• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 G
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• pp.2956-2958
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• 1999

The classical solution to the noise removal problem is the Wiener filter, which utilizes the second-order statistics of the Fourier decomposition. We discuss a Bayesian formalism which gives rise to a type of wavelet threshold estimation in non-parametric regression. A prior distribution is imposed on the wavelet coefficients of the unknown response function, designed to capture the sparseness of wavelet expansion common to most application. For the prior specified, the posterior median yields a thresholding procedure

• 한국데이터정보과학회:학술대회논문집
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• 한국데이터정보과학회 2005년도 춘계학술대회
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• pp.83-126
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• 2005

Single-index models have found applications in econometrics and biometrics, where multidimensional regression models are often encountered. Here we propose a nonparametric estimation approach that combines wavelet methods for non-equispaced designs with Bayesian models. We consider a wavelet series expansion of the unknown regression function and set prior distributions for the wavelet coefficients and the other model parameters. To ensure model identifiability, the direction parameter is represented via its polar coordinates. We employ ad hoc hierarchical mixture priors that perform shrinkage on wavelet coefficients and use Markov chain Monte Carlo methods for a posteriori inference. We investigate an independence-type Metropolis-Hastings algorithm to produce samples for the direction parameter. Our method leads to simultaneous estimates of the link function and of the index parameters. We present results on both simulated and real data, where we look at comparisons with other methods.

• Journal of applied mathematics & informatics
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• 제17권1_2_3호
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• pp.759-769
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• 2005

We first discuss jump discontinuity in higher dimension, and then prove a local convergence theorem for wavelet approximations in higher dimension. We also redefine the concept of Gibbs phenomenon in higher dimension and show that wavelet expansion exhibits Gibbs phenomenon.

• 정보통신설비학회논문지
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• 제5권1호
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• pp.37-42
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• 2006

A reversible audio watermarking algorithm is presented in this paper. This algorithm transforms the audio signal with the integer wavelet transform first in order to enhance the correlation between neighbor audio samples. Audio signal has low correlation between neighbor samples, which makes it difficult to apply difference expansion scheme. Second, a novel difference expansion scheme is used to embed more data by reducing the size of location map. Therefore, the difference expansion scheme used in this paper theoretically secures high embedding capacity under low perceptual distortion. Experiments show that this scheme can hide large number of information bits and keeps high perceptual quality.

• 한국음향학회지
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• 제15권4호
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• pp.50-57
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• 1996

본 논문에서는 최적의 웨이브렛 선택방법과 이 선택된 웨이브렛으로 F-검정을 이용하여 AR파라메터를 전개시키는 방법을 제안하였으며 웨이브렛 선택 방법으로서 평가함수를 도입하였다. 이 평가함수를 이용하여 웨이브렛들(D4-D20)을 합성신호에 대해서 시험하였다. 이때 선택된 웨이브렛을 이용하여 합성신호와 실제 음성신호에 대해서 AR파라메터들을 웨이브렛 전개 했을때의 웨이브렛 계수를 구하였다. 제안된 방법을 평가하기 위해서 칼만필터 알고리즘과 비교하였다. 그 결과 제안된 알고리즘이 칼만필터보다 약5-10dB정도 더 우수한 성능을 나타내었다.

• 한국정보통신학회논문지
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• 제11권10호
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• pp.1828-1834
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• 2007

본 논문에서는 웨이블릿 변환을 기반으로 한 새로운 컬러영상 워터마킹 기법을 제안한다. 먼저 RGB컬러영역을 YCbCr 좌표계로 변환한다. 그리고 워터마크에 대해 Arnold 변환을 하여 워터마크의 상관성을 적게 만든다. 그 후, 선형비트확장 기법을 적용하여 확대된 워터마크를 웨이블릿 변환된 컬러 영상의 Y 영역-저주파대에 일정한 강도로 삽입한다. 워터마크를 추출할 때는 F-노름(norm) 함수를 이용한다. 다양한 칼라영상에 대해 실험을 한 결과 제안한 방법은 충실도와 강인성 측면에서 우수한 특성을 가짐을 확인하였다.

• Journal of applied mathematics & informatics
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• 제9권2호
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• pp.657-666
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• 2002

ThE Gibbs' phenomenon in the classical Fourier series is well-known. It is closely related with the kernel of the partial sum of the series. In fact, the Dirichlet kernel of the courier series is not positive. The poisson kernel of Cesaro summability is positive. As the consequence of the positiveness, the partial sum of Cesaro summability does not exhibit the Gibbs' phenomenon. Most kernels associated with wavelet expansions are not positive. So wavelet series is not free from the Gibbs' phenomenon. Because of the excessive oscillation of wavelets, we can not follow the techniques of the courier series to get rid of the unwanted quirk. Here we make a positive kernel For Meyer wavelets and as the result the associated summability method does not exhibit Gibbs' phenomenon for the corresponding series .

• 반도체디스플레이기술학회지
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• 제6권3호
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• pp.55-59
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• 2007

Wavelet Transform is amenable to efficient algorithms. So wavelet transform was adopted many signal processing and communication applications. For example, the wavelet transform was adopted as the transform for JPEG2000. However, Wavelet has weakness about smoothness along the contours and limited directional information. Hence, recently, some new transforms have been introduced to take advantage of this property. So we use to other transform, called contourlet transform in compression. In this paper, we propose a new method for image compression based on the contourlet transform, which has been recently introduced. Contourlet transform has a good result about images with smooth contours. Moreover, Contourlet is feasible multiresolution and multidirection expansion using non-separable filter bank. This treatise shows a good image representation after compressing using contourlet transform.

• Journal of applied mathematics & informatics
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• 제16권1_2호
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• pp.613-620
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• 2004

The concept of Gibbs’ phenomenon has not been made for higher dimension in wavelets. In this paper we extend the concept in two dimensional wavelets. We give the fundamental concept of jump discontinuity in two dimensions. We provide the criteria for the existence of Gibbs phenomenon for both separable and tensor product wavelets.

• 한국방사선학회논문지
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• 제2권1호
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• pp.23-29
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• 2008

본 연구에서는 웨이블릿 변환과 경계선 검출 필터를 이용하여 초음파영상의 다해상도 분해를 한 후 경계선 검출 필터링을 통해 초음파 영상의 화질을 개선하는 방안을 제안하였다. 제안된 방법에서는 잡음을 줄이고 에지를 강화하기 위해 웨이블릿 변환된 영상으로부터 얻어진 저해상도 영상에서 고해상도 영상으로 단계적으로 영역별 선택계수 조정과 방향성을 고려한 에지 필터링을 수행하였다. 이를 통해 반점영역의 픽셀은 웨이블릿 계수를 줄여 에지를 제외한 영역에서 선택적 저역통과 필터링 효과를 만들고, 에지에서는 접선 방향으로 평활화를 하여 연속성을 향상시키고, 법선 방향으로는 세선화를 하여 contrast를 높였다. 실험을 통해 단일해상도에서 비선형적 이방성의 확산모델을 이용한 필터링 방법과 웨이블릿 수축구조를 이용한 필터링 방법에 대해 비교하였다.