EP1547398A2

EP1547398A2 - Production of simulated 3-d images

Info

Publication number: EP1547398A2
Application number: EP03744915A
Authority: EP
Inventors: Michael John Hanney; Christopher John Ferrari; Graham Thomas
Original assignee: Living Ad Ltd
Current assignee: Living Ad Ltd
Priority date: 2002-03-25
Filing date: 2003-03-25
Publication date: 2005-06-29
Also published as: AU2003226508A8; AU2003226508A1; WO2003081920A2; GB0207014D0; WO2003081920A3

Abstract

Optical apparatus is described which provides a viewer with the impression of an image floating in space distanced from the apparatus itself. The apparatus of the invention overcomes certain disadvantages of known apparatus for producing such an effect particularly its large size. The apparatus may consist of an image-generating display screen, for example an LCD screen (10), a Fresnel lens optical system (12, 13) through which the screen is viewed. A corrector plate (11) is provided between screen (10) and the optical system (12, 13), enabling a relatively distortion-free image to be viewed in focus from a viewpoint located on an image plane (15) located at a distance from the Fresnel optics, the image appearing to float in front of the optical system, which is located in a suitable housing.

Description

PRODUCTION OF SIMULATED 3-D IMAGES

This invention relates to the production of simulated 3-D images.

There are many occasions where the visual impact of a three-dimensional image is very much greater than that of a conventional two-dimensional or "flat screen" image. The realism is enhanced and this is of particular value when it is desired that the image be eye-catching, for example in connection with advertising.

Many attempts have been made in the past to impart to essentially two- dimensional images a three-dimensional appearance, for example by varying the focus or definition of parts of the image compared with other parts, or by interleaving two images each in the form of a series of narrow stripes, and placing a lenticular sheet above them so that the ocular separation of the viewer means that two slightly different images are seen, one by each eye, which are merged to give the impression of a three-dimensional image in fashion similar to that used in a Victorian stereoscope.

In recent years, optical systems have been developed which provide the impression of a three-dimensional image floating in space. For example, Projectavision, Inc. of New York has disclosed in a number of published patent specifications a variety of proposed systems for displaying images in a fashion providing a simulation of three-dimensionality. WO 98/10584 discloses display systems designed to provide an experience of three-dimensional viewing. Such commercial devices as have appeared in the marketplace have been bulky and have not provided a convenient and convincing three-dimensional image to the viewer.

A known arrangement for producing a simulated three-dimensional image which appears to float in space consists of a CRT or LCD display device to which appropriate signals are fed to provide a static or moving image, a simple full silvered mirror, and three Fresnel lenses. The arrangement of these is illustrated in Figure 1 of the accompanying drawings, which shows the known system diagrammatically.

As shown in Figure 1 the system consists of a housing indicated in dashed lines CRT/LCD display device 1 positioned at the bottom of the system and arranged to project an image upwards through a pair of Fresnel lenses 2. The image is then reflected from a mirror 3 mounted at 45° and then passes out of the system through a further Fresnel lens 4. The focal lengths of the Fresnel lenses 2 and 4 are chosen so that an image of the graphics presented on the CRT/LCD is focussed some distance in front of the system, indicated at 5 on the drawing. If this image is viewed by a person on the optical axis of the system, or not too far from that axis, the image appears to be focussed in space and to float in front of the housing. The illusion is apparent over a wide distance range of the viewer to the housing, e.g. 1 to 3 metres.

The known system uses three Fresnel lenses in order to give the desired focussed image size and position. Commercially available off the shelf Fresnel optics are used to build a cost effective system. The Fresnel lenses 2 mounted together form a composite lens with a focal length shorter than either of the two lenses on their own. This technique is used to derive different focal lengths from a limited range of available lens focal lengths, but has to be limited in its use since additional optics in the system will contribute to light losses and optical aberrations. Such systems can produce images which appear quite sharp at the centre of the field of view, but the image quality degrades towards the edges of the image field.

We have now found that much improved 3-D image simulations may be secured with the use of an optical system which, in addition to the image- generating device and the Fresnel lens optics, includes a corrector plate between those optics and the image-generating device. The use of a corrector plate also enables systems to be designed using the shelf Fresnel lenses, rather than requiring the use of bespoke manufactured ones.

Thus, according to a first feature of the present invention, there is provided apparatus for generating an apparent suspended image when viewed which comprises a light-emitting screen, means to generate an image on the screen, a Fresnel lens-based optical system adapted to create, on the side of the optical system opposite to that in which the screen is located, an apparent visual image of the image displayed on the screen, and characterised by a corrector plate located between the screen and the Fresnel lens-based optical system.

We have found that, by the use of an appropriate design of Fresnel lens- based optical system and of the corrector plate, compact systems may be produced which provide a realistic image when viewed of the image generated on the screen. Although that image is effectively generated in flat form in a plane perpendicular to the optical axis of the corrector plate and Fresnel lens- based optical system, the projected image appears to an observer in front of the optical system and on the optical axis thereof, or not too far away, to float in space in front of the system and to have three-dimensionality. By appropriate design, the length of the optical axis of the system from screen to final Fresnel lens may be kept sufficiently short to enable it to be straight, i.e. to avoid the necessity of using one or more mirrors to fold the optical path of the apparatus so as to enable the components to be assembled compactly. The present invention makes use of an optical device known as a corrector plate. Such plates were originally developed in the field of optical astronomy and are often known as a result as Schmidt corrector plates. The manufacture of such Schmidt corrector plates, which are used to correct field aberrations in terrestrial telescopes, is well-established, though the degree of distortion and aberration in such terrestrial telescope apparatus is generally relatively small and the optical power of regions of the plate does not accordingly have to be very substantial. The corrector plates used in the construction of apparatus in accordance with the present invention generally need to have rather greater optical power in order to compensate for the rather more substantial distortions and aberrations introduced by Fresnel lens systems, but, by careful design and appropriate location of the corrector plate between the display device and the Fresnel optical system, it is possible to produce a viewed image which is sufficiently free of distortion to appear realistic.

It should be noted that while the use of a corrector plate enables the viewed image to be substantially free of distortion, there may be cases in which a practical corrector plate design, or one which is economically manufacturable, will not wholly remove the distortions from the optical system. In such cases, or in cases where an exceptional degree of freedom from optical distortion is required, it is possible to achieve the desired result by applying an appropriate "counter-distortion" to the electronically generated image on the light emitting screen.

The image-generating device is preferably a high-powered LCD screen. These are commercially available from a variety of sources and to an appropriate degree of definition. The technology to generate an image on such a display device is well-established. Apparatus manufactured in accordance with the invention may include such image-generating means, or simply an interface which can be connected to an appropriate computer-based system in known fashion. While, as just noted, high-powered LCD screens are commercially available from a variety of sources, we have found that commercially available high- powered LCD screen units can give rise to an unsatisfactory appearance of a greyish aura around the apparently suspended or floating image. Put another way, commercially available high-powered LCD screens are not good at producing a black background which is completely invisible around the perceived image, e.g. of a consumer product. We have now found that if the high-powered LCD screen unit contains built into it an appropriate mirror having a generally central aperture and graduated filters over the mirror allowing more light to be reflected from parts of the mirror closer to the centre of the screen than from parts more remote from the centre of the screen, the grey aura or like effect can be materially diminished.

Conventional high-powered LCD screen constructions consist of a frame supporting a liquid crystal screen unit behind which are a plurality of so-called enhancement lenses (plastics films used for directing the light), a diffuser panel and a white usually acrylic sheet, with fluorescent illumination tubes being located to the sides of the device. Generally speaking, the fluorescent so-called backlights are provided on two opposite edges on an overall frame which serves to hold the various components together.

We have now found, and this constitutes a further feature of the present invention, that if between the fluorescent light sources and the liquid crystal screen there is placed a graduated mirror mask having a central optical aperture centred on the liquid crystal screen itself, then there is an apparently continuous black surround to the image on the screen when viewed directly and no halo or aura of grey around the image viewed using the apparatus of the present invention. The graduated mirror may be produced by, for example, taking a mirror finish film having a central aperture not covered by a mirror finish and superimposing over it at least one and preferably three transmissive films having an opaque graduated pattern or texture applied thereto such that the light transmissivity of the films decreases from a position at the edge of a central transparent area as one approaches the edges of the sheet. This may be achieved, for example, by printing a series of graduated black dots on to the sheet. A typical apparatus constructed in this way may, for example, have, behind the LCD screen as viewed from the front, a mirrored sheet with the mirror surface facing away from the screen and three closely adjacent acrylic sheets printed with graduated black dots, dot size increasing with distance from the sheet centre. We have found that using such a construction, the light reflected back gives rise to a much cleaner- looking viewed image. The standard white acrylic sheet may be left out if desired.

In order to generate a convincing appearance of an image floating in front of the apparatus where an observer looks into the optical system, or, strictly speaking, looks at the image on the screen via the optical system, it is highly desirable that the image appears against a dark, preferably almost black, background. This can sometimes be difficult to achieve using conventional LCD high power screens, where the contrast between an image and an object against a dark background is not always as great as desired. In a preferred form of apparatus according to the invention, accordingly, one or more optical filters may be interposed between the screen and the Fresnel lens-based optical system, or between components of the latter, in order to filter out screen background. Such optical filters may be used with high-emitting screens of standard type and of the improved type disclosed above. For the same reason, and to minimise the effect of stray illumination from the LCD screen, it is desired to locate the corrector plate, which is usually of rather smaller dimensions than the LCD screen, in an opaque frame.

In order to maintain the components of the optical system of apparatus in accordance with the invention clean and free from dust or other contamination, it is convenient to enclose the optical system and light-emitting screen in an overall casing which is opaque on all sides save the side from which the apparatus is viewed. This side naturally needs to have a transparent window in it if the image is to be viewed. This window which, for example, typically extends over the entire width and height of a generally rectangular casing, may be made of any convenient light transmissive material, most conveniently an acrylic sheet. Such sheets are conventionally produced with a highly reflective surface, which clearly can give rise to undesirable stray reflections where the apparatus is installed in an appropriate location. In order to reduce such reflection, the window may be coated on one or both sides with an anti- reflective coating of known type. The window may also bear a polariser film applied to the side of the window closer to the high-powered LCD screen, over which an anti- reflective coating may also be applied.

In the case of a screen with a polarised film applied thereto, this may be of a known electrically controllable type so that the properties of the window may be adjusted for the best match to ambient conditions when the apparatus of the present invention is installed. The window can accordingly be a laminated polarised window incorporating a so-called light control filter. This will consist of an interlayer with the structure of the window, e.g. of a circularly polarised material with suitable electronic contacts to enable the device to be controlled. Such items are available to special order from a number of suppliers, for example Optical Filters Limited of Thame, Oxfordshire, UK.

The apparatus according to the invention is of particular value in providing an eye-catching image which will hold the attention of the viewer in circumstances where that is desired. In particular, the apparatus is of major value in drawing attention to the existence of purchaseable products in retail environments. By the careful choice of location, preferably in an area not overly illuminated at high level, the image presented to the viewer may be very effectively deployed. In particular, the certain appearance of an apparently floating image as the eyes of the viewer move into the field of view of the apparatus can provide a startlingly realistic effect.

In order to assist in catching the viewer's eye, the apparatus according to the invention may incorporate sound-generating means, for example one or more loudspeakers adjacent the front of the apparatus and to one side of the Fresnel lens most remote from the image-generating screen. Further enhancements are possible: for example, by fitting a proximity sensor to the apparatus, the approach of a potential viewer may be signalled and this may be used, e.g. to animate or change the image displayed, and/or to trigger some other form of signal, for example an audible signal, or, e.g., the release of a small quantity of perfume. This last provides a particularly interesting advertising and promotional experience: the potential purchaser can see, e.g., a floating, rotating image of a perfume bottle and experience the scent provided by the contents of a real one.

By way of further explanation, Figures 2 and 3 of the accompanying drawings show one example of apparatus in accordance with the invention. In Figure 2, the apparatus is illustrated in principle, and Figure 3 shows a perspective diagrammatic view of a practical embodiment.

Referring to Figure 2, the apparatus consists of an LCD display device 10, a corrector plate 11, a first Fresnel lens 12 and a second Fresnel lens 13 spaced therefrom, all located within a housing indicated by the dashed lines. As can be seen from the raytrace indications on the diagram, the image on display device 10 passes through the corrector plate 11 , is modified by the two Fresnel lenses 12, 13 and comes to a virtual focus in a plane 15 on the right hand side of the diagram. An observer to the right of the apparatus of Figure 2 sees a focussed image which appears to float in space in front of lens 13, i.e. to the right of the housing as shown in Figure 2. As can be seen from Figure 2, the image as viewed is inverted top-to-bottom compared with that on the screen, but it is, of course, straightforward to display the image on the screen, as viewed directly, upside down so that the apparent 3-D image is seen the right way up.

Due to the high level of optical power in the system, the floating image system performance of the apparatus shown in Figure 2 can be adjusted by moving the position of the lens system 12, 13 relative to screen 10, but this can only be done to determine the initial parameters for the system, since the corrector plate design depends on the finally chosen LCD to lens system set-up. For example, the dimensions for three systems are as set out in the following table:

The tabulated values above show approximate dimensions which can be used to benchmark the system at different optical zoom positions. It can be seen that, as the lens pair 12, 13 is moved closer to the assembly of LCD screen 10 and corrector plate 11 , the magnification of the system increases, producing a bigger image at 15, but the field of view decreases, as is common in any optical imaging system (telescope, camera, etc.).

The preferred system is System 1 as set out in the table, which gives a good quality image over a wide 60 field of view and a moderate image magnification. The 1.5x magnification of the system means that if the graphic on the LCD screen is 100mm in dimension, the projected floating image will be 150mm in dimension. A larger graphic size on the LCD can be used to provide a larger floating image, but the trade-off will again be field of view since the larger image will impinge the edge of the screen as the viewer's perspective is moved through the field in front of the system.

The two Fresnel lenses 12, 13 need to be of the required focal lengths to provide the desired effects. This may be achieved by the use of compound lenses, i.e. two Fresnel lenses adjacent one another, but it is usually preferred to keep the number of lenses small to improve the light transmission of the system and this also reduces the potential for manufacturing errors in the Fresnel lenses to generate visible distortion in the final image. We have also found that internal reflections in the optical system may be reduced by coating the side of some or all of the Fresnel lenses towards the high-emitting screen, with an anti-reflective coating of known type.

Referring now to Figure 3 of the drawings, this shows diagrammatically one practical form of apparatus in accordance with the present invention. Like components to those shown in principle in Figure 2 bear the same reference numbers.

As can be seen from Figure 3, the apparatus basically consists of a generally cubic box casing 20 which is closed on all sides save its front face which has a substantial aperture 29 cut in it. The upper face of the housing 20, denoted 28 in Figure 3, is shown cut away so that the components internal to the casing 20 may be seen.

Mounted on the rear wall of casing 20 is a high-powered LCD screen 10. Spaced in front of LCD screen 10 is an opaque sheet 21 which has in its centre a rectangular aperture into which the corrector plate is fitted. Immediately in front of the plate 21 is a filter plate 22 which serves to reduce the amount of light coming from screen 10. Located near the front of housing 20 are the two Fresnel lenses 12 and 13 with a further filter plate 23 located between them. Filter plates 22 and 23 may be of the same material, e.g. a commercially available smoked acrylic panel.

The front of Fresnel lens 13 can be seen through aperture 29 and essentially constitutes the front of the optical system which can be looked at by a person who will, if the apparatus is unpowered, essentially see a black rectangle.

To either side of aperture 29 are a pair of side extensions or wings, each of which carries two small loudspeakers 25 indicated merely diagrammaiically. The overall appearance of the apparatus of Figure 3 seen from the front (bottom right as shown in the drawing) is accordingly that of a somewhat square-looking screen display unit, but, in marked contrast to the normal appearance of e.g. a cathode ray tube-based screen display unit, or a flat plasma screen, the image produced by the apparatus of the present invention is not a generally flat image viewable over a wide range of viewing angle by anyone in front ^"of the apparatus, but rather is a blackened aperture into which one should look if one wishes to see an image.

Signals corresponding to an appropriate image to be reproduced on screen 10 may be fed in via a standard multi pin connector 26 located on the side of housing 20 near its base. That socket may also include pins for connection to the loudspeakers 25.

It has been found that the appearance of the image is enhanced if the corrugated sides of Fresnel lenses 12 and 13 face one another rather than both facing the same direction, or facing apart.

The apparatus shown in Figure 3 is configured in particular for use as an in- store advertising display module. In order, for example, to demonstrate an eye-catching image of an item for sale in the store, a video tape or other optical record such as a DVD is first prepared showing the item in question. The image may be static, but is normally dynamic, i.e. moving, for greater visual attraction, and the video or DVD record may comprise an appropriate audio signal, for example background music, commentary, or other audibly perceptible signal. The video reproduction device, such as a video cassette player or a DVD player, may be connected to socket 26 via a suitable connector and used to drive the high density LCD display panel 10 as well as to produce appropriate audible signals via the loudspeakers 25.

The combined use of audible reproduction means and the image display is of particular value since, by use of an appropriate "soundtrack", the attention of a potential viewer of the image may be drawn to the unit itself and, assuming that the listener is then in the field of view of the optical system, when the listener turns his or her head to locate the source of the sound, i.e. loudspeakers 25, the viewer automatically looks to the aperture 29 between the speakers and appears to see the image which is being generated on screen 10 floating somewhat in front of lens 13. Because the image seems to be suspended in space, the brain perceives the image as being 3-dimensional rather than 2-dimensional, which perception is enhanced if, for example, the image is essentially a 2-dimensional "photograph" of an object, but the object is made to move, e.g. to rotate about an axis passing through it.

When, in such circumstances, the viewer, some distance away from the apparatus and in the direction of the bottom right of the drawing identified as Figure 3, looks towards aperture 29, he or she sees the image apparently floating against a black or very dark background. The appearance of the image floating in front of lens 13 is materially enhanced by the fact that, as an observer looking at lens 13 moves, the image of the object being displayed via screen 10 appears to move relative to the edges of aperture 29 and in a way which tricks the eye into believing that the image is a real one located floating in space in front of lens 13.

In a practical embodiment of the invention as shown in Figure 3, the area of the display screen 10 was 246 mm x 1845 mm, and the area of the corrector plate located in frame 21 was 15 cm x 15 cm. The corrector plate was shaped in accordance with the following formula:

Y²/R x = + A₄Y⁴+AeY⁶+A₈Y⁸...A_nYⁿ

where x is the curve sag distance

Y is the radial distance from axis of rotation of the curve R is the vertex radius of the aspheric base curve

K is the conic constant, and

A is the nth aspheric coefficient, the first few significant terms being typically A₄ = -1.5 x 10^"4 A₁₂ = -1.28 x 10^_18

A₆ = 2:11 x 10^"8 A₁₄ = 14.8 x 10^"16

A₈ = -1.48 x 10^"11 A₁₆ = 7.0 x 10^"27

A₁₀ = 5.82 x 10^"15

The maximum image size displayed on the screen was 100 mm x 100 mm. The distance from screen to corrector plate was 5 mm, and from corrector plate to Fresnel lens 12 was 150 mm. The space between Fresnel lenses 12 and 13 was 280 mm. The focal length of Fresnel lens 12 was 280 mm, while that of Fresnel lens 13 was 317 mm. Both Fresnel lenses were aspheric with infinite conjugate.

Compared with the known prior art devices, the present invention provides a compact effective apparatus which can be used, with appropriate image- storing and -generating apparatus such as a video tape player or DVD player, to produce arresting visual effects. Compactness is achieved without the need for a mirror, and because of the use of the corrector plate, filters and masks, the lens system is simplified and can be arranged close to the screen, to provide a high contrast apparently floating 3-D image well defined against an essentially dark background when viewed, and with a low level of image distortion.

Claims

1. Apparatus for generating an apparent suspended image when viewed which comprises a light-emitting screen, means to generate an image on the screen, a Fresnel lens-based optical system adapted to create, on the side of the optical system opposite to that in which the screen is located, an apparent visual image of the image displayed on the screen device, and characterised by a corrector plate located between the screen and the Fresnel lens-based optical system.

2. Apparatus according to Claim 1 wherein the light emitting screen is a high- powered LCD screen.

3. Apparatus according to Claim 2 wherein the light-emitting screen is in the form of a screen unit including a graduated reflecting mirror having a central transparent portion.

4. Apparatus according to any one of Claims 1 to 3 and including one or more optical filters between the screen and the Fresnel lens-based optical system.

5. Apparatus according to any one of Claims 1 to 4 wherein the screen and optical system are located in an opaque casing having a window through which the optical system may be viewed.

6. Apparatus according to Claim 5 wherein the window is polarised.

7. Apparatus according to any one of Claims 1 to 6 and incorporating an audio output device.