• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.3 s.234
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• pp.314-321
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• 2005

Discrete Wavelet Transform (DWT) has been applied to the Direct Numerical Simulation (DNS) data of turbulent channel flow. DWT splits the turbulent flow into two orthogonal parts, one corresponding to coherent structures and the other to incoherent background flow. The coherent structure is extracted from not vorticity field but velocity's since the channel flow is not isoropic. By comparing DWT's result of channel flow with that of isotropic flow, it is shown that coherent structure maintains the properties of original channel flow. The velocity field of coherent structures can be represented by few wavelet modes and that these modes are sufficient to reproduce the velocity probability density function (PDF) and the energy spectrum over the entire inertial range. The remaining incoherent background flow is homogeneous, has small amplitude, and is uncorrelated. These results are compared with those obtained for the same compression rate using large eddy simulation (LES) filtering. In contrast to the incoherent background flow of DWT, the LES subgrid scales have a much larger amplitude and are correlated, which makes their statistical modeling more difficult.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1813-1818
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• 2004

Discrete Wavelet Transform (DWT) has been applied to the Direct Numerical Simulation (DNS) data of turbulent channel flow. DWT splits the turbulent flow into two orthogonal parts, one corresponding to coherent structures and the other to incoherent background flow. The coherent structure is extracted from not vorticity field but velocity's since the channel flow is not isotropic. By comparing DWT's result of channel flow with that of isotropic flow, it is shown that coherent structure maintains the properties of original channel flow. The velocity field of coherent structures can be represented by few wavelet modes and that these modes are sufficient to reproduce the velocity probability distribution function (PDF) and the energy spectrum over the entire inertial range. The remaining incoherent background flow is homogeneous, has small amplitude, and is uncorrelated. These results are compared with those obtained for the same compression rate using large eddy simulation (LES) filtering. In contrast to the incoherent background flow of DWT, the LES subgrid scales have a much larger amplitude and are correlated, which makes their statistical modeling more difficult.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.11C
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• pp.1053-1059
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• 2005

The computer generated hologram (CGH) designs and produces digital information for generating 3-D (3-Dimension) image using computer and software instead of optically-sensed hologram of light interference, and it can synthesis a virtual object which is physically not in existence. Since digital hologram includes an amount of data as can be seen at the process of digitization, it is necessary that the data representing digital hologram is reduced for storing, transmission, and processing. As the efforts that are to handle hologram with a type of digital information have been increased, various methods to compress digital hologram called by fringe pattern are groped. Suitable proposal is encoding of hologram. In this paper, we analyzed the properties of CGH using tools of frequency transform, assuming that a generated CGH is a 2D image by introducing DWT that is known as the better tool than DCT for frequency transform. The compression and reconstruction result which was extracted from the wavelet-based codecs illustrates that it has better properties for reconstruction at the maximum 2 times higher compression rate than the Previous researches of Yoshikawa[2] and Thomas[3].

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.12
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• pp.2146-2152
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• 2008

In In this paper, we proposed a new JPEG2000 codec using multiresolution-based rendering (MRBR) technique for video compression of 3-dimensional digital cinema. We introduced discrete wavelet transform (DWT) for stereoscopic image and stereo matching technique in the wavelet domain. The disparity was extracted using stereo matching and transmitted with the reference (left) image. Since the generated right image was degraded by the occlusion lesion, the residual image which is generated from difference between the original right image and the generated one was transmitted at the same tine. The disparity data was extracted using the dynamic programming method in the disparity domain. There is high correlation between the higher and lower subbands. Therefore we decreased the calculation amount and enhanced accuracy by restricting the search window and applying the disparity information generated from higher subband.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.5
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• pp.1245-1252
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• 2013

As the usage of digital image contents increase, a security problem for the payed image data or the ones requiring confidentiality is raised. This paper propose a depth-map image contents encryption methodology to hide the depth information. This method is performed on the frequency coefficients in the Wavelet domain. This method, by selecting the level and threshold value for the wavelet transform, encryption at various strengths are possible. The experimental results showed that encrypting only 0.048% of the entire data was enough to hide the constants of the depth-map. The encryption algorithm expected to be used effectively on the researches on encryption and others for image processing.

• Journal of Broadcast Engineering
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• v.22 no.3
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• pp.295-312
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• 2017

Digital video content is the most information-intensive and high-value content. Therefore, it is necessary to protect the intellectual property rights of these contents, and this paper also proposes a watermarking method of digital image for this purpose. The proposed method uses the frequency characteristics of 2-Dimensional Discrete Wavelet Transform (2D-DWT) for digital images and digital watermark on global data without using local or specific data of the image for watermark embedding. The method to insert digital watermark data uses a simple Quantization Index Modulation (QIM) and a multiple watermarking method that inserts the same watermark data in multiple. When extracting a watermark, multiple watermarks are extracted and the final watermark data is determined by a simple statistical method. This method is an empirical method for experimentally determining the parameters in the watermark embedding process. The proposed method performs experiments on various images against various attacks and shows the superiority of the proposed method by comparing the performance with the representative existing methods.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.5 s.305
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• pp.173-180
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• 2005

In this paper, we proposed the image hiding method which decreases calculation amount by encrypt partial data using discrete wavelet transform(DWT) and linear scale quantization which were adopted as the main technique for frequency transform in JPEG2000 standard. Also we used the chaotic system and cat map which has smaller calculation amount than other encryption algorithms and then dramatically decreased calculation amount. This method operates encryption process between quantization and entropy coding for preserving compression ratio of images and uses the subband selection method. Also, suggested encryption method to JPEG2000 progressive transmission. The experiments have been performed with the Proposed methods implemented in software for about 500 images. Consequently, we are sure that the proposed is efficient image encryption methods to acquire the high encryption effect with small amount of encryption. It has been shown that there exits a relation of trade-off between the execution time and the effect of the encryption. It means that the proposed methods can be selectively used according to the application areas.

• The Journal of the Korea Contents Association
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• v.10 no.6
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• pp.55-63
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• 2010

In this paper, a new video watermarking algorithm using 3D wavelet transform and position encoding of spread spectrum correlation is proposed as a method for ensuring enough payload in order to protect copyright for video contents. This algorithm provides better robustness than other watermarking methods in bit error and rotation because it uses the position encoding and $4{\times}4$ sample space instead of $1{\times}1$ pixel to express a digit. The evaluation result over 6 video clips shows that the PSNR is over 31dB at strength 11 when histogram is narrow and it satisfies the transparency. Also, it shows the robustness of the proposed watermark algorithm that the BER is 0% to three codecs.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.1-10
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• 1997

Viscous flow around actual ship is calculated by an use of RANS equations. The propriety of this computing method, usefulness to hull form design and the scale effect which is the effect of viscous flow depending on the scale of ship model are investigated. Reynolds stress is modelled by using k-${\varepsilon}$ turbulence model and the law of wall is applied near the body. Body fitted coordinates are introduced for the treatment of the arbitrary 3-dimensional shape of the ship hull form. The transformed equations in the computational domain are numerically solved by an employment of FVM. In the calculation of pressure, SIMPLE method is adopted and the solution of the discretized equation is obtained by the line-by-line method with the use of TDMA The calculations of two ships, 4410 TEU container carrier and 50,000 DWT class bulk carrier, are performed at model and actual ship scale. The results are compared and discussed with the model test results which are viscous resistance, nominal wake distribution at propeller plane and limiting streamline on the hull surface. They describe the effect of stem form and the scale effect very well. In particular, the calculated nominal wake distribution and limiting streamline are agreed qualitatively with the experiments and the viscous resistance values are estimated within ${\pm}5%$ difference from the resistance tests.