Adversarial Mixture Density Network and Uncertainty-Based Joint Learning for 360 ^\circ Monocular Depth Estimation

Due to the increased demand of 360^\circ images (e.g., virtual reality), estimating 360^\circ depths via deep learning has drawn attention recently. However, all previous studies share the same fundamental limitation: a lack of data. To address the issue of data insufficiency, self-supervised learning and uncertainty-aware learning based on a mixture density network (MDN) have been actively studied and have achieved great success on various tasks. Unfortunately, under the harsh training environment of 360^\circ depth estimation tasks (e.g., a large field-of-view, distortion), we observe that the practical difficulties of self-supervised learning and MDN-based uncertainty-aware learning become a critical factor degrading the depth results. In this article, we propose an adversarial mixture density network (AMDN) and uncertainty-based joint learning to improve the depth qualities by addressing the data insufficiency issue properly. For the AMDN, architectures and objective functions of the MDN are redesigned in an adversarial manner. For uncertainty-based joint supervised and self-supervised learning, the negative effects of the self-supervised learning of 360^\circ depths are filtered out based on the epistemic uncertainties of the AMDN. Therefore, only the positive effects of self-supervised learning can be realized. Through extensive experiments, we demonstrate that the proposed approaches achieve much more accurate depths as compared with very recent studies for various datasets. Moreover, the proposed approaches also yield sophisticated uncertainties in a single forward path, in which previous studies could not.