U.S. patent application number 13/709623 was filed with the patent office on 2013-04-25 for projection apparatus and method for pepper's ghost illusion.
The applicant listed for this patent is Ian O'Connell, James Rock. Invention is credited to Ian O'Connell, James Rock.
Application Number | 20130100415 13/709623 |
Document ID | / |
Family ID | 34957256 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130100415 |
Kind Code |
A1 |
O'Connell; Ian ; et
al. |
April 25, 2013 |
Projection Apparatus and Method for Pepper's Ghost Illusion
Abstract
An image projection apparatus includes a projector, a frame, and
a partially transparent screen. The frame retains the screen under
tension, such that the screen is inclined at an angle with respect
to a plane of emission of light from the projector. The screen has
a front surface arranged such that light emitted from the projector
is reflected therefrom. The projector projects an image such that
light forming the image impinges upon the screen such that a
virtual image is created from light reflected from the screen, the
virtual image appearing to be located behind the screen.
Inventors: |
O'Connell; Ian; (London,
GB) ; Rock; James; (London, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
O'Connell; Ian
Rock; James |
London
London |
|
GB
GB |
|
|
Family ID: |
34957256 |
Appl. No.: |
13/709623 |
Filed: |
December 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13011452 |
Jan 21, 2011 |
8328361 |
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13709623 |
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10599553 |
Sep 30, 2006 |
7883212 |
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PCT/GB2004/001414 |
Apr 1, 2004 |
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13011452 |
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Current U.S.
Class: |
353/10 |
Current CPC
Class: |
G02B 30/60 20200101;
G03B 21/28 20130101; G02B 30/56 20200101; A63J 25/00 20130101; G02B
27/0018 20130101 |
Class at
Publication: |
353/10 |
International
Class: |
G02B 27/24 20060101
G02B027/24 |
Claims
1. An image projection apparatus, comprising: an image source, a
frame, a light source and an at least partially transparent screen;
the frame being arranged to retain the screen under tension, such
that the tension of the screen can be independently varied at a
plurality of positions along at least one edge of said screen; the
light source arranged to illuminate at least part of the apparatus;
the screen inclined at an angle with respect to a plane of emission
of light from the image source and the screen having a front
surface arranged such that light emitted from the image source is
reflected therefrom; and the image source being arranged to project
an image such that light forming the image impinges upon the screen
such that a virtual image is created from light reflected from the
screen, the virtual image appearing to be located behind the
screen; wherein the screen is foil and the frame comprises first
and second retention members arranged to sandwich an edge region of
the screen therebetween; and wherein the first and second retention
members are connected to one or more flexible tensioning members,
which extend from the frame, the foil, flexible tensioning members
and the frame lying in a common inclined plane, with the tension on
the foil being applied in the plane of the flexible tensioning
members and the foil.
2. The apparatus according to claim 1 wherein the foil is polymeric
foil.
3. The apparatus according to claim 1 wherein: the first and second
retention members comprise respective openings therethrough
arranged to collocate with respective openings in the screen; and
the openings are arranged to receive fixing members to clamp the
screen between the first and second retention members.
4. The apparatus according to claim 1 wherein the frame is arranged
to retain the screen under tension such that the tension of the
screen can be varied at a plurality of positions along at least one
edge of the screen such that the screen is substantially wrinkle
free.
5. The apparatus according to claim 1 wherein the image source is a
projector, an LCD or a television display.
6. The apparatus according to claim 1 further comprising a
pigmented reflective member in an optical pathway between the image
source and the screen.
7. The apparatus according to claim 6 wherein the pigmented
reflected member is grey in color.
8. An image projection apparatus, comprising: an image source, a
frame and an at least partially transparent screen; the frame being
arranged to retain the screen under tension, such that the tension
of the screen can be independently varied at a plurality of
positions along at least one edge of said screen; the screen
inclined at an angle with respect to a plane of emission of light
from the image source and the screen having a front surface
arranged such that light emitted from the image source is reflected
therefrom; and the image source being arranged to project an image
such that light forming the image impinges upon the screen such
that a virtual image is created from light reflected from the
screen, the virtual image appearing to be located behind the
screen; wherein the screen is foil and the frame comprises first
and second retention members arranged to sandwich an edge region of
the screen therebetween; and wherein the first and second retention
members are connected to one or more flexible tensioning members,
which extend from the frame, the foil, flexible tensioning members
and the frame lying in a common inclined plane, with the tension on
the foil being applied in the plane of the flexible tensioning
members and the foil.
9. The apparatus according to claim 8 further comprising a light
source arranged to illuminate at least part of the apparatus.
10. The apparatus according to claim 8 wherein at least one of the
faces of the first and second retention members comprises an
abrasive coating arranged to contact the screen.
11. The apparatus according to claim 10 wherein the abrasive
coating is sandpaper.
12. The apparatus according to claim 8 further comprising a light
source arranged to illuminate at least part of a stage lying behind
the screen.
13. The apparatus of claim 8 wherein both of the faces of the first
and second retention members comprise an abrasive coating.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
application Ser. No. 13/011,452 filed on Jan. 21, 2011 (now
allowed), which is a continuation of U.S. application Ser. No.
10/599,553, filed on Sep. 30, 2006 (now U.S. Pat. No. 7,883,212),
which is a U.S. National Phase entry of PCT/GB2004/001414, filed on
Apr. 1, 2004, the disclosures of which are incorporated herein by
reference in their entirety.
[0002] This invention relates to a projection apparatus and method.
More particularly, but not exclusively, it relates to a projection
apparatus arranged to project an image of an object upon an
inclined, partially reflective, screen so as to give a false
perception of depth and a method for constructing such an
apparatus.
BACKGROUND OF THE INVENTION
[0003] The projection of an image upon a partially reflective
screen such that is observable by a viewer positioned in front of
the screen is known, the so-called "Peppers ghost" arrangement that
is known form fairground shows.
[0004] This has been applied to publicity and promotional displays
where a presenter resides behind an inclined, partially reflective
screen, typically a tensioned foil, onto which an image of, for
example, a motor vehicle is projected, via at least one reflective
surface, see for example EP 0799436. The location of the presenter
behind the projected image has a number of inherent advantages over
systems where the presenter stands in front of a screen, not least
of which is that the presenter does not obscure the projected image
when walking across the projected image. Additionally, the use of
an inclined screen results in a viewer of the image perceiving the
image as having depth rather than merely being a two dimensional
image, for example where a motor vehicle is seen to rotate upon a
turntable.
[0005] However, current image projection apparatus' do have a
number of problems associated with them, for example, mounting of
the foil can prove difficult which in turn leads to uneven
tensioning of the foil and wrinkles upon the foil, that impair the
viewed quality of the image projected onto the foil. Also, in
mounting the foil the foil must be laid out upon a clean dust free
piece of cloth or plastic sheet, which is larger than the foil, in
order to prevent particles adhering to the foil, such particles can
scratch the surface of the foil and impair the viewed quality of
the projected image or act as scattering centres from which
projected light is incoherently scattered, thereby detracting from
the viewed quality of the image as this scattered light does not
contribute to the viewed image.
[0006] Also, as the illusion of peppers ghost relies on the
reflected image formed by light contrasting with its immediate
surroundings and background. The stronger the reflected image, the
more solid that reflected image looks, the more vibrant the colours
will be, and the more visible the reflected image is to an
audience. In circumstances where the presenter may be unable to
control high levels of ambient light forward of the foil, e.g. from
an auditorium at a trade show, the high level of ambient light
results in significant levels of reflection of the ambient light
from the screen detracting from the strength of the reflected image
over the background. In these circumstances a bright projector
(8000 lumens+) is desirable. However, the use of a bright projector
results in unwanted light hitting the projection surface and
reflecting through the foil to create a milky hue upon the stage
and around the area where the reflected image appears.
[0007] Another problem with current image projection apparatus is
that projectors used with such apparatus are very powerful,
typically 8,000 to 27,000 lumens and consequently project a
significant amount of light into areas of an image where there is
no object within the image. This is an inherent feature of
projectors and results in low contrast ratios which leads to a
milky hue spread over the part of the film where the projector is
creating an image when the projector is switched on. The milky hue
is clearly undesirable as it detracts from the viewer's perception
that there is no screen present.
[0008] The level of the milky hue relative to the brightness of the
image is, at least partially, determined by the level of contrast
ratio offered in the projector. The higher the contrast ratio, then
the brighter the image can be relative to the brightness level of
the milky hue. Even projectors with contrast rations as high as
3000:1 still emit a milky light hue when used in a "Pepper's Ghost"
arrangement.
[0009] A further problem associated with some projectors is the
"keystone" effect, in which distorted, typically elongated, images
(up and down) occur due to angled projection. This is of particular
relevance where depth perception is of importance. The solution
employed in modern, expensive projectors is to employ digital
correction of keystone distortions. However, older, less-expensive
or even some specialist High Definition projectors do not employ
such digital keystone correction and are therefore difficult to
configure for use with current image projection apparatus. High
definition (HD) projectors do not offer keystone adjustment because
when keystone correction is attempted in conjunction with the
increased number of pixels about an image's edge causes the pixels
about the edge of the image to appear `crunched`. Additionally,
when processing moving images HD projectors compromise projector
processing speed. When the processing power is used to carry out
both keystone correction and motion processing the image is seen to
jerk during movements, an effect known as "chokking". In general,
it can be said that the use of electronic keystone correction to
alter a video image will result in the degradation of picture
quality compared to an image which is not subject to such a
process.
[0010] Additionally, current systems do not allow for the projected
image to apparently disappear and re-appear from behind a solid 3D
object placed upon the stage, as the screen lies in front of the
presenter and closest to the viewing audience.
SUMMARY OF THE INVENTION
[0011] According to a first aspect of the present invention there
is provided a image projection apparatus comprising a projector, a
frame, and an at least partially transparent screen:
[0012] the frame being arranged to retain the screen under tension,
such that the screen is inclined at an angle with respect to a
plane of emission of light from the projector;
[0013] the screen having a front surface arranged such that light
emitted from the projector is reflected therefrom; and
[0014] the projector being arranged to project an image such that
light forming the image impinges upon the screen such that a
virtual image is created from light reflected from the screen, the
virtual image appearing to be located behind the screen.
[0015] Such an apparatus is advantageous over present systems in
that the screen need not be coated with an expensive, partially
reflective coating, an angular dependence of reflectivity of
transparent dielectric materials can be used to bring about partial
reflectance of the projected image. Thus, this apparatus simplifies
the manufacture of such systems and also reduces their production
costs. Additionally, the use of a frame frees the screen from
having to be fixed directly to a ceiling, or a floor, and therefore
increases the utility of apparatus over the prior art systems.
[0016] The screen may be a foil. The foil may be rolled about a
cylinder when not in use. The screen may be inclined at
approximately 45.degree. to the plane of emission of light from the
projector. The screen may comprise a partially reflective layer
upon the front surface.
[0017] The use of a foil screen reduces the weight of the
apparatus, this allows ready transportation of the apparatus
between sites. Rolling the foil onto a cylinder when not in use
serves to protect the foil from damage during transportation and
also allows ready transportation of the apparatus between sites.
The use of a partially reflective screen can increase the degree of
light reflected from the screen and can increase the audience
perceived strength of the virtual image.
[0018] The screen may be attached to the frame at the screen's
upper and/or lower edges. The frame may comprise first and second
retention members arranged to sandwich an edge region of the screen
therebetween. At least one of the first and second retention
members may comprise an abrasive coating, typically sandpaper,
arranged to contact the screen. The first and second retention
members may comprise respective openings therethrough that may be
arranged to collocate with openings in respective jaws of clamping
members attached to tensioning straps, the openings may be arranged
to receive a fixing means so as to clamp the screen between the
first and second retention members. The tensioning straps may be
attached to a truss arrangement and may be adjustable such that the
tension of the screen within the truss arrangement can be varied
about the periphery of the screen. Preferably, the retention
members are substantially parallel to truss members comprising the
truss arrangement.
[0019] The use of a variable tensioning arrangement allows wrinkles
upon the screen to be minimised, and ideally eradicated to present
a smooth surface for upon which the image can be projected. An
abrasive surface upon at least one of the retention members
increases the grip between the retention member and the screen
thereby reducing the likelihood of the screen slipping when held by
the retention member.
[0020] The apparatus may comprise a pigmented reflective member in
an optical pathway between the projector and the screen. The
pigmented member may reflect only part of the visible spectrum of
light, typically the pigmented member will appear grey or white to
a viewer.
[0021] It has been found that the use of a grey reflective member
in the optical pathway between the projector and the screen reduces
the outline of the reflective member upon the screen compared to
when a white reflective member is used, and also reduces the level
of the milky white hue associated with the projector emitting light
where there is no image of an object to be projected.
[0022] The pigmented reflective member may be inclined at an angle
with respect to the plane of emission of light from the projector.
The angle of inclination of the member with respect to the plane of
emission of light from the projector may be variable. The member
may comprise a plurality of sections each of which may have an
independently variable angle of inclination with respect to the
plane of emission of light from the projector.
[0023] The inclination of the reflective member can compensate, at
least partially and in some instances completely, for keystone
effect. The variation of the angle of inclination or distance of
the reflective member allows for a variation of the apparent depth
and/or position of an object when projected upon the screen. This
is because the virtual image appears as far behind the screen as
the real image is in front of the screen.
[0024] There may be a reflective device, typically a mirror,
arranged to direct light projected from the projector on to the
reflective member. Typically, the reflective device is mounted upon
an upper part of the framework. The reflective member may be
parallel, or substantially parallel, to the reflective device. In
some embodiments the projector may be mounted upon an upper truss
of the framework and may be aligned with the horizontal, typically
light projected from the projector is directed on to the reflective
device.
[0025] Such an arrangement compliments the keystone correction
achievable by the inclination of the screen and the reflective
member and is particularly useful where an HD projector is used in
order to compensate for the keystone effect without the use of the
projector's processing power.
[0026] The reflective member may comprise a mask corresponding to
the apparent location of a prop in the screen to an audience.
Typically, the mask will absorb light over at least a fraction of
the visible spectrum and preferably the mask will be black. The
mask may be arranged to produce an area upon the screen upon which
the image is not projected. The mask may vary in extent and shape,
for example by the use of a sliding element that is moved in and
out of position upon the reflective member.
[0027] The mask can be used to make the illusion of an article
disappearing and reappearing behind a prop that is placed upon a
stage, either behind or in front of the screen.
[0028] The apparatus may comprise a light source arranged to
selectively illuminate an area of stage comprising the prop. The
light source may be a white light source
[0029] Lighting the prop causes the prop to become more visible and
better defined against the dark, typically black, background. This
enhances the three dimensional effect of the projected image
interacting with the prop. Also directing bright light upon the
prop serves to reduce the contrast ratio of the projected image
upon the prop, which typically remains slightly visible even when a
mask is used in the prop's shadow upon the reflective member, thus
enhancing the illusion of the projected image disappearing behind
the prop.
[0030] The apparatus may comprise a light source arranged to
illuminate at least part of a stage. The light source may be
located to the rear of the screen, typically along a top edge of
the frame and/or along either side of the stage. The apparatus may
comprise a plurality of light sources. The apparatus may comprise a
lighting desk equipped with faders arranged to control the level of
each light source, or selection means arranged to selectively
control the supply of power to each light source.
[0031] Such a light source is used in order that the colour and
light levels of the area immediately surrounding the peppers ghost
image, the stage background, can most closely match the colour of
the projection surface background, excluding the area on both which
is carrying the image. This, reduces the milky hue perceived by the
audience. The use of a plurality of light sources increases the
uniformity of lighting of the stage, in order to produce a similar
effect to the way light emitted from a projector hits the
projection screen. By controlling each light source separately the
lighting levels upon the stage can be controlled to closely match
the levels of light as dictated by the show performance, or the
levels of unwanted light hitting the projection surface of the
screen.
[0032] The projector may comprise a standard projector, for example
a JVC ML4000, or a Barco G5. Alternatively, the projector may
comprise an LCD, or a television display. The display may comprise
at least one element arranged to be non-emitting in response to
control from a processor. The at least one element may form a mask
arranged to produce an area upon the screen upon which the image is
not projected. The mask may correspond to the shape and location of
a prop upon stage. The prop may be three dimensional.
[0033] According to a second aspect of the present invention there
is provided a method of providing a projection apparatus comprising
the steps of:
[0034] (i) resting a frame upon a number of elevation means;
[0035] (ii) attaching leg sections to the frame;
[0036] (iii) increasing the height of the elevation means;
[0037] (iv) adding further leg sections;
[0038] (v) attaching a lower edge of a screen to a lower rear piece
of the frame;
[0039] (vi) raising an upper edge of the screen to adjacent an
upper front section of the frame; and
[0040] (vii) attaching the upper edge of the screen to the upper
front section of the frame.
[0041] The method may comprise providing the elevation means in the
form of a jack.
[0042] The method may comprise providing the screen in the form of
a film. The method may comprise removing a roll of screen film from
a protective cylindrical casing. The method may comprise laying the
screen upon a dust-free protective sheet.
[0043] The method may comprise placing the lower edge of the screen
between jaws of a first retention member and may further comprise
securing the screen in position using a fixing means passing
through the retention member and the screen and a locking means
arranged to lock the fixing means being arranged to secure the
locking means in position. The method may comprise providing the
fixing means in the form of a bolt and the locking means in the
form of a nut.
[0044] The method may comprise attaching tensioning means to the
retention member adjacent at least some of the fixing means.
[0045] The method may comprise attaching the tensioning means to
the lower rear piece of the frame. The method may comprise
attaching a second retention member to an upper edge of the film
screen, typically in the same manner as the first retention member
is attached to the lower edge. The method may comprise attaching
tensioning means to the second retention member. The method may
comprise providing the tensioning members in the form of ratchet
straps.
[0046] The method may comprise attaching a rope to the second
retention member and passing the rope over the upper frame and
using the rope in step (vii) to raise the screen.
[0047] The method may include tensioning each of the tensioning
means such that the screen is flat and substantially wrinkle
free.
[0048] The method may include depending a projector from the upper
frame.
[0049] The method may include placing a pigmented reflective board
between the screen and a front edge of the frame. The method may
comprise reflecting light emitted by the projector from the board
onto the screen.
[0050] The method may comprise forming the frame from a truss
work.
[0051] According to a third aspect of the present invention there
is provided a projection apparatus constructed according to the
second aspect of the present invention.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0052] The invention will now be described, by way of example only,
with reference to the accompanying drawings, in which:
[0053] FIG. 1 is a schematic representation of a first embodiment
of a projection apparatus according to at least an aspect of the
present invention;
[0054] FIG. 2 is a side view of a the projection apparatus of FIG.
1 showing a pigmented reflective member in first and second
positions;
[0055] FIG. 2a is a schematic representation of an alternative
projection arrangement, suitable for use with the apparatus of
FIGS. 1 and 2;
[0056] FIG. 3 is a schematic representation of a second embodiment
of a projection apparatus according to at least an aspect of the
present invention;
[0057] FIG. 4 is a perspective view of a screen clamping
arrangement of FIGS. 1, 2 and 3; and
[0058] FIG. 5 is a schematic view of a projection apparatus being
constructed according to the second aspect of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0059] Referring now to FIGS. 1, 2 and 4, a projection apparatus
100 comprises a box frame 102 formed of trusses 104, a projector
106, a support frame 108, a screen 110 held within the support
frame 108 and a grey pigmented reflective board 112.
[0060] The projector 106 depends from a front upper cross-piece
truss 104a of the box frame 102. The board 112 lies below the
projector 106 at the base of the box frame 102. The screen 110, is
inclined at approximately 45.degree. to the horizontal and the
front edge of the screen 110 is proximate the front upper
cross-piece truss 104a of the box frame 102 and the rear edge of
the screen is proximate a stage 109 that lies to the rear of the
box frame 102.
[0061] The screen 110 is typically a polymeric foil, which can have
a partially reflective coating upon a front face of the foil. The
screen 110 is retained within the box frame 102 by means of
tensioning straps 114 attached to the box frame 102, at the top and
bottom edges of the screen 110. At a free end of each of the
tensioning straps 114 there is pair of clamp jaws 116 which have
respective openings 118,120 passing therethrough. The faces of the
jaws 116 are optionally coated with an abrasive 121, such as
sandpaper, in order to enhance the grip of the jaws 116 upon the
screen 110.
[0062] Edges of the screen 110 are placed between the jaws 116 and
a bolt 122 is placed through the openings 118, 120 and passes
through the screen 110. A nut 124 is threaded onto the bolt 122 and
tightened to hold the screen 110 between the jaws 116. The
tensioning straps 114 pass through the trusses 104 and are
tightened using a friction locking buckle arrangement 128.
[0063] Each of the tensioning straps 114 can be tightened or
loosened individually so as to allow an even tension to be applied
over the whole surface of the screen 110 thereby reducing, and
ideally eliminating, the formation of wrinkles upon the screen 110
which reduce the quality of an image projected upon the screen
110.
[0064] The reflective board 112 lies below the projector 106
adjacent to a lower front cross-piece truss 104b of the box frame
102. The projector 106 is directed such that light emitted by the
projector 106 strikes the reflective board 112. The board 112 is
inclined so that the light emitted by the projector 106 is
reflected upwards from the board 112 onto the screen 110. The use
of a grey, or otherwise coloured board 112 reduces the milky hue
associated with light from the projector where there is no image to
be projected.
[0065] A fraction of the projected light striking the screen 110 is
reflected from the front surface of the screen 110 where is can be
viewed by an audience. A presenter upon the stage 109 behind the
screen 110 can also be viewed by the audience but does not
interfere with the viewing of the image by the audience.
[0066] The board 112 is connected to a hinge arrangement 130 along
a rear edge thereof. The hinge arrangement 130 allows the board 112
to be raised and lowered, typically be a hydraulic ramp 132
controlled by a computer 134, in order to compensate for the
`keystone` effect. Alternatively, the board 112 can be raised and
lowered by the person pulling upon a string, or an electric motor
to drive the board up and down.
[0067] The raising and lowering of the board 112 also allows for
the audience's perception of the positional depth upon the stage of
an element of a projected image to be altered by varying the height
of the element of the image upon the screen 110. It is envisaged
that the board 112 may comprise a number of individual sections
each of which may be raised an lowered individually in order to
allow the perceived depth of an individual element of an image to
be varied independently of other elements of the image.
[0068] A non-reflective mask 136 in the shape of a prop 138, in
this example a rock, is placed upon the board 112. The prop 138 is
place upon the stage 109, typically behind the screen 110. The mask
136 is placed such that the board 112 is obscured in a region
corresponding to where the prop 138 is located with respect to the
screen 110. This arrangement of mask 136 and prop 138 results in an
image, or part of the image, projected upon the screen 110
apparently disappearing as the image, or part of the image, passes
over prop 138 and reappearing once the image, or part, of the image
has passed over the prop 138 as the mask 136 prevents light being
reflected onto the region of the screen 110 corresponding to the
location of the prop 138. The mask 136 can be variable in size and
shape, for example by means of a sliding panel that is moved into
location and varied in size according to the size of the prop 138.
This also allows for the depth perception of props to be varied as
their apparent effect upon variable depth image elements, as
discussed hereinbefore, can be varied appropriately, for example a
given size of rock will obscure proportionately more of a distant
image than the same rock will of a near image.
[0069] A light source 140 is mounted upon the box frame 102 and
illuminates the prop 138 in order to reduce the effect of any
residual light reflected from the board 112 onto the prop.
[0070] Referring now to FIG. 2a, an alternative projection
arrangement 200, suitable for use with the apparatus of FIGS. 1 and
2 with an additional truss, comprises the projector 106 depending
from a truss 202 forward of the screen 110, an inclined mirror 204
of variable inclination depending from a second truss 206 forward
of projector 110. The projector 106 projects an image on to the
mirror 204 such that the image is projected on to the reflective
board 112 and on to the screen 110. The mirror 204 is typically
arranged to be perpendicular to the board 112, and in embodiments
where the board 112 has a variable angle of inclination the mirror
204 will usually be arranged to track, synchronously, with any
variation in the angle of inclination of the board 112.
[0071] It will be appreciated that the term mirror is used herein
to describe any reflective surface that reflects substantially all,
typically in excess of 50% preferably in excess of 80%, light
impinging upon it.
[0072] Referring now to FIG. 3, a projection apparatus 300 is
substantially similar to that of FIGS. 1 and 2 accordingly
identical parts to those of FIGS. 1 and 2 are accorded similar
reference numerals in the three hundred series.
[0073] A projection screen 306 resides in front of the screen 310
adjacent the lower front cross-piece truss 304b. The projection
screen 306 is typically a liquid crystal display (LCD) screen or a
television screen. The projection screen 306 projects an image
upwards onto the front surface of the screen 310. The use of a
projection screen 306 removes the `keystone` effect associated with
conventional projectors.
[0074] A mask 336 can be formed upon the screen by use of a
computer 340 to control the projection screen 306 to black out the
appropriate part of the projection screen 306 electronically. This
removes the need for a physical mask to be produced. The computer
340 can be used to switch of areas of the projection screen 306
which do not contain part of an image to be projected, this reduces
the milky white hue associated with such areas when using
conventional projectors. Also, the use of a computer 340 to control
the projection screen 306, together with image sizing in relation
to image movement allows an image to be readily scaled and
positioned upon the projection screen 306 to enhance an audience's
perception of depth and movement of a projected image using known
image processing techniques. Alternatively, the projection screen
306, or sections of the projection screen 306, can be raised and
lowered under the control of the computer 340 in order to enhance
the audience's perception of depth of the projected image.
[0075] Referring now to FIG. 5, a box truss framework 500 comprises
a square upper truss work 502 and leg trusses 504. In constructing
the framework 500 the upper truss work 502 rests upon a number of
jacks 506. First sections 508 of the leg trusses 504 that extend at
right angles to the upper truss work 502 are added at the corners
of the upper truss work 502. The height of the jacks 506 is
increased to allow additional sections 510 of the leg trusses 504
to be added until the desired height of the box truss framework 500
is achieved.
[0076] A cross-piece truss 512 is fixed to two of the leg trusses
504 such that it horizontally spans the gap therebetween at a
height close to, and typically slightly below, the level of a stage
floor 514. The leg trusses 504 spanned by the cross-piece truss 512
constitute the rear legs of the framework 500 and are located
adjacent the front of the stage floor 514.
[0077] A dust-free protective plastic sheet 515 is laid across the
width of the stage floor 514 in front of the rear legs of the
framework 500. A roll of screen film 518 is removed from a
protective cylindrical casing 520 and is unwound across the width
of the stage floor 514. The film 518 is placed upon the sheet 515
in order to prevent damage to the surface from dust particles or
other sharp protrusions.
[0078] A lower edge 522 of the film 518 is placed between jaws
524a,b of a retention member 526, each jaw 524a,b having opposed
openings therethrough spaced at approximately 0.5 m intervals.
Bolts 528 are placed through the openings, and through the film
518, and secured in position using respective nuts. Ratchet straps
532 are attached to the retention member 526 adjacent alternate
bolts 528, having a spacing of approximately Im, and are then
attached to the cross-piece truss 512.
[0079] A second retention member 534 is attached to an upper edge
536 of the film 518 in a similar manner to how the retention member
526 is attached to the lower edge 522. Ratchet straps 538 are
attached to the second retention member 534.
[0080] A rope 540 is tied to the second retention member 534 and is
passed over the upper truss work 502 opposite the cross-piece truss
512. The film raised into position using the rope 540 and the
ratchet straps 538 are attached to the upper truss work 502. Both
sets of ratchet straps 532, 538 are tightened individually until
the screen film is tensioned such that the film 518 is flat and,
ideally, free from wrinkles.
[0081] A projector 542 is depended from the upper truss work 502
and a pigmented reflective board 544 is placed between the screen
518 and the front edge of the box truss framework 500 such that
light emitted by the projector 542 is reflected from the board 544
onto the screen 518. The screen 518 reflects at least part of the
light from a front surface thereof away from the stage and into an
auditorium to be viewed by and audience.
[0082] In order to prevent the audience observing the projection
apparatus both side and front drapes 546 are used to screen the
apparatus from the audience.
* * * * *