Subjective and Viewport-based Objective Quality Assessment of 360-degree videos.

Visual distortions in processed 360-degree visual content and consumed through head-mounted displays (HMDs) may be perceived very differently when compared to traditional 2D content. Thus, new subjective and objective quality assessment methods for this emerging type of content are required. Aiming at better understanding how compression-related artifacts affect the overall perceived quality, this paper presents a subjective quality assessment study focused on 360-degree video when consumed through HMDs and analyzes the performance of objective quality assessment metrics to correlate with the gathered subjective scores. In contrast to previous related work, the proposed study focuses on the equiangular cubemap projection and includes specific visual distortions (blur, blockiness, H. 264 compression, and cubemap seams) on both monoscopic and stereoscopic 360-degree video sequences. The objective metrics performance analysis are based on both metrics computed in the projection domain and in viewports, which is closer to what the user sees when watching 360-degree videos in HMDs. The proposed subjective dataset and objective metrics analysis serve as a benchmark in the development of new perceptually-optimized quality assessment algorithms for 360-degree videos, which is overall still an open research problem.