  Facial action unit recognition has many applications from market research to
psychotherapy and from image captioning to entertainment. Despite its recent
progress, deployment of these models has been impeded due to their limited
generalization to unseen people and demographics. This work conducts an
in-depth analysis of performance across several dimensions: individuals(40
subjects), genders (male and female), skin types (darker and lighter), and
databases (BP4D and DISFA). To help suppress the variance in data, we use the
notion of self-supervised denoising autoencoders to design a method for deep
face normalization(DeepFN) that transfers facial expressions of different
people onto a common facial template which is then used to train and evaluate
facial action recognition models. We show that person-independent models yield
significantly lower performance (55% average F1 and accuracy across 40
subjects) than person-dependent models (60.3%), leading to a generalization gap
of 5.3%. However, normalizing the data with the newly introduced DeepFN
significantly increased the performance of person-independent models (59.6%),
effectively reducing the gap. Similarly, we observed generalization gaps when
considering gender (2.4%), skin type (5.3%), and dataset (9.4%), which were
significantly reduced with the use of DeepFN. These findings represent an
important step towards the creation of more generalizable facial action unit
recognition systems.
