37-Issue 4

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https://diglib.eg.org/handle/10.2312/2632568

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Browsing 37-Issue 4 by Subject "Computing methodologies → Reflectance modeling"

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    A Composite BRDF Model for Hazy Gloss
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Barla, Pascal; Pacanowski, Romain; Vangorp, Peter; Jakob, Wenzel and Hachisuka, Toshiya
    We introduce a bidirectional reflectance distribution function (BRDF) model for the rendering of materials that exhibit hazy reflections, whereby the specular reflections appear to be flanked by a surrounding halo. The focus of this work is on artistic control and ease of implementation for real-time and off-line rendering. We propose relying on a composite material based on a pair of arbitrary BRDF models; however, instead of controlling their physical parameters, we expose perceptual parameters inspired by visual experiments [VBF17]. Our main contribution then consists in a mapping from perceptual to physical parameters that ensures the resulting composite BRDF is valid in terms of reciprocity, positivity and energy conservation. The immediate benefit of our approach is to provide direct artistic control over both the intensity and extent of the haze effect, which is not only necessary for editing purposes, but also essential to vary haziness spatially over an object surface. Our solution is also simple to implement as it requires no new importance sampling strategy and relies on existing BRDF models. Such a simplicity is key to approximating the method for the editing of hazy gloss in real-time and for compositing.
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    A Physically-based Appearance Model for Special Effect Pigments
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Guo, Jie; Chen, Yanjun; Guo, Yanwen; Pan, Jingui; Jakob, Wenzel and Hachisuka, Toshiya
    An appearance model for materials adhered with massive collections of special effect pigments has to take both high-frequency spatial details (e.g., glints) and wave-optical effects (e.g., iridescence) due to thin-film interference into account. However, either phenomenon is challenging to characterize and simulate in a physically accurate way. Capturing these fascinating effects in a unified framework is even harder as the normal distribution function and the reflectance term are highly correlated and cannot be treated separately. In this paper, we propose a multi-scale BRDF model for reproducing the main visual effects generated by the discrete assembly of special effect pigments, enabling a smooth transition from fine-scale surface details to large-scale iridescent patterns. We demonstrate that the wavelength-dependent reflectance inside the pixel's footprint follows a Gaussian distribution according to the central limit theorem, and is closely related to the distribution of the thin-film's thickness. We efficiently determine the mean and the variance of this Gaussian distribution for each pixel whose closed-form expressions can be derived by assuming that the thin-film's thickness is uniformly distributed. To validate its effectiveness, the proposed model is compared against some previous methods and photographs of actual materials. Furthermore, since our method does not require any scene-dependent precomputation, the distribution of thickness is allowed to be spatially-varying.