• The Journal of the Acoustical Society of Korea
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• v.18 no.8
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• pp.48-53
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• 1999

This paper presents an analytic derivation of the erroneous effect when the sliding-DFT is implemented in a recursive way with the finite-bit approximation of the twiddle factors. The analysis result is obtained in a closed form equation of the noise-to-signal power ratio(NSR) employing the zero-mean white Gaussian signal as the target input of the DFT. The parameters of the wordlength used in representing the twiddle factors and the blocklength of the DFT appear in the NSR explicitly as its function variables. The derivation is based on the error dynamic equation which is derived from the recursive SDFT, and on the analytic exploration of the statistical characteristics of the approximation coefficients treating them as random variables of having spatial distributions. The analytically derived results are verified through the comparison with the data actually measured from the computer simulation experiment.

• The Journal of the Acoustical Society of Korea
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• v.13 no.1E
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• pp.71-81
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• 1994

In this paper, we propose a pseudo-cepstral representation of line spectrum pair(LSP) frequencies and evaluate speech recognition performance with cepstral lift using the pseudo-cepstrum. The pseudo-cepstrum corresponding to LSP frequencies is derived by approxmating the relationship between LPC-cepstrum and LSP frequencies. Three cepstral liftering procedures are applied to the pseudo-cepstrum to improve the performance of speech recognition. They are the root-power-sums ligter, the general exponential lifter, and the bandpass lifter. Then, the liftered psedudo-cepstra are warped into a mel-frequency scale to obtain feature vectors for speech recognition. Among the three lifters, the general exponential lifter results in the best performance on speech recognition. When we use the proposed pseudo-cepstra feature vectors for recognizing noisy speech, the signal-to-noise ratio (SNR) improvement of about 5~10dB LSP is obtained.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.840-843
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• 2014

사실적 피부 렌더링은 피부 표면에서 일어나는 확산반사(Diffusion) 및 경면반사(Specular) 뿐 만 아니라 피부층 내에서 산란되어 나오는 산란광과 얇은 피부층을 통과하는 투과광 등을 고려하여 렌더링 되어야 한다. 이를 물리적인 개념들을 사용하여 실시간으로 계산하여 표현하는 것은 많은 계산량과 시간을 필요로 하므로 확산 반사 및 경면 반사 등을 미리 계산하여 텍스쳐로 저장하고 재사용하는 사전정의 BRDF 방법으로 근사화하여 표현할 수 있다. 하지만 사전정의 BRDF를 통해 생성된 피부 투과광색상 텍스쳐 맵은 그 색상이 고정되어있어 조명의 색상이 바뀌어도 피부를 투과하는 빛의 색상이 변하지 않아 부자연스러움을 보인다. 본 논문에서는 이러한 문제를 해결하기 위해 물체와 조명간의 거리를 이용하여 빛의 감쇠비율을 구하고 조명의 색상 값과 감쇠비율을 이용하여 피부 투과광 색상 텍스쳐 맵의 RGB채널 수정을 통해 피부 렌더링에서의 자연스러운 투과광 표현이 가능함을 보였다.

• Journal of Internet Computing and Services
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• v.6 no.1
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• pp.85-93
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• 2005

This paper describes how to distribute high multi-dimensional facial expression data of vast quantity over a suitable space and produce facial expression animations by selecting expressions while animator navigates this space in real-time. We have constructed facial spaces by using about 2400 facial expression frames on this paper. These facial spaces are created by calculating of the shortest distance between two random expressions. The distance between two points In the space of expression, which is manifold space, is described approximately as following; When the linear distance of them is shorter than a decided value, if the two expressions are adjacent after defining the expression state vector of facial status using distance matrix expressing distance between two markers, this will be considered as the shortest distance (manifold distance) of the two expressions. Once the distance of those adjacent expressions was decided, We have taken a Floyd algorithm connecting these adjacent distances to yield the shortest distance of the two expressions. We have used CCA(Curvilinear Component Analysis) technique to visualize multi-dimensional spaces, the form of expressing space, into two dimensions. While the animators navigate this two dimensional spaces, they produce a facial animation by using user interface in real-time.

• Journal of Korea Game Society
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• v.9 no.5
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• pp.137-144
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• 2009

This paper predicts 6 facial regions that may have sharply different scattering properties, rendering the face more realistically based on their diffusion profiles. The scattering properties are acquired in the form of high dynamic range by photographing the pattern formed around an unit ray incident on facial skin. The acquired data are fitted to a 'linear combination of Gaussian functions', which well approximates the original diffusion profile of skin and has good characteristics as the filter. During the process, to prevent its solutions from converging into local minima, we take advantage of the genetic algorithm to set up the initial value. Each Gaussian term is applied to the irradiance map as a filter, expressing subsurface scattering effect. In this paper, to efficiently handle the maximum 12 Gaussian filterings, we make use of the parallel capacity of CUDA.

• The KIPS Transactions:PartA
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• v.11A no.2
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• pp.189-194
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• 2004

This paper describes method to distribute much high-dimensional facial expression motion data to 2 dimensional space, and method to create facial expression animation by select expressions that want by realtime as animator navigates this space. In this paper composed expression space using about 2400 facial expression frames. The creation of facial space is ended by decision of shortest distance between any two expressions. The expression space as manifold space expresses approximately distance between two points as following. After define expression state vector that express state of each expression using distance matrix which represent distance between any markers, if two expression adjoin, regard this as approximate about shortest distance between two expressions. So, if adjacency distance is decided between adjacency expressions, connect these adjacency distances and yield shortest distance between any two expression states, use Floyd algorithm for this. To materialize expression space that is high-dimensional space, project on 2 dimensions using Sammon's Mapping. Facial animation create by realtime with animators navigating 2 dimensional space using user interface.

• Science of Emotion and Sensibility
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• v.8 no.4
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• pp.355-363
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• 2005

The adjectives for represnting emotions is important to evaluate and select the colors or color patterns. In this paper, we perform the MDS analysis, factor analysis, and cluster analysis to the Soen's experimental data obtained from the evaluation of random color patterns with 13 adjective pairs. As a result, those adjectives can be reduced 3 different factors representing emotions of weight, activity and temperature, which is approximately corresponds the results of previous researches on single colors. Also, we show that the adjectives for preference can be approximate4 by other primary adjectives for color patterns using regression analysis. This implies that one can construct a uniform emotion space for evaluating and selecting color patterns regardless of objects such as wall papers, carpets, and so on.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.677-680
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• 2008

The paper deals with the analysis of radiation characteristics of antenna in the multi-layered media structures. The dyadic Green's function for three layer medium is complex because the Green's functions belonging to the kernel of the integral equation are expressed as Sommerfeld integrals, in which surface wave effects are automatically included. When certain condition are met, the integral can be evaluated approximated by the method of Saddle-point integration. In this study, we propose a method to calculate a radiation pattern for several antennas by using the method of Saddle-point integration. Numerical results show how the radiation characteristics are affected by parameter of dielectric media.

• 한국공간정보시스템학회:학술대회논문집
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• 2007.06a
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• pp.169-174
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• 2007

식생지수 시계열 자료를 이용한 식생 및 토지피복 모니터링을 수행하기 위해서는 구름으로 인한 누락 및 왜곡된 식생지수 문제를 먼저 해결해야만 한다. 특히 한반도와 같이 여름철 집중 호우기에 대부분의 영상에 구름이 존재하는 경우 이들 구름화소를 제거하거나 복원하지 않을 경우, 분석 결과에 상당한 왜곡이 발생하거나 특정 시기의 영상자료를 분석에 반영할 수 없는 경우가 발생하게 된다. HANTS 알고리즘은 이 같은 구름 화소 문제를 해결하기 위한 알고리즘으로 연중 식생지수의 변화는 비교적 단순한 반복적 주기함수의 형태를 가지므로 소수의 cos 함수를 이용한 푸리에 근사식으로 전체 연중 식생지수를 표현할 수 있다는 가정에서 출발한다. 이 때 구름화소로 인한 원식생지수와의 차이가 특정 임계값을 초과하였을 경우 해당 관측치를 근사과정에서 제외함으로써 구름의 영향을 받지 않은 식생지수 시계열 자료만을 이용하게 된다. 이 과정을 수행하기 위해서는 몇몇 제어변수의 설정이 필요한데, 본 연구에서는 한반도와 같이 특정 시기에 장기간 구름이 분포하는 상황에서 최적의 식생지수 복원을 위한 HANTS 알고리즘의 제어변수를 선정하고 재구축된 식생지수를 평가하였다. 이를 위한 실험으로 2002년 대전 지역의 MODIS Terra 식생지수 시계열 영상을 대상으로 HANTS 알고리즘을 주요 식생피복별로 적용해 보았다.

• The Korean Journal of Applied Statistics
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• v.21 no.5
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• pp.801-811
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• 2008

Modeling financial phenomena with diffusion processes is a commonly used methodology in the area of modern finance. Recently, various types of diffusion models have been suggested to explain the specific financial processes, and their related inference methodology have been also developed. In particular, likelihood methods for the efficient and accurate inference have been explored in various ways. In this paper, we review the mathematical properties of an approximated likelihood method, which is obtained by linearizing the drift coefficient of a diffusion process.