APSNet: Toward Adaptive Point Sampling for Efficient 3D Action Recognition

Observing that it is still a challenging task to deploy 3D action recognition methods in real-world scenarios, in this work, we investigate the accuracy-efficiency trade-off for 3D action recognition. We first introduce a simple and efficient backbone network structure for 3D action recognition, in which we directly extract the geometry and motion representations from the raw point cloud videos through a set of simple operations (i.e., coordinate offset generation and mini-PoinNet). Based on the backbone network, we propose an end-to-end optimized network called adaptive point sampling network (APSNet) to achieve the accuracy-efficiency trade-off, which mainly consists of three stages: the coarse feature extraction stage, the decision making stage, and the fine feature extraction stage. In APSNet, we adaptively decide the optimal resolutions (i.e., the optimal number of points) for each pair of frames based on any input point cloud video under the given computational complexity constraint. Comprehensive experiments on multiple benchmark datasets demonstrate the effectiveness and efficiency of our newly proposed APSNet for 3D action recognition.