• Journal of Broadcast Engineering
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• v.18 no.1
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• pp.21-30
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• 2013

It is a challenging problem to most of the image processing when the light source is unknown. The color of the light source must be estimated in order to compensate color changes. To estimate the color of the light source, additional assumption is need, so that we assumed color distribution according to the light source. If the pixels, which do not satisfy the assumption, are used, the estimation fails to provide an accurate result. The most popular color distribution assumption is Grey-World Assumption (GWA); it is the assumption that the color in each scene, the surface reflectance averages to gray or achromatic color over the entire images. In this paper, we analyze the characteristics of the camera response function, and the effect of the Grey-World Assumption on the pixel value and chromaticity, based on the inherent characteristics of the light source. Besides, we propose a novel method that detects important pixels for the color estimation of the light source. In our method, we firstly proposed a method that gives weights to pixels satisfying the assumption. Then, we proposed a pixel detection method, which we modified max-RGB method, to apply on the weighted pixels. Maximum weighted pixels in the column direction and row direction in one channel are detected. The performance of our method is verified through demonstrations in several real scenes. Proposed method better accurately estimate the color of the light than previous methods.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.6
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• pp.110-121
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• 2016

The primary aim of the color constancy algorithm is to estimate illuminant chromaticity. There are various statistical-based, learning-based and combinational-based color constancy algorithms already exist. However, the statistical-based algorithms can only perform well on images that satisfy certain assumptions, learning-based methods are complex methods that require proper preprocessing and training data, and combinational-based methods depend on either pre-determined or dynamically varying weights, which are difficult to determine and prone to error. Therefore, this paper presents a new optimization based illuminant estimation method which is free from complex preprocessing and can estimate the illuminant under different environmental conditions. A strong color cast always has an odd standard deviation value in one of the RGB channels. Based on this observation, a cost function called the degree of illuminant tinge(DIT) is proposed to determine the quality of illuminant color-calibrated images. This DIT is formulated in such a way that the image scene under standard illuminant (d65) has lower DIT value compared to the same scene under different illuminant. Here, a swarm intelligence based particle swarm optimizer(PSO) is used to find the optimum illuminant of the given image that minimizes the degree of illuminant tinge. The proposed method is evaluated using real-world datasets and the experimental results validate the effectiveness of the proposed method.

• Korean Architects
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• no.9 s.245
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• pp.60-67
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• 1989

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.1411-1412
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• 2015

본 연구에서는 맥박 측정에서 생기는 잡음들 중 많은 오류를 생기게 하는 동잡음 개선을 위하여 회로를 제안하고 설계하였다. 기존의 맥박추정 장비에서 가변저항, 광원 스위칭, 디지털 필터를 사용함으로써 정확도 향상을 위한 연구를 하였다. 손가락에서 광전용적맥파를 측정시 측정부의 광원을 2개를 사용하고, 이를 스위칭을 통해 파형을 측정을 하였다. 실험에서 PPG의 측정은 반사형 방식을 사용하고 이를 광원스위칭을 통해 신호를 받아들였다. 이를 저주파통과필터와 고주파통과필터를 사용하여 0.5~5Hz대역을 필터링 함으로써 PPG이외의 잡음을 제거하고 신호를 검출하였다. 검출된 파형을 지수가중이중필터로 필터링을 함으로써 정확성을 높였다. 이를 통하여 광원스위칭을 통한 PPG의 출력과 발광다이오드 한 개를 사용한 출력을 비교 분석을 보여줄 것이다.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.3
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• pp.52-59
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• 2009

In general, methods based on histogram or a correction of gamma curve are usually utilized to enhance the contrast of captured image in the dark scene. These methods are efficient to enhance the contrast globally, however, they locally induced the low quality of image. Recently, to resolve the problem, the multi-scaled refiner algorithm improving the contrast with locally averaged lightness is proposed. However, estimating the locally averaged lightness, if there is the object with a high saturated color, the color distortion might be induced by the color of object. Thus, in this paper, the dominant chromaticity of image is estimated to correct the locally averaged lightness in multi-scaled retinex algorithm. Because the average chromaticity of image includes the chromaticity of illumination, the dominant chromaticity is estimated with dividing the average chromaticity of image by the estimated chromaticity of illumination from highlight region. In addition, to improve the lower chroma by multi-scaled retinex algorithm generally, the chroma was compensated preserving the hue in the CIELAB color space.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.49 no.4
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• pp.1-9
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• 2012

A method to estimate the 3-D shape of surface with specular reflection is proposed, where the difference between the images reflected from a flat surface and a curved surface is used. First, we analyzed the geometry of the spatial reflection at specular surface and the variation of reflected light due to curved surface, whose results are used to estimate 3-D shape. The proposed method is shown to be effective via experiments using the illumination with spatially distributed light source and the CCD camera to capture the light reflected from a surface. In experiments, the captured images from curved surface with specular reflection are processed to approximately estimate 3-D shape.

• Proceedings of the Korea Information Processing Society Conference
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• 2016.04a
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• pp.808-810
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• 2016

Color constancy는 다양한 광원 아래에서 사물의 색을 인지하는 능력이다. 사람의 눈은 절대적인 색상을 인지하는 것이 아니라 주변 환경과의 상대적인 색상을 인지하지만[1], 기계는 절대적인 색상 값으로 받아들이므로 기계가 광원의 영향을 받은 사물의 색상을 정확히 알기 위해서는 기계가 받아들이는 색상 값에서 광원의 영향을 제거해 주는 과정이 필요하다. 이를 카메라에서는 화이트 밸런싱 또는 칼라 밸런싱이라 부르기도 하며 이러한 과정을 위해서 다양한 기법들이 존재하는데, 영상 전체의 각 색상 채널의 평균값은 무채색이라는 Grey world 기법[2]부터, 영상에서 가장 높은 색상 값을 갖는 곳이 광원을 가장 잘 표현한다고 가정하는 White patch(Max RGB)기법[1], 색상 히스토그램 보정을 통한 화이트 밸런싱[3], 최근에는 무채색 지점에서의 각 색상 채널의 변화량이 모두 같다는 가정을 통해 무채색 지점을 찾는 Grey pixel[4] 등 많은 기법이 연구되었다. 본 연구에서는 칼라 히스토그램 보정으로 칼라 대비 개선 효과를 통해 각 색상 채널의 비율이 비슷한 곳을 무채색 지점으로 표본을 수집하여 해당 표본으로부터 칼라 벡터로서 PCA를 통한 대표 값을 추출하여 광원을 예측하는 기법을 소개한다.

• Journal of the Korea Computer Graphics Society
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• v.18 no.1
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• pp.1-9
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• 2012

Video-based modeling / rendering developed to produce photo-realistic video contents have been one of the important research topics in computer graphics and computer visions. To smoothly combine original input video clips and 3D graphic models, geometrical information of light sources and cameras used to capture a scene in the real world is essentially required. In this paper, we present a simple technique to estimate the position and orientation of an optimal light source from the topology of objects and the silhouettes of shadows appeared in the original video clips. The technique supports functions to generate well matched shadows as well as to render the inserted models by applying the estimated light sources. Shadows are known as an important visual cue that empirically indicates the relative location of objects in the 3D space. Thus our method can enhance realism in the final composed videos through the proposed shadow generation and rendering algorithms in real-time.

• Journal of Broadcast Engineering
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• v.13 no.3
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• pp.339-349
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• 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 the Institute of Electronics Engineers of Korea SP
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• v.38 no.3
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• pp.292-303
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• 2001

Object color can be determined by the characteristic of scene illuminant and surface. In this paper, perceived illumination effect is extended and with the highlight analysis, hybrid approach is proposed to estimate the illuminant chromaticity. The perceived illumination approach provides a stable candidate range for the estimation of illuminant chromaticity, however, the accuracy is slightly degraded depending on the image contents. The highlight approach does not depend on the image contents and provides an accurate solution of the scene illuminant chromaticity, however, it is difficult to determine the final solution among many cross-points. These two approaches are in effect mutually compensating. The solution from perceived illumination can be used as a starting point or as base information for the highlight approach to get the final solution.