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Intra Predictive Depth Map Coding using Flexible Block Partitioning

Lucas, L. ; Wegner, KW ; Rodrigues, Nuno M. M. ; Pagliari, C.L.P. ; Silva, E. ; Faria, S.M.M.

IEEE Trans. on Image Processing Vol. 24, Nº 11, pp. 4055 - 4068, November, 2015.

ISSN (print): 1057-7149
ISSN (online): 1057-7149

Journal Impact Factor: 3,315 (in 2008)

Digital Object Identifier: 10.1109/TIP.2015.2456509

Abstract
A complete encoding solution for efficient intra-based depth map compression is proposed in this paper. The algorithm, denominated Predictive Depth Coding (PDC), was specifically developed to efficiently represent the characteristics of depth maps, mostly composed by smooth areas delimited by sharp edges. At its core, PDC involves a directional intra prediction framework and a straightforward residue coding method, combined with an optimised flexible block partitioning scheme. In order to improve the algorithm in the presence of depth edges that cannot be efficiently predicted by the directional modes, a constrained depth modelling mode, based on explicit edge representation, was developed. For residue coding a simple and low complexity approach was investigated, using constant and linear residue modelling, depending on the prediction mode. The performance of the proposed intra depth map coding approach was evaluated based on the quality of the synthesised views using the encoded depth maps and original texture views. Experimental tests based on all-intra configuration demonstrated the superior RD performance of PDC, with average bitrate savings of 6%, when compared with the current state-of-the-art intra depth map coding solution present in the 3D extension of High Efficiency Video Coding (3D-HEVC) standard. By using view synthesis optimisation in both PDC and 3D-HEVC encoders, the average bitrate savings increases to 14.3%. This suggests that the proposed method, without using transform-based residue coding, is an efficient alternative to the current 3D-HEVC algorithm for intra depth map coding.