Lightness Perception in Complex Scenes

Lightness perception is the perception of achromatic surface colors: black, white, and shades of grey. Lightness has long been a central research topic in experimental psychology, as perceiving surface color is an important visual task but also a difficult one due to the deep ambiguity of retinal images. In this article, I review psychophysical work on lightness perception in complex scenes over the past 20 years, with an emphasis on work that supports the development of computational models. I discuss Bayesian models, equivalent illumination models, multidimensional scaling, anchoring theory, spatial filtering models, natural scene statistics, and related work in computer vision. I review open topics in lightness perception that seem ready for progress, including the relationship between lightness and brightness, and developing more sophisticated computational models of lightness in complex scenes. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Approximate Image-Space Multidirectional Occlusion Shading Model for Direct Volume Rendering

Understanding and perceiving three-dimensional scientific visualizations, such as volume rendering, benefit from visual cues produced by the shading models. The conventional approaches are local shading models since they are computationally inexpensive and straightforward to implement. However, the local shading models do not always provide proper visual cues since non-local information is not sufficiently taken into account for the shading. Global illumination models achieve better visual cues, but they are often computationally expensive. It has been shown that alternative illumination models, such as ambient occlusion, multidirectional shading, and shadows, provide decent perceptual cues. Although these models improve upon local shading models, they still require expensive preprocessing, extra GPU memory, and a high computational cost, which cause a lack of interactivity during the transfer function manipulations and light position changes. In this paper, we proposed an approximate image-space multidirectional occlusion shading model for the volume rendering. Our model was computationally less expensive compared to the global illumination models and did not require preprocessing. Moreover, interactive transfer function manipulations and light position changes were achievable. Our model simulated a wide range of shading behaviors, such as ambient occlusion and soft and hard shadows, and can be effortlessly applied to existing rendering systems such as direct volume rendering. We showed that the suggested model enhanced the visual cues with modest computational costs.

Roundabouts in the United States: An International Comparison of Illuminance Requirements and Costs

United States federal guidelines recommend systematic illumination of roundabouts in both rural and urban areas. However, competing conventional intersections in rural areas can be kept unlit. Highway illumination is also a major contributor to intersection operating and maintenance costs. This paper reviews roundabout illumination policies from 44 countries to determine if systematic illumination is normal practice and if not, to identify the warranting conditions. In addition, this paper compares the illumination level requirements and implied costs for three reference U.S. rural roundabouts with their equivalents from 15 selected countries. Professional lighting design software, DIALux®, was used to build roundabout illumination models corresponding to the recommended illuminances in the study countries and the simulation outputs were converted into annual operating costs to facilitate the comparisons. The findings indicate that most countries (approximately 59%) do not require systematic illumination of roundabouts in rural areas. While a few countries (approximately 16%) do attempt to illuminate all roundabouts it is more common to find such a requirement in urban areas. The study also finds that the average minimum maintained illuminance is higher in the U.S.A. than in Europe and the United Kingdom. However, the U.S. tax payer pays significantly less than their counterparts in the other countries studied. These findings are significant because the desired proliferation of roundabouts in the U.S.A. would receive a significant boost if the U.S.A. were to adopt lower illuminance levels, a non-systematic illumination policy, or both, for rural roundabouts.

Serious Gaming for Virtual Archaeoastronomy

Many cultures worldwide have left traces of sacred architecture and monuments which often show correlation to astronomical events like solstitial sunrises. Virtual archaeology can be used to explore such orientation patterns using digital reconstructions and positions of celestial objects computed from modern astronomical models. Most 3D editing systems used to build virtual reconstructions of such monuments however fail to provide astronomically accurate solar illumination models which can recreate the slightly different solar positions of antiquity or even prehistory, and even worse, any usable representation of the night sky. In recent years, two systems created independently by the authors of this study have been utilized for investigations into the orientation of architecture with respect to celestial processes. Both had their advantages and shortcomings compared to each other. One extended a dedicated open-source desktop astronomy program with a 3D rendering engine where such monuments can be investigated in the first-person perspective by interactive walkthrough. The other system uses a game engine and external online resources which provides only solar or planetary positions, but no star data. This study presents ways of connecting both systems in an attempt to take advantage of the best of both approaches.