• 대한전자공학회논문지SD
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• 제39권8호
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• pp.17-23
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• 2002

전자빔 증착 장비를 이용하여 SrS:CuCl TFEL 소자를 제작한 후, 발광특성을 조사하였다. 형광체 모체는 SrS 분말을 사용하였고, 발광중심체로는 CuCl 분말을 0.05 ~ 0.6 at% 범위에서 첨가하였다. 증착 온도 500℃, 전자빔 전류 20 ~ 40 mA 및 증착율 5 ~ 10 /sec의 조건에서 형광층 두께를 6000 으로 증착시켰다. CuCl 농도가 낮을 때에는 monomer, dimer, trimer 및 tetramer 발광센터에 의한 청색 발광을 확인할 수 있었으나 휘도가 낮았다. CuCl 농도가 높을 때에는 dimer와 trimer 발광센터에 의한 밝은 녹청색 빛을 방출하였다. 최적의 발광특성은 CuCl 농도를 0.2 at% 첨가한 SrS:CuCl TFEL 소자에서 관찰되었으며, 문턱전압, 휘도(L/sub 40/), 효율(η/sub 20/) 및 CIE 색좌표는 각각 55 V, 728 cd/㎡, 0.49 lm/W 및 (0.21, 0.33)을 나타내었다.

• 전자공학회논문지D
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• 제35D권6호
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• pp.21-27
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• 1998

E-beam 장비로 ZnS:Mn/Zns:Tb 2층 구조의 TFEL 소자를 제작하여 전기, 광학적 특성을 조사하였다. ITO 투명전극과 ATO 절연체가 증착된 유리기판(corning 7059 glass) 위에 E-beam 장비를 이용하여 ZnS:Mn, ZnS:Tb 형광체를 각각 3000 A로 증착하여 총 두께 6000 Å 갖도록 제작하였다. ZnS:Mn/ZnS:Tb TFEL 소자의 스펙트럼은 Mn/sup 2+/ 이온과 Tb/sup 3+/ 이온의 고유한 발광 스펙트럼을 모두 포함하여 540㎚에서 640㎚에 이르는 매우 넓은 범위의 발광 스펙트럼을 나타내었다. 휘도는 인가전압의 크기가 112V에서부터 급격히 증가하여 155 V에서 포화 휘도 1025 Cd/㎡를 나타내었고 최대 전압 185 V에서의 휘도는 2080 Cd/㎡이었다. Capacitance-voltage(C-V) 및 transferred charge-phosphor voltage(Q/sub t/-V/sub p/) 특성으로부터 형광층 capacitance (C/sub p/)와 절연층 capacitance (C/sub i/)가 각각 13.5 nF/㎠, 60 nF/㎠됨을 알 수 있었고, 인가전압의 최대치를 155 V에서 185 V로 증가시킬수록 TFEL 소자의 문턱전압(V/sub thl/)이 126 V에서 93 V로 감소함을 알 수 있었다. 이것은 인가전압을 증가시킬수록 polarization charge가 증가되고 polarization charge에 의해 형성된 형광체 내부전압이 증가되었기에 문턱전압이 감소한 것이다. 또한 처음으로 문턱전압에 관한 수식을 제안하였으며 문턱전압의 이론치와 실험치가 일치하는 것을 확인하였다.

• 전자공학회논문지
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• 제52권5호
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• pp.147-154
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• 2015

본 논문에서는 주변의 밝기에 대한 HVS의 민감도를 모델링한 JND (Just Noticeable Difference)를 비디오 코딩에 적용함으로써, JND 모델에 따른 임계치를 기준으로 현재 코딩 유닛에 적용 가능한 최대 양자화 파라미터를 결정하여 유사한 주관적 화질에서 비트율을 절감시키는 방법을 제안한다. 제안하는 방법은 입력된 현재 코딩 유닛에 대하여 기준이 되는 양자화 파라미터가 적용된 복원 신호 대비 더 높은 양자화 파라미터를 적용한 복원 신호가 JND 관점에서 유사하게 인지되는 경우에 더 높은 양자화 파라미터를 선택함으로써 비트율을 절감시킨다. 제안하는 알고리즘의 성능 검증을 위하여 최신 비디오 압축 표준인 HEVC (High Efficiency Video Coding)의 참조 소프트웨어인 HM16.0에 본 알고리즘을 적용하였으며, HM16.0을 통해 압축된 영상 대비 유사한 화질에서 최대 20.21%, 평균적으로 약 6.18%의 비트율 절감을 달성하였다.

• Journal of information and communication convergence engineering
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• 제12권3호
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• pp.168-172
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• 2014

In this paper, we propose an algorithm that can efficiently detect and monitor multiple ships in real-time. The proposed algorithm uses morphological operations and edge information for detecting and tracking ships. We used smoothing filter with a $3{\times}3$ Gaussian window and luminance component instead of RGB components in the captured image. Additionally, we applied Sobel operator for edge detection and a threshold for binary images. Finally, object labeling with connectivity and morphological operation with open and erosion were used for ship detection. Compared with conventional methods, the proposed method is meant to be used mainly in coastal surveillance systems and monitoring systems of harbors. A system based on this method was tested for both stationary and non-stationary backgrounds, and the results of the detection and tracking rates were more than 97% on average. Thousands of image frames and 20 different video sequences in both online and offline modes were tested, and an overall detection rate of 97.6% was achieved.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권2호
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• pp.837-856
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• 2016

Underwater image enhancement has received considerable attention in last decades, due to the nature of poor visibility and low contrast of underwater images. In this paper, we propose a new automatic underwater image enhancement algorithm, which combines nonsubsampled contourlet transform (NSCT) domain enhancement techniques with the mechanism of the human visual system (HVS). We apply the multiscale retinex algorithm based on the HVS into NSCT domain in order to eliminate the non-uniform illumination, and adopt the threshold denoising technique to suppress underwater noise. Our proposed algorithm incorporates the luminance masking and contrast masking characteristics of the HVS into NSCT domain to yield the new HVS-based NSCT. Moreover, we define two nonlinear mapping functions. The first one is used to manipulate the HVS-based NSCT contrast coefficients to enhance the edges. The second one is a gain function which modifies the lowpass subband coefficients to adjust the global dynamic range. As a result, our algorithm can achieve contrast enhancement, image denoising and edge sharpening automatically and simultaneously. Experimental results illustrate that our proposed algorithm has better enhancement performance than state-of-the-art algorithms both in subjective evaluation and quantitative assessment. In addition, our algorithm can automatically achieve underwater image enhancement without any parameter tuning.

• 한국전기전자재료학회논문지
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• 제15권2호
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• pp.110-118
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• 2002

Organic thin film transitors(OTFT) are of interest for use in broad area electronic applications. And recently organic electroluminescent devices(OELD) have been intensively investigated for using in full-color flat-panel display. We have fabricated inverted-staggered structure OTFTs at lower temperature using the fused-ring polycyclic aromatic hydrocarbon pentacene as the active eletronic material and photoacryl as the organic gate insulator. The field effect mobility is 0.039∼0.17 ㎠/Vs, on-off current ratio is 10$\^$6/, and threshold voltage is -7V. And here we report the study of driving emitting, Ir(ppy)$_3$, phosphorescent OELD with all organic thin film transistor and investigated its electrical characteristics. The OELD with a structure of ITO/TPD/8% Ir(ooy)$_3$ doped in BCP/BCP/Alq$_3$/Li:Al/Al and OTFT with a structure of inverted-stagged Al(gate electrode)/photoacry(gate insulator)/pentacene(p-type organic semiconductor)/ Au(source-drain electrode) were fabricated on the ITP patterned glass substrate. The electrical characteristics are turn-on voltage of -10V, and maximum luminance of about 90 cd/㎡. Device characteristics were quite different with that of only OELD.

• 한국재료학회지
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• 제30권8호
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• pp.421-425
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• 2020

A transparent quantum dot (QD)-based light-emitting diode (LED) with silver nanowire (Ag NW) and indium-tin oxide (ITO) hybrid electrode is demonstrated. The device consists of an Ag NW-ITO hybrid cathode (-), zinc oxide, poly (9-vinylcarbazole) (PVK), CdSe/CdZnS QD, tungsten trioxide, and ITO anode (+). The device shows pure green-color emission peaking at 548 nm, with a narrow spectral half width of 43 nm. Devices with hybrid cathodes show better performances, including higher luminance with higher current density, and lower threshold voltage of 5 V, compared with the reference device with a pure Ag NW cathode. It is worth noting that our transparent device with hybrid cathode exhibits a lifetime 9,300 seconds longer than that of a device with Ag NW cathode. This is the reason that the ITO overlayer can protect against oxidization of Ag NW, and the Ag NW underlayer can reduce the junction resistance and spread the current efficiently. The hybrid cathode for our transparent QD LED can applicable to other quantum structure-based optical devices.

• Journal of Ubiquitous Convergence Technology
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• 제2권1호
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• pp.18-26
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• 2008

The invariance relation existing in the non-negative matrix factorization (NMF) is used for constructing robust image hashes in this work. The image is first re-scaled to a fixed size. Low-pass filtering is performed on the luminance component of the re-sized image to produce a normalized matrix. Entries in the normalized matrix are pseudo-randomly re-arranged under the control of a secret key to generate a secondary image. Non-negative matrix factorization is then performed on the secondary image. As the relation between most pairs of adjacent entries in the NMF's coefficient matrix is basically invariant to ordinary image processing, a coarse quantization scheme is devised to compress the extracted features contained in the coefficient matrix. The obtained binary elements are used to form the image hash after being scrambled based on another key. Similarity between hashes is measured by the Hamming distance. Experimental results show that the proposed scheme is robust against perceptually acceptable modifications to the image such as Gaussian filtering, moderate noise contamination, JPEG compression, re-scaling, and watermark embedding. Hashes of different images have very low collision probability. Tampering to local image areas can be detected by comparing the Hamming distance with a predetermined threshold, indicating the usefulness of the technique in digital forensics.

• 한국인터넷방송통신학회논문지
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• 제13권1호
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• pp.135-142
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• 2013

본 외곽선 탐지는 모양 판별 및 객체 인식과 같은 많은 컴퓨터 시각 분야에 있어서 중요한 문제이다. 대부분의 경우에 지역적인 휘도 변화가 객체 윤곽선에서 보다는 무늬 영역에서 보다 강하게 나타나는 것으로 판명되고 있다. 따라서 각 화소의 가까운 인접된 부분에서만 볼 수 있는 지역적인 에지 특징들은 하나의 윤곽선 존재의 믿을만한 정보가 될 수 없기 때문에 전체적인 분석이 요구되고 있다. 본 연구에서는 형태심리학적 원리를 바탕으로 가상 연산자의 변형된 형태로서 적응성을 갖는 확대 연산자에 의한 지역적인 윤곽선 탐지 기법을 제안한다. 제안 방식의 새로운 점은 확대 방식에 있어서 각 윤곽선 화소에 관해 계산 기하학의 관점에서 Delaunary 다이어그램을 사용한다는 것이다. 윤곽선 그룹화와 관련하여 다중 임계 알고리즘이 도입되고, 각 임계 단계에서 작은 크기의 윤곽선 그룹들은 삭제되며, 자연 3차 스플라인 보간법을 통해 재구축되는 방식의 외형을 나타낸다. 또한, 상이한 임계들의 학습을 통해 입력 인자들의 값에 제안된 알고리즘이 민감하지 않은 견고한 성질을 유지하도록 한다. 본 연구의 구현에서는 기존 접근방식과의 비교를 통해 제안된 외형 결정 방식이 이미지에서 제거된 많은 텍스처들이 있음에도 불구하고 견고하고, 낮은 대비의 외형을 쉽게 감지하는데 효과적임을 보인다.

• Journal of Electrical Engineering and Technology
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• 제12권4호
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• pp.1605-1610
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• 2017

The electrochemical luminescence (ECL) device was investigated, which has similar structure to the dye-sensitized solar cell. The structure of the ECL cell in this experiment reliably induces a large amount of the oxidation around electrodes. The band gap of the ECL electrode is of 3.0 - 3.2 eV. Titanium dioxide ($TiO_2$) nanoparticle has following properties: a band gap of 3.4 eV, a low-priced material, and 002 preferred orientation (Z-axis). Zinc Oxide (ZnO) nanorod is easy to grow in a vertical direction. In this paper, in order to determine material suitable for the ECL device, the properties of various materials for electrodes of ECL devices such as ZnO nanorod (ZnO-NR) and $TiO_2$ nanoparticle ($TiO_2-NP$) were compared. The threshold voltage of the light emission of the ZnO-NR was 2.0 V which is lower than 2.5 V of $TiO_2-NP$. In the other hand, the luminance of $TiO_2-NP$ was $44.66cd/m^2$ and was higher than that of $34cd/m^2$ of ZnO-NR at the same applied voltage of 4 V. Based on the experimental results, we could conclude that $TiO_2-NP$ is a more suitable electrode material in ECL device than the ZnO-NR.