Modeling the non‑uniform retinal perception for viewport‑dependent streaming of immersive video

Viewport-dependent streaming (VDS) of immersive video typically devises the attentive viewport (or FoV - Field of View) with high-quality compression but low-quality compressed content outside of it to reduce bandwidth. It, however, assumes uniform compression within the viewport, completely neglecting visual redundancy caused by non-uniform perception in central and peripheral vision areas when consuming the content using a head-mounted display (HMD). Our work models the unequal retinal perception within the instantaneous viewport and explores using it in the VDS system for non-uniform viewport compression to further save the data volume. To this end, we assess the just-noticeable-distortion moment of the rendered viewport frame by carefully adapting image quality-related compression factors like quantization stepsize q and/or spatial resolution s zone-by-zone to explicitly derive the imperceptible quality perception threshold with respect to the eccentric angle. Independent validations show that the visual perception of the immersive images with non-uniform FoV quality guided by our model is indistinguishable from that of images with default uniform FoV quality. Our model can be flexibly integrated with the tiling strategy in popular video codecs to facilitate non-uniform viewport compression in practical VDS systems for significant bandwidth reduction (e.g., about 40% reported in our experiments) at similar visual quality.