Joint image-instance spatial–temporal attention for few-shot action recognition

Few-shot Action Recognition (FSAR) constitutes a crucial challenge in computer vision, entailing the recognition of actions from a limited set of examples. Recent approaches mainly focus on employing image-level features to construct temporal dependencies and generate prototypes for each action category. However, a considerable number of these methods utilize mainly image-level features that incorporate background noise and focus insufficiently on real foreground (action-related instances), thereby compromising the recognition capability, particularly in the few-shot scenario. To tackle this issue, we propose a novel joint Image-Instance level Spatial–temporal attention approach (I${}^2$ST) for Few-shot Action Recognition. The core concept of I${}^2$ST is to perceive the action-related instances and integrate them with image features via spatial–temporal attention. Specifically, I${}^2$ST consists of two key components: Action-related Instance Perception and Joint Image-Instance Spatial–temporal Attention. Given the basic representations from the feature extractor, the Action-related Instance Perception is introduced to perceive action-related instances under the guidance of a text-guided segmentation model. Subsequently, the Joint Image-Instance Spatial–temporal Attention is used to construct the feature dependency between instances and images. To enhance the prototype representations of different categories of videos, a pair of spatial–temporal attention sub-modules is introduced to combine image features and instance embeddings across both temporal and spatial dimensions, and a global fusion sub-module is utilized to aggregate global contextual information, then robust action video prototypes can be formed. Finally, based on the video prototype, a Global–Local Prototype Matching is performed for reliable few-shot video matching. In this manner, our proposed I${}^2$ST can effectively exploit the foreground instance-level cues and model more accurate spatial–temporal relationships for the complex few-shot video recognition scenarios. Extensive experiments across standard few-shot benchmarks demonstrate that the proposed framework outperforms existing methods and achieves state-of-the-art performance under various few-shot settings.