18 research outputs found

    A Novel Light Field Coding Scheme Based on Deep Belief Network and Weighted Binary Images for Additive Layered Displays

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    Light field display caters to the viewer's immersive experience by providing binocular depth sensation and motion parallax. Glasses-free tensor light field display is becoming a prominent area of research in auto-stereoscopic display technology. Stacking light attenuating layers is one of the approaches to implement a light field display with a good depth of field, wide viewing angles and high resolution. This paper presents a compact and efficient representation of light field data based on scalable compression of the binary represented image layers suitable for additive layered display using a Deep Belief Network (DBN). The proposed scheme learns and optimizes the additive layer patterns using a convolutional neural network (CNN). Weighted binary images represent the optimized patterns, reducing the file size and introducing scalable encoding. The DBN further compresses the weighted binary patterns into a latent space representation followed by encoding the latent data using an h.254 codec. The proposed scheme is compared with benchmark codecs such as h.264 and h.265 and achieved competitive performance on light field data

    Soppressione centrale intermittente: confronto tra soggetti presbiti e non-presbiti

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    Dopo una breve introduzione che mira a descrivere cos’è e a che cosa è dovuta la presbiopia, ho illustrato la relazione che lega la fisiologica riduzione dell’ampiezza accomodativa e il fenomeno della soppressione centrale intermittente. Grazie all’utilizzo di un questionario, della Wesson Card, del cover test e di alcuni test optometrici presenti su un tablet 3D con sistema a dissociazione senza occhiali, ho indagato circa le condizioni in cui si presenta tale fenomeno e le conseguenze che comporta. After a brief introduction aimed at describing what presbyopia is and what it is due to, I illustrated the relationship that links the physiological reduction of accommodative amplitude and the phenomenon of intermittent central suppression. Thanks to the use of a questionnaire, the Wesson Card, the cover test and some optometric tests on a 3D tablet with dissociation system without glasses, I investigated the conditions in which this phenomenon occurs and the consequences that involves

    Compression and visual quality assessment for light field contents

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    Since its invention in the 19th century, photography has allowed to create durable images of the world around us by capturing the intensity of light that flows through a scene, first analogically by using light-sensitive material, and then, with the advent of electronic image sensors, digitally. However, one main limitation of both analog and digital photography lays in its inability to capture any information about the direction of light rays. Through traditional photography, each three-dimensional scene is projected onto a 2D plane; consequently, no information about the position of the 3D objects in space is retained. Light field photography aims at overcoming these limitations by recording the direction of light along with its intensity. In the past, several acquisition technologies have been presented to properly capture light field information, and portable devices have been commercialized to the general public. However, a considerably larger volume of data is generated when compared to traditional photography. Thus, new solutions must be designed to face the challenges light field photography poses in terms of storage, representation, and visualization of the acquired data. In particular, new and efficient compression algorithms are needed to sensibly reduce the amount of data that needs to be stored and transmitted, while maintaining an adequate level of perceptual quality. In designing new solutions to address the unique challenges posed by light field photography, one cannot forgo the importance of having reliable, reproducible means of evaluating their performance, especially in relation to the scenario in which they will be consumed. To that end, subjective assessment of visual quality is of paramount importance to evaluate the impact of compression, representation, and rendering models on user experience. Yet, the standardized methodologies that are commonly used to evaluate the visual quality of traditional media content, such as images and videos, are not equipped to tackle the challenges posed by light field photography. New subjective methodologies must be tailored for the new possibilities this new type of imaging offers in terms of rendering and visual experience. In this work, we address the aforementioned problems by both designing new methodologies for visual quality evaluation of light field contents, and outlining a new compression solution to efficiently reduce the amount of data that needs to be transmitted and stored. We first analyse how traditional methodologies for subjective evaluation of multimedia contents can be adapted to suit light field data, and, we propose new methodologies to reliably assess the visual quality while maintaining user engagement. Furthermore, we study how user behavior is affected by the visual quality of the data. We employ subjective quality assessment to compare several state-of-the-art solutions in light field coding, in order to find the most promising approaches to minimize the volume of data without compromising on the perceptual quality. To that means, we define and inspect several coding approaches for light field compression, and we investigate the impact of color subsampling on the final rendered content. Lastly, we propose a new coding approach to perform light field compression, showing significant improvement with respect to the state of the art

    Ultrathin, polarization-independent, and focus-tunable liquid crystal diffractive lens for augmented reality

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    Despite the recent advances in augmented reality (AR), which has shown the potential to significantly impact on our daily lives by offering a new way to manipulate and interact with virtual information, minimizing visual discomfort due to the vergence-accommodation conflict remains a challenge. Emerging AR technologies often exploit focus-tunable optics to address this problem. Although they demonstrated improved depth perception by enabling proper focus cues, a bulky form factor of focus-tunable optics prevents their use in the form of a pair of eyeglasses. Herein, we describe an ultrathin, focus-tunable liquid crystal (LC) diffractive lens with a large aperture, a low weight, and a low operating voltage. In addition, we show that the polarization dependence of the lens, which is an inherent optical property of LC lenses, can be eliminated using birefringent thin films as substrates and by aligning the optical axes of the birefringent substrates and LC at a specific angle. The polarization independence eliminates the need for a polarizer, thus further reducing the form factor of the optical system. Next, we demonstrate a prototype of AR glasses with addressable focal planes using the ultrathin lens. The prototype AR glasses can adjust the accommodation distance of the virtual image, mitigating the vergence-accommodation conflict without substantially compromising the form factor or image quality. This research on ultrathin lens technology shows promising potential for developing compact optical displays in various applications.Comment: 23 pages, 9 figure

    A comprehensive framework for visual quality assessment of light field tensor displays

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    In recent years, light field technology has attracted the interest of academia and industry, thanks to the possibility of rendering 3D scenes in a more realistic and immersive way. In particular, light field displays have been consistently investigated for their ability to offer a glass-free 3D viewing experience. Among others, tensor displays represent a promising way to render light field contents. However, only a few prototypes of such type of displays have been implemented and are available to the scientific community. As a direct consequence, the visual quality of such displays has not been rigorously investigated. In this paper, we propose a new framework to assess the visual quality of light field tensor displays on conventional 2D screens. The multilayer components of the tensor displays are virtually rendered on a typical 2D monitor through the use of a GUI, and different viewing angles can be accessed by simple mouse interactions. Both single and double stimulus methodologies for subjective quality assessment of light field contents are supported in this framework, while the total time of interaction is recorded for every stimulus. Results obtained in two different laboratory settings demonstrate that the framework can be successfully used to perform subjective quality assessment of different compression solutions for light field tensor displays

    Light field image processing: an overview

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    Light field imaging has emerged as a technology allowing to capture richer visual information from our world. As opposed to traditional photography, which captures a 2D projection of the light in the scene integrating the angular domain, light fields collect radiance from rays in all directions, demultiplexing the angular information lost in conventional photography. On the one hand, this higher dimensional representation of visual data offers powerful capabilities for scene understanding, and substantially improves the performance of traditional computer vision problems such as depth sensing, post-capture refocusing, segmentation, video stabilization, material classification, etc. On the other hand, the high-dimensionality of light fields also brings up new challenges in terms of data capture, data compression, content editing, and display. Taking these two elements together, research in light field image processing has become increasingly popular in the computer vision, computer graphics, and signal processing communities. In this paper, we present a comprehensive overview and discussion of research in this field over the past 20 years. We focus on all aspects of light field image processing, including basic light field representation and theory, acquisition, super-resolution, depth estimation, compression, editing, processing algorithms for light field display, and computer vision applications of light field data

    Situated Displays in Telecommunication

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    In face to face conversation, numerous cues of attention, eye contact, and gaze direction provide important channels of information. These channels create cues that include turn taking, establish a sense of engagement, and indicate the focus of conversation. However, some subtleties of gaze can be lost in common videoconferencing systems, because the single perspective view of the camera doesn't preserve the spatial characteristics of the face to face situation. In particular, in group conferencing, the `Mona Lisa effect' makes all observers feel that they are looked at when the remote participant looks at the camera. In this thesis, we present designs and evaluations of four novel situated teleconferencing systems, which aim to improve the teleconferencing experience. Firstly, we demonstrate the effectiveness of a spherical video telepresence system in that it allows a single observer at multiple viewpoints to accurately judge where the remote user is placing their gaze. Secondly, we demonstrate the gaze-preserving capability of a cylindrical video telepresence system, but for multiple observers at multiple viewpoints. Thirdly, we demonstrated the further improvement of a random hole autostereoscopic multiview telepresence system in conveying gaze by adding stereoscopic cues. Lastly, we investigate the influence of display type and viewing angle on how people place their trust during avatar-mediated interaction. The results show the spherical avatar telepresence system has the ability to be viewed qualitatively similarly from all angles and demonstrate how trust can be altered depending on how one views the avatar. Together these demonstrations motivate the further study of novel display configurations and suggest parameters for the design of future teleconferencing systems

    무안경식 3 차원 디스플레이와 투사형 디스플레이를 이용한 깊이 융합 디스플레이의 관찰 특성 향상

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    학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 이병호.In this dissertation, various methods for enhancing the viewing characteristics of the depth-fused display are proposed with combination of projection-type displays or integral imaging display technologies. Depth-fused display (DFD) is one kind of the volumetric three-dimensional (3D) displays composed of multiple slices of depth images. With a proper weighting to the luminance of the images on the visual axis of the observer, it provides continuous change of the accommodation within the volume confined by the display layers. Because of its volumetric property depth-fused 3D images can provide very natural volumetric images, but the base images should be located on the exact positions on the viewing axis, which gives complete superimpose of the images. If this condition is not satisfied, the images are observed as two separated images instead of continuous volume. This viewing characteristic extremely restricts the viewing condition of the DFD resulting in the limited applications of DFDs. While increasing the number of layers can result in widening of the viewing angle and depth range by voxelizing the reconstructed 3D images, the required system complexity also increases along with the number of image layers. For solving this problem with a relatively simple configuration of the system, hybrid techniques are proposed for DFDs. The hybrid technique is the combination of DFD with other display technologies such as projection-type displays or autostereoscopic displays. The projection-type display can be combined with polarization-encoded depth method for projection of 3D information. Because the depth information is conveyed by polarization states, there is no degradation in spatial resolution or video frame in the reconstructed 3D images. The polarized depth images are partially selected at the stacked polarization selective screens according to the given depth states. As the screen does not require any active component for the reconstruction of images, projection part and reconstruction part can be totally separated. Also, the projection property enables the scalability of the reconstructed images like a conventional projection display, which can give immersive 3D experience by providing large 3D images. The separation of base images due to the off-axis observation can be compensated by shifting the base images along the viewers visual axis. It can be achieved by adopting multi-view techniques. While conventional multi-view displays provide different view images for different viewers positions, it can be used for showing shifted base images for DFD. As a result, multiple users can observe the depth-fused 3D images at the same time. Another hybrid method is the combination of floating method with DFD. Convex lens can optically translate the depth position of the object. Based on this principle, the optical gap between two base images can be extended beyond the physical dimension of the images. Employing the lens with a short focal length, the gap between the base images can be greatly reduced. For a practical implementation of the system, integral imaging method can be used because it is composed of array of lenses. The floated image can be located in front of the lens as well as behind the lens. Both cases result in the expansion of depth range beyond the physical gap of base images, but real-mode floating enables interactive application of the DFD. In addition to the expansion of depth range, the viewing angle of the hybrid system can be increased by employing tracking method. Viewer tracking method also enables dynamic parallax for the DFD with real-time update of base images along with the viewing direction of the tracked viewers. Each chapter of this dissertation explains the theoretical background of the proposed hybrid method and demonstrates the feasibility of the idea with experimental systems.Abstract i Contents iv List of Figures vi List of Tables xii Chapter 1 Introduction 1 1.1 Overview of three-dimensional displays 1 1.2 Motivation 7 1.3 Scope and organization 9 Chapter 2 Multi-layered depth-fused display with projection-type display 10 2.1 Introduction 10 2.2 Polarization-encoded depth information for depth-fused display 12 2.3 Visualization with passive scattering film 16 2.4 Summary 30 Chapter 3 Compact depth-fused display with enhanced depth and viewing angle 31 3.1 Introduction 31 3.2 Enhancement of viewing characteristics 34 3.2.1 Viewing angle enhancement using multi-view method 34 3.2.2 Depth enhancement using integral imaging 37 3.2.3 Depth and viewing angle enhancement 39 3.3 Implementation of experimental system with enhanced viewing parameters 44 3.4 Summary 51 Chapter 4 Real-mode depth-fused display with viewer tracking 52 4.1 Introduction 52 4.2 Viewer tracking method 55 4.2.1 Viewer-tracked depth-fused display 55 4.2.2 Viewer-tracked integral imaging for a depth-fused display 58 4.3 Implementation of viewer-tracked integral imaging 63 4.4 Summary 71 Chapter 5 Conclusion 72 Bibliography 74 초록 83Docto
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