FCS: Feature Calibration and Separation for Non-Exemplar Class Incremental Learning

Non-Exemplar Class Incremental Learning (NECIL) involves learning a classification model on a sequence of data without access to exemplars from previously encountered old classes. Such a stringent constraint always leads to catastrophic forgetting of the learned knowledge. Currently, existing methods either employ knowledge distillation techniques or preserved class prototypes to sustain prior knowledge. However, two critical issues still persist. On the one hand, as the model is continually updated, the preserved prototypes of old classes will inevitably derive from the suitable location in the feature space of the new model. On the other hand, due to the lack of exemplars, the features of new classes will take the place of similar old classes which breaks the classification boundary. To address these challenges, we propose a Feature Calibration and Separation (FCS) method for NECIL. Our approach comprises a Feature Calibration Network (FCN) that adapts prototypes of old classes to the new model via optimal transport learning, approximating the drift of prototypes caused by model evolution. Additionally, we also propose a Prototype-Involved Contrastive Loss (PIC) that enhances feature separation among different classes. Specifically, to mitigate the boundary distortion arising from the interplay of classes from different learning stages, prototypes are involved in pushing the feature of new classes away from the old classes. Extensive experiments on three datasets with different settings have demonstrated the superiority of our FCS method against the state-of-the-art class incremental learning approaches. Code is available at https://github.com/zhoujiahuan1991/CVPR2024-FCS.