  To render a spherical (360 degree or omnidirectional) image on planar
displays, a 2D image -- called as viewport -- must be obtained by projecting a
sphere region on a plane, according to the users viewing direction and a
predefined field of view (FoV). However, any sphere to plan projection
introduces geometric distortions, such as object stretching and/or bending of
straight lines, which intensity increases with the considered FoV. In this
paper, a fully automatic content-aware projection is proposed, aiming to reduce
the geometric distortions when high FoVs are used. This new projection is based
on the Pannini projection, whose parameters are firstly globally optimized
according to the image content, followed by a local conformality improvement of
relevant viewport objects. A crowdsourcing subjective test showed that the
proposed projection is the most preferred solution among the considered
state-of-the-art sphere to plan projections, producing viewports with a more
pleasant visual quality.
