• 대한기계학회논문집B
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• 제22권7호
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• pp.1030-1040
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• 1998

One of the main unresolved issues in large-eddy simulation(LES) of wall-bounded turbulent flows is the requirement of high spatial resolution in the near-wall region, especially in the spanwise direction. Such high resolution required in the near-wall region is generally used throughout the computational domain, making simulations of high Reynolds number, complex-geometry flows prohibitive. A grid-embedding strategy using a nonconforming spectral domain-decomposition method is proposed to address this limitation. This method provides an efficient way of clustering grid points in the near-wall region with spectral accuracy. LES of transitional and turbulent channel flow has been performed to evaluate the proposed grid-embedding technique. The computational domain is divided into three subdomains to resolve the near-wall regions in the spanwise direction. Spectral patching collocation methods are used for the grid-embedding and appropriate conditions are suggested for the interface matching. Results of LES using the grid-embedding strategy are promising compared to LES of global spectral method and direct numerical simulation. Overall, the results show that the spectral domain-decomposition grid-embedding technique provides an efficient method for resolving the near-wall region in LES of complex flows of engineering interest, allowing significant savings in the computational CPU and memory.

• Korean Journal of Mathematics
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• 제16권1호
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• pp.25-40
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• 2008

We are concerned with a free boundary problem for the 2D Stokes channel flows, which determines the profile of the wing for the channel, so that the given traction force is to be distributed along the wing of the channel. Using the domain embedding technique, the free boundary problem is transferred into the shape optimization problem through the compliant formulation by releasing the traction condition along the variable boundary. The justification of the formulation will be discussed.

• Journal of Information Processing Systems
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• 제12권4호
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• pp.681-687
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• 2016

Today's modern world requires a digital watermarking technique that takes the redundancy of an image into consideration for embedding a watermark. The novel algorithm used in this paper takes into consideration the redundancies of spatial domain and wavelet domain for embedding a watermark. Also, the cryptography-based secret key makes the algorithm difficult to hack and help protect ownership. Watermarking is blind, as it does not require the original image. Few coefficient matrices and secret keys are essential to retrieve the original watermark, which makes it redundant to various intentional attacks. The proposed technique resolves the challenge of optimizing transparency and robustness using a Canny-based edge detector technique. Improvements in the transparency of the cover image can be seen in the computed PSNR value, which is 44.20 dB.

• 한국멀티미디어학회논문지
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• 제8권6호
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• pp.783-789
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• 2005

This paper is proposed a watermarking technique for copyright protection of multimedia contents. We proposed adaptive watermark detection algorithm using stochastic perceptual model and statistical decision method in DMWT(discrete multi wavelet transform) domain. The stochastic perceptual model calculates NVF(noise visibility function) based on statistical characteristic in the DMWT. Watermark detection algorithm used the likelihood ratio depend on Bayes' decision theory by reliable detection measure and Neyman-Pearson criterion. To reduce visual artifact of image, in this paper, adaptively decide the embedding number of watermark based on DMWT, and then the watermark embedding strength differently at edge and texture region and flat region embedded when watermark embedding minimize distortion of image. In experiment results, the proposed statistical decision method based on multiwavelet domain could decide watermark detection.

• 인터넷정보학회논문지
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• 제11권2호
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• pp.99-107
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• 2010

본 연구에서는 디지털 영상의 블라인드 워터마킹 알고리즘을 제안하였다. 제안한 알고리즘은 웨이블릿 평면에서 처리되는 변환 평면 워터마킹 알고리즘으로서 2차원 EMD을 이용하여 분해된 워터마크의 EMF 성분들이 웨이블릿 대역에 삽입되어, 각 웨이블릿 대역은 워터마크의 일부 정보만을 포함하고 있는 것을 특징으로 하고 있다. 워터마크의 추출은 각 웨이블릿 대역에서 추출한 워터마크의 일부 정보들을 2차원 EMD의 선형적인 특징에 의해 산술적 또는 논리적 연산을 통하여 회복할 수 있도록 하였다. 개발한 워터마킹 알고리즘은 비가시성, 강인성 등 워터마킹 알고리즘에서 요구되는 조건들에 대한 실험을 수행하여 성능을 비교 분석하였다.

• 대한전자공학회논문지SP
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• 제43권4호
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• pp.27-36
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• 2006

무손실 정보은닉은 정보를 삽입하되 추출과정에서 원본 영상으로의 완벽한 복원이 가능하도록 정보를 삽입하는 기술이다. 본 논문에서는 웨이블릿 영역에서 영상에 대한 무손실 정보은닉 알고리즘을 제안한다. 제안된 알고리즘은 히스토그램 수정을 웨이블릿 계수에 적용한 방법으로 두 단계의 삽입과정으로 이루어진다. 1차 삽입과정에서 히스토그램을 수정함으로써 웨이블릿 계수에 정보를 은닉한다. 2차 삽입과정은 1차 삽입 과정에서 발생한 영상의 왜곡을 줄이는 동시에 정보를 은닉할 수 있는 방법으로 높은 삽입용량을 얻을 수 있게 한다. 제안 알고리즘은 모의실험을 통해 기존의 방법들보다 삽입용량 대 PSNR 측면에 서 향상된 성능을 보여주었다.

• 방송공학회논문지
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• 제6권2호
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• pp.169-176
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• 2001

기존의 비디오 워터마킹 알고리즘은 실시간 처리가 대부분 불가능하였는데, 가장 큰 이유는 압축에 강인한 알고리즘을 개발하 기 위해 삽입과 추출과정이 계산량이 많은 주파수 공간에서 이루어지기 때문이다 보통 기존의 방법들은 비디오 압축처리 중에 워터마크를 삽입하는 과정을 첨가하여 실시간 처리를 지원토록 해왔다. 그러나, 본 논문에서는 공간영역과 주파수영역에서 모두 처리하는 과정을 거치도록 하여 실시간 처리가 가능한 새로운 알고리즘을 제안하였다. 제안된 방법은 먼저 워터마크를 퓨리에 주파수 영역에서 변환하여 생성한 후, 이를 공간영역으로 역변환 한 후. 공간 영역에서 비디오에 직접 삽입한다. 이 과정은 계산량이 딴이 소비되는 주파수 영역에서의 작업을 따로 실행하지 않아 실시간 처리가 가능해진다. 또한 이 방법은 비디오 스트림에도 적용 가능하며 MPEG압축과 기하학적 변화등의 다양한 공격에도 매우 강인한 결과를 보여준다.

• Journal of Information Technology Applications and Management
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• 제14권1호
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• pp.137-144
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• 2007

In this paper, we propose a rotation resistant robust logo embedding watermarking technique. Geometric manipulations make the detection process very complex and difficult. Watermark embedding in the normalized image directly suffers from smoothing effect due to the interpolation during the image normalization. This can be avoided by estimating the transform parameters using image normalization angle and moments, instead of embedding in the normalized image. Conventional rotation resistant schemes that use full frame transform. In this paper we adopt DCT and calculate masking using a spatio-frequency localization of the $8{\times}8$ block DCT coefficients. Experimental results show that the proposed algorithm is robust against rotation process.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 G
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• pp.2427-2429
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• 1998

Digital watermarking is the techinque which embeds the invisible signal into multimedia data such as audio, video, images, for copyright protection, including owner identification and copy control information. This paper proposes a new watermark embedding and extraction technique by extending the direct sequence spread spectrum technique. The proposed technique approximates the frequency component of pixels in spatial domain by using Laplacian mask and adaptively embeds the watermark considering the HVS to reduce the degradation of Image. In watermark extraction process, the proposed technique strengthens the high frequency components of image and extracts the watermark by demodulation. All this processes are performed in spatial domain to reduce the processing time.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(4)
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• pp.319-322
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• 2002

In this paper, we present a digital authentication technique using content-based watermarking in digital images. To digest the image contents, Hopfield network is employed on the block-based edge image. The Hopfield function extracts the same tit fur similarly looking blocks so that the values are unlikely to change to the innocuous manipulations while being changed far malicious manipulations. By inputting the extracted bit sequence with secret key to the cryptographic hash function, we generate a watermark for each block by seeding a pseudo random number generator with a hash output Therefore, the proposed authentication technique can distinguish between malicious attacks and innocuous attacks. Watermark embedding is based on the block-based spread spectrum method in DCT domain and the strength of watermark is adjusted according to the local statistics of DCT coefficients in a zig-zag scan line in AC subband. The numerical experiments show that the proposed technique is very efficient in the performance of robust authentication.