• 대한원격탐사학회지
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• 제31권4호
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• pp.337-346
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• 2015

Water body extraction based on backscatter information is an essential process to analyze floodaffected areas from Synthetic Aperture Radar (SAR) image. Water body in SAR image tends to have low backscatter values due to homogeneous surface of water, while non-water body has higher backscatter values than water body. Non-water body, however, may also have low backscatter values in high resolution SAR image such as Kompsat-5 image, depending on surface characteristic of the ground. The objective of this paper is to present a method to increase backscatter contrast between water body and non-water body and also to remove efficiently misclassified pixels beyond true water body area. We create an entropy image using a Gray Level Co-occurrence Matrix (GLCM) and classify the entropy image into water body and non-water body pixels by thresholding of the entropy image. In order to reduce the effect of threshold value, we also propose Water Body Texture Index (WBTI), which measures simultaneously the occurrence of repeated water body pixel pair and the uniformity of water body in the binary entropy image. The proposed method produced high overall accuracy of 99.00% and Kappa coefficient of 90.38% in water body extraction using Kompsat-5 image. The accuracy analysis indicates that the proposed WBTI method is less affected by the choice of threshold value and successfully maintains high overall accuracy and Kappa coefficient in wide threshold range.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권12호
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• pp.6028-6042
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• 2019

Since Sparse Nonnegative Matrix Factorization (SNMF) method can control the sparsity of the decomposed matrix, and then it can be adopted to control the sparsity of facial feature extraction and recognition. In order to improve the accuracy of SNMF method for facial feature recognition, new additive iterative rules based on the improved iterative step sizes are proposed to improve the SNMF method, and then the traditional multiplicative iterative rules of SNMF are transformed to additive iterative rules. Meanwhile, to further increase the sparsity of the basis matrix decomposed by the improved SNMF method, a threshold-sparse constraint is adopted to make the basis matrix to a zero-one matrix, which can further improve the accuracy of facial feature recognition. The improved SNMF method based on the additive iterative rules and threshold-sparse constraint is abbreviated as ASNMF, which is adopted to recognize the ORL and CK+ facial datasets, and achieved recognition rate of 96% and 100%, respectively. Meanwhile, from the results of the contrast experiments, it can be found that the recognition rate achieved by the ASNMF method is obviously higher than the basic NMF, traditional SNMF, convex nonnegative matrix factorization (CNMF) and Deep NMF.

• Restorative Dentistry and Endodontics
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• 제41권3호
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• pp.159-166
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• 2016

The purpose of this review was to suggest practical criteria for the clinical translucency evaluation of direct esthetic restorative materials, and to review the translucency with these criteria. For the evaluation of reported translucency values, measuring instrument and method, specimen thickness, background color, and illumination should be scrutinized. Translucency parameter (TP) of 15 to 19 could be regarded as the translucency of 1 mm thick human enamel. Visual perceptibility threshold for translucency difference in contrast ratio (${\Delta}CR$) of 0.07 could be transformed into ${\Delta}TP$ value of 2. Translucency differences between direct and indirect resin composites were perceivable (${\Delta}TP>2$). Universal and corresponding flowable resin composites did not show perceivable translucency differences in most products. Translucency differed significantly by the product within each shade group, and by the shade group within each product. Translucency of human enamel and perceptibility threshold for translucency difference may be used as criteria for the clinical evaluation of translucency of esthetic restorative materials.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.1150-1153
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• 2006

In this paper, we investigated the effect of solvent on electrical properties of triisopropylsilyl (TIPS) pentacene organic thin-film transistors (OTFTs). The TIPS pentacene was spin coated by using chlorobenzene, p-xylene, chloroform and toluene as solvent. Fabricated OTFT with chlorobenzene showed field-effect mobility of $0.01\;cm^2/V{\cdot}s$, on/off ratio $4.3{\times}10^3$ and threshold voltage of 5.5 V. In contrast, with chloroform the mobility was $5.8{\times}10^{-7}\;cm^2/Vs$, on/off ratio $1.1{\times}10^2$ and threshold voltage of 1.7 V.

• 한국통신학회논문지
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• 제21권12호
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• pp.3246-3255
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• 1996

A threshold voltage extraction scheme which does not need matched replica of the MOSFET under test is proposed. In contrast to alternative methods, the accuracy of the proposed scheme does not depend on the matching of the test transistors. The proposed scheme has been implemented in a matching-free way using a switched-capacitor subtracting ampliier and a dynmic current mirror. Nonideal effects associated with these circuits, such as non-zero offset voltages and finite gains of op-amps, capcitor mismateches, and charge injection of MOS switches, are investigated and compensated. The circuit has been designed using ISRC 1.5.mu.m CMOS process parameters andfabricated at Inter-University semiconductor Research Center, and its performance has been evaluated.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 춘계학술대회 논문집
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• pp.125-128
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• 1998

The electro-optical properties of PDLCs ( Polymer Dispersed Liquid Crystals ) that have been interested for applications to projection display devices lately are significantly improved. For this improvement, we optimized not only the material parameters of liquid crystal and polymer but also the process conditions. Using TL series liquid crystals and polymer PN393 provided from Merck, we obtained the optimized process conditions such as cell gap, LC concentration, curing temperature and curing time. Under these conditions, we have achieved PDLC cells of threshold voltage 2.6V. contrast ratio 260 and negligible hysteresis.

• 정보보호학회논문지
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• 제10권3호
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• pp.37-48
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• 2000

서울Visual cryptography scheme is a simple method in which can be directly decoded the secret information in human visual system without performing any cryptographic computations. This scheme is a kind of secret sharing scheme in which if a secret of image type is scattered to n random images(slides) and any threshold (or more) of them are stacked together the original image will become visible. In this paper we consider (2, n) visual cryptography scheme and propose a new construction method in which the number of expanded pixels can be reduced by using the sample matrix. The proposed scheme can futhermore distribute the multiple secret image to each group according to the difference of relative contrast.

• 대한원격탐사학회지
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• 제29권6호
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• pp.645-655
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• 2013

As one of segmentation techniques for Synthetic Aperture Radar (SAR) image with oil spill, we applied a bimodal histogram method to discriminate oil pixels from non-oil pixels. The threshold of each moving window was objectively determined using the two peaks in the histogram distribution of backscattering coefficients from ENVISAT ASAR image. To reduce the effect of wind speed on oil spill detection, we selected ASAR image which satisfied a limit of wind speeds for successful detection. Overall, a commonly used adaptive threshold method has been applied with a subjectively-determined single threshold. In contrast, the bimodal histogram method utilized herein produces a variety of thresholds objectively for each moving window by considering the characteristics of statistical distribution of backscattering coefficients. Comparison between the two methods revealed that the bimodal histogram method exhibited no significant difference in terms of performance when compared to the adaptive threshold method, except for around the edges of dark oil spots. Thus, we anticipate that the objective method based on the bimodality of oil slicks may also be applicable to the detection of oil spills from other SAR imagery.

• 한국방사선학회논문지
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• 제17권5호
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• pp.717-723
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• 2023

간 질환을 포함한 여러 복부 질환은 사망에 영향을 줄 수 있다. 복부 질환 진료 시 전산화단층검사는(CT; Computed Tomography) 필수적으로 사용되고 있다. 판독에 유리한 영상을 만들기 위해서 높은 방사선 노출이 따르는데, 이에 대한 화질관리와 환자의 피폭 관리를 위한 다양한 노력이 필요하다. 복부 CT 영상의 화질개선을 위해서 후처리 방식의 웨이블릿(Wavelet) 알고리즘을 제안하였다. 웨이블릿은 입력 영상의 종류에 따라 역치(Threshold) 값을 설정해 주어야 하는 단점이 있기 때문에 본 연구에서는 역치 값을 실험적으로 제안하였고 화질 평가도 하였다. 실험결과, 복부 CT 영상의 최적 역치 값은 50으로 계산되었다. 실험영상 1의 경우 49%, 실험 영상 2의 경우 29% 노이즈가 개선되었고, 대조도도 크게 상승 하였다. 본 연구 결과를 저선량 복부 CT 영상을 획득 후 후처리 방법으로 적용한다면, 화질을 개선시킬 수 있어 질병 판독에 도움을 줄 것으로 판단한다.

• 방송공학회논문지
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• 제18권5호
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• pp.722-729
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• 2013

영상의 밝기가 집중되어 콘트라스트가 낮은 영상의 경우 히스토그램 평활화를 이용하면 영상내의 정보를 쉽게 분별할 수 있다. 기존의 기법에서는 콘트라스트 향상이 초점이었기 때문에 과한 콘트라스트 향상은 인지적으로 부자연스러운 영상을 생성하는 문제가 있었다. 이를 해결하기 위해서 CLAHE 방법은 일정크기로 콘트라스트 향상을 제한하는 기법으로 부자연스러움을 해결하였으나 이러한 경우 영상 내 디테일 정보가 은닉되는 문제가 발생하게 된다. 본 논문에서는 콘트라스트의 제한으로 인한 디테일 정보의 손실을 피하기 위해서 다중 레이어 블록 오버랩 히스토그램 평활화 기법을 기반으로 원 영상의 디테일에 대한 판별을 통해 각 레이어의 마스크를 이용한 디테일 맵을 구성한다. 각 레이어별로 디테일 맵을 이용한 제한된 콘트라스트 향상으로 생성된 영상들을 병합하여 영상 내 정보의 손실을 최소화하였다.