POAR: Towards Open Vocabulary Pedestrian Attribute Recognition

Pedestrian attribute recognition (PAR) aims to predict the attributes of a target pedestrian. Recent methods often address the PAR problem by training a multi-label classifier with predefined attribute classes, but they can hardly exhaust all possible pedestrian attributes in the real world. To tackle this problem, we propose a novel Pedestrian Open-Attribute Recognition (POAR) approach by formulating the problem as a task of image-text search. Our approach employs a Transformer-based Encoder with a Masking Strategy (TEMS) to focus on the attributes of specific pedestrian parts (e.g., head, upper body, lower body, feet, etc.), and introduces a set of attribute tokens to encode the corresponding attributes into visual embeddings. Each attribute category is described as a natural language sentence and encoded by the text encoder. Then, we compute the similarity between the visual and text embeddings to find the best attribute descriptions for the input images. To handle multiple attributes of a single pedestrian, we propose a Many-To-Many Contrastive (MTMC) loss with masked tokens. In addition, we propose a Grouped Knowledge Distillation (GKD) method to minimize the disparity between visual embeddings and unseen attribute text embeddings. We evaluate our proposed method on three PAR datasets with an open-attribute setting. The results demonstrate the effectiveness of our method as a strong baseline for the POAR task. Our code is available at https://github.com/IvyYZ/POAR.