Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02107127 1999-O1-14
AN APPARATUS FOR GENERATING THREE-DIMENSIONAL IMAGES
The present invention relates to an apparatus for
generating three-dimensional images.
An object of the present invention is to provide an
apparatus of this kind that, as viewed by an observer, a
three-dimensional image appears to float freely in space in
front of the apparatus, and can thus be combined with
1o actual objects or persons. A feature of the three-
dimensional images that float freely in space, is that they
can be enlarged or reduced to a certain extent, and can be
superimposed over or faded into actual objects or persons.
Apparatus for generating a three-dimensional image of an
object according to the present invention includes a fixed
observation area and a stage. A first (front) concave
mirror is adjacent to the observation area, and a second
(rear) concave mirror is located away from the observation
2o area, with the reflecting surfaces of the two concave
mirrors facing one another. The first concave mirror has a
partial area which is transparent so that at least a
partial area of the second concave mirror can be seen from
the observation area. The first concave mirror is located
in such a way that a virtual image of an object disposed
between the two concave mirrors is projected onto the stage
so that it can be combined with real objects or persons
located there.
3o The object that is to be projected, which is preferably
disposed close to the second (remote or rear from a
viewer's standpoint) concave mirror, is reflected in the
first (adjacent or front) concave mirror and the image is
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projected onto the rear concave mirror which can be seen by
the observer. The distortion of the first reflection is
eliminated as a result of the second concave mirror which
preferably has the same radius of curvatures the image that
is viewed by the observer is sharp and appears to the
observer to be formed at a considerable distance in front
of the surface of the rear concave mirror.
The concave mirrors can be slightly elliptical or
1o parabolic. An image that is especially free of distortion
results if two spherical concave mirrors of the same radius
of curvature are used.
If the concave mirrors are in the form of a spherical cap
and their centres lie on one axis, and if the object that
is to be projected is arranged in the vicinity of this axis
close to the surface of the rear concave mirror (as viewed
by the observer) and if a viewing aperture is located in
the front concave mirror, close to the axis, then the
2o three-dimensional image will be visible from all sides in a
cone-shaped area. Using such an apparatus, it is possible,
for example, to display advertising images in store windows
or on buildings or in open areas, to a large number of
spectators.
Depending on the dimensions of the apparatus, the area that
is visible to the observer can be so large that the object
can move within it. In this way, animated objects or live
persons can be projected and the apparatus can be used for
3o all types of presentations or theatrical performances, as
well as for special effects in movie making.
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The three-dimensional image can be either enlarged or
reduced by changing the position of the concave mirrors
relative to each other, for example, by axial displacement
or by tilting one of the two concave mirrors. If the sur-
faces of the mirrors are moved away from each other, the
image can be enlarged to a certain extent; if the surfaces
of the mirrors are moved closer together, the image becomes
smaller. A similar effect can also be achieved by moving
the object. If the object moves towards the surface of the
1o front concave mirror, it appears enlarged on the other
hand, if it moves away from the surface, it is reduced.
The radius of curvature of the mirror has to be suffi-
ciently large in order that this change in the size of the
image does not cause troublesome distortion. On the other
hand, this enlargement and reduction can be used to good
effect in order to achieve special effects.
Generally speaking, it is preferable that the radius of
2o curvature of the concave mirrors is at least five times
greater than a maximum extent of the object whose image is
to be projected, a height of a spherical cap forming the
concave mirror is at least 1.2 times as great as that
extent, a cap diameter of the concave mirrors is at least
six times greater than that extent, and a diameter of the
viewing aperture is at least 1.5 times as great as the
maximum extent.
If the apparatus is used in theatres or for concerts, when
3o the audience is located only within a specific angular
range in front of the stage, it is sufficient if the
concave mirrors in the apparatus form only portions of a
spherical cap. This brings about a considerable reduction
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in the space required for the apparatus, which is quite
large, especially for forming images of people. Black
walls should be adjacent to the peripheral edges of these
concave mirrors and these, together with the concave
mirrors, can form an essentially enclosed space so that no
unwanted reflections are projected by the concave mirrors
towards the observers. If the concave mirrors can be moved
relative to each other by means of hydraulic mechanisms or
other means, in order to exploit the enlargement or reduc-
io tion effects, or if they can be pivoted by such means, then
these walls should be either in the form of bellows and
move with the mirrors or, in the case of a purely axial
movement or a pure pivoting movement of the concave
mirrors, they should be so configured that the mirror lies
tight against the walls in any position.
The sources of light that illuminate an object that is to
be projected and which is not bright in and of itself, can
either be arranged in the area in front of the apparatus
20 (as viewed by the observer) or be arranged in areas of the
apparatus that cannot be seen by the observer, for example,
directly around the viewing aperture, or around the edges
of the concave mirrors. The object itself can be illumin-
ated both directly and also by way of reflections in the
concave mirrors. The image can be made unfamiliar and the
quality of the images can be influenced by selection of the
light sources, for example, lights or laser light that can
be varied with respect to beam width, colour, shape, and
direction. The sharpest images are formed by illumination
3o using coherent white laser light. If the sources of the
laser light are in a scanner that can vary the direction of
the laser beam and is computer-controlled, then in addition
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to this effect, laser show effects can be generated with
the help of this device and then can be projected.
In addition to the projection of images of actual objects
and persons, it is of course possible to project the images
onto viewing screens. Because the apparatus for projecting
the images has to be inclined for a viewing public on one
level, it can be useful to arrange the objects that are to
be projected on a flat area and reflect them into the
1o projection apparatus by way of a plane mirror.
It is advantageous to conceal the projection apparatus from
direct viewing by the spectators. To this end, a semi-
transparent screen can be arranged in front of the projec-
tion apparatus (as viewed by the spectators). The object
must be illuminated with sufficient power in order that the
spectators can still view the three-dimensional image
through the semi-transparent screen. The outside of the
apparatus as well as of the concave mirrors, should be kept
2o as dark as possible in order that they cannot be seen
through the semi-transparent screen. The most effective
concealment for the projection apparatus will result if the
semi-transparent screen is opaque in its edge areas and the
transparency of the screen increases continuously in an
inward direction, so that the greatest transparency is
found in the area in front of the viewing aperture.
The semi-transparent screen can be between the viewing
aperture and the imaging region in which the three-dimen-
3o sional image appears to be located, or it can be within the
image area. In the second case, the three-dimensional
image appears to penetrate the wall that is formed by the
semi-transparent screen.
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If a mirrored semi-transparent screen is used, the three-
dimensional image will appear in front of the reflected
background, e.g., the black observation area, although it
may form no reflected image in this screen itself.
If the semi-transparent screen is not mirrored, or if one
surface is mirrored and the other is not but is partially
diffuse, pictures or films can be projected onto it by
means of a projector; these can then be combined with the
1o three-dimensional image. When this is done, the brightness
of the light from the projector and from the object that is
to be projected have to be so balanced that both the
picture or the film and the three-dimensional image are
clearly visible to the spectator.
Additional features of the present invention will be
apparent from the following description of several specific
embodiments of the invention, taken in conjunction with the
accompanying drawings, in which:
2o Figure l: a perspective drawing illustrating the principle
behind the apparatus according to the present
invention;
Figure 2: a side view of an embodiment of the apparatus,
that is integrated into a theatre;
Figure 3: a side view of a further embodiment with concave
mirrors that can be tilted relative to each
other;
Figure 4: a view of the front concave mirror as in Figure
3, as seen from below;
3o Figure 5: a side view of one embodiment of the apparatus
with a semi-transparent screen.
The drawings that are described serve to illustrate
operating principles of the apparatus and are not to scale.
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The relationships, in particular between the object that is
to be projected, the curvature of the concave mirror, and
the distance between the concave mirrors, are to be adapted
to each particular and specific application.
The apparatus that is shown in Figure 1 consists of two
hemi-spherical concave mirrors 2, 3 of which the front
(first) one 2 (from a viewer's standpoint) incorporates a
viewing aperture 6. An observer can see an annular area of
1o the rear (second) concave mirror 3 in an angular area 4
that is conical, within which the object 5 that has been
placed in the apparatus is reflected by the front concave
mirror 2. Because of the fact that both concave mirrors 2,
3 have the same radius of curvature, abberations in the
reflections cancel each other out. Because of the doubled
reflection in a spherical concave mirror, a three-dimen-
sional image 1 of the object 5 is formed for the observer,
and this appears to be located at a considerable distance
in front of the rear concave mirror 3, in the area of the
2o viewing aperture 6. Given the appropriate type and quality
of the mirroring on the concave mirrors 2, 3, the image
will appear to be absolutely real. The image of an object
that is located close to the surface of the lower concave
mirror 3 in the area of its axis of rotation 7 appears to
be all but distortion-free. A coin lying in the area of
the axis 7 on the surface of the concave mirror 3 would,
for example, appear at actual size in the viewing aperture
6 when viewed by the observer.
3o If the three-dimensional image 1 that is generated is to be
combined with an actual object, the viewing aperture 6 can
be covered with a glass plate 8, on which actual objects
can be placed.
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The embodiment of the invention that is shown in Figure 2
is used in order to provide for the clearest and least
distorted image of large objects, such as, for example,
actors. The concave mirrors 12, 13 have a radius of curva-
ture that is between 10 and 20 m. In order that the appa-
ratus can be integrated structurally into a theatre or a
stage, the bulged areas of the sphere will be eliminated
from the spherical caps that form the concave mirrors 12,
13. Here, the concave mirrors 12, 13 form what is more or
less the upper or lower third of a hemisphere so that given
a sphere radius of 10 m, a maximum extent of 6 m will
result for the superimposed concave mirrors 12, 13.
Figure 2 also shows an object stage 16 which is used to
accommodate the object 5' whose image is to be projected.
That part of the stage 16 that cannot be seen from the
observation area 4' is preferably black, in order that it
radiates no unwanted light. The area of the stage 16 that
is within sight of the observation area 4' is to be trans-
2o parent in order that reflection is not disrupted.
Depending on the purpose for which the apparatus is used,
this stage 16 can be made so that it can be pivoted,
rotated, moved, or raised or lowered by means of suitable
drive means.
The hydraulic cylinders 15 with which the front concave
mirror 12 is articulated on the supporting frame 14 make it
possible to change the axial distance between the concave
mirrors 12, 13, by which means it is possible to vary the
3o size of a projection 1'.
The viewing aperture 6' within the area of which the
projection 1' appears to stand, as viewed by the observer,
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is integrated into a stage 17. In order to permit
unrestricted combination of the three-dimensional image 1'
with actual objects, a part of the stage 17 extends into
the viewing aperture 6'. This part is to be transparent in
order that it does not cover that area of the rear concave
mirror 13, in which the three-dimensional image 1' is
formed. The spectator seating area 19 is situated facing
the viewing aperture 6', in the viewing area 4'.
1o The whole apparatus has to be tilted relative to the hori-
zontal in order that the three-dimensional image 1' can be
seen by all the spectators in the viewing area 4'. The
greater the inclination of the axis of rotation 7' of the
concave mirrors 12, 13 relative to the vertical, the flat-
ter the spectator seating 19 may be made. A versatile
device will incorporate mechanical or hydraulic means by
which this inclination can be varied.
A light source 20 is arranged in the area close to the
2o viewing aperture 6' behind the front concave mirror 12, as
seen by the observer. The object 5' whose image is to be
projected can be illuminated by this light source, either
directly or by reflected light.
Since in a theatre only part of the cylindrically-shaped
observation area 4' is filled with members of the audience
and it is possible to see into only the part of the second
concave mirror 13 which faces the audience and enables the
reflections in the rear part of the first concave mirror 12
3o to be seen, it is possible to dispense with the front
portion of the projecting device.
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Figure 3 shows an embodiment of the apparatus in which only
portions of spherical caps form the concave mirrors 22, 23,
and Figure 4 is the front concave mirror 22 as seen from
below in inverted plan view.
The installed size of the apparatus is further reduced by
eliminating that part of the concave mirrors 22, 23 that
cannot be viewed. In this embodiment, the concave mirrors
22, 23 are arranged so as to pivot about an axis 25. A
1o winch 27 is arranged on a platform 26 on the supporting
frame 14' and the cable 28 is secured to the front concave
mirror 22. The front concave mirror 22 can be tilted
relative to the rear concave mirror 23 by using this winch.
This results in the enlargement and reduction effects of
the three-dimensional image 1" that has been described
heretofore. There is scarcely any distortion of this image
since both concave mirrors are of identical radius of
curvature at each point.
2o A blind 24 can be arranged in front of the viewing aperture
6" in order to cover a direct view of the object to be
projected from the observation area 4", and it can be
deployed and retracted automatically, if desired.
In this embodiment, light source 20' is arranged in an edge
region of the front concave mirror 22.
The partial area of the spherical cap that forms the hollow
mirrors can be further reduced depending on the appli-
3o cation. In the inverted plan view of the front concave
mirror 22 that is shown in Figure 4, the part 29 of the
spherical cap that can, for example, be used for an
apparatus which is essentially right in front of the
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observers is indicated by a dashed line. The partial area
30 that is indicated by the dashed and dotted line in
Figure 4 is suitable for an apparatus that is to be viewed
only from a fixed point of observation, such as the~loca-
tion of the camera when a movie is being shot. The open
areas between the concave mirrors 12, 13, 22, 23 of the
apparatuses shown in Figures 2 and 3 are to be closed off
with preferably black wall material (not shown in the
drawings) in order to prevent the ingress of troublesome
1o incident light. Light-proof black material, bellows
devices, or even rigid black walls suitable for this
purpose if the concave mirrors 12, 13, 22, 23 do not have a
particularly large degree of freedom relative to each
other.
Projection is not confined to fixed objects moving live or
animated objects can also be projected. In this case, the
projection apparatus is to be designed so as to take the
anticipated area of movement of the object into account.
In addition, images that are projected onto viewing
screens, such as television images, transparencies, films,
or laser projections, can also be shown. In the event that
the angle of inclination of the axis 7', 7" of the appa-
ratus is too great in an apparatus for projecting images to
an audience that is seated horizontally, the object that is
on a horizontal stage can be reflected into the apparatus
by a plane mirror that is arranged in the vicinity of the
axis 7', 7", close to the rear concave mirror 13, 23.
It is important that the concave mirrors are of a precisely
spherical shape in order to achieve optimal image quality.
In addition, the mirrors should be mirrored on their
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surfaces, because an additional transparent layer between
the object and the mirrored surface could cause double
reflections, interference, and distortion. At least one
sub-region of the viewing aperture can be covered by a
semi-transparent concave mirror whose reflecting surface
lies on a spherical surface with the first concave mirror.
Figure 5 shows the apparatus as shown in Figure 3 combined
with a stage 17 for actual objects and persons, and a semi-
to transparent screen 31 that covers the device from direct
view from the observation area 4". The semi-transparent
screen 31 can be extended between the ceiling and the stage
17.
The upper edge area 32 of the transparent screen 31 is
opaque, as is indicated by the hatching. The transparency
of the screen 31 increases in an inward direction, so that
the greatest transparency of the screen 31 is directly in
front of the viewing aperture 6". The object that is to be
2o projected must be illuminated with sufficient strength by
the light source 20' so that the three-dimensional image 1"
can be seen through the screen 31.
A film projector 33 is installed in front of the screen 31
and this projects a film image onto the screen 31 in the
area of the viewing aperture 6". If the power of illum-
ination of the object that is to be projected is stronger
in the apparatus than the light strength of the image that
is projected by the projector 33, then the three-dimen-
3o sional image will appear to be in front of the projected
image.
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