# Chapter 6

Depth image coding using piecewise-linear functions

* “One would only need to cut these paintings out... assemble them
following the indications given by the colours, to end up in front of a
sculpture.”*

* * Pablo Picasso. Spanish painter.

* This chapter proposes a novel depth image coding algorithm which
concentrates on the special characteristics of depth images: smooth regions
delineated by sharp edges. The algorithm models these smooth regions using
piecewise-linear functions and sharp edges by a straight line. To define the area of
support for each modeling function, we employ a quadtree decomposition that
divides the image into blocks of variable size, each block being approximated by
one modeling function containing one or two surfaces. The subdivision
of the quadtree and the selection of the type of modeling function are
optimized, such that a global rate-distortion trade-off is realized. Experimental
results show that the described techniques improve the resulting quality of
compressed depth images by up to 3 dB, when compared to a JPEG-2000
encoder.*

6.2 Geometric modeling of depth images

6.2.1 Overview of the depth image coding algorithm

6.2.2 Modeling-function definitions

6.2.3 Estimation of model coefficients

6.3 Bit-allocation strategy

6.3.1 Modeling function selection

6.3.2 Quadtree decomposition

6.3.3 Quantizer selection

6.3.4 Summary of the complete algorithm

6.4 Experimental results

6.4.1 Coding experiments

6.4.2 Rendering experiments based on encoded depth

6.4.3 Comparisons with H.264/MPEG-4 AVC and MVC

6.5 Conclusions and perspectives