• Journal of Electrical Engineering and Technology
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• 제13권4호
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• pp.1673-1681
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• 2018

In this paper, the fabrication of a white light-emitting diode (WLED) package capable of producing different color rendering indexes (CRI ($R_a$)) using different types of phosphors (YAG:Ce, Silicate, Nitride, LuAG) for the LEDs is presented. The color quality is evaluated based on the current and temperature variation conditions. The evaluation method for color quality compares the existing CIE 13.3 method and the new IES TM-30-15 method. The CRI ($R_a$) defined in the conventional CIE 13.3 has the disadvantage. This cannot offer any information relevant to the user's preference. However, the newly proposed IES TM-30-15 method suggests the additional measure related to user's preference such as Color Gamut ($R_g$). The present experimental results obtained using the IES TM-30-15 show that the color quality of the WLEDs using green and red phosphors are better than that of the WLEDs using yellow phosphor, but their luminous efficacies are lower. The color quality of WLEDs using green and red phosphors are more stable than that of the WLEDs using yellow phosphor, for current and temperature variations, and it is verified that the phosphor causes this change. The evaluation method for color quality, based on IES TM-30-15, is proved to be capable of overcoming the problems of the existing evaluation methods by this study.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 C
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• pp.449-451
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• 2000

Crosstalk is the primary cause of image distortion in active matrix liquid crystal displays (AMLCD). Crosstalk produces voltage errors that limit gray scale fidelity and consequently, degrades display resolution, contrast ratio, color fidelity, and image quality. In this study, crosstalk phenomena of some methods to compensate level shift voltages has been simulated. This will be contributed to find the way to design the excellent image quality of the TFT-LCDs.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.1224-1227
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• 2009

When evaluating the quality of images and displays, it is important to combine the characteristics as perceived by the human visual system and measured by equipment using subjective and objective methods, respectively. In the case of objective methods, the quality of a display is measured using colorimetric or radiometric devices according to existing standards covering the color temperature, gamut size, gamma characteristic, and device characterization. Meanwhile, subjective methods assess the quality of an image using the human visual system based on a comparison with a reference or counterpart using such metrics as the sharpness, noise, contrast, saturation, and color accuracy. Objective and subjective methods are usually used together in comparison, as ultimately it is observers watching images on a display. In addition to existing objective methods, a new image quality metric is also introduced as regards the JPEG compression ratio that is reflected in the relationship between the gamut size and the color fidelity in CIELAB color space.

• 반도체디스플레이기술학회지
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• 제16권3호
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• pp.82-86
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• 2017

High dynamic range (HDR) imaging offers a radically approach of representing colors in digital images. Instead of using the range of colors produced by given devices, HDR imaging method manipulates and stores all colors and brightness levels visible to the human eye. To faithfully represent, store and then reproduce all these effects, the original scene must be stored and treated using high fidelity HDR techniques. Then, tone mapping is required to accommodate HDR image to low dynamic range (LDR) devices, and tone mapping operation of HDR image for realistic display is commonly researched. However, color visualization for analyzing scene luminance in HDR imaging has less attention from researches. This paper presents and implements a method for reproduction and visualization of the false color in HDR images. We produce a color visualization framework with several mapping functions, and evaluate their effectiveness by using RMAE and SNR with commonly used HDR image data. Experiment reveals that the sigmodal mapping function shows better performance in the false color visualization, compared to other methods.

• Journal of the Optical Society of Korea
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• 제7권4호
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• pp.234-239
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• 2003

Objective methods to assess quantitatively port wine stain (PWS) blanching in response to laser therapy are needed to improve laser therapeutic outcome. Previous studies have attempted to assess objectively PWS color based on point measurement devices. To date, these approaches have typically been limited by a number of factors such as small test area and need for contact. To address these issues, a polarization spectral imaging system and an image analysis method have been developed to evaluate quantitatively erythema and melanin content distribution in skin. The developed polarization spectral imaging system minimizes artifacts such as glaring, shadowing, and non-uniform illumination that interfere with image fidelity. Furthermore, the image analysis method has been employed to get images of skin melanin and erythema indices from the acquired color images for quantitative analysis. Finally, using PWS patient color image, the effectiveness in laser treatment of PWS was evaluated by calculating relative erythema index image that is the relative erythema index of PWS region to the normal region. The developed device and analysis method appears to be a simple and effective method for quantitative analysis of PWS blanching.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(4)
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• pp.239-242
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• 2000

The color television signal and color receivers should be balanced for the same value of reference white to achieve colorimetric fidelity and to minimize interference. The NTSC signal is balanced for white at 6774 K and most existing receivers are balanced between 6500 K and 10000 K for many reasons. In this paper, we analyze beam current ratio, lightness, and channel gain ratio according to the color temperature for the three-tube projection HDTV. We also propose the brighter reference white for the three-tube projection HDTV based on the Helmholtz-Kohlrausch effect and the optical resolution of the image. In computer simulation we confirmed the most suitable reference white using the proposed analysis method.

• 한국정보통신학회논문지
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• 제11권10호
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• pp.1828-1834
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• 2007

본 논문에서는 웨이블릿 변환을 기반으로 한 새로운 컬러영상 워터마킹 기법을 제안한다. 먼저 RGB컬러영역을 YCbCr 좌표계로 변환한다. 그리고 워터마크에 대해 Arnold 변환을 하여 워터마크의 상관성을 적게 만든다. 그 후, 선형비트확장 기법을 적용하여 확대된 워터마크를 웨이블릿 변환된 컬러 영상의 Y 영역-저주파대에 일정한 강도로 삽입한다. 워터마크를 추출할 때는 F-노름(norm) 함수를 이용한다. 다양한 칼라영상에 대해 실험을 한 결과 제안한 방법은 충실도와 강인성 측면에서 우수한 특성을 가짐을 확인하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.443-444
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• 2006

In this paper, a spatial-based perceptual watermarking considering human visual system (HVS) that is proposed for small-size images such as internet shopping-mall image. In our method, a multi-bit data can be embedded in luminance component of color images still keeping the perceptual quality of image. Experimental results demonstrated that watermarks can be strongly embedded while preserving a good fidelity.

• 대한전자공학회논문지SP
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• 제41권6호
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• pp.33-41
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• 2004

본 논문에서는 모니터와 모바일 디스플레이간의 복잡한 색 정합 과정을 단순화시키는 3차원의 색 정합 look-up table(LUT)을 설계하였다. 색 정합을 위해서는 우선 영상의 색을 CIEXYZ 혹은 CIELAB 등의 장치 독립적인 색 공간에서 처리하여야 한다. 장치 의존적인 RGB 색 공간의 데이터에서 장치 독립적인 색 공간의 데이터를 얻기 위해서는 디스플레이 특성화 과정이 필요하다. 기존의 S-curve 모델을 이용하여 LCD를 특성화 하면 LCD의 비선형적인 계조 특성으로 인해 특성화 오차가 허용 오차보다 커지게 된다. 본 논문에서는 X, Y, Z의 전기-빛 입출력 특성을 이용하여 S-curve 모델의 특성화 오차를 줄였다. 또한 모니터와 모바일 디스플레이간의 색 정합을 수행함으로써 색 표현력이 향상된 영상을 모바일 디스플레이에서 획득할 수 있었으며, 실험을 통하여 허용오차 내의 색 정합 LUT의 최소 크기가 64(4×4×4)라는 것을 확인하였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 춘계종합학술대회
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• pp.127-130
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• 2007

본 논문에서는 컬러 영상에 대한 웨이블릿 변환 기반의 디지털 워터마킹을 하는 새로운 기법을 제안한다. 먼저 워터마크에 대해 Arnold 변환을 하여 워터마크의 상관성을 적게 만든다. 그 후, 선형 비트확장 기법을 적용하여 확대된 워터마크를 웨이블릿 변환 된 컬러 영상의 Y 영역의 저주파대에 일정한 강도로 삽입한다 워터마크를 추출 할 때는 F-노름 (norm)함수를 이용한다. 다양한 컬러 영상에 대해 실험한 결과 제안방법은 충실도와 강인성 측면에서 우수한 특성을 가짐을 확인하였다.