Unleashing the Potential of Hierarchical Region Clues for Open-Vocabulary Multi-Label Classification

Open-vocabulary multi-label classification (OV-MLC) aims to leverage the rich multi-modal knowledge from Vision-language pre-training (VLP) models to further improve the recognition ability for unseen (novel) classes beyond the training set in multi-label scenarios. Existing OV-MLC methods only perform predictions on single hierarchical regions, and aggregate the prediction scores of these regions through simple <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">top-k</i> mean pooling. This fails to unleash the potential of rich hierarchical region clues in multi-label images and does not fully exploit the discriminative information from all regions in the image, resulting in sub-optimal performance. In this work, we propose a novel OV-MLC framework to fully harness the power of multiple hierarchical region clues. Specifically, we first design a hierarchical clue gathering (HCG) module to gather different hierarchical clues, enabling more precise recognition of multiple object categories with different sizes in a multi-label image. Then, by viewing multi-label classification as single-label classification of each region within the image, we present a novel hierarchical score aggregation (HSA) approach, thereby better utilizing the predictions of each image region for each class. We also utilize a well-designed region selection strategy (RSS) to eliminate noise or background regions in an image that are irrelevant to classification, achieving higher multi-label classification accuracy. In addition, we propose a hybrid prompt learning (HPL) strategy to enhance visual-semantic consistency while preserving the generalization capability of label embeddings for unseen classes. Extensive experiments on public benchmark datasets demonstrate that our method significantly outperforms the current state-of-the-art.