Browsing by Author "Bilgili, Ahmet"

Now showing 1 - 5 of 5

Citation - WoS: 3
Citation - Scopus: 5
A copula-based BRDF model
(Blackwell Publishing Ltd, 2010) Aydin Öztürk; Murat Kurt; Ahmet Bilgili; Kurt, Murat; Bilgili, Ahmet; Ozturk, Aydin
In this paper we introduce a novel approach for modeling surface reflection. We focus on using a family of probability distributions called Archimedean copulas as BRDF models. The Archimedean representation has an attractive property in that the multivariate distributions are characterized by their marginal distributions through a single univariate function only. It is shown that the proposed model meets the reciprocity property of reflection. Based on measured BRDF data we demonstrate that the proposed approach provides a good approximation to BRDF. Empirical comparisons are made with some classically used BRDF models. © 2010 The Eurographics Association and Blackwell Publishing Ltd. © 2018 Elsevier B.V. All rights reserved.
Citation - WoS: 34
Citation - Scopus: 40
A General BRDF Representation Based on Tensor Decomposition
(WILEY, 2011) Ahmet Bilgili; Aydin Ozturk; Murat Kurt; Kurt, Murat; Bilgili, Ahmet; Öztürk, Aydin
Generating photo-realistic images through Monte Carlo rendering requires efficient representation of lightsurface interaction and techniques for importance sampling. Various models with good representation abilities have been developed but only a few of them have their importance sampling procedure. In this paper we propose a method which provides a good bidirectional reflectance distribution function (BRDF) representation and efficient importance sampling procedure. Our method is based on representing BRDF as a function of tensor products. Four-dimensional measured BRDF tensor data are factorized using Tucker decomposition. A large data set is used for comparing the proposed BRDF model with a number of well-known BRDF models. It is shown that the underlying model provides good approximation to BRDFs.
Copula tabanlı yeni bir yansıma modeli
(2010) Bilgili, Ahmet; Öztürk, Aydın
Citation - Scopus: 1
Modeling BRDF by a probability distribution
(2010) Aydin Öztürk; Murat Kurt; Ahmet Bilgili; Kurt, Murat; Bilgili, Ahmet; Öztürk, Aydin
In this work we investigate reciprocity and energy conservation properties of a BRDF model which is based on a probability distribution. Representational ability of underlined model is demonstrated using a measured BRDF data set. We show that our model satisfies both reciprocity and energy conservation properties of BRDF. © 2013 Elsevier B.V. All rights reserved.
Representing BRDF by wavelet transformation of pair-copula constructions
(2012) Ahmet Bilgili; Aydin Öztürk; Murat Kurt; Kurt, Murat; Bilgili, Ahmet; Ozturk, Aydn
Bidirectional Reflectance Distribution Functions (BRDFs) are wellknown functions in computer graphics and these special functions represent the surface reflectance of materials. BRDFs can be viewed as multivariate probability density function (pdf) of incoming photons leaving in a particular outgoing direction. However constructing a multivariate probability distribution for modeling a given BRDF is difficult. A family of distributions namely Copula distributions have been used to approximate BRDF. In this work we employ the Pair-Copula constructions to represent the measured BRDF densities. As the measured BRDF densities have large storage needs we use Wavelet transforms for a compact BRDF representation. We also compare the proposed BRDF representation with a number of well-known BRDF models and show that our compact BRDF representation provides good approximation to measured BRDF data. © 2013 ACM. © 2013 Elsevier B.V. All rights reserved.