Multiview video plus depth is emerging as the most flexible format for three-dimensional video representation, as witnessed by the current standardization efforts by ISO and ITU. In particular, in depth representation, arguably the most important information lies in object contours. As a consequence, an interesting approach consists in performing a lossless coding of object contours, possibly followed by a lossy coding of per-object depth values. In this context, we propose a new technique for lossless coding of object contours, based on the elastic deformation of curves. Using the square-root velocity representation for the elements of the space of curves, we can model a continuous evolution of elastic deformations between two reference contour curves. An elastically deformed version of the reference contours can be sent to the decoder with a reduced coding cost and used as side information to improve the lossless coding of the actual contour. Experimental results on several multiview video sequences show remarkable gains with respect to the reference techniques and to the state of the art.

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Multi-view video plus depth is emerging as the most flexible format for 3D video representation, as witnessed by the current standardization efforts by ISO and ITU. The depth information allows synthesizing virtual view points, and for its compression various techniques have been proposed. It is generally recognized that a high quality view rendering at the receiver side is possible only by preserving the contour information since distortions on edges during the encoding step would cause a sensible degradation on the synthesized view and on the 3D perception. As a consequence recent approaches include contour-based coding of depths. However, the impact of contour-preserving depth-coding on the perceived quality of synthesized images has not been conveniently studied. Therefore in this paper we make an investigation by means of a subjective study to better understand the limits and the potentialities of the different techniques.Our results show that the contour information is indeed relevant in the synthesis step: preserving the contours and coding coarsely the rest typically leads to images that users cannot tell apart from the reference ones, even at low bit rate. Moreover, our results show that objective metrics that are commonly used to evaluate synthesized images may have a low correlation coefficient with MOS rates and are in general not consistent across several techniques and contents.

Multi-view video plus depth is emerging as the most flexible format for 3D video representation, as witnessed by the current standardization efforts by ISO and ITU. The depth information allows synthesizing virtual view points, and for its compression various techniques have been proposed. We make a preliminary investigation of the effects on the synthesized views of two different approaches: object-based and block-based, from a perceptual point of view. Index Terms-perceived quality, 3D video, multiple-views-plusdepth, contour coding, elastic curves.