Micro-Facial Movement Detection Using Individualised Baselines and Histogram-Based Descriptors

Detecting micro-facial movements in a video sequence is the first step in realising a system that can pick out rapid movements automatically as a person is being recorded. This paper proposes a new method of micro-movement detection by applying Histogram of Oriented Gradients as a feature descriptor on our in-house high-speed video dataset of spontaneous micro-facial movements. Firstly the algorithm aligns and crops faces for each video using automatic facial point detection and affine transformation. Then a de-noising algorithm is applied to each video before splitting them into blocks where the Histogram of Oriented Gradient features are calculated for each frame in every video block. The Chi-Squared distance measure is then used to calculate dissimilarity in the spatial appearance between frames at a set interval. The final feature vector is calculated after normalisation of the raw distance values and peak detection is applied to 'spot' micro-facial movements. An individualised baseline threshold is used to determine the value a peak must exceed to be classed as a movement. The result is compared with a benchmark algorithm - feature difference analysis techniques for micro-facial movements using Local Binary Patterns. Results indicate the proposed method achieves higher Recall of 0.8429 and F1-measure of 0.7672.