• 한국통신학회논문지
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• 제21권4호
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• pp.822-833
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• 1996

The video coding for very low bit rate has recently received considerable attention, but conventional block based transform coding schemes suffer from the blocking effect for the constraints of bit rates. In this paper, we present a video coding sysem suing multi-resolution motion estimation/compensation with variable size block(VMRME/C) and multi-resolution vector quantization(MRVQ) in wavelet transform domain for very low bit rate coding. It is shown that the presented scheme has better performance in the peak signal-to-nose ratio(RSNR) by 0.2-0.6 dB as well as subjective quality than that of conventional block based transform video coding techniques(especially, H. 263 which is DCT based video coding).

• Journal of Information Processing Systems
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• 제15권2호
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• pp.261-270
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• 2019

In order to protect secret digital documents against vulnerabilities while communicating, steganography algorithms are applied. It protects a digital file from unauthorized access by hiding the entire content. Pixel-value-difference being a method from spatial domain steganography utilizes the difference gap between neighbor pixels to fulfill the same. The proposed approach is a block-wise embedding process where blocks of variable size are chosen from the cover image, therefore, a stream of secret digital contents is hidden. Least significant bit (LSB) substitution method is applied as an adaptive mechanism and optimal pixel adjustment process (OPAP) is used to minimize the error rate. The proposed application succeeds to maintain good hiding capacity and better signal-to-noise ratio when compared against other existing methods. Any means of digital communication specially e-Governance applications could be highly benefited from this approach.

• Educational Technology International
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• 제22권1호
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• pp.1-21
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• 2021

This study examined the effects of egocentric distance and screen size on learners' perceived virtual presence in a virtual reality environment with a large-screen display. Sixty-four undergraduate students participated in the study, which used a 3×2 randomized-block factorial design with repeated measures. Two independent variables were included: 1) egocentric distance, or the physical distance between the viewer's position and a screen display, and 2) screen size, or different screen heights with fixed width. Learners' perceived virtual presence, comprising involvement, spatial presence, and realness, was the dependent variable. Results showed that egocentric distance had significant effects on virtual presence, while screen size had none. A detailed discussion and implications are provided.

• ETRI Journal
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• 제30권4호
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• pp.506-515
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• 2008

The H.264/AVC standard has adopted new coding tools such as intra-prediction, variable block size, motion estimation with quarter-pixel-accuracy, loop filter, and so on. The adoption of these tools enables an H.264/AVC-coded bitstream to have more information than was possible with previous standards. In this paper, we propose an effective spatial error concealment method with low complexity in H.264/AVC intra-frame. From information included in an H.264/AVC-coded bitstream, we use prediction modes of intra-blocks to recover a damaged block. This is because the prediction direction in each prediction mode is highly correlated to the edge direction. We first estimate the edge direction of a damaged block using the prediction modes of the intra-blocks adjacent to a damaged block and classify the area inside the damaged block into edge and flat areas. Our method then recovers pixel values in the edge area using edge-directed interpolation, and recovers pixel values in the flat area using weighted interpolation. Simulation results show that the proposed method yields better video quality than conventional approaches.

• 한국해양공학회지
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• 제6권1호
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• pp.96-104
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• 1992

Aircraft structures and engineering structures are always subject to variable amplitude loads. Variable amplitude loads include some kind of loading history; for example, constant amplitude load, single peak overload and block overload etc. Crack growth under variable amplitude loading exhibits retardation effect. In this study, the 4 point bending fatigue test was performed by hydrolic servo fatigue testing machine on 7075-T6 Al-alloy. The retardation effect of overload ratio and numbers of overload cycle was quantitatively studied. 1) Change of retardation effect against increment of overload ratio is more evident when the multiple overload is applied than single overload is done. 2) The number of overload cycle is very important factor about the crack growth retardation effect when the overload ratio is more than 1.75; that is not when the overload ratio is less than 1.75. 3) Overload affected zone size increased gradually by increment of crack growth retardation effect. 4) Crack driving force is more greatly reduced when the crack tip branched off two direction than it sloped to one direction.

• 한국멀티미디어학회:학술대회논문집
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• 한국멀티미디어학회 2001년도 추계학술발표논문집
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• pp.137-142
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• 2001

입체 시점 확장을 위하여 많은 양의 영상 데이터가 필요하다. 그러나 이를 전송하치 위해서는 전송량, 장치 등의 여러 어려움이 존재한다. 이에 소량의 영상 데이터를 보내고 수신 측에서 시점을 확장하는 방법으로 중간 영상 합성이 연구되고 있다. 중간 영상 합성을 위해서는 많은 방법들이 제안되었다 블록 매칭, 화소 기반 매칭, 에페폴라 방식, 옵티컬 플로워 등이 그것이다. 본 고에서는 위의 방법들 중에서 블록 매칭 방법을 기본으로, 블록을 생성하는 과정에서 고정 블록이 아닌 영상의 차분 신호를 이용하여 가변 블록을 생성하게 되며, 좌에서 우나 우에서 좌의 단방향이 아닌 양 방향으로 매칭하는 방법을 제안한다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 신호처리소사이어티 추계학술대회 논문집
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• pp.87-90
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• 2003

This paper presents a variable block size motion estimation (ME) algorithm and hardware architectures dedicated to H.264/AVC. Proposed ME architecture can achieve real-time processing for 720$\times$480@30Hz with search range of [-64, +63] in the horizontal and [-32, +31] in the vertical direction at integer-pel accuracy and upto 7 reference frames at the operating frequency of 54MHz.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 신호처리소사이어티 추계학술대회 논문집
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• pp.141-144
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• 2003

가장 최근의 동영상 압축 표준인 H.264는 매크로블록의 최적 모드를 결정하기 위하여 총 7가지 모드를 사용하여 움직임 예측을 수행하기 때문에 부호화 효율과 수행 성능 면에서 기존의 방식에 비해 좋은 결과를 보이지만, 움직임 예측 과정에서 많은 계산 시간을 필요로 한다는 것이 커다란 단점으로 지적되고 있다. 따라서, 본 논문에서는 H.264에서 가변 블륵 단위의 움직임 예측 시 인접한 블록과의 상관성을 분석하여 다음 움직임 예측 모드의 사용 여부를 결정하는 블록 병합 알고리즘을 HEXBS(Hexagon-based Search) 고속 움직임 탐색 알고리즘에 적용하여 움직임 예측 시간을 효율적으로 절약하는 방법을 제안한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.190-193
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• 1988

Lucifer - type algorithms with variable length of block size are presented. They are investigated and compared in the viewpoint of the intersymbol dependence. The results show that the S-box and the number of rounds are very important factors in achieving the complete dependence.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 추계학술대회
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• pp.293-296
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• 1996

In this paper, we studied two image characteristics, similarity and smoothness, which give rise to local and global redundancy in image representation. The similarty means that any patterns in the image repeat itself anywhere in the rest of image. The smoothness means that the gray level values within a given block vary gradually rather than abruptly. In this sense, we propose a lossless medical image compression scheme which exploits both types of redundancy. This method segments the image into variable size blocks and encodes them depending on characteristics of the block. The proposed compression schemes works better than other compression schemes such as the huffman, the arithmetic, the Lempel-Ziv and the lossless scheme of JPEG.