• Proceedings of the KSRS Conference
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• 2008.10a
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• pp.426-429
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• 2008

In this study, we propose the calibration algorithm for the solar channel (550 ${\sim}$ 900 nm) of MTSAT 1R which is the Japanese geostationary satellite launched on 26 Feb. 2005 and located at $140^{\circ}E$. We developed a method utilizing MODIS-derived BRDFs for the solar channel calibration over the bright desert area. Targets are selected based on the desert's brightness, spatial uniformity, temporal stability and spectral stability. The 6S model has been incorporated to account for directional effects of the surface using MODIS-derived BRDF parameters within the spectral interval in interest. Results based on the analysis for the period from November 2007 to June 2008 suggest that MTSAT-1R solar channel measurements have a low bias within 5%.

• Korean Journal of Remote Sensing
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• v.30 no.3
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• pp.367-373
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• 2014

Albedo is one of the critical parameters for understanding global climate change and energy/water balance. In this study, we used red and NIR reflectance from Satellite Pour I'Obervation de la Terre (SPOT)/Vegetation (VGT) S1 product. The product is preprocessed for users that they are atmospherically corrected using Simple Method Atmospheric Correction (SMAC) by Vision on Technology (VITO) for calculating broadband albedo. Roujean's Bi-directional Reflectance Distribution Function (BRDF) model is a semi-empirical method used for BRDF angular integration and inversion. Each kernel of Roujean's model was multi integrated by angle components (i.e., viewing zenith, solar zenith, and relative azimuth angle). Black-sky hemispherical function is integrated by observational angle; whereas, white-sky hemispherical efficient is integrated by incident angle. Estimated spectral albedo of red ($0.61{\sim}0.68{\mu}m$, B2) and near infrared ($0.79{\sim}0.89{\mu}m$, B3) have a good agreement with MODIS albedo products.

• 한국HCI학회:학술대회논문집
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• 2006.02a
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• pp.1222-1227
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• 2006

본 연구의 목적은 객체의 형상정보(3D mesh)와 색/질감정보(image)를 이용하여 텍스쳐 맵핑된 고품질의 가상모델을 생성하는데 있다. 3 차원 형상정보에 대응하는 이미지 상의 텍스쳐 좌표 관계를 구하기 위해 오브젝트 좌표계와 카메라 좌표계 사이의 변환행렬, 카메라의 초점거리, 카메라 CCD 와 프레임상의 이미지 사이의 aspect ratio 를 파라미터로 하는 3D-2D 정합을 수행한다. 이러한 3D-2D 정합을 효율적으로 수행하기 위하여, 카메라 내부파라미터 검정단계, 신뢰도가 높은 초기해 설정단계, 비선형 최적화(Newton method) 단계로 접근한다. 또한, 색/질감정보로 이용되는 객체의 이미지는 촬영조건에 의해 스펙큘러(specular)나 이미지 픽셀값의 포화상태(saturation) 등의 결점을 포함한다. 영상내의 스펙큘러 좌표와 3D-2D 정합의 결과를 이용하여 촬영 당시의 광원을 추정하고, 근사화된 빛반사도 함수(BRDF)를 이용하여, 텍스쳐의 픽셀값 변조를 통해 이미지 촬영 당시의 광원효과가 제거된 디퓨즈 텍스쳐를 획득한다. 본 연구에서는 퐁(Phong)의 모델을 근사화한 빛 반사도 함수 모델로 사용하였다.

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.10
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• pp.491-498
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• 2001

We present a method of modeling lights from photographs taken with conventional imaging equipment. It does not use both any geometrical information and special apparatus to calculate surface reflection properties. To represent surface reflection properties of the scene, we use BRDFs which are calculated by radiance values of surface elements and light sources. And the BRDF data of each surface is further transformed to the spherical harmonic domain for efficient storage. Thus it allows to reconstruct the photo-realistic scene under different light sources, to manipulate diversely the arbitrary light source and to control exposure time of camera sensor. Moreover we test our algorithm with real image instead of synthetic image.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.53-56
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• 2007

The Korean Geostationary satellite (COMS) to fly in year 2009 will carry a meteorological sensor from which visible channel measurements will be available. We developed a method utilizing satellite-derived BRDFs for the solar channel calibration over the bright desert area. The 6S model has been incorporated to account for directional effects of the surface using MODIS-derived BRDF parameters within the spectral interval in interest. Simulated radiances over the desert targets were compared with MODIS and SeaWiFS measured spectral radiances in order to examine the feasibility of the developed calibration algorithm. We also simulated TOA radiance over ocean targets to verify the consistency and reliability of the result. It was shown that simulated 16-day averaged radiances are in good agreement with the satellite-measured radiances within about ${\pm}5%$ uncertainty range for the year 2005, suggesting that the developed algorithm can be used for calibrating the COMS visible channel within about 5% uncertainty level.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.101-103
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• 2005

Vicarious calibration method using MODIS-derived surface reflectivity data as inputs to a radiative transfer model have been developed for the planned COMS solar channel. Pilot test was conduced over the Simpson Desert targets in Australia. Results suggested that calibration can be achieved within $5\%$ error range.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10b
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• pp.499-501
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• 2001

본 논문에서는 각 광원의 위치에 대해 미리 구한 라디안스 맵에 시간-색 공간에서의 반사요소 분리방법을 적용하여 난반사 라디안스 맵과 거울반사 라디안스 맵을 구한다. 필셀 BRDF를 얻기 위한 입력으로 반사요소가 분리된 라디안스 맵을 사용하였다. 따라서, 광원의 조작에 대해 난반사와 거울반사 이미지를 각각 제어할 수 있다. 시간-색 공간에서의 반사요소 분리방법을 사용함으로써, 이미지의 전역 정보가 아니라 지역 정보만을 이용한 반사요소 분리가 가능하다.

• Korean Journal of Remote Sensing
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• v.35 no.6_3
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• pp.1299-1312
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• 2019

As land remote sensing applications are expanding to the extraction of quantitative information, the importance of atmospheric correction is increasing. Considering the difficulty of atmospheric correction for land images, it should be applied when it is necessary. The quantitative information extraction and time-series analysis on biophysical variables in land surfaces are two major applications that need atmospheric correction. Atmospheric aerosol content and column water vapor, which are very dynamic in spatial and temporal domain, are the most influential elements and obstacles in retrieving accurate surface reflectance. It is difficult to obtain aerosol and water vapor data that have suitable spatio-temporal scale for high- and medium-resolution multispectral imagery. Selection of atmospheric correction method should be based on the availability of appropriate aerosol and water vapor data. Most atmospheric correction of land imagery assumes the Lambertian surface, which is not the case for most natural surfaces. Further BRDF correction should be considered to remove or reduce the anisotropic effects caused by different sun and viewing angles. The atmospheric correction methods of optical imagery over land will be enhanced to meet the need of quantitative remote sensing. Further, imaging sensor system may include pertinent spectral bands that can help to extract atmospheric data simultaneously.

• The Journal of the Korea Contents Association
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• v.10 no.1
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• pp.1-9
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• 2010

In this paper we present a shading technique for realistic rendering of the surfaces with irregular and complex textures using a single photograph. So far, most works have been using many photographs or special photographing equipment to render the surfaces with irregular and complex textures as well as dividing texture regions manually. We present an automatic selection method of the region segmentation techniques according to properties of materials. As our technique produces a reflectance model and the approximated Bidirectional Reflection Distribution Function(BRDF) parameters, it allows the recovery of the photometric properties of diffuse, specular, isotropic or anisotropic textured objects. Also it make it possible to present several synthetic images with novel lighting conditions and views.

• Journal of Korea Multimedia Society
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• v.14 no.5
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• pp.691-702
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• 2011

Recently, several researchers have attempted to combine human visual perception and computer graphics. Cole et. al. suggest the study results in which line drawing algorithm in computer graphics characterize the properties of line drawing made by artists. The paper also evaluates CG line drawing algorithms depending on whether people recognize effectively specific 3D shape from the image made by those CG line drawing algorithms. However, human recognizes the shape of objects more effectively in image made by BRDF shading model than line drawing algorithm. It means that the shading factor is important to recognize shape with human perception. In this paper, we analyze the correlation between shading made by human artists and that made by CG shading algorithms. The study is to characterize the mathematical properties of artists' shading and CG shading. This type of analysis can guide the future development of new CG shading algorithm in computer graphics for the purpose of shape perception.