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Weijun Wang

Ecole Centrale de Nantes

+ 33 2 40 37 69 10

ECN Bat.S :201

Weijun.Wang@irccyn.ec-nantes.fr

Equipe de recherche:
Ingénierie des Systèmes, Produits, Performances et Perceptions

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Nombre de publications : 29

12 3

A computational model of stereoscopic 3D visual saliency
J. Wang, M. Perreira Da Silva, P. Le Callet, V. Ricordel.
IEEE Transactions on Image Processing, (2013), Vol PP, 99, pp. 1, [hal-00788847].

RésuméMany computational models of visual attention performing well in predicting salient areas of 2D images have been proposed in the literature. The emerging applications of stereoscopic 3D display bring additional depth information affecting the human viewing behavior, and require extensions of the efforts made in 2D visual modeling. In this paper, we propose a new computational model of visual attention for stereoscopic 3D still image. Apart from detecting salient areas based on 2D visual features, the proposed model takes depth as an additional visual dimension. The measure of depth saliency is derived from the eye movement data obtained from an eye-tracking experiment using synthetic stimuli. Two different ways of integrating depth information in the modeling of 3D visual attention are then proposed and examined. For the performance evaluation of 3D visual attention models, we have created an eye-tracking database which contains stereoscopic images of natural content and is publicly available along with this paper. The proposed model gives a good performance, compared to that of state-of-the-art 2D models on 2D images. The results also suggest that a better performance is obtained when depth information is taken into account through the creation of a depth saliency map rather than when it is integrated by a weighting method.

Mots clés: 3DTV, depth saliency, eye-tracking, saliency map, stereoscopy, visual attention.

Stereoscopic 3D video coding quality evaluation with 2D objective metrics
K. Wang, K. Brunnström, M. Barkowsky, M. Urvoy, M. Sjöström, P. Le Callet, S. Tourancheau, B. Andrén.
SPIE Electronic Imaging 2013, San franscisco, États-Unis, (2013-02-03), pp. pp.1-7, [hal-00789082].

RésuméThe 3D video quality is of highest importance for the adoption of a new technology from a user's point of view. In this paper we evaluated the impact of coding artefacts on stereoscopic 3D video quality by making use of several existing full reference 2D objective metrics. We analyzed the performance of objective metrics by comparing to the results of subjective experiment. The results show that pixel based Visual Information Fidelity metrics fits subjective data the best. The 2D stereoscopic video quality seems to have dominant impact on the coding artefacts impaired stereoscopic videos.

Mots clés: 3D, stereoscopic, video quality, objective metrics.

Towards standardized 3DTV QoE assessment: Cross-lab study on display technology and viewing environment parameters
M. Barkowsky, J. Li, T. Han, S. Youn, J. Ok, Ch. Lee, Ch. Hedberg, I-V. Ananth, K. Wang, K. Brunnström, P. Le Callet.
SPIE Electronic Imaging, San franscisco, États-Unis, (2013-02-03), pp. pp.1-7, [hal-00789054].

RésuméSubjective assessment of Quality of Experience in stereoscopic 3D requires new guidelines for the environmental setup as existing standards such as ITU-R BT.500 may no longer be appropriate. A first step is to perform cross-lab experiments in different viewing conditions on the same video sequences. Three international labs performed Absolute Category Rating studies on a freely available video database containing degradations that are mainly related to video quality degradations. Different conditions have been used in the labs: Passive polarized displays, active shutter displays, differences in viewing distance, the number of parallel viewers, and the voting device. Implicit variations were introduced due to the three different languages in Sweden, South Korea, and France. Although the obtained Mean Opinion Scores are comparable, slight differences occur in function of the video degradations and the viewing distance. An analysis on the statistical differences obtained between the MOS of the video sequences revealed that obtaining an equivalent number of differences may require more observers in some viewing conditions. It was also seen that the alignment of the meaning of the attributes used in Absolute Category Rating in different languages may be beneficial. Statistical analysis was performed showing influence of the viewing distance on votes and MOS results.

Mots clés: Subjective assessment, Viewing environment, Stereoscopic Displays, 3D Quality of Experience, Cross-Lab Validation, Standardization.

Study of Center-Bias in the Viewing of Stereoscopic Image and a Framework for Extending 2D Visual Attention Models to 3D
J. Wang, M. Perreira Da Silva, P. Le Callet, V. Ricordel.
SPIE Electronic Imaging 2013, San franscisco, États-Unis, (2013-02-03), pp. pp.1-9, [hal-00790559].

RésuméCompared to the good performance that can be achieved by many 2D visual attention models, predicting salient regions of a 3D scene is still challenging. An e cient way to achieve this can be to exploit existing models designed for 2D content. However, the visual con icts caused by binocular disparity and changes of viewing behavior in 3D viewing need to be dealt with. To cope with these, the present paper proposes a simple framework for extending 2D attention models for 3D images, as well as evaluates center-bias in 3D-viewing condition. To validate the results, a database is created, which contains eye-movements of 35 subjects recorded during free viewing of eighteen 3D images and their corresponding 2D version. Fixation density maps indicate a weaker center-bias in the viewing of 3D images. Moreover, objective metric results demonstrate the e ciency of the proposed model and a large added value of center-bias when it is taken into account in computational modeling of 3D visual attention.

Mots clés: Visual attention, stereoscopy, 3DTV, center bias, eye-tracking, gaze pattern.

How Does Image Content Affect the Added Value of Visual Attention in Objective Image Quality Assessment?
H. Liu, U. Engelke, J. Wang, P. Le Callet, I. Heynderickx.
IEEE Signal Processing Letters, (2013), Vol PP, 99, pp. 1, [hal-00788386].

RésuméOur previous research [1] has demonstrated that adding natural scene saliency (NSS) obtained from eye-tracking data may improve an objective metrics performance in predicting perceived image quality. In this letter, we further investigate the image content dependency of this improvement. Results show that the variation in saliency between observers highly depends on image content, and that this variation predicts the extent to which a certain image may profit from adding saliency in the objective image quality assessment.

Mots clés: Eye tracking, image quality assessment, objective metric, saliency map, visual attention.

Perceived 3D TV Transmission Quality Assessment: Multi-Laboratory Results Using Absolute Category Rating on Quality of Experience Scale
K. Wang, M. Barkowsky, K. Brunnström, M. Sjöström, R. Cousseau, P. Le Callet.
IEEE Transactions on Broadcasting, (2012-12-01), Vol 58, 4, pp. pp.544-557, [hal-00724397].

RésuméInspired by the rapidly increasing popularity of 3D movies, there is an industrial push for 3DTV services to the home. One important factor for the success and acceptance by the viewers is a positive quality of experience (QoE) of the new service when delivered. The questions of how to efficiently deliver 3DTV service to the home, and how to evaluate the visual quality perceived by end users are a recent research focus. We have investigated users' experience of stereoscopic 3D video quality by preparing two subjective assessment datasets. The first dataset aimed at the evaluation of efficient transmission in the transmission error free case, while the second focused on error concealment. A total of three subjective assessments, two for first dataset and one for the second, were performed using the Absolute Category Rating with Hidden unimpaired Reference video (ACR-HR) method. The experimental setup allows to show that the ACR-HR subjective method provides repeatable results across labs and across conditions for video quality. It was also verified that MVC is more efficient than H.264 simulcast coding. Furthermore it was discovered that based on the same level of quality of experience spatial down-sampling may lead to better bitrate efficiency while temporal down-sampling is not acceptable. When network impairments occur, traditional error 2D concealment methods need to be reinvestigated as they were outperformed by displaying the same view for both eyes (switching to 2D presentation).

Mots clés: 3DTV , QoE , error concealment , subjective experiment methodology , subjective video quality assessment , video coding.

On LARS/homotopy equivalence conditions for over-determined LASSO
J. Duan, Ch. Soussen, D. Brie, J. Idier, Y-P. Wang.
IEEE Signal Processing Letters, (2012-12), Vol 19, 12, pp. 894-897, [hal-00738715].

RésuméWe revisit the positive cone condition given by Efron et al. [1] for the over-determined least absolute shrinkage and selection operator (LASSO). It is a sufficient condition ensuring that the number of nonzero entries in the solution vector keeps increasing when the penalty parameter decreases, based on which the least angle regression (LARS) [1] and homotopy [2] algorithms yield the same iterates. We show that the positive cone condition is equivalent to the diagonal dominance of the Gram matrix inverse, leading to a simpler way to check the positive cone condition in practice. Moreover, we elaborate on a connection between the positive cone condition and the mutual coherence condition given by Donoho and Tsaig [3], ensuring the exact recovery of any k-sparse representation using both LARS and homotopy.

Mots clés: l1-norm; k-step solution property; LARS; LASSO; positive cone condition; diagonally dominant; homotopy.

Saillance Visuelle, de la 2D à la 3D Stéréoscopique : Examen des Méthodes Psychophysique et Modélisation Computationnelle
J. Wang.
2012-11-16, Dir.: Patrick Le Callet, Organisme: Université de Nantes Angers Le Mans, : Mathématiques, Sciences et Technologies de l'Information (Informatique), [tel-00785971].

RésuméL'attention visuelle est l'un des mécanismes les plus importants mis en oeuvre par le système visuel humain (SVH) afin de réduire la quantité d'information que le cerveau a besoin de traiter pour appréhender le contenu d'une scène. Un nombre croissant de travaux est consacré à l'étude de l'attention visuelle, et en particulier à sa modélisation computationnelle. Dans cette thèse, nous présentons des études portant sur plusieurs aspects de cette recherche. Nos travaux peuvent être classés globalement en deux parties. La première concerne les questions liées à la vérité de terrain utilisée, la seconde est relative à la modélisation de l'attention visuelle dans des conditions de visualisation 3D. Dans la première partie, nous analysons la fiabilité de cartes de densité de fixation issues de différentes bases de données occulométriques. Ensuite, nous identifions quantitativement les similitudes et les différences entre carte de densité de fixation et carte d'importance visuelle, ces deux types de carte étant les vérités de terrain communément utilisées par les applications relatives à l'attention. Puis, pour faire face au manque de vérité de terrain exploitable pour la modélisation de l'attention visuelle 3D, nous procédons à une expérimentation oculométrique binoculaire qui aboutit à la création d'une nouvelle base de données avec des images stéréoscopiques 3D. Dans la seconde partie, nous commençons par examiner l'impact de la profondeur sur l'attention visuelle dans des conditions de visualisation 3D. Nous quantifions d'abord le " biais de profondeur " lié à la visualisation de contenus synthétiques 3D sur écran plat stéréoscopique. Ensuite, nous étendons notre étude avec l'usage d'images 3D au contenu naturel. Nous proposons un modèle de l'attention visuelle 3D basé saillance de profondeur, modèle qui repose sur le contraste de profondeur de la scène. Deux façons différentes d'exploiter l'information de profondeur par notre modèle sont comparées. Ensuite, nous étudions le biais central et les différences qui existent selon que les conditions de visualisation soient 2D ou 3D. Nous intégrons aussi le biais central à notre modèle de l'attention visuelle 3D. Enfin, considérant que l'attention visuelle combinée à une technique de floutage peut améliorer la qualité d'expérience de la TV-3D, nous étudions l'influence de flou sur la perception de la profondeur, et la relation du flou avec la disparité binoculaire.

Mots clés: Attention visuelle, modèle computationnel, occulométrie, 3DTV, saillance visuelle, importance visuelle, expérience subjective, stéréoscopie.

Study of depth bias of observers in free viewing of still stereoscopic synthetic stimuli
J. Wang, P. Le Callet, S. Tourancheau, V. Ricordel, M. Perreira Da Silva.
Journal of Eye Movement Research, (2012-09-06), Vol 5, 5, pp. pp. 1-11, [hal-00730667].

RésuméObservers' fixations exhibit a marked bias towards certain areas on the screen when viewing scenes on computer monitors. For instance, there exists a well-known "center-bias" which means that fixations are biased towards the center of the screen during the viewing of 2D still images. In the viewing of 3D content, stereoscopic displays enhance depth perception by the mean of binocular parallax. This additional depth cue has a great influence on guiding eye movements. Relatively little is known about the impact of binocular parallax on visual attention of the 3D content displayed on stereoscopic screen. Several studies mentioned that people tend to look preferably at the objects located at certain positions in depth. But studies proving or quantifying this depth-bias are still limited. In this paper, we conducted a binocular eye-tracking experiment by showing synthetic stimuli on a stereoscopic display. Observers were required to do a free-viewing task through passive polarized glasses. Gaze positions of both eyes were recorded and the depth of eyes' fixation was determined. The stimuli used in the experiment were designed in such a way that the center-bias and the depth-bias affect eye movements individually. Results indicate the existence of a depth-bias: objects closer to the viewer attract attention earlier than distant objects, and the number of fixations located on objects varies as a function of objects' depth. The closest object in a scene always attracts most fixations. The fixation distribution along depth also shows a convergent behavior as the viewing time increases.

Mots clés: visual attention ; 3DTV ; stereoscopy ; eye-tracking ; depth bias.

Walking and steering control for a 3D biped robot considering ground contact and stability
T. Wang, Ch. Chevallereau, C. Rengifo.
Robotics and Autonomous Systems, (2012-07), Vol 60, 7, pp. 962-977, [hal-00794617].

RésuméThis paper presents a stable walking control method for a 3D bipedal robot with 14 joint actuators. The overall control law consists of a ZMP (zero moment point) controller, a swing ankle rotation controller and a partial joint angles controller. The ZMP controller guarantees that the stance foot remains in flat contact with the ground. The swing ankle rotation controller ensures a flat foot impact at the end of the swinging phase. Each of these controllers creates 2 constraints on joint accelerations. As a consequence, the partial joint angles controller is implemented to track only 10 independent outputs. These outputs are defined as a linear combination of the 14 joint angles. The most important question addressed in this paper is how this linear combination can be defined in order to ensure walking stability. The stability of the walking gait under closed loop control is evaluated with the linearization of the restricted Poincare map of the hybrid zero dynamics. As a result, the robot can achieve an asymptotically stable and periodic walking along a straight line. Finally, another feedback controller is supplemented to adjust the walking direction of the robot and some examples of the robot steered to walk along different paths with mild curvature are given.

Mots clés: Bipedal robots Steering control Zero-moment-point control On line trajectory-modification.