Pattern projection profilometry is a powerful tool to reconstruct three-dimensional (3D) surface of diffuse objects. A
variety of pattern projection methods for 3D capture of objects is based on the generation of sinusoidal fringes. A
sinusoidal phase grating under divergent coherent illumination with a point source produces high visibility and high
spectral purity sinusoidal fringes in a large longitudinal region. In the present work we study the speckle suppression in
the fringes by using a polychromatic light source. Such an approach makes use of the fact that the lateral fringe spacing
does not depend on the wavelength of the illuminating light. The wavelength has an impact on the locations and the
number of the Talbot planes, where self-imaging of the grating occurs, and on variation of the contrast and the frequency
content of fringes along the distance from the grating. We analyze the multi-wavelength illumination of the grating by
solving the Fresnel diffraction integral for a point source illumination in paraxial approximation. We verified the
obtained results by experiments with a thin holographic grating recorded on a silver-halide holographic plate under
illumination with a laser diode operating in single mode and multimode regimes.
Infrared digital holograms of different statuettes are acquired. For each object, a sequence of holograms is recorded
rotating the statuette with an angular step of few degrees. The holograms of the moving objects are used to compose
dynamic 3D scenes that, then, are optically reconstructed by means of spatial light modulators (SLMs) using an
illumination wavelength of 532 nm. This kind of reconstruction allows to obtain a 3D imaging of the statuettes that could
be exploited for virtual museums.
"True 3D" display technologies target replication of physical volume light distributions. Holography is a promising
true 3D technique. Widespread utilization of holographic 3D video displays is hindered by current technological
limits; research activities are targeted to overcome such difficulties. Rising interest in 3D video in
general, and current developments in holographic 3D video and underlying technologies increase the momentum
of research activities in this field. Prototypes and recent satisfactory laboratory results indicate that holographic
displays are strong candidates for future 3D displays.
A liquid crystal panel for a video projector is often used for holographic television. However, its pixel size and pixel number are not enough for practical holographic 3-D display. Therefore, a multipanel configuration is generally used to increase the viewing window and displayed image size, and many spatial light modulators should be used in them. We propose a novel method to increase the viewing window of a holographic display system. The proposed method, which is implemented by using a mirror module and 4-f lens set, is to reconfigure the beam shape reflected by a spatial light modulator. The equipment is applied to a holographic display system, which has only a single spatial light modulator; a hologram could be displayed in a wider viewing window by the equipment than that of the conventional method. By the proposed method, the resolution of the reconfigured spatial light modulator has double resolution in the horizontal direction. Inversely, the vertical resolution is decreased. Even if the vertical resolution is decreased, a viewer could get 3-D effect because humans get more 3-D information in the horizontal direction. We have experimented using a liquid crystal on silicon (LcOS), whose resolution is 4096×2160 pixels. The reconfigured resolution by the mirror module is 8192×1080 pixels. From the experiments, the horizontal viewing window is almost two times wider than that without the mirror module. As a result, the hologram can be observed binocularly.
A liquid crystal panel is often used for holographic television.
However, its pixel size and pixel number are not enough for practical holographic 3D display.
Therefore, multi-panel configuration is often used to increase the viewing angle and displayed image size.
However, many spatial light modulators should be used in them. In this paper, we propose a novel method to increase the viewing angle of a holographic display system.
The proposed method, which is implemented by a mirror module, is to reconfigure the beam shape reflected by a spatial light modulator.
In this paper, the equipment is applied to a holographic display system, which has only a single spatial light modulator and can display a hologram in wider viewing angle than that of the conventional method.
By the proposed method, the resolution of the reconfigured spatial light modulator has double resolution in horizontal direction.
Inversely, the vertical resolution is decreased because the human get more 3D information in horizontal direction.
We have experimented using a Liquid Crystal on Silicon, whose resolution is 4,096 x 2,160 pixels.
And the reconfigured resolution by the mirror module is 8,192 x 1,080 pixels.
From the experimental results, the horizontal viewing angle is almost two times wider than that of the conventional method without the mirror module.
We have achieved that the hologram can be observed binocularly.
A common difficulty in displaying a Fresnel hologram in real time the required calculation of huge amounts of information. We propose a novel digital hologram generation method for real-time holographic display. It depends on compensation of the phase-added stereogram, and can generate high-quality holograms rapidly. We describe a generation algorithm for the phase-added stereogram, using the fast Fourier transform (FFT) for fast calculation, and the compensated phase-added stereogram to get a reconstructed image as clear as the Fresnel hologram. Moreover, we present a method to define the optimum size of segmentation to get a clear reconstruction image and to achieve fast computation using the FFT. We have built a demonstration system to implement the proposed method. The system consists of a server, a client, and an optical holographic display system for real-time holographic display. The server generates 3-D information and transmits it on Ethernet. The client receives the information and generates a digital hologram using the compensated phase-added stereogram. Finally, the generated hologram is displayed on the optical holographic display system in real time. We have achieved display of digital holograms at 15 frames/s with 1000 object points.
A typical difficulty to display the Fresnel hologram in real time is calculation of huge information. In this paper,
we propose a method to define the optimum size of segmentation for the Phase-Added Stereogram, which can
generate high quality hologram rapidly, and describe a generation algorithm of the Phase-Added Stereogram
using the Fast-Fourier Transform for fast calculation. Moreover, we have built an optical holographic display
system for real-time holographic display to implement the proposed method. To generate the fringe pattern,
we used 3D information, which is a set of the 3D points converted from a 3D model. Finally, the generated
hologram is displayed on the optical holographic display system in real time. In consequence, we could achieved
that digital hologram can be displayed at 15 frame/second with 1,000 object points.
In this paper, we propose a novel method that can generate a computer-generated hologram (CGH) from the depth stream and color video outputs provided by ENG camera. To generate CGH, distinguished from an existing electronic holographic display system that uses a computer graphic model, we utilizes video image from a depth camera. This procedure consists of two steps that the acquisition of a depth-annotated image of real object, and generation of CGH according to the 3D information that is extracted from the depth cue. Experimentally, we display the generated CGH via a holographic display system using liquid-crystal display.
This study is focused on proposing a creative system that can display 3D hologram on the real-time basis. This method applies 3D display on volume hologram based on CGH. The process of implementing the system consists of two stages of fringe pattern recording for passive component that includes information on hologram, and irradiating object beam. Distinguished from an existing electronic holographic display system, this system is free from the process of a huge calculation that is necessary to compose CGH for a real-time 3D display. Clarifying a theoretical basis on this method, we have proved validity through results of experiments.