Emotions are considered to convey much meaning in communication. Hence,
artificial methods for emotion categorization are being developed to
meet the increasing demand to introduce intelligent systems, such as
robots, into shared workspaces. Deep learning algorithms have
demonstrated limited competency in categorizing images from posed
datasets with the main features of the face being visible. However, the
use of sunglasses and face masks are common in our daily lives,
especially with the outbreak of communicable diseases such as the recent
coronavirus. Anecdotally, partial coverings of the face reduce the
effectiveness of human communication, so would this have hampering
effects on computer vision, and if so, would different emotion
categories be affected equally? Here, we analyze the performance of
emotion classification systems when faces are partially covered with
simulated sunglasses and face masks. Deep neural networks consider all
pixels in an image as equally important unlike the neuroscientific
findings on how humans recognize emotions. Hence, we propose a method
that considers different constituent parts (e.g. mouth, eyes, and jaw)
separately, giving more attention to relevant (uncovered) regions of the
face. The method is compared with three standard, partial
coverings-based and attention-based methods. We found that face
coverings worsen emotion categorization by up to 74% for the
state-of-the-art methods, whereby emotion categories are affected
differently by different coverings, e.g. clear mouth coverings have
little effect on categorizing happiness, but sadness is affected badly.
The proposed method (on average 60.43%) has significantly improved the
performance over the standard deep learning (< 46% on
average), partial coverings-based (< 47% on average), as well
as the attention-based (< 51% on average) methods for both
the CK+, KDEF, and RAF-DB datasets when faces were partially covered
with sunglasses or different face masks.