프랙탈 코딩을 이용한 영상 압축 기법에 관한 연구

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.

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>

An Image Quality Assessment Scheme based on HVS using Gabor Function

Minyoung Eom,Yoonsik Choe 대한전자공학회 2004 International Conference on Electronics, Informati Vol.2004 No.8

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>

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.

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>

깊이도를 고려한 인페인팅기반 홀필링 기법

최장원(Choi, Jangwon),최윤식(Choe, Yoonsik),김용구(Kim, Yong-Goo) 한국방송·미디어공학회 2011 한국방송공학회 학술발표대회 논문집 Vol.2011 No.7

본 논문에서는 DIBR(Depth image-based rendering)을 통해 생성되는 3D 영상의 홀을 고품질로 채우는 방법을 제안한다. 이를 위해, 생성된 영상의 깊이도를 고려한 희소성(Sparsity) 기반의 인페인팅 알고리즘을 홀 채우기에 적용하였다. 본 논문에서 제안하는 알고리즘은 홀 주변의 전경 텍스쳐를 제외한 배경 텍스쳐 정보만을 이용하기 때문에, 홀 채우기 시 전경 텍스쳐와 배경 텍스쳐가 혼합되는 문제점이 발생하지 않는다. 또한 희소성 기반의 인페인팅을 이용하기 때문에 에지 정보를 활용한 고품질의 홀 채우기가 가능하다. 본 논문에서 제안하는 알고리즘과 기존의 홀 채우기 알고리즘과의 주관적 화질 비교 결과, 본 논문에서 제안하는 알고리즘의 우수성을 확인할 수 있었다.

Frame Rate Up-Conversion Technique Using Hardware-Efficient Motion Estimator Architecture for Motion Blur Reduction of TFT-LCD

HWANG, Jonghee,CHOI, Yongwoo,CHOE, Yoonsik The Institute of Electronics, Information and Comm 2011 IEICE transactions on electronics Vol.94e.c No.5

<P>Motion blur in TFT-LCD is caused by sample and hold characteristic, slow response time of liquid crystal, and the inconsistency between object tracking of the human eye and the actual object location. In order to solve this problem, a high frame rate driving method based on motion estimation and motion compensation has been applied to LCD products. However, as the required processing time of motion estimation increases in LCD TV and monitor systems, real-time video image processing becomes more difficult. Frame interpolation through the large macro block (MB) size has limitations to detect small objects. So, this paper proposes the efficient motion estimator architecture which uses seven kinds of macro blocks to enhance the accuracy of motion estimation and combines the parallel processing with pre-computation technology and hardware optimization for high-speed processing. Also, for increased efficiency in the hardware architecture, we employed an I2C (Inter Integrated Circuit) communication unit to control the key parameters easily through the personnel computer. Simulation results show that the critical path at the motion estimator is reduced by about 27.47% compared to the conventional structure. As a result, the proposed motion estimator will be applicable for the high-speed frame interpolation of variable video.</P>