This paper presents Ske2Grid, a new representation learning framework for improved skeleton-based action recognition. In Ske2Grid, we define a regular convolution operation upon a novel grid representation of human skeleton, which is a compact image-like grid patch constructed and learned through three novel designs. Specifically, we propose a graph-node index transform (GIT) to construct a regular grid patch through assigning the nodes in the skeleton graph one by one to the desired grid cells. To ensure that GIT is a bijection and enrich the expressiveness of the grid representation, an up-sampling transform (UPT) is learned to interpolate the skeleton graph nodes for filling the grid patch to the full. To resolve the problem when the one-step UPT is aggressive and further exploit the representation capability of the grid patch with increasing spatial size, a progressive learning strategy (PLS) is proposed which decouples the UPT into multiple steps and aligns them to multiple paired GITs through a compact cascaded design learned progressively. We construct networks upon prevailing graph convolution networks and conduct experiments on six mainstream skeleton-based action recognition datasets. Experiments show that our Ske2Grid significantly outperforms existing GCN-based solutions under different benchmark settings, without bells and whistles. Code and models are available at https://github.com/OSVAI/Ske2Grid

该研究提出了Ske2Grid，这是一个用于改进基于骨骼的动作识别的新型表示学习框架。Ske2Grid通过在人体骨骼的一种新颖的网格表示上定义规则卷积操作来构建和学习一个紧凑的图像样式的网格块，并提出了三种新的设计来保证其双射属性和增强网格表示的表达能力。经过实验证明，在六种主流基于骨骼的动作识别数据集上，Ske2Grid明显优于现有的基于图卷积网络的解决方案，且不需添加额外的修饰。

Ske2Grid: 面向动作识别的骨架到网格表示学习