Digital Holography Research Papers - Academia.edu (original) (raw)

A new optical method capable of measuring out-of-plane deformations of rotating objects based on the Fourier transform phase decoding technique is presented. Digital holography is used to test the method, which digitally derotates one of the holograms at its phase reconstruction stage to accurately remove object rotation fringes, uniquely rendering phase maps that quantitatively show the out-of-plane deformation. Commonly, object

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- Digital Holography, Optical physics, Fourier transform, Fourier Optics

The wave-splitting phase-shifting digital holography using a pixelated microretarder array is proposed. By using four intensity images recorded by the pixelated microretarder array, Stokes parameters of the incident wave can be calculated. The fully complex amplitude distribution of the object wave can be obtained by using Stokes parameters, if the polarization states of the object and reference waves are linear and orthogonal. Two sets of experimental results are provided to verify the feasibility of the proposed method. One is the result for a movie recording using a CW laser and the other is the result for instant recording using a single pulsed laser.

- by Takanori Nomura
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- Digital Holography, Optical

An information security method that uses a digital holographic technique is presented. An encrypted image is stored as a digital hologram. The decryption key is also stored as a digital hologram. The encrypted image can be electrically decrypted by use of the digital hologram of the key. This security technique provides secure storage and data transmission. Experimental results are presented to demonstrate the proposed method.

Featured Application: The proposed method is applicable for static 3D advertising and holographic packaging. Abstract: A fast calculation method for the full parallax high-resolution hologram is proposed based on the 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 calculation of each hogel is independent. A high-resolution hologram with the resolution of 20,0000×20,0000 pixels is calculated only within 8 minutes. Full parallax high-resolution 3D displays are realized by optical reconstructions.

- by Hongbo Zhang
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- Digital Holography, Holographic Display
- by Edward Buckley and +1
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- Optics, Digital Holography, Human Factors, Displays

A digital hologram is recorded by a 2D CCD array by superposition of the wavefield reflected or scattered from a scene and a coherent reference wave. If the recorded digital hologram is fed to a spatial light modulator (SLM) and this is illuminated by the reference wave, then the whole original wavefield can be reconstructed. The reconstructed wavefield contains phase and intensity distributions, which means it is full 3D, exhibiting such effects as depth and parallax. Therefore, the concept of digital holography is a promising approach to 3D-TV. In one of our previous works the preliminaries of an all-digital-holographic approach to 3D-TV were given. Here one of our approaches is experimentally verified and its capabilities and limitations are investigated.

- by Mostafa Agour
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- Visualization, Digital Holography, Virtual Environment, Image Reconstruction

Digital holographic microscopy (DHM) can be described as a non-invasive metrological tool for inspection and characterization of microelectromechanical structures (MEMS). DHM is a quick, non-contact and non-invasive technique that can offer a high resolution in both lateral and vertical directions. It has been employed for the characterization of the undesired out-of-plane deformations due to the residual stresses introduced by technological processes. The characterization of these deformations is helpful in studying and understanding the effect of residual stress on the deformation of a single microstructure. To that end, MEMS with different geometries and shapes, such as cantilever beams, bridges and membranes, have been characterized. Moreover, DHM has been applied efficiently to evaluate variations of the structure profile due to some external effects. As an example, the characterization of a cantilever subjected to a thermal process has been described. The results reported show that DHM is a useful non-invasive method for characterizing and developing reliable MEMS.

- by Andrea Finizio
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- Digital Holography

In this paper, the phenomenon of virtual idol Hatsune Miku will be analyzed in the context of critical theory, emerging technologies, and theory of digital art practices. The first part focuses on the phenomenon of the virtual celebrity seen as Deleuze and Guattari’s concept of ‘body without organs.’ The second part examines how the state-of-the-art technologies have enabled the existence of Hatsune Miku who is simultaneously a corporate software product, a pop icon, a performance artist, and a collaborative multimedia artwork. Based on the reading of Hatsune Miku as a hybrid product emerging from the fusion of arts and IT, the last part revolves around the concept of ‘aura’ (Benjamin) generated by virtual idol’s presence. Finally, the notion of hyperterminality is introduced not only to differentiate between entities/identities appearing on the surface of the screen and those virtual constructs co-existing with us in the spaces of physical reality, but also to explore how these newly emerging “phygital” entities transform the existing conceptions of body and identity.

A method for allowing direct perfect superimposition and comparison of Fresnel-transform reconstructions of digital holograms recorded of the same object at different distances and wavelengths is proposed and demonstrated. The method takes into account the dependence of the reconstruction pixel on the distance and the wavelength by the Fresnel-transform algorithm. The method avoids the need for image scaling at the end of the reconstruction process that usually is performed in multi-wavelength digital holography. Demonstration is given by superposing the numerical reconstructions of holograms recorded at different distances and wavelengths. The method can be potentially very useful for real-time monitoring in biological processes or for recognition and ranging by multiple wavelengths of a target with fast movements or finally for very fast investigation and study of very fast processes.

- by Andrea Finizio
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- Computer Science, Optics, Digital Holography, Optical physics
- by ligia jeon
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- Human Computer Interaction, Digital Holography, Interaction Design

Using the Chinese cosmological understanding of “shadow and soul” or ying hun (影魂), this chapter seeks to frame innovations in holographic technologies that facilitate the stereoscopic re-projections of departed Hong Kong- and Taiwan-based transnational Chinese celebrities such as Bruce Lee, Wong Kar Kui and Teresa Teng. It argues that the rising popularity of such presentations in concerts and advertisements stems not just from the visual spectacle of these unprecedented animated holograms. Instead, audiences may be held by latent beliefs of the immanence of departed stars whose presences have been maintained by media technologies from the analogue phonogram of the past, to the digital performance capture and holographic representation of contemporary convergent media. Such developments provide new platforms for the ying hun of these personalities to be replayed and resurrected.

Medieval hagiographies abound with tales of post-mortem visits and miracles by saints. The saint was a powerful religious individual both in life and in death, a conduit of divine grace and lightning rod for Christian fervour. With her post-mortem presence, the presumptive boundary between living and dead, spirit and flesh, is rent apart: showing the reality of the hereafter and shattering the fantasies of the mortal world. The phenomenon of a glorified individual returning to a worshipful community after their apparent mortal expiration is not just medieval. In April 2012,
the rapper Tupac Shakur “performed” on stage at the Coachella music festival. Tupac was murdered in 1996; his ghostly presence was the result of a hologram. His holographic form, the “Pac-O-Gram”, took to the stage to a breathless crowd of fans.
The holographic performance is a product of technological advances. Yet reports of the holographic performance were filled with references to Tupac’s “resurrection”, a significant word choice, and one which links the rapper’s return with medieval
hagiography more than the advance of technology. What can an examination of the modern example of the Pac-O-Gram and examples drawn from medieval hagiography of the dead returning to life add to each other? "

- by Alicia Spencer-Hall
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- Digital Holography, Medieval Women, Tupac Shakur, Resurrection

Phase-only holographic projection has prompted
a great deal of research and has often been cited as a desirable
method of 2-D image formation, since such a technique offers
a number of advantages over conventional imaging projection
technology [1], [2]. Although holographic image formation was
demonstrated some forty years ago [3], efforts at realizing a
real-time 2-D video projection system based on this technique
have not been successful, principally due to the computational
complexity of calculating diffraction patterns in real time and
the poor quality of the resultant images. In this paper, a new
approach to hologram generation and display is presented which
overcomes both of these problems, enabling—for the first time—a high-quality real-time holographic projector.

- by Edward Buckley
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- Digital Holography, Laser, Optical Communication, LCOS

Sevgili okuyucular, 2015 yılı için hazırladığımız "Eğitim Teknolojileri Okumaları" el kitabı sizlerden gelen katkı ve değerlendirmeler doğrultusunda, bizleri Eğitim Teknolojileri Okumaları 2016 çalışmasını gerçekleştirmeye yönlendirdi. Bu çalışmamızı 2015 yılında olduğu gibi yine IETC-TOJET işbirliği ile sizlere ulaştırıyoruz. Ülkemizin farklı üniversitelerinden 61 akademisyenin 35 bölüme katkıda bulunduğu okumalar alanımızdaki hareketliliğe uygun olarak güncel konuları içermektedir. Bu çalışmanın sizlere ulaşmasındaki katkısından dolayı IETC-TOJET ailesine ve tüm çalışmaların kontrolünü gerçekleştiren Dr. Gökhan DAĞHAN'a sonsuz teşekkürlerimizi sunarız.

We demonstrate a novel computational method for high resolution image recovery from a single digital hologram frame. The complex object field is obtained from the recorded hologram by solving a constrained optimization problem. This approach which is unlike the physical hologram replay process is shown to provide high quality image recovery even when the dc and the cross terms in the hologram overlap in the Fourier domain. Experimental results are shown for a Fresnel zone hologram of a resolution chart, intentionally recorded with a small off-axis reference beam angle. Excellent image recovery is observed without the presence of dc or twin image terms and with minimal speckle noise.

- by Dr Samsheer Ali P T
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- Digital Holography, Microscopy

Dennis Gabor devised a new concept for optical imaging in 1947 that went by a variety of names over the following decade: holoscopy, wavefront reconstruction, interference microscopy, diffraction microscopy and Gaboroscopy. A well-connected and creative research engineer, Gabor worked actively to publicize and exploit his concept, but the scheme failed to capture the interest of many researchers. Gabor’s theory was repeatedly deemed unintuitive and baffling; the technique was appraised by his contemporaries to be of dubious practicality and, at best, constrained to a narrow branch of science. By the late 1950s, Gabor’s subject had been assessed by its handful of practitioners to be a white elephant. Nevertheless, the concept was later rehabilitated by the research of Emmett Leith and Juris Upatnieks at the University of Michigan, and Yury Denisyuk at the Vavilov Institute in Leningrad. What had been judged a failure was recast as a success: evaluations of Gabor’s work were transformed during the 1960s, when it was represented as the foundation on which to construct the new and distinctly different subject of holography, a re-evaluation that gained the Nobel Prize for Physics for Gabor alone in 1971. This paper focuses on the difficulties experienced in constructing a meaningful subject, a practical application and a viable technical community from Gabor’s ideas during the decade 1947-1957.

Scope of the book:
This book focusses on the technical concepts of deep learning and its associated branch Neural Networks for the various dimensions of image processing applications. The proposed volume intends to bring together researchers to report the latest results or progress in the development of the above-mentioned areas. Since there is a deficit of books on this specific subject matter, the editors aim to provide a common platform for researchers working in this area to exhibit their novel findings.
Topics of Interest:
This book solicits contributions, which include the fundamentals in the field of Deep Artificial Neural Networks and Image Processing supported by case studies and practical examples. Each chapter is expected to be self-contained and to cover an in-depth analysis of real life applications of neural networks to image analysis.

- by Vania V Estrela
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- Applied Mathematics, Computer Graphics, Artificial Intelligence, Computer Vision

| This paper presents an overview of the potential of free space optical technology in information security, encryption, and authentication. Optical waveform posses many degrees of freedom such as amplitude, phase, polarization, spectral content, and multiplexing which can be combined in different ways to make the information encoding more secure. This paper reviews optical techniques for encryption and security of two-dimensional and three-dimensional data.

The emerging technological developments across various scientific fields have brought about radical changes in the ways we perceive and define what it means to be human in today’s highly technologically oriented society. Advancements in robotics, AI research, molecular biology, genetic engineering, nanotechnology, medicine, etc., are mostly still in an experimental phase, but it is likely that they will become a part of our daily experience. However, human enhancement and emergence of autonomous artificial beings have long been a part of futures imagined in SF and cyberpunk. While focusing on the phenomenon of cyborg as a product of both social reality and fiction, this chapter will attempt to offer a new perspective on selected SF and cyberpunk narratives by treating them not only as fictions but as theories of the future as well. Furthermore, selected examples of the existing real-life cyborgs will show that SF narratives are not merely limited to the scope of imagination but are a constituent part of lived experience, thus blurring the boundaries between reality and fiction.

- by Jelena Guga
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- Artificial Intelligence, Cyborg Theory, Digital Holography, Cyberpunk

Spatial light modulators (SLM) are devices used to modulate amplitude, phase or polarization of a light wave in space and time. Current SLMs are based either on MEMS (micro-electro-mechanical system) or LCD (liquid crystal display) technology. Here we report on the parameters, trends in development and applications of phase SLMs based on liquid crystal on silicon (LCoS) technology. LCoS technology was developed for front and rear projection systems competing with AMLCD (active matrix LCD) and DMD (Digital Mirror Device) SLM. The reflective arrangement due to silicon backplane allows to put a high number of pixels in a small panel, keeping the fill-factor ratio high even for micron-sized pixels. For coherent photonics applications the most important type of LCoS SLM is a phase modulator. In the paper at first we describe the typical parameters of this device and the methods for its calibration. Later we present a review of applications of phase LCoS SLMs in imaging, metrology and beam manipulation, developed by the authors as well as known from the literature. These include active and adaptive interferometers, a smart holographic camera and holographic display, microscopy modified in illuminating and imaging paths and active sensors.

- by Chang Hwan Park
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- Optics, Digital Holography, Optical Metrology, Phase Modulation

The emerging technological developments across various scientific fields have brought about radical changes in the ways we perceive and define what it means to be human in today"s highly technologically oriented society. Advancements in robotics, AI research, molecular biology, genetic engineering, nanotechnology, medicine, etc., are mostly still in an experimental phase but it is likely that they will become a part of our daily experience. However, human enhancement and emergence of autonomous artificial beings have long been a part of futures imagined in SF and cyberpunk. While focusing on the phenomenon of cyborg as a product of both social reality and fiction, this paper will attempt to offer a new perspective on selected SF and cyberpunk narratives by treating them not only as fictions but as theories of the future as well.

- by Jelena Guga
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- Artificial Intelligence, Cyborg Theory, Digital Holography, Cyberpunk

Using an 850-nanometer-wavelength free-space optical (FSO) communications system of our own design, we acquired field data for the transmitted and received signals in fog at Point Loma, CA for a range of optical depths within the multiple-scattering regime. Statistical estimators for the atmospheric channel transfer function and the related coherency function were computed directly from the experimental data. We interpret the resulting channel transfer function estimates in terms of the physics of the atmospheric propagation channel and fog aerosol particle distributions. We investigate the behavior of the estimators using both real field-test data and simulated propagation data. We compare the fielddata channel transfer function estimates against the outputs from a computationally-intensive radiative-transfer theory model-based approach, which we also developed previously for the FSO multiplescattering atmospheric channel. Our results show that the data-driven channel transfer function estimates are in close agreement with the radiative transfer modeling, and provide comparable receiver signal detection performance improvements while being significantly less time and computationally-intensive.

- by Colin Reinhardt and +1
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- Digital Holography, LiDAR, Modeling and Simulation, Signal Detection Theory

Recording digital holograms without wave interference simplifies the optical systems, increases their power efficiency and avoids complicated aligning procedures. We propose and demonstrate a new technique of digital hologram acquisition without two-wave interference. Incoherent light emitted from an object propagates through a random-like coded phase mask and recorded directly without interference by a digital camera. In the training stage of the system, a point spread hologram (PSH) is first recorded by modulating the light diffracted from a point object by the coded phase masks. At least two different masks should be used to record two different intensity distributions at all possible axial locations. The various recorded patterns at every axial location are superposed in the computer to obtain a complex valued PSH library cataloged to its axial location. Following the training stage, an object is placed within the axial boundaries of the PSH library and the light diffracted from the object is once again modulated by the same phase masks. The intensity patterns are recorded and superposed exactly as the PSH to yield a complex hologram of the object. The object information at any particular plane is reconstructed by a cross-correlation between the complex valued hologram and the appropriate element of the PSH library. The characteristics and the performance of the proposed system were compared with an equivalent regular imaging system.

- by Joseph Rosen
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- Digital Holography

We present a new method to numerically reconstruct images on a tilted plane by digital holography in Fourier configuration. The proposed technique is based on a quadratic deformation of spatial coordinates of the digital hologram. By this approach we demonstrate that it is possible to recover the extended focus image (EFI) of a tilted object in a single reconstruction step from the deformed hologram.

- by Pietro Ferraro
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- Algorithms, Digital Holography, Fourier Analysis, Holography

Nous proposons une méthode permettant la suppression d’images jumelles lors de la
reconstruction des hologrammes numériques enregistrés dans la configuration in-line. Cette
méthode est basée sur la séparation aveugle de mélanges convolutifs de sources. Le procédé
est composé de deux étapes: un schéma de lifting en quinconce basé sur la transformée en
ondelettes, dont le rôle est de permettre une décorrélation des images holographiques d'entrée,
et un algorithme de déconvolution géométrique pour la tâche de séparation. Les résultats
expérimentaux confirment l’efficacité de la séparation aveugle de sources pour l’élimination
de l’image jumelle à partir d'hologrammes numériques de particules.

- by samir belaid
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- Digital Holography, Blind Source Separation, Wavelet Transforms

Digital holograms recorded with a charge-coupled device array are numerically reconstructed in amplitude and phase through calculation of the Fresnel-Kirchhoff integral. The flexibility offered by the reconstruction process in digital holography allows exploitation of new possibilities of application in microscopy. Through the reconstruction process we will show that it is possible to control image parameters as focus distance, image size, and image resolution. Those explored potentialities open further the novel prospective of application of digital holography in single-and multiwavelengths operation either for display or metrological applications. We demonstrate the concept of controlling parameters in image reconstruction of digital holograms in some real situations for inspecting silicon microelectronic-mechanical systems structures.

- by Pietro Ferraro
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- Quantum Physics, Digital Holography, Image Reconstruction, Mechanical systems

We show that digital holography can be combined easily with optical coherence tomography approach. Varying the reference path length is the means used to acquire a series of holograms at different depths, providing after reconstruction images of slices at different depths in the specimen thanks to the shortcoherence length of light source. A metallic object, covered by a 150᎑m-thick onion cell, is imaged with high resolution. Applications in ophthalmology are shown: structures of the anterior eye, the cornea, and the iris, are studied on enucleated porcine eyes. Tomographic images of the iris border close to the pupil were obtained 165 m underneath the eye surface.

Digital holographic microscopy based on Gabor in-line holography is a well-known method to reconstruct both the amplitude and phase of small objects. To reconstruct the image of an object from its hologram, obtained under illumination by monochromatic scalar waves, numerical calculations of Fresnel integrals are required. To improve spatial resolution in the resulting reconstruction, we resample the holographic data before application of the reconstruction algorithm. This procedure amounts to inverting an interpolated Fresnel diffraction image to recover the object. The advantage of this method is demonstrated on experimental data, for the case of visible-light Gabor holography of a resolution grid and a gnat wing.

- by Sergey Podorov
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- Digital Holography, Coherent Diffractive Imaging

Direct-write digital holographic printing (DWDH) is a technique by which color reflection holograms or white-light transmission holograms of an object or a scene can be produced out of a series of suitable perspective images. The technique is well suited to the production of scaled up or down holographic images of objects or scenes allowing at the same time slight movements, animation, layering and multiple channels to be encoded. The series of perspective images can be digitally captured in video or photographs or be produced by rendering frames of a 3d model with the aid of 3d computer graphics software. The Hellenic Institute of Holography (HiH) has been testing the process since 2009 producing suitable series of perspective images by using most of the available image capturing techniques and subsequently printing rendered data by Geola Digital for the visualization of artworks and historic sites. The produced holograms range from small artworks to large scale scenes incorporating in most cases layering, movement or animation. It is of great significance that the video or photographically captured perspective views of a real object or scene, as processed by Geola, result in holograms which recreate 3d images with details resolution far better than those of a 3D model produced from the 2D-to-3D conversion of the same set of perspective views. In this paper we present DWDH printed holograms of various artworks and historic sites, the various methods used for capturing perspective views and the underlying printing processes for eventual use in cultural heritage preservation.

- by Andreas Sarakinos and +2
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- Cultural Heritage, Digital Holography, Museums and Exhibition Design

Progress in image sensors and computation power has fueled studies to improve acquisition, processing, and analysis of 3D streams along with 3D scenes/objects reconstruction. The role of motion compensation/ motion estimation (MCME) in 3D TV from end-to-end user is investigated in this chapter. Motion vectors (MVs) are closely related to the concept of disparities, and they can help improving dynamic scene acquisition, content creation, 2D to 3D conversion, compression coding, decompression/decoding, scene rendering, error concealment, virtual/augmented reality handling, intelligent content retrieval, and displaying. Although there are different 3D shape extraction methods, this chapter focuses mostly on shape-from-motion (SfM) techniques due to their relevance to 3D TV. SfM extraction can restore 3D shape information from a single camera data.

- by Vania V Estrela
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- Computer Science, Computer Graphics, Human Computer Interaction, Computer Vision

This paper describes an imaging microscopic technique based on heterodyne digital holography where subwavelength-sized gold colloids can be imaged in cell environments. Surface cellular receptors of 3T3 mouse fibroblasts are labeled with... more

- by Michael Atlan
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- Optics, Digital Holography, Microscopy, Nanoparticles

Holographic Displays (HDs) provide 3D images with all natural depth cues via computer generated holograms (CGHs) implemented on spatial light modulators (SLMs). HDs are coherent light processing systems based on interference and diffraction, thus they generally use laser light. However, laser sources are relatively expensive, available only at some particular wavelengths and difficult to miniaturize. In addition, highly coherent nature of laser light makes some undesired visual effects quite evident, such as speckle noise, interference due to stray light or defects of optical components. On the other hand, LED sources are available in variety of wavelengths, has small die size, and no speckle artifact. However, their finite spatial size introduce some degree of spatial incoherence in an HD system and degrade image resolution, which is the subject of the study in this paper. Our theoretical analysis indicates that the amount of resolution loss depends on the distance between hologram and SLM image planes. For some special configurations, the source size has no effect at all. We also performed experiments with different configurations using lasers and LEDs with different emission areas that vary from 50 µm to 200 µm, and determined Contrast Transfer Function (CTF) curves which agree well with our theoretical model. The results show that it is possible to find configurations where LEDs combined with pinholes almost preserve natural resolution limit of human eye while keeping the loss in light efficiency within tolerable limits.

- by vahid pourreza ghoushchi and +1
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- Digital Holography, LED Lighting, Coherence, Spatial Coherence

Digital holography is an imaging technique that enables recovery of topographic 3D information about an object under investigation. In digital holography, an interference pattern is recorded on a digital camera. Therefore, quantization of the recorded hologram is an integral part of the imaging process. We study the influence of quantization error in the recorded holograms on the fidelity of both the intensity and phase of the reconstructed image. We limit our analysis to the case of lensless Fourier off-axis digital holograms. We derive a theoretical model to predict the effect of quantization noise and we validate this model using experimental results. Based on this, we also show how the resultant noise in the reconstructed image, as well as the speckle that is inherent in digital holography, can be conveniently suppressed by standard speckle reduction techniques. We show that high-quality images can be obtained from binary holograms when speckle reduction is performed.

- by Nitesh Pandey
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- Mechanical Engineering, Digital Holography, Applied Optics, Optical physics

This paper assesses the ergonomics of the air tap, a 3D gesture used to interact with the Hololens™, a head-mounted optical see-through display being developed by Microsoft™. After reviewing ergonomics literature we found the air tap appeared to be outside of known anthropometric and biomechanical limits and tolerances. Because the Hololens was unavailable for testing at the time of writing, the air tap was evaluated using methods that support general, observational data. The Rapid Entire Body Assessment (REBA), Rapid Upper Body Assessment (RULA) and Novel Ergonomic Postural Assessment (NERPA) methods were used to assess the gesture as observed in four videos. For all methods, higher scores suggested further investigation was required to avoid risk of developing musculoskeletal disorders. Although the neck trunk and leg portion of the REBA score was low, the arm and wrist portions gained more points. This was further reflected in overall high RULA and NERPA scores which focused more on the upper region of the body. Although these findings cannot be used to accurately assess whether the air tap suffers from poor ergonomics or puts the user at risk of developing musculoskeletal disorders, they do suggest the gesture might benefit from a more thorough investigation. This paper concludes by proposing future research into developing and validating an ergonomic framework designers and developers can use to develop 3D gestures.

- by Jed Looker
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- Ergonomics, Digital Holography, Interaction Design, Holography

Digital hologram rendering can be performed by a convolutional neural network, trained with image pairs calculated by numerical wave propagation from sparse generating images. 512-by-512 pixel digital Gabor magnitude holograms are successfully estimated from experimental interferograms by a standard UNet trained with 50,000 synthetic image pairs over 70 epochs. Convolutional neural networks already have demonstrated their potential for digital hologram rendering from optically-acquired interferograms in free-space propagation conditions [1-4] and through scattering media [5-7]. Our aim here is to determine whether an auto-encoder convolutional neural network, a UNet [8], can be trained over a synthetic database for digital hologram rendering from experimental interferograms. A model of wave propagation is used to create synthetic Gabor interferograms and synthetic Gabor magnitude holograms from random images. This image formation model is based on angular spectrum propagation and magnitude calculation of the wave field from the object to the sensor array, and from the sensor to the object. In contrast with previously reported computational image rendering schemes with convolutional neural networks, where image formation is statistically inferred through experimental data [1-4], in our approach it is inferred from synthetic data created by physical modeling of wave interference and propagation. Since the UNet training strategy relies on the strong use of a large and diverse database [8], training on synthetic data alleviates the need for numerous experimental data and data augmentation. The convolutional neural network used in this study is (sketched in Fig. 1) is a standard UNet [8] with an input image of 512 2 pixels, a depth of 7 down sampling blocks and 7 up sampling blocks. Convolution kernels are 3-by-3-by-n pixels, where n is the number of channels of the input feature map. The first set of 16 kernels generates a feature map of n = 16 channels from the input image which has only n = 1 channel. In the down sampling part, the lateral size of the features is divided by two and the number of channels n is multiplied by two between blocks. In the up sampling part, the lateral size of the features is multiplied by two and the number of channels n is divided by two between blocks. Mirror features from the down sampling part are concatenated to their up sampling counterparts. The UNet is trained with 50,000 image pairs (among which 15% are used for validation purposes). The chosen loss function is the mean-square error between predicted image H ′ and actual training output H during the validation process. It is used to measure their inconsistency; the optimization (or deep learning) of the network consists in finding the set of network weights for which this loss function is minimum. The learning rate controls how much the weights of the network are adjusted with respect to the gradient of the loss function. We construct a database of training input and output image pairs by the procedure illustrated in the flowchart from Fig. 2. A square generating image A of 512 2 pixels that describes the amplitude transmission function of a synthetic object is constructed by setting a given number N of source points at random locations with random brightness on a black background, and spatial filtering by a circular aperture in the Fourier plane. The diameter of the aperture is one half of the diagonal of the reciprocal plane. The values of the array A are positive real numbers. A synthetic Gabor interferogram I is calculated from this generating image A by angular spectrum propagation [10] of the wave field described by the transmission function A with a distance parameter −z, followed by a rectification consisting of taking the magnitude of the complex-valued array points

- by Michael Atlan
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- Digital Holography

A digital holographic microscope (DHM) has been employed in the retrieval and analysis of morphological images of bovine's sperm cells. Digital holography is a noncontact technique capable of investigating the shape of the sample without altering its characteristics and has been used for the first time in retrieving quantitative morphological information of sperm cells. Different spermatozoa have been analyzed by means of this technique allowing us to obtain 3-D images with precise topographical details and valuable information about morphological defects, provided with biological considerations. Moreover, by making use of a microfluidic system, the digital holographic technique has been employed to analyze unstained spermatozoa in their natural physiological surroundings. Detailed information on morphological images of spermatozoa acquired by DHM is expected to provide a better understanding of various reproductive pathways, which, in turn, can help in improving infertility management. This could constitute the basis of an alternative method for the zoothecnic industry aimed at the investigation of morphological features and the sorting of the motile sperm cells.

We propose and demonstrate a digital holographic technique for 3D object recognition and classification. One Fresnel digital hologram of each of the 3D objects to be classified is recorded. The electronic holograms are processed digitally to retrieve 3D object information as 2D digital complex images. We use this method to classify four physical objects in a 3D scene into two classes. Results are presented from an experiment to demonstrate the proof of the concept.

- by Joby Joseph
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- Digital Holography, Wavelets, Object Recognition, Matched Filter
- by Polat DALKIRAN
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- Digital Holography, Holography, Holographic Display, Holomap

We develop a deterministic algorithm for coherent diffractive imaging (CDI) that employs a modified Fourier transform of a Fraunhofer diffraction pattern to quantitatively reconstruct the complex scalar wavefield at the exit surface of a sample of interest. The sample is placed in a uniformly-illuminated rectangular hole with dimensions at least two times larger than the sample. For this particular scenario, and in the far-field diffraction case, our non-iterative reconstruction algorithm is rapid, exact and gives a unique analytical solution to the inverse problem. The efficacy and stability of the algorithm, which may achieve resolutions in the nanoscale range, is demonstrated using simulated X-ray data.

- by Sergey Podorov
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- Mechanics, Digital Holography, Alignment, Fourier Analysis

We propose a full color computer generated holographic near-eye display (NED) based on white light illumination. The method inspired from color rainbow holography is used for calculation of 2D and 3D color holograms. The parameters of the color hologram calculation are designed based on the parameters of the spatial light modulator (SLM) with 4K resolution. A slit type spatial filter is designed in frequency domain to extract red, green and blue frequency components for full color display. A NED system including a white light source, an achromatic collimating lens, a 4K SLM, a 4f optical filtering system, and an achromatic lens as eyepiece is designed and developed. The main contribution of this paper is the first time to apply the rainbow holography concept to the dynamic full color NED with a compact display system. The optical experiments prove the feasibility of the proposed method.

- by Hongbo Zhang
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- Digital Holography, Holographic Display

In this study, we propose a method for calculating a large scale high resolution synthetic color
rainbow hologram using the frequency domain splicing technique. This method is motivated by
the observation that if the plane wave is used as the reference light, the spectra of the three
primary colors of the object light in the color rainbow hologram frequency domain are mutually
separated frequency bands. According to this principle, the color views of different angles of a
colored 3D object are separated and interpolated, and 2D Fourier transform is performed to form
an object light spectrum distribution of the color rainbow hologram. Following the operation,
efficient one-dimensional Fourier inverse transform in the row and column directions of the
frequency is conducted. The proposed method is able to achieve a significant boost in terms of
large scale high resolution hologram computational speed. We demonstrate that a synthetic color
rainbow hologram with a size of 30 × 30 mm and a resolution of 94 340 × 94 340 is achieved
through our holographic printing system with an unprecedented time of only 25 min. The
method is also able to achieve a visually appealing computer generated white light color rainbow
hologram, thus having great potential to be used for a practical holographic 3D display.

- by Hongbo Zhang
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- Digital Holography, Computer Generated Holograms, 3D Imaging

One of the main drawbacks of Digital Holography (DH) is the coherent nature of the light source, which severely corrupts the quality of holographic reconstructions. Although numerous techniques to reduce noise in DH have provided good results, holo-graphic noise suppression remains a challenging task. We propose a novel framework that combines the concepts of encoding multiple uncorrelated digital holograms, block grouping and collaborative filtering to achieve quasi noise-free DH reconstructions. The optimized joint action of these different image-denoising methods permits the removal of up to 98% of the noise while preserving the image contrast. The resulting quality of the hologram reconstructions is comparable to the quality achievable with non-coherent techniques and far beyond the current state of art in DH. Experimental validation is provided for both single-wavelength and multi-wavelength DH, and a comparison with the most used holographic denoising methods is performed.

- by Pietro Ferraro and +2
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- Digital Holography, Holography, Holography Laser Projection, Holographic Display

Advances in image sensors and evolution of digital computation is a strong stimulus for development and implementation of sophisticated methods for capturing, processing and analysis of 3-D data from dynamic scenes. Research on perspective time-varying 3-D scene capture technologies is important for the upcoming 3DTV displays. Methods such as shape-from-texture, shape-from-shading, shape-from-focus, and shape-from-motion extraction can restore 3-D shape information from a single camera data. The existing techniques for 3-D extraction from single-camera video sequences are especially useful for conversion of the already available vast mono-view content to the 3DTV systems. Sceneoriented single-camera methods such as human face reconstruction and facial motion analysis, body modeling and body motion tracking, and motion recognition solve efficiently a variety of tasks. 3-D multicamera dynamic acquisition and reconstruction, their hardware specifics including calibration and synchronization and software demands form another area of intensive research. Different classes of multiview stereo algorithms such as those based on cost function computing and optimization, fusing of multiple views, and feature-point reconstruction are possible candidates for dynamic 3-D reconstruction. High-resolution digital holography and pattern projection techniques such as coded light or fringe projection for real-time extraction of 3-D object positions and color information could manifest themselves as an alternative to traditional camera-based methods. Apart from all of these approaches, there also are some active imaging devices capable of 3-D extraction such as the 3-D time-of-flight camera, which provides 3-D image data of its environment by means of a modulated infrared light source.

- by Nikolaos Grammalidis
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- Image Processing, Signal Processing, Digital Holography, Face Recognition

In this study, we demonstrate a practical synthetic hologram with a size of 30 mm × 30 mm at resolution of 94340 × 94340. The high-definition large-scale computer-generated full-parallax synthetic hologram is achieved through frequency mosaic with different perspective images. The sparsity characteristics mosaic frequency of full parallax synthetic hologram is analyzed for reducing the complexity of computation. Following elimination of the sparsity, the hologram is calculated by normalization of 2D inverse Fourier transform of the mosaic frequency. The error and object point size are analyzed and we conclude that the error is sufficiently small for human visual perception given that parallax angle and object depth are within acceptable limits.

A technique based on superresolution by digital holographic microscopic imaging is presented. We used a two dimensional (2-D) vertical-cavity self-emitting laser (VCSEL) array as spherical-wave illumination sources. The method is defined in terms of an incoherent superposition of tilted wavefronts. The tilted spherical wave originating from the 2-D VCSEL elements illuminates the target in transmission mode to obtain a hologram in a Mach-Zehnder interferometer configuration. Superresolved images of the input object above the common lens diffraction limit are generated by sequential recording of the individual holograms and numerical reconstruction of the image with the extended spatial frequency range. We have experimentally tested the approach for a microscope objective with an exact 2-D reconstruction image of the input object. The proposed approach has implementation advantages for applications in biological imaging or the microelectronic industry in which structured targets are being inspected.