Traffic signs are important facilities to ensure traffic safety and smooth
flow, but may be damaged due to many reasons, which poses a great safety
hazard. Therefore, it is important to study a method to detect damaged traffic
signs. Existing object detection techniques for damaged traffic signs are still
absent. Since damaged traffic signs are closer in appearance to normal ones, it
is difficult to capture the detailed local damage features of damaged traffic
signs using traditional object detection methods. In this paper, we propose an
improved object detection method based on YOLOv5s, namely MFL-YOLO (Mutual
Feature Levels Loss enhanced YOLO). We designed a simple cross-level loss
function so that each level of the model has its own role, which is beneficial
for the model to be able to learn more diverse features and improve the fine
granularity. The method can be applied as a plug-and-play module and it does
not increase the structural complexity or the computational complexity while
improving the accuracy. We also replaced the traditional convolution and CSP
with the GSConv and VoVGSCSP in the neck of YOLOv5s to reduce the scale and
computational complexity. Compared with YOLOv5s, our MFL-YOLO improves 4.3 and
5.1 in F1 scores and mAP, while reducing the FLOPs by 8.9%. The Grad-CAM heat
map visualization shows that our model can better focus on the local details of
the damaged traffic signs. In addition, we also conducted experiments on
CCTSDB2021 and TT100K to further validate the generalization of our model.

我们提出了基于 YOLOv5s 的改进目标检测方法 MFL-YOLO（互补特征级别损失增强 YOLO），通过设计简单的跨级别损失函数，使得模型的每个级别都具有自己的作用，有助于学习更多多样化的特征并提高细粒度。相比 YOLOv5s，我们的 MFL-YOLO 在 F1 得分和 mAP 上分别提高了 4.3 和 5.1，同时减少了 8.9% 的 FLOPs。Grad-CAM 热图可视化显示我们的模型能更好地关注损坏交通标志的局部细节。此外，我们还对 CCTSDB2021 和 TT100K 进行了实验证明我们模型的泛化性。