) model.fc = nn.Sequential( nn.Linear(512, 256), nn.ReLU(), nn.Linear(256, 10) # 修改输出维度 )插入注意力机制在中间层注入注意力模块（如SEBlock）：
class SEBlock(nn.Module): def __init__(self, channels, reduction=16): super().__init__() self.squeeze = nn.AdaptiveAvgPool2d(1) self.excitation = nn.Sequential( nn.Linear(channels, channels // reduction), nn.ReLU(), nn.Linear(channels // reduction, channels), nn.Sigmoid() ) model.layer2.add_module("se_block", SEBlock(128))特征融合注入通过跳跃连接将不同层特征融合：
class FusionModule(nn.Module): def __init__(self, in_channels): super().__init__() self.conv = nn.Conv2d(in_channels*2, in_channels, 1) def forward(self, x1, x2): x = torch.cat([x1, x2], dim=1) return self.conv(x) fusion = FusionModule(64) model.layer1.register_forward_hook(lambda m, inp, out: fusion(out, inp[0]))注入后的微调策略
分层学习率设置对注入模块使用更高学习率，预训练层采用较低学习率：
optimizer = torch.optim.SGD([ {'params': model.parameters(), 'lr': 0.001}, {'params': fusion.parameters(), 'lr': 0.01} ], momentum=0.9)渐进式解冻先冻结所有层仅训练注入模块，逐步解冻深层：
for param in model.parameters(): param.requires_grad = False fusion.train() # 后续按epoch逐步解冻layer4、layer3等验证注入效果
特征可视化使用Grad-CAM等工具比较注入前后特征响应：
from torchcam.methods import GradCAM cam_extractor = GradCAM(model, 'layer4') activations = cam_extractor(input_tensor)性能指标对比记录注入前后的验证集准确率、推理速度等关键指标，确保注入不会显著降低模型效率。典型评估流程：
with torch.no_grad(): for data in val_loader: outputs = model(data) # 计算accuracy, F1-score等rogbbs.asus.com.cn/topics/101/feeds/63030
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