  Object detection is an important computer vision task with plenty of
real-world applications; therefore, how to enhance its robustness against
adversarial attacks has emerged as a crucial issue. However, most of the
previous defense methods focused on the classification task and had few
analysis in the context of the object detection task. In this work, to address
the issue, we present a novel class-aware robust adversarial training paradigm
for the object detection task. For a given image, the proposed approach
generates an universal adversarial perturbation to simultaneously attack all
the occurred objects in the image through jointly maximizing the respective
loss for each object. Meanwhile, instead of normalizing the total loss with the
number of objects, the proposed approach decomposes the total loss into
class-wise losses and normalizes each class loss using the number of objects
for the class. The adversarial training based on the class weighted loss can
not only balances the influence of each class but also effectively and evenly
improves the adversarial robustness of trained models for all the object
classes as compared with the previous defense methods. Furthermore, with the
recent development of fast adversarial training, we provide a fast version of
the proposed algorithm which can be trained faster than the traditional
adversarial training while keeping comparable performance. With extensive
experiments on the challenging PASCAL-VOC and MS-COCO datasets, the evaluation
results demonstrate that the proposed defense methods can effectively enhance
the robustness of the object detection models.
