Training-free Graph-based Imputation of Missing Modalities in Multimodal Recommendation
This work addresses the challenge in multimodal recommendation systems where items lacking certain modalities—such as images or text—are often discarded, degrading overall performance. The paper formally characterizes this missing-modality problem and introduces a training-free graph propagation approach: it constructs an item co-purchase graph from user–item interactions and leverages graph signal interpolation to propagate available modality features to missing nodes. The method highlights the critical role of feature homophily over the item graph in enabling effective interpolation. It can be seamlessly integrated into existing recommender systems and consistently outperforms conventional imputation strategies across diverse missing-modality scenarios, while preserving—and often amplifying—the performance advantage of multimodal over unimodal recommendation models.