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강경인(Kang Kyeong In),김정일(Kim Jeong Il),정근원(Jeong Keun Won),이광배(Lee Kwang Bae),김현욱(Kim Hyen Ug) 한국정보처리학회 1997 정보처리학회논문지 Vol.4 No.3
In this paper, we propose a new algorithm to perform DCT(Discrete Cosine Transform) within the area reduced by predicting position of quantization coefficients to be zero. This proposed algorithm not only decreases the encoding time and the decoding time by reducing computation amount of FDCT(Forward DCT) and IDCT(Inverse DCT) but also increases compression ratio by performing each different horizontal-vertical zig-zag scan according to the classified block size for each block on the huffman coding. Traditional image coding method performs the same DCT computation and zig-zag scan over all blocks, however this proposed algorithm reduces FDCT computation time by setting to zero instead of computing DCT for quantization coefficients outside classified block size on the encoding. Also, the algorithm reduces IDCT computation time by performing IDCT for only dequantization coefficients within classified block size on the decoding. In addition, the algorithm reduces Run-Length by carrying out horizontal-vertical zig-zag scan appropriate to the classified block characteristics, thus providing the improvement of the compression ratio. On the other hand, this proposed algorithm can be applied to 16*16 block processing in which the compression ratio and the image resolution are optimal but encoding time and the decoding time take long. Also, the algorithm can be extended to motion image coding requiring real time processing.
박경배(Park Kyung Bae),정우석(Jung Woo Suk),김정일(Kim Jung Il),정근원(Jeong Keun Won),이광배(Lee Kwang Bae),김현욱(Kim Hyen Ug) 한국정보처리학회 1995 정보처리학회논문지 Vol.2 No.5
Most fractal image codings using fractal concept require long encoding time because a large amount of computation is needed to find an optimal affine transformation point. Such a problem can be solved by designing a block classifier fitted to characteristics of image blocks. In general, it is possible to predict more precise and various types of blocks in frequency domain than in spatial domain. In this paper, we propose a block classifier to predict the block type using characteristics of DCT(Discrete Cosine Transform). This classifier has merits to enhance the quality of decoded images as well as to reduce the encoding time by meeting fractal features. AC coefficient values in frequency domain make it possible to predict various types of blocks. As the results, the number of comparisons between a range block and the corresponding domain blocks to reach an optimal affine transformation point can be reduced. Specially, signs of DCT coefficients help to find the optimal affine transformation point with only two isometric transformations by eliminating unnecessary isometric transformations among eight isometric transformations used in traditional fractal codings.
한지훈(Han Ji Hoon),박경배(Park Gyong Bae),곽승욱(Kwak Seung Uk),김정일(Kim Jeong II),정근원(Jeong Keun Won),송인근(Song In Keun),이광배(Lee Kwang Bae),김현욱(Kim Hyen Uk) 한국정보처리학회 1999 정보처리학회논문지 Vol.6 No.1
Uses can share information and use resources effectively by using TCP/IP-based networks. So, a protocol to manage complex networks effectively is needed. For the management of the distributed networks, the SNMP(Simple Network Management Protocol) has been adopted as an international standard in 1989, and the SNMPv2 in which a security function was added was published in 1993. There are two encryption schemes in SNMPv2, the one is a DES using symmetric encryption scheme and the other is a MD5(Message Digest5) hash function for authentication. But the DES has demerits that a key length is a few short and the encryption and the authentication is executed respectively. In order to solve these problems, we use a RSA cryptography in this paper. In this paper, we examine the items related with SNMP. In addition to DES and MD5 proposed in SNMPv3, we enhance security functionality be adopting RSA, a public key algorithm executing the encryption and the authentication simultaneously. The proposed SNMPv3 security module is written in JAVA under Windows NT environment.