Applied Sciences

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17 pages, 27572 KiB

Open AccessArticle

Intra Prediction-Based Hologram Phase Component Coding Using Modified Phase Unwrapping

by Jin-Kyum Kim, Kwan-Jung Oh, Jin-Woong Kim, Dong-Wook Kim and Young-Ho Seo

Appl. Sci. 2021, 11(5), 2194; https://doi.org/10.3390/app11052194 - 03 Mar 2021

Cited by 1 | Viewed by 1630

In this paper, we propose a method for compressing the phase component of a full-complex hologram. The JPEG (Joint Photographic Experts Group) Pleno is undergoing standardization for compressing full-complex holograms. If the full-complex hologram is compressed in the form of amplitude and phase [...] Read more.

In this paper, we propose a method for compressing the phase component of a full-complex hologram. The JPEG (Joint Photographic Experts Group) Pleno is undergoing standardization for compressing full-complex holograms. If the full-complex hologram is compressed in the form of amplitude and phase components, the three-dimensional information of the hologram may be better preserved. Therefore, in order to solve the disadvantages of the method of independently compressing real and imaginary parts, we propose a method for directly compressing phase information. We select the HEVC (High Efficiency Video Coding), which has the best performance in compressing holograms from previous studies, as the anchor codec, and propose an algorithm for converting the phase information into the form suitable for the HEVC. Since the phase component is very random, we propose a modified phase unwrapping technique to improve this. In addition, in order to make good use of the property of HEVC Intra coding, the phase unwrapping considering Intra prediction is applied, and the most suitable HEVC Intra coding condition is searched. Compared with the result of compressing the phase using the HEVC, the hologram was improved by 2 dB or more and the reconstruction result was improved by more than 4 dB at a compression ratio of 80:1. If the compression ratio is increased, the proposed method has better results. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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8 pages, 5244 KiB

Open AccessArticle

Study of Non-Periodic Pinhole Array Filter for Decreasing High-Order Noise for Compact Holographic Display

by Yoo Kwang Kim, Won Jong Ryu and Jin Su Lee

Appl. Sci. 2020, 10(23), 8671; https://doi.org/10.3390/app10238671 - 04 Dec 2020

Cited by 2 | Viewed by 1997

Abstract

The non-periodic pinhole array filtering of a spatial light modulator (SLM) is proposed for filtering the high-order noise and DC noise of a holographic display. Conventionally, DC and high-order noise sources are filtered by a 4f filtering system. Because the 4f filtering system [...] Read more.

The non-periodic pinhole array filtering of a spatial light modulator (SLM) is proposed for filtering the high-order noise and DC noise of a holographic display. Conventionally, DC and high-order noise sources are filtered by a 4f filtering system. Because the 4f filtering system requires a long optical path length, noise filtering is a stumbling block when attempting to realize a compact holographic display. By contrast, the proposed method simply uses a thin filter fabricated by photolithography. In order to verify this concept, we confirmed the feasibility of the filter with a numerical simulation and with a custom-made non-periodic pinhole array filter used in a practical experiment. The proposed method was shown to have the potential to be used in applications ranging from compact wearable devices to table-top holographic displays. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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13 pages, 5771 KiB

Open AccessArticle

Efficient Hogel-Based Hologram Synthesis Method for Holographic Stereogram Printing

by Erkhembaatar Dashdavaa, Anar Khuderchuluun, Hui-Ying Wu, Young-Tae Lim, Chang-Won Shin, Hoonjong Kang, Seok-Hee Jeon and Nam Kim

Appl. Sci. 2020, 10(22), 8088; https://doi.org/10.3390/app10228088 - 15 Nov 2020

Cited by 14 | Viewed by 3267

Abstract

With the development of the holographic printer, printing synthetic hologram requires smaller holographic element (hogel) size to improve spatial resolution of the reconstruction. On the contrary, a larger hogel size affords higher angular resolution, but it leads to a lower lateral resolution and [...] Read more.

With the development of the holographic printer, printing synthetic hologram requires smaller holographic element (hogel) size to improve spatial resolution of the reconstruction. On the contrary, a larger hogel size affords higher angular resolution, but it leads to a lower lateral resolution and there exists a trade-off problem. In this paper, a hologram synthesis method based on three-dimensional (3D) rendering of computer-generated holographic stereogram (HS) is proposed to limit the spatial-angular trade-off problem. The perspectives of the 3D scene are captured by re-centering the camera method and transformed into parallax-related images by a proposed pixel re-arrangement algorithm for holographic printing. Unlike the conventional approaches, the proposed algorithm not only improves the angular resolution of the reconstruction while maintaining the hogel size fixed, but also keeps the spatial resolution without degradation. The effectiveness of the proposed method is verified by numerical simulation and an optical experiment. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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14 pages, 23068 KiB

Open AccessArticle

Holographic Micromirror Array with Diffuse Areas for Accurate Calibration of 3D Light-Field Display

by Lode Jorissen, Ryutaro Oi, Koki Wakunami, Yasuyuki Ichihashi, Gauthier Lafruit, Kenji Yamamoto, Philippe Bekaert and Boaz Jessie Jackin

Appl. Sci. 2020, 10(20), 7188; https://doi.org/10.3390/app10207188 - 15 Oct 2020

Cited by 3 | Viewed by 2174

Abstract

Light field 3D displays require a precise alignment between the display source and the micromirror-array screen for error free 3D visualization. Hence, calibrating the system using an external camera becomes necessary, before displaying any 3D contents. The inter-dependency of the intrinsic and extrinsic [...] Read more.

Light field 3D displays require a precise alignment between the display source and the micromirror-array screen for error free 3D visualization. Hence, calibrating the system using an external camera becomes necessary, before displaying any 3D contents. The inter-dependency of the intrinsic and extrinsic parameters of display-source, calibration-camera, and micromirror-array screen, makes the calibration process very complex and error-prone. Thus, several assumptions are made with regard to the display setup, in order to simplify the calibration. A fully automatic calibration method based on several such assumptions was reported by us earlier. Here, in this paper, we report a method that uses no such assumptions, but yields a better calibration. The proposed method adapts an optical solution where the micromirror-array screen is fabricated as a computer generated hologram with a tiny diffuser engraved at one corner of each elemental micromirror in the array. The calibration algorithm uses these diffusing areas as markers to determine the relation between the pixels of display source and the mirrors in the micromirror-array screen. Calibration results show that virtually reconstructed 3D scenes align well with the real world contents, and are free from any distortion. This method also eliminates the position dependency of display source, calibration-camera, and mirror-array screen during calibration, which enables easy setup of the display system. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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12 pages, 2979 KiB

Open AccessArticle

A Hybrid Diffractive Optical Element Design Algorithm Combining Particle Swarm Optimization and a Simulated Annealing Algorithm

by Ping Su, Chao Cai, Yuming Song, Jianshe Ma and Qiaofeng Tan

Appl. Sci. 2020, 10(16), 5485; https://doi.org/10.3390/app10165485 - 07 Aug 2020

Cited by 11 | Viewed by 2170

Abstract

With the rapid development of computer hardware and the emergence of the parallel calculation of diffraction fields, a breakthrough has been made in terms of the limitation of the unacceptable amount of computational cost to design diffractive optical elements (DOEs), and more accurate [...] Read more.

With the rapid development of computer hardware and the emergence of the parallel calculation of diffraction fields, a breakthrough has been made in terms of the limitation of the unacceptable amount of computational cost to design diffractive optical elements (DOEs), and more accurate global search algorithms can be introduced to the design of complex DOEs and holographic projections instead of traditional iterative algorithms. In this paper, a hybrid algorithm which combines particle swarm optimization (PSO) with a simulated annealing (SA) algorithm is proposed for the designing of DOEs and projecting holographic images with less noise. PSO is used to reduce the invalid disturbance in SA, and SA can jump out from local extreme points to find the global extreme points. Compared with the traditional Gerchberg–Saxton (GS) algorithm, the simulation and experimental results demonstrate that the proposed SA–PSO hybrid algorithm can improve uniformity by more than 10%. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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27 pages, 32615 KiB

Open AccessArticle

Providing a Visual Understanding of Holography Through Phase Space Representations

by Tobias Birnbaum, Tomasz Kozacki and Peter Schelkens

Appl. Sci. 2020, 10(14), 4766; https://doi.org/10.3390/app10144766 - 10 Jul 2020

Cited by 10 | Viewed by 2952

Abstract

Digital holograms are a prime example for signals, which are best understood in phase space—the joint space of spatial coordinates and spatial frequencies. Many characteristics, as well as optical operations can be visualized therein with so called phase space representations (PSRs). However, literature [...] Read more.

Digital holograms are a prime example for signals, which are best understood in phase space—the joint space of spatial coordinates and spatial frequencies. Many characteristics, as well as optical operations can be visualized therein with so called phase space representations (PSRs). However, literature relies often only on symbolic PSRs or on, in practice, visually insufficient PSRs like the Wigner–Ville representation. In this tutorial-style paper, we will showcase the S-method, which is both a PSR that can be calculated directly from any given signal, and that allows for a clear visual interpretation. We will highlight the power of space-frequency analysis in digital holography, explain why this specific PSR is recommended, discuss a broad range of basic operations, and briefly overview several interesting practical questions in digital holography. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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14 pages, 39162 KiB

Open AccessArticle

Optimization of Phase-Only Computer-Generated Holograms Based on the Gradient Descent Method

by Shujian Liu and Yasuhiro Takaki

Appl. Sci. 2020, 10(12), 4283; https://doi.org/10.3390/app10124283 - 22 Jun 2020

Cited by 16 | Viewed by 3881

Abstract

The Gerchberg–Saxton (GS) algorithm is a Fourier iterative algorithm that can effectively optimize phase-only computer-generated holograms (CGHs). This study proposes a new optimization technique for phase-only CGHs based on the gradient descent method. The proposed technique evaluates the intensity distributions of reconstructed images [...] Read more.

The Gerchberg–Saxton (GS) algorithm is a Fourier iterative algorithm that can effectively optimize phase-only computer-generated holograms (CGHs). This study proposes a new optimization technique for phase-only CGHs based on the gradient descent method. The proposed technique evaluates the intensity distributions of reconstructed images to directly obtain the phase distributions of the CGHs, whereas the GS algorithm equivalently evaluates the amplitude distributions of reconstructed images and extracts phase distributions from complex-amplitude distributions of the holograms using a constant-amplitude constraint. The proposed technique can reduce the errors in the reconstructed images with fewer iterations than the GS algorithm. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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8 pages, 1294 KiB

Open AccessArticle

Partially Overlapping Printing with Digital Filter to Improve Quality of Volume Hologram Printer – Numerical Simulation –

by Hangbo Hua, Takeshi Yamaguchi and Hiroshi Yoshikawa

Appl. Sci. 2020, 10(11), 3963; https://doi.org/10.3390/app10113963 - 07 Jun 2020

Cited by 1 | Viewed by 2453

Abstract

The volume hologram printer is useful for 3D display, because it is selective to the wavelength and be able to reconstruct with the natural illumination. There are many studies of a volume hologram printer been studied to output a volume hologram from a [...] Read more.

The volume hologram printer is useful for 3D display, because it is selective to the wavelength and be able to reconstruct with the natural illumination. There are many studies of a volume hologram printer been studied to output a volume hologram from a computer-generated hologram. The final volume hologram consists of tiled small holograms and the tiling manner often causes spilt lines which will have impact on image quality. With an intent to get rid of the split lines and improve the quality, fully overlapping printing was proposed recently. Each elemental hologram is overlapped both in vertical and horizontal directions by 50%. Then, the hologram is printed four times in each area and it makes the printing speed four times slower. For this case, partially overlapping printing is proposed in this paper to improve image quality with small effect in printing speed. For partial overlapping, a digital spatial filter is projected and added to every elemental hologram. Using the digital spatial filter, different partially overlapped holograms are calculated and reconstructed to compare to the non-overlapped ones. The simulation result shows that the overlapped one (10% in both vertical and horizontal) has much weaker gaps and black lines. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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11 pages, 6355 KiB

Open AccessArticle

Weighted Constraint Iterative Algorithm for Phase Hologram Generation

by Lizhi Chen, Hao Zhang, Zehao He, Xiaoyu Wang, Liangcai Cao and Guofan Jin

Appl. Sci. 2020, 10(10), 3652; https://doi.org/10.3390/app10103652 - 25 May 2020

Cited by 40 | Viewed by 4302

Abstract

A weighted constraint iterative algorithm is presented to calculate phase holograms with quality reconstruction. The image plane is partitioned into two regions where different constraint strategies are implemented during the iteration process. In the image plane, the signal region is constrained directly according [...] Read more.

A weighted constraint iterative algorithm is presented to calculate phase holograms with quality reconstruction. The image plane is partitioned into two regions where different constraint strategies are implemented during the iteration process. In the image plane, the signal region is constrained directly according to the amplitude distribution of the target image based on an adaptive strategy, whereas the non-signal region is constrained indirectly by total energy control of the hologram plane based on the energy conservation principle. The weighted constraint strategy can improve the reconstruction quality of the phase holograms by broadening the optimizing space of the iterative algorithm, leading to effective convergence of the iteration process. Finally, numerical and optical experiments have been performed to validate the feasibility of our method. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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14 pages, 4830 KiB

Open AccessArticle

Enhancing the Quality of Sampled Phase-Only Hologram (SPOH) Based on Time-Division Comb Filtering

by Peter W. M. Tsang, Jung-Ping Liu, Hoson Lam and Ting-Chung Poon

Appl. Sci. 2020, 10(8), 2732; https://doi.org/10.3390/app10082732 - 15 Apr 2020

Cited by 3 | Viewed by 2189

Abstract

Generation of digital phase-only Fresnel holograms is an important research area in digital holography, as it leads to a substantial simplification of a holographic display system. However, the quality of the reconstructed image of a hologram without the magnitude component is heavily degraded. [...] Read more.

Generation of digital phase-only Fresnel holograms is an important research area in digital holography, as it leads to a substantial simplification of a holographic display system. However, the quality of the reconstructed image of a hologram without the magnitude component is heavily degraded. The problem can be reduced by down-sampling the intensity of an image prior to generating the hologram. The method, referred to as “sampled phase-only hologram” (SPOH) generation, results in reconstructed images that are masked with the pattern of the down-sampling lattice. This paper reports a novel, low complexity method to alleviate this problem through the concept of comb filtering. Results reveal prominent enhancement on the reconstructed image of a SPOH. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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11 pages, 2544 KiB

Open AccessArticle

Reducing Computational Complexity and Memory Usage of Iterative Hologram Optimization Using Scaled Diffraction

by Tomoyoshi Shimobaba, Michal Makowski, Takayuki Takahashi, Yota Yamamoto, Ikuo Hoshi, Takashi Nishitsuji, Naoto Hoshikawa, Takashi Kakue and Tomoyoshi Ito

Appl. Sci. 2020, 10(3), 1132; https://doi.org/10.3390/app10031132 - 07 Feb 2020

Cited by 6 | Viewed by 2271

Abstract

A complex amplitude hologram can reconstruct perfect light waves. However, as there are no spatial light modulators that are able to display complex amplitudes, we need to use amplitude, binary, or phase-only holograms. The images reconstructed from such holograms will deteriorate; to address [...] Read more.

A complex amplitude hologram can reconstruct perfect light waves. However, as there are no spatial light modulators that are able to display complex amplitudes, we need to use amplitude, binary, or phase-only holograms. The images reconstructed from such holograms will deteriorate; to address this problem, iterative hologram optimization algorithms have been proposed. One of the iterative algorithms utilizes a blank area to help converge the optimization; however, the calculation time and memory usage involved increases. In this study, we propose to reduce the computational complexity and memory usage of the iterative optimization using scaled diffraction, which can calculate light propagation with different sampling pitches on a hologram plane and object plane. Scaled diffraction can introduce a virtual blank area without using physical memory. We further propose a combination of scaled diffraction-based optimization and conventional methods. The combination algorithm improves the quality of a reconstructed complex amplitude while accelerating optimization. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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10 pages, 4365 KiB

Open AccessArticle

High-Resolution Hologram Calculation Method Based on Light Field Image Rendering

by Xin Yang, FuYang Xu, HanLe Zhang, HongBo Zhang, Kai Huang, Yong Li and QiongHua Wang

Appl. Sci. 2020, 10(3), 819; https://doi.org/10.3390/app10030819 - 23 Jan 2020

Cited by 12 | Viewed by 4373

Abstract

A fast calculation method for a full parallax high-resolution hologram is proposed based on elemental light field image (EI) rendering. A 3D object located near the holographic plane is firstly rendered as multiple EIs with a pinhole array. Each EI is interpolated and [...] Read more.

A fast calculation method for a full parallax high-resolution hologram is proposed based on elemental light field image (EI) rendering. A 3D object located near the holographic plane is firstly rendered as multiple EIs with a pinhole array. Each EI is interpolated and multiplied by a divergent sphere wave and interfered with a reference wave to form a hogel. Parallel acceleration is used to calculate the high-resolution hologram because the calculation of each hogel is independent. A high-resolution hologram with the resolution of 200,000 × 200,000 pixels is calculated within only eight minutes. Full parallax high-resolution 3D displays are realized by optical reconstructions. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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12 pages, 5250 KiB

Open AccessArticle

Iterative Phase-Only Hologram Generation Based on the Perceived Image Quality

by Haining Yang and Daping Chu

Appl. Sci. 2019, 9(20), 4457; https://doi.org/10.3390/app9204457 - 21 Oct 2019

Cited by 4 | Viewed by 2345

Abstract

Image quality metrics are a critical element in the iterative Fourier transform algorithms (IFTAs) for the computer generation of phase-only holograms. Conventional image quality metrics such as root-mean-squared error (RMSE) are sensitive to image content and unable to reflect the perceived image quality [...] Read more.

Image quality metrics are a critical element in the iterative Fourier transform algorithms (IFTAs) for the computer generation of phase-only holograms. Conventional image quality metrics such as root-mean-squared error (RMSE) are sensitive to image content and unable to reflect the perceived image quality accurately. This would have a significant impact on the calculation speed and the quality of the generated hologram. In this work, the structure similarity (SSIM) was proposed as an image quality metric in IFTAs due to its ability to predict the perceived image quality in the presence of the white Gaussian noise and its independence on the image content. This would enable IFTAs to terminate when further iterations would no longer lead to improvement in the perceived image quality. As a result, up to 75% of unnecessary iterations were eliminated by the use of SSIM as the image quality metric. Full article

(This article belongs to the Special Issue Practical Computer-Generated Hologram for 3D Display)

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