How to measure the relevance of a retargeting approach?

International audienceMost cell phones today can receive and display video content. Nonetheless, we are still significantly behind the point where premium made for mobile content is mainstream, largely available, and affordable. Significant issues must be overcome. The small screen size is one of them. Indeed, the direct transfer of conventional contents (not specifically shot for mobile devices) will provide a video in which the main characters or objects of interest may become indistinguishable from the rest of the scene. Therefore, it is required to retarget the content. Different solutions exist, either based on distortion of the image, on removal of redundant areas, or cropping. The most efficient ones are based on dynamic adaptation of the cropping window. They significantly improve the viewing experience by zooming in the regions of interest. Currently, there is no common agreement on how to compare different solutions. A retargeting metric is proposed in order to gauge its quality. Eye-tracking experiments, zooming effect through coverage ratio and temporal consistency are introduced and discussed

Inter-prediction methods based on linear embedding for video compression

International audienceThis paper considers the problem of temporal prediction for inter-frame coding of video sequences using locally linear embedding (LLE). LLE-based prediction, first considered for intra-frame prediction, computes the predictor as a linear combination of K nearest neighbors (K-NN) searched within one or several reference frames. The paper explores different K-NN search strategies in the context of temporal prediction, leading to several temporal predictor variants. The proposed methods are tested as extra inter-frame prediction modes in an H.264 codec, but the proposed concepts are still valid in HEVC. The results show that significant rate-distortion performance gains are obtained with respect to H.264 (up to 15.31% bit-rate saving)

Learning Clustering-Based Linear Mappings for Quantization Noise Removal

International audienceThis paper describes a novel scheme to reduce the quantization noise of compressed videos and improve the overall coding performances. The proposed scheme first consists in clustering noisy patches of the compressed sequence. Then, at the encoder side, linear mappings are learned for each cluster between the noisy patches and the corresponding source patches. The linear mappings are then transmitted to the decoder where they can be applied to perform de-noising. The method has been tested with the HEVC standard, leading to a bitrate saving of up to 9.63%

Clustering-based Methods for Fast Epitome Generation

International audienceThis paper deals with epitome generation, mainly dedicated here to image coding applications. Existing approaches are known to be memory and time consuming due to exhaustive self-similarities search within the image for each non-overlapping block. We propose here a novel approach for epitome construction that first groups close patches together. In a second time the self-similarities search is performed for each group. By limiting the number of exhaustive searches we limit the memory occupation and the processing time. Results show that interesting complexity reduction can be achieved while keeping a good epitome quality (down to 18.08 % of the original memory occupation and 41.39 % of the original processing time)

Toward Haptic Cinematography: Enhancing Movie Experience with Haptic Effects based on Cinematographic Camera Motions

International audienceHaptics, the technology which brings tactile or force-feedback to users, has a great potential for enhancing movies and could lead to new immersive experiences. In this paper we introduce \textit{Haptic Cinematography} which presents haptics as a new component of the filmmaker's toolkit. We propose a taxonomy of haptic effects and we introduce novel effects coupled with classical cinematographic motions to enhance video viewing experience. More precisely we propose two models to render haptic effects based on camera motions: the first model makes the audience feel the motion of the camera and the second provides haptic metaphors related to the semantics of the camera effect. Results from a user study suggest that these new effects improve the quality of experience. Filmmakers may use this new way of creating haptic effects to propose new immersive audiovisual experiences

De l'optimisation globale à l'optimisation locale psycho-visuelle en codage vidéo

Le codage est un maillon essentiel de la chaîne de production-distribution-rendu vidéo. Il détermine la qualité perçue par l'observateur et participe à l'appréciation globale de la qualité d'expérience (ou QoE). Un codeur vidéo est un système complexe qui met en œuvre de nombreux aspects et nécessite un savoir faire spécifique pour spécifier le bon algorithme de codage en fonction des contraintes applicatives. Ce travail parcourt les principaux points à considérer, propose des solutions innovantes et montre leurs efficacités. La première partie est une introduction au codage vidéo et aux formats d'images avec quelques rappels des principes généraux nécessaires à la compréhension de ce mémoire. Les notions d'échantillonnage spatial et temporel et les bases de la colorimétrie en vidéo sont rappelées, pour présenter ensuite le codage proprement dit. Les différents mécanismes utilisés sont présentés, ainsi que les principaux standards de codage pertinents au regard de ce travail. L'impact des différents formats vidéo sur le codage est aussi abordé pour démontrer que le format progressif présente de nombreux intérêts, mais n'est pas encore largement utilisé du fait de la compatibilité requise avec l'existant. Enfin l'importance de connaître le contexte applicatif est discutée, en particulier dans le cadre de codage adapté aux formats vidéo de très hautes qualités utilisés en production professionnelle. La deuxième partie est consacrée aux algorithmes globaux d'optimisation basés complexité-distorsion et débit-distorsion, où la distorsion est principalement la minimisation de la différence mathématique entre le signal décodé et l'original. Un premier chapitre aborde l'adéquation de l'algorithme avec la plate-forme de codage cible. Dans ce mémoire la cible sera un circuit intégré considéré aujourd'hui comme le plus performant de sa génération. Un focus particulier est effectué dans les autres chapitres sur les techniques, fondamentales en codage vidéo, d'adaptation du codage au signal, au canal et à l'utilisateur. La troisième partie aborde une voie de recherche qui semble gagner un certain intérêt dans le monde académique, celui du codage perceptuel local. Après l'introduction des notions de modélisation du système visuel humain, de métriques de distorsion et d'aspect subjectifs, différentes recherches sont présentées. Elles introduisent l'aspect d'adaptation locale du codage dans l'image basée sur la perception. Autrement dit comment chaque région d'une image peut-elle être codée pour subjectivement donner une meilleure impression. C'est une voie assez récente en codage mais elle ouvre de nouvelles perspectives non encore complètement explorées. Enfin des extensions ou des perspectives complémentaires aux travaux de ce mémoire sont proposées dans la conclusion.Video coding is an essential part of the production-delivery-rendering video chain. The efficiency of the coding scheme gives the quality perceived by the final user and contributes to the evaluation of the quality of experience (or QoE). A video encoder is a complex system with many different aspects requiring a specific know-how to specify the right algorithm for the considered application. This work deals with the main topics to be considered, proposes innovative solutions and discusses their respective performances. The first part is an introduction to the coding of video signals with some remainders on the general principles necessary to understand this thesis. Spatial sampling, temporal sampling and colorimetry theories are first discussed, and the encoding is introduced just after. The different tools and mechanisms are described, as well as the main existing standards relevant regarding this work. The video formats impact is discussed to demonstrate the interest of the progressive scanning format, even if it is not yet largely diploid because of the necessary backward compatibility. Finally, we demonstrate the importance of knowing the applicative context in a particular case, the professional video production where very high quality video is required. The second part is dedicated to the global optimisation issues based on both the complexity-distortion and rate-distortion functions, where the distortion is mainly the mathematical difference between the original and decoded signals. The first chapter introduces the adequacy between the algorithm and the considered platform. We discuss here a specific IC considered today as one of the most efficient IC of its generation. A particular focus is proposed in the other chapters regarding adaptive coding techniques for the signal, channel or user. The third part introduces a new research area recently attracting a lot of attention from the academic researchers, the local perceptual coding. After an introduction of the human visual system, distortion metrics and other subjective aspects, different research studies are presented. It is proposed to use local adaptation based on the human perception. In other words we propose to study how each picture area can be encoded to provide a better subjective quality. It is a recent research topic but it opens new perspectives not yet fully explored. Finally, extensions and perspectives are proposed in the conclusion to complete this work.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Recommendation on the Strategy of Using the Different Scanning Formats

The purpose of this recommendation is to update the Recommendation on Scanning Formats formulated by the RACE Image Communication Project Line 4 in January 1994. This update takes into account the studies performed in WP2 within the framework of the Scanning Formats Extension. This paper also discusses the strategy to follow in order to adopt a progressive format for the coding of digital television. The work performed within the framework of the RACE 2110 HAMLET Extension on Scanning Formats, leads to the following statements : 1. Interlaced format has been chosen in the early years of television considering it was one of the most interesting solution to achieve compression with regard to the available technology [1]. 2. The improved quality of today's television sources and displays make the viewers less tolerant of the defects of the interlaced format (i.e. interline flicker, line crawling and field aliasing), especially for large displays, close viewing distance and high brightnes..

Progressive versus Interlaced Coding

Interlaced versus progressive scanning is an important issue when dealing with digital television. Not only because the change from analog to digital communication may be seen as an opportunity to move to other formats, but also because of the well-known artifacts of interlaced scanning (interline twitter, line crawling, and field aliasing) compared to the natural way of representing two-dimensional images as the progressive format does. However, digital broadcasting has to face the problem of transmitting twice the number of pels of the progressive format. It is the purpose of this article to study this problem, and especially to check if the increased vertical and temporal correlations of the progressive pictures provide a significant improvement in the bit-rate reduction efficiency. In that case, progressive scanning may also be used as an intermediate transmission format to improve the compression performances of interlaced sequences. 1. Introduction Interlaced scanning was introd..

Which saliency weighting for omni directional image quality assessment?

International audienc