• Title/Summary/Keyword: Digital fourier transform

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A Comparison between Abel-Fourier and Digital Linear Filter Methods (Abel-Fourier법과 디지탈 선형필터법과의 비교)

  • Kim, Hee Joon
    • Economic and Environmental Geology
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    • v.20 no.2
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    • pp.119-123
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    • 1987
  • Hankel transform of order 0 can be represented by a combination of Abel transform and Fourier transform. This Abel-Fourier method can offer computational advantages over a conventional digital linear filter method through the uses of a rapid Abel transform with shift variant recursive filter and of a fast Fourier transform. The Abel-Fourier method, however, is generally less accurate than a well-designed digital linear filter method. In geoelectrical applications, the digital linear filter method seems to be more flexible than the Abel-Fourier method.

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Phase Retrieval Using an Additive Reference Signal: I. Theory (더해지는 기준신호를 이용한 위성복원: I. 이론)

  • Woo Shik Kim
    • Journal of the Korean Institute of Telematics and Electronics B
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    • v.31B no.5
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    • pp.26-33
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    • 1994
  • Phase retrieval is concerned with the reconstruction of a signal from its Fourier transform magnitude (or intensity), which arises in many areas such as X-ray crystallography, optics, astronomy, or digital signal processing. In such areas, the Fourier transform phase of the desired signal is lost while measuring Fourier transform magnitude (F.T.M.). However, if a reference 'signal is added to the desired signal, then, in the Fourier trans form magnitude of the added signal, the Fourier transform phase of the desired signal is encoded. This paper addresses uniqueness and retrieval of the encoded Fourier phase of a multidimensional signal from the Fourier transform magnitude of the added signal along with the Fourier transform magnitude of the desired signal and the information of the additive reference signal. In Part I, several conditions under which the desired signal can be uniquely specified from the two Fourier transform magnitudes and the additive reference signal are presented. In Part II, the development of non-iterative algorithms and an iterative algorithm that may be used to reconstruct the desired signal(s) is considered.

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Phase Retrieval Using an Additive Reference Signal: II. Reconstruction (더해지는 기준신호를 이용한 위성복원: II. 복원)

  • Woo Shik Kim
    • Journal of the Korean Institute of Telematics and Electronics B
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    • v.31B no.5
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    • pp.34-41
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    • 1994
  • Phase retrieval is concerned with the reconstruction of a signal from its Fourier transform magnitude (or intensity), which arises in many areas such as X-ray crystallography, optics, astronomy, or digital signal processing In such areas, the Fourier transform phase of the desired signal is lost while measuring Fourier transform magnitude (F.T.M.). However, if a reference 'signal is added to the desired signal, then, in the Fourier trans form magnitude of the added signal, the Fourier transform phase of the desired signal is encoded This paper addresses uniqueness and retrieval of the encoded Fourier phase of a multidimensional signal from the Fourier transform magnitude of the added signal along with Fourier transform magnitude of the desired signal and the information of the additive reference signal In Part I, several conditions under which the desired signal can be uniquely specified from the two Fourier transform magnitudes and the additive reference signal are presented In Part II, the development of non-iterative algorithms and an iterative algorithm that may be used to reconstruct the desired signal (s) is considered

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Study on the Two-wavelength Digital Holography Using Double Fourier Transform (이중푸리에변환을 이용한 2 파장 디지털 홀로그래픽 연구)

  • Shin, Sang-Hoon;Jung, Won-Ki;Yu, Young-Hun
    • Korean Journal of Optics and Photonics
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    • v.21 no.3
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    • pp.91-96
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    • 2010
  • The size of a reconstructed image depends on the reconstruction distance and wavelength. The double fourier transform method is proposed to eliminate the dependence on the reconstruction distance and wavelength. We can get a fixed reconstructed image size by using the double fourier transform method. Two wavelength digital holography is proposed to measure the step height, which is larger than a single wavelength. The two image size of different wavelength holograms should be the same in order to apply two wavelength digital holography. We use two wavelength digital holography and double fourier transforms to measure the step height. The measured data were reasonable and we found that the double fourier transform is useful in two wavelength digital holography.

A study on the Variable Elimination of the 0-th order Diffraction Using the Fourier Transform in the Digital Holography Microscope System

  • Choi, Kyu-Hwan;Kim, Sung-Kyu
    • 한국정보디스플레이학회:학술대회논문집
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    • 2009.10a
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    • pp.1357-1360
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    • 2009
  • In this study, the 0-th order diffraction could be efficiently removed with the obtained data for one hologram using the numerical reconstruction method. This method has a reduced data acquisition and processing time compared with the existing method wherein the data for two or more phase holograms are obtained for regeneration, and efficiently eliminates the 0-th order diffraction.

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Effects and Limitations of Separating Overlapped Fingerprints Using Fast Fourier Transform (고속 푸리에 변환(fast Fourier transform, FFT)을 이용한 겹친지문 분리의 효과와 한계)

  • Kim, Chaewon;Kim, Chaelin;Lee, Hanna;Yu, Jeseol;Jang, Yunsik
    • 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.

Analysis Method of Digital Forgeries on the Filtered Tampered Images

  • Kim, Jin-Tae;Joo, Chang-Hee
    • Journal of information and communication convergence engineering
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    • v.9 no.1
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    • pp.95-99
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    • 2011
  • Digital forensics is the emerging research field for determining digital forgeries. Key issues of the tampered images are to solve the problems for detecting the interpolation factor and the tampered regions. This paper describes a method to detect the interpolation factors and the forged maps using the differential method and fast Fourier transform(FFT) along the horizontal, vertical, and diagonal direction, respectively from digital filtered tampered images. The detection map can be used to find out interpolated regions from the tempered image. Experimental results demonstrate the proposed algorithm proves effective on several filtering images by adobe $Photoshop^{TM}$ and show a ratio of detecting the interpolated regions and factors from digital filtered composite images.

Study of robust watermarking method in medical image (의료영상에서의 강인한 워터마킹 기법에 관한 연구)

  • 남기철;박무훈
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2003.05a
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    • pp.255-258
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    • 2003
  • Recently, Digital Watermarking is used to authenticate data and to determine whether the data are distorted or not in medical images which is digitalized. The Fourier Mellin method using the Fourier Transform and the Log-Polar coordinate transform gets an invariant feature for RST distortion in images. But there are several problems in the real materialization. Interpolation of the image value should be considered according to the pixel position and so a watermark loss, original image distortion, numerical approximation is happened. Therefore there should be solved to realization of the Fourier Mellin method. Using the Look up table, there reduce the data loss caused by the conversion between Rectangular and Polar coordinate. After diagnose, medical images are transformed the Polar coordinate and taken the Discrete Fourier transform in the center of ROI region. Maintaining the symmetry in Fourier magnitude coefficient, the gaussian distributed random vectors and binary images are embedded in medical images.

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Performance Analysis of digital phase shifter using Hilbert transform (힐버트 변환을 이용한 디지털 위상천이기의 성능 분석)

  • Seo, Sang Gyu;Jeong, Bong-Sik
    • Journal of the Institute of Convergence Signal Processing
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    • v.14 no.1
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    • pp.39-44
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    • 2013
  • In this paper digital phase-shifter for multi-arm spiral antennas was designed by using Hilbert transform. All frequency components in input signal are phase-shifted for 90 degree by Hilbert transform, and the transform is implemented by FIT and IFIT. Digital phase-shifter generates two signals with phase difference of 90 degree by using Hilbert transform from input signals sampled by analog-digital converter(ADC), and then the input signal is phase-shifted for a given phase by using two signals. Hilbert transform based on digital phase-shifter is designed by Xilinx System generator, and the effects of input noise, FIT point, sampling period, initial phase of input signal, and shifted phase are simulated and its results are compared with Matlab results.