• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2003.11a
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• pp.55-58
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• 2003

3차원 메쉬 영상의 압축 알고리듬들은 예측 부호화 및 엔트로피(entropy) 부호화를 기본 기법으로 이용하므로, 압축된 비트열(bitstream)의 네트워크 전송에서 전송 오류에 매우 민감한 단점을 지닌다. 따라서 본 논문에서는 전송 오류에 강인하고 점진적 부호기를 기본으로 하는 3차원 메쉬 영상의 오류은닉 알고리듬을 제안한다. 전송 오류에 강인한 알고리듬을 개발하기 위해, 3차원 원본 메쉬 영상을 여러 파티션(partition)으로 분할하고, 각각의 파티션을 독립적으로 점진 부호화한다. 복호기에서는 오류가 발생하지 않은 주변 표면 정보를 이용하는 오류 은닉 알고리듬을 오류에 의해 손상 받은 파티션 표면에 적용하여 손상된 파티션의 시각적 손상 정도를 감쇄시킨다. 전산 모의 실험을 통해, 제안하는 알고리듬의 오류에 대한 강인성 및 오류 발생시 손상된 파티션 표면이 제안하는 오류 은닉 알고리듬을 통해 화질이 개선됨을 확인하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2018.10a
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• pp.264-267
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• 2018

본 연구에서는 API 호출을 은닉할 수 있는 새로운 유형의 유저모드 기반 루트킷으로 Cuckoo Sandbox를 회피하는 기법과 이를 탐지하기 위한 연구를 한다. Cuckoo Sandbox의 행위 분석을 회피하기 위해 잠재적으로 출현 가능한 은닉된 코드 이미지 기반의 신종 루트킷 원리를 연구하고 탐지하기 위한 방안을 함께 연구한다. 네이티브 API 호출 코드 영역을 프로세스 공간에 직접 적재하여 네이티브 API를 호출하는 기법은 Cuckoo Sandbox에서 여전히 잠재적으로 행위 분석 회피가 가능하다. 본 연구에서는 은닉된 외부주소 호출 코드 영역의 탐지를 위해 프로세스의 가상메모리 공간에서 실행 가능한 페이지 영역을 탐색 후 코사인 유사도 분석으로 이미지 탐지 실험을 하였으며, 코드 영역이 맵핑된 정렬 단위의 4가지 실험 조건에서 평균 83.5% 유사도 탐지 결과를 확인하였다.

• Proceedings of the Korea Multimedia Society Conference
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• 2003.05b
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• pp.334-337
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• 2003

본 논문에서는 멀티웨이브릿 변환영역에서 스토케스틱 모델과 지각적 동조특성을 이용한 적응 디지털 워터마크 은닉 방법을 제안한다. 워터마크는 4레벨로 분해된 멀티웨이브릿 변환영역에서 최저주파 영역과 최고주파 대역들을 제외한 중간 및 고주파 영역에, 인간 시각 시스템(human visual model ： HVS)을 이용한 JND(just noticeable difference) 특성과 NVF(noise visibility function)를 이용한 통계적 특성을 기반으로 정상상태 가우시안 모델에 따라 지각적 동조 특성을 이용하여 적응적으로 은닉된다. 실험 결과 제안한 방법에서 에지나 텍스쳐 영역에 더 강하게 삽입할 수 있었고, 평탄영역에서 보다 적응적으로 은닉할 수 있었으므로 우수한 비가시성과 강인성을 확인하였다

• Journal of Korea Society of Industrial Information Systems
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• v.14 no.3
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• pp.37-43
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• 2009

Steganography conceals the fact that hidden message is being sent on the internet. Steganalysis can be detected the abrupt changes in the statistics of a stego-data. After message embedding, I have analyzed for the statistical significance of the fact the occurrence of differences among the four-neighboring pixels. In this case, when a embedding messages within a images is small, use EC value and chi-square test to determine whether a distribution in an images matches a distribution that shows distortion from stego-data.

• Journal of the Institute of Convergence Signal Processing
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• v.4 no.2
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• pp.31-39
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• 2003

The MPEG-2 source coding algorithm is very sensitive to transmission errors due to using of variable-length coding. When the compressed data are transmitted, transmission errors are generated and error correction scheme is not able to be corrected well them. In the decoder error concealment (EC) techniques must be used to conceal errors and it is able to minimize degradation of video quality. The proposed algorithm is method to conceal successive macroblock errors of I-frame and utilize temporal information of B-frame and spatial information of P-frame In the previous GOP which is temporally the nearest location to I-frame. This method can improve motion distortion and blurring by temporal and spatial errors which cause at existing error concealment techniques. In network where the violent transmission errors occur, we can conceal more efficiently severe slice errors. This algorithm is Peformed in MPEG-2 video codec and Prove that we can conceal efficiently slice errors of I-frame compared with other approaches by simulations.

• Journal of IKEEE
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• v.9 no.2 s.17
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• pp.170-178
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• 2005

The video data corrupted by the transmission error due to packet loss induce error propagation in decoded video data, and cause poor video quality. To remedy these corrupted video data, there have been introduced two types of error concealment techniques: spatial or temporal error concealment algorithm. Computational overhead by using spatial error concealment algorithm is a serious disadvantage in mobile video data streaming environment. In this paper, we propose hybrid type error concealment technique recovering video quality of mobile device using MPEG-4 video streaming on error-prone wireless network. Our algorithm is implemented in MPEG-4 decoder. The algorithm adopts Intel Wireless MMX technology to provide high performance of portable embedded multimedia mobile device. It is proven that the proposed algorithm shows expected performance for a mobile streaming system(PDA) on IP channels. Our approach showed better processing speed and better video quality comparing with traditional error concealment algorithm.

• The Journal of the Acoustical Society of Korea
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• v.23 no.1
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• pp.47-53
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• 2004

We propose a new speech enhancement algorithm based on left-right Hidden Markov Model (HMM) with state decision using Log-likelihood Ratio Test (LRT). Since the conventional HMM-based speech enhancement methods try to improve speech quality for all states, they introduce huge computational loads inappropriate to real-time implementation. In the left-right HMM, only the current and the next state are considered for a possible state transition so to reduce the computational complexity. In this paper, we propose a method to decide the current state by using the LRT on the previous state. Experimental results show that the proposed method improves the speed up to 60% with 0.2∼0.4 dB degradation of speech quality compared to the conventional method.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.25 no.6
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• pp.1485-1494
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• 2015

Traditionally, data hiding has been done mainly in such a way that insert the data into the large-capacity multimedia files. However, the document files of the previous versions of Microsoft Office 2003 have been used as cover files as their structure are so similar to a File System that it is easy to hide data in them. If you open a compound-document file which has a secret message hidden in it with MS Office application, it is hard for users who don't know whether a secret message is hidden in the compound-document file to detect the secret message. This paper presents an analysis of Compound-File Binary Format features exploited in order to hide data and algorithms to detect the data hidden with these exploits. Studying methods used to hide data in unused area, unallocated area, reserved area and inserted streams led us to develop an algorithm to aid in the detection and examination of hidden data.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.6
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• pp.641-651
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• 2002

Recently, many advanced video application services over the mobile wireless networks have required a transcoder which can efficiently reduce the size of compressed video bitstreams. The transcoder can be worked in either the spatial domain or the DCT domain. In this paper, we propose a new fast hybrid-type transcoder which can efficiently reduce the frame size with keeping the visual quality. The proposed scheme consists of two major processes: a transform domain process and a spatial domain process. We also propose a scheme for coding mode selection and motion vector refinement. Experimental results show that our approach can reduce the computational complexity more than any other conventional spatial-domain transcoder with keeping the visual quality.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.6
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• pp.630-640
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• 2002

The compressed video bitstream is very sensitive to transmission errors. If we lost packet or received with errors during the transmission, not only the current frame will be corrupted, but also errors will propagate to succeeding frames. Error concealment is a data recovery technique that enables the decoder to conceal effects of transmission errors by predicting the lost or corrupted video data from the previously reconstructed error free information. Motion vection recovery and motion compensation with the estimated motion vector is a good approach to conceal the corrupted macroblock data. In this paper, we prove that it is reasonable to use the estimated motion vector to conceal the lost macroblock by providing macroblock distortion models. After we propose a new motion vector recovery algorithm based on optical flow fields, we compare its performance to those of conventional error concealment methods. The proposed algorithm has smaller computational complexity than those of conventional algorithms.