• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.908-911
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• 2002

본 논문에서는 영상의 불법적인 복사를 방지하기 위해 사용되는 워터마킹을 내장한 JPEG 압축용 DCT의 VHDL 모델을 제시한다. 워터마킹 방법은 사람의 시각 시스템을 이용하여 주파수 영역에서 영상의 시각적인 특성에 적응하는 워터마크를 내장한다. 영상 압축시에 주파수 영역으로 변환해주는 DCT와 함께 화질저하에 대한감소와 공격에 강한 water marking을 구현함으로서 손실 압축에서도 방지 기능을 유지하면서 시스템의 효율적인 구성을 얻을 수 있다. 구현된 DCT의 VHDL 모델을 사용한 시뮬레이션 결과 고주파 성분이 많은 복잡한 영상과 저주파 성분이 많은 단순한 영상에 적용하여 워터마크가 시각적으로 보이지 않고 JPEG 손실압축과 잡음에도 견고함을 가지며, 기능을 추가하여도 기존에 비해 면적을 적게 차지하여 빠른 속도를 얻을 수 있어, 소형 시스템에 솔루션에 적용이 적합하다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.3
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• pp.378-385
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• 1998

A three-dimensional finite difference time domain (3-D FDTD) algorithm of calculation for the characteristics of coaxial-to-cavity filter including a discended probe and a tuning post is presented. In the arrangement the inner coaxial conductor protrudes into the cavity and operates as a probe radiator. And the height of the rectangular tuning post determines the resonant frequency. The validation of this method is confirmed by comparing the calculated values with experimental results for the designed filter.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.43.1-43.1
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• 2011

근적외영역의 타이탄 측광영상에서 나타나는 주연감광(Limb Darkening) 및 주연증광(Limb Brightening) 현상의 원인을 설명하기 위해 구면기하(spherical geometry)에 의한 효과 외에 헤이즈(haze) 자체의 성질 변화량을 추정해 본다. 근적외영역의 강한 메탄 흡수 밴드 부근에서 타이탄의 대기를 관측하면 파장에 따라 표면 부근에서 성층권 사이의 정보를 얻을 수 있으며, 이를 복사전달모델과 비교해 대기 중에 존재하는 연무 입자의 성질을 유추할 수 있다. 관측자료는 2006년 2월 Gemini/North Observatory의 Near-Infrared Integral Field Spectrometer(NIFS)를 이용해 얻은 측 분광 자료를 사용하였다. NIFS의 공간분해능은 화소당 0.05"로, 타이탄의 적도부분을 약 17화소로 분해할 수 있으므로, 각 지역별로 분광선 모델을 만들어 관측자료와 비교하는 데에 용이하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.05a
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• pp.655-658
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• 2003

멀티미디어 기술과 인터넷의 급속한 발전으로 인해 영상 데이터의 복사가 더욱 쉬워지고 있다. 이러한 작품들을 보호하기 위해 데이터 안에 저작권을 표시할 수 있는 기술들이 필요해지고 지난 몇 년간 데이터에 다른 정보를 삽입할 수 있는 많은 기법들이 제안되어 왔다. 본 논문에서는 RGB 칼라 영상을 인간 시각 특성을 나타내는 I.UV 좌표계로 변화하여 인간 시각에 둔감한 U영역에 키를 이용하여 랜덤하게 워터마크를 삽입하고 추출하는 워터마킹 기법을 제안한다. 또한 웨이브릿(Wavelet) 변환을 사용하였으며 비교적 공격에 강한 고주파수 영역에 삽입하였고 추출시는 삽입한 키 값을 이용하여 워터마크를 추출한다. 제안한 워터마킹 기법은 시각적으로 보이지 않고, 가우시안 노이즈(Gaussian Noise) 및 필터링(filtering)에도 견고함을 보인다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2018.11a
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• pp.143-144
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• 2018

360 비디오는 VR 응용의 확산과 함께 몰입형 미디어로 주목 받고 있으며, JVET(Joint Video Experts Team)에서 post-HEVC 로 진행중인 VVC(Versatile Video Coding)에 360 비디오 부호화도 함께 고려하고 있다. 360 비디오 부호화를 위하여 변환된 2D 영상은 투영 면(face) 간의 불연속성과 비활성 영역이 존재할 수 있으며 이는 부호화 효율을 저하시키는 원인이 된다. 본 논문에서는 SSP(Segmented Projection)에서의 이러한 불연속성과 비활성 영역을 줄이는 효율적인 기하학적 패딩(padding) 기법을 제시한다. 실험결과 제안 기법은 복사에 의한 패딩을 사용하는 기존 SSP 대비 주관적 화질이 향상된 것을 확인 할 수 있었다.

• KIPS Transactions on Computer and Communication Systems
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• v.7 no.2
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• pp.49-58
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• 2018

A certificate is a means to certify users by conducting the identification of the users, the prevention of forgery and alteration, and non-repudiation. Most people use an accredited certificate when they perform a task using online banking, and it is often used for the purpose of proving one's identity in issuing various certificates and making electronic payments in addition to online banking. At this time, the issued certificate exists in a file form on the disk, and it is possible to use the certificate issued in an existing device in a new device only if one copies it from the existing device. However, most certificate duplication methods are a method of duplication, entering an 8-16 digit verification code. This is inconvenient because one should enter the verification code and has a weakness that it is vulnerable to security issues. To solve this weakness, this study proposes a method for enhancing security certificate duplication in a multi-channel using TCP and BLE. The proposed method: 1) shares data can be mutually authenticated, using BLE Advertising data; and 2) encrypts the certificate with a symmetric key algorithm and delivers it after the certification of the device through an ECC-based electronic signature algorithm. As a result of the implementation of the proposed method in a mobile environment, it could defend against sniffing attacks, the area of security vulnerabilities in the existing methods and it was proven that it could increase security strength about $10^{41}$ times in an attempt of decoding through the method of substitution of brute force attack existing method.

• Journal of Digital Contents Society
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• v.16 no.3
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• pp.389-395
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• 2015

Digital image provides many conveniences at the internet environment recently. A great number of applications, like Digital Library, Stock Image, Personal Image and Important Information, require the use of digital image. However it has fatal defect which is easy to be modified because digital image is only electronic file. Numerous digital image forgeries have become a serious problem due to the sophistication and accessibility of image editing software. Copy-Move forgery is the simplest type of forgery that involves copying portion of an image and paste it on different location within the image. There are many approaches to detect Copy-Move forgery, but all of them have their own limitations. In this paper, visual and invisible feature based forgery detection techniques are tested and analyzed. The analysis shows that pros and cons of these two techniques compensate each other. Therefore, a hybrid of visual based and invisible feature based forgery detection that combine the merits of both techniques is proposed. The experimental results show that the proposed algorithm has enhanced performance compared to individual techniques. Moreover, it provides more information about the forgery, like identifying copy and duplicate regions.

• Korean Journal of Remote Sensing
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• v.24 no.6
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• pp.559-569
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• 2008

The Geostationary Ocean Color Imager (GOCI) on board the Communication Ocean Meteorological Satellite (COMS), the first geostationary ocean color sensor, requires accurate atmospheric correction since its eight bands are also affected by atmospheric constituents such as gases, molecules and atmospheric aerosols. Unlike gases and molecules in the atmosphere, aerosols can interact with sunlight by complex scattering and absorption properties. For the purpose of qualified ocean remote sensing, understanding of aerosol-radiation interactions is needed. In this study, we show micro-physical and optical properties of aerosols using the Optical Property of Aerosol and Cloud (OPAC) aerosol models. Aerosol optical properties, then, were used to analysis the relationship between theoretical satellite measured radiation from radiative transfer calculations and aerosol optical thickness (AOT) under various environments (aerosol type and loadings). It is found that the choice of aerosol type makes little different in AOT retrieval for AOT<0.2. Otherwise AOT differences between true and retrieved increase as AOT increases. Furthermore, the differences between the AOT and angstrom exponent from standard algorithms and this study, and the comparison with ground based sunphotometer observations are investigated. Over the northeast Asian region, these comparisons suggest that spatially averaged mean AOT retrieved from this study is much better than from standard ocean color algorithm. Finally, these results will be useful for aerosol retrieval or atmospheric correction of COMS/GOCI data processing.

• Korean Journal of Remote Sensing
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• v.37 no.5_2
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• pp.1269-1279
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• 2021

Geostationary Ocean Color Imager II (GOCI-II), which are now operated successfully since its launch in 2020, acquires local area images with 12 Level 1B slot images that are sequentially acquired in a 3×4 grid pattern. The boundary areas between the adjacent slots are prone to discontinuity in radiance, which becomes even more clear in the following Level 2 data, and this warrants the precise analysis and correction before the distribution. This study evaluates the relative radiometric biases between the adjacent slots images, by exploiting the overlapped areas across the images. Although it is ideal to derive the statistics from humongous images, this preliminary analysis uses just the scenes acquired at a specific time to understand its general behavior in terms of bias and variance in radiance. Level 1B images of February 21st, 2021 (UTC03 = noon in local time) were selected for the analysis based on the cloud cover, and the radiance statistics were calculated only with the ocean pixels. The results showed that the relative bias is 0~1% in all bands but Band 1 (380 nm), while Band 1 exhibited a larger bias (1~2%). Except for the Band 1 in slot pairs aligned North-South, biases in all direction and in all bands turned out to have biases in the opposite direction that the sun elevation would have caused.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.1
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• pp.36-42
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• 2016

In multi-level-cell based storage devices, TLC NAND has been employed solid state drive due to cost effectiveness. Since TLC has slow performance and low endurance compared with MLC, TLC based storage has adopted SLC buffer scheme to improve performance. To improve SLC buffer scheme, this paper proposes page overwriting method in SLC block. This method provides data updates without erase operation within a limited number. When SLC buffer area is filled up, FTL should execute copying valid pages and erasing it. The proposed method reduces erase counts by 50% or more compared with previous SLC buffer scheme. Simulation results show that the proposed SLC buffer overwrite method achieves 2 times write performance improvement.