A Fourier theory for cast shadows

Ramamoorthi, Ravi; Koudelka, Melissa L.; Belhumeur, Peter N.

doi:10.1109/tpami.2005.22

Cited by 45 publications

(11 citation statements)

References 20 publications

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“…Other image processing problems, such as image restoration, aging modeling, face recognition, security, 3D object recognition, content-based image retrieval [85], and many other tasks can and should benefit from BTF comprehensive information. An example of usefulness of BTF data is a study of cast shadows by material structure in [79] and the analysis of material dimensionality in [82]. Moreover, a recent psychophysical studies of these data in [22] and [21], together with a study present in this paper, has shown that analysis of different BTF samples can help us to understand human perception of different real-world materials.…”

Section: Introductionmentioning

confidence: 80%

Bidirectional Texture Function Modeling: A State of the Art Survey

Filip

Haindl

2009

IEEE Trans. Pattern Anal. Mach. Intell.

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Abstract-An ever-growing number of real-world computer vision applications require classification, segmentation, retrieval, or realistic rendering of genuine materials. However, the appearance of real materials dramatically changes with illumination and viewing variations. Thus, the only reliable representation of material visual properties requires capturing of its reflectance in as wide range of light and camera position combinations as possible. This is a principle of the recent most advanced texture representation, the Bidirectional Texture Function (BTF). Multispectral BTF is a seven-dimensional function that depends on view and illumination directions as well as on planar texture coordinates. BTF is typically obtained by measurement of thousands of images covering many combinations of illumination and viewing angles. However, the large size of such measurements has prohibited their practical exploitation in any sensible application until recently. During the last few years, the first BTF measurement, compression, modeling, and rendering methods have emerged. In this paper, we categorize, critically survey, and psychophysically compare such approaches, which were published in this newly arising and important computer vision and graphics area.

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Section: Introductionmentioning

confidence: 80%

Bidirectional Texture Function Modeling: A State of the Art Survey

Filip

Haindl

2009

IEEE Trans. Pattern Anal. Mach. Intell.

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“…In the context of inverse lighting, Okabe et al showed that high frequency components of the appearance of an object surface could retain significant energy by taking the cast shadow on the object surface as well as its BRDF into account (Okabe et al, 2004). Recently, Ramamoorthi et al provided an analysis of cast shadows for 3D textures based on canonical configurations of V-groove type structure (Ramamoorthi et al, 2005). It is interesting to extend their analysis to the task of appearance sampling of objects with complex shapes by considering other geometric configurations.…”

Section: Discussion On Geometric Effectsmentioning

confidence: 99%

Appearance Sampling of Real Objects for Variable Illumination

2007

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Abstract. The appearance of an object greatly changes under different lighting conditions. Even so, previous studies have demonstrated that the appearance of an object under varying illumination conditions can be represented by a linear subspace. A set of basis images spanning such a linear subspace can be obtained by applying the principal component analysis (PCA) for a large number of images taken under different lighting conditions. Since little is known about how to sample the appearance of an object in order to correctly obtain its basis images, it was a common practice to use as many input images as possible. In this study, we present a novel method for analytically obtaining a set of basis images of an object for varying illumination from input images of the object taken properly under a set of light sources, such as point light sources or extended light sources. Our proposed method incorporates the sampling theorem of spherical harmonics for determining a set of lighting directions to efficiently sample the appearance of an object. We further consider the issue of aliasing caused by insufficient sampling of the object's appearance. In particular, we investigate the effectiveness of using extended light sources for modeling the appearance of an object under varying illumination without suffering the aliasing caused by insufficient sampling of its appearance.

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“…We build on recent approaches that have studied the frequency aspects of light transport in static scenes, e.g. [Ramamoorthi and Hanrahan 2001;Durand et al 2005;Ramamoorthi et al 2005]. They presented a priori frequency analysis to perform adaptive sampling and appropriate reconstruction, reduce the number of samples needed for advanced rendering, and effectively share samples across pixels when possible.…”

Section: Sparse and Low-rank Approximations Of Light Transportmentioning

confidence: 99%

5D Covariance tracing for efficient defocus and motion blur

et al. 2013

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The rendering of effects such as motion blur and depth-of-field requires costly 5D integrals. We dramatically accelerate their computation through adaptive sampling and reconstruction based on the prediction of the anisotropy and bandwidth of the integrand. For this, we develop a new frequency analysis of the 5D temporal light-field, and show that first-order motion can be handled through simple changes of coordinates in 5D. We further introduce a compact representation of the spectrum using the covariance matrix and Gaussian approximations. We derive update equations for the 5 × 5 covariance matrices for each atomic light transport event, such as transport, occlusion, BRDF, texture, lens, and motion. The focus on atomic operations makes our work general, and removes the need for special-case formulas. We present a new rendering algorithm that computes 5D covariance matrices on the image plane by tracing paths through the scene, focusing on the single-bounce case. This allows us to reduce sampling rates when appropriate and perform reconstruction of images with complex depth-of-field and motion blur effects.

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A Fourier theory for cast shadows

Cited by 45 publications

References 20 publications

Bidirectional Texture Function Modeling: A State of the Art Survey

Bidirectional Texture Function Modeling: A State of the Art Survey

Appearance Sampling of Real Objects for Variable Illumination

5D Covariance tracing for efficient defocus and motion blur

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