Murat Kurt | Ege University (original) (raw)

Papers by Murat Kurt

Multi-layered materials are layered structures of composing anisotropic media where each layer ma... more Multi-layered materials are layered structures of composing anisotropic media where each layer may have a separate scattering behavior. Multi-layered materials are widely used in cosmetics, jewelry or automobile paint industries. In addition, many real world materials may consist of microscopic particles that can lead to goniochromatic and/or sparkling appearance. Therefore, the accurate representation of these effects is crucial for the photorealistic appearance of the material and many models have been proposed to overcome this problem. In this paper, we analyze various models proposed for representing goniochromatic and sparkle effects and run experiments on their capability of accurately simulating the final appearance of a multi-layered automobile paint structure. We also compare the performance of each model providing their computation times in the experiments. Finally, we provide a table for the readers which summarizes the complex special effects included in each model.

We present a novel genetic algorithm-based approach for the compact representation of heterogeneo... more We present a novel genetic algorithm-based approach for the compact representation of heterogeneous, optically thick, translucent materials. Utilizing genetic optimization, we also find the best transformation to represent measured subsurface scattering data. We employ a factored subsurface scattering representation, based on a singular value decomposition (SVD), separately applying the SVD per-color channel of the transformed profiles. In order to achieve a compact, accurate representation, we perform this iteratively on the model errors. By allowing the number of iterations to be customized, our representation provides a mechanism to trade the visual quality possible against the level of compression achieved through our representation. We validate our approach by analyzing a range of real-world translucent materials, geometries and lighting conditions. For heterogeneous translucent materials, we further demonstrate that for the same level of compression, our method achieves greater visual accuracy than alternative techniques. Finally, we present an application of our factored representation, which can be used to convert heterogeneous materials into homogeneous material representations.

In this paper, we present a novel heterogeneous subsurface scattering (sss) representation, which... more In this paper, we present a novel heterogeneous subsurface scattering (sss) representation, which is based on a combination of Singular Value Decomposition (SVD) and genetic optimization techniques. To find the best transformation that is applied to measured subsurface scattering data, we use a genetic optimization framework, which tries various transformations to the measured heterogeneous subsurface scattering data to find the fittest one. After we apply the best transformation, we compactly represent measured subsurface scattering data by separately applying the SVD per-color channel of the transformed profiles. In order to get a compact and accurate representation, we apply the SVD on the model errors, iteratively. We validate our approach on a range of optically thick, real-world translucent materials. It's shown that our genetic algorithm based heterogeneous subsurface scattering representation achieves greater visual accuracy than alternative techniques for the same level of compression.

Measured materials are rapidly becoming a core component in the photo-realistic image synthesis p... more Measured materials are rapidly becoming a core component in the photo-realistic image synthesis pipeline. The reason is that data-driven models can easily capture the underlying, fine details that represent the visual appearance of materials, which can be difficult or even impossible to model by hand. There are, however, a number of key challenges that need to be solved in order to enable efficient capture, representation and interaction with real materials. This paper presents two new data-driven BRDF models specifically designed for 1D separability. The proposed 3D and 2D BRDF representations can be factored into three or two 1D factors, respectively, while accurately representing the underlying BRDF data with only small approximation error. We evaluate the models using different parameterizations with different characteristics and show that both the BRDF data itself and the resulting renderings yield more accurate results in terms of both numerical errors and visual results compared to previous approaches. To demonstrate the benefit of the proposed factored models, we present a new Monte Carlo importance sampling scheme and give examples of how they can be used for efficient BRDF capture and intuitive editing of measured materials.

In this research study, effects of mesh simplification on visual quality are examined by using qu... more In this research study, effects of mesh simplification on visual quality are examined by using quadric edge collapse decimation method. In this context, we analyze simplifications of various objects by investigating the Peak Signal-to-Noise Ratio (PSNR) values, difference images, and compression ratios. Experiments are performed in MeshLab environment and it is shown that when model is chosen as complex, simplification error between reference and simplified models increases much more in comparison with simpler models. At the same time, if we use high compression ratio, higher simplification error is reached. It could be concluded that compression ratio affects the error linearly.

This paper presents a plugin that adds an efficient representation of heterogeneous translucent m... more This paper presents a plugin that adds an efficient representation of heterogeneous translucent materials to the Blender 3D modeling tool. Algorithm of the plugin is based on Singular Value Decomposition (SVD) method and Mitsuba renderer is the default rendering software used by the proposed plugin. We validate the efficiency of the proposed plugin by using a set of measured heterogeneous subsurface scattering data sets.

In this paper, we propose a novel real-time Bidirectional Reflectance Distribution Function (BRDF... more In this paper, we propose a novel real-time Bidirectional Reflectance Distribution Function (BRDF) shading interface for creating isotropic BRDFs in image-based lighting. Our proposed BRDF shading interface allows users to generate new BRDFs by tweaking parameters of underlying BRDF model, which is Phong BRDF model. The implementation of our BRDF shading interface utilizes programmable graphics hardware through Shadertoy, and it provides a real-time visualization of the material on an object in environment lighting.

Measuring and representing light reflection and transmission accurately are core to high fidelity... more Measuring and representing light reflection and transmission accurately are core to high fidelity visual simulation of materials. In this paper, we analyze state-of-the-art Bidirectional Scattering Distribution Function (BSDF) measurements and models. We show that the most of the state-of-the-art BSDF models do not suggest a general solution for any surface class, from glasses to metals, isotropic to anisotropic materials, and daylight redirecting films. Furthermore, it's shown that an accurate and dense BSDF acquisition is not a trivial task at especially some specific measurement angles, such as normal incidence and grazing angles. In this paper, we address the problem of finding a general solution for efficient BSDF measurement and representation. We also outline the main issues that do not allow the effective use of current BSDF representations. Finally, we suggest open research issues that need to be investigated in BSDF literature.

This paper presents a novel approach for efficient sampling of isotropic Bidirectional Reflectanc... more This paper presents a novel approach for efficient sampling of isotropic Bidirectional Reflectance Distribution Functions (BRDFs). Our approach builds upon a new pa-rameterization, the Projected Deviation Vector parameteri-zation, in which isotropic BRDFs can be described by two 1D functions. We show that BRDFs can be efficiently and accurately measured in this space using simple mechanical measurement setups. To demonstrate the utility of our approach, we perform a thorough numerical evaluation and show that the BRDFs reconstructed from measurements along the two 1D bases produce rendering results that are visually comparable to the reference BRDF measurements which are densely sampled over the 4D domain described by the standard hemispherical parameterization.

The Bidirectional Scattering Distribution Function (BSDF) describes the appearance of an opticall... more The Bidirectional Scattering Distribution Function (BSDF) describes the appearance of an optically thin, translucent material by its interaction with light at a surface point. Various BSDF models have been proposed to represent BSDFs. In this paper, we experimentally analyze a few of BSDF models in terms of their accuracy to represent measured BSDFs, their required storage sizes and computation times. To make a fair comparison of BSDF models, we measured three samples of optically thin, translucent materials (hunter douglas, orange glass, structured glass) by using pgII gonio-photometer. Based on rendered images, required storage sizes and computation times, we compare the performance of the BSDF models. We show that data-driven BSDF models give a more accurate representation of measured BSDFs, while data-driven BSDF models require much more storage sizes and computation times. We also show that BSDF measurements from highly anisotropic translucent materials can not be expressed by an analytical BSDF model visually correctly.

We present a data-driven Bidirectional Scattering Distribution Function (BSDF) representation and... more We present a data-driven Bidirectional Scattering Distribution Function (BSDF) representation and a model-free technique that preserves the integrity of the original data and interpolates reflection as well as transmission functions for arbitrary materials. Our interpolation technique employs Radial Basis Functions (RBFs), Radial Basis Systems (RBSs) and displacement techniques to track peaks in the distribution. The proposed data-driven BSDF representation can be used to render arbitrary BSDFs and includes an efficient Monte Carlo importance sampling scheme. We show that our data-driven BSDF framework can be used to represent measured BSDFs that are visually plausible and demonstrably accurate.

Measuring and representing reflection and transmission accurately are core to high fidelity visua... more Measuring and representing reflection and transmission accurately are core to high fidelity visual simulation of materials. However, state-of-the-art Bidirectional Scattering Distribution Function (BSDF) models do not suggest a general solution for any surface class, from glasses to metals, isotropic to anisotropic materials, and daylight redirecting films. Furthermore, an accurate BSDF acquisition is not a trivial task at especially some specific measurement angles, such as normal incidence and grazing angles. In this paper, we address the problem of finding a general solution for efficient BSDF measurement and representation. We also outline the main issues that do not allow the effective use of current BSDF representations. Finally, we suggest specific solutions that could be investigated in order to address these challenges.

We address the problem of measuring and representing reflection and transmission for anisotropic ... more We address the problem of measuring and representing reflection and transmission for anisotropic materials without relying on mathematical models or a large sample database. By eliminating assumptions of material behavior, we arrive at a general method that works for any surface class, from metals to fabrics, fritted glazing, and prismatic films. To make data gathering practical, we introduce a robust analysis method that interpolates a sparse set of incident angle measurements to obtain a continuous function over the full 4-D domain. We then convert this interpolant to a standard representation tailored for efficient rendering and supported by a common library that facilitates data sharing. We conclude with some remaining challenges to making anisotropic BSDF measurements truly practical for rendering.

In this work, we study the understanding of 3D visual objects which are generated by augmented re... more In this work, we study the understanding of 3D visual objects which are generated by augmented reality techniques. 3D glasses are typically highly priced, and so they are not purchasable for most consumers. Instead, we consider low-priced red-cyan (anaglyph) glasses. We generate the left and right views so that they are comfortable for human eyes.

In this paper, we developed an interactive global illumination application for mobile devices and... more In this paper, we developed an interactive global illumination application for mobile devices and we show that interactive filtered importance sampling is possible even with a low-power mobile graphics processing unit (GPU). Taking the limited power and the screen size of mobile devices into account, we designed a user interface that allows selecting different predefined objects, environments and textures. With our implementation, desired materials can be visualized interactively by changing the parameters of Bidirectional Reflectance Distribution Function (BRDF).

In this thesis, we review subsurface scattering models used for representing subsurface scatterin... more In this thesis, we review subsurface scattering models used for representing subsurface scattering light transport effects in translucent materials. In addition, we propose novel compact factored subsurface scattering representations for measured subsurface scattering data.

Subsurface scattering effects in translucent materials are represented by the multidimensional Bidirectional Scattering Surface Reflectance Distribution Function (BSSRDF). By exploiting the diffusion property of multiple scattering in optically thick materials, these eight dimensional (8D) BSSRDF can be reduced to a four dimensional (4D) function. To compactly represent tabulated measured 4D BSSRDFs and achieve accurate approximations, we used factorization based techniques, such as Tucker and Singular Value Decomposition (SVD). We showed that the proposed factored subsurface scattering models provide high compression ratio while maintaining visual fidelity.

To validate the performance of the proposed factored subsurface scattering models, extensive comparisons are carried out using measured heterogeneous subsurface scattering data sets.

This paper presents a novel compact factored subsurface scattering representation for optically t... more This paper presents a novel compact factored subsurface scattering representation for optically thick, heterogeneous translucent materials. Our subsurface scattering representation is a combination of Tucker-based factorization and a linear regression method. We first apply Tucker factorization on the intensity profiles of the heterogeneous subsurface scattering responses. Next, we fit a polynomial model for characterizing the differences between the different color channels with a linear regression procedure. We show that our method achieves good compression while maintaining visual fidelity. We validate our heterogeneous subsurface scattering representation on various real-world heterogeneous translucent materials, geometries and lighting conditions

This poster presents a novel compact and efficient factored subsurface scattering representation ... more This poster presents a novel compact and efficient factored subsurface scattering representation for heterogeneous translucent materials. Our subsurface scattering representation consists of two parts, namely, a matrix factorization and a linear regression method. We first apply a matrix factorization method on the intensity profiles of the heterogeneous subsurface scattering responses. Next, we fit a polynomial model for characterizing the differences between the different color channels with a linear regression procedure. We validate our heterogeneous subsurface scattering representation on various real-world heterogeneous translucent materials, geometries and lighting conditions. We show that our method provides good compression at acceptable visual accuracy.

To validate the performance of the proposed factored subsurface scattering models, extensive comparisons are carried out using measured heterogeneous subsurface scattering data sets.