  Depth coding in 3D-HEVC for the multiview video plus depth (MVD) architecture
(i) deforms object shapes due to block-level edge-approximation; (ii) misses an
opportunity for high compressibility at near-lossless quality by failing to
exploit strong homogeneity (clustering tendency) in depth syntax, motion vector
components, and residuals at frame-level; and (iii) restricts interactivity and
limits responsiveness of independent use of depth information for "non-viewing"
applications due to texture-depth coding dependency. This paper presents a
standalone depth sequence coder, which operates in the lossless to
near-lossless quality range while compressing depth data superior to lossy
3D-HEVC. It preserves edges implicitly by limiting quantisation to the
spatial-domain and exploits clustering tendency efficiently at frame-level with
a novel binary tree based decomposition (BTBD) technique. For mono-view coding
of standard MVD test sequences, on average, (i) lossless BTBD achieved $\times
42.2$ compression-ratio and $-60.0\%$ coding gain against the pseudo-lossless
3D-HEVC, using the lowest quantisation parameter $QP = 1$, and (ii)
near-lossless BTBD achieved $-79.4\%$ and $6.98$ dB Bj{\o}ntegaard delta
bitrate (BD-BR) and distortion (BD-PSNR), respectively, against 3D-HEVC. In
view-synthesis applications, decoded depth maps from BTBD rendered superior
quality synthetic-views, compared to 3D-HEVC, with $-18.9\%$ depth BD-BR and
$0.43$ dB synthetic-texture BD-PSNR on average.
