The MIT Mark IV holographic display system employs a novel anisotropic leaky-mode spatial light modulator that allows for the simultaneous and superimposed modulation of red, green, and blue light via wavelength-division multiplexing. This WDM-based scheme for full-color display requires that incoming video signals containing holographic fringe information are comprised of non-overlapping spectral bands that fall within the available 200 MHz output bandwidth of commercial GPUs. These bands correspond to independent color channels in the display output and are appropriately band-limited and centered to match the multiplexed passbands and center frequencies in the frequency response of the mode-coupling device. The computational architecture presented in this paper involves the computation of holographic fringe patterns for each color channel and their summation in generating a single video signal for input to the display. In composite, 18 such input signals, each containing holographic fringe information for 26 horizontal-parallax only holographic lines, are generated via three dual-head GPUs for a total of 468 holographic lines in the display output. We present a general scheme for full-color CGH computation for input to Mark IV and furthermore depict the adaptation of the diffraction specific coherent panoramagram approach to fringe computation for the Mark IV architecture.
This article [Opt. Eng.. 52, (5 ), 055801 (2013)] was originally published on 7 May 2013 with an error in Eq. (1). The second plus sign was corrected to a minus sign, as it appears below:
W(x,s)=∫ ∞ −∞ U(x+x ′ 2 )U ∗ (x−x ′ 2 )e −j2πx ′ s dx ′ . (1).
Minor grammatical corrections were also made.
The paper was corrected online on 8 May 2013. It appears correctly in print.
The Authors
An optical architecture for updatable photorefractive polymer-based holographic displays via the direct fringe writing of computer-generated holograms is presented. In contrast to interference-based stereogram techniques for hologram exposure in photorefractive polymer (PRP) materials, the direct fringe writing architecture simplifies system design, reduces system footprint and cost, and offers greater affordances over the types of holographic images that can be recorded. This paper reviews motivations and goals for employing a direct fringe writing architecture for photorefractive holographic imagers, describes our implementation of direct fringe transfer, presents a phase-space analysis of the coherent imaging of fringe patterns from spatial light modulator to PRP, and presents resulting experimental holographic images on the PRP resulting from direct fringe transfer.
We have previously introduced an architecture for updatable photorefractive holographic display based around direct fringe writing of computer-generated holographic fringe patterns. In contrast to interference-based stereogram techniques for hologram exposure in photorefractive polymer (PRP) materials, the direct fringe writing architecture simplifies system design, reduces system footprint and cost, and offers greater affordances over the types of holographic images that can be recorded. In this paper, motivations and goals for employing a direct fringe writing architecture for photorefractive holographic imagers are reviewed, new methods for PRP exposure by micro-optical fields generated via spatial light modulation and telecentric optics are described, and resulting holographic images are presented and discussed. Experimental results are reviewed in the context of theoretical indicators for system performance.
A holographic television system, featuring realtime incoherent 3D capture and live holographic display is used for experiments
in depth perception. Holographic television has the potential to provide more complete visual representations,
including latency-free motion parallax and more natural affordances for accommodation. Although this technology has potential
to improve realism in many display applications, we investigate benefits in uses where direct vision of a workspace
is not possible. Applications of this nature include work with hazardous materials, teleoperation over distance, and laparoscopic
surgery. In this study, subjects perform manual 3D object manipulation tasks where they can only see the
workspace through holographic closed-circuit television. This study is designed to compare performance at manual tasks
using holographic television compared to performance with displays that mimic 2D, and stereoscopic television.
We have previously introduced the Diffraction Specific Coherent Panoramagram - a multi-view holographic stereogram
that provides correct visual accommodation as well as smooth motion parallax with far fewer views than a normal stereogram.
This method uses scene depth information to generate directionally-varying wavefront curvature, and can be computed
at interactive rates using off-the-shelf graphics processors. In earlier work we used z-buffer information associated
with parallax views rendered from synthetic graphics models; in this paper we demonstrate the computation of Diffraction
Specific Coherent Panoramagrams of real-world scenes captured by cameras.
Image-based holographic stereogram rendering methods for holographic video have the attractive properties of moderate
computational cost and correct handling of occlusions and translucent objects. These methods are also subject to the
criticism that (like other stereograms) they do not present accommodation cues consistent with vergence cues and thus
do not make use of one of the significant potential advantages of holographic displays. We present an algorithm for the
Diffraction Specific Coherent Panoramagram -- a multi-view holographic stereogram with correct accommodation cues,
smooth motion parallax, and visually defined centers of parallax. The algorithm is designed to take advantage of parallel
and vector processing in off-the-shelf graphics cards using OpenGL with Cg vertex and fragment shaders. We introduce
wavefront elements - "wafels" - as a progression of picture element "pixels", directional element "direls", and holographic
element "hogels". Wafel apertures emit controllable intensities of light in controllable directions with controllable
centers of curvature, providing accommodation cues in addition to disparity and parallax cues. Based on simultaneously
captured scene depth information, sets of directed variable wavefronts are created using nonlinear chirps, which
allow coherent diffraction of the beam across multiple wafels. We describe an implementation of this algorithm using a
commodity graphics card for interactive display on our Mark II holographic video display.
Horizontal-parallax-only holographic stereograms of nearly SDTV resolution (336 pixels by 440 lines by 96 views) of
textured and normal-mapped models (500 polygons) are rendered at interactive rates (10 frames/second) on a single
dual-head commodity graphics processor for use on MIT's third-generation electro-holographic display. The holographic
fringe pattern is computed by a diffraction specific holographic stereogram algorithm designed for efficient
parallelized vector implementation using OpenGL and Cg vertex/fragment shaders. The algorithm concentrates on lightfield
reconstruction by holographic fringes rather than the computation of the interferometric process of creating the
holographic fringes.
The novel frequency-multiplexed modulator architecture of the MIT Mark III holo-video display poses a significant
challenge in generation of appropriate video signals. Unlike in our previous work, here it is necessary to generate a
group of adjacent single-sideband RF signals; as this display is intended to be manufacturable at consumer-electronics
prices we face the added requirement of compact and inexpensive electronics that are compatible with standard PC
graphics processors. In this paper we review the goals and architecture of Mark III and then describe our experiments
and results in the use of a hardware/software implementation of Weaver's single-sideband modulation method to upconvert
six 200MHz baseband analog video signals to a set of RF signals covering a nearly contiguous 1GHz range. We
show that our method allows efficient generation of non-overlapping signals without aggressive filtering.
We introduce reconfigurable image projection (RIP) holograms and a method for computing RIP holograms of three-dimensional (3-D) scenes. RIP holograms project one or more series of parallax views of a 3-D scene through one or more holographically reconstructed projection surfaces. Projection surfaces are defined at locations at which the hologram reconstructs a variable number of real or virtual images, called holographic primitives, which collectively compose the surface and constitute exit pupils for the view pixel information. RIP holograms are efficiently assembled by combining a sweep of 2-D parallax views of a scene with instances of one or more precomputed diffractive elements, which are permitted to overlap on the hologram, and which reconstruct the holographic primitives. The technique improves on the image quality of conventional stereograms while affording similar efficient computation: it incorporates realistic computer graphic rendering or high-quality optical capture of a scene, it eliminates some artifacts often present in conventional computed stereograms, and its basic multiply-and-accumulate operations are suitable for hardware implementation. The RIP approach offers flexible tuning of capture and projection together, according to the sampling requirements of the scene and the constraints of a given display architecture.
The MIT second-generation holographic video system is a real-time electro-holographic display. The system produces a single-color horizontal parallax only (HPO) holographic image. To reconstruct a three-dimensional image, Holovideo uses a computed fringe pattern with an effective resolution of 256K samples wide by 144 lines high by 8 bits per sample. In this paper we first describe the implementation of a new computational subsystem for Holovideo, replacing custom computing hardware with commodity PC graphics chips, and using OpenGL. We also report the implementation of stereogram computing techniques that employ the PC hardware acceleration to generate and update holographic images at rates of up to two frames per second. These innovations shrink Holovideo’s physical footprint to fit on the table-top and mark the fastest rate at which full computation and update have been achieved on this system to date. Finally we present first results of implementing the Reconfigurable Image Plane (RIP) method of computing high-quality holograms on this new system.
Simulating mobility tasks in a virtual environment reduces risk for research subjects, and allows for improved experimental control and measurement. We are currently using a simulated shopping mall environment (where subjects walk on a treadmill in front of a large projected video display) to evaluate a number of ophthalmic devices developed at the Schepens Eye Research Institute for people with vision impairment, particularly visual field defects. We have conducted experiments to study subject's perception of "safe passing distance" when walking towards stationary obstacles. The subject's binary responses about potential collisions are analyzed by fitting a psychometric function, which gives an estimate of the subject's perceived safe passing distance, and the variability of subject responses. The system also enables simulations of visual field defects using head and eye tracking, enabling better understanding of the impact of visual field loss. Technical infrastructure for our simulated walking environment includes a custom eye and head tracking system, a gait feedback system to adjust treadmill speed, and a handheld 3-D pointing device. Images are generated by a graphics workstation, which contains a model with photographs of storefronts from an actual shopping mall, where concurrent validation experiments are being conducted.
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