Optical: systems and elements – Holographic system or element – Copying by holographic means
Reexamination Certificate
1998-11-18
2001-07-24
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Holographic system or element
Copying by holographic means
C359S022000, C359S023000, C359S034000, C359S035000
Reexamination Certificate
active
06266167
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to the field of holography and, more particularly, to an apparatus and method for replicating a hologram using a steerable beam.
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of holography. More particularly, it concerns methods and devices for creating, replicating, and printing variable size and variable resolution holographic stereograms, holograms, and holographic optical elements using computer rendered images of three-dimensional computer models or using computer processed images.
A holographic stereogram is a type of hologram synthesized or composed from a set of two-dimensional views of a subject. A holographic stereogram is capable of creating the convincing illusion of a solid three-dimensional subject from closely spaced, discrete-perspective, two-dimensional component views. In addition, if the two-dimensional component views are properly generated, a holographic stereogram can also create the illusion of an animated image. Although holographic stereograms can project such special effects, due to limitations in the methods and techniques for printing holographic stereograms, holographic stereograms have generally been expensive, difficult, and time consuming to produce.
Techniques have been developed for reducing the number of steps involved in producing holographic stereograms to one optical printing step. One-step technology usually involves using computer processed images of objects or computer models of objects to build a hologram from a number of contiguous, small, elemental pieces, known as elemental holograms or hogels. This one-step technology eliminates the need to create a preliminary hologram.
To produce a full-parallax, holographic stereogram using traditional one-step technology, a three-dimensional computer model of an object or a scene is created. There are numerous computer graphic modeling programs, rendering programs, animation programs, three dimensional digitalization systems, or combinations of the programs or systems that can be used to generate and manipulate a three-dimensional computer model of an object or a scene. Examples of such programs or systems include, but are not limited to, computer-aided-design (CAD) programs, scientific visualization programs, and virtual reality programs.
In addition, to produce a holographic stereogram using one-step technology requires that the position of the hologram surface and individual elemental holograms relative to an object or a scene be determined. Furthermore, a proper computer graphic camera(s)'s description for an elemental hologram and the size and location of a spatial light modulator (SLM), a device that can display a two-dimensional image, need to be determined.
Once all the aforementioned initial parameters are determined, a two-dimensional projection on the SLM for each elemental hologram is computed based on the computer graphic model of the object or scene that was created, the positions of the elemental holograms, and the computer graphic camera's description for the elemental holograms The two-dimensional projection on the SLM for each elemental hologram may be rendered using various computer graphic techniques. The process of creating two-dimensional views from a three-dimensional object and adding qualities such as variations in color and shade to a computer graphic model is often referred to as rendering. There are numerous methods for rendering. One method is ray-tracing, which computes images by accurately simulating sampled light rays in a computer model. Another method is scan-line conversion, which computes images one raster or line at a time. Typically scan-line rendering does not produce as realistic results as ray tracing. However, scan-line rendering is frequently used in animation packages because it is faster. Another method for using computer graphics to render images for one-step, full-parallax holographic stereograms is described in an article by Halle and Kropp. Halle, M. and Kropp, A., “Fast Computer Graphics Rendering for Full Parallax Spatial Displays,”
Proc. Soc. Photo
-
Opt. Instrum. Eng
. (SPIE), 3011:105-112 (Feb. 10-11, 1997), the disclosure of which is incorporated herein by reference.
When holographic stereograms are produced by either the multi-step or one-step techniques, the reconstructed images may have geometric image distortions. These geometric image distortions may be very apparent, especially in large, billboard size holographic displays or holographic displays in other geometries, such as an alcove or a partial cylinder.
One solution that has been incorporated into multi-step techniques to correct for geometric image distortions for multiplex holograms is discussed in an article by Okada. Okada, K., et. al., “A Method of Distortion Compensation of Multiplex Holograms,”
Optics Communications
, vol. 48, no. 3, pp. 167-170 (Dec. 1, 1983), the disclosure of which is incorporated herein by reference. The technique discussed in Okada's article to correct distortion is a method to correct geometrical and time distortion of a single or monocular viewpoint of a finished hologram. Because it is a post-processing method that takes place after image acquisition, Okada's technique would be inefficient if adopted to generate animated computer graphics for one-step, holographic stereograms. Moreover, Okada's method only produces horizontal-parallax-only transmission type holograms.
Others have developed techniques for pre-distorting one-step, holographic stereograms to reduce distortion in the final holographic display. One such pre-distortion technique is described in a paper by Halle and others. Halle, M. et. al., “The Ultragram: A Generalized Holographic Stereogram,”
Proc. Soc. Photo
-
Opt. Instrum. Eng
. (SPIE), vol. 1461, Practical Holography V, p. 142 (February 1991), the disclosure of which is incorporated herein by reference. Although widely used, typical pre-distortion techniques for one-step methods for producing full-parallax, holographic stereograms are significantly limited by available computer processing speeds and the resolution of images produced by traditional one-step methods. In addition, techniques for pre-distorting one-step, full-parallax, holographic stereograms have not been able to produce comprehensible, animated, one-step, full-parallax, holographic stereograms.
Apparatus for printing one-step, monochromatic, holographic-stereograms have been developed. Typically, such prior art printers, as depicted in
FIG. 1
, include: a monochrome coherent light source
1
, lenses
42
, mirrors
40
, an optical system
89
, a shutter
10
, a mechanism for translating film
69
, holographic recording material
70
, usually in the form of film, a personal computer
85
to control the timing for the exposure sequence, and a separate high-speed computer
87
for image calculations. The prior art printer depicted in
FIG. 1
, was discussed in two articles by Yamaguchi. Yamaguchi, M., et. al., “Development of a Prototype Full-Parallax Holoprinter,”
Proc. Soc. Photo
-
Opt. Instrum. Eng
. (SPIE), vol. 2406, Practical Holography IX, pp. 50-56 (February 1995); and Yamaguchi, M., et. al., “High-Quality Recording of a Full-Parallax Holographic Stereogram with a Digital Diffuser,”
Optics Letters
, vol. 19, no. 2, pp. 135-137 (Jan. 20, 1994), the disclosures of each are incorporated herein by reference. The prior art printer depicted in
FIG. 1
is capable of producing monochromatic holographic stereograms, but not full-color holographic stereograms.
A typical prior art hologram printer, like the one depicted in
FIG. 1
, usually is supported by a vibration isolation table
80
. In addition, the prior art printer depicted by
FIG. 1
uses a HeNe laser for a light source
1
that produces a coherent light beam
5
that may be collimated. A shutter
10
is placed at the output of light source
1
. A beam-splitter
15
splits the light
5
from the light source
1
into an object beam
20
and a reference beam
25
. The polariz
Ferdman Alejandro Jose
Holzbach Mark E.
Klug Michael Anthony
Curtis Craig
Skjerven Morrill & MacPherson LLP
Spyrou Cassandra
Zebra Imaging, Inc.
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