Méthodes pour l'évaluation et la prédiction de la Qualité d'expérience, la préférence et l'inconfort visuel dans les applications multimédia. Focus sur la TV 3D stéréoscopique

Multimedia technology is aiming to improve people's viewing experience, seeking for better immersiveness and naturalness. The development of HDTV, 3DTV, and Ultra HDTV are recent illustrative examples of this trend. The Quality of Experience (QoE) in multimedia encompass multiple perceptual dimensions. For instance, in 3DTV, three primary dimensions have been identified in literature: image quality, depth quality and visual comfort. In this thesis, focusing on the 3DTV, two basic questions about QoE are studied. One is "how to subjectively assess QoE taking care of its multidimensional aspect?". The other is dedicated to one particular dimension, i.e., "what would induce visual discomfort and how to predict it?". In the first part, the challenges of the subjective assessment on QoE are introduced, and a possible solution called "Paired Comparison" is analyzed. To overcome drawbacks of Paired Comparison method, a new formalism based on a set of optimized paired comparison designs is proposed and evaluated by different subjective experiments. The test results verified efficiency and robustness of this new formalism. An application is the described focusing on the evaluation of the influence factor on 3D QoE. In the second part, the influence of 3D motion on visual discomfort is studied. An objective visual discomfort model is proposed. The model showed high correlation with the subjective data obtained through various experimental conditions. Finally, a physiological study on the relationship between visual discomfort and eye blinking rate is presented.La technologie multimédia vise à améliorer l'expérience visuelle des spectateurs, notamment sur le plan de l'immersion. Les développements récents de la TV HD, TV 3D, et TV Ultra HD s'inscrivent dans cette logique. La qualité d'expérience (QoE) multimédia implique plusieurs dimensions perceptuelles. Dans le cas particulier de la TV 3D stéréoscopique, trois dimensions primaires ont été identifiées dans la littérature: qualité d'image, qualité de la profondeur et confort visuel. Dans cette thèse, deux questions fondamentales sur la QoE sont étudiés. L'une a pour objet "comment évaluer subjectivement le caractère multidimensionnel de la QoE". L'autre s'intéresse à une dimension particuliére de QoE, "la mesure de l'inconfort et sa prédiction?". Dans la première partie, les difficultés de l'évaluation subjective de la QoE sont introduites, les mérites de méthodes de type "Comparaison par paire" (Paired Comparison en anglais) sont analysés. Compte tenu des inconvénients de la méthode de Comparaison par paires, un nouveau formalisme basé sur un ensemble de comparaisons par paires optimisées, est proposé. Celui-ci est évalué au travers de différentes expériences subjectives. Les résultats des tests confirment l'efficacité et la robustesse de ce formalisme. Un exemple d'application dans le cas de l'étude de l'évaluation des facteurs influençant la QoE est ensuite présenté. Dans la seconde partie, l'influence du mouvement tri-dimensionnel (3D) sur l'inconfort visuel est étudié. Un modèle objectif de l'inconfort visuel est proposé. Pour évaluer ce modèle, une expérience subjective de comparaison par paires a été conduite. Ce modèle de prédiction conduit à des corrélations élevées avec les données subjectives. Enfin, une étude sur des mesures physiologiques tentant de relier inconfort visuel et fréquence de clignements des yeux présentée

Analyzing autostereoscopic environment confgurations for the design of videogames

Stereoscopic devices are becoming more popular every day. The 3D visualization that these displays ofer is being used by videogame designers to enhance the user’s game experience. Autostereoscopic monitors ofer the possibility of obtaining this 3D visualization without the need for extra device. This fact makes them more attractive to videogame developers. However, the confguration of the cameras that make it possible to obtain an immersive 3D visualization inside the game is still an open problem. In this paper, some system confgurations that create autostereoscopic visualization in a 3D game engine were evaluated to obtain a good accommodation of the user experience with the game. To achieve this, user tests that take into account the movement of the player were carried out to evaluate diferent camera confgurations, namely, dynamic and static converging optical axis and parallel optical axis. The purpose of these tests is to evaluate the user experience regarding visual discomfort resulting from the movement of the objects, with the purpose of assessing the preference for one confguration or the other. The results show that the users tend to have a preference trend for the parallel optical axis confguration set. This confguration seems to be optimal because the area where the moving objects are focused is deeper than in the other confgurations

Quality of Experience Comparison of Stereoscopic 3D Videos in Different Projection Devices: Flat Screen, Panoramic Screen and Virtual Reality Headset

The use of Stereoscopic 3D (S3D) videos has been popular in commercial markets with ongoing developments in the field of visual entertainment in recent years. A wide variety of projection methods of 3D video content is currently available, such as projection to a panoramic screen and projection of omnidirectional video content from head mounted displays using Virtual Reality (VR) technology. This article investigates the Quality of Experience (QoE) and associated Visually Induced Motion Sickness (VIMS) caused by the viewing of S3D videos. The investigations used three different projection screens: a 3D flat screen, a 3D panoramic screen in a hemispherical shaped room and a VR headset. Several assessment methods including a Simulator Sickness Questionnaire (SSQ), ElectroEncephaloGraphy (EEG), and measurement tools for eye blink rate detection were applied to measure the QoE experienced by viewers. The SSQ scores were also compared with the behavioral data such as attention and meditation levels and enjoyment ratings acquired from different video content and projection screens. The results indicate that the projection screen is a key factor affecting the level of visual fatigue, VIMS and QoE assessments, which are discussed in-depth in the article

Effects of task duration, display curvature, and presbyopia on physiological and perceived visual fatigue for 27??? desktop monitors

Department of Human and Systems EngineeringWith the advancement of display technologies, more diverse display products are available around us. VDT (Visual Display Terminal) tasks are, however, associated with various visual fatigue symptoms that can reduce work efficiency and task performance. Such results can be more severe for older individuals with diminished visual abilities, which typically start around the age of 40. However, studies on visual fatigue of older individuals are relatively fewer than those for younger individuals. Though, proper work-rest schedules are deemed to reduce visual fatigue, workers have difficulty in taking rest breaks due to many reasons. It is expected that a real-time rest reminder will be effective because the time to onset of visual fatigue can vary as visual fatigue is affected by many factors including individual and task characteristics. Curved displays provide relatively even viewing distances across their display surface for the center viewer than flat displays, which could benefit viewing experience while reducing visual fatigue. Indeed, some studies on display curvature demonstrated that curved displays are more effective than flat displays in terms of task performance, visual fatigue, and preference. Previously, various physiological measures (e.g. accommodation amplitude and near point accommodation) were considered as indices of visual fatigue. Using these measures to predict visual fatigue in daily life are, however, not practical because of difficulties in measuring and/or needs for high-cost equipment. The aims of the current study were 1) to examine the effects of task duration, display curvature, and presbyopia on physiological and perceived visual fatigue and display satisfaction associated with performing proofreading tasks on 27??? displays, and 2) to develop a prediction model for visual fatigue using pupil- and bulbar conjunctiva-related measurements which can be easily obtained in daily life. A total of 64 participants (32 for each age group) performed a 1-hr proofreading task. The current study considered task duration (within-subjects0, 15, 30, 45, and 60 min), display curvature (between-subjects600mm, 1140mm, 4000mm, and flat) and age group [between-subjectsyounger (20-35 yrs) and older (45-60 yrs)] as independent variables. Pupil diameter, bulbar conjunctival redness, perceived visual fatigue [measured in ECQ (Eye Complaint Questionnaire) scores], and display satisfaction were obtained every 15 minutes, while CFF (Critical Fusion Frequency) was obtained pre and post the 1-hr proofreading task. The rear-projection environment was comprised of 27??? curved rear screens, a beam projector, and the Warpalizer software. Environmental factors that can affect visual fatigue were controlled. An eye tracking system, a digital camera, and a flicker fusion system were used to measure physiological measures of visual fatigue, and a series of questionnaires were used to measure perceived visual fatigue and satisfaction of display. 3-way ANOVA was used to examine how 3 independent variables and their interactions affected each of 5 dependent variables. Four methods were considered in developing prediction models for visual fatigue and display satisfaction, and the developed models were compared in terms of predictive accuracy. The results showed that over the 1-hr task, pupil diameters decreased (5.1%), bulbar conjunctival redness increased (18.8%), CFF thresholds decreased (0.94%), and ECQ scores increased (207%), all indicating an increase in visual fatigue. Even with a 15 min of VDT task, visual fatigue increased significantly. At the 1140mm curvature, pupil diameters were the largest, indicating less visual fatigue, and the display satisfaction of the older group, though not significant, gradually increased over the 1-hr task, indicating a less increase in visual fatigue. Display satisfaction was not affected by any independent variables. In terms of predictive accuracy of visual fatigue, the artificial neural network model was the best followed by the 3rd degree polynomial regression model. The results of this study can be utilized when scheduling work-rest, determining a better display curvature for 27??? displays, and predicting visual fatigue in real time to notify the time to take a rest.ope

Biosignalų požymių regos diskomfortui vertinti išskyrimas ir tyrimas

Comfortable stereoscopic perception continues to be an essential area of research. The growing interest in virtual reality content and increasing market for head-mounted displays (HMDs) still cause issues of balancing depth perception and comfortable viewing. Stereoscopic views are stimulating binocular cues – one type of several available human visual depth cues which becomes conflicting cues when stereoscopic displays are used. Depth perception by binocular cues is based on matching of image features from one retina with corresponding features from the second retina. It is known that our eyes can tolerate small amounts of retinal defocus, which is also known as Depth of Focus. When magnitudes are larger, a problem of visual discomfort arises. The research object of the doctoral dissertation is a visual discomfort level. This work aimed at the objective evaluation of visual discomfort, based on physiological signals. Different levels of disparity and the number of details in stereoscopic views in some cases make it difficult to find the focus point for comfortable depth perception quickly. During this investigation, a tendency for differences in single sensor-based electroencephalographic EEG signal activity at specific frequencies was found. Additionally, changes in eye tracker collected gaze signals were also found. A dataset of EEG and gaze signal records from 28 control subjects was collected and used for further evaluation. The dissertation consists of an introduction, three chapters and general conclusions. The first chapter reveals the fundamental knowledge ways of measuring visual discomfort based on objective and subjective methods. In the second chapter theoretical research results are presented. This research was aimed to investigate methods which use physiological signals to detect changes on the level of sense of presence. Results of the experimental research are presented in the third chapter. This research aimed to find differences in collected physiological signals when a level of visual discomfort changes. An experiment with 28 control subjects was conducted to collect these signals. The results of the thesis were published in six scientific publications – three in peer-reviewed scientific papers, three in conference proceedings. Additionally, the results of the research were presented in 8 conferences.Dissertatio

Une méthode pour l'évaluation de la qualité des images 3D stéréoscopiques.

Dans le contexte d'un intérêt grandissant pour les systèmes stéréoscopiques, mais sans méthodes reproductible pour estimer leur qualité, notre travail propose une contribution à la meilleure compréhension des mécanismes de perception et de jugement humains relatifs au concept multi-dimensionnel de qualité d'image stéréoscopique. Dans cette optique, notre démarche s'est basée sur un certain nombre d'outils : nous avons proposé un cadre adapté afin de structurer le processus d'analyse de la qualité des images stéréoscopiques, nous avons implémenté dans notre laboratoire un système expérimental afin de conduire plusieurs tests, nous avons crée trois bases de données d'images stéréoscopiques contenant des configurations précises et enfin nous avons conduit plusieurs expériences basées sur ces collections d'images. La grande quantité d'information obtenue par l'intermédiaire de ces expérimentations a été utilisée afin de construire un premier modèle mathématique permettant d'expliquer la perception globale de la qualité de la stéréoscopie en fonction des paramètres physiques des images étudiée.In a context of ever-growing interest in stereoscopic systems, but where no standardized algorithmic methods of stereoscopic quality assessment exist, our work stands as a step forward in the understanding of the human perception and judgment mechanisms related to the multidimensional concept of stereoscopic image quality. We used a series of tools in order to perform in-depth investigations in this direction: we proposed an adapted framework to structure the process of stereoscopic quality assessment, we implemented a stereoscopic system in our laboratory for performing various tests, we created three stereoscopic datasets with precise structures, and we performed several experimental studies using these datasets. The numerous experimental data obtained were used in order to propose a first mathematical framework for explaining the overall percept of stereoscopic quality in function of the physical parameters of the stereoscopic images under study.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Remote Visual Observation of Real Places Through Virtual Reality Headsets

Virtual Reality has always represented a fascinating yet powerful opportunity that has attracted studies and technology developments, especially since the latest release on the market of powerful high-resolution and wide field-of-view VR headsets. While the great potential of such VR systems is common and accepted knowledge, issues remain related to how to design systems and setups capable of fully exploiting the latest hardware advances. The aim of the proposed research is to study and understand how to increase the perceived level of realism and sense of presence when remotely observing real places through VR headset displays. Hence, to produce a set of guidelines that give directions to system designers about how to optimize the display-camera setup to enhance performance, focusing on remote visual observation of real places. The outcome of this investigation represents unique knowledge that is believed to be very beneficial for better VR headset designs towards improved remote observation systems. To achieve the proposed goal, this thesis presents a thorough investigation of existing literature and previous researches, which is carried out systematically to identify the most important factors ruling realism, depth perception, comfort, and sense of presence in VR headset observation. Once identified, these factors are further discussed and assessed through a series of experiments and usability studies, based on a predefined set of research questions. More specifically, the role of familiarity with the observed place, the role of the environment characteristics shown to the viewer, and the role of the display used for the remote observation of the virtual environment are further investigated. To gain more insights, two usability studies are proposed with the aim of defining guidelines and best practices. The main outcomes from the two studies demonstrate that test users can experience an enhanced realistic observation when natural features, higher resolution displays, natural illumination, and high image contrast are used in Mobile VR. In terms of comfort, simple scene layouts and relaxing environments are considered ideal to reduce visual fatigue and eye strain. Furthermore, sense of presence increases when observed environments induce strong emotions, and depth perception improves in VR when several monocular cues such as lights and shadows are combined with binocular depth cues. Based on these results, this investigation then presents a focused evaluation on the outcomes and introduces an innovative eye-adapted High Dynamic Range (HDR) approach, which the author believes to be of great improvement in the context of remote observation when combined with eye-tracked VR headsets. Within this purpose, a third user study is proposed to compare static HDR and eye-adapted HDR observation in VR, to assess that the latter can improve realism, depth perception, sense of presence, and in certain cases even comfort. Results from this last study confirmed the author expectations, proving that eye-adapted HDR and eye tracking should be used to achieve best visual performances for remote observation in modern VR systems

Multimodality for Passive Experience: Effects of Visual, Auditory, Vibration and Draught Stimuli on Sense of Presence

Adequate use of multimodal stimuli plays a crucial role in help forming the sense of presence within a virtual environment. While most of the presence research attempts to engage more sensory modalities to induce a higher sense of presence, this paper investigates the relevance of each sensory modality and different combinations on the subjective sense of presence using a specifically designed scenario of a passive experience. We chose a neutral test scenario of “waiting at a train station while a train is passing by” to avoid the potential influence of story narrative on mental presence and replicated realistic multimodal stimuli that are highly relevant to our test setting. All four stimuli -visual, auditory, vibration, and draught -with 16 possibilities of combinations were systematically evaluated with 24 participants. The evaluation was performed on one crucial aspect of presence –“realness” to reflect user presence in general. The perceived realism value was assessed using a scalometer. The findings of main effects indicate that the auditory stimuli had the most significant contribution in creating the sense of presence. The results of interaction effects suggest the impact of draught stimuli is significant in relation to other stimuli -visual and auditory. Also, the gender effects revealed that the sense of presence reported by female participants is influenced by more factors than merely adding more sensory modalities