A Magnitude and Angle Combined Optical Flow Feature for Micro-Expression Spotting

Micro-Expression (ME) spotting is a crucial step for emotion analysis to detect people's true emotions. However, the short duration, small motion amplitude and limited sample number make accurate spotting and ME-locating challenging. To address these problems, we make two contributions in this paper, including an ME dataset SDU2 and a spotting method. The dataset SDU2 contains hybrid expressions of 1602 video clips labeled by professional psychologists, covering 6 main categories of emotions with balanced distribution. Our ME spotting method is based on a magnitude and angle combined optical flow feature, exploiting the angle information which has been overlooked by other spotting methods. In this method, we select four most discriminative Regions of Interest (ROIs) and determine the appearance of MEs using the proposed feature and a novel decision criterion based on the characteristic of the optical flow angle and magnitude. We have conducted experiments on SDU2 and CASME II datasets. The results demonstrate that our method achieves much better performance compared to other state-of-the-art methods in terms of spotting accuracy.