• Proceedings of the Korean Printing Society Conference
• /
• 2000.04a
• /
• pp.35-44
• /
• 2000

Because Image on the CRT change under different illuminants, human is difficult to see original color of object. If what is information of used illuminant on capturing object know, image can be transformed according to viewing condition using the linear matrix method. To know information of used illuminant at an image, the spectral radiance of illuminant can be estimated using the linear model of Maloney and Wandell form an image. And then image can be properly transformed it using color appearance model. In this paper, we predict the spectral radiance of illuminant using spectral power distribution of specular light and using surface spectral reflectance at maximum gray area. and then we perform visual experiments for the corresponding color reproduction according to viewing condition. In results, we ensure that the spectral radiance of illuminant at an image can be well estimated using above algorithms and that human visual system is 70% adapted to the monitor's white point and 30% to ambient light when viewing softcopy images.

• Journal of Korea Society of Digital Industry and Information Management
• /
• v.13 no.1
• /
• pp.125-133
• /
• 2017

Color in an image is determined by illuminant and surface reflectance. So, to recover unique color of object, estimation of exact illuminant is needed. In this study, the illumination models suggested to get the object color constancy with the physical illumination model based on physical phenomena. Their characteristics and application limits are presented and the necessity of an extended illumination model is suggested to get more appropriate object colors recovered. The extended illumination model should contain an additional term for the ambient light in order to account for spatial variance of illumination in object images. Its necessity is verified through an experiment under simple lighting environment in this study. Finally, a reconstruction method for recovering input images under standard white light illumination is experimented and an useful method for computing object color reflectivity is suggested and experimented which can be induced from combination of the existing illumination models.

• Journal of Broadcast Engineering
• /
• v.19 no.1
• /
• pp.75-82
• /
• 2014

This paper proposes an illuminant compensation method using a camera noise analysis without segmentation in the dichromatic reflectance model. In general, pixels within highlight regions include large amounts of information on the image illuminant. Thus, the analysis of highlight regions provides a relatively easy means of determining the characteristics of an image illuminant. Currently, conventional methods require regional segmentation and the accuracy of this segmentation then affects the illuminant estimation. Therefore, the proposed method estimates the illuminant without segmentation based on a conformity assessment of highlight regions. Furthermore, error factors, such as noise and sensor non-uniformity, can be reduced by the conformity assessment.

• Proceedings of the Korean Information Science Society Conference
• /
• 2000.10b
• /
• pp.419-421
• /
• 2000

정확한 색 재현(Color Reproduction)을 위해서 영상 입력 장치(Image Input Device)의 조명색(Illuminant Color)에 따른 영상 변화를 분석하는 것은 중요하다. 영상 입력 장치는 피사체(Object)를 비추는 조명의 색 특성에 따라 영상을 생성한다. 이는 인간 시각 시스템(Human Visual System)이 가지는 색 불변성(Color Constancy)과는 다른 특성이며, 정확한 색 재현을 위해 필요한 색 실현 모델(Color Appearance Model)이 영상을 변환하는데 문제점으로 작용한다. 따라서, 영상 입력 장치가 생성하는 영상으로부터 조명 정보를 분석하여 인간 시각 시스템의 색 불변성을 재현할 필요가 있다. 본 논문에서는 영상의 조명 정보를 평가하기 위해 채도(Chroma)가 높은 기준 색 샘플들의 rgb 색도를 이용하여 색도 평면에 색도 다각형(Chromaticity Polygon)을 구성하고 영상의 모든 픽셀들의 rgb 색도 분포와 기준 색 샘플들의 색도 다각형간의 포함 관계에 따라 조명 정보를 평가한다.

• Restorative Dentistry and Endodontics
• /
• v.28 no.5
• /
• pp.402-408
• /
• 2003

This study was done to present a criterion in selection of the most proper light sources and materials by measuring metamerism index(MI) of the light curing composite resins with spectrocolorimeter. Metamerism is defined when two objects appear to be the same color in one illuminant but different in another. This is due to the fact that they have different spectral curves that fail to match under the second illuminant. In this study, A1 & A3 shade of five light curing composite resins (Esthet-X, Filteck Z250, Filteck A110. Charisma. Vitalescence) were chosen based on Vita shade. Five samples were made for shade of each product with Teflon mold (diameter: 15mm, thickness: 2mm). Metamerism index of each samples on a Barium sulfate plate($L^{*}=96.54,{\;}a^{*}=0.19,{\;}b^{*}=0.01$) prepared for sample fixation were measured with spectrocolorimeter(Miniscan XE plus. Model 4000s. Hunter Lab. USA) by applying standard light source D^{65}, C. Fcw, TL84 and A. Standardization was done with reference standard(X=80.8, Y=85.7, Z=90.8) and light trap. The results were as follows. 1. Different resins with same Vita shade showed recognizable color difference (${\delta}E^{*}>2$). 2. All composites had MI below accepted value 0.5 between standard illuminant(D$_{65}$, C, & A) and below 1.5 under fluorescent condition (Fcw & TL84). 3. MI value between $D^{65}$ and A showed higher value than MI value between other source of light(p<0.01). 4. All resins except Z250 showed MI value that A3 is higher than A1 between $D^{65}$ and A(p<0.05).except Z250 showed MI value that A3 is higher than A1 between $D^{65}$ and A(p<0.05).

• Journal of Korea Multimedia Society
• /
• v.13 no.5
• /
• pp.674-683
• /
• 2010

For the purpose of color reproduction under standard viewing conditions, recently, color display devices have developed for the colorimetric color reproduction. However the real viewing condition of color display devices is quite different from that. Therefore, it is very important for reproduced colors viewed under real conditions to match the color appearance under standard situations. There are various models that can be used to reproduce corresponding colors considering the chromatic adaptation of the human visual system. However neutral point or chromatic adaptation for the luminance level is not enough. In this paper, we propose a model that find adapting white points for the variations of the luminance levels under the same illuminant. This model is modeled by the proportion of Euclidian distance for luminance level. It is the adapting white function of the sigmoid type for surround luminance level. In the model, the optimal coefficients are obtained from the Hunt's experimental result. It is applied in the chromatic adaptation model using the neutral point of the various viewing conditions. And the neutral point can be used as the theoretical standard which determines the reference white of the color display devices.

• Proceedings of the Korea Multimedia Society Conference
• /
• 2000.11a
• /
• pp.218-223
• /
• 2000

영상에서 색상은 조명과 물체의 반사 특성에 의해 걸정되므로고 정확한 조명성분 추출을 통해 물체 고유의 색상을 복원할 수 있다. 물체 색상과 하이라이트 색상의 분포와 이들간의 관계를 잘 반영하여 모델링한 Dichromatic 반사 모델에서는, 3차원 RGB 공간에서의 하이라이트(highlight) 영역에 의한 클러스터 분포형상으로부터 표면반사벡터를 구해 이것을 조명벡터로 결정하였다. 그러나, 표면반사벡터의 방향은 물체색상의 영향을 받아 실제 조명벡터와 동일한 방향을 나타내지 못한다는 것을 실험을 통해 알 수 있었다. 실제적으로 하이라이트영역에 대한 클러스터는 물체 색상으로부터 조명색상에 근접한 방향으로 형성되며, 조명벡터로는 글러스터의 최대값으로 향하는 것을 취하는 것이 보다 정확하다는 특성이 있음을 확인하였다. 본 논문에서는 여러 가지 실험을 통해 이러한 특성이 타당함을 제시하고, 그래픽반사모델을 이용하여 하이라이트 색상에 대한 새로운 해석 방법을 제시한다.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.41 no.1
• /
• pp.37-46
• /
• 2004

In this paper, we propose an improved reproduction algorithm for a realistic image of the real scene based on the spectral distribution of lights and objects. The proposed method for the realistic image is focused on a more accurate reproduction of an image incident on the sight of the viewer. At first, to reproduce an image accurately incident on a sight of viewer, we used the backward ray tracing method based on spectral distribution of object and illuminant representing its physical characteristic used in real. Next, we propose utilizing the improved shading model of the reproduction algorithm of realistic image by applying Bouguer-Beer's law to consider an optical absorptive property of transparent objects. We also define a new ambient light term which is considered the diffuse reflection of neighboring objects instead of constant ambient light. The simulation results show that the proposed algorithm can reproduce the visually similar image with a scene incident on a sight of viewer.

• Journal of Broadcast Engineering
• /
• v.13 no.3
• /
• pp.339-349
• /
• 2008

We present a novel method to estimate the light source direction and relight a face texture image of a single 3D model under arbitrary unknown illumination conditions. We create a virtual irradiance sphere to detect the light source direction from a given illuminated texture image using both normal vector mapping and weighted bilinear interpolation. We then induce a relighting equation with estimated ambient and diffuse coefficients. We provide the result of a series of experiments on light source estimation, relighting and face recognition to show the efficiency and accuracy of the proposed method in restoring the shading and shadows areas of a face texture image. Our approach for face relighting can be used for not only illuminant invariant face recognition applications but also reducing visual load and Improving visual performance in tasks using 3D displays.

• Journal of Broadcast Engineering
• /
• v.17 no.1
• /
• pp.195-198
• /
• 2012

The N basis functions are typically chosen so that Surface reflectance functions(SRFs) and spectral power distributions (SPDs) can be accurately reconstructed from their N-dimensional vector codes. Typical rendering applications assume that the resulting mapping is an isomorphism where vector operations of addition, scalar multiplication, component-wise multiplication on the N-vectors can be used to model physical operations such as superposition of lights, light-surface interactions and inter-reflection. The vector operations do not mirror the physical. However, if the choice of basis functions is restricted to characteristic functions then the resulting map between SPDs/SRFs and N-vectors is anisomorphism that preserves the physical operations needed in rendering. This paper will show how to select optimal characteristic function bases of any dimension N (number of basis functions) and also evaluate how accurately a large set of Munsell color chips can approximated as basis functions of dimension N.