• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10B
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• pp.1963-1970
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• 1999

Researches in draft recommendation H.263 have been made in ITU-T LBC group to broaden its range of useful application and to improve its compression performance. The form of added and revised draft text of H.263 is informally known as “H.263+”. In this paper, we analyzed the characteristics of H.263+ negotiable option modes for four image classes. Based on the analysis results, we proposed the adaptive selection scheme of H.263+ option modes by using a scene change detector for a mixed image class. In case of using the proposed scheme, we obtained the 1.6dB improvement in PSNR compared to the basic mode of H.263, and the 0.4~1.0 dB improvement in PSNR compared to the fixed usage scheme of H.263+ negotiable option modes. In respect to used bits per frame, fewer bits are produced than the basic mode H.263 and the foxed usage scheme of H.263+ option modes.

• Journal of Broadcast Engineering
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• v.14 no.1
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• pp.28-35
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• 2009

H.264/AVC, a recently developed video compression standard, is used for various applications because of its high coding efficiency. Variable block mode plays important role in the high coding efficiency of H.264/AVC but involves significant computations to select the optimal mode. In this paper, a fast mode decision method for H.264/AVC P slices is presented. To reduce computations for mode decision, the proposed mode decision method skips the mode decision processes for small partition modes using distortions of SKIP mode and intra16x16 mode. The experimental results show that the proposed method can reduce encoding time up to 66.41% while maintaining compression efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2C
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• pp.193-202
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• 2010

In this paper, we propose a fast algorithm that can reduce the complexity for inter mode decision of the H.264 encoder. The main idea consists of two techniques. The first one is the technique early terminating mode decision process. We focused on the skip and $16{\times}16$ mode because these modes occupies the largest portion in most of sequences. The second one is the technique skipping unnecessary $8{\times}8$ modes. The time consumption caused by the $8{\times}8$ mode is very considerable. Therefore if we can extract the unnecessary $8{\times}8$ mode calculation well, a large amount of time can be saved in total encoding process. The experimental results show that the proposed algorithm can achieve up to 43% speed up ratio with insignificant PSNR loss. The increase of total bits encoded is also not noticeable.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.65-75
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• 2006

Nonlinear pushover analysis is used to evaluate the earthquake response of building structures. To accurately predict the inelastic response of a structure, the prescribed story load profile should be able to describe the earthquake force profile which actually occurs during the time-history response of the structure. In the present study, a new modal combination method was developed to predict the earthquake load profiles of building structures. In the proposed method, multiple story load profiles are predicted by combining the modal spectrum responses multiplied by the modal combination factors. Parametric studies were performed far moment-resisting frames and walls. Based on the results. the modal combination factors were determined according to the hierarchy of each mode affecting the dynamic responses of structures. The proposed modal combination method was applied to prototype buildings with and without vertical irregularity. The results showed that the proposed method predicts the actual story load profiles which occur during the time-history responses of the structures.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.4C
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• pp.321-329
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• 2008

H.264/AVC video coding standard enables a considerably higher improvement in coding efficiency compared with previous standards such as MPEG-2, H.263 and MPEG-4. To achieve this, for each macro-block in H.264/AVC, Rate-Distortion Optimization (RDO) technique is employed to select the best motion vector, reference frame, and macro-block mode. As a result, computational complexity is increased significantly whereas RDO achieve higher improvement. This paper presents fast intra mode selection algorithm based on constraints of frequency characteristics which are derived from intra coding modes of H.264/AVC. First of all, we observe the features of each intra mode through the frequency analysis of image. And then proposed Frequency Error Costs (FECs) are calculated to select the best mode which has minimum cost. Computational complexity is considerably reduced because rate-distortion costs only calculate the candidate modes which are set of best mode and its neighbouring two modes. Experimental results show that proposed algorithm reduces the complexity dramatically maintaining the rate-distortion performance compared with H.264/AVC reference software.

• Journal of Satellite, Information and Communications
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• v.9 no.2
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• pp.74-79
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• 2014

Conventional ScanSAR mode has been adopted in Envisat or Radarsat and played an important role to acquire wide swath SAR images for environmental surveillance. However, it suffers from the undesirable scalloping effect caused by non-homogeneity of antenna pattern while the image resolution is sacrificed. In recent years, TOPS mode has been suggested and put into use to overcome the disadvantages of the conventional scanning mode. Although TOPS mode is able to produce wide-swath SAR image in a short time interval, it demands highly complicated system design knowledge. In this paper, we present the operation principle of TOPS mode and a full SAR simulation is performed to generate TOPS SAR raw data. Azimuth antenna pattern is modified during TOPS mode operation and it is shown that the undesired scalloping effect is suppressed in the generated SAR image.

• Journal of Broadcast Engineering
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• v.15 no.3
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• pp.380-390
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• 2010

The most recent standard video codec, H.264/AVC achieves significant coding efficiency by using a rate-distortion optimization(RDO). The RDO is a measurement for selecting the best mode which minimizes the Lagrangian cost among several modes. As a result, the computational complexity is increased drastically in encoder. In this paper, a method for fast intra prediction mode decision is proposed to reduce the RDO complexity. To speed up Intra$4{\times}4$ and Chroma Intra encoding, the proposed method decides the case that MPM (Most Probable Mode) is the best prediction mode. In this case, the RDO process is skipped, and only MPM is used for encoding the block in Intra$4{\times}4$. And the proposed method is also applied to the chroma Intra prediction mode in a similar way to the Intra$4{\times}4$. The experimental results show that the proposed method achieves an average encoding time saving of about 63% with negligible loss of PSNR (Peak Signal-to-Noise Ratio).

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.6
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• pp.11-18
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• 2011

Accurate modal identification analysis is required to reasonably perform a seismic qualification of safety-related electric equipment installed in nuclear power plants (NPPs). This study evaluates a variation of the modal properties of an electric equipment cabinet structure in NPPs according to the excitation levels. For the study, an actual electric equipment cabinet was selected as a specimen and was dynamically tested by using a portable exciter in accordance with the level of input vibration energy. Tests were classified into two sets: with-door cases, and without-door cases. Frequency response functions were computed from the signals of the acceleration responses and input motions measured from the vibration tests. A polynomial curve fitting algorithm was used to extract the modal properties from the frequency response functions. This study reviews the variation of the modal properties according to the variation of the excitation levels. The results of the study show that the modal frequencies and the modal dampings of the object specimen varies nonlinearly according to the excitation level of the test motion. Attaching the door increases the modal damping of the cabinet.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1061-1066
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• 2016

Corrugation of a corrugated panel dramatically increases the bending stiffness per weight. However, corrugated panels show lower sound insulation performance than that of the flat plate having the same weight. Especially, in a particular frequency region, the sound transmission loss significantly decreases. Main reason of the problem is known as the local resonance. A number of local resonance modes occur above a certain frequency band and modal density rapidly increases. In this study, we investigate the relation of the sound transmission loss and the modal density. Finally, we propose a design methodology in terms of the modal density to improve the sound insulation performance of the corrugated panels without weight increase.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.224-225
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• 2003

이 연구에서는 광결정 (photonic crystal) 박막 (slab) 위에 제작된 막대형 공진기의 공진모드의 특성을 보고한다. 먼저 3차원 FDTD 방법을 이용하여 각각의 공진 모드들의 모드 형태, 공진주파수, 품위값(Q factor) 등을 구하였다. 광결정 격자의 주기가 $\alpha$ 일 때, 슬랩의 두께는 0.4 $\alpha$ , 구멍의 반지름은 0.35 $\alpha$ 로 하였다. 슬랩의 굴절률 (n) 은 실험에서 사용한 InP의 1.55 $\mu$m 에서의 굴절률 값인 3.4 로 정하였다. (중략)