Partial Depth Image Based Re-Rendering for Synthesized View Distortion Computation

3D video systems transmit depth maps in order to render synthesized views (SVs) at a receiver. To anticipate this purpose when processing a depth map, a sender-side depth processing algorithm (DPA), e.g. a depth encoder, can also render the SVs, compute their SV distortion (SVD), and adapt to it. This requires a low-complexity algorithm as computational resources are usually limited. We propose such an algorithm in this paper. First, we discuss a measure that relates a depth change to an SVD change using rendering. Then, we present an optimized process combining basic rendering steps, as warping, occlusion handling, interpolation, hole filling, and blending. Furthermore, we analyze which parts of an SV are affected by a depth change and modify the process to re-render only them. The resulting algorithm is significantly less complex than an unoptimized rendering-based variant and quantifies the SVD more accurately than existing estimation methods. The algorithm is used by the 3D-High Efficiency Video Coding reference software encoder as the main method for distortion computation and can also be used by other DPAs.