METHOD AND APPARATUS FOR VOLUMETRIC DISPLAYING

Abstract: Three-dimensional imagery based on a series of two-dimensional images is produced and displayed. A frame (20) housing a series of image displays (22) displaced at differing radial distances from the center (39) of the frame is rotated at 60 hertz or greater. As each display rotates past the viewer, a different sectional slice of a three-dimensional image is displayed. Thus, a full rotation of the frame provides the viewer with a full view of the three-dimensional object. The high rotational speed of the system visually merges the slices and the radial displacement of the displays provides depth to the image. This combination results in the presentation of a true three-dimensional image without the need for viewing aids. Additionally, multiple viewers can view the same or differing three-dimensional images.

Description: METHOD AND APPARATUS FOR VOLUMETRIC DISPLAYING BACKGROUND OF THE INVENTION Field of the Invention The invention relates to the projection of two-dimensional imagery to produce a three-dimensional image that can be presented to viewers, without the need for special viewing aids such as polarized glasses or shutters. Description of the Related Art Over the last 100 years, advancements in the display and presentation of electronically generated imagery have ranged from photographic techniques to television displays. The early techniques were directed to displaying two-dimensional (2-D) images. While an important step, these systems fell far short of being able to replicate real world three-dimensional images. Initial attempts at generating three-dimensional electronically generated imagery were primarily limited to two- dimensional, two and one half-dimensional, or at best, stereoscopic techniques, such as shuttered, polarized and len- ticular systems. In a shutter system, a viewer is required to wear a set of special shuttered glasses to view the images. Mounted within each lens is a liquid-crystal shutter that alternates between clear and opaque positions. A display shows a sequences of images presented in correct per- spective for one eye and then the other. A control system coordinates the shutter position so that only the appropriate eye sees its corresponding image. This switching takes place at a rate of approximately 120 Hertz thus giving the viewer the sense of seeing a three-dimensional image. See Stereo Moni tors Put Images in Perspective, Laser Focus World, 41, October 1989, and S. Wixson, Three-dimensional Presentations, Information Display, 24-26, July/August 1989. In a polarizing system the viewer wears a special set of glasses whose lenses are polarized in opposite directions (horizontal/vertical or clockwise/counterclockwise) . The display device is also fitted with a polarizing filter that switches between the different directions. In a circular polarized system, a polarizing filter alternates between two circular polarization states; clockwise and counter clockwise. When the polarization of the screen matches the polarization of one of the lenses, the picture on the screen is visible. When the polarizations are out of phase, the image is blocked. The linear polarized system, operates in much the same manner with the filter and glasses having a vertical and horizontal polarization state. However, in a linear polarized system head position must be maintained in a near vertical position to see the image, whereas with the circular system a viewer can tilt his head and still not lose the three-dimensional effect. The drawback of a circular system is that the lenses and screens typically cost 20% more than those for linear systems. See Stereo Moni tors Put Images in Perspective, Laser Focus World, 41, October 1989, and S. Wixson, Three-dimen sional Presentations , Information Display, 24-26, July/August 1989. A lenticular system can be implemented in a variety of fashions. For example, a common approach is to mount a series of identical cameras adjacent to one another and focus them on a desired object. This produces a series of images of the object from slightly different views. These images are multiplexed and fed to a series of image projectors in a one-to-one correspondence with the cameras. The image projectors simultaneously project their corresponding images onto a lenticular display screen creating a stereoscopic view of the image that produces a three-dimensional affect. See N. Nithiyanandam, K Balasubramonian and K.P. Rajappan, A Real -Time 3 -D TV By Autostereoscopic Methods of Imaging, Journal of Optics, Vol. 11, No. 1, 6-8, January- March 1982, and R. Bόrner, 3D TV Proj ection , Electronics and Power, 379-382, June 1987. While the above systems are better than standard two- dimensional images, they still are unable to present true three-dimensional imagery. In addition, the systems generally require the viewer to wear some form of viewing aid such as glasses or goggles, or require special set up and equipment which are costly. As such, further work has been undertaken in an attempt to develop true three-dimensional viewing systems which do not have these constraints . B. Daviss, Boob Cube, Discover, 30, December 1995, and P. Soltan, M. Lasher, W. Dahlke, N. Acantilado and M. Mc- Donald, Laser Projection 3 -D Vol umetric Displays , Naval Command, Control and Ocean Surveillance Center, February 1996 discloses a rotating helix system that permits images to be displayed in a three-dimensional format without special glasses. In a rotating helix system a double-helix is rotated within a glass cylinder. The helix rotates at a rate of approximately 20 hertz which is fast enough to provide a flicker free image when written upon. Mirrors are placed at the top of the glass cylinder to reflect pulses of laser light received from a series of red, green, and blue lasers down upon the helix creating visible points of light where the beam intersects the helix. These intersections are otherwise known as voxels. As the rotating helix sweeps out the cylindrical envelope it creates a three-dimensional image. While the system does produce true three-dimensional imagery, the system is of lower resolution than desired for most three • dimensional displays applications. In addition, the system is susceptible to visual artifacts and is quite complex and costly. R.L. Hotz, A 3 -D System That Works wi thout Glasses , Los Angles Times, Al, A31, 30 August 1996 describes a viewing cube, developed at Stanford University, that is composed of multiple layers of glass coated with rare earth phosphor compound. A series of computer controlled lasers project respective beams of light through the cube thereby generating a luminescence where two beams intersect. By scanning the cube rapidly, the lasers produce a true three- dimensional image. The viewing cube has been limited to very small displays, of approximately three cubic centimeters or less. In addition, the development of larger displays is hampered by the inability to develop suitable materials in large enough volume and scan with lasers at a high enough rate . J.C. Russ, The Image Processing Handbook, CRC Press, 406-408, 1992, discloses a varifocal mirror system in which a cathode ray tube (CRT) display projects a series of slices of a three-dimensional image. These images slices are not viewed directly by the viewer but are reflected off a moving mirror. As each different slice is projected, a speaker voice coil displaces the mirror slightly to give the impression of depth. The technique is usually restricted to simple outline drawings as the system is incapable of providing complete images slices at a fast enough rate. If the slices are not normal to the x, y, z axis, the trigonometric calculations required to offset the image further reduce system performance. While the above mentioned techniques do provide true three-dimensional imagery these systems are quite complex, costly and are generally not well suited for adverse environments. In addition, all three systems have a greater affinity to the production of display artifacts such as ghost images, speckle, and unwanted defects. SUMMARY OF THE INVENTION The present invention relates to a system and a method for producing complex, high resolution, three-dimensional images from two-dimensional imagery. An image source generates a sequence of two-dimensional images and sends them to a series of display image sources that are mounted around a rotational frame structure. The display image source projects the images which are then focused onto a plurality of display screens posi- tioned around the frame at varying radii. A viewer sees a sequence of two-dimensional images that are visually fused by the rotational speed of the system and given depth by radial displacement . The fusion and depth together present a true three-dimensional image. With this system, a viewer is capable of viewing true three-dimensional images without the need of special viewing aids. While it is initially envisioned that the display screens would be flat, in an alternate configuration the display screens could be curved. Furthermore, the display screen itself could be the image display source, thus eliminating the need to have intermediate optics and a subsequent display screen. While it is initially envisioned that the frame would be rotated in a vertical manner about a horizontal axis, it could be rotated horizontally about a vertical axis. This orientation would make it possible to have multiple viewers utilizing the system. In a multiple viewer configuration, viewers would be located at differing positions around the system and could view the same or different images. These and other features, aspects and advantages of the invention will be apparent to those skilled in the art from the following detailed description, together with the accompanying drawings . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is block diagram of a three-dimensional volumetric display system in accordance with the invention,- FIG. 2 is a partially sectioned plan view of the three-dimensional volumetric display system depicting the rotation of the system in a vertical orientation; FIG. 3 is a sectional view of the three-dimensional volumetric display system operating in a vertical orientation taken along the lines 3-3 of FIG. 2 ; FIG. 4 is a timing diagram depicting sequential display of images by the three-dimensional volumetric display system; FIG. 5 is a sectional view of an alternate design of the three-dimensional volumetric display's rotational frame utilizing counterbalancing weights as viewed in the same direction as FIG. 2 ; FIG. 6 is a sectional view of a second alternate design of the three-dimensional volumetric display's rotational frame, as viewed in the same direction as FIG. 2, utilizing curved display screens; FIG. 7 is a sectional view of an third alternate design of the three-dimensional volumetric display's rotational frame, as viewed in the same direction as FIG. 2, utilizing image display sources alone,- FIG. 8 is a partially sectioned planned view of the three-dimensional volumetric display system operated in a horizontal configuration; FIG. 9 is a sectional view of the three-dimensional volumetric display system, operated in a horizontal configuration, as taken along lines 9-9 of FIG. 8 which permits multiple viewers. DETAILED DESCRIPTION OF THE INVENTION The present invention provides a system and method for the presentation of three-dimensional imagery based on a series of two-dimensional images. A frame housing a series of image displays displaced at differing radial distances from the center of the frame is rotated at a frequency sufficient to avoid display flicker, e.g., 60 Hertz or greater, about an axis extending through the center of the frame. As each display rotates past the viewer, a differ- ent sectional depth slice of a three-dimensional image is displayed. Thus, a full rotation of the frame provides the viewer with the desired three-dimensional view of the object or scene. The high rotational speed of the system visually merges the slices and the radial separation of the displays provides depth to the image. This combination results in the presentation of a true three-dimensional volumetric image that can be viewed without viewing aids . Additionally, multiple viewers can view the same or differing three-dimensional images in a volumetric presentation. As depicted in FIG. 1, a three-dimensional system 19 includes a rotatable frame 20 which houses a series of image displays 22. Each image display 22 includes a display image source 24, a series of intermediate optics 26 and a display screen 28. Display image source 24 is preferably a flat panel display device that receives images from an image source 30 and projects them onto intermediate optics 26, which in turn focus the images upon display screen 28, preferably a translucent rear projection display screen. Depending upon the approach, image source 30 may re- ceive images from an external source 38 or generate them internally using an image generation software package. For each image display 22, display screen 28 is displaced at a differing radial distance from the center of frame 20. This displacement provides different depth layers of the three-dimensional image to be displayed. The number of image displays 22 determines the system's depth resolution,- the greater the number the greater the depth resolution. A mounting structure 32, as shown in FIG. 2, supports frame 20 and permits it to rotate around its axis. A rota- tional motor on mounting structure 32 rotates frame 20. A system controller 36, suitably a commercially available numeric or servo controller, controls motor 34 and image source 30 to maintain the speed of frame 20 and to coordinate the projection of images by display 22. External im- age source 38 provides image source 30 with images received external to the system. As further shown in FIG. 2, frame 20, in a preferred configuration, is mounted in mounting structure 32 in a vertical fashion with its axis of rotation 39 being hori- zontal . Motor 34 rotates frame 20 about a central hub 40 which contains a rotational electrical connector (not shown) . Hub 40 includes two sections, one section mounted to mounting structure 32 and a second section mounted to frame 20. A series of rotational electrical connectors are located between the two sections which allow the electrical signals to be passed between the sections. Thus, an electrical signal received from image source 30 passes through the rotational connector and is provided to its respective display image source 24. Frame 20 and mounting structure 32 are preferably located within a housing 42 having one or more viewing locations 44. Housing 42 is preferably maintained at or near a vacuum, thus minimizing the air resistance experienced by frame 20 during rotation. Housing 42 can either be sealed to prevent vacuum loss or can be connected to a series of vacuum pumps (not shown) which are used to maintain the vacuum level. A cabinet 46 surrounds housing 42 and provides a series of viewing locations 48 in direct correspondence with housing viewing locations 44. A series of electrical connectors 50 and 52 pass through housing 42. Connector 50 is connected between image source 30 and the first half of central hub 40. Thus, a signal sent from image source 30 passes through housing 42 and is received by central hub 40, which in turn pro- vides the signals to its corresponding display image source 24. Connector 52 is connected to system controller 36, passes through housing 42, and is connected to motor 34. As shown in FIG. 3, each image display includes a display image source 24 mounted radially close to the center 53 of frame 20. It is preferable that display image source 24 be located as closely as possible to the center of frame 20 so as to minimize the centrifugal effect upon the display image source. Display image source 24 can be a variety of flat panel displays including, but not limited to, liquid crystal displays (LCD) , field emission displays (FED) , electroluminescent displays (ELD) or plasma display panels (PDP) . It is further preferred that these displays be high resolution, having greater than or equal to 1280 x 1024 pixels (horizontally and vertically) , although it is still valid for low resolution applications. Display image source 24 is connected to the second section of central hub 40 by an electrical lead 54. Moving radially outward from display image source 24 is located intermediate optics 26. Moving further radially outward is located display screen 28. Like display image source 24, intermediate optics 26 is also mounted within frame 20. They receive the projected image by display image source 24 and in turn focus the image upon the display screen 28. Each display screen 28 is located at a differing ra- dial distance from the center of frame 20. This varying radial distance provides differing depth layers of the image presented, thus providing true three-dimensional imagery. Display screen 28 can be a variety of commercially available rear projection display devices including, but not limited to, flexible and rigid diffuse screens, and 10 hybrid systems consisting of a combination of lens systems or holographic elements. A series of transparent sheets 56 are mounted parallel to display screen 28 to balance the system and prevent wobble during rotation. Sheets 56 allow the image provided to or from display screen 28 to pass through to the viewer. If required, a series of counter balance weights (not shown) can be used to further balance the rotational system. In operation, motor 34 rotates frame 20 at a speed of 60 Hz or greater. While frame 20 is rotating, image source 30 either generates internally, or receives from external source 38, a three-dimensional image to be displayed . In either case, image source 30 slices the three-dimensional image into a series of two-dimensional sections. The num- ber of sections is in a one-to-one correspondence with the number of image displays 22 utilized by the system. The input could consists of a layered data base initially, so no "slicing" would be required. If the image is received from an external source 38, the image consists of a series of multiple views of the same image or a series of three-dimensional data points, all of which must be merged by image source 30 to create a three-dimensional image. For example, if the three-dimensional volumetric display system were used for air traffic control purposes, image source 30 would, at a minimum, receive information on each aircraft's altitude and latitudinal and longitudinal position relative to a fixed position, an airport runway. Image source 30 takes these data and generates a three-dimensional model of the airport region showing the location of aircraft. The model is then sliced into a series of two-dimensional images whose number is in a one-to-one correspondence with the number of image displays 22 utilized by the system. Image source 30 provides the corresponding image slices to their respective display image source 24. Spe- 11 cifically, image source 30 passes the signal through housing 42 to hub 40 via electric connector 50. Within hub 40, the electrical signals are passed to the individual display image sources 24 by a series of electrical leads 54. The image is relayed by intermediate optics 26, which also focus the image upon its corresponding display screen 28. Just prior to display screen 28 reaching viewing locations 44/48, the image is projected upon display screen 28. At a minimum, the image is maintained throughout the entire time interval display screen 28 is visible through viewing locations 44/48. As the next image display 22 approaches viewing location 44/48 it too is activated in a similar manner to display its respective image slice. This sequencing is the responsibility of controller 36, which not only controls which image display 22 receives, but also the rotational speed of frame 20. This sequencing of the individual image displays is depicted in the timing diagram shown in FIG. 4. The image display time (W) for an individual display image source 24, at a minimum, is a function of the number of displays (N) and the time required for frame 20 to make a complete rotation. Thus, W < T/N. As frame 20 rotates, the viewer sees, in a sequential fashion, each slice of the image. For each full rotation of frame 20 a complete series of slices of the three-dimensional image is presented. The high rotational speed of frame 20 results in the slices becoming visually merged and the radial displacement of display screens 28 provides depth to the image. This combination results in the presentation of a true three-dimen- sional image to a viewer located at locations 44/48. While FIG. 4 depicts a dynamic display, if a static image is to be displayed, display 22 can remain active throughout the rotation of frame 20. In an alternate configuration of the three-dimensional volumetric display system, as shown in FIG. 5, sheets 56 12 are not utilized. For the purpose of balancing, a series of counter balance weights (not shown) are mounted on frame 20 to eliminate wobble during rotation. This alternate approach has the advantage that the projected and then fo- cused images are not attenuated by passing through transparent sheets 56. In a second alternate configuration of the three-dimensional volumetric display system, as shown in FIG. 6, display screen 28 and transparent section 56 are formed in a single cylindrical as opposed to a multifaceted polygonal structure. This alternate configuration has the advantage that the system can be easily balanced and also reduce the number of individual parts necessary to fabricate the system. In a third alternate configuration of the three-dimensional volumetric display system as shown in FIG. 7, display image source 24 is mounted in frame 20 at the point where display screen 28 is normally located. This system has the added advantage that no intermediate optics nor display screen are necessary. However, with this configuration the selection of display image source 24 is important. Since display image source 24 has been moved further radially outward, the centrifugal forces experienced by the individual display image source 24 are greater. As such, some displays, for example liquid-crystal displays (LCD) might experience liquid flow in the displays under rotation. In addition, balancing may be required to eliminate wobble during rotation. In a fourth alternate configuration of the three-di- mensional volumetric display system, as shown in FIG. 8 and 9, frame 20 is rotated in a horizontal configuration having its axes of rotation vertical. With this configuration, multiple viewers could be displaced around the system viewing the same or different three-dimensional images. Thus, it is possible for a series of viewers to be located around 13 the system with each viewing an entirely different images, all three-dimensional. While the system of the invention has been initially described for use in displaying singular three-dimensional objects, the invention has applicability to a variety of other display scenarios. For example, the system could be used for a tactical display in navigation and command and control applications such as for vessel traffic control, air traffic control, computer aided design and manufacturing, medical imaging, simulation and/or training. Although the present invention has been described in considerable detail with reference to certain preferred configurations thereof, other versions are possible. Therefore, the spirit and scope of the appended claim should not be limited to their preferred versions contained therein.

Claims: 14 WE CLAIM : 1. A three dimensional volumetric display system (19) , comprising: a frame (20) ; a plurality of image displays (22) mounted around said frame at differing radial distances from the center of said frame (39) ,- an image source (30) that provides two-dimensional images to said image displays; a motor (32) that rotates said frame about an axis through its center; and a controller (36) that synchronize the rotation of said motor to the display of said images such that a viewer sees a sequence of said images that are visually fused and given depth to present a true three-dimensional image. 2. The system of claim 1, wherein each of said image displays comprise: a display image source (24) mounted within said frame that receives and projects said images,- a display screen (28) mounted in said frame at a location radially farther from the center of said frame than the location of said display image source,- and intermediate optics (26) , mounted within said frame between said display image source and said display screen, that focus said image upon said display screen. 3. The system of claim 1, wherein said frame is mounted within a housing (42) which has a transparent surface (44) for viewing said image displays and wherein said housing provides a vacuum that reduces air resistance on said rotating frame. 4. The system of claim 1, wherein said motor rotates said frame at 60 Hz or more. 15 5. A method for presenting three-dimensional imagery, comprising: rotating a frame (20) around its axis of rotation (39) , said frame containing a plurality of image displays (22) that are mounted around said frame at different radial distances from the center of said frame,- providing each image display with a different two-dimensional sectional slice of a three-dimensional image,- displaying each sectional image slice on its corresponding image display as such frame is rotating, synchronizing the speed of rotation of said frame to the display of said sectional image slices such that a viewer sees a sequence of said images that are visually fused and given depth to present a true three-dimensional image . 6. The method of claim 5, further comprising: displaying each of said sectional image slice to a viewer, in a sequential manner such that the viewer perceives a three-dimensional image. 7. The method of claim 5, wherein said image display displays said sectional image slice by: providing said sectional image slice to an image source (30) ; projecting said sectional image slice through intermediate optics (26) ; and focusing said projected image upon a display screen (28) . 8. The method of claim 5, wherein said section image slices are displayed at a frequency of about 60 Hz or more. 9. The method of claim 6, wherein said sectional image slices are displayed at more then one location (44) . 16 10. The method of claim 5, wherein said sectional image slices are provided by an image source.

Inventors: FREEMAN JERRY E, GOLD RONALD S, FREEMAN, JERRY, E., GOLD, RONALD, S.
Applicants: RAYTHEON CO, RAYTHEON COMPANY
Application year: 1999
Main classification: H04N13
IPC codes: G02B27, H04N13