Recommended by A. Enis Ç etinThe video-plus-depth data representation uses a regular texture video enriched with the so-called depth map, providing the depth distance for each pixel. The compression efficiency is usually higher for smooth, gray level data representing the depth map than for classical video texture. However, improvements of the coding efficiency are still possible, taking into account the fact that the video and the depth map sequences are strongly correlated. Classically, the correlation between the texture motion vectors and the depth map motion vectors is not exploited in the coding process. The aim of this paper is to reduce the amount of information for describing the motion of the texture video and of the depth map sequences by sharing one common motion vector field. Furthermore, in the literature, the bitrate control scheme generally fixes for the depth map sequence a percentage of 20% of the texture stream bitrate. However, this fixed percentage can affect the depth coding efficiency, and it should also depend on the content of each sequence. We propose a new bitrate allocation strategy between the texture and its associated per-pixel depth information. We provide comparative analysis to measure the quality of the resulting 3D + t sequences.

The problem of multimedia communications over best-effort networks is addressed here with multiple description coding (MDC) in a distributed framework. In this paper, we first compare four video MDC schemes based on different time splitting patterns and temporal two-or three-band motion-compensated temporal filtering (MCTF). Then, the latter schemes are extended with systematic lossy description coding where the original sequence is separated into two subsequences, one being coded as in the latter schemes, and the other being coded with a Wyner-Ziv (WZ) encoder. This amounts to having a systematic lossy Wyner-Ziv coding of every other frame of each description. This error control approach can be used as an alternative to automatic repeat request (ARQ) or forward error correction (FEC), that is, the additional bitstream can be systematically sent to the decoder or can be requested, as in ARQ. When used as an FEC mechanism, the amount of redundancy is mostly controlled by the quantization of the Wyner-Ziv data. In this context, this approach leads to satisfactory rate-distortion performance at the side decoders, however it suffers from high redundancy which penalizes the central description. To cope with this problem, the approach is then extended to the use of MCTF for the Wyner-Ziv frames, in which case only the low-frequency subbands are WZ-coded and sent in the descriptions.

Depth image-based rendering (DIBR) is the process of synthesizing some new "virtual" views from one "real" view and the associated per-pixel depth information. The most important problem in this process is to deal with the newly exposed areas (holes) appearing in the virtual images. One common solution to decrease the number of holes is to pre-process the depth map, before the warping. In this paper, we present a new filtering technique for depth image-based rendering. In order to reduce or completely remove the newly exposed areas an efficient smoothing is necessary for the sharp depth changes near object boundaries. In the meantime it is useless to filter the smooth areas in the depth map. Our solution is based on a weighted Gaussian filter taking into account the distance to the contours. By this way, the geometric distortions and the computation time are reduced compared to a uniform filtering of the depth map. We present some results in the context of creation of stereoscopic views for 3D TV.

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