  Cross-Database Micro-Expression Recognition (CDMER) aims to develop the
Micro-Expression Recognition (MER) methods with strong domain adaptability,
i.e., the ability to recognize the Micro-Expressions (MEs) of different
subjects captured by different imaging devices in different scenes. The
development of CDMER is faced with two key problems: 1) the severe feature
distribution gap between the source and target databases; 2) the feature
representation bottleneck of ME such local and subtle facial expressions. To
solve these problems, this paper proposes a novel Transfer Group Sparse
Regression method, namely TGSR, which aims to 1) optimize the measurement and
better alleviate the difference between the source and target databases, and 2)
highlight the valid facial regions to enhance extracted features, by the
operation of selecting the group features from the raw face feature, where each
region is associated with a group of raw face feature, i.e., the salient facial
region selection. Compared with previous transfer group sparse methods, our
proposed TGSR has the ability to select the salient facial regions, which is
effective in alleviating the aforementioned problems for better performance and
reducing the computational cost at the same time. We use two public ME
databases, i.e., CASME II and SMIC, to evaluate our proposed TGSR method.
Experimental results show that our proposed TGSR learns the discriminative and
explicable regions, and outperforms most state-of-the-art
subspace-learning-based domain-adaptive methods for CDMER.
