Rate-complexity tradeoff for client-side free viewpoint image rendering

Free viewpoint video enables a client to interactively choose a viewpoint from which to synthesize an image via depth-image-based rendering (DIBR). However, synthesizing a novel viewpoint image using texture and depth maps from two nearby views entails a sizable computation overhead. Further, to reduce transmission rate, recent proposals synthesize the second reference view itself using texture and depth maps of the first reference view via a complex inpainting algorithm to complete large disocclusion holes in the second reference image-a small amount of auxiliary information (AI) is transmitted by sender to aid the inpainting process-resulting in an even higher computation cost. In this paper, we study the optimal tradeoff between transmission rate and client-side complexity, so that in the event that a client device is computation-constrained, complexity of DIBR-based view synthesis can be scalably reduced at the expense of a controlled increase in transmission rate. Specifically, for standard view synthesis paradigm that requires texture and depth maps of two neighboring reference views, we design a dynamic programming algorithm to select the optimal subset of intermediate virtual views for rendering and encoding at server, so that a client performs only video decoding of these views, reducing overall view synthesis complexity. For new view synthesis paradigm that synthesizes the second reference view itself from the first, we optimize the transmission of AI used to assist inpainting of large disocclusion holes, so that some computation-expensive exemplar block search operations are avoided, reducing inpainting complexity. Experimental results show that the proposed schemes can scalably and gracefully reduce client-side complexity, and the proposed optimizations achieve better rate-complexity tradeoff than competing schemes.