GB2284487A

GB2284487A - Display for 3D images

Info

Publication number: GB2284487A
Application number: GB9324703A
Authority: GB
Inventors: Graham John Woodgate; David Ezra; Basil Arthur Omar
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 1993-12-01
Filing date: 1993-12-01
Publication date: 1995-06-07
Also published as: GB9324703D0

Abstract

Apparatus for displaying three dimensional images comprises means for adjusting the relative positions of at least one spatial light modulator 1a, 1b and at least one source of illumination 2a, 2b so as to dynamically control the position of a first viewing region in which a first observer perceives an autostereoscopic three dimensional image. The illuminators may be physically movable or be a plurality of switchable sources or a CRT. Tracking of the observer to control the viewing region may be achieved by a joystick, ultrasonic or magnetic fields, a camera or voice-command. Plural illuminators may allow several simultaneous observers. <IMAGE>

Description

DISPLAY FOR 3D IMAGES The present invention relates to a display for three dimensional images.

Known display devices for producing three dimensional (3D) images create the illusion of a 3D opaque object by displaying a number of two dimensional (2D) images to the observer. Each of the 2D images is a view of the object from a particular direction and, during reproduction of the 3D image, each component 2D image is replayed in its respective direction.

The freedom of movement of the viewer location is limited by the total angular range over which the views are imaged. Known displays capable of imaging only a low number of 2D views provide a 3D image within a highly restricted range of viewing angles. Consequently the viewer is constrained to be within a limited range of positions in order to maintain the appearance of a 3D image. Similarly, the number of observers of a 3D image may also be restricted due to the limited number of 2D views.

"Subjective Assessments of the Resolution of Viewing Directions in a Multi Viewpoint 3D TV System", S. Pastoor, K. Schenke, p 217 Proc. SID Vol. 30/3 1989 describes the requirement for the number of views in a 3D display. It is estimated that, for a typical scene, 60 or more views may be required in an interocular spacing. For a wide field of view, several hundred views will have to be displayed at some time. It is currently not possible to achieve this with a simultaneous view presentation type of display.

A display described by Akiyama.K, and Tetsutani,N in a paper titled "Three dimensional visual communication" 1991 ITE Annual convention, p607, has a two view display produced by providing an interlaced image on a liquid crystal device behind a lenticular screen. The position of an observer is monitored, and as the observer moves from an orthoscopic viewing zone to a pseudoscopic viewing zone, the sequence in which the images are interlaced is reversed so as to maintain the appearance of an orthoscopic image to the observer. Such a system requires precise tracking of the observer's head so as to determine the time at which the image sequence should be reversed. Further, such a display is limited to use by a single observer and the black mask of the LCD is made visible by the lenticular screen.

EP-AX 404 289 "Television set or the like for creating a three dimensional perception of images and apparatus for creation of same" describes a 3D display in which a lenticular screen is moved with respect to a high resolution display device in response to movement of an observer. Such an apparatus requires very precise control of the motion of the lenticular screen and is limited for use by a single observer.

According to the present invention there is provided a display apparatus for displaying three dimensional images, comprising adapting means for adapting the relative positions of at least one lens disposed adjacent at least one spatial light modulator and at least one source of illumination so as to dynamically control the position of a first viewing region in which a first observer perceives an autostereoscopic three dimensional image.

In one embodiment, the at least one spatial light modulator may cooperate with two respective lenticular screens so as to provide angular multiplexing of a plurality of 2D images used to create the 3D image.

Alternatively, the at least one spatial light modulator may be arranged to cooperate with two respective parallax screens to provide angular multiplexing of the 2D images.

As a further alternative, the at least one spatial light modulator and the source of illumination may be controlled so as to provide temporal multiplexing of the 2D images.

In a further embodiment, images from two spatial light modulators may be combined by a beam combiner, for instance using an arrangement of the type disclosed in British Patent Application No.9226272.4. Each spatial light modulator may have a respective at least one illumination means for providing at least one source of illumination. Alternatively the spatial light modulators may share at least one illumination means.

The source of illumination may, for example, comprise a light and a spatial light modulator (SLM), a cathode ray tube (CRT) or plurality of light sources. The adapting means may control the position of the source of illumination. The adapting means may physically move the or each light source or control a plurality of light sources so as to control the position from which light emanates. Alternatively the adapting means may control a CRT or a SLM to produce a movable source of light.

The present invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a display apparatus using a beam combiner and constituting a first embodiment of the present invention; Figure 2 is a schematic diagram showing the first embodiment in use with two observers; Figure 3 is a schematic diagram of a display apparatus using a beam combiner and a single source of illumination and constituting a second embodiment of the present invention; Figure 4 is a schematic diagram of a projection display apparatus constituting a third embodiment of the present invention; Figure 5 is a schematic diagram of a display apparatus constituting a fourth embodiment of the present invention; Figure 6 is a schematic diagram of a display apparatus constituting a fifth embodiment of the present invention;; Figures 7a-7f are schematic representations of the illumination pattern generated by the source of illumination in response to different movements of at least one observer; Figure 8 is a diagrammatic representation of a 3D display system incorporating a display apparatus constituting an embodiment of the present invention; and Figure 9 is a schematic diagram of a display apparatus constituting a further embodiment of the invention.

Figure 1 shows a plan view of a direct view 3D display incorporating a beam combiner. First and second image data are presented to first and second spatial light modulators la and lb, respectively, for production of first and second 2D images. Each of the first and second spatial light modulators la and 1b is illuminated by a respective movable illuminator 2a and 2b providing movable sources of illumination. Light from the illuminators 2a and 2b is directed by respective lenses 3a and 3b towards the spatial light modulators la and 1b. The light is intensity modulated by the spatial light modulators 1a and 1b to form two 2D images. In order to create a 3D image, the 2D images are of the same object or objects, but from different directions. The images are then combined by a beam combiner 4 to create the 3D image.

The sources of illumination 2a and 2b are arranged to produce light emanating from the positions indicated as "A" with the observer at position 1 as shown in Figure 1. If, however, the observer moves to position 2, then the light emanates from the positions "B" in order to maintain the appearance of a 3D image. Thus the relative positions of the sources of illumination 2a and 2b with respect to the lenses 3a and 3b adjacent the SLMs 1 a and 1 b are controlled in response to movement of the observer. The display may be controlled so as to maintain the appearance of a 3D image in response to movement by the observer, but maintaining the same point of view.Alternatively, the image data presented to the SLMs may be modified in response to movement of the observer so as to present appropriate new views, for example to simulate movement around an object.

The display is also suitable for use with a plurality of observers, as shown in Figure 2. The illuminators 2a and 2b comprise a plurality of light sources arranged such that two or more light sources can be in use simultaneously. Both viewers can then view the same 3D image simultaneously and from the same point of view.

In an example embodiment, each of the spatial light modulators may be a 250mm diagonal dimension liquid crystal device (LCD). The illuminators may be spaced 5OOmm from the respective LCDs and the optical path length from the LCDs to the observer position may be nominally one metre. The illuminators may then consist of illuminator elements 32.5mm wide (so that the window size at the observer is nominally 65mm wide) which perform translatory movement, or which are switched on and off so as to simulate movement in a step wise manner, in response to lateral movement of the observer, at half the speed of the observer.

The optical system, i.e. the lenses 3, SLMs 1 and the beam combiner 4, make efficient use of the light available from the illuminators 2a and 2b, giving rise to a bright image.

In an alternative arrangement, a single illuminator 5 is shared by both spatial light modulators, as shown in Figure 3. The illuminator is arranged to undergo, or simulate, movement along at least the y' direction so as to track observer movement laterally to the display, i.e. in the y direction. Light from the illuminator is directed towards mirrors 8a and 8b by a beam splitter 7. The mirrors 8a and 8b reflect light from the source 5 towards the lenses, such as Fresnel lenses, 3a and 3b associated with the SLMs la and ib. The illuminator may also be movable in a z' direction so as to track vertical movement of the observer in the z direction.The illuminator may be further arranged to undergo movement in an x' direction so as to track movement of the observer towards and away from the display in an x direction, thereby ensuring that the image plane of the light focused by the lenses 3a and 3b is controlled to track the position of the observer. Sharing of a single illuminator 5 simplifies the complexity of the illuminator position control system.

Figure 4 shows a protection display apparatus. Apparatuses of this type 93 Z Si1 o2 * 9 are disclosed in an earlier British Patent Applicationlfiied in the name of the present applicant and referred to by Marks & Clerk reference no.

230P67614. As described hereinabove, image data for two views are presented to two SLMs 1 a and 1 b. The SLMs spatially modulate light from respective illuminators to form two 2D images which are then combined by a beam combiner 4. However, instead of being directly viewed by the observer, the illuminators are imaged into the aperture of a projection lens 10. The total output numerical aperture defines the maximum angular extent of the output view directions when the final image screen is a lens.

However, if a combination of first and second lenticular screens 12 and 14 acting as an angular amplifying element is used as an output element, as shown, then output lobes are generated by the second lenticular screen 14 enhancing the total viewing cone of the display. The first lenticular screen 12 is arranged to form an image at a diffuser 16. The diffuser 16 lies in the object plane of the second lenticular screen 14. As with the other embodiments described hereinbefore, the positions of the illuminators are controlled so as to track the movement of the at least one observer. In an example display system, 50mm LCD screens are imaged by an 80mm f#1.9 projection lens to a 250mm image size at a 3:1 angular amplifying screen. The observer distance from the screen will be 1000mm with approximately 200mm lateral freedom of movement.

Vertical movement can be accommodated in a number of ways. The illuminators' image at the viewer plane can be vertically extended, thereby giving a wide range of possible viewing heights from which the image can be seen. The at least one illuminator may provide vertically extended sources of illumination or a vertical diffuser element may be provided at the output screen plane. Alternatively, the position of the at least one source of illumination may be moved vertically in correspondence with the movement of the observer or observers.

Tilting of the observer's head can be accommodated, in displays which do not use arrays of (cylindrical) lenticules, by tilting the or each source of illumination. However, the image has to be modified in order to maintain the 3D autostereoscopic effect. Similarly, the size of the illuminated area of the or each illuminator may be altered if the or each illuminator is moved longitudinally in response to longitudinal movement of the observer, so as to compensate for the change in the angle subtended at the observer's eyes.

The movable illuminators can also be incorporated in a display device using time multiplexing, as shown in Figure 5. The illuminator 20 is controlled in correspondence with the image data presented to the SLM 22 so as to present images to the left and right eyes of the observer, sequentially. However, the general position of the source of illumination is also controlled in response to movement of the observer's head. Thus the illuminator is at position A so that the light comes alternately from positions A' and A" when the observer is at position 1 of Figure 5, but the illuminator is moved to position B so that the light comes from positions B' and B" when the observer is at position 2.

Figure 6 shows an arrangement in which a temporally multiplexed SLM 24 is interposed between the lenticular screens 26 and 28 to form the 2D images. The arrangement of the SLM and the lenticular screens is disclosed in European Patent application 93303590.9 filed 10 May 1993 and titled "OPTICAL DEVICE". The position of the illuminator 20 is controlled in correspondence with the image data presented to the SLM.

One or both of the lenticular screens may be replaced by an array of apertures. The device comprises a first two < limensional array of lenses or apertures having a number N of groups of lenses or apertures, each of which comprises Z lenses or apertures where Z is an integer greater than one, the lenses or apertures of the first array being disposed with a pitch p in a first dimension; and a second two-dimensional array of lenses or apertures facing the first array and having a number N of lenses or apertures disposed with a pitch P in the first dimension, where P > p and each lens or aperture of the second array is associated with a respective group of lenses or apertures of the first array. The spatial light modulator comprises a plurality of modulating cells, each of which substantially corresponds to and is aligned with a respective one of the lenses or apertures of the first array.

The illuminator tracking of the observer may be achieved in a number of ways. The position of the source of illumination may be physically moved, for example by translatory movement of the source and/or by use of movable mirrors. Alternatively the source may be a CRT or a SLM used to modulate a bright extended light source so that the position from which light emanates from the source can be controlled without physically moving the position of the source.

The tracking data may be presented to the display in a number of ways.

The at least one observer may communicate his position by way of an input device such as a joy stick. Alternatively the or each observer's position may be sensed by an ultrasonic tracking system or the or each observer may wear a magnet to indicate his position to a magnetic tracking system. As further alternatives, one or more cameras may scan the viewing region to determine the at least one observer's position or the at least one observer may issue voice commands, such as UP,LEFT,HERE etc to direct the display or to allow an audio controlled tracking system to identify the position of the source of the observer's voice.

Figures 7a to 7f represent examples of the shape and position of the source of illumination in response to movement of an observer. The hatched areas of the source represent the area from which light is emitted. The illustration is for a temporally multiplexed display, in which the light hatching represents the area from which light is emitted for presenting an image to the left eye, and the dark hatching represents the area from which light is emitted for presenting an image to the right eye.

Figure 7a shows the source position for an observer directly in front of the display. Figures 7b and 7c shown the source position when the observer moves to the left and downwards, respectively. Figure 7d shows the source orientation when the observer tilts his head to the left about a horizontal axis, while Figure 7e shows the source shape when the observer has moved longitudinally. Figure 7f represents the source when two observers are present. When the observer rotates his head about a vertical axis while looking at the display, a change in the effective interocular separation results. This can be compensated by reducing the lateral size of the illuminator elements.

The changes in size and orientation of the source of illumination can easily be produced when the illuminator comprises a SLM used to modulate an extended light source.

Figure 8 shows a display system. Image data, representing multiple views of an object 26 captured by a plurality of cameras 28 or generated by computer 30, are presented via an image controller 30 to a system controller 32. The system controller 32 is responsive to the position of an observer as determined by an observer tracking detector 34. The system controller 32 issues instructions to an illuminator position controller 36 to control the illuminators. The system controller 32 also determines which of the views are reproduced by the spatial light modulators of the autostereoscopic 3D display 38.

Figure 9 shows a further embodiment of a projection display apparatus.

Image data for two views are presented to spatial light modulators 40a and 40b. Each of the spatial light modulators is illuminated by a respective movable illuminator 42a and 42b. Light from the illuminator 42a is directed onto the spatial light modulator 40a via a lens 44a.

Similarly light from the illuminator 42b is directed onto the spatial light modulator 40b via a lens 44b. The images formed at the spatial light modulators 40a and 40b are imaged onto an angular amplifying element 46 (for example of the type comprising first and second lenticular screens 12 and 14 and a diffuser, as described hereinabove with reference to Figure 4). The images are imaged through respective lenses 48a and 48b whose apertures are superimposed at a beam combiner 50. Such superimposition of the images substantially eliminates keystone distortion of the two images relative to each other. This arrangement enables two spatial light modulators to be imaged in a beam combiner configuration without the need for a projection lens having a large back working distance.

It is thus possible to provide a 3D display system which tracks the or each observer so as to maintain the appearance of a 3D image to the or each observer.

Claims

1 A display apparatus for displaying three dimensional images, comprising adapting means for adapting the relative positions of at least one lens disposed adjacent at least one spatial light modulator and at least one source of illumination so as to dynamically control the position of a first viewing region in which an autostereoscopic three dimensional image is perceptible to a first observer.

2 An apparatus as claimed in Claim 1, further comprising observer tracking means for tracking the position of the first observer, the adapting means being responsive to the observer tracking means for controlling the position of the first viewing region to move in response to movement of the first observer.

3 A display as claimed in any one of the preceding claims, arranged to form at least one further three dimensional image in at least one further viewing region.

4 A display as claimed in Claim 3 when dependent on Claim 2, in which the observer tracking means is further arranged to track the position of at least one further observer, and in which the adapting means is arranged to control the position of the at least one further viewing region to move with the respective at least one further observer.

5 A display as claimed in any one of the preceding claims, in which the display is a beam combiner type display comprising first and second spatial light modulators and combining means for combining images from the first and second spatial light modulators for viewing by at least the first observer,in which the source of illumination comprises first and second sources of illumination for illuminating the first and second spatial light modulators, respectively, and in which the first and second sources of illumination are movable in correspondence with movement of at least the first observer so as to maintain the appearance of a 3D image at least the first observer.

6 An apparatus as claimed in Claim 5, in which the first and second sources of illumination comprise first and second illuminators for illuminating the first and second spatial light modulators, respectively.

7 An apparatus as claimed in Claim 5, in which the source of illumination comprises a single movable illuminator and a first and second optical paths for providing light to the first and second spatial light modulators, respectively.

8 An apparatus as claimed in Claim 7, in which the first and second optical paths include a shared beam splitter.

9 An apparatus as claimed in any one of Claims 1 to 4, comprising a temporally multiplexed spatial light modulator.

10 An apparatus as claimed in any one of Claims 1 to 4, further comprising a first two dimensional array of lenses having a number N of groups of lenses, each of which comprises Z lenses where Z is an integer greater than one, the lenses of the first array being disposed with a pitch p in a first dimension; and a second twoclimensional array of lenses facing the first array and having a number N of lenses disposed with a pitch P in a first dimension, where P > p and each lens of the second array is associated with a respective group of lenses of the first array, the at least one spatial light modulator being disposed between the first and second two dimensional arrays.

11 An apparatus as claimed in any one of the preceding claims, further comprising projection means for projecting the image onto a projection element.

12 An apparatus as claimed in Claim 11, in which the projection element is a field lens.

13 An apparatus as claimed in Claim 11, in which the projection element is an angular amplifier comprising first and second lenticular screens.

14. An apparatus as claimed in Claim 11, in which the projection element is an autocollimating screen.

15 An apparatus as claimed in Claim 11, in which the projection means is a projection lens.

16 An apparatus as claimed in any one of the preceding claims, in which the source of illumination comprises at least one rear illuminated spatial light modulator.

17 An apparatus as claimed in Claim 16, in which the at least one spatial light modulator is a liquid crystal device.

18 An apparatus as claimed in any one of Claims 1 to 15, in which the position of the source of illumination is controlled by translatory movement of an illuminator.

19 An apparatus as claimed in any one of Claims 1 to 15, in which the position of the source of illumination is defined by at least one cathode ray tube.

20 An apparatus as claimed in any one of the preceding claims, in which the brightness of the source of illumination is a function of observer position so as to maintain substantially constant brightness.

21 An apparatus substantially as described herein with reference to Figure 1 of the accompanying drawings.

22 An apparatus substantially as described herein with reference to Figure 2 of the accompanying drawings.

23 An apparatus substantially as described herein with reference to Figure 3 of the accompanying drawings.

24 An apparatus substantially as described herein with reference to Figure 4 of the accompanying drawings.

25 An apparatus substantially as described herein with reference to Figure 5 of the accompanying drawings.

26 An apparatus substantially as described herein with reference to Figure 6 of the accompanying drawings.

27 An apparatus substantially as described herein with reference to Figure 8 of the accompanying drawings.

28 An apparatus substantially as described herein with reference to Figure 9 of the accompanying drawings.