We analyzed the strong impact of noise on the reconstructed images in a self-interference incoherent digital holographic (SIDH) system with spatially incoherent illumination. The analysis involved numerical modelling of the propagation and manipulation of the spherical waves emitted by the point sources that formed the object from the system entrance to the optical sensor, as well as recording of four 8-bit encoded phase-shifted incoherent holograms contaminated by detector shot noise. We synthesized a computer-generated hologram for the point sources in a plane parallel to the sensor plane, using our approach based on the similarities in the holograms of unit amplitude point sources. We assessed the quality of the reconstructed images using popular metrics such as MSE, PSNR, and SSIM. We compared simulation to experimental reconstructions and observed the same noise behavior in both cases.
In this work, we propose to leverage a deep-learning (DL) based reconstruction framework for high quality Swept-Source Optical Coherence Tomography (SS-OCT) images, by incorporating wavelength (λ) space interferometric fringes. Generally, the SS-OCT captured fringe is linear in wavelength space and if Inverse Discrete Fourier Transform (IDFT) is applied to extract depth-resolved spectral information, the resultant images are blurred due to the broadened Point Spread Function (PSF). Thus, the recorded wavelength space fringe is to be scaled to uniform grid in wavenumber (k) space using k-linearization and calibration involving interpolations which may result in loss of information along with increased system complexity. Another challenge in OCT is the speckle noise, inherent in the low coherence interferometry-based systems. Hence, we propose a systematic design methodology WAVE-UNET to reconstruct the high-quality OCT images directly from the λ-space to reduce the complexity. The novel design paradigm surpasses the linearization procedures and uses DL to enhance the realism and quality of raw λ-space scans. This framework uses modified UNET having attention gating and residual connections, with IDFT processed λ-space fringes as the input. The method consistently outperforms the traditional OCT system by generating good-quality B-scans with highly reduced time-complexity.
Dynamic speckle technique (DST) is based on speckle formation on the surface of objects illuminated with coherent light. Temporal speckle intensity fluctuations depend on the speed of micro-changes ongoing within the controlled objects. The DST visualizes as a set of 2D activity maps the temporal change of spatial speed distributions. In general, the DST set-up comprises components as a laser source with the required optics, vibration-isolated table, high-resolution camera and computer for data storage and image processing. Such setups are stationary, massive and relatively expensive, which decreases the number of possible DST biological or industrial applications. In this paper we propose a miniature portable device, based on a low-cost laser attached to a smartphone, and checked its efficiency under the field conditions. A strong argument for using a portable set-up is the fact that the absolute values of the speckle intensity are not needed to construct a reliable activity map. We proved this conclusion by numerical simulation of DST in noisy environment. We studied speckle patterns captured with a smartphone’s camera. A personal computer (PC) was used for postprocessing of speckle images. We conducted four sets of experiments. The raw data were recorded on the PC while the smartphone was connected as i) IP-camera and ii) USB-camera. In the third experiment, speckle images were captured and stored in the smartphone’s memory. Data were transferred to the PC after the end of recording. To obtain ground truth activity maps, we repeated the experiment with the same object under laboratory conditions.
We have successfully implemented and reported 360-degree viewable tabletop-style holographic display prototype systems. In order to support 360 degree horizontal viewing angle, which is very much wider than previous systems, we used binary amplitude modulating DMD device as SLM of the display system. DMD has higher total data rate due to its high refresh rate, which is denoted as extended SBP or eSBP, than other SLM devices like LCD or LCoS. This is much beneficial for the system design aiming at wider viewing angle or larger image size. However, Binary amplitude modulating hologram has inherent limitation in terms of resulting hologram image quality, and thus there has been lots of studies on quality-improving coding algorithms like BERD or DBS. In this paper, pros and cons of using DMD in holographic display system are discussed, and in-depth analysis and experimental results are presented on the behavior and limitations of the reconstructed image quality based on our prototype system. Image quality is measured with various metrics like 3D-MTF, depth resolution and color reproducing fidelity for different pixel resolutions from QVGA up to 4K UHD. 3D-MTF represents lateral image resolution and depth resolution has to do with degree of supporting accommodation of human vision in holographic displays. Based on these observations, we draw some projection on the required pixel resolutions of binary modulating SLM device for achieving acceptable hologram image quality.
Generally in electronic holographic display systems, coherent light sources are used to reconstruct holograms. The random distribution of phase profile of an object image causes unwanted dark and bright spots to degrade reconstructed hologram images. In addition, a periodic structure of available spatial light modulators such as liquid crystal on silicon devices and digital micro-mirror devices generates various diffractive signals when they are illuminated by coherent light sources. Consequently, it is necessary to select a proper signal band in spatial frequency domain by effectively filtering out unwanted signals. In this paper, the speckle pattern in a table-top holographic display system is measured and the method for reducing the speckle patterns is to be shown.
We have designed and successfully implemented 360-degree viewable holographic display prototype systems. Core idea of the system design lies in the exploitation of fast operating speed of DMD for binary amplitude modulation of light field, being distributed to more than 1,000 viewpoints along the 360 degree viewing circumference. Slanted downward viewing angle and 360 degree viewable 3-dimensional(3D) image over the center of tabletop display is achieved by specially designed optics. As a result, solid-looking 3D moving color images of larger than 3 inches are rendered and observed by several viewers at the same time from different viewing positions. We have implemented and experimented several variations of the system. They are tiling of SLM modules(2x2 tiling with 4 DMDs for mono-color display and 1x2 tiling with 6 DMDs for color display), using different SLMs(DMD of pixel pitch 13.68μm and resolution 1,024x768, DMD of pixel pitch 10.8μm and resolution 1,920x1,200), and applying different structure of image floating optics((1)double parabolic mirrors, (2)one parabolic mirror and one beam splitter, (3)two spherical and one flat mirror). We report the result of various display system implementations based on several combinations of above-mentioned design options.
Space bandwidth product (SBP) is one of the most significant limitation for displaying the digital holographic display. Due to the SBP problem, the size and viewing angle of displayed holograms cannot be enlarged simultaneously. To overcome the SBP problem, holographic projection system has been researched. It uses a field lens to converge diffracted light from a spatial light modulator (SLM) into a viewing window, where the observer can see whole hologram image displayed on the SLM. However, it has a problem that the viewing distance between the display and observer cannot be controlled and fixed on the viewing window plane. We propose a method to control the position of viewing window formation in the holographic projection system by using an electrically focus tunable lens. We added the focus tunable lens in the holographic projection system, and the position of the viewing window can be controlled by its lens power variation. The principle of controlling viewing window in the proposed system is described, and the relationship among the optical power of focus tunable lens, location and size of the viewing window is analyzed. A computer generated hologram encoding based on Fresnel diffraction theory is developed to generate hologram contents for the proposed system with consideration of varying optical power of the focus tunable lens. Test-bed is built to verify the feasibility of the proposed method, and the experimental results confirm that the proposed method can effectively control the viewing window position of the holographic projection system.
In this paper, we use an optical method for the implementation of spatially-tiled digital micro-mirror devices (DMDs) to expand space bandwidth product in general digital holographic display systems. In concatenating more than two spatial light modulators (SLMs) optically, there may exist both phase discontinuity and amplitude mismatching of hologram images emanating from two adjacent SLMs. To observe and estimate those properties in digital holographic display systems, we adopt quantitative phase imaging technique based on transport of intensity equation.
Autostereoscopic (glasses-free) displays provide perspectives of images according to the position of the observer. This book introduces various autostereoscopic technologies, from the fundamental principles of the parallax-barrier method to the latest multi-projection, super multi-view displays. Display basics and fundamentals of 3D displays are presented first, followed by descriptions of multi-view system configurations. Because the technological advancement of conventional 2D display affects the development of 3D displays, the book also covers the basics of 2D displays, including flat panel and projection-type displays. For readers with some knowledge of 3D display technologies, detailed explanations of advanced display technologies such as the slanted lens technique and multi-projection system are also included. The book is suitable for readers ranging from undergraduate students to display manufacturers in the industry.
Conventionally the elemental lenses of the lens-array used in integral imaging have spherical surface profiles, thus they suffer from intrinsic lens aberrations such as spherical aberration and astigmatism. Aberrations affect the ability of the lens to focus light in a single point, or to collimate light from a point source. In integral imaging, this results in a loss of image quality of the reconstructed image due to distortions. The viewing characteristics of the integral imaging system, such as viewing angle and image resolution, are also affected by aberrations. We propose the use of a custom made aspherical lens-array which was specifically designed to minimize distortions due to aberrations and hence improve the reconstructed image quality. Ray optics calculations are used in order to analyze the aberrations and find the initial lens surface profile. Lens optimization is performed with the aid of numerical simulation software. The designed lens-array is compared to a conventional spherical lens-array of same properties. The design, optimization, and fabrication processes are described and the experiments are presented and compared with the computer simulations.
We proposed a glasses-free randot stereotest using a multiview display system. We designed a four-view parallax barrier system and proposed the use of a random-dot multigram as a set of view images for the glasses-free randot stereotest. The glasses-free randot stereotest can be used to verify the effect of glasses in a stereopsis experience. Furthermore, the proposed system is convertible between two-view and four-view structures so that the motion parallax effect could be verified within the system. We discussed the design principles and the method used to generate images in detail and implemented a glasses-free randot stereotest system with a liquid crystal display panel and a customized parallax barrier. We also developed graphical user interfaces and a method for their calibration for practical usage. We performed experiments with five adult subjects with normal vision. The experimental results show that the proposed system provides a stereopsis experience to the subjects and is consistent with the glasses-type randot stereotest and the Frisby–Davis test. The implemented system is free from monocular cues and provides binocular disparity only. The crosstalk of the system is about 6.42% for four-view and 4.17% for two-view, the time required for one measurement is less than 20 s, and the minimum angular disparity that the system can provide is about 23 arc sec.
In this paper, we propose a glasses-free random dot stereoacuity test using a multi-view display system. We use a multiview display system with a liquid crystal display panel and a parallax barrier. We generate the random dot base images with different disparities. The multi-view system and the generated base images provide several random dot stereotest images to the patient. The proposed method can offer not only binocular disparity but also motion parallax. We implement 4-view parallax barrier system with a 5K liquid crystal display monitor, and generate the random dot base images for the system. For the practical usage, we also develop graphical user interface of the stereoacuity test which contains the personal calibration function in pixel unit.
An Airy beam is a non-diffractive wave which propagates along a ballistic trajectory without any external force.
Although it is impossible to implement ideal Airy beams because they carry infinite power, so-called finite Airy beams
can be achieved by tailoring infinite side lobes with an aperture function and they have similar propagating
characteristics with those of ideal Airy beams. The finite Airy beam can be optically generated by several ways: the
optical Fourier transform system with imposing cubic phase to a broad Gaussian beam, nonlinear generation of Airy
beams, curved plasma channel generation, and electron beam generation. In this presentation, a holographic generation
of the finite Airy beams will be discussed. The finite Airy beams can be generated in virtue of holographic technique by
‘reading’ a hologram which is recorded by the interference between a finite Airy beam generated by the optical Fourier
transform and a reference plane wave. Moreover, this method can exploit the unique features of holography itself such as
successful reconstruction with the imperfect incidence of reference beam, reconstruction of phase-conjugated signal
beam, and multiplexing, which can shed more light on the characteristics of finite Airy beams. This method has an
advantage in that once holograms are recorded in the photopolymer, a bulky optics such as the SLM and lenses are not
necessary to generate Airy beams. In addition, multiple Airy beams can be stored and reconstructed simultaneously or
individually.
KEYWORDS: Holograms, Wavefronts, 3D image reconstruction, Digital holography, Holography, Charge-coupled devices, Image processing, Interferometry, Near field optics, Wave propagation
We propose a digital hologram generation method from diffracted intensity images based on the transport of intensity
equation. In this paper we do experiment to verify the proposed method with coherent illumination with simple
experiment setup using the intensity images capture process. The experiment results show that our proposed method has
advantages compared to both the conventional holography with interferometry and the hologram generation based on
multiple intensity images.
We propose three-dimensional floating display which uses a concave cylindrical mirror (CCM), wedge prisms, and a
digital micro-mirror device (DMD). Wedge prisms can make the direction of projected images tilt by a specific angle
from the incident direction. In our system, wedge prisms are rotated to project images to whole direction of the
cylindrical mirror. Projected images from the DMD projector are reflected and distorted by the CCM simultaneously. We
generate inversely distorted images to correct the image distortions to display original images. As the wedge prisms
rotate, the tilt angle in the longitudinal plane of the CCM rotates. This means that images from the DMD can be
projected in any horizontal direction. Viewers can see 3D objects with horizontal parallax in any horizontal direction.
The further explanation of the proposed system is provided, and the experimental results are also presented.
KEYWORDS: 3D image processing, 3D image reconstruction, 3D displays, Integral imaging, 3D acquisition, Clouds, Optical flow, 3D modeling, OpenGL, Image processing
Computational reacquisition for real 3D object in integral imaging is proposed. The pseudoscopic problem and matching
of lens array in pickup and display are fundamental problems for real-time broadcasting based on integral imaging. We
propose the reconstruction method of real 3D object and computational reacquisition method without matching of pickup
and display lens array. In reconstruction, the real 3D object is reconstructed with volumetric information using depth
extraction and triangular mesh, which can be rotated and translated in orthoscopic geometry. In reacquisition, the virtual
lens array can generate the elemental image without matching of pickup lens array using OpenGL.
Accommodative response measurement according to angular resolution in autostereoscopic display based on lenticular
lens and lens array method is presented. Conflict between accommodation and convergence is one of the most dominant
factors leading to visual fatigue in viewing three-dimensional display. The conflict originates from directional rays that
do not have enough angular resolution density. Therefore the purpose of this paper is to verify the relationship between
angular resolution density of elemental images and accommodation-convergence conflict. For measurement of
accommodation response of a single eye, we used lens arrays and elemental images with different resolution densities.
A sub-pixel resolution disparity estimation method using MAP registration in elemental image based on integral imaging
is proposed. Accurate depth map extraction method is an important research issue in the latest researches about threedimensional
(3D) content developments. We capture a 3D object using lens array, and generate elemental images. Many
previous researches calculated disparity of each elemental image using sum of square distance; however, the accuracy of
disparity is limited by one pixel unit. For enhancing accuracy of estimated disparity, we adapt the maximum a priori
(MAP) registration algorithm to elemental image set. The proposed method can calculate each disparity of elemental
image set in sub-pixel resolution using MAP registration optimization.
In this paper, a high-definition integral floating display is implemented. Integral floating display is composed of an
integral imaging system and a floating lens. The integral imaging system consists of a two-dimensional (2D) display and
a lens array. In this paper, we substituted multiple spatial light modulators (SLMs) for a 2D display to acquire higher definition. Unlike conventional integral floating display, there is space between displaying regions of SLMs. Therefore, SLMs should be carefully aligned to provide continuous viewing region and seamless image. The implementation of the system is explained and three-dimensional (3D) image displayed by the system is represented.
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