RNAS-MER: A Refined Neural Architecture Search with Hybrid Spatiotemporal Operations for Micro-Expression Recognition

Existing neural architecture search (NAS) methods comprise linear connected convolution operations and use ample search space to search task-driven convolution neural networks (CNN). These CNN models are computationally expensive and diminish the quality of receptive fields for tasks like micro-expression recognition (MER) with limited training samples. Therefore, we propose a refined neural architecture search strategy to search for a tiny CNN architecture for MER. In addition, we introduced a refined hybrid module (RHM) for inner-level search space and an optimal path explore network (OPEN) for outer-level search space. The RHM focuses on discovering optimal cell structures by incorporating a multilateral hybrid spatiotemporal operation space. Also, spatiotemporal attention blocks are embedded to refine the aggregated cell features. The OPEN search space aims to trace an optimal path between the cells to generate a tiny spatiotemporal CNN architecture instead of covering all possible tracks. The aggregate mix of RHM and OPEN search space availed the NAS method to robustly search and design an effective and efficient framework for MER. Compared with contemporary works, experiments reveal that the RNAS-MER is capable of bridging the gap between NAS algorithms and MER tasks. Furthermore, RNAS-MER achieves new state-of-the-art performances on challenging MER benchmarks, including 0.8511%, 0.7620%, 0.9078% and 0.8235% UAR on COMPOSITE, SMIC, CASME-II and SAMM datasets respectively.