SVSRD: Spatial Visual and Statistical Relation Distillation for Class-Incremental Semantic Segmentation

Class-incremental semantic segmentation (CISS) aims to incrementally learn novel classes while retaining the ability to segment old classes, and suffers catastrophic forgetting since the old-class labels are unavailable. Most existing methods typically impose strict constraints on the consistency between the extracted features or output logits of each pixel from old and current models in an attempt to prevent forgetting through knowledge distillation (KD), which 1) results in a significant transfer of redundant knowledge while limiting the restoration of old classes (rigidity) due to potentially overlooking essential knowledge extraction, and 2) imposes strong constraints at the pixel level making it challenging for the model to learn novel classes (plasticity). To solve the above limitations, we propose a novel Spatial Visual and Statistical Relation Distillation (SVSRD) by applying multi-scale visual and statistical position relation distillation for CISS, which enjoys several merits. First, we introduce a region-based similarity matrix and impose a consistency constraint between current and old models, which preserves the essential visual knowledge to enhance the rigidity. Second, we propose a novel statistical feature calculation algorithm to investigate the distribution of the data and further preserve the rules of statistics through statistical consistency, which also promotes the model on the novel-class learning for improving the plasticity. Finally, the aforementioned constraints are jointly applied in multiple scales to alleviate old-class forgetting and enhance novel-class learning. Extensive experiments on Pascal-VOC 2012 and ADE20 K demonstrate that the proposed approach performs favorably against the state-of-the-art CISS methods.