Transductive Parameter-Free Propagation Framework for Few-Shot Distribution Rectification

Few-shot learning (FSL) is challenging due to the scarce labeled novel-class data. Researchers have to train the embedding function with auxiliary base-class data to obtain the novel-class embeddings. However, the domain gap makes the novel-class embedding unsatisfactory, as the novel class and the base class are disjoint. Recent studies prove that embedding rectification shows great potential, introduces miscellaneous variants, and achieves similar performances. Nonetheless, while each method demonstrates unique strengths, they often address distinct challenges in isolation, limiting their applicability in more complex or diverse scenarios. In this article, we take a closer look at these methods and hypothesize that a general embedding rectification framework is more essential to the model's performance. To verify our observation, we propose: 1) a distribution propagation (DisP) layer distinguishes the inter-class margin and increases intra-class aggregation, performing the task-level rectification; and 2) a prototype propagation (ProtoP) layer moves the prototype toward the ideal class center, applying the prototype-query level rectification. Our framework aims to maximize the actual data distribution. Although pseudo-labeling proves effective in achieving this goal, a significant challenge is ensuring the reliable retention of only high-confidence predictions. To overcome this, we introduce a distribution-based pseudo-labeling method pseudo-query upgrade (PseQUp) that provides more reliable pseudo-labeling samples without relying on confidence scores. We evaluate the proposed method in both transfer learning and meta-learning scenarios. Empirical experiments show the applicable and plug-and-play ability of the proposed methods.