WO2004066038A1

WO2004066038A1 - Improved hologram display system

Info

Publication number: WO2004066038A1
Application number: PCT/NZ2003/000005
Authority: WO
Inventors: John Stuart Fleming
Original assignee: John Stuart Fleming
Priority date: 2003-01-23
Filing date: 2003-01-23
Publication date: 2004-08-05
Also published as: AU2003206463A1; EP1616226A1

Abstract

An improved system is disclosed for displaying multi-image or animated holograms, in which the angle at which the incoming light illuminates the hologram is varied over time. In a preferred form, the display includes an enclosure (76) having top and bottom portions (78, 80), two sides portions (82, 84), rear and front portions (86, 88) with a viewing opening (90). A hologram (10) is attached to the inner wall (86) of the enclosure. At one side (84) of the enclosure, a mirror (92) is mounted in place by bracket (94), and at the other side (82), a light assembly (96) directs light emitted by a movable lamp (110) to the mirror (92) from which it is reflected onto the hologram (10).

Description

IMPROVED HOLOGRAM DISPLAY SYSTEM

FIELD OF THE INVENTION

The present invention relates generally to the field of producing and displaying holographic images. More particularly, it relates to multiple-image holographic displays in which the distance from the hologram to its light source is preferably minimized to permit the hologram and light source to be contained within a minimally sized enclosure. BACKGROUND OF THE INVENTION

Where a hologram is to be displayed it can be important to minimize the distances from the hologram to the hologram's light source while at the same time minimizing the intrusion of the light source into the viewing space. This is especially so when the light source is to be contained in an enclosure together with the hologram and where it is desirable or necessary to limit the size of the enclosure.

For a substantially planar hologram, minimization of these distances substantially parallel to the hologram minimizes the width of the enclosure. Minimization of the distance substantially pe endicular to the hologram minimizes the depth of the enclosure. For a 600 millimetre x 600 millimetre square planar hologram the minimum distance to the light source with present technology is approximately 1400 mm, and it will readily be appreciated that an enclosure depth of 1400 mm is a severe limitation on the display embodiments.

It is possible to reduce this depth by reflecting the light from the light source through mirrors, but there are significant limitations on the enclosure depth that still arise, and with present technology with a 600 mm square planar hologram, while illuminating all of the hologram, the minimum enclosure depth that results is 854 mm, which is still a severe limitation on the display embodiments.

This present limitation on the minimum enclosure depth arises because of certain characteristics of a hologram, which can be illustrated by reference to a planar reflection hologram as shown in Figure 1. In Figure 1, there is a planar hologram 10 (shown from the rear), which is viewable through an observable angle 6 within a nominal viewing plane 12. The hologram is illuminated by light along a path 11. The illumination angle is defined as the angle between the light striking the hologram at a point and the normal (N) to the hologram at that point. There is an optimum illumination angle 7 between the incoming light to the hologram and the normal to the hologram where the light strikes the hologram, which gives optimum reconstruction of the light from the hologram. For example, using parallel light striking the centre of the hologram, the angle 7 might typically be 50 degrees from the normal to the centre of the hologram as shown in Figure 1. It is possible to vary the illumination angle by plus or minus a certain number of degrees (angles 8 and 9 respectively) before the image produced disappears or suffers unacceptable distortion due to destructive interference of the wavefronts. The acceptable degree of variation might typically be 25 degrees, so that the actual illumination angle could vary between 25 to 75 degrees from the normal to the centre of the hologram while still producing an acceptable viewable image.

The range of acceptable illumination angles is a function of the grating spacing and thickness of the holographic film. A lower film thickness allows a greater illumination angle, but as the film thickness decreases, the diffraction efficiency decreases and because of this the brightness also decreases. There is, therefore, a practical limit that is reached. The grating spacing is determined by the wavelength of the light that is to be reconstructed and, hence practically, by the need to view at least the primary colours red, blue and green. This is true even in the case of viewing a black and white hologram. As the illumination angle is varied, it is possible to have the reconstructed light from the hologram show a different scene, forming an animated hologram. To avoid smearing of (or cross talk between) scenes of the animation, each scene must occupy a subtended angle, which may be no less than a certain value. This dictates that there are a certain maximum number of different scenes that may be viewed by varying the illumination angle. This subtended angle is the angle subtended either by the lens of the eye at a given distance from the hologram in the case where the viewing plane is perpendicular to the plane in which the illumination angle is varied, or between the eyes on the viewing plane at a given distance from the hologram in the case where the viewing plane is parallel to the plane in which the illumination angle is varied. The subtended angle is much lower when the plane in which the illumination is varied is perpendicular to the viewing plane, and hence for a given variation in illumination angle, it is possible to have more scenes in this configuration. The different scenes may be arranged to be time- dependent views of the same scene, and in this way varying the illumination angle gives rise to animation of the scene.

Because the number of scenes has a practical maximum, the total amount of animation also has a practical limit. In either case it is desirable to be able to maximize the possible number of scenes, whether of animation or of static scenes.

Another limitation on enclosure size arises from the need to avoid having the light source occlude the hologram when viewing a reflection hologram through a viewing opening in the enclosure. The light source and all other physical parts must not be situated in the line of sight between the hologram and the viewing opening, but must stay outside or on an imaginary surface that includes all lines drawn from all points on the edges of the viewing opening to all points on the edge of the hologram when viewed from each point on the edge of the viewing opening in turn. When the viewing opening and hologram are planar and parallel to one another and the viewing opening is the same size as the hologram and is directly in front of the hologram, this surface consists of planes drawn from each side of the hologram coaxially with the perpendicular to the hologram. As shown in Figure 2, in the case of the minimum illumination angle, the light source must be at least as far away as dimension Dl if it is not to encroach on the viewing opening. If the illumination angle is changed to 50 degrees, then the light source need only be distance D2 away from the hologram, but if this were the minimum illumination angle then the numbers of scenes viewable by altering the illumination angle would be decreased.

Even allowing for reflecting the light source through mirrors, with the above geometry, in the case of a 600 mm square hologram with a minimum distance from the centre of the hologram to the light source of 1400 mm, to avoid intrusion of the light source into the viewing opening while still illuminating the complete hologram, the last mirror in the reflection chain may not be closer to the hologram than distance Dl. This distance Dl is the minimum depth of any enclosure. With the above geometry, Dl is 854 mm which, although less than the 1400 mm distance to the light source, still represents a severe limitation on the display embodiments. SUMMARY OF THE INVENTION In a basic aspect, the invention is a display system for a multi-image hologram (such as, for example, an animation hologram) that comprises a hologram, a light source, and at least one reflecting surface (generically referred to herein as a mirror) for reflecting light from the light source to the hologram, wherein the angle between the incoming light illuminating the hologram from the mirror and a normal to the hologram where the light strikes the hologram (i.e., the angle of illumination or illumination angle) is varied over time. The angle of iU--mination can be varied by moving the light source, or the mirror(s) or both. The components are preferably all contained within or on the surface of an enclosure having a viewing opening for viewing the hologram. As used herein, reference to the light source means -a physical light source or lamp that is used to illuminate the hologram. Reference to the incoming light means the light that shines on the hologram, typically after being reflected from the light source through one or more mirrors. Reference to an apparent light source generally means a virtual light source positioned at the location from which the actual incoming light source appears to be coming when viewed from the illumination target.

In the preferred embodiment, the light from the light source is reflected through one or more mirrors (i.e., reflective surfaces) and the illumination angle of the light striking the hologram is varied in such a way that, for all particular points on the surface of angle alteration for the incoming light, a plane tangent to the surface of angle alteration (defined below) at that particular point is not always the same plane as the illumination plane (defined below) for that light source at that same particular point. Thus, for at least some points on the surface of angle alteration for the incoming light, a plane tangent to the surface of angle alteration at that particular point is not the same plane as the iUumination plane for that light source at that particular point. This allows the depth of the enclosure to be reduced to D2, less than Dl, while still maintaining the same number of scenes or frames of animation as if the distance was Dl. With the geometry described above, and referring again to Figure 2, D2 can be reduced to less than half of Dl , while still maintaining the same number of scenes or frames of animation as if the distance was Dl. It will be appreciated that the reduction in enclosure depth by such a large margin greatly increases the number of possible practical display embodiments and their usefulness. In practical terms it allows a hologram to be mounted in an enclosure or cabinet with a self-contained light source and of a depth acceptable for mounting on, against or at least partially within a wall. Without this depth reduction, this is not practically possible in many situations because any the enclosure, including its light source, would intrude substantially into the room space where the hologram was to be displayed. One specific application in which this aspect of the invention would be useful is in the case of a holographic .fireplace display in which it would be desirable to be able to fit all of the components of the display (including the light source) within the confines of a standard fireplace despite the enclosure being relatively shallow from front-to-back. Another specific application is in point of sale displays, for example in the front panel of a vending machine.

The surface in which the illumination angle is altered, or the surface of angle alteration for a particular apparent light source, is the surface that is the locus of all lines drawn from the nominal centre of the apparent light source to the corresponding point of greatest light intensity on the hologram, as the position of the apparent light source for the light illuminating the hologram varies. For example, referring to Figure 3, a planar hologram is shown having a line N normal to its centre. If the direction of the incoming light (or the location of the apparent light source) were varied between paths AO, BO and CO, the surface of angle alteration would be a surface that includes all those paths (and all other paths that are followed as the direction of the light source is moved between points A, B and C). When points A, B and C are in a straight line, if the apparent light source is moved linearly between positions A, B and C while always pointing at point O, the surface will be a plane as shown by plane 14 in Figure 3.

As the angle of illumination is varied and the path of the incoming light to the hologram changes, there is a different illumination plane associated with each different pathway. The illumination plane for any position of the incoming light (or the corresponding apparent light source) is the plane that includes both (1) the imaginary line drawn between the centre of the incoming light (or the corresponding apparent light source) and the corresponding point of greatest light intensity on the hologram and (2) the imaginary line normal to that corresponding point. In Figure 3, the illumination plane 16 is shown when the apparent light source is at location A. The plane includes (1) the line from location A to the centre of the hologram and (2) the line normal to the centre of the hologram. The illumination plane for any position of the incoming light will intersect the plane (or surface) of angle alteration because both planes include the line between the incoming light source at that position and the centre of the hologram. Alternatively, the nominal illumination line of a particular apparent light source is the line drawn from the nominal centre of the apparent light source to the corresponding point of greatest light intensity on the hologram.

The surface of angle alteration is the surface that is the locus of all nominal illumination lines as the position of the corresponding apparent light source for the light illuminating the hologram varies. This surface may be disjoint as for example in the sense of consisting of, for example, several planes intersecting each other at angles. In one embodiment, the hologram display system is characterized in that, for any part of the hologram, the surface of angle alteration is not the same as any optimum illumination plane, and all optimum illumination planes are within 50 degrees of the nominal viewing plane. An optimum illumination plane is defined as the plane of points on an optimum illumination angle line and the line of the normal to the hologram used to define that optimum illumination angle. For a given incoming light source on a planar hologram, there is only one optimum illumination plane. In a related embodiment, the hologram is a planar hologram, and for any incoming light to the hologram, the surface of angle alteration and the optimum illumination plane are 90 degrees apart, or approximately 90 degrees apart.

Another embodiment comprises a hologram display system in which the surface of angle alteration is not the same as any optimum illumination plane, and all optimum illumination planes are within 50 degrees of the nominal viewing plane. The nominal viewing plane is defined as the horizontal plane through the centre of the hologram when the hologram is aligned in a manner suitable for viewing. The actual viewing plane (which is the plane defined by the nodes of the lenses of the eyes and the centre of the hologram) may differ from the nominal viewing plane.

Another embodiment comprises a reflection hologram display system wherein a hologram is at least partially enclosed and at least one mirror is inteφosed between the light source and the hologram so that the distance from an edge or apex of the mirror is within the larger of either 500 mm, or thirty percent of the largest dimension of the hologram, from any surface of a volume defined by the shape of the viewing opening projected along the normal to any part of the hologram.

In another embodiment, a reflection hologram display system that has at least one hologram at least partially enclosed, and at least one mirror is inteφosed between a light source illuminating the hologram so that no part of any mirror is contained within a volume defined by the shape of the viewing opening projected along the normal to any part of that hologram.

In another embodiment, a reflection hologram display system is characterized in that any mirror that sends light originating from any light source in a straight line to the hologram is arranged so that the angle at which at least one incoming light path to the mirror for reflecting light to the hologram is within 20 degrees of a line drawn through the point of reflection parallel to a plane tangential to the hologram where that light path strikes the hologram.

In another embodiment, a reflection hologram display system is characterized in that any mirror that sends light originating from any light source in a straight line to the hologram is arranged so that any incoming light path to the mirror does not pass through and beyond a plane parallel to the plane tangential to the hologram where that light path strikes the hologram, with the parallel plane positioned through the point on the mirror which has the greatest distance to the hologram in the direction of the normal to the hologram where that light path strikes the hologram.

In another embodiment, a reflection hologram display system having first and second reflective surfaces for reflecting light from a light source to the first mirror, and from the first mirror to the second mirror, and from the second mirror to the hologram is characterized in that the edge or point of the first mirror that is most distant from the hologram is no further away from the hologram than the edge or point on the second mirror that is furthest away from the hologram. In a related embodiment, the first mirror that is most distant from the hologram is within 50 to 150 percent of the distance from the hologram of me edge or point on the second mirror mat is furthest away from the hologram. In another embodiment, a hologram display system uses at least one partial mirror such that the outline of the portion of the surface that reflects 50 percent or more of the incident light on that portion encompasses only the area necessary to reflect light to the hologram so that all parts of the hologram are illuminated by the reflected light for all the required angles of alteration to cause the reconstruction of the chosen scenes contained within the hologram. In another embodiment, a hologram display system utilizes at least one partial mirror such that the outline of the portion of the surface that reflects 50 percent or more of the incident light on that portion encompasses between 70 percent and 130 percent of the minimum area necessary to reflect light to all parts of the hologram so that the hologram is illuminated by the reflected light for all the required angles of alteration to cause the reconstruction of the chosen scenes contained within the hologram. In another embodiment, a hologram display system utilizes at least one mirror such that the incoming light path to the mirror that subsequently reaches the centre of the hologram is within 15 degrees of the nominal viewing plane of the hologram.

In another embodiment, a hologram display system includes at least one mirror and at least one hologram curved so that the illumination angle of all light in the nominal viewing plane reaching the hologram from a specific mirror is within 5 degrees of the same value. DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a flat planar hologram showing the viewing plane and angle of orientation of incoming light.

Figure 2 is a perspective view of a flat planar hologram showing the relationship between angle of illumination and enclosure depth.

Figure 3 is a perspective view of a flat planar hologram showing a surface of illumination and a surface of angle alteration.

Figure 4 is a viewing taken from the front of a hologram display system according to the present invention, showing details of the enclosure. Figures 5 and 6 are, respectively, left and right side views of the enclosure in Figure 4, taken along the line A-A in Figure 4.

Figure 7 is a top plan view of a display system in accordance with the present invention, with the top of the enclosure removed to show the relationship of the hologram and mirrors within the enclosure.

Figure 8 is a front view of the display system shown in Figure 7, with the front of the enclosure removed and showing a system for moving the mirrors in coordination. Figure 9 is a front view of the display system in accordance with the present invention, with the front of the enclosure removed, showing the details of various slots and openings in the enclosure.

Figure 10 is similar to Figure 9 with the back of the enclosure removed and with the addition of a mechanism for coordinating movement of the light source and a mirror. Figure 11 is a perspective view of a mirror for use in a system in accordance with the present invention, showing the pivot rod and pivot control rod.

Figure 12 is a top view of a mirror and mounting bracket for mounting the mirror to a drive belt in one embodiment of a system in accordance with the present invention.

Figures 13 and 14 illustrate the path of light reflected from a light source to a hologram through two mirrors in accordance with one embodiment of the present invention, from in front of the display and from above the display.

Figures 15 and 16 show exemplary shapes of first and second mirrors for use in one embodiment of the present invention.

Figure 17 is a perspective view of an enclosure for a display system in accordance with the present invention.

Figures 18, 19 and 20 are front, top and side views of an embodiment of the present invention, showing the relationship between the hologram, mirror and light source apparatus.

Figure 21 shows the details of a lamp assembly for use in the embodiment shown in Figures 18, 19 and 20. Figure 22 is a frontal view of the light source apparatus of the embodiment shown in Figures 18, 19 and

20, illustrating various details of the mounting of the lamp assembly to the drive belts.

Figures 23 and 24 are similar to Figures 19 and 20, and show an internal housing for enclosing the light source assembly within the enclosure.

Figure 25 illustrates the changes in orientation of a single lamp assembly as it revolves in a circuit on belts in the embodiment reflected in Figures 18-20 and 22, and the guide strip that controls the orientation of the lamps.

Figure 26 is a perspective view of the internal housing shown in Figures 23 and 24, showing additional details of a shutter mechanism on the front of the housing.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention can be implemented using a variety of combinations, numbers and configurations of light sources and mirrors, and by moving either the mirror(s) or the light source(s) or both. The embodiments described below are examples of configurations that can be used to practice the invention.

It will be appreciated that the examples described below are based on illuminating all of the hologram from the light source. It is possible to reduce the distances given by not illuminating all parts of the hologram. This results in loss of detail in the reconstructed image, and this is essentially the same as the result achieved by using the constructions given on a smaller hologram. A similar situation occurs for transmission holograms, but in that case the problems associated with blocking the viewing opening are not present because the transmission hologram is illuminated from behind rather than from the front as in the case of a reflection hologram. In contrast, the limiting case giving the minimum enclosure size is obtained by positioning the closest point of the last mirror on the edge of the hologram. Figures 4 through 16 show the details of one exemplary hologram display according to the present invention, in which the light source is reflected onto the hologram through two mirrors that move in coordination with one another.

Referring first to Figures 4-8, the display generally includes an enclosure 18 for enclosing a hologram 10 and its associated components. The enclosure can be made from any of a variety of materials, including sheet metal for ease of fabrication. It includes a back portion 20, a top portion 22, bottom portion 23, first and second side portions 24 and 26, and a front portion 28 having a viewing opening 30. As shown in Figures 7-10, the enclosure houses a hologram 10 preferably mounted to the inner back surface of the enclosure. It also houses a light source 32, and one or more mirrors (in this case first and second mirrors 34 and 36) as well as other components (described below) for permitting coordinated movement of the mirror(s) and the light source.

Figures 8-12 show the details of the arrangements for coordinating movement of the mirrors and the light source. As shown in Figure 8 the first mirror 34 is pivotally attached to a first vertically oriented belt 38 at one side of the enclosure, and the second mirror 36 is pivotally attached to a second vertically oriented belt 40 at the opposite side of the enclosure. As shown in Figure 9 (in which the mirrors are not shown to reveal underlying structures), each of the belts turns on an upper pulley 42 and a lower pulley 44 respectively connected to the top of the enclosure by tensioning brackets 46. The upper or lower pulleys (and preferably the lower pulleys) are supported and turned by a drive mechanism, causing the belts to turn in unison and thereby move the mirrors up and down in unison within the enclosure. The drive mechanism can be a drive shaft 48 supported by bearings 49 that extends through the centre of the drive pulleys 44, and a motor 50 for turning the shaft to move the belts. The motor 50 can be any of a number of different types, but is preferably a stepping motor controlled by a microprocessor. The motor can also be a speed controlled AC motor operating through a geared reduction with reversing clutches. It would be possible to use a DC motor, but it is believed that reliability would not be as good as with an AC motor. The direction or speed of movement of the mirrors can be controlled by controlling the direction or speed of rotation of the motor via a controller 52 (such as a microprocessor) or some other means. The shaft 48 can be rotated in a regular pattern to raise the mirrors up and down to the same points in a repeating cycle, or to raise and lower them together in a random or varying pattern. For instance, in the case of a holographic fireplace display or other similar scene, a non-repetitive pattern of movement for the mirrors is desirable to avoid constantly repeating the same sequence of scenes from the hologram.

As the angle of alteration changes, both mirrors move in the vertical (Z) direction. The mirrors are required to rotate also, so that the hght path from the centre of the hologram to the light source is the same. This means that the last mirror is required to rotate in the XZ plane (parallel to the hologram) and the XY plane (orthogonal to the hologram), and the first mirror is required to rotate in the XZ plane. Thus, as the first and second mirrors move up and down within the enclosure, they also pivot to ensure that the light source will be reflected continuously onto the centre of the hologram. To accomplish this, each of the mirrors is pivotally attached to the corresponding belt via a bracket 54 fixed to the belt, as best shown in Figures 8 and 12.

As shown in Figure 11, each mirror has a pair of generally horizontal rods glued or otherwise fixed onto the back of the mirror. The first rod 56 extends beyond both sides of the mirror and extends through holes in the bracket 54 on either side of the mirror, as shown in Figure 12 with respect to the first mirror 34. A similar arrangement is provided for the second mirror 36. The second rod 58 in each mirror extends beyond the edge of the mirror adjacent the rear of the enclosure and is used to control the pivoting of the mirror as it moves vertically with the belt. As shown in Figure 9, first and second slots 60 and 62 are cut into the enclosure, preferably on the rear 20 of the enclosure. The rod 58 of the first mirror 34 extends into the slot 60, and the rod 58 of the second mirror extends into the second slot 62. Each slot is shaped so as to cause the associated mirror to pivot about the pivot rod 56 as the mirror is moved up and down inside the enclosure to ensure that the mirror will be angled properly as it moves up and down within the enclosure. The specific angles at which the mirrors are mounted and the specific shape of the slots that guide the pivoting of the mirrors will of course vary depending on the shape and size of the enclosure and geometry of the specific display.

As shown in Figure 10, the light source 32 in the embodiment shown is preferably mounted in an opening 64 in the top of the enclosure and is adapted to track the movement of the first mirror 34, so as to shine directly onto the first mirror 34 even as the mirror moves up and down within the enclosure. The light source 32 is pivotally mounted to the enclosure 18 via a bracket 64 that carries an axle 66 extending through the light source assembly, allowing the light source to pivot in the bracket. To coordinate the movement of the light source 32 and the first mirror 34, the first mirror 34 and the light source 32 are linked together via a rod 68, a member 70 and a bushing 72 that is attached to the end of the member 70. The member 70 is attached at one end to the belt (for example to the bracket 54 that holds the first mirror 34 to the belt) and moves up and down with the mirror. The bushing 72 is attached to the upper end of the member 70, and a portion of the bushing engages a slot 74 in the back of the enclosure, shown in Figures 9 and 10. As the mirror moves up and down, the bushing 72 slides within the slot 74.

The rod 68 extends from the light source 32 and through a bore in the bushing 72. As the bushing 72 moves within the slot 74, the adjacent end of the rod 68 is lifted or lowered, thereby causing the light source to pivot The rod 68 is able to slide within the bore in the bushing 72, to accommodate the movement of the bushing relative to the light source.

As shown in Figures 13 and 14, as the first and second mirrors 34 and 36 move up and down with the rotation of the belts, they are coordinated with one another and with the light source 32, to ensure that the light from the light source 32 will be continually directed onto the hologram. At any instant, the effect is the same as if a direct light source (shown as the apparent light source in Figures 13 and 14), much farther from the hologram 10 than the actual light source 32, was being used to illuminate the hologram.

The orientation of the last mirror in the chain of mirrors from the light source to the hologram may have an influence on the depth of an enclosure. Keeping in mind that the mirrors should not move so as to be visible through the viewing opening of the enclosure, the last mirror may not be rotated clockwise (when viewed from above) beyond some point without increasing the overall depth of the enclosure. As shown in Figure 14, the distance from an imaginary line 73 across the front edges of the mirrors (i.e., the edges closest to the front of the enclosure) to the centre of the hologram would be greater than the distance from the end of the last miιτor to the centre of the hologram. In addition, if the last mirror is rotated too far counter clockwise (when viewed from above), then the overall width of the enclosure must increase.

The minimum vertical size of the enclosure is determined by the distances of the extreme top and bottom edges of the last mirror above and below the hologram respectively at the mirror positions given by the maximum angles of alteration. It is possible to rotate the first mirror so that the mechanical parts of the light source do not extend outside the enclosure size dictated by this. It is also desirable to minimize the amount of light not coming directly from the hologram that can emanate from the enclosure. This gives the greatest shaφness and contrast to the viewed image and can be thought of as giving the best signal to noise ratio. Because of this it is desirable to ensure that only the necessary light reaches the hologram and that all other light is blocked and/or attenuated before exiting the enclosure. It is therefore desirable that the mirrors are only of sufficient size to just illuminate the hologram at all the allowable angles of alteration. As shown in Figure 14, the first mirror is in a position such that the horizontal distance from the outermost edge of that mirror is the same distance from the edge of the hologram as the distance from the hologram to the outermost edge of the last mirror. This gives horizontal symmetry to the enclosure, while still maintaining the minimum horizontal enclosure size. It is also possible to arrange the first mirror so that the beam from the centre of the hologram to the light source becomes vertical before the first mirror, but this is at the expense of additional horizontal width of the enclosure. That does, however, increase the efficiency of illumination and also means that the first mirror does not need to rotate as the angle of alteration changes.

It is advantageous to have the light path to the centre of the hologram being horizontal (i.e., in the nominal viewing plane) before the last mirror. This minimizes the horizontal size of the enclosure for a given number of frames to be viewed. The maximum angles of alteration for the last mirror are then plus and minus the same angle about the horizontal, and this means that the distance of the edge of the mirror furthest away from the hologram is minimized. If the light path were not horizontal, then the maximum angle above the horizontal for the last mirror would not be the same as the maximum angle below the horizontal, and the furthest away edge of the mirror would be greater for the case of the larger of these two angles.

The sizes of the mirrors shown in Figures 15 and 16 are the minima for those mirrors for the specific angle of alteration such that all parts of the hologram are illuminated. As the angle of alteration changes, so the positions and shapes of these mirrors change. To have fixed mirror sizes for all the angles of alteration needed for a given design, the minimum mirror sizes are given by the loci of the corresponding corners of the mirrors for all the mirror shapes for all the possible mirror positions. The geometries shown in Figures 13 and 14 give rise to mirror shapes similar to those shown in Figure 15 for the last mirror and in Figure 16 for the first mirror. The mirror shapes can be attained, for example, by cutting reflective sheet material to the patterns shown in Figures 15 and 16, or by using a rectangular or other shape and coating or blanking it so that the highly reflective portions of the sheets correspond to the shapes shown. Different geometries for the light source and mirrors will of course give rise to different mirror shapes, but the principle remains the same.

As the distance to the point light source increases, the last mirror changes so that the distance from its extreme left-hand edge to the edge of the hologram becomes less, and therefore the overall width of the enclosure becomes less. There is therefore a maximum distance for the point light source to the hologram such that the mechanical parts of the light source just reach the extreme left hand edge of the last mirror. It is this geometry that gives the least size enclosure for a given hologram.

It can be seen that these arrangements give rise to a minimum size for an enclosure for a given size hologram, when the hologram, light source and mirrors are arranged such that for all particular points on the surface of angle alteration for the light that illuminates the hologram, a plane tangent to the surface of angle alteration at that particular point is not always the same plane as the illumination plane for that hght source at that same particular point. It will be appreciated that certain small variations in mirror positions and angles close to the optima described will also give acceptable viewing results, while compromising the enclosure size only slightly.

The diagrams given have been shown with respect to a planar hologram and a coplanar viewing opening. However the same principles apply to curved or non-planar holograms and to non-planar viewing openings. In the case of non-planar holograms, the hologram can be thought of as being constructed of a series of finite planar elements joined at their edges, and the principles and diagrams can be applied to each element in turn. In practice holograms may be thought of as, or actually made up of, individual holographic elements called hogels. The principles and diagrams may be applied to each hogel.

This method can also be used for holograms that are curved in two planes substantially at right angles to each other. It is possible to significantly reduce the distance to a point light source even when mirrors are not used by curving the hologram so that the normal to the hologram at a particular point is displaced towards a line drawn from the point to the light source. This has the effect of reducing the angle of incidence and therefore allows the light source to be brought closer to the hologram before the reconstruction of the scene is affected.

Where the scene being viewed is an animation, it is desirable that the animation be viewed at a set or nominal frame rate which is related to the need for the viewer to see a smoothly altering scene. If the frame rate alters from the nominal rate, then the animation appears to speed up or slow down. By altering the speed with which the mirrors move in the Z direction it is possible to alter the rate of animation, and objects in the scene appear to speed up or slow down. This may be used in the case of a fire scene, for example, to change between a fast highly active flame and a slow lazy flame. In addition, since the vertical distance between scenes varies with the Z position of the mirrors, for a constant chosen animation rate it is necessary to vary the speed in the Z direction for the mirrors to maintain a fixed animation rate. For many animations this is a critical factor: failure to alter the mirror speed in the Z direction may give rise to undesirable variations in animation rate which detract from viewing. In other cases, varying the speed may give rise to special effects that are desirable.

As noted above, animation of holograms is achieved by varying the angle of illumination from the incoming light to the hologram. This causes a viewer to see different images of the same scene shifted in time relative to the preceding image as the illumination angle advances in a given direction. In this way the scene appears to animate. There are fixed limits to the numbers of frames that may be reconstructed from a given hologram. This means that there is a fixed limit to the duration of the animation before the animation ceases, reverses or repetition occurs. It is desirable in many uses to maximize the duration of animation between repetitions.

With some types of animations it is not possible to discern whether the animation is going forwards or backwards with respect to time. Some examples are a field of flowers waving in a swirling wind, a flame in a fireplace, or a panning view of a bird against a cloudless sky. This type of animation is said to be isochronous. For isochronous animation, it is possible to achieve an extremely large number, or even an infinite number of animation sequences before any repetition occurs. This may be done by changing the angle of illumination to the hologram such that the angle increases in a given direction, and then reverses direction from time to time. Depending on the actual scene to be animated, this may be on a random basis, a timed basis, or may be keyed to specific frames.

For example, where there are 150 frames of the scene which constitute the animation, the animation could advance to say the 50^Λ frame, then reverse to say the 39^th frame, and then advance to say the 75 ^h frame etc. This would represent three sequences. These types of sequences may continue for a very large or even an infinite number of sequences before any actual repetition of a sequence is necessary. By this means the time between actual repetitions of a sequence may be significantly extended.

For some scenes it may be necessary to define the actual sequence of frames where the animation reverses to ensure that the animation appears to behave in way that we would expect. For other scenes a random or timed reversal may be sufficient. Some animation sequences that are not isochronous may be made isochronous by removing any non-isochronous elements from each frame before encoding it in the hologram. For example, a fire may generate smoke or sparks, and the animation of these in reverse would be anomalous. Removing these elements from each frame would leave an isochronous animation. The above-described technique for extending animations may be used with any of the display systems disclosed or claimed herein, but is not limited to such systems or to any other type of display or display system and is equally applicable to other display systems.

Figures 17 through 26 show another embodiment that is particularly advantageous with holograms that allow high illumination angles, such as those having optimum illumination angles approaching about 70 degrees. This embodiment does not require any moving mirrors. Instead, it comprises a single fixed mirror, and two light sources that move in unison. As shown in Figure 17, the display includes an enclosure 76 having a top portion 78, a bottom portion 80, first and second side portions 82 and 84, a rear or back portion 86 and a front portion 88 with a viewing opening 90. A hologram 10 is attached to the inner rear wall 86 of the enclosure. As shown in Figure 18 and 19, at one side of the enclosure a static mirror 92 is mounted in place by a bracket 94 or other suitable means. At the other side of the enclosure is a light assembly 96 that directs light to the mirror 92, from which it is reflected onto the hologram 10 to illuminate the hologram.

The light assembly 96 includes two side-by-side spaced-apart belts 98 and 100 that are each carried on an upper pulley 102 and a lower pulley 104, and that rotate in unison about the pulleys. The belts 98 and 100 are driven in unison by a stepping motor 106 that engages and turns both upper pulleys 102 via a drive shaft 108 that extends from the motor and through both upper pulleys. As best seen in Figure 18, first and second lamps 110 and 112 are carried at opposite ends of the twin belts 98 and 100, with each lamp 110 or 112 being attached to the twin belts by a mounting assembly described below, such that they ride in the space between the spaced-apart belts. As the belts 98 and 100 revolve on the pulleys in unison, they carry the lamps 110 and 112 in a continuous circuit around the upper and lower pulleys 102 and 104. As the belts rotate in unison, one of the lamps 110 or 112 will always be on the side of the circuit facing the mirror 92, except when the lamps are transitioning simultaneously through the extreme top and bottom of the circuit defined by the revolution of the belts.

At any given moment, one of the lamps 110 or 112 (whichever happens to be on the side of the circuit adjacent to the mirror) will be shining on the mirror. As that lamp moves vertically, the angle of that lamp is altered in a manner described below, so that the light from the center of the lamp will hit the mirror 92 in such a way as to be continuously reflected onto the center of the hologram 10, even as the lamp moves vertically.

Turning next to Figure 21, each lamp 110 or 112 is carried on a generally u-shaped mounting bracket 114. Axles 116 extend from opposite sides of each bracket 114. As shown in Figure 22, each of the axles is pivotally held by a flange or member 118 that extends from the corresponding belt 98 or 100, thus attaching the bracket 114 to the belts and permitting the bracket 114 and its associated lamp 110 or 112 to pivot between the belts, much like a chair on a Ferris wheel. The axle 116 nearest the rear wall 86 of the enclosure 76 extends through the flange 118. A fixed arm 117 is connected to the end of the axle that extends through the flange. The distal end of the arm 117 includes a bushing or wheel 120, the pinpose of which will become apparent. As shown in Figures 23 and 24, the entire lamp assembly (including the belts, pulleys, lamps and their associated components) is contained within a housing 122 inside the enclosure. The housing serves to block extraneous light from the lamp 110 or 112 that is on the backside of the circuit and thus not actively illuminating the hologram. The housing 122 fully encloses the lamp assembly, except on the front side of the housing, i.e., the side facing the mirror, which is open. The motor 106 is preferably mounted on the outer surface of the housing 122, with the shaft 108 extending through the wall of the housing and through the pulleys within the housing, and being supported by the opposed sidewalls of the housing. The axle for the lower pulleys is similarly supported by the sidewalls of the housing.

A slot formed from raised strips or walls 124 extends inwardly from the sidewall of the enclosure, adjacent to arm 117 as shown in Figure 21. The strips are preferably thin strips of steel with their edges welded to the inner surface of the enclosure. The p-upose of this slot 124 is to control the orientation of each lamp as the lamp travels around the circuit, by guiding the wheel or bushing 120 at the end of the arm 117 in a predetermined path. The strip is generally shaped to follow the locus of points traversed by the wheel 120 as the associated lamp assembly makes a complete loop of the circuit while oriented in the desired direction at each spot along the circuit, as shown in Figure 25. The slot 124 controls the position and orientation of arm 117, which in turn controls the angular orientation of the brackets 114 of each of the lamps 110 and 112.

Each lamp can use a standard MR16 or similar bulb that comes pre-mounted with a parabolic reflecting assembly to provide greater light intensity for a given wattage. Power is provided to each lamp by electrical wires (not shown) that extend into the housing 122 but remain situated on the outside of the plane of the outermost (from the hologram) pulleys. To prevent the wires from twisting as the lamps travel around the circuit, the movement of each lamp 110 and 112 is controlled by the slot 124 so that the lamp does not pivot through a complete circle as it travels around the circuit defined by the revolution of the belts, as shown in Figure 25, Thus, as shown in Figure 25, each lamp remains pointed in the general direction of the mirror, even when the lamp is on the backside of the circuit opposite the mirror, except that it can be deliberately tilted in some positions so as to minimize the enclosure size adjacent to the light source assembly or to avoid the upper drive shaft or lower axle when it traverses the top or bottom of the circuit.

Turning to Figure 26, a shutter assembly is provided to shield the hologram from extraneous light from whichever lamp is not directed at the hologram at any given moment. The shutter assembly occupies the open front of the housing 122, and generally comprises an upper shield 126 at the top of the front opening and a lower shield 128 at the bottom of the opening and a shutter 134. In a typical display, the shields will each be approximately 50 mm tall, and will extend across the entire width of the front of the housing. The shutter is typically a flat sheet with slot 132 to allow passage of light. The shutter structure 134 is held in a groove or channel 133 formed on the sides of the front opening in such a manner that the shutter structure is able to slide up and down in the groove or channel. When the lamp assembly that is shining on the mirror 92 nears the top pulley, a pin or other structure 138 attached to the shutter 134 and extending into the housing from the shutter 134 is engaged by a portion of the lamp assembly, such as arm 117. At that instant the light from the lower lamp (which is simultaneously approaching the lower pulley) is still shielded by the lower shield 128. As the upper lamp continues to move upward, it raises the shutter 134 and the pin 138 with it. As the upper lamp begins to move rearward and over the top of the upper pulleys 102, the pin 138 moves away from aim 117, allowing the shutter 134 and pin 138 to drop back into place when the upper lamp is at or close to the top of its travel. The shutter is shown in a position where this action is about to occur. By that time, the lamp that has just started its upward journey is sufficiently high to clear the lower shield 128 once the shutter 134 has dropped back into place. This cycle is repeated continuously as the lamps move around the pulleys in a continuous circuit. To further protect the hologram from extraneous light, a shield can be positioned between the belts, from the upper pulleys to the lower pulleys, provided the shield must not interfere with the pivoting of the lamps between the belts. It should be kept in mind if the active lamp (i.e., the lamp on the side of the circuit facing the mirror) travels at a uniform speed when illuminating the hologram, the rate of change of the angle of alteration will vary depending on the lamp's location. This will in turn affect the rate at which the animation is reconstructed. If it is desirable to have the animation displayed at a constant rate, the speed of the belts must be controlled accordingly. While the lamps in the above-described embodiment have been described as moving vertically upward while illuminating the hologram, they could also move downward. The direction of revolution of the belts could also be reversed from time to time.

Another embodiment uses a transmission hologram mounted at the front of the enclosure with the mechanisms behind it. A red lamp mechanism and mirror, a green lamp mechanism and mirror, and a blue lamp mechanism and mirror are provided within the enclosure, with each mechanism separated by an angle, for example of 60 degrees. The separation is necessary in a transmission hologram to ensure that light from a particular colour lamp is at a great enough angle to prevent reconstruction of the scenes encoded on the hologram by the other colours. A reflection hologram only reflects reconstructed light for the corresponding particular wavelengths of light, i.e., red with red, green with green, blue with blue, and not red with green, or red with blue and so on. The advantage of this arrangement is that the view at the front of the enclosure is that of the whole width of the hologram, and not a reduced size as is required with a reflection hologram by the necessity to have a direct line of view from the eyes to the hologram.

A significant time and cost element in the production of holograms is that of producing the images that are encoded on the hologram. This is frequently done by producing an animated computer model and rendering the required number of frames from the model or by filming an actual scene. The time to produce the model or film and its cost is proportional to the number of frames of animation, and the time and cost of rendering is proportional to the number of frames rendered. For example the cost of rendering 80,000 frames might be USD 20,000 and it may take 2 weeks to complete this process, while the cost of rendering 20,000 frames might be only USD 5,000 and it may take only 3.5 days. It is therefore desirable to minimize these costs and times by minimizing the number of frames of animation and the number of frames to be rendered. It is also desirable however for a viewer of the hologram to have the sensation of a smoothly changing image from any reasonable viewing position and for the duration of the animation between repetitions to be as long as possible, but these requirements tend to lead to more frames of animation and more rendered frames, and hence more time and cost.

In the present invention it is possible to minimize the cost and time of production of holograms by minimizing both the number of frames of animation and the number of rendered frames and it is also possible to maximize the duration of animation.

To minimize the number of frames of animation, at any given illumination angle, a viewer positioned normally to the center of the hologram and at the desired viewing distance should be able to see predominantly one image but should also be able to see the preceding and succeeding images in the animation sequence at reduced brightnesses. If the viewer is able to see more images in the animation sequence, the image tends to become blurry. If the viewer is able to see only one image, although this results in fewer frames of animation for any given movement of the illumination source, the animation sequence tends to become jerky or discontinuous as the illumination source moves, and the duration of animation between the extremes of illumination source position becomes less, as it is necessary for the rate of change of illumination angle to increase to offset the tendency for the sequence to become jerky. This is especially so if there is a gap or blank area between images as the illumination source is moved. When the viewed image has been set up as described so that the viewer sees predominantly one image, it is also not necessary to run the image rate at 24 frames per second, which is the nominal for motion pictures. In a motion picture, the reaction rate of the eye to a changing image is relied on to create the sensation of a smoothly changing image rather than the actual case of a step wise progression of different image frames. In the case of a hologram, because the eye sees some of the two adjacent image frames in the hologram, there is a natural blurring effect that enhances the one created by the eye itself. Consequently it is not necessary to run through the hologram frames as fast as 24 frames per second, and frame rates as low as 12 frames per second would be satisfactory using the embodiments described herein. This has the result of halving the rate of motion of the illumination source and doubling the duration of the animation achievable. The number of rendered frames may also be minimized. When the illumination source is at one extreme, a viewer normal to the center of the hologram sees one predominant frame, designated frame 1. When the illumination source is at its other extreme, the same viewer sees another frame which we will designate frame 151. It will be appreciated that there may be more or less than 151 frames in the animation sequence, and this number is chosen only for the pmposes of illustration. The frame seen depends on the angle between the nominal illumination line and the line from the viewer to intersection of the nominal illumination line and the hologram, so that, for example, if the apparent illumination source is at its first extreme and the viewer moves so that the angle reduces, the predominant frame that the viewer sees becomes successively frames 2, 3, 4 in the sequence. If the viewer moves so that the angle increases, the viewer would see the frame preceding frame 1. If there is no preceding frame encoded on the hologram, the view will blank out. A corresponding situation occurs when the illumination source is at its other extreme. It is therefore necessary that the animation sequence extend beyond frames 1 and 151 so viewers who are not on the normal to the hologram at the intersection of the nominal illumination line and the hologram can see a continuous uninterrupted animation sequence. This may be done by simply adding more animation frames and rendering them, but that is expensive: if another 300 frames was required, for example, the cost would be approximately three times that for the original 150 frames.

It is possible to avoid this by using the same sequence repeatedly. If frame 151 is the same or sufficiently similar to frame 1 then frames 152, 153, 154... in the sequence may be frames 2, 3, 4... respectively. Similarly the frames preceding frame 1: 0, -1, -2 ... may become frames 150, 149, 148... respectively. Hence there is no need to render more frames than is necessary for the sequence 1 to 151, while viewers who are not on the normal to the hologram at the intersection of the nominal illumination line and the hologram can see a continuous uninterrupted animation sequence.

It may not be necessary to encode all frames of the repeated sequence onto the hologram for all viewers to still be able to see continuous uninterrupted animation, and the cost of the hologram may be minimized by encoding onto it only the minimum parts of the repeated sequence that are so required. While this has been illustrated with reference to a sequence of 151 frames, it will be appreciated that the same principle applies to other sequence lengths.

While the invention has been described by reference to various exemplary or preferred embodiments, the invention is not limited to those embodiments and persons of ordinary skill in the art will recognize that different embodiments or variations could also be used without departing from the scope and spirit of the invention as set forth in the following claims.

Claims

1. A system for displaying a hologram comprising:

(a) a hologram;

(b) a light source for illuminating the hologram; and (c) a mirror for reflecting light from the light source to the hologram; wherein the angle between the light illuminating the hologram and a normal to the hologram where the light illuminates the hologram is varied over time.

2. The hologram display system of claim 1 wherein the angle of illumination is varied by moving the mirror.

3. The hologram display system of claim 1 wherein the angle of illumination is varied by moving the light source.

4. The system of claim 1 wherein, for points on the surface of angle alteration for light that iUuminates the hologram, a plane tangent to the surface of angle alteration at those points is not the same plane as the illumination plane at that same particular point.

5. The system of claim 1 wherein, for all points on the surface of angle alteration for light that illuminates the hologram, a plane tangent to the surface of angle alteration at any particular point is not always the same plane as the illumination plane at that same particular point.

6. The hologram display system of claim 1 wherein, for at least one particular point on the surface of angle alteration for any light source, a plane tangent to the surface of angle alteration at that point requires rotation by 20 degrees or more to become coplanar with the illumination plane for that light source at that same particular point.

7. The hologram display system of claim 1 comprising first and second mirrors, wherein the light from the light source is directed at the first mirror and is reflected from the first mirror to the second mirror and from the second mirror to the hologram.

8. The hologram display system of claim 7 wherein the first mirror moves relative to the hologram and the direction of the light from the light source is adjusted to track the movement of the first mirror.

9. The hologram display system of claim 8 wherein the second mirror moves in coordination with the first mirror.

10. The hologram display system of claim 3 wherein the light source moves relative to both the mirror and the hologram, and rotates as it moves to continue directing light onto the mirror for reflection onto the hologram.

11. The hologram display system of claim 10 wherein the light source moves vertically from a point at least as low as the lowermost point of the hologram to a point at least as high as the uppermost point of the hologram.

12. The hologram display system of claim 3 comprising a plurality of light sources that move relative to the hologram and the mirror and wherein each of the plurality of light sources illuminates the hologram in turn.

13. The hologram display system of claim 3 wherein each of the plurality of light sources is moved in a continuous circuit such that, at any given time, at least some of light sources are illuminating the hologram and some of the light sources are not illuminating the hologram.

14. The hologram display system of claim 1 wherein the angle of illumination to the hologram is changed such that the angle from time to time increases in a given direction and then reverses.

15. The hologram display system of claim 14, wherein the increases or reversals in the angle of illumination occur on a random basis.

16. The hologram display system of claim 14, wherein the increases or reversals in the angle of illumination occur on a timed basis.

17. The hologram display system of claim 14, wherein the increases or reversals in the angle of illumination are keyed to specific frames.

18. A system for displaying a hologram comprising:

(a) a hologram; and (b) a light source for illuminating the hologram; wherein the apparent light source moves over time such that a casual viewer of the hologram sees an apparent non discontinuous animation sequence and the rate of movement of the apparent light source is such that the time between frames in the animation sequence is on average less than l/24th of a second.

19. A system for displaying a hologram comprising: (a) a hologram; and

(b) a light source for illuminating the hologram; wherein the apparent light source moves over time such that when it is at the extreme ends of its locations on its surface of angle alteration there is no difference between the content of the images seen by a stationary viewer of the hologram.

20. A system for displaying a hologram comprising:

(a) a hologram; and

(b) a light source for illuminating the hologram; wherein the apparent light source moves over time such that when it is adjacent to the extreme ends of its locations on its surface of angle alteration a stationary casual viewer of the hologram detects no apparent difference between the content of at least one image when the apparent light source is adjacent to a particular extreme and the content of another image when the apparent light source is adjacent to the opposite extreme.

21. A system for displaying a hologram comprising:

(a) a hologram; and

(b) a light source for illuminating the hologram; wherein the same sequence of frames is encoded more than once on the hologram such that there is no difference in the content or phase of the sequence seen by a viewer normal to the hologram where the light illuminates the hologram and by a stationary viewer positioned in at least one other location.

22. A system for displaying a hologram comprising: (a) a hologram; and (b) a light source for illuminating the hologram; wherein two or more sufficiently similar sequences of frames are encoded on the hologram such that a casual viewer normal to the hologram where the light illuminates the hologram does not detect any apparent difference in the content or phase of the sequences from that seen by a stationary casual viewer positioned in at least one other location.