Learning to Identify Seen Unseen and Unknown in the Open World: A Practical Setting for Zero-Shot Learning

Sethupathy Parameswaran, Yuan Fang, Chandan Gautam, Savitha Ramasamy, Xiaoli Li; Proceedings of the Winter Conference on Applications of Computer Vision (WACV), 2025, pp. 6868-6878

As vision-language models advance addressing the Zero-Shot Learning (ZSL) problem in the open world becomes increasingly crucial. Specifically a robust model must handle three types of samples during inference: seen classes with visual and semantic information provided in training unseen classes with only the semantic information in training and unknown samples with no prior information from training. Existing methods either handle seen and unseen classes together (ZSL) or seen and unknown classes (known as Open-Set Recognition OSR). However none addresses the simultaneous handling of all three which we term Open-Set Zero-Shot Learning (OZSL). To address this problem we propose a two-stage approach for OZSL that recognizes seen unseen and unknown samples. The first stage classifies samples as either seen or not while the second stage distinguishes unseen from unknown. Furthermore we introduce a cross-stage knowledge transfer mechanism that leverages semantic relationships between seen and unseen classes to enhance learning in the second stage. Extensive experiments demonstrate the efficacy of the proposed approach compared to naively combining existing ZSL and OSR methods. The code is available at https://github.com/smufang/OZSL.