Night rendering

Journal ArticleThe issues of realistically rendering naturally illuminated scenes at night are examined. This requires accurate models for moonlight, night skylight, and starlight. In addition, several issues in tone reproduction are discussed: eliminatiing high frequency information invisible to scotopic (night vision) observers; representing the flare lines around stars; determining the dominant hue for the displayed image. The lighting and tone reproduction are shown on a variety of models

Fast Local Tone Mapping, Summed-Area Tables and Mesopic Vision Simulation

広島大学(Hiroshima University)博士(工学)Engineeringdoctora

Advanced techniques for atmospheric effects

Over the last few years, open world videogames have been gaining lots of interest in the gaming industry. Open world videogames not only allow the player to freely roam over a vast terrain but also aim to recreate a believable dynamic world. Thus, one of the basic elements that such a videogame should feature is a day and night cycle. In this thesis, all of the intricacies that are involved in developing a physically based day and night cycle solution in a real-time rendering context are discussed. The main topics that will be covered are atmosphere rendering, celestial bodies positioning, celestial bodies rendering and nighttime scenes rendering

Rods progressively escape saturation to drive visual responses in daylight conditions

Rod and cone photoreceptors support vision across large light intensity ranges. Rods, active under dim illumination, are thought to saturate at higher (photopic) irradiances. The extent of rod saturation is not well defined; some studies report rod activity well into the photopic range. Using electrophysiological recordings from retina and dorsal lateral geniculate nucleus of cone-deficient and visually intact mice, we describe stimulus and physiological factors that influence photopic rod-driven responses. We find that rod contrast sensitivity is initially strongly reduced at high irradiances, but progressively recovers to allow responses to moderate contrast stimuli. Surprisingly, rods recover faster at higher light levels. A model of rod phototransduction suggests that phototransduction gain adjustments and bleaching adaptation underlie rod recovery. Consistently, exogenous chromophore reduces rod responses at bright background. Thus, bleaching adaptation renders mouse rods responsive to modest contrast at any irradiance. Paradoxically, raising irradiance across the photopic range increases the robustness of rod responses.Peer reviewe

Source Separation, Frequency Dynamics and Lighting Dependency of Electrophosphenes in Human Vision

Exposure to electromagnetic fields (EMF) can produce illusory perceptions of light referred to as phosphenes. Various exposure guidelines around the world use phosphene perception as an indicator that environmental EMF may be affecting the central nervous system, however many of them are based on low quality legacy literature. While exposure guidelines should consider all commonly encountered ambient lighting conditions, there are no studies examining electrophosphenes in commonly encountered mesopic (i.e., dim) lighting conditions. As a result, conclusions drawn from these guidelines may not be reliable or encompass all plausible EMF exposure conditions. Additionally, the roles of the retina and visual cortex in electrophosphene generation have not yet been adequately separated. Given the importance of understanding the effects of EMF exposure on human health, it is crucial to investigate the factors that affect sensitivity to phosphenes in a rigorous and systematic manner. This thesis examined the effects of transcranial electrical stimulation (tES) using different electrode placements, stimulation parameters, and ambient lighting conditions on phosphene detection thresholds using a large sample size, as well as robust experimental and analytical techniques. Detection thresholds across the three experiments (presented in Chapters 2 – 4) showed that up to 74% less current had to be applied to induce phosphenes in mesopic conditions compared to well-lit and dark conditions, indicating that existing guidelines have used relatively insensitive scenarios to determine safe levels of EMF exposure. Lower phosphene detection thresholds in frontal montages suggested that the retina was the most likely source of tES-induced phosphenes. However, the double dissociation analysis in Chapter 3 showed that additional stimulation over the visual cortex lowered the current strength required to induce phosphenes by stimulation near the retina (from 130.7 μA to 87.5 μA). It appears then that electrical stimulation over the cortex can facilitate phosphene detection. Chapter 4 showed that phosphenes were more readily perceived when stimulation was set to specific frequencies in each of the dark (10 Hz), mesopic (16 Hz) and well-lit (20 Hz) conditions. Frequency dependence in these well-lit and dark conditions was in-line with: 1) previously reported dominant electroencephalograph (EEG) frequency bands in the cortex; and 2) sensitivity to stimulation found in rod and cone photoreceptors in the retina. All three experiments found that stimulation at 16 Hz produced the strongest electrophosphenes in mesopic conditions. While this does not align with any known EEG frequency response in the visual cortex, it closely aligns with the rod-cone phase delay mechanism found in the retina at 15 Hz, suggesting that the frequency component of tES-induced phosphenes may be driven by the frequency dynamics of retinal photoreceptors. Overall, the findings of this thesis indicate that exposure guidelines for EMF need to consider mesopic lighting if they intend to encompass all plausible exposure scenarios. Additionally, tES over the visual cortex can influence phosphene perception. Finally, ambient lighting conditions strongly affect the frequency dynamics and current strength required for tES to produce phosphenes

Rendering non-pictorial (Scientific) high dynamic range images

In recent years, the graphics community is seeing an increasing demand for the capture and usage of high-dynamic-range (HDR) images. Since the production of HDR imagery is not solely the domain of the visualization of real life or computer generated scenes, novel techniques are also required for imagery captured from non-visual sources such as remote sensing, medical imaging, astronomical imaging, etc. This research proposes to integrate the techniques used for the display of high-dynamic-range pictorial imagery for the practical visualization of non-pictorial (scientific) imagery for data mining and interpretation. Nine algorithms were utilized to overcome the problem associated with rendering the high-dynamic-range image data to low-dynamic-range display devices, and the results were evaluated using a psychophysical experiment. Two paired-comparison experiments and a target detection experiment were performed. Paired-comparison results indicate that the Zone System performs the best on average and the Local Color Correction method performs the worst. The results show that the performance of different encoding schemes depend on the type of data being visualized. The correlation between the preference and scientific usefulness judgments (R2 = 0.31) demonstrates that observers tend to use different criteria when judging the scientific usefulness versus image preference. The experiment was conducted using observers with expertise (Radiologists) for the Medical image to further elucidate the success of HDR rendering on these data. The results indicated that both Radiologists and Non-radiologists tend to use similar criteria regardless of their experience and expertise when judging the usefulness of rendered images. A target detection experiment was conducted to measure the detectability of an embedded noise target in the Medical image to demonstrate the effect of the tone mapping operators on target detection. The result of the target detection experiment illustrated that the detectability of targets the image is greatly influenced by the rendering algorithm due to the inherent differences in tone mapping among the algorithms