Krzysztof Wegner

High Efficiency 3D Video Coding Using New Tools Based on View Synthesis

We propose a new coding technology for 3D video represented by multiple views and the respective depth maps. The proposed technology is demonstrated as an extension of the recently developed high efficiency video coding (HEVC). One base views are compressed into a standard bitstream (like in HEVC). The remaining views and the depth maps are compressed using new coding tools that mostly rely on view synthesis. In the decoder, those views and the depth maps are derived via synthesis in the 3D space from the decoded baseview and from data corresponding to small disoccluded regions. The shapes and locations of those disoccluded regions can be derived by the decoder without any side information transmitted. To achieve high compression efficiency, we propose several new tools such as depth-based motion prediction, joint high frequency layer coding, consistent depth representation, and nonlinear depth representation. The experiments show high compression efficiency of the proposed technology. The bitrate needed for transmission of two side views with depth maps is mostly less than 50% than that of the bitrate for a single-view video.

Distortions of synthesized views caused by compression of views and depth maps

The paper deals with prospective 3D video transmission systems that would use compression of both multiview video and depth maps. The paper addresses the problem of quality of views synthesized from other views transmitted together with depth information. For the state-of-the-art depth map estimation and view synthesize techniques, the paper proves that AVC/SVC-based Multiview Video Coding technique can be used for compression of both view pictures and depth maps. The paper reports extensive experiments where synthesized video quality has been estimated by use of both PSNR index and subjective assessment. Defined is the critical value of depth quantization parameter as a function of the reference view quantization parameter. For smaller depth map quantization parameters, depth map compression has negligible influence on fidelity of synthesized views.

Coding of multiple video+depth using HEVC technology and reduced representations of side views and depth maps

During the last two decades, a new technology generation of video compression was introduced about each 9 years. Each new compression-technology generation provides halving of necessary bitrates as compared to the last previous generation. This increasing single-view compression performance is related to increasing compression performance of multiview video coding. For multiview video with associated depth maps, additional significant bitrate reduction may be achieved. The paper reports the original compression technology that was designed and developed at Poznań University of Technology in response to MPEG Call for Proposals on 3D Video Coding Technology. The main idea of this technique is to predict very efficiently the side views and the depth maps from the base view.

Extensions of the HEVC technology for efficient multiview video coding

The paper deals with multiview video coding using the new technology of High Efficiency Video Coding (HEVC). Implementation of multiview video coding in the framework of HEVC is described together with new specific tools proposed by the authors. Extensive experimental results are reported for compression performance comparison of MVC (ISO 14496-10), HEVC simulcast and two versions of proposed “multiview HEVC”. For “multiview HEVC” the results indicate significant bitrate reduction of about 50%, as compared to the state-of-the-art MVC technology standardized as a part of AVC (MPEG-4, H.264).

A practical approach to acquisition and processing of free viewpoint video

We deal with the processing of multiview video acquired by the use of practical thus relatively simple acquisition systems that have a limited number of cameras located around a scene on independent tripods. The real-camera locations are nearly arbitrary as it would be required in the real-world Free-Viewpoint Television systems. The appropriate test video sequences are also reported. We describe a family of original extensions and adaptations of the multiview video processing algorithms adapted to arbitrary camera positions around a scene. The techniques constitute the video processing chain for Free-Viewpoint Television as they are aimed at estimating the parameters of such a multi-camera system, video correction, depth estimation and virtual view synthesis. Moreover, we demonstrate the need for new compression technology capable of efficient compression of sparse convergent views. The experimental results for processing the proposed test sequences are reported.

Intra Predictive Depth Map Coding Using Flexible Block Partitioning

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 optimized 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 modeling mode, based on explicit edge representation, was developed. For residue coding, a simple and low complexity approach was investigated, using constant and linear residue modeling, depending on the prediction mode. The performance of the proposed intra depth map coding approach was evaluated based on the quality of the synthesized views using the encoded depth maps and original texture views. The experimental tests based on all intra configuration demonstrated the superior rate-distortion 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 a high-efficiency video coding (3D-HEVC) standard. By using view synthesis optimization in both PDC and 3D-HEVC encoders, the average bitrate savings increase 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.

Similarity measures for depth estimation

This paper deals with similarity measures for stereoscopic depth estimation. These measures are used for matching of image pairs, which is the first step of the estimation process. We analyze influence of these similarity measures on performance of depth estimation with use of commonly known measures and compare the results with some novel proposals. The performance is judged by increase of quality of view synthesis, which is the main aim of this paper. Experimental results over a variety of moving material demonstrate that considerable gain can be attained without any modifications to estimation core and with tuning of matching stage only. Finally, some guidelines on design of well performing similarity measures are given. For the sake of paper, the whole work is described in context of belief-propagation algorithm, but the results and conclusions apply in general for many other state-of-the art optimization techniques.

Error concealment for MVC and 3D video coding

In this paper we propose a novel approach to error concealment that can be applied to MVC and other 3D video coding technologies. The image content, that is lost due to errors, is recovered with use of multiple error-concealment techniques. In our work we have used three techniques: well-known temporal- and intra-based techniques and a novel inter-view technique. Proposed inter-view recovery employs Depth Image Based Rendering (DIBR), which requires neighboring views and corresponding depth maps. Those depth maps can be delivered in the bit-stream or estimated in the receiver. In order to obtain the final reconstruction, the best technique is selected locally. For that, an original recovery quality measurement method, based on cross-checking, has been proposed. The idea has been implemented and assessed experimentally, with use of 3D video test sequences. The objective and subjective results show that the proposed approach provide good quality of reconstructed video.

3D video compression by coding of disoccluded regions

In this paper, we present the most efficient coding tools that are used in a new video compression technology for multiple views with the depth maps. This very well performing technology was designed and developed in response to MPEG Call for Proposals on 3D Video Coding Technology. The proposed technology exploits a tool that reduces the side views and the side depth maps to small disoccluded regions. This way only one central view and one depth map are coded in the HEVC syntax while the remaining views and the depth maps are synthesized in the decoder from the small disoccluded regions and from the central-view data. Therefore, the bitrate needed for a side view is mostly below 20% of the bitrate for single-view video.

New visual coding exploration in MPEG: Super-MultiView and Free Navigation in Free viewpoint TV

ISO/IEC MPEG and ITU-T VCEG have recently jointly issued a new multiview video compression standard, called 3D-HEVC, which reaches unpreceded compression performances for linear,dense camera arrangements. In view of supporting future highquality,auto-stereoscopic 3D displays and Free Navigation virtual/augmented reality applications with sparse, arbitrarily arranged camera setups, innovative depth estimation and virtual view synthesis techniques with global optimizations over all camera views should be developed. Preliminary studies in response to the MPEG-FTV (Free viewpoint TV) Call for Evidence suggest these targets are within reach, with at least 6% bitrate gains over 3DHEVC technology.