Early Skip/DIS: uma heurística para redução de complexidade no codificador de mapas de profundidade do 3D-HEVC

Abstract

3D videos provides a visual experience with depth perception through the usage of special displays that project a three-dimensional scene from slightly different directions for the left and right eyes. Despite this improved visual experience, the coded-video data volume tends to linearly increases with the number of processed views, mainly considering conventional 3D video formats. In this scenario emerges the Multiview plus Depth (MVD) format, which informs the distance between scene objects and the recording camera (depth maps), allowing an eficiently view-synthesis process while reducing the number of views to be transmitted. Unlike previous multiview video coding standards, 3D-HEVC is able to manipulate depth maps in an eficient way due the new defined tools which explores the depth maps characteristics. Although this fact leads to an improvement of 3D-HEVC compression eficiency, the addition of new coding tools also increases the coding process complexity. Thus, solutions, which reduces the 3D-HEVC coding time while does not affecting the compression eficiency at all, are important in this scenario. This work presents a complexity reduction heuristic for the 3D-HEVC depth maps coder, called Early Skip/DIS. Initially, an analysis about 3D-HEVC depth-maps coder is presented. This analysis showed that the 2Nx2N is the most used partitioning mode, since some eficient coding tools, like Skip and DIS, are applied exclusively over this partitioning mode. This analysis also showed that, beyond the 2Nx2N partitioning mode is the most used mode, the exclusion of the other partition modes causes an imperceptible impact in the encoding eficiency and a low impact in processing time. This fact leads to the development of an Early decision heuristic called Early Skip/DIS, which avoids the encoder checking unnecessary modes based on the RD cost generated by the Skip and DIS modes. The thresholds used in this solution are defined in an adaptively way, observing the occurrence rate of those modes as a function of its generated RD costs. Simulation results demonstrated that the proposed solution is able to reduce the depth-map coding time up to 33.7% while affecting the texture compression eficiency in 0.047% (in terms of BD-rate). The propose heuristic presented the best depth-map complexity reduction result among other related works.