Multi-view facial action unit detection via DenseNets and CapsNets

Though the standard convolutional neural networks (CNNs) have been proposed to increase the robustness of facial action unit (AU) detection regarding pose variations, it is hard to enhance detection performance because the standard CNNs are not robust enough to affine transformation. To address this issue, two novel architectures termed as AUCaps and AUCaps++ are proposed for multi-view and multi-label facial AU detection in this work. In these two architectures, one or more dense blocks and one capsule networks (CapsNets) are stacked. Specifically, The dense blocks prefixed before CapsNets are used to learn more discriminative high-level AU features, and the CapsNets is exploited to learn more view-invariant AU features. Moreover, the capsule types and digit capsule dimension are optimized to avoid the computation and storage burden caused by the dynamic routing in standard CapsNets. Because the AUCaps and AUCaps++ are trained by jointly optimizing multi-label loss of AU and reconstruction loss of viewpoint image, the proposed method could achieve high F1 score and learn human face roughly in the reconstruction images over different AUs. Numerical results of within-dataset and cross-dataset show that the average F1 scores of the proposed method outperform the competitors using hand-crafted features or deep learning features by a big margin on two public datasets.