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Pont, S.C. (author), van Doorn, A.J. (author), Koenderink, J.J. (author)We studied whether human observers can estimate the illumination direction from 3D textures of random Brownian surfaces, containing undulations over a range of scales. The locally Lambertian surfaces were illuminated with a collimated beam from random directions. The surfaces had a uniform albedo and thus texture appeared only through shading...journal article 2017
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Van Doorn, A.J. (author), Koenderink, J.J. (author), Leyssen, M.H.R. (author), Wagemans, J. (author)We study the effect of stylistic differences on the nature of pictorial spaces as they appear to an observer when looking into a picture. Four pictures chosen from diverse styles of depiction were studied by 2 different methods. Each method addresses pictorial depth but draws on a different bouquet of depth cues. We find that the depth...journal article 2012
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Koenderink, J.J. (author), Van Doorn, A.J. (author)“Pictorial space” is the mental structure that appears to be the scaffold for the visual awareness when looking “into” (as opposed to “at”) a picture. Its structure differs from the “visual space” that is the scaffold for the visual awareness when looking into the scene in front of the observer. The structure of pictorial space has been probed...journal article 2012
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Koenderink, J.J. (author), Richards, W. (author), Van Doorn, A.J. (author)Local space-time scrambling of optical data leads to violent jerks and dislocations. On masking these, visual awareness of the scene becomes cohesive, with dislocations discounted as amodally occluding foreground. Such cohesive space-time of awareness is technically illusory because ground truth is jumbled whereas awareness is coherent....journal article 2012
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Koenderink, J.J. (author), Richards, W. (author), Van Doorn, A.J. (author)We consider operations that change the size of images, either shrinks or blow-ups. Image processing offers numerous possibilities, put at everyone’s disposal with such computer programs as Adobe Photoshop. We consider a different class of operations, aimed at immediate visual awareness, rather than pixel arrays. We demonstrate cases of blow-ups...journal article 2012
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Van Doorn, A.J. (author), Koenderink, J.J. (author), Todd, J.T. (author), Wagemans, J. (author)Human observers group local shading patterns into global super-patterns that appear to be illuminated in some unitary fashion. Many years ago, this was noticed for the case of uniform, unidirectional illumination. Recently, we found that it also applies to convergent and divergent illumination flows, but that human observers are blind to...journal article 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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Wagemans, J. (author), Van Doorn, A.J. (author), Koenderink, J.J. (author)In the physical environment familiar size is an effective depth cue because the distance from the eye to an object equals the ratio of its physical size to its angular extent in the visual field. Such simple geometrical relations do not apply to pictorial space, since the eye itself is not in pictorial space, and consequently the notion ...journal article 2011
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Koenderink, J.J. (author), Van Doorn, A.J. (author), Wagemans, J. (author)Depth is the feeling of remoteness, or separateness, that accompanies awareness in human modalities like vision and audition. In specific cases depths can be graded on an ordinal scale, or even measured quantitatively on an interval scale. In the case of pictorial vision this is complicated by the fact that human observers often appear to apply...journal article 2011
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Wagemans, J. (author), Van Doorn, A.J. (author), Koenderink, J.J. (author)We propose a novel method to probe the depth structure of the pictorial space evoked by paintings. The method involves an exocentric pointing paradigm that allows one to find the slope of the geodesic connection between any pair of points in pictorial space. Since the locations of the points in the picture plane are known, this immediately...journal article 2011
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Van Doorn, A.J. (author), Koenderink, J.J. (author), Wagemans, J. (author)From a theoretical point of view, the use of the shading cue involves estimates of the light field and thus observers need to judge the light field and the shape simultaneously. The conventional stimulus in perceptual experiments, a circular disk filled with a monotonic gradient on a uniform surround, represents a local shading or tonal gradient...journal article 2011
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Wagemans, J. (author), Van Doorn, A.J. (author), Koenderink, J.J. (author)The shading cue is supposed to be a major factor in monocular stereopsis. However, the hypothesis is hardly corroborated by available data. For instance, the conventional stimulus used in perception research, which involves a circular disk with monotonic luminance gradient on a uniform surround, is theoretically ‘explained’ by any quadric...journal article 2010
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Norman, J.F. (author), Kappers, A.M.L. (author), Beers, A.M. (author), Scott, A.K. (author), Norman, H.F. (author), Koenderink, J.J. (author)Two experiments evaluated the ability of older and younger adults to perceive the three-dimensional (3D) shape of object surfaces from active touch (haptics). The ages of the older adults ranged from 64 to 84 years, while those of the younger adults ranged from 18 to 27 years. In Experiment 1, the participants haptically judged the shape of...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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Koenderink, J.J. (author)The prior statistics of object colors is of much interest because extensive statistical investigations of reflectance spectra reveal highly non-uniform structure in color space common to several very different databases. This common structure is due to the visual system rather than to the statistics of environmental structure. Analysis involves...journal article 2010
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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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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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Richards, W. (author), Koenderink, J.J. (author), Van Doorn, A. (author)Unlike the Metelli monochrome transparencies, when overlays and their backgrounds have chromatic content, the inferred surface colors may not always be physically realizable, and are in some sense “imaginary.” In these cases, the inferred chromatic transmittance or reflectance of the overlay lies outside the RGB spectral boundaries. Using the...journal article 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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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