1,721,222 research outputs found
Depth map coding by dense disparity estimation for MVD compression
No full textIn multiview video representation, one of the most popular format is the so-called multiple view video plus depth. This representation is made up of N image sequences, each accompanied by a sequence of depth maps, telling the distance of each represented pixel from the observing camera. The depth maps are needed at the decoder side in order to generate intermediate views and therefore to enrich the user experience. This format is very flexible but also very demanding, in terms of storage space or and transmission bandwidth. Therefore, compression is needed. At this end, one of the key steps is an efficient representation of depth maps. In this work we build over a proposed method for multiple view video coding, based on dense disparity estimation between views. This allows us to obtain a compact and high-quality depthmap representation. In particular we explore the complex relationship between estimation and encoding parameters, showing that an optimal parameter set exist, that allows a fine-tuning of the estimation phase and an adaption of its results to the subsequent compression phase. Experiments are encouraging, showing remarkable gain over simple methods such as H.264/AVC simulcast, and even some gain with respect to more sophisticated techniques such as MVC. © 2011 IEEE
Introducing differential motion estimation into hybrid video coders
No full textDifferential motion estimation produces dense motion vector fields which are far too demanding in terms of coding rate in order to be used in video coding. However, a pel-recursive technique like that introduced by Cafforio and Rocca can be modified in order to work using only the information available at the decoder side. This allows to improve the motion vectors produced in the classical predictive modes of H.264. In this paper we describe the modification needed in order to introduce a differential motion estimation method into the H.264 codec. Experimental results will validate a coding mode, opening new perspectives in using differential-based motion estimation techniques into classical hybrid codecs. © 2010 SPIE
Emerging Technologies for 3D Video: Creation, Coding, Transmission and Rendering
No full textWith the expectation of greatly enhanced user experience, 3D video is widely perceived as the next major advancement in video technology. In order to fulfil the expectation of enhanced user experience, 3D video calls for new technologies addressing efficient content creation, representation/coding, transmission and display. Emerging Technologies for 3D Video will deal with all aspects involved in 3D video systems and services, including content acquisition and creation, data representation and coding, transmission, view synthesis, rendering, display technologies, human perception of depth and quality assessment. Key features: Offers an overview of key existing technologies for 3D video. Provides a discussion of advanced research topics and future technologies. Reviews relevant standardization efforts. Addresses applications and implementation issues. Includes contributions from leading researchers. The book is a comprehensive guide to 3D video systems and services suitable for all those involved in this field, including engineers, practitioners, researchers as well as professors, graduate and undergraduate students, and managers making technological decisions about 3D video. © 2013 by John Wiley & Sons, Ltd
ROI-based rate control using tiles for an HEVC encoded video stream over a lossy network
No full textThe growth in the use of high definition (HD) and above video resolutions streams has outstripped the rate at which network infrastructure has been deployed. Video streaming applications require appropriate rate control techniques that make use of the specific characteristics of the video content, such as the regions of interest (ROI). With the introduction of high efficiency video coding (HEVC) streams, we consider new coding features to make a novel ROI-based rate control (RC) algorithm. The proposed approach introduces tiling in a ROI-based rate control scheme. It aims at enhancing the quality of important regions (i.e. faces for a videoconferencing system) considering independently coded regions lying within an ROI and helps evaluating the ROI quality under poor channel conditions. Our work consists of two major steps. First, we designed a RC algorithm based on an independent processing of tiles of different regions. Second, we investigate the effect of ROI- and tile-based rate control algorithm on the decoded quality of the stream transmitted over a lossy channel
Image denoising by adaptive lifting schemes
No full textIn this paper, we study the problem of image denoising by using an adaptive lifting scheme. Such a scheme can adapt itself well to the analyzed signal, which allows to keep important information for denoising applications. However, it results in a non-isometric transform which can be an important limitation as most of the denoising approaches rely on the estimation of the noise energy in the subbands. In a previous work, it has been shown how to evaluate the subband energies of an uncorrelated signal, in the wavelet domain when using such an adaptive scheme. Based on this previous work, we propose in this paper an estimation of the noise energies in the subband and use it to perform image denoising. Experimental results illustrate that this approach is more effective, in image denoising, than the classical non adaptive lifting schemes both considering perceptual and non perceptual image quality measures. ©2010 IEEE
Low-latency video streaming with congestion control in mobile Ad-Hoc networks
No full textIn this paper, we address the challenge of delivering a video stream, encoded with multiple descriptions, in a mobile ad-hoc environment with low-latency constraints. This kind of application is meant to provide an efficient and reliable video communication tool in scenarios where the deployment of an infrastructure is not feasible, such as military and disaster relief applications. First, we present a recently proposed protocol that employs a reliable form of one-hop broadcast to build an efficient overlay network according to a multi-objective function that minimizes the number of packets injected in the network and maximizes the path diversity among descriptions. Then, we introduce the main contribution of this paper: a cross-layer congestion control strategy where the MAC layer is video-coding aware and adjusts its transmission parameters (namely, the RTS retry limit) via congestion/distortion optimization. The main challenge in this approach is providing a reliable estimation of congestion and distortion, given the limited information available at each node. Our simulations show that, if a stringent constraint of low delay is imposed, our technique grants a consistent gain in terms of both PSNR and delay reduction, for bitrates up to a few megabits per second. © 2012 IEEE
High order motion interpolation for side information improvement in DVC
No full textA key step in distributed video coding is the generation of the side information (SI) i.e. the estimation of the Wyner-Ziv frame (WZF). This step is also frequently called image interpolation. State-of-the-art techniques perform a motion estimation between adjacent key frames (KFs) and linear interpolation in order to assess object positions in the WZF, and then the SI is produced by motion compensating the KFs. However the uniform motion model underlying this approach is not always able to produce a satisfying estimation of the motion, which can result in a low SI quality. In this paper we propose a new method for the generation of SI, based on higher order motion interpolation. We use more than two KFs to estimate the position of the current WZF block, which allows us to correctly estimate more complex motion (such as, for example, uniform accelerated motion). We performed a number of tests for the fine tuning of the parameters of the method. Our experiments show that the new interpolation technique has a small computational cost increase with respect to state of the art, but provides remarkably better performance with up to 0.5 dB of PSNR improvement in SI quality. Moreover the proposed method performs consistently well for several GOP sizes. ©2010 IEEE
Estimation of quantization noise for adaptive-prediction lifting schemes
No full textThe lifting scheme represents an easy way of implementing the wavelet transform and of constructing new content-adapted transforms. However, the adaptive version of lifting schemes can result in strongly non-isometric transforms. This can be a major limitation, since all most successful coding techniques rely on the distortion estimation in the transform domain. In this paper we focus on the problem of evaluating the reconstruction distortion (due to quantization noise) in the wavelet domain when a non-isometric adaptive-prediction lifting scheme is used. The problem arises since these transforms are nonlinear, and so common techniques for distortion evaluation cannot be used in this case. We circumvent the difficulty by computing an equivalent time-varying linear filter, for which it is possible to generalize the distortion computation technique. In addition to the theoretical formulation of the distortion estimation, in this paper we provide experimental results proving the reliability of this estimation, and the consequent improvement of RD performance, thanks to a more effective resource allocation which can be performed in the transform domain. © 2009 IEEE
Adaptive video streaming with long term feedbacks
No full textThis paper proposes a video streaming system optimizing resource utilization when the media server only disposes of long term feedbacks from the client. Based on a partial knowledge of the network, we developed a scheduling algorithm that exploits the scalable video coding (SVC) properties to estimate packets importance and that takes into account packet delay dependencies to better anticipate congestion situations. Compared to more conventional streaming systems, experimental results show that our approach allows to better face network condition degradation like bandwidth reduction or packet error rate increase. ©2009 IEEE
Contour-Based Depth Coding: A Subjective Quality Assessment Study
No full textMulti-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
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