  Objective quality assessment of stereoscopic panoramic images becomes a
challenging problem owing to the rapid growth of 360-degree contents. Different
from traditional 2D image quality assessment (IQA), more complex aspects are
involved in 3D omnidirectional IQA, especially unlimited field of view (FoV)
and extra depth perception, which brings difficulty to evaluate the quality of
experience (QoE) of 3D omnidirectional images. In this paper, we propose a
multi-viewport based fullreference stereo 360 IQA model. Due to the freely
changeable viewports when browsing in the head-mounted display (HMD), our
proposed approach processes the image inside FoV rather than the projected one
such as equirectangular projection (ERP). In addition, since overall QoE
depends on both image quality and depth perception, we utilize the features
estimated by the difference map between left and right views which can reflect
disparity. The depth perception features along with binocular image qualities
are employed to further predict the overall QoE of 3D 360 images. The
experimental results on our public Stereoscopic OmnidirectionaL Image quality
assessment Database (SOLID) show that the proposed method achieves a
significant improvement over some well-known IQA metrics and can accurately
reflect the overall QoE of perceived images.
