• Korean Journal of Computational Design and Engineering
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• v.13 no.6
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• pp.469-477
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• 2008

Physically-based rendering is an image synthesis technique based on simulation of physical interactions between light and surface materials. Since generated images are highly photorealistic, physically-based rendering has become an indispensable tool in advanced design visualization for manufacturing and architecture as well as in film VFX and animations. Especially, BRDF (bidirectional reflectance distribution function) is critical in realistic visualization of materials since it models how an incoming light is reflected on the surface in terms of intensity and outgoing angles. In this paper, we introduce techniques to represent BRDF as B-spline volumes and to utilize them in physically-based rendering. We show that B-spline volume BRDF (BVB) representation is suitable for measured BRDFs due to its compact size without quality loss in rendering. Moreover, various CAGD techniques can be applied to B-spline volume BRDFs for further controls such as refinement and blending.

• Proceedings of the IEEK Conference
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• 2003.11b
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• pp.91-94
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• 2003

In this paper, we present a simple framework to measure BRDF(Bidirectional Reflectance Distribution Function) values of objects and to render them using the values more realistically. There are lots of BRDF measurement methods, but the methods have been separated from the effective rendering of the values. Therefore, we suggest the framework which includes the BRDF measurement methods of objects and the effective rendering methods of the measured BRDF data. Before measuring the BRDFs, we do light sources analysis, camera calibration and display device characterization. After measuring them, we apply them to the characterized display device for rendering effectively and realistically.

• Korean Journal of Computational Design and Engineering
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• v.14 no.5
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• pp.346-354
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• 2009

BRDF (bidirectional reflectance distribution function) is critical in realistic simulation of material appearances since it models the directional characteristics of reflection of light. Although many BRDF models have been proposed so far, it is still not easy to find one specific model that could represent all the reflection properties of real materials such as generalized diffusion, off-specular reflection, Fresnel effect, and back scattering. In this paper, we compare three BRDF models including B-spline volume BRDF (BVB), Cook-Torrance, and Lafortune in their ability to represent the measured BRDF data for physically-based rendering. We show that B-spline volume BRDF surpass the others in quality of data fitting and rendering, especially for materials without specular reflections.

• Journal of Computational Design and Engineering
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• v.2 no.1
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• pp.1-15
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• 2015

Measured bidirectional reflectance distribution function (BRDF) data have been used to represent complex interaction between lights and surface materials for photorealistic rendering. However, their massive size makes it hard to adopt them in practical rendering applications. In this paper, we propose an adaptive method for B-spline volume representation of measured BRDF data. It basically performs approximate B-spline volume lofting, which decomposes the problem into three sub-problems of multiple B-spline curve fitting along u-, v-, and w-parametric directions. Especially, it makes the efficient use of knots in the multiple B-spline curve fitting and thereby accomplishes adaptive knot placement along each parametric direction of a resulting B-spline volume. The proposed method is quite useful to realize efficient data reduction while smoothing out the noises and keeping the overall features of BRDF data well. By applying the B-spline volume models of real materials for rendering, we show that the B-spline volume models are effective in preserving the features of material appearance and are suitable for representing BRDF data.

• Journal of the Korea Computer Graphics Society
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• v.16 no.3
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• pp.1-10
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• 2010

In this paper, we propose a novel noiseless method of BRDF rendering on a GPU in real-time. Illumination at a surface point is formulated as an integral of BRDF producted with incident radiance over the hemi-sphere domain. The most popular method to compute the integral is the Monte Carlo method, which needs a large number of samples to achieve good image quality. But, it leads to increase of rendering time. Otherwise, a small number of sample points cause serious image noise. The main contribution of our work is a new importance sampling scheme producing a set of incoming ray samples varying continuously with respect to the eye ray. An incoming ray is importance-based sampled at different latitude angles of the eye ray, and then the ray samples are linearly connected to form a curve, called a thread. These threads give continuously moving incident rays for eye ray change, so they do not make image noise. Since even a small number of threads can achieve a plausible quality and also can be precomputed before rendering, they enable real-time BRDF rendering on the GPU.

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.3
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• pp.184-193
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• 2010

This paper proposes a biological iridescence BRDF(Bidirectional Reflectance Distribution Function) compression and rendering method. In the graphics technology, iridescence sometimes is named structure colors. The main features of these symptoms are shown transform of color and brightness by varying viewpoint. Graphics technology to render this is the BRDF technology. The BRDF methods enable realistic representation of varying view direction, but it requires a lot of computing power because of large data. In this paper, we obtain reflection map from iridescence BRDF, analyze color of reflection map and propose representation method by several colorfully concentric circle. The one concentric circle represents beam width of reflection ray by one normal vector. In this paper, we synthesize rough concentric by using several virtually optical normal vectors. And we obtain spectrum information from concentric circles passing through the center point. The proposed method enables IBR(image based rendering) technique which results is realistic illuminance and spectrum distribution by one texture from reduced BRDF data within spectrum.

• 한국HCI학회:학술대회논문집
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• 2007.02a
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• pp.1019-1024
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• 2007

그래픽스 분야에서 다양한 재질을 사실감 있게 표현하려는 연구가 활발히 진행되고 있는 가운데, 다양한 재질의 반사특성을 측정하는 방법들이 시도되고 있다. 본 연구에서는 디지털 카메라를 이용하여 영상 기반 양방향 반사 분포함수(BRDF: Bidirectional Reflectance Distribution Function)를 획득할 수 있는 측정 시스템을 구축하였다, 이를 통한 BRDF 모델은 경험적(empirical)혹은 물리(physical)기반의 모델에 비해 보다 사실성 높은 표현이 가능하다. 영상 기반으로 양방향 반사 분포함수를 생성하는 과정에서 노출시간을 달리한 여러 장의 영상을 가지고 HDR(High Dynamic Range) 영상을 생성하였다. 또한 원색재현을 위해 표준광원을 사용하고 컬러차트와 회귀분석을 통해 컬러 보정을 수행하였다. 본 연구에서는 플라스틱이나 금속재질같이 불투명한 등방성(isotropic) 재질을 사용하였고, 이러한 재질의 BRDF데이터를 통해 산업제품에서 많이 사용되는 재질의 모델을 보다 실감나게 렌더링(rendering)할 수 있다.

• 한국HCI학회:학술대회논문집
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• 2007.02a
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• pp.1037-1044
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• 2007

Metallic paint is one of the most widely used coating in automotive, cosmetic and other applications because of its well-known ability to give a product realistic look which creates widespread consumer appeal. But, this coating has complicated subsurface structure which includes pigments, flakes, and transparent clearcoat. Though various analytic reflection models are available to simulate appearance of various surfaces, it is difficult to select an appropriate reflection model with faithful parameters for simulating this coating due to the complex subsurface structure of metallic paints. This paper presents a framework for accurate modeling of metallic coating by determining an appropriate reflection model among various existing BRDF (Bidirectional Reflectance Distribution Function) models. The selection of the appropriate model is achieved by measuring BRDF of various metallic paint samples using a BRDF measuring device i.e. gonioreflectometer and fitting an existing model to the measured data. Then, this model is effectively realized by rendering metallic painted surfaces. We believe that this framework can serve as a guide for those who wants to render metallic painted surfaces accurately with analytic BRDF model without expending time on extracting BRDF data using gonioreflectometer from real metallic paint sample.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.840-843
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• 2014

사실적 피부 렌더링은 피부 표면에서 일어나는 확산반사(Diffusion) 및 경면반사(Specular) 뿐 만 아니라 피부층 내에서 산란되어 나오는 산란광과 얇은 피부층을 통과하는 투과광 등을 고려하여 렌더링 되어야 한다. 이를 물리적인 개념들을 사용하여 실시간으로 계산하여 표현하는 것은 많은 계산량과 시간을 필요로 하므로 확산 반사 및 경면 반사 등을 미리 계산하여 텍스쳐로 저장하고 재사용하는 사전정의 BRDF 방법으로 근사화하여 표현할 수 있다. 하지만 사전정의 BRDF를 통해 생성된 피부 투과광색상 텍스쳐 맵은 그 색상이 고정되어있어 조명의 색상이 바뀌어도 피부를 투과하는 빛의 색상이 변하지 않아 부자연스러움을 보인다. 본 논문에서는 이러한 문제를 해결하기 위해 물체와 조명간의 거리를 이용하여 빛의 감쇠비율을 구하고 조명의 색상 값과 감쇠비율을 이용하여 피부 투과광 색상 텍스쳐 맵의 RGB채널 수정을 통해 피부 렌더링에서의 자연스러운 투과광 표현이 가능함을 보였다.

• Journal of Korea Game Society
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• v.21 no.4
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• pp.109-116
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• 2021

In this paper, we considered that recently 3D game characters have been almost alike realistic expression because of a great mathematical computation and efficient techniques on GPU hardware. We presented the rendering technique and analysis for 3D game characters to simulate and render mathematical approach model from recent researches to perform the game engine for the surface reflection of lighting model. We compare our approach with the existing variant rendering techniques here using Open GL shader language on game engine. The experimental result will be provided the view-dependent visual appearance of variant and effective modeling characters for realistic expression using existing methods on the GPU for effective simulations and rendering process. Since there are many operations that are used redundantly while performing mathematical operations, the necessary functions and requirements have been to compute in advance.