Facial Micro-Expressions: An Overview

Micro-expression (ME) is an involuntary, fleeting, and subtle facial expression. It may occur in high-stake situations when people attempt to conceal or suppress their true feelings. Therefore, MEs can provide essential clues to people's true feelings and have plenty of potential applications, such as national security, clinical diagnosis, and interrogations. In recent years, ME analysis has gained much attention in various fields due to its practical importance, especially automatic ME analysis in computer vision as MEs are difficult to process by naked eyes. In this survey, we provide a comprehensive review of ME development in the field of computer vision, from the ME studies in psychology and early attempts in computer vision to various computational ME analysis methods and future directions. Four main tasks in ME analysis are specifically discussed, including ME spotting, ME recognition, ME action unit detection, and ME generation in terms of the approaches, advance developments, and challenges. Through this survey, readers can understand MEs in both aspects of psychology and computer vision, and apprehend the future research direction in ME analysis.