“…For addressing the problem of MER, many approaches including conventional and deep methods have been developed to model the fleeting subtle changes of spontaneous microexpressions towards the individual-database task. The conventional methods [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18] usually extract handcrafted features, e.g., local binary patterns on three orthogonal planes (LBP-TOP) [5], [8], second-order Gaussian jet on LBP-TOP [6], LBP six intersection points (LBP-SIP) [7], local spatiotemporal directional features (LSDF) [10], spatiotemporal LBP (STLBP) [9], spatiotemporal completed local quantization patterns (STCLQP) [12], discriminative spatiotemporal LBP (DSLBP) [16], directional mean optical-flow (MDMO) [14], bi-weighted oriented optical flow (Bi-WOOF) [17] and fuzzy histogram of optical flow orientation (FHOFO) [18], and then construct a classifier, e.g., support vector machine (SVM) [5], [11], [9], [12], [17] and random forest (RF) [5], [8], [13], [15], specially for MER. Although these handcrafted features continue to improve the representation ability for MER, it is still difficult to manually design good representations for capturing quick subtle changes of micro-expressions.…”