• Current Optics and Photonics
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• v.6 no.1
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• pp.51-59
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• 2022

Holographic display technology is one of the promising 3D display technologies. However, the large amount of computation time required to generate computer-generated holograms (CGH) is a major obstacle to the commercialization of digital hologram. In various systems such as multi-depth head-up-displays with hologram contents, it is important to transmit hologram data in real time. In this paper, we propose a rapid CGH computation method by applying an arraying of a down-scaled hologram with the multiplication of a shifted concave lens function array. Compared to conventional angular spectrum method (ASM) calculation, we achieved about 39 times faster calculation speed for 3840 × 2160 pixel CGH calculation. Through the numerical investigation and experiments, we verified the degradation of reconstructed hologram image quality made by the proposed method is not so much compared to conventional ASM.

• The Journal of the Acoustical Society of Korea
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• v.8 no.4
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• pp.23-28
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• 1989

In this paper, the construction of ultrasonic hologram and the image reconstruction using computer have been studied, and it has been compared with optical reconstruction. The ultrasonic hologram has been constructed using c-scanning method$(128\times128 step)$and the image of the object has been reconstructed by computer using Rayleigh -Sommerfeld formula and DFT algorithm. In this experiment, the holography system has been builted with the transducer of 5MHz center frequency and 5cm focal length, and the mechanical c-scanning system. It has been shown that the reconstructed image using computer for aluminum plane with the 'S' shaped defect has been displayed image of high quality.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.70-77
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• 2016

This paper proposes an optical system for complex holographic display that enhances the quality of the reconstructed three-dimensional image. This work focuses on a new design for an optical system and the evaluation of the complex holographic display, using a single spatial light modulator (SLM) and a circular grating. The optical system is based on a 4-f system in which the imaginary and real information of the hologram is displayed on concentric rectangular areas of the SLM and circular grating. Thus, this method overcomes the lack of accuracy in the pixel positions between two window holograms in previous studies, and achieves a higher intensity of the real object points of the reconstructed hologram than the original phase-reconstructed hologram. The proposed method provides approximately 30% less NMRS (Normal Root Mean Square) error, compared to previous systems, which is verified by both simulation and optical experiment.

• Journal of information and communication convergence engineering
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• v.11 no.3
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• pp.185-189
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• 2013

A digital hologram generated by a computer calculation (computer-generated hologram or capture using charge-coupled device [CCD] camera) is one of the most expensive types of content, and its usage is expanding. Thus, it is highly necessary to protect the ownership of digital holograms. This paper presents an efficient visual security scheme for holographic image reconstruction with a low scrambling cost. Most recent studies on optical security concentrate their focus on security authentication using optical characteristics. However, in this paper, we propose an efficient scrambling method to protect a digital hologram. Therefore, we introduce in this paper several scrambling attempts in both the spatial domain and frequency domain on the basis of the results of analyzing the properties of the coefficients in each domain. To effectively hide the image information, 1/4, 1/256, and 1/16,384 of the original digital hologram needs to be scrambled for the spatial-domain scheme, Fresnel-domain scheme, and discrete cosine transform-domain scheme, respectively. The encryption schemes and the analyses in this paper can be expected to be useful in the research on encryption and other works on digital holograms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3C
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• pp.255-261
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• 2008

Conventional look-up table(LT) has gained a lot of speed increase in generation of digital holograms for 3D objects, but it has required an enormous memory size of the LT. In this paper, a novel approach to dramatically reduce the size of the conventional LT, still keeping its advantage of fast computational speed is proposed, which is called here a N-LT(novel look-up table) method. In the proposed method, only the fringe patterns of the center points on each image plane are pre-calculated, called elemental fringe patterns and stored in the look-up table. Then, the fringe patterns for other object points on each image plane can be obtained by simply shifting this pre-calculated elemental fringe pattern according to the displaced values from the center to those points and adding them together. Some experimental results revealed that the computational speed and the required memory size of the proposed approach are found to be 48.7 times faster than that of the ray-tracing method and 217 times smaller than that of the conventional LT method, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10B
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• pp.1076-1085
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• 2009

In this paper, a new method for efficient computation of CGH patterns for 3-D video images is proposed by combined use of temporal redundancy and look-up table techniques. In the conventional N-LT method, fringe patterns for other object points on that image plane can be obtained by simply shifting these pre-calculated PFP (Principle Fringe Patterns). But there have been many practical limitations in real-time generation of 3-D video holograms because the computation time required for the generation of 3-D video holograms must be massively increased compared to that of the static holograms. On the other hand, as ordinary 3-D moving pictures have numerous similarities between video frames, called by temporal redundancy, and this redundancy is used to compress the video image. Therefore, in this paper, we proposed the efficient hologram generation method using the temporal redundancy of 3-D video image and N-LT method. To confirm the feasibility of the proposed method, some experiments with test 3-D videos are carried out, and the results are comparatively discussed with the conventional methods in terms of the number of object points and computation time.

• Broadcasting and Media Magazine
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• v.16 no.2
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• pp.109-117
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• 2011

디지털 홀로그래피는 현재 입체영상 서비스의 주류를 이루고 있는 스테레오스코픽(Stereoscophic)이나 다시점(Multi-view) 3D와 달리 주어진 관찰각도에서 관찰자의 위치에 따른 입체영상을 볼 수 있다. 또한 입체영상을 디스플레이하는 장치가 물리적 매체가 아닌 공간으로 한다는 점에서도 차이가 있다. 최근 홀로그래피, 홀로그램이란 용어가 상업적인 용도로 사용되면서 해당기술의 본질적인 의미가 상당히 변질되는 경우가 많이 있다. 본 기고에서는 일부에서 변질/왜곡하여 사용하고 있는 "유사한 홀로그래피(Fake holography)"가 아닌 간섭현상(Interference)을 수학적으로 모델링한 후 이를 컴퓨터에서 계산하여 디지털 홀로그램을 생성하는 컴퓨터 생성 홀로그램(Computer-Generated Hologram, CGH) 기술을 다룬다. 특히, 국내외의 연구개발 결과 중에서 전용 하드웨어나 범용 프로세서 등을 이용해 CGH 연산을 고속화하는 기술에 중점을 두었다.

• Journal of the Optical Society of Korea
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• v.15 no.3
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• pp.244-251
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• 2011

We propose a new 2-step phase-shifting digital holographic optical encryption technique and analyze tolerance error for this cipher system. 2-step phase-shifting digital holograms are acquired by moving the PZT mirror with phase step of 0 or ${\pi}$/2 in the reference beam path of the Mach-Zehnder type interferometer. Digital hologram with the encrypted information is Fourier transform hologram and is recorded on CCD camera with 256 gray-level quantized intensities. The decryption performance of binary bit data and image data is analyzed by considering error factors. One of the most important errors is quantization error in detecting the digital hologram intensity on CCD. The more the number of quantization error pixels and the variation of gray-level increase, the more the number of error bits increases for decryption. Computer experiments show the results to be carried out encryption and decryption with the proposed method and the graph to analyze the tolerance of the quantization error in the system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.1197-1202
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• 2001

Near-field acoustic holography is a powerful tool to visualize sound sources. This method requires pressure measurement at many points for a good hologram. Thus one has to measure carefully so that errors due to the uncertainty of position, sensor mismatch, and so on are reduced. A method to solve this problem is to use a well-designed measurement system. This paper introduces a sound visualization system at center for noise and vibration control (NOVIC), KAIST, and addresses the advantages in terms of the error reduction. The system consists of array microphones, array jigs, a system to control the position and the velocity of the jigs, a data acquisition system, and a monitoring system. This paper also shows some sound visualization results when the system is applied to a speaker and a computer. The results verifies that the sound visualization system is useful for identifying sound sources.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.04a
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• pp.123-127
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• 1993

소음방사의 이해 및 효과적인 소음제어를 위해서는 소음원의 특성, 음장의 공간상 방사 특성 등을 아는 것이 중요하며, 이를 위해 많은 연구가 진행되 어 왔다. 특히 다수의 마이크로폰 어레이를 이용한 음향 홀로그래피 방법에 의한 실험적 음장 예측 방법이 소개되었고 연구가 진행됨에 따라 많은 실용 가능성을 보여 주었다. 음향 홀로그래피 방법에는 측정상 제한이 필연적으로 존재할 수밖에 없는데, 이에 따른 오차가 존재하며 결국 예측음장의 신뢰도 를 떨어뜨리는 요인이 된다. 본 연구의 목적은 측정조건에 따른 오차의 요인 을 고찰하고 이를 정량적으로 표현함으로써 음향 홀로그래피 방법의 적용에 도움을 주고자 한다. 평면 음향 홀로그래피에 나타나는 오차는 둘러 싸기 오 차(wraparound error), 앨리애싱(aliasing), 창문영향(window effect)으로 나 눌 수 있는데, 오차는 측정구경의 크기와 마이크로폰 사이의 간격등의 측정 조건 뿐만 아니라 음원의 특성, 홀로그램 평면의 위치 등에 직접적인 영향을 받게 된다. 본 연구에서는 오차해석을 위한 기본 연구로써 점음원(monopole) 과 쌍극자(dipole)음장의 파수 스펙트럼을 해석적으로 구하고 이를 기본으로 평면 음향 홀로그래피 적용시 존재하는 앨리애싱에 대해 고찰하고 전산기 모의 실험 (computer simulation)을 통해 오차를 최소화하는 측정조건을 제 시하고자 한다.