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최윤식,김용구 연세대학교 대학원 1995 延世論叢 Vol.31 No.1
Abstract In this paper, a conceptual linkge between existing fractal image coding algorithms and classical fractal studies is made. Proposed fractal image coding is accomplished by the use of scale property, which represents the self-affinity of fractal and is defined on fractional white Gaussian noise process(FWGNP) and fractional Brownian motion process (FBMP). For a quantitative fractal measure, an image is modeled by fractional differencing model(FDM) which is Known as a discrete version of FWGNP. Since differencing parameter of the model is related to Hurst coefficient, H, the range of this parameter makes an image categorized into a sample path of FWGNP or FBMP and the parameter value plays a central role in calculating the contractivity of each scale theorem defined on FWGNP and FBMP. In order to prove the feasibility of our fractal image coding scheme, it is compared with existing fractal image compression algorithms proposed by Jacquin and Fisher et. al. Result shows dramatically reduced computational burden, while reconstructed image quality of our scheme is nearly the same or higher than that of the existing algorithms.
DCT 변환 영상의 블록효과 제거를 위한 고속 알고리듬
박정우,최윤식 연세대학교 산업기술연구소 1997 논문집 Vol.29 No.2
A fast algorithm for removing blocking artifacts in DCT coded images is proposed. In conventional algorithms, reconstructed images are deteriorated by blurring or having heavy computational complexity. For these reasons, in this paper an edge directional space-variant low pass filtering algorithm is proposed to reduce image blurring and computational complexity. For the directional edge block classification, Gersho's block classification algorithm is modified by applying in edge directions. That is, a 2D LPF is used for the monotone block and a ID directional LPF is applied parallelly to the direction of edge blocks, respectively. This approach can remove blocking artifacts preventing image blurring efficiently, since the blocking artifacts are caused by pixel discontinuities in block boundary, thus the low pass filtering only on the boundary of blocks prevents the inner block blurring.
Balanced bitrate control of multiple videos in transcoding for multi-view service
Gankhuyag, Ganzorig,Choe, Yoonsik The Institute of Internet 2015 International Journal of Internet, Broadcasting an Vol.7 No.2
In this paper, a balanced bitrate control in transcoding process based on video complexity measure for multi-view system which simultaneously shows multiple channels or video contents in single screen, is proposed. In order to consider the total quality of multiple video streams, the proposed algorithm reduces the complexity of multiple video stream and video quality differences at the same time by controlling bitrates of each stream by weighting when they are stitched for single screen. For the measure of complexity and quality differences between video streams, two different data: histogram of macroblock type and bitrate for each stream are used. The experimental result indicates that proposed algorithm decreases fluctuation of quality difference between videos in the multi-view system.
Balanced bitrate control of multiple videos in transcoding for multi-view service
Ganzorig Gankhuyag,Yoonsik Choe 한국인터넷방송통신학회 2015 International Journal of Internet, Broadcasting an Vol.7 No.2
In this paper, a balanced bitrate control in transcoding process based on video complexity measure for multi-view system which simultaneously shows multiple channels or video contents in single screen, is proposed. In order to consider the total quality of multiple video streams, the proposed algorithm reduces the complexity of multiple video stream and video quality differences at the same time by controlling bitrates of each stream by weighting when they are stitched for single screen. For the measure of complexity and quality differences between video streams, two different data: histogram of macroblock type and bitrate for each stream are used. The experimental result indicates that proposed algorithm decreases fluctuation of quality difference between videos in the multi-view system.
Efficient Motion Vector Re-Estimation Based on a Novel Cost Model for a H.264/AVC Transcoder
HONG, Soongi,CHOE, Yoonsik,KIM, Yong-Goo 'Institute of Electronics, Information and Communi 2016 IEICE transactions on information and systems Vol.99e.d No.3
<P>In transcoding, it is well known that refinement of the motion vectors is critical to enhance the quality of transcoded video while significantly reducing transcoding complexity. This paper proposes a novel cost model to estimate the rate-distortion cost of motion vector composition in order to develop a reliable motion vector re-estimation method that has reasonable computation cost. Based on a statistical analysis of motion compensated prediction errors, we design a basic form of the proposed cost model as a function of distance from the optimal motion vector. Simulations with a transcoder employing the proposed cost model demonstrate a significant quality gain over representative video transcoding schemes with no complexity increase.</P>
Robust PCA Based on Incoherence With Geometrical Interpretation
Lee, Jieun,Choe, Yoonsik IEEE 2018 IEEE TRANSACTIONS ON IMAGE PROCESSING - Vol.27 No.4
<P>Robust principal component analysis, which extracts low-dimensional data from high-dimensional data, can also be regarded as a source separation problem of the sparse error matrix and the low-rank matrix. Until recently, various methods have attempted to precisely predict the discrete rank function by assigning a weight to the nuclear norm. However, if the weights are not in ascending order, the algorithms will diverge and exhibit high computational complexity. Moreover, from the viewpoint of source separation, these methods overlook the fact that two components must be sufficiently different for accurate demixing. In this paper, we employ the incoherence term with convex shape, which considers that components must appear different from one another for boosting separability. Since it is intractable to directly exploit mutual incoherence defined in linear algebra, we guarantee the incoherence by indirectly making the sparse matrix lack the low-rank property by using the duality norm principle. This approach can also be associated with the null space. To analyze the results of the proposed algorithm geometrically, we measure the geodesic distance between the tangent spaces of the manifolds of two separate components. As this distance increases, the degree of dissimilarity of the two components is adequately assured; thus, separation succeeds. Furthermore, this paper is the first to provide insights into the relationship between source separation conditions and the derivatives of the nuclear norm and <TEX>$L_{1}$</TEX> norm. Experiments are conducted on still image separation and background subtraction to confirm the superiority of the proposed methods both qualitatively and quantitatively.</P>
Efficient Schemes for Compressed-Domain Image Resizing
KIM, Do Nyeon,CHOE, Yoonsik,RAO, K.R. The Institute of Electronics, Information and Comm 2009 IEICE transactions on fundamentals of electronics, Vol.92 No.2
<P>Fast schemes for compressed-domain image size change, are proposed. Fast Winograd DCTs are applied to resizing images by a factor of two to one. First, we speed up the DCT domain downsampling scheme which uses the bilinear interpolation. Then, we speed up other image resizing schemes which use DCT lowpass truncated approximations. The schemes proposed here reduce the computational complexities significantly, while there is no difference in the overall quality of the images compared to previous works.</P>