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Mury, A.A. (author), Pont, S.C. (author), Koenderink, J.J. (author)We present a method for measurement and reconstruction of light fields in finite spaces. Using a custom-made device called a plenopter, we can measure spatially and directionally varying radiance distribution functions from a real-world scene up to their second-order spherical harmonics approximations. Interpolating between measurement points,...journal article 2009
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Pont, S.C. (author)The appearance of objects in scenes is determined by their shape, material properties and by the light field, and, in contradistinction, the appearance of those objects provides us with cues about the shape, material properties and light field. The latter so-called inverse problem is underdetermined and therefore suffers from interesting...conference paper 2009
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Wijntjes, M.W.A. (author), Volcic, R. (author), Pont, S.C. (author), Koenderink, J.J. (author), Kappers, A.M.L. (author)In this study we demonstrate that touch decreases the ambiguity in a visual image. It has been previously found that visual perception of three-dimensional shape is subject to certain variations. These variations can be described by the affine transformation. While the visual system thus seems unable to capture the Euclidean structure of a shape...conference paper 2009
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Wijntjes, M.W.A. (author), Volcic, R. (author), Pont, S.C. (author), Koenderink, J.J. (author), Kappers, M.L. (author)We studied the influence of haptics on visual perception of three-dimensional shape. Observers were shown pictures of an oblate spheroid in two different orientations. A gauge-figure task was used to measure their perception of the global shape. In the first two sessions only vision was used. The results showed that observers made large errors...journal article 2009
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Karlsson, S.M. (author), Pont, S.C. (author), Koenderink, J.J. (author)The theory of illuminance flow estimation by structure tensors is generalized for oblique viewing of anisotropic texture. An added benefit is that the theory predicts the behavior of unsupervised illuminant tilt estimators. The previous theory is refined with general matrix formulations and compacted by exploiting general properties of the...journal article 2009
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Mury, A.A. (author), Pont, S.C. (author), Koenderink, J.J. (author)Light fields [J. Math. Phys. 18, 51 (1936) ;The Photic Field (MIT, 1981)] of natural scenes are highly complex and vary within a scene from point to point. However, in many applications complex lighting can be successfully replaced by its low-order approximation [J. Opt. Soc. Am. A 18, 2448 (2001); Appl. Opt. 46, 7308 (2007)]. The purpose of...journal article 2009
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Wijntjes, M.W.A. (author), Pont, S.C. (author)It has recently been shown that an increase of the relief height of a glossy surface positively correlates with the perceived level of gloss (Y.-H. Ho, M. S. Landy, & L. T. Maloney, 2008). In the study presented here we investigated whether this relation could be explained by the finding that glossiness perception correlates with the...journal article 2010
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Karlsson, S.M. (author), Pont, S.C. (author), Koenderink, J.J. (author), Zisserman, A. (author)We investigate the estimation of illuminance flow using Histograms of Oriented Gradient features (HOGs). In a regression setting, we found for both ridge regression and support vector machines, that the optimal solution shows close resemblance to the gradient based structure tensor (also known as the second moment matrix). Theoretical results...journal article 2010
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Wijntjes, W.A. (author), Pont, S.C. (author)It has recently been shown that an increase of the relief height of a glossy surface positively correlates with the perceived level of gloss (Y.-H. Ho, M. S. Landy, & L. T. Maloney, 2008). In the study presented here we investigated whether this relation could be explained by the finding that glossiness perception correlates with the skewness of...journal article 2010
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Wijntjes, W.A. (author), Doerschner, K. (author), Kucukoglu, G. (author), Pont, S.C. (author)Among other cues, the visual system uses shading to infer the 3D shape of objects. The shading pattern depends on the illumination and reflectance properties (BRDF). In this study, we compared 3D shape perception between identical shapes with different BRDFs. The stimuli were photographed 3D printed random smooth shapes that were either painted...journal article 2011
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Pont, S.C. (author), Van Doorn, A.J. (author), Te Pas, S.F. (author), Wijntjes, M.W.A. (author), Koenderink, J.J. (author)We present a novel setup in which real objects made of two different materials can be mixed optically in a linearly weighted manner. We conducted a psychophysical experiment in which observers rated optical mixtures of the three combinations of glossy, matte, and velvety green birds. The observers rated the materials on four scales: matte-glossy...conference paper 2012
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Pont, S.C. (author), Koenderink, J.J. (author), Van Doorn, A.J. (author), Wijntjes, M.W.A. (author), Te Pas, S.F. (author)We present a novel setup in which real objects made of different materials can be mixed optically. For the materials we chose mutually very different materials, which we assume to represent canonical modes. The appearance of 3D objects consisting of any material can be described as linear superposition of 3D objects of different canonical...conference paper 2012
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Koenderink, J.J. (author), Van Doorn, A.J. (author), Pont, S.C. (author)Shape from shading arose from artistic practice, and later experimental psychology, but its formal structure has only been established recently by computer vision. Some of its algorithms have led to useful applications. Psychology has reversely borrowed these formalisms in attempts to come to grips with shading as a depth cue. Results have been...journal article 2012
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De Ridder, H. (author), Pont, S.C. (author)In the past decades perceptual (or perceived) image quality has been one of the most important criteria for evaluating digitally processed image and video content. With the growing popularity of new media like stereoscopic displays there is a tendency to replace image quality with viewing experience as the ultimate criterion. Adopting such a...conference paper 2012
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Nefs, H.T. (author), Van Bilsen, A. (author), Pont, S.C. (author), De Ridder, H. (author), Wijntjes, M.W.A. (author), Van Doorn, A.J. (author)In this paper, we focus on how people perceive the aspect ratio of city squares. Earlier research has focused on distance perception but not so much on the perceived aspect ratio of the surrounding space. Furthermore, those studies have focused on “open” spaces rather than urban areas enclosed by walls, houses and filled with people, cars, etc....journal article 2013
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Xia, L. (author), Pont, S.C. (author), Heynderickx, I.E.J.R. (author)Human observers’ ability to infer the light field in empty space is known as the “visual light field.” While most relevant studies were performed using images on computer screens, we investigate the visual light field in a real scene by using a novel experimental setup. A “probe” and a scene were mixed optically using a semitransparent mirror....journal article 2014
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Koepsell, D.R. (author), Brinkman, W.P. (author), Pont, S.C. (author)Human research ethics has developed in both theory and practice mostly from experiences in medical research. Human participants, however, are used in a much broader range of research than ethics committees oversee, including both basic and applied research at technical universities. Although mandated in the United States, the United Kingdom,...journal article 2014
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Kartashova, T. (author), Sekulovski, D (author), de Ridder, H. (author), te Pas, SF (author), Pont, S.C. (author)Human observers have been demonstrated to be sensitive to the local (physical) light field, or more<br/>precisely, to the primary direction, intensity, and diffuseness of the light at a point in a space. In the<br/>present study we focused on the question of whether it is possible to reconstruct the global visual light field, based on observers’...journal article 2016
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Xia, L. (author), Pont, S.C. (author), Heynderickx, I.E.J.R. (author)The lighting and furnishing of an interior space (i.e., the reflectance of its materials, the geometries of the furnishings, and their arrangement) determine the appearance of this space. Conversely, human observers infer lighting properties from the space's appearance. We conducted two psychophysical experiments to investigate how the...journal article 2016
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Zhang, F. (author), de Ridder, H. (author), Fleming, Ronald W. (author), Pont, S.C. (author)MatMix 1.0 is a novel material probe we developed for quantitatively measuring visual perception of materials. We implemented optical mixing of four canonical scattering modes, represented by photographs, as the basis of the probe. In order to account for a wide range of materials, velvety and glittery (asperity and mesofacet scattering) were...journal article 2016