Perceptual models for high-refresh-rate rendering

Rendering realistic images requires substantial computational power. With new high-refresh-rate displays as well as the renaissance of virtual reality (VR) and augmented reality (AR), one cannot expect that GPU performance will scale fast enough to meet the requirements of immersive photo-realistic rendering with current rendering techniques. In this dissertation, I follow the dual of the well-known computer vision approach: vision is inverse graphics: to improve graphical algorithms, I consider the operation of the human visual system. I propose to model and exploit the limitations of the visual system in the context of novel high-refresh-rate displays; specifically, I focus on spatio-temporal perception, a topic that has received remarkably less attention than spatial-only perception so far. I present three main contributions. First, I demonstrate the validity of the perceptual approach by presenting a conceptually simple rendering technique motivated by our eyes' limited sensitivity to high spatio-temporal change which reduces the rendering load and transmission requirement of current-generation VR headsets without introducing perceivable visual artefacts. Second, I present two visual models related to motion perception: (a) a metric for detecting flicker; and (b) a comprehensive visual model to predict perceived motion quality on monitors with arbitrary refresh rates and monitor resolutions. Third, I propose an adaptive rendering algorithm that utilises the proposed models. All algorithms operate on physical colorimetric units (instead of display-referenced pixel values), for which I provide the appropriate display measurements and models. All proposed algorithms and visual models are calibrated and validated with psychophysical experiments

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Inverse tone mapping

The introduction of High Dynamic Range Imaging in computer graphics has produced a novelty in Imaging that can be compared to the introduction of colour photography or even more. Light can now be captured, stored, processed, and finally visualised without losing information. Moreover, new applications that can exploit physical values of the light have been introduced such as re-lighting of synthetic/real objects, or enhanced visualisation of scenes. However, these new processing and visualisation techniques cannot be applied to movies and pictures that have been produced by photography and cinematography in more than one hundred years. This thesis introduces a general framework for expanding legacy content into High Dynamic Range content. The expansion is achieved avoiding artefacts, producing images suitable for visualisation and re-lighting of synthetic/real objects. Moreover, it is presented a methodology based on psychophysical experiments and computational metrics to measure performances of expansion algorithms. Finally, a compression scheme, inspired by the framework, for High Dynamic Range Textures, is proposed and evaluated

The modulation of simultaneous chromatic contrast induction

A coloured background may induce a contrasting colour in a target figure set against it. This effect, known as 'simultaneous chromatic contrast induction', can strongly influence the way in which we perceive colours and may therefore play an important role in our colour perception. Yet in order to support putative roles in phenomena such as colour-constancy, simultaneous contrast effects must be in some way 'regulated', otherwise they would cause objects to change colour when moved from one setting to another. Here we investigate a number of candidate cues that might be expected to influence the strength of simultaneous chromatic contrast. In experiment 1, we investigate the influence of global illumination cues that can indicate whether a colour change is consistent with a change in the illumination over the entire scene, or with a localised change in the background colour. Global illumination changes have already been shown to facilitate simultaneous contrast induction, and we further find that this effect is diminished by increasing the luminance contrast between the elements that make up the scene. Contrary to our expectations, increasing the number of distinct chromaticities in the surround does not have any effect. Finally, we attempt to discover whether this effect occurs at a monocular or a binocular site, by presenting different elements of the stimuli either to the same eye as the target, or to different eyes. Here, our results suggest that the effect is probably binocular. In experiment 2, we investigate how the strength of simultaneous contrast induction changes when textured backgrounds and targets are substituted for the uniformly shaded backgrounds and targets that have been studied in most recent investigations of simultaneous contrast induction. Texture in the background reduces the strength of simultaneous contrast induction for uniform targets. However, texture in targets set against a uniform background strongly inhibits simultaneous contrast induction. When both background and target are textured, simultaneous contrast induction is partially restored suggesting that texture may exert its influence due to segmentation effects. However, another result shows that simultaneous contrast is primarily determined at a local level, arguing against this interpretation of the effect. We do show that the effects of texture are tightly tuned to the cardinal axes, implicating early visual mechanisms in the functioning of simultaneous chromatic contrast effects. In experiment 3, we investigate two other strong segmentation cues: binocular disparity and differential motion between a target and its immediate surround. Our results show that differential motion may facilitate simultaneous contrast induction, strengthening its effects. However the effect is small and is often inconsistent between observers.EThOS - Electronic Theses Online ServicePhysiological SocietyBarbour FoundationRidley Family FundGBUnited Kingdo

Advances in Reinforcement Learning

Reinforcement Learning (RL) is a very dynamic area in terms of theory and application. This book brings together many different aspects of the current research on several fields associated to RL which has been growing rapidly, producing a wide variety of learning algorithms for different applications. Based on 24 Chapters, it covers a very broad variety of topics in RL and their application in autonomous systems. A set of chapters in this book provide a general overview of RL while other chapters focus mostly on the applications of RL paradigms: Game Theory, Multi-Agent Theory, Robotic, Networking Technologies, Vehicular Navigation, Medicine and Industrial Logistic

Correcciones para la presbicia : implicaciones ópticas, perceptuales y adaptativas

Tesis de la Universidad Complutense de Madrid, Facultad de Óptica y Optometría, leída el 18-05-2016Presbyopia is the physiological inability of the crystalline lens to accommodate for objects at near distance. While accommodative lenses are the ideal solutions for presbyopia, current optical solutions rely on providing an acceptable quality of vision at near and far distances. Optimization of the optical solutions rely on better understanding of how the visual system copes with the visual quality produced by the various optical solutions. The aim of this thesis is to study optical, visual and perceptual performance of different presbyopic corrections such as alternating vision, monovision and simultaneous vision, and to study the effect of adaptation on perceptual performances. Methods: We measured and corrected ocular aberrations using custom developed adaptive optics setup, used images blurred by real aberrations of different orientation and/or magnitude and measured the internal code for blur in eyes with long term differences in blur magnitude or orientation using a classification-image like technique. We later used numerically convolved images of different far/near energy and different near additions to study the short term adaptation to pure simultaneous vision using single stimulus detection and scoring tasks...La presbicia es la incapacidad del cristalino para enfocar objetos cercanos. Mientras que las lentes acomodativas son una buena solución para la presbicia, las soluciones más actuales se basan en una corrección aceptable de la visión cercana y lejana simultáneamente. La optimización de estas soluciones pasa por comprender cómo reacciona el sistema a las diferentes correcciones ópticas. El objetivo de esta tesis es el estudio óptico, visual y perceptual de diferentes correcciones a la presbicia como la visión alternante, la mono visión y la visión simultánea, y el estudio del efecto dela adaptación desde el punto de vista perceptual. MétodosSe han medido y corregido las aberraciones oculares mediante un sistema de óptica adaptativa de construcción propia y se han usado imágenes desenfocadas con aberraciones reales con diferentes magnitudes y/u orientaciones para medir el código interno de emborronamiento en los ojos para los diferentes desenfoques y orientaciones mediante métodos de clasificación de imágenes. Posteriormente se han usado imágenes convolucionadas numéricamente con diferentes proporciones en las energías del enfoque cercano o lejano y con diferentes adiciones para estudiar laadaptación a corto plazo en la visión simultánea pura a través de la detección y valoración de estímulos individuales...Fac. de Óptica y OptometríaTRUEunpu

Inverse tone mapping

The introduction of High Dynamic Range Imaging in computer graphics has produced a novelty in Imaging that can be compared to the introduction of colour photography or even more. Light can now be captured, stored, processed, and finally visualised without losing information. Moreover, new applications that can exploit physical values of the light have been introduced such as re-lighting of synthetic/real objects, or enhanced visualisation of scenes. However, these new processing and visualisation techniques cannot be applied to movies and pictures that have been produced by photography and cinematography in more than one hundred years. This thesis introduces a general framework for expanding legacy content into High Dynamic Range content. The expansion is achieved avoiding artefacts, producing images suitable for visualisation and re-lighting of synthetic/real objects. Moreover, it is presented a methodology based on psychophysical experiments and computational metrics to measure performances of expansion algorithms. Finally, a compression scheme, inspired by the framework, for High Dynamic Range Textures, is proposed and evaluated.EThOS - Electronic Theses Online ServiceEngineering and Physical Sciences Research Council (EPSRC) (EP/D032148)GBUnited Kingdo

The neurophysiology of stereoscopic vision

PhD ThesisMany animals are able to perceive stereoscopic depth owing to the disparity information that arises from the left and right eyes' horizontal displacement on the head. The initial computation of disparity happens in primary visual cortex (V1) and is largely considered to be a correlation-based computation. In other words, the computational role of V1 as it pertains to stereoscopic vision can be seen to roughly perform a binocular cross-correlation between the images of the left and right eyes. This view is based on the unique success of a correlation-based model of disparity-selective cells { the binocular energy model (BEM). This thesis addresses two unresolved challenges to this narrative. First, recent evidence suggests that a correlation-based view of primary visual cortex is unable to account for human perception of depth in a stimulus where the binocular correlation is on average zero. Chapters 1 and 2 show how a simple extension of the BEM which better captures key properties of V1 neurons allows model cells to signal depth in such stimuli. We also build a psychophysical model which captures human performance closely, and recording from V1 in the macaque, we then show that these predicted properties are indeed observed in real V1 neurons. The second challenge relates to the long-standing inability of the BEM to capture responses to anticorrelated stimuli: stimuli where the contrast is reversed in the two eyes (e.g. black features in the left eye are matched with identical white features in the right eye). Real neurons respond less strongly to these stimuli than model cells. In Chapter 3 and 4, we make use of recent advances in optimisation routines and exhaustively test the ability of a generalised BEM to capture this property. We show that even the best- tting generalised BEM units only go some way towards describing neuronal responses. This is the rst exhaustive empirical test of this in uential modelling framework, and we speculate on what is needed to develop a more complete computational account of visual processing in primary visual cortex

Naturalistic depth perception and binocular vision

Humans continuously move both their eyes to redirect their foveae to objects at new depths. To correctly execute these complex combinations of saccades, vergence eye movements and accommodation changes, the visual system makes use of multiple sources of depth information, including binocular disparity and defocus. Furthermore, during development, both fine-tuning of oculomotor control as well as correct eye growth are likely driven by complex interactions between eye movements, accommodation, and the distributions of defocus and depth information across the retina. I have employed photographs of natural scenes taken with a commercial plenoptic camera to examine depth perception while varying perspective, blur and binocular disparity. Using a gaze contingent display with these natural images, I have shown that disparity and peripheral blur interact to modify eye movements and facilitate binocular fusion. By decoupling visual feedback for each eye, I have found it possible to induces both conjugate and disconjugate changes in saccadic adaptation, which helps us understand to what degree the eyes can be individually controlled. To understand the aetiology of myopia, I have developed geometric models of emmetropic and myopic eye shape, from which I have derived psychophysically testable predictions about visual function. I have then tested the myopic against the emmetropic visual system and have found that some aspects of visual function decrease in the periphery at a faster rate in best-corrected myopic observers than in emmetropes. To study the effects of different depth cues on visual development, I have investigated accommodation response and sensitivity to blur in normal and myopic subjects. This body of work furthers our understanding of oculomotor control and 3D perception, has applied implications regarding discomfort in the use of virtual reality, and provides clinically relevant insights regarding the development of refractive error and potential approaches to prevent incorrect emmetropization