1. Introduction
Omnidirectional imaging is currently experiencing a surge in popularity, thanks to the advent of interactive panorama photo sharing on social media platforms, the rise of small, affordable cameras like the Ricoh Theta and Sam-sung Gear360, and the host of potential applications that arise from capturing wide field of view (FoV) in a single frame. At the same time, deep learning has never been a more useful tool for solving computer vision tasks from object recognition to 3D reconstruction. In order to fully utilize this rising form of media, we must extend existing deep learning methods to the omnidirectional domain. Unfortunately, this is not necessarily a trivial task. Due to the radically different camera models, deep networks trained on perspective images do not transfer well to omnidirectional images. Omnidirectional images replace the concept of the image plane with that of the image sphere. Yet because we require a 2D planar representation of the image, omnidirectional cameras typically provide outputs as 180° × 360° FoV equirectangular projections. This representation of the spherical image, while compact, suffers from significant horizontal distortion, especially near the poles.