Abstract
Human observers have been demonstrated to be sensitive to the local (physical) light field, or more precisely, to the primary direction, intensity, and diffuseness of the light at a point in a space. In the present study we focused on the question of whether it is possible to reconstruct the global visual light field, based on observers' inferences of the local light properties. Observers adjusted the illumination on a probe in order to visually fit it in three diversely lit scenes. For each scene they made 36 settings on a regular grid. The global structure of the first order properties of the light field could then indeed be reconstructed by interpolation of light vectors coefficients representing the local settings. We demonstrate that the resulting visual light fields (individual and averaged) can be visualized and we show how they can be compared to physical measurements in the same scenes. Our findings suggest that human observers have a robust impression of the light field that is simplified with respect to the physical light field. In particular, the subtle spatial variations of the physical light fields are largely neglected and the visual light fields were more similar to simple diverging fields than to the actual physical light fields.
Highlights
It is fascinating how light manipulations can change the appearance of an object or a scene (Cuttle, 1973; Ganslandt & Hofmann, 1992; Hunter, Biver, & Fuqua, 2007)
Measuring visual light fields is a novel technique that reveals how human observers make inferences about the structure of the physical light field. We developed this method by merging existing approaches of measuring the physical light field (Mury et al, 2009) and the local visual light field (Koenderink et al, 2007)
Our results revealed some dependencies of the visual light field on the features of the scenes, which is especially apparent in the similarities between the settings on the spheres and light location estimates
Summary
It is fascinating how light manipulations can change the appearance of an object or a scene (Cuttle, 1973; Ganslandt & Hofmann, 1992; Hunter, Biver, & Fuqua, 2007). Many professionals—artists, photographers, light designers, and architects—use practical knowledge about light in their work They put things in a spotlight to put attention on them, they use diffuse lighting to make surfaces look smoother, or play more sophisticated tricks with our visual system to create illusions. We are not aware of any lighting design books that address how complicated optical interactions between lighting, spatial geometry, materials, and objects result in the light distribution or light field in a space. Most literature in this field focuses on providing enough light (intensity) on working surfaces, people, and objects (Boyce, 1981).
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