A luminance-contrast-aware disparity model and applications

Binocular disparity is one of the most important depth cues used by the human visual system. Recently developed stereo-perception models allow us to successfully manipulate disparity in order to improve viewing comfort, depth discrimination as well as stereo content compression and display. Nonetheless, all existing models neglect the substantial influence of luminance on stereo perception. Our work is the first to account for the interplay of luminance contrast (magnitude/frequency) and disparity and our model predicts the human response to complex stereo-luminance images. Besides improving existing disparity-model applications (e.g., difference metrics or compression), our approach offers new possibilities, such as joint luminance contrast and disparity manipulation or the optimization of auto-stereoscopic content. We validate our results in a user study, which also reveals the advantage of considering luminance contrast and its significant impact on disparity manipulation techniques.National Science Foundation (U.S.) (CGV-1111415

Methods for reducing visual discomfort in stereoscopic 3D: A review

This work was supported by the EPSRC Grant EP/M01469X/1, “Geometric Evaluation of Stereoscopic Video”

Astigmatism and Pseudoaccommodation in Pseudophakic Eyes

noAdvanced IOLs with circumferential zones of different power provide pseudoaccommodation. We investigated the potential for power variation with meridian, namely astigmatism, to provide pseudo-accommodation. With appropriate power and axis orientations, acceptable pseudo-accommodation can be achieved

Compression and Subjective Quality Assessment of 3D Video

In recent years, three-dimensional television (3D TV) has been broadly considered as the successor to the existing traditional two-dimensional television (2D TV) sets. With its capability of offering a dynamic and immersive experience, 3D video (3DV) is expected to expand conventional video in several applications in the near future. However, 3D content requires more than a single view to deliver the depth sensation to the viewers and this, inevitably, increases the bitrate compared to the corresponding 2D content. This need drives the research trend in video compression field towards more advanced and more efficient algorithms. Currently, the Advanced Video Coding (H.264/AVC) is the state-of-the-art video coding standard which has been developed by the Joint Video Team of ISO/IEC MPEG and ITU-T VCEG. This codec has been widely adopted in various applications and products such as TV broadcasting, video conferencing, mobile TV, and blue-ray disc. One important extension of H.264/AVC, namely Multiview Video Coding (MVC) was an attempt to multiple view compression by taking into consideration the inter-view dependency between different views of the same scene. This codec H.264/AVC with its MVC extension (H.264/MVC) can be used for encoding either conventional stereoscopic video, including only two views, or multiview video, including more than two views. In spite of the high performance of H.264/MVC, a typical multiview video sequence requires a huge amount of storage space, which is proportional to the number of offered views. The available views are still limited and the research has been devoted to synthesizing an arbitrary number of views using the multiview video and depth map (MVD). This process is mandatory for auto-stereoscopic displays (ASDs) where many views are required at the viewer side and there is no way to transmit such a relatively huge number of views with currently available broadcasting technology. Therefore, to satisfy the growing hunger for 3D related applications, it is mandatory to further decrease the bitstream by introducing new and more efficient algorithms for compressing multiview video and depth maps. This thesis tackles the 3D content compression targeting different formats i.e. stereoscopic video and depth-enhanced multiview video. Stereoscopic video compression algorithms introduced in this thesis mostly focus on proposing different types of asymmetry between the left and right views. This means reducing the quality of one view compared to the other view aiming to achieve a better subjective quality against the symmetric case (the reference) and under the same bitrate constraint. The proposed algorithms to optimize depth-enhanced multiview video compression include both texture compression schemes as well as depth map coding tools. Some of the introduced coding schemes proposed for this format include asymmetric quality between the views. Knowing that objective metrics are not able to accurately estimate the subjective quality of stereoscopic content, it is suggested to perform subjective quality assessment to evaluate different codecs. Moreover, when the concept of asymmetry is introduced, the Human Visual System (HVS) performs a fusion process which is not completely understood. Therefore, another important aspect of this thesis is conducting several subjective tests and reporting the subjective ratings to evaluate the perceived quality of the proposed coded content against the references. Statistical analysis is carried out in the thesis to assess the validity of the subjective ratings and determine the best performing test cases

Perceptual Requirements for World-Locked Rendering in AR and VR

Stereoscopic, head-tracked display systems can show users realistic, world-locked virtual objects and environments. However, discrepancies between the rendering pipeline and physical viewing conditions can lead to perceived instability in the rendered content resulting in reduced realism, immersion, and, potentially, visually-induced motion sickness. The requirements to achieve perceptually stable world-locked rendering are unknown due to the challenge of constructing a wide field of view, distortion-free display with highly accurate head- and eye-tracking. In this work we introduce new hardware and software built upon recently introduced hardware and present a system capable of rendering virtual objects over real-world references without perceivable drift under such constraints. The platform is used to study acceptable errors in render camera position for world-locked rendering in augmented and virtual reality scenarios, where we find an order of magnitude difference in perceptual sensitivity between them. We conclude by comparing study results with an analytic model which examines changes to apparent depth and visual heading in response to camera displacement errors. We identify visual heading as an important consideration for world-locked rendering alongside depth errors from incorrect disparity

Optical and visual quality of two scleral lenses

Dissertação de mestrado em Optometria AvançadaAtualmente, as lentes esclerais são bastante adaptadas em pacientes que sofrem de doenças da superfície ocular. Estes dispositivos são também indicados em várias doenças ou irregularidades corneais devido à sua capacidade de criarem um reservatório de líquido, que irá compensar a maior parte das irregularidades da superfície. As inovações tecnológicas têm providenciado uma larga diversidade de desenhos e materiais de lentes esclerais. Contudo, ainda existem poucos estudos que reportem o uso prolongado destas lentes e como a qualidade ótica pode ser influenciada por este uso prolongado. Assim, com este trabalho pretende-se avaliar a resposta da superfície ocular quando uma lente nova e diferente é adaptada bem como entender se é possível readaptar usuários habituais de lentes esclerais a partir dos dados obtidos com a topografia corneal. Neste estudo, os resultados com uma lente escleral (Senso Mini Sclera, 16.4 mm), usada durante mais de 12 meses, foram comparados com os resultados de uma nova lente de outra marca de lentes esclerais (ICD, 16.5 mm), readaptada e usada durante 1 mês. Dos principais resultados obtidos, observou-se que existiam algumas diferenças na qualidade ótica entre a Senso Mini Sclera e a ICD, no entanto os resultados subjetivos não mostraram diferenças significativas relativamente à visão e ao conforto entre ambas as lentes. Os dados da resposta da superfície ocular mostraram valores significativamente mais baixos de hiperemia bulbar, hiperemia limbar, tingido limbar e tingido corneal após 1 mês de uso da lente ICD, quando comparados aos valores obtidos imediatamente após retirar a Senso Mini Sclera. Os resultados mostraram que os dados de elevação na corda de 6mm, obtidos com um topografo corneal comum, estavam correlacionados com as alturas sagitais das lentes ICD diagnóstico e finais. Os resultados com a lente ICD em duas visitas diferentes (após 3h, na visita de entrega, e após 1 mês) não revelaram diferenças significativas, mostrando que a avaliação a curto prazo é um bom preditor dos resultados a médio prazo. Em conclusão, com este estudo foi verificado que pode ser possível readaptar usuários habituais de lentes esclerais com outra lente escleral, apesar de possuírem características diferentes, mantendo a qualidade ótica e o conforto. As pequenas diferenças entre as duas lentes podem estar relacionadas com o tempo de uso da Senso Mini Sclera, que pode ter um pequeno impacto na degradação da qualidade ótica. Os resultados deste estudo sugerem que as maiores respostas da superfície ocular com a Senso Mini Sclera podem ser devido à degradação que a lente sofre com o tempo ou devido às diferenças nos materiais das lentes.Nowadays, scleral lenses are largely fitted to patients who suffer from ocular surface diseases. These devices are also indicated in several corneal disorders or irregularities due to the capability of create a fluid reservoir, which will compensate most of the surface irregularities. Technological innovations have provided a large diversity of scleral lenses designs and materials. However, there are still very few studies reporting the long-term use of these lenses and how optical quality could be influenced by this long-term use. This work intents to evaluate the ocular surface response when a new different lens is fitted and to understand if it is possible to refit habitual scleral lenses users, from the data obtained with corneal topography. In this study, the results with a scleral lens (Senso Mini Sclera, 16.4 mm), used for more than 12 months, were compared to the results of a new lens from another scleral lens (ICD, 16.5 mm), refitted and used during 1 month. From the main outcomes obtained, it was observed that there were a few differences on optical quality between Senso Mini Sclera and ICD, although the subjective results showed no significant differences relatively to vision and comfort between both lenses. The data from ocular surface response showed lower statistically significant values of bulbar hyperemia, limbal hyperemia, limbal staining and corneal staining after 1 month of ICD lens wear when compared to the values immediately after Senso Mini Sclera removal. The results showed that the 6mm chord elevation data, obtained with a common corneal topographer, was correlated with diagnostic and final sagittal depth of ICD lenses. The results with ICD in two different visits (after 3h on the dispensing visit and after 1 month) did not reveal significative differences, showing that the short-term evaluation is a good predictor of the medium-term behavior. In conclusion, with this study we verified that might be possible to refit habitual scleral lens users with another scleral lens, despite the different characteristics, maintaining the optical quality and comfort. The small differences between the two lenses may be correlated with Senso Mini Sclera lifetime, which could have a small impact on optical quality degradation. The results of this study suggest that the highest ocular surface response values with Senso Mini Sclera might be due to the degradation that lens suffered over time or due to the differences on lenses material

Stereoscopic Cinema

International audienceStereoscopic cinema has seen a surge of activity in recent years, and for the first time all of the major Hollywood studios released 3-D movies in 2009. This is happening alongside the adoption of 3-D technology for sports broadcasting, and the arrival of 3-D TVs for the home. Two previous attempts to introduce 3-D cinema in the 1950s and the 1980s failed because the contemporary technology was immature and resulted in viewer discomfort. But current technologies – such as accurately-adjustable 3-D camera rigs with onboard computers to automatically inform a camera operator of inappropriate stereoscopic shots, digital processing for post-shooting rectification of the 3-D imagery, digital projectors for accurate positioning of the two stereo projections on the cinema screen, and polarized silver screens to reduce cross-talk between the viewers left- and right-eyes – mean that the viewer experience is at a much higher level of quality than in the past. Even so, creation of stereoscopic cinema is an open, active research area, and there are many challenges from acquisition to post-production to automatic adaptation for different-sized display. This chapter describes the current state-of-the-art in stereoscopic cinema, and directions of future work

A wearable biofeedback device to improve motor symptoms in Parkinson’s disease

Dissertação de mestrado em Engenharia BiomédicaThis dissertation presents the work done during the fifth year of the course Integrated Master’s in Biomedical Engineering, in Medical Electronics. This work was carried out in the Biomedical & Bioinspired Robotic Devices Lab (BiRD Lab) at the MicroElectroMechanics Center (CMEMS) established at the University of Minho. For validation purposes and data acquisition, it was developed a collaboration with the Clinical Academic Center (2CA), located at Braga Hospital. The knowledge acquired in the development of this master thesis is linked to the motor rehabilitation and assistance of abnormal gait caused by a neurological disease. Indeed, this dissertation has two main goals: (1) validate a wearable biofeedback system (WBS) used for Parkinson's disease patients (PD); and (2) develop a digital biomarker of PD based on kinematic-driven data acquired with the WBS. The first goal aims to study the effects of vibrotactile biofeedback to play an augmentative role to help PD patients mitigate gait-associated impairments, while the second goal seeks to bring a step advance in the use of front-end algorithms to develop a biomarker of PD based on inertial data acquired with wearable devices. Indeed, a WBS is intended to provide motor rehabilitation & assistance, but also to be used as a clinical decision support tool for the classification of the motor disability level. This system provides vibrotactile feedback to PD patients, so that they can integrate it into their normal physiological gait system, allowing them to overcome their gait difficulties related to the level/degree of the disease. The system is based on a user- centered design, considering the end-user driven, multitasking and less cognitive effort concepts. This manuscript presents all steps taken along this dissertation regarding: the literature review and respective critical analysis; implemented tech-based procedures; validation outcomes complemented with results discussion; and main conclusions and future challenges.Esta dissertação apresenta o trabalho realizado durante o quinto ano do curso Mestrado Integrado em Engenharia Biomédica, em Eletrónica Médica. Este trabalho foi realizado no Biomedical & Bioinspired Robotic Devices Lab (BiRD Lab) no MicroElectroMechanics Center (CMEMS) estabelecido na Universidade do Minho. Para efeitos de validação e aquisição de dados, foi desenvolvida uma colaboração com Clinical Academic Center (2CA), localizado no Hospital de Braga. Os conhecimentos adquiridos no desenvolvimento desta tese de mestrado estão ligados à reabilitação motora e assistência de marcha anormal causada por uma doença neurológica. De facto, esta dissertação tem dois objetivos principais: (1) validar um sistema de biofeedback vestível (WBS) utilizado por doentes com doença de Parkinson (DP); e (2) desenvolver um biomarcador digital de PD baseado em dados cinemáticos adquiridos com o WBS. O primeiro objetivo visa o estudo dos efeitos do biofeedback vibrotáctil para desempenhar um papel de reforço para ajudar os pacientes com PD a mitigar as deficiências associadas à marcha, enquanto o segundo objetivo procura trazer um avanço na utilização de algoritmos front-end para biomarcar PD baseado em dados inerciais adquiridos com o dispositivos vestível. De facto, a partir de um WBS pretende-se fornecer reabilitação motora e assistência, mas também utilizá-lo como ferramenta de apoio à decisão clínica para a classificação do nível de deficiência motora. Este sistema fornece feedback vibrotáctil aos pacientes com PD, para que possam integrá-lo no seu sistema de marcha fisiológica normal, permitindo-lhes ultrapassar as suas dificuldades de marcha relacionadas com o nível/grau da doença. O sistema baseia-se numa conceção centrada no utilizador, considerando o utilizador final, multitarefas e conceitos de esforço menos cognitivo. Portanto, este manuscrito apresenta todos os passos dados ao longo desta dissertação relativamente a: revisão da literatura e respetiva análise crítica; procedimentos de base tecnológica implementados; resultados de validação complementados com discussão de resultados; e principais conclusões e desafios futuros