11 research outputs found
Low-Complexity Context-Based Motion Compensation for VLBR Video Encoding
A significant improvement of block-based motion estimation strategies is presented, which provides fast computation and very low bitrate coding. For each block, a spatio-temporal context is defined based on nearest neighbors in the current and previous frames, and a prediction list is built. Then, the best matching vector within the list is chosen as an estimation of the block motion. Since coder and decoder are synchronous, only the index of the selected vector is needed at the decoder to reconstruct the motion field. To avoid the propagation of the error, an additional correction vector can be sent when prediction error exceeds a threshold. Furthermore, bitrate saving is achieved through an adaptive sorting of the prediction list of each block, which allows to reduce the entropy of the motion indexes. Tests demonstrate that the proposed method ensures a speed up over 1:200 as compared to full search, and a coding gain above 2, with a negligible loss of accuracy. This allows real-time implementation of VLBR software video coders on conventional PC platforms
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A new efficient similarity metric and generic computation strategy for pattern-based very low bit-rate video coding
In the context of very low bit-rate video coding, pattern representations of a moving region (MR) in block-based motion estimation and compensation has become increasingly attractive. Generally, all existing pattern-matching algorithms apply a similarity metric, involving elementary operations, to compute the mismatch between an MR and a particular fixed pattern in order to select the best-matching pattern from a fixed-size codebook of predefined patterns. An efficient similarity metric, together with a new generic computation strategy, is presented by considering only the mismatch areas of MRs. It is theoretically proven that for a specific MR in a macroblock, the new similarity metric selects exactly the same pattern as existing metrics, while the resulting computational coding efficiency is improved by between 21% and 58% compared with the H.263 low bit-rate coding standard
Codificação de vĂdeo: priorização do menor custo de codificação na otimização em taxa-distorção
Tese (doutorado) - Universidade Federal de Santa Catarina, Centro TecnolĂłgico, Programa de PĂłs-Graduação em Engenharia ElĂ©trica, FlorianĂłpolis, 2009.O presente trabalho propĂ”e duas novas estratĂ©gias para compressĂŁo de sinais de vĂdeo atravĂ©s de algoritmos otimizados em taxa-distorção (RD), focando aplicaçÔes tĂpicas de vĂdeo digital para operação em baixas taxas de bits. As estratĂ©gias propostas sĂŁo implementadas em um codificador de vĂdeo baseado no padrĂŁo H.264, o qual apresenta uma alta complexidade computacional devido principalmente ao grande nĂșmero de modos de codificação disponĂvel. SĂŁo apresentadas duas propostas de redução da complexidade, mantendo o desempenho RD prĂłximo Ă quele do codificador H.264 otimizado em RD usando busca exaustiva. A primeira proposta (denominada rate sorting and truncation - RST) realiza o ordenamento tanto dos vetores de movimento (VMs) quanto dos modos de codificação em ordem ascendente de taxa de bits. O processo de codificação Ă© interrompido quando a taxa de bits dos novos VMs e modos de codificação exceder Ă menor taxa jĂĄ obtida para um prĂ©-estabelecido nĂvel de qualidade de imagem. Assim, um grande nĂșmero de VMs e diversos modos de codificação sĂŁo descartados antes que sejam avaliados. A segunda proposta consiste em um algoritmo rĂĄpido, baseado no perfil de distribuição de vetores do codificador H.264, para estimação de movimento (denominado logarithmic diamond shape search - LDSS). O uso da estratĂ©gia RST associada ao algoritmo LDSS reduz atĂ© 98% a carga computacional com perda marginal de desempenho RD.This research work proposes two new video compression strategies, aiming at typical low bit rate video applications using rate-distortion (RD) optimized algorithms. The proposed strategies are implemented on an H.264 video encoder, which has high computational complexity due mainly to the large number of coding modes available. Two approaches are presented for reducing the encoder computational complexity, maintaining the RD performance close to the full search RD optimized H.264 encoder. The first approach (termed rate sorting and truncation - RST) is based on sorting the motion vectors (MVs) and coding modes in an ascending rate order. This sorting and encoding process, which is stopped when the rate value exceeds the previous best rate for a required image quality level, allows the elimination of MVs and coding modes before checking their distortion. Apart from obtaining a significant complexity reduction, the process still remains optimized in RD sense. The second approach is an algorithm (termed logarithmic diamond shape search - LDSS), which explores the MVs distribution profile for the RD optimized H.264 encoder. The use of the RST strategy associated with LDSS algorithm yields up to a 98% reduction in the computational burden, with insignificant RD performance loss
Codage par compétition des vecteurs mouvements : que doit-on vraiment transmettre ?
Le standard de compression vidéo H.264/AVC obtient des gains significatifs par rapport
Ă ses prĂ©dĂ©cesseurs en diminuant fortement lâentropie des rĂ©siduels de texture Ă lâaide,
notamment, dâune augmentation du nombre de possibilitĂ©s de codage. Les travaux pour une
future norme ont dĂ©jĂ commencĂ© au sein de chacun des deux groupes Ă lâorigine de la norme
H.264/AVC. La mĂ©thode de codage de lâinformation de mouvement par compĂ©tition de prĂ©diction
de vecteurs a été proposée dans le cadre des travaux exploratoires du groupe VCEG.
Cette mĂ©thode visant Ă rĂ©duire la quantitĂ© dâinformation de mouvement a Ă©tĂ© intĂ©grĂ©e dans le
logiciel JM-KTA visant à préparer le nouveau standard. Dans cet article, une amélioration de
cette méthode est proposée, permettant de limiter le débit des indices de prédicteurs. Elle est
basée sur les caractéristiques de la fonction de sélection du meilleur prédicteur qui est reproduite
au décodeur. Cette méthode, testée dans le JM-KTA, élimine 10 % des indices de prédicteurs
et rĂ©duit ainsi le dĂ©bit de lâinformation de mouvement.The H.264/AVC video coding standard obtains significative compression gains compared
to its predecessors. These gains come from a reduction of the texture residual entropy
by, notably, increasing the amount of coding possibilities. The work for the future standard
have already started in both groups that normalized H.264/AVC. The competition based
scheme for motion vectors prediction has been proposed for the exploratory work of VCEG.
This scheme dedicated to the reduction of the motion information was also integrated in the
JM-KTA software. In this paper, an improvement of the motion vector competition scheme is
proposed to reduce the bitrate of the predictors indexes. This scheme is based on the properties
of the best predictors selection function which is used at the decoder side. This scheme,
tested in the JM-KTA, removes 10% of the predictor indexes and thus reduces the bitrate dedicated
to the motion information
Temporal Video Transcoding in Mobile Systems
La tesi analizza il problema della transcodifica temporale per la trasmissione del video in tempo reale su reti mobili. Viene proposta unâarchitettura di transcodifica temporale e un nuovo algoritmo di ricalcolo dei vettori di moto per il transcoder temporale H.264. Per fronteggiare il problema della riduzione costante della banda del canale wireless nelle reti infrastrutturate, vengono proposte diverse politiche di frame skipping basate sul dimensionamento del buffer del transcoder per garantire una comunicazione in tempo reale. Il moto di un frame e il numero di frames consecutivi scartati vengono inoltre considerati per migliorare la qualitĂ del video transcodificato. Eâ stato inoltre proposto e studiato un sistema di trasmissione video per reti veicolari con protocollo IEEE 802.11, basato su transcodifica temporale. Questo sistema permette di scartare quei frames il cui tempo di trasmissione supera un massimo ritardo ammisssibile al di sopra del quale tali frames non verrebbero comunque visualizzati. Il sistema proposto permette un notevole risparmio di banda e migliora la qualitĂ del video evitando che molti frames consecutivi vengano scartati a causa della congestione
Video object segmentation for interactive multimedia
Ankara : Department of Electrical and Electronics Engineering and Institute of Engineering and Sciences, Bilkent Univ., 1998.Thesis (Master's) -- Bilkent University, 1998.Includes bibliographical references leaves 67-74.Recently, trends in video processing research have shifted from video compression to video analysis, due to the emerging standards MPEG-4 and MPEG-7. These standards will enable the users to interact with the objects in the audiovisual scene generated at the userâs end. However, neither of them prescribes how to obtain the objects. Many methods have been proposed for segmentation of video objects. One of the approaches is the âAnalysis Modelâ (AM) of European COST-211 project. It is a modular approach to video object segmentation problem. Although AM performs acceptably in some cases, the results in many other cases are not good enough to be considered as semantic objects. In this thesis, a new tool is integrated and some modules are replaced by improved versions. One of the tools uses a block-based motion estimation technique to analyze the motion content within a scene, computes a motion activity parameter, and skips frames accordingly. Also introduced is a powerful motion estimation method which uses maximum a posteriori probability (MAP) criterion and Gibbs energies to obtain more reliable motion vectors and to calculate temporally unpredictable areas. To handle more complex motion in the scene, the 2-D affine motion model is added to the motion segmentation module, which employs only the translational model. The observed results indicate that the AM performance is improved substantially. The objects in the scene and their boundaries are detected more accurately, compared to the previous results.Ekmekçi, TolgaM.S
Novel block-based motion estimation and segmentation for video coding
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Cumulative index to NASA Tech Briefs, 1986-1990, volumes 10-14
Tech Briefs are short announcements of new technology derived from the R&D activities of the National Aeronautics and Space Administration. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This cumulative index of Tech Briefs contains abstracts and four indexes (subject, personal author, originating center, and Tech Brief number) and covers the period 1986 to 1990. The abstract section is organized by the following subject categories: electronic components and circuits, electronic systems, physical sciences, materials, computer programs, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences