U.S. patent application number 11/427655 was filed with the patent office on 2006-10-26 for video hologram and device for reconstructing video holograms using wavefront at eyes.
This patent application is currently assigned to SEEREAL TECHNOLOGIES GMBH. Invention is credited to ARMIN SCHWERDTNER.
Application Number | 20060238844 11/427655 |
Document ID | / |
Family ID | 32308559 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060238844 |
Kind Code |
A1 |
SCHWERDTNER; ARMIN |
October 26, 2006 |
VIDEO HOLOGRAM AND DEVICE FOR RECONSTRUCTING VIDEO HOLOGRAMS USING
WAVEFRONT AT EYES
Abstract
A method of computing a hologram by determining the wavefronts
at the approximate observer eye position that would be generated by
a real version of an object to be reconstructed. In normal computer
generated holograms, one determines the wavefronts needed to
reconstruct an object; this is not done directly in the present
invention. Instead, one determines the wavefronts at an observer
window that would be generated by a real object located at the same
position of the reconstructed object. One can then back-transform
these wavefronts to the hologram to determine how the hologram
needs to be encoded to generate these wavefronts. A suitably
encoded hologram can then generate a reconstruction of the
three-dimensional scene that can be observed by placing one's eyes
at the plane of the observer window and looking through the
observer window.
Inventors: |
SCHWERDTNER; ARMIN;
(DRESDEN, DE) |
Correspondence
Address: |
SYNNESTVEDT LECHNER & WOODBRIDGE LLP
P O BOX 592
PRINCETON
NJ
08542-0592
US
|
Assignee: |
SEEREAL TECHNOLOGIES GMBH
BLASWITZER STRASSE43
DRESDEN
DE
|
Family ID: |
32308559 |
Appl. No.: |
11/427655 |
Filed: |
June 29, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10534877 |
May 12, 2005 |
|
|
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PCT/DE03/03791 |
Nov 11, 2003 |
|
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11427655 |
Jun 29, 2006 |
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Current U.S.
Class: |
359/32 |
Current CPC
Class: |
G03H 1/08 20130101; G03H
2001/0858 20130101; G03H 1/2294 20130101; G03H 2001/2271 20130101;
G03H 2210/30 20130101; G03H 2222/22 20130101; G03H 2226/05
20130101; G03H 1/16 20130101; G03H 2001/2242 20130101; G03H 2222/34
20130101; G03H 2001/2236 20130101; G03H 1/2286 20130101 |
Class at
Publication: |
359/032 |
International
Class: |
G03H 1/22 20060101
G03H001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 13, 2002 |
DE |
10253292.3 |
Claims
1. A method of computing a hologram by determining the wavefronts
at the approximate observer eye position that would be generated by
a real version of an object to be reconstructed.
2. The method of claim 1 in which the wavefronts are reconstructed
by the hologram.
3. The method of claim 1 in which the wavefronts are calculated for
one or more observer windows.
3. The method of claim 1 in which the hologram is illuminated by a
light source and an optical system such that only when an
observer's eyes are positioned approximately at the image plane of
the light source can the holographic reconstruction be seen
properly.
4. The method of claim 1 in which a reconstructed point of the
object is visible from the observer eye position, and is
characterized in that: a region on the hologram (a) encodes
information for that reconstructed point and (b) is the only region
in the hologram encoded with information for that point, and (c) is
restricted in size to form a portion of the entire hologram, the
size being such that multiple reconstructions of that point caused
by higher diffraction orders are not visible at the observer eye
position.
5. The method of claim 1 comprising the step of generating the
holographic information by time sequentially re-encoding a hologram
on the hologram-bearing medium for the left and then the right eye
of an observer.
6. The method of claim 1 in which the holographic reconstruction of
the point is the Fresnel transform of the hologram and not the
Fourier transform of the hologram.
7. The method of claim 1 in which the encoding is such that, on
reconstruction, a direct or inverse Fourier transform of the
hologram is generated at the observer eye position.
8. The method of claim 1 in which the reconstructed three
dimensional scene can be anywhere within a volume defined by a
medium bearing the hologram and the observer eye position.
9. The method of claim 1 in which the observer eye position is
smaller than a medium bearing the hologram.
10. The method of claim 1 in which there are separate observer
windows, one for each eye of an observer.
11. The method of claim 10 in which each observer window is
approximately 1 cm.times.1 cm.
12. The method of claim 1 in which the location of an observer's
eyes are tracked and the observer eye position is altered so that
the observer can maintain a view of a reconstruction of the object
even when moving his or her head.
13. The method of claim 1 in which the size of the observer eye
position is calculated as a function of the periodicity interval of
the hologram.
14. The method of claim 1 in which a medium bearing the hologram is
a TFT flat screen.
15. The method of claim 1 in which a medium bearing the hologram is
a display screen in a television.
16. The method of claim 1 in which a medium bearing the hologram is
a display screen in a multimedia device.
17. The method of claim 1 in which a medium bearing the hologram is
a display screen in a gaming device.
18. The method of claim 1 in which a medium bearing the hologram is
a display screen in a medical image display device.
19. The method of claim 1 in which a medium bearing the hologram is
a display screen in a military information display device.
20. A holographic reconstruction generated from a hologram computed
using the method defined in claim 1.
21. A computer adapted to generate holographic reconstructions
using video holograms computed using the method defined in claim
1.
22. A method of generating a holographic reconstruction of a three
dimensional scene using a display device and a computer, the device
including a light source and an optical system to illuminate a
hologram-bearing medium; comprising the steps of: (a) using the
computer to encode a hologram on the hologram-bearing medium; the
hologram having been computed using the method of claim 1; (b)
illuminating the hologram bearing medium using the light source and
optical system so that the reconstructed three dimensional scene is
visible.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/534,877 filed by A. Schwerdtner on May 12,
2005 entitled "Video Hologram and Device for Reconstructing Video
Holograms", the contents of which are hereby incorporated by
reference.
[0002] U.S. patent application Ser. No. 10/534,877 application is,
in turn, related to, and claims priority from, PCT patent
application PCT/DE03/03791 filed on Nov. 11, 2003 and to German
Patent application DE 10253292.3 filed on Nov. 13, 2002, the
contents of both of which are hereby incorporated by reference.
FIELD OF THE INVENTION
[0003] The present invention relates to a video hologram and a
device for reconstructing video holograms having an optical system
that includes at least one light source, a lens and a
hologram-bearing medium composed of cells arranged in a matrix or
an otherwise regular pattern, with at least one opening per cell,
and with the phase or amplitude of the opening being
controllable.
BACKGROUND OF THE INVENTION
[0004] Devices for reconstructing video holograms using
acousto-optical modulators (AOM) are known from prior art, as
detailed in, for instance, U.S. Pat. No. 5,172,251 issued to Benton
et al. on Dec. 15, 1992 entitled "Three dimensional display
system," the contents of which are hereby incorporated by
reference. Such acousto-optical modulators transform electric
signals into optical wave fronts, which are recomposed in a video
frame using deflection mirrors to form two-dimensional holographic
areas. A scene visible for the viewer is reconstructed from the
individual wave fronts using further optical elements. The optical
means used, such as lenses and deflection elements, have the
dimensions of the reconstructed scenes. Due to their great depth,
these elements are voluminous and heavy. It is difficult to
miniaturize them, so that their range of applications is
limited.
[0005] Another way to generate large video holograms is the
so-called "tiling method", using computer-generated holograms
(CGH). This method is described in for instance PCT patent
publication WO 00/75698 of PCT Patent application PCT/GB2000/001901
filed on May 18, 2000 by Pain et. al entitled "Holographic
Displays" and in U.S. Pat. No. 6,437,919 B1 issued to Brown, et al.
on Aug. 20, 2002 "System for the production of a dynamic image for
display", both of which are hereby incorporated by reference. In
the tiling method, small CGHs having a small pitch are created
using an optical system. In the first step of the method, the
required information is written to fast matrices that have a small
pitch, such as electronically addressable spatial light modulators
(EASLM). These fast matrices are then reproduced on to a portion of
a suitable holographic medium. A large video hologram is composed
of the tiled replicas of the fast matrices. Usually, an optically
addressable spatial light modulator (OASLM) is used as holographic
medium. In a second step, the composed video hologram is
reconstructed with coherent light in transmission or
reflection.
[0006] In the CGH with controllable openings arranged in a matrix
or in an otherwise regular pattern as described in, for instance,
PCT publications number WO 01/95016 A1 of PCT patent application
PCT/GB2001/002302 filed on May 24, 2001 by Payne et al. entitled
"Computation Time Reduction for Three-Dimensional Displays" or in
Fukaya et al., "Eye-position tracking type electro-holographic
display using liquid crystal devices", Proceedings of EOS Topical
Meeting on Diffractive Optics, 1997, the diffraction on small
openings is taken advantage of for encoding the scenes. The wave
fronts emerging from the openings converge in object points of the
three-dimensional scene before they reach the viewer. The smaller
the pitch, and thus the smaller the openings in the CGHs, the
greater is the diffraction angle, i.e. the viewing angle.
Consequently, with these known methods enlarging the viewing angle
means to improve the resolution.
[0007] As is generally known, in Fourier holograms the scene is
reconstructed as a direct or inverse Fourier transform of the
hologram in a plane. This reconstruction is continued periodically
at a periodicity interval, the extension of the periodicity
interval being inversely proportional to the pitch in the
hologram.
[0008] If the dimension of the reconstruction of the Fourier
hologram exceeds the periodicity interval, adjacent diffraction
orders will overlap. As the resolution is gradually decreased, i.e.
as the pitch of the openings increases, the edges of the
reconstruction will be increasingly distorted by overlapping higher
diffraction orders. The usable extent of the reconstruction is thus
gradually limited.
[0009] If greater periodicity intervals and thus greater viewing
angles are to be achieved, the required pitch in the hologram comes
closer to the wavelength of the light. Then, the CGHs must be
sufficiently large in order to be able to reconstruct large scenes.
These two conditions require a large CGH having a great number of
openings. However, this is currently not feasible in the form of
displays with controllable openings, as discussed in, for instance,
U.S. Pat. No. 6,831,678 issued to Travis on Dec. 14, 2004 entitled
"Autostereoscopic display", the contents of which are hereby
incorporated by reference. CGH with controllable openings only
measure one to several inches, with the pitches still being
substantially greater than 1 .mu.m.
[0010] The two parameters, pitch and hologram size, are
characterized by the so-called space-bandwidth product (SBP) as the
number of openings in the hologram. If the reconstruction of a CGH
with controllable openings that has a width of 50 cm is to be
generated so that a viewer can see the scene at a distance of 1 m
and in a 50-cm-wide horizontal viewing window, the SBP in
horizontal direction is about 0.5.times.10.sup.6. This corresponds
to 500,000 openings at a distance of 1 .mu.m in the CGH. Assuming
an aspect ratio of 4:3, 375,000 openings are required in the
vertical direction. Consequently, the CGH comprises
3.75.times.10.sup.11 openings, if three color sub-pixels are taken
into consideration. This number will be tripled if the fact is
taken into account that the CGH with controllable openings usually
only allows the amplitudes to be affected. The phases are encoded
taking advantage of the so-called detour phase effect, which
requires at least three equidistant openings per sampling point.
SLM having such a great number of controllable openings are
hitherto unknown.
[0011] The hologram values must be calculated from the scenes to be
reconstructed. Assuming a color depth of 1 Byte for each of the
three primary colors and a frame rate of 50 Hz, a CGH requires an
information flow rate of 50*10.sup.12=0.5*10.sup.14 Byte/s. Fourier
transformations of data flows of this magnitude exceed the
capabilities of today's computers by far and do thus not allow
holograms to be calculated based on local computers. However,
transmitting such an amount of data through data networks is
presently unfeasible for normal users.
[0012] In order to reduce the enormous number of computations it
has been proposed not to calculate the entire hologram, but only
such parts of it that can be seen directly by the viewer, or such
parts that change. The kind of hologram which consists of
addressable sub-regions, such as the above-mentioned "tiling
hologram", is disclosed in the above-mentioned patent specification
WO 01/95016 A1. Starting point of the calculations is a so-called
effective exit pupil, the position of which can coincide with the
eye pupil of the viewer. The image is tracked as the viewer
position changes by continuous recalculation of the hologram part
that generates the image for the new viewer position. However, this
partly nullifies the reduction in the number of computations.
[0013] The disadvantages of the known methods can be summarized as
follows: Arrangements with acousto-optical modulators are too
voluminous and cannot be reduced to dimensions known from
state-of-the-art flat displays; video holograms generated using the
tiling method are two-stage processes which require enormous
technical efforts and which cannot easily be reduced to desktop
dimensions; and arrangements based on SLM with controllable
openings are too small to be able to reconstruct large scenes.
There are currently no large controllable SLM with extremely small
pitches, which would be needed for this, and this technology is
further limited by the computer performance and data network
bandwidth available today.
SUMMARY OF THE INVENTION
[0014] The invention is defined in Claim 1. In one implementation,
video holograms and devices for reconstructing video holograms with
controllable openings according to the present invention are
characterized in that in the viewing plane at least one viewing
window is formed in a periodicity interval as a direct or inverse
Fourier transform of the video hologram, said viewing window
allowing a viewer to view a reconstruction of a three-dimensional
scene. The maximal extent of the viewing window corresponds to the
periodicity interval in the plane of the inverse Fourier
transformation in the image plane of the light source. A frustum
stretches between the hologram and the viewing window. This frustum
contains the entire three-dimensional scene as a Fresnel transform
of the video hologram.
[0015] The viewing window is limited approximately to and
positioned in relation to one eye, an eye distance of a viewer or
to another suitable area.
[0016] In an implementation, another viewing window is provided for
the other eye of the viewer. This is achieved by the fact that the
observed light source is displaced or added a second, real or
virtual, adequately coherent light source at another suitable
position to form a pair of light sources in the optical system.
This arrangement allows the three-dimensional scene to be seen with
both eyes through two associated viewing windows. The content of
the video hologram can be changed, i.e. re-encoded, according to
the eye position in synchronism with the activation of the second
viewing window. If several viewers view the scene, more viewing
windows can be generated by turning on additional light
sources.
[0017] In another implementation of the device for reconstructing a
video hologram, the optical system and the hologram-bearing medium
are arranged so that the higher diffraction orders of the video
hologram have a zero point for the first viewing window or an
intensity minimum at the position of the second viewing window.
This prevents the viewing window for one eye to cross-talk the
other eye of the viewer or to other viewers. It is thus taken
advantage of the decrease in intensity of the light towards higher
diffraction orders, which is due to the finite width of the
openings of the hologram-bearing medium and/or the minima of the
intensity distribution. The intensity distribution for rectangular
openings, for example, is a sinc.sup.2 function which rapidly
decreases in amplitude and forms a sin.sup.2 function which
decreases as the distance grows.
[0018] The number of openings in the display determines the maximum
number of values that must be calculated for the video hologram.
The transmission of data from a computer or through a network to
the display representing the video hologram is limited to the same
number of values. The data flow rate does not substantially differ
from the data flow rates known from typical displays used today.
Now, this will be illustrated with the help of an example.
[0019] If the viewing window is reduced, for example, from 50 cm
(horizontal) by 37.5 cm (vertical) to 1 cm by 1 cm by choosing a
sufficiently low-resolution display, the number of openings in the
hologram will drop to 1/1875. The required bandwidth is reduced in
the same way during data transmission through a network. Video
holograms created with known methods require 10.sup.12 openings,
while this number is reduced to 510.sup.8 pixels in this example.
The scene can be viewed in full through the remaining viewing
window. These requirements on pitch and hologram size according to
the space-bandwidth product can already be fulfilled by displays
available today. This allows the inexpensive realization of large
real-time video holograms on displays with large pitches and having
a large viewing window.
[0020] The viewing window is tracked by mechanically or
electronically displacing the light sources, by using movable
mirrors or by using light sources which can be adequately
positioned in any other way. The viewing windows are displaced
according to the displacement of the light source images. If the
viewer moves, the light source(s) is (are) spatially displaced so
that the viewing windows follow the eyes of the viewer(s). This is
to ensure that the viewers can also see the reconstructed
three-dimensional scene when they move, so that their freedom of
movement is not limited. Several systems are known for detecting
the position of the viewers, e.g. systems based on magnetic sensors
can be used beneficially for this.
[0021] An implementation of this invention also allows the
efficient reconstruction of a video hologram in color. Here, the
reconstruction is performed with at least three openings per cell,
representing the three primary colors. The amplitude or phase of
the openings may be controllable, and the openings may be encoded
individually for each of the primary colors. Another possibility of
reconstructing a video hologram in color is to perform at least
three reconstructions one after another, namely for the individual
primary colors, using the device of the present invention.
[0022] An implementation of this invention allows the efficient
generation of holographic reconstructions of spatially extended
scenes through controllable displays, such as TFT flat screens, in
real-time and providing large viewing angles. These video holograms
can be used beneficially in TV, multimedia, game and design
applications, in the medical and military sectors, and in many
other areas of economy and society. The three-dimensional scenes
can be generated by a computer or in any other way.
[0023] These and other features of the invention will be more fully
understood by references to the following drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] An embodiment of the present invention is illustrated and
explained below in conjunction with the accompanying drawings,
wherein
[0025] FIG. 1 is a general illustration of a video hologram and a
device for reconstructing video holograms showing the generation of
the diffraction orders and the position of a viewing window;
[0026] FIG. 2 is a general illustration of a device for
reconstructing video holograms showing a three-dimensional scene
which can be viewed through a viewing window;
[0027] FIG. 3 is a general illustration of a device for
reconstructing video holograms showing the encoding of the
three-dimensional scene in a part of the video hologram;
[0028] FIG. 4 is a diagram showing the light intensity distribution
in the viewing plane depending on the diffraction orders; and
[0029] FIG. 5 is a general illustration of a device for
reconstructing video holograms showing the position of the viewing
windows for both eyes of a viewer with regard to the diffraction
orders to prevent cross-talking.
DETAILED DESCRIPTION
[0030] A device for reconstructing video holograms comprises the
hologram-bearing medium, a sufficiently coherent, real or virtual,
point or line light source and an optical system. The video
hologram-bearing medium itself consists of cells which are arranged
in a matrix or in an otherwise regular pattern with at least one
opening per cell, the phase or amplitude of said opening being
controllable. The optical system for reconstructing the video
hologram can be realized by an optical imaging system known in the
art, consisting of a point or line laser or a sufficiently coherent
light source.
[0031] FIG. 1 shows the general arrangement of a video hologram and
its reconstruction. A light source 1, a lens 2, a hologram-bearing
medium 3 and a viewing plane 4 are arranged one after another, seen
in the direction of the propagating light. The viewing plane 4
corresponds with the Fourier plane of the inverse transform of the
video hologram with the diffraction orders.
[0032] The light source 1 is imaged on to the viewing plane 4
through an optical system, represented by the lens 2. If a
hologram-bearing medium 3 is inserted, it is reconstructed in the
viewing plane 4 as an inverse Fourier transform. The
hologram-bearing medium 3 with periodic openings creates
equidistantly staggered diffraction orders in the viewing plane 4,
where the holographic encoding into higher diffraction orders takes
place, e.g. by way of the so-called detour phase effect. Because
the light intensity decreases towards higher diffraction orders,
the 1.sup.st or -1.sup.st diffraction order is used as the viewing
window 5. If not explicitly expressed otherwise, the 1.sup.st
diffraction order will be taken as a basis in the further
description of the invention.
[0033] The dimension of the reconstruction was chosen here to
correspond with the dimension of the periodicity interval of the
1.sup.st diffraction order in the viewing plane 4. Consequently,
higher diffraction orders are attached without forming a gap, but
also without overlapping.
[0034] Being the Fourier transform, the selected 1.sup.st
diffraction order forms the reconstruction of the hologram-bearing
medium 3. However, it does not represent the actual
three-dimensional scene 6. It is only used as the viewing window 5
through which the three-dimensional scene 6 can be observed (see
FIG. 2). The actual three-dimensional scene 6 is indicated in the
form of a circle inside the bundle of rays of the 1.sup.st
diffraction order. The scene is thus located inside the
reconstruction frustum which stretches between the hologram-bearing
medium 3 and the viewing window 5. The scene 6 is rendered as the
Fresnel transform of the hologram-bearing medium 3, whereas the
viewing window 5 is a part of the Fourier transform.
[0035] FIG. 3 shows the corresponding holographic encoding. The
three-dimensional scene is composed of discrete points. A pyramid
with the viewing window 5 being the base and the selected point 7
in the scene 6 being the peak, is prolonged through this point and
projected on to the hologram-bearing medium 3. A projection area 8
is created in the hologram-bearing medium 3 that point being
holographically encoded in the projection area. The distances
between the point 7 to the cells of the hologram-bearing medium 3
can be determined in order to calculate the phase values. This
reconstruction allows the size of the viewing window 5 to be
constrained by the periodicity interval. If, however, the point 7
was encoded in the entire hologram-bearing medium 3, the
reconstruction would extend beyond the periodicity interval. The
viewing zones from adjacent diffraction orders would overlap, which
would result in the viewer seeing a periodic continuation of the
point 7. The contours of a surface encoded in this manner would
appear blurred due to multiple overlapping.
[0036] The intensity decrease towards higher diffraction orders is
taken advantage of to suppress cross-talking to other viewing
windows. FIG. 4 shows schematically a light intensity distribution
over the diffraction orders, said distribution being determined by
the width of the openings in the CGH. The abscissa shows the
diffraction orders. The 1.sup.st diffraction order represents the
viewing window 5 for the left eye, i.e. the left viewing window,
through which the three-dimensional scene can be viewed.
Cross-talking into a viewing window for the right eye is suppressed
by the decrease in light intensity towards higher diffraction
orders and, additionally, by the zero point of the intensity
distribution.
[0037] Of course, the viewer can view the scene 6 of the hologram 3
with both eyes (see FIG. 5). For the right eye, the right viewing
window 5' represented by the -1.sup.st diffraction order of the
light source 1' was chosen. As can be seen in the drawing, this
light influences the left eye at a very low intensity. Here, it
corresponds to the -6.sup.th diffraction order.
[0038] For the left eye, the 1.sup.st diffraction order
corresponding to the position of the light source 1 was chosen. The
left viewing window 5 is formed likewise. According to an
implementation of this invention, the corresponding
three-dimensional scenes 6 and 6' (not shown) are reconstructed
using the light sources 1 and 1' in a fix position in relation to
the eyes. For this, the hologram 3 will be re-encoded when the
light sources 1 and 1' are turned on. Alternatively, the two light
sources, 1 and 1', can simultaneously reconstruct the hologram 3 in
the two viewing windows 5 and 5'.
[0039] If the viewer moves, the light sources 1 and 1' are tracked
so that the two viewing windows 5 and 5' remain localized on the
eyes of the viewer. The same applies for movements in the normal
direction, i.e. perpendicular to the video hologram.
[0040] Further, several viewers can view a three-dimensional scene
if additional viewing windows are created by turning on additional
light sources.
[0041] Although the invention has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the invention defined in the appended claims
is not necessarily limited to the specific features or acts
described. Rather, the specific features and acts are disclosed as
exemplary forms of implementing the claimed invention.
Modifications may readily be devised by those ordinarily skilled in
the art without departing from the spirit or scope of the present
invention.
* * * * *