• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.1
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• pp.13-21
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• 2003

To investigate the safety and stability of a concrete lining, numerous studies have been conducted over the years and several methods have been developed. Most signal processing techniques of NDT have been based on Fourier analysis. However, the application of Fourier analysis to analyze recorded vibrational signal shows results in the frequency domain only, and it is not enough to analyze transient waves precisely. In this study, Wavelet theory was employed for the analysis of non-stationary wave induced by mechanical impact on tunnel concrete lining. The Wavelet transform of transient signals provides a method for mapping the frequency spectrum as a function of time. To verify the availability of Wavelet transform as a time-frequency analysis tool, model experiments have been conducted and the thickness of the concrete lining was estimated based on the proposed theory. From this study, it was found that the contour map by Wavelet transform provides more distinct results than the power spectrum by Fourier transform and it was also found that Wavelet transform was also an effective tool for the analysis of dispersive waves in tunnel concrete linings.

• Proceedings of the Optical Society of Korea Conference
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• 1996.09a
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• pp.50-50
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• 1996

• Korean Security Journal
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• no.61
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• pp.377-400
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• 2019

Photography is the most commonly used method of documenting the crime and incident scene as it helps maintaining chain of custody (COC) and prove integrity of the physical evidence. It can also capture phenomena as they are. However, digital images can be manipulated and lose their authenticity as admissible evidence. Thus only limited techniques can be used to enhance images, and one of them is Fourier transform. Fourier transform refers to transformation of images into frequency signals. Fast Fourier transform (FFT) is used in this study. In this experiment, we overlapped fingerprints with graph paper or other fingerprints and separated the fingerprints. Then we evaluated and compared quality of the separated fingerprints to the original fingerprints, and examined whether the two fingerprints can be identified as same fingerprints. In the case of the fingerprints on graph paper and general pattern-overlapping fingerprints, fingerprint ridges are enhanced. On the other hand, in case of separating complicated fingerprints such as core-to-core overlapping and delta-to-delta overlapping fingerprints, quality of fingerprints can be deteriorated. Quality of fingerprints is known to possibly bring negative effects on the credibility of examiners. The result of this study may be applicable to other areas using digital imaging enhancement technology.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.2
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• pp.379-385
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• 2004

Medical images are being managed more by PACS in general medical institutions. It is important to protect patients from being invaded their privacy related to the images. It is also necessary to confirm the ownership, the right of property of the medical images and notice whether the data are modified. In this paper, we propose a robust watermarking against RST attacks in medical images on the PACS. The proposed scheme modifies and improves Log-Polar Mapping and Fourier Mellin Transform in order to realize and recover serious image degradation and watermark data loss caused by the conversion between cartesian coordinate and log-polar coordinate. We used the radius and theta Look Up Table to solve the realization of the Fourier Mellin Transform, and inserted a watermark into 2D-DFT magnitudes using Spread Spectrum. Experimental results shows that this method are robust to rotation attack.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.2
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• pp.82-90
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• 1993

전자파에 의한 산란현상의 해석은 지금까지 주로 시간조화함수의 형태를 지닌 전원에 의한 정 상상태의 산란에 관하여 이루어졌다. 그러나 레이다나 피파괴 검사, 전송선로 점검 등의 응용에서는 주로 펄스형태의 전자파를 사용하며, 따라서 시간에 따라 변화하는 함수형태의 전원에 의한 전자파의 산란해 석이 중요한 문제로 등장하였다. 또한 통신선로에서 외부의 잡음에 대한 혼신 등을 해석하거나, 낙뢰가 송 전선로에 미치는 영향을 해석하는 데에도 펄스신호의 산란해석이 필수적이다. 일반적인 함수의 형태를 지닌 전원에 의한 산란현상을 해석하기 위해서는 전원함수를 Fourier 변환하 여 주파수 영역의 스펙트럼을 구하고, 주파수영역에서의 산란해를 이용하여 Fourier 역변환을 하여 시간 영역의 해를 구할 수 있다. 주파수 영역에서의 산란판의 해를 Fourier 역변환 하기 위해서는 적분을 행하여야 하며, 일반적으로 적분과정에서 매우 복잡한 계산이 필요하고, 산란체의 구조가 복잡하여 해석 적인 해를 구할수 없는 경우에는 해석적으로 시간영역의 해를 구하는 것이 불가능하다. 시변 함수에 의 한 산란파를 구하기 위한 수치해석적 방법으로는 모멘트방법이나 유한요소법(Finite Element Method), 경계요소법(Boundary Element Method), 유한차분법(Finite Difference Method)등이 있으며, 해석적 해 를구할 수 없는 경우에 적용할 수 있는 반면에 많은 계산량이 요구된다.

• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.154-160
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• 1997

On the base of the fractional Fourier transform(FRT) which is known as a generalized form of the conventional Fourier transform, the fractional correlation has been implemented. Shift-variance property of the fraction correlation has been evaluated and compared with the shift-invariance of the conventional correlation. The fractional correlation operation has been implemented by using a planar optics configuration which integrates all of the optical components on a single glass substrate. A good agreement between the experimental and calculated results has been obtained.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.1
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• pp.10-16
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• 2000

Spatially resolved liquid volume fractions from a set of line-of-sight laser diffraction measurements for axisymmetric sprays generated from a pintle-type gasoline injector have been tomographically reconstructed by Abel transformation, Fourier transformation and onion peeling method. Spatially resolved liquid volume fractions classified into 32 size groups were translated characteristics of SI engine fuel sprays. These data were also obtained from the phase Doppler measurements for the same sprays. The comparison between laser deffraction measurements and transformation reconstructs more reasonable spatially resolved characteristics for axisymmetric sprays as well as for asymmetric sprays.

• Journal of the Korean Magnetics Society
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• v.22 no.2
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• pp.33-36
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• 2012

We propose a simple prescription for resolving the general-$N$ problem existing in the old-fashioned mixed-radix fast Fourier transformation FORTRAN subroutine by Singleton in 1968. After a brief investigation on the problem, we discuss our prescription with the worst case analysis within the dynamical allocation. The analysis reveals that our implementation is superior, at least for multi-variate data set, than previously proposed data copying methods.

• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.6
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• pp.759-763
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• 2004

In this paper, real-time voice change method using pitch change technique is proposed to change one's voice to the other voice. For this purpose, sampling rate change method using DFT (Discrete Fourier Transform) method and time scale modification method using SOLA (Synchronized Overlap and Add) method is combined to change pitch. In order to evaluate the performance of the proposed method, voice transformation experiments were conducted. Experimental results showed that original speech signal is changed to the other speech signal in which original speaker's identity is difficult to find. The system is implemented using TI TMS320C6711DSK board to verify the system runs in real time.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.255-259
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• 2003

In this paper, we propose an improved image encryption and decryption method using a virtual image and a joint transform correlator (JTC). The encrypted image is obtained by the Fourier transform of the product of a virtual-phase image and a random-phase image, and a Fourier transform of the decrypting key generated by the proposed phase assignment rule is used as the Fourier decrypting key. Based on the solution, the original image is reconstructed using JTC in the frequency-domain. The proposed method using a virtual image, which does not contain any information from the original image, prevents the possibility of counterfeiting by unauthorized people. And also the auto-correlation terms, which are the drawback of a JTC system, contribute to reconstructing the original image rather than to disturbing its identification. But because phase-only encryptions are sensitive to noise and scratches, phase errors can be generated in fabricating the encrypted image or the Fourier decrypting key so the errors that are responsible for degradation of the quality of the reconstructed image are analyzed and the solution is demonstrated. Computer simulations show the solution, and the proposed method is very useful for JTC architecture.