Alleviating Catastrophic Forgetting of Incremental Object Detection via Within-Class and Between-Class Knowledge Distillation

Incremental object detection (IOD) task requires a model to learn continually from newly added data. However, directly fine-tuning a well-trained detection model on a new task will sharply decrease the performance on old tasks, which is known as catastrophic forgetting. Knowledge distillation, including feature distillation and response distillation, has been proven to be an effective way to alleviate catastrophic forgetting. However, previous works on feature distillation heavily rely on low-level feature information, while under-exploring the importance of high-level semantic information. In this paper, we discuss the cause of catastrophic forgetting in IOD task as destruction of semantic feature space. We propose a method that dynamically distills both semantic and feature information with consideration of both between-class discriminativeness and within-class consistency on Transformer-based detector. Between-class discriminativeness is preserved by distilling class-level semantic distance and feature distance among various categories, while within-class consistency is preserved by distilling instance-level semantic information and feature information within each category. Extensive experiments are conducted on both Pascal VOC and MS COCO benchmarks. Our method outperforms all the previous CNN-based SOTA methods under various experimental scenarios, with a remarkable mAP improvement from 36.90% to 39.80% under one-step IOD task.