**Katarzyna Go´sciewska \* and Dariusz Frejlichowski**

Faculty of Computer Science and Information Technology, West Pomeranian University of Technology, Szczecin, Zolnierska 52, 71-210 Szczecin, Poland; dfrejlichowski@wi.zut.edu.pl

**\*** Correspondence: kgosciewska@wi.zut.edu.pl

Received: 04 August 2020; Accepted: 23 September 2020; Published: 25 September 2020

**Abstract:** This paper presents the idea of using simple shape features for action recognition based on binary silhouettes. Shape features are analysed as they change over time within an action sequence. It is shown that basic shape characteristics can discriminate between short, primitive actions performed by a single person. The proposed approach is tested on the Weizmann database using a various number of classes. Binary foreground masks (silhouettes) are replaced with convex hulls, which highlights some shape characteristics. Centroid locations are combined with some other simple shape descriptors. Each action sequence is represented using a vector with shape features and Discrete Fourier Transform. Classification is based on leave-one-sequence-out approach and employs Euclidean distance, correlation coefficient or C1 correlation. A list of processing steps for action recognition is explained and followed by some experiments that yielded accuracy exceeding 90%. The idea behind the presented approach is to develop a solution for action recognition that could be applied in a kind of human activity recognition system associated with the Ambient Assisted Living concept, helping adults increasing their activity levels by monitoring them during exercises.

**Keywords:** action recognition; silhouette sequences; shape features; ambient assisted living; active ageing
