Abstract:
A 3-D display may comprise a rotating optical diffuser for displaying 3-D parallax images in specific substantially unidirectional viewing zones as the rotating optical diffuser rotates; and a projector for projecting images through the rotating optical diffuser.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority to U.S. provisional application 60/535,874, filed Jan. 12, 2004, the entire disclosure of which is hereby incorporated by reference. 

   BACKGROUND 
   Spatial 3-D displays such as Actuality Systems Inc.&#39;s Perspecta® Display create 3-D imagery that fills a volume of space and that appears to be 3-D to the naked eye. One such spatial 3-D display is described in U.S. Pat. No. 6,554,430, “Volumetric three-dimensional display system.” This display is formed in the shape of a transparent dome and contains a rotating screen orientated vertically within the dome. As the screen spins it displays a previously recorded image for example at every 1 degree of rotation for 360 degrees. Human persistence of vision combines these images to create a 3-D view of the previously recorded image. This display with its vertical dome shape can be placed on top of a tabletop for example. One feature of this type of 3-D display is that the imagery provides motion parallax in every direction; in other words, it is a full parallax display. 
   Some 3-D displays provide motion parallax information with only one degree of freedom. A well-known family of 3-D displays with restricted motion parallax are horizontal parallax only (HPO) displays. Known HPO displays provide motion parallax along one axis, normally in the horizontal direction, corresponding to left-right motion; when the user moves vertically, the 3-D image appears to track the user&#39;s motion because of the lack of vertical parallax information. Displays of this type are taught in: U.S. Pat. No. 3,178,720, “Three dimensional unaided viewing method and apparatus,”; D. J. DeBitetto, “Holographic Panoramic Stereograms Synthesized from White Light Recordings,” in  Applied Optics , Vol 8(8), pp. 1740-1741 (August 1969); and U.S. Pat. No. 5,132,839, “Three dimensional display device.” 
   Another type of restricted parallax display can be called the theta parallax only (TPO) display, which provides motion parallax for a user moving angularly around the display. A 360-degree hologram is a display hologram of this type, as described in R. Hioki and T. Suzuki, “Reconstruction of Wavefronts in All Directions,” in  Japanese Journal of Applied Physics , Vol. 4, p. 816 (1965); and in T. H. Jeong, P. Rudolf, and A. Luckett, “360° Holography,” in  Journal of the Optical Society of America , Vol. 56(9), pp. 1263-1264 (September 1966). A cylindrical hologram is another display of this type. As taught in the present application, one embodiment described below is a new example of a TPO display and is a circular display located in a top or in the middle of a table for use with multiple users sitting around a conference room table. 
   SUMMARY OF THE INVENTION 
   An embodiment of the present 3-D display may comprise a rotating optical diffuser for displaying 3-D parallax images in specific substantially unidirectional viewing zones as the rotating optical diffuser rotates; and a projector for projecting images through the rotating optical diffuser. 
   An embodiment of the present 3-D display may comprise optical means for displaying 3-D parallax images in specific substantially unidirectional viewing zones; and a projector for projecting images to the optical means. 
   An embodiment of the present display may be an in-table top 3-D display and may comprise optical means located in a plane of a flat table top for displaying 3-D parallax images; and a projector for projecting images to the optical means. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which: 
       FIG. 1  is a perspective view of an embodiment of tabletop plane TPO display. 
       FIG. 2  is a side view of an embodiment of a tabletop plane TPO display. 
       FIG. 3  is perspective view of an embodiment of a camera as it images a 3-D subject. 
       FIG. 4  is perspective view of an embodiment of a camera as it images a 3-D subject along a circular track. 
       FIG. 5  is a cut away side view of an embodiment of a TPO display. 
       FIG. 6A  is a side view of an embodiment of a TPO display. 
       FIG. 6B  is a perspective view of an embodiment of a TPO display. 
       FIG. 7A  is a ray diagram of an embodiment of a TPO display. 
       FIG. 7B  is a ray diagram of an embodiment of a TPO display. 
       FIG. 8  is a ray diagram of an embodiment of a TPO display. 
       FIG. 9  is an embodiment of a TPO display. 
       FIGS. 10A and 10B  collectively referred to as  FIG. 10  depicts a scan sequence diagram of an embodiment of a TPO display. 
       FIG. 11  is an embodiment of a TPO display. 
       FIG. 12  is an embodiment of a TPO display. 
       FIG. 13  is an embodiment of a TPO display. 
       FIG. 14  is a diagram of a conical hologram. 
       FIG. 15  is a diagram of a perspective camera system. 
       FIG. 16  is a diagram of a conical hologram recording scheme. 
       FIG. 17  is a recording scheme for recording a color holographic stereogram. 
       FIG. 18  is an off axis Fresnel lens. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present specification describes theta-parallax-only (TPO) displays which provide motion parallax to a user or users. In one embodiment, as shown in  FIGS. 1-2 , an “in-tabletop TPO display”  10  is shown. With this display, a user may move circumferentially about a flat display surface  1  of the “in-tabletop” TPO display  10  while viewing a 3-D image  2  located towards the center of the flat display surface  1 . 
   One exemplary application is a conference room “in-tabletop” display for military visualization, in which 3-D imagery floats above and/or within the table. Additional applications may include, but are not limited to, medical visualization, teleconferencing for mechanical design, and entertainment. Additionally, as shown in  FIG. 2 , the in-table top TPO display  10  may enable the projection of parallax “private images”  3  which are only visible from a given seating position. 
   Thus, as shown in  FIGS. 1 and 2 , 3-D imagery can be positioned anywhere along the line of sight  4  that connects each active display element of the tabletop and the viewer&#39;s eyes  5 . For a given eye position, the associated display space is conical. Therefore 3-D imagery can appear to float above, to straddle, or to lie deep within the table. “Window violations” may occur if any parts of the 3-D scene fall out of the display space. Several 3-D displays fall within the TPO family. These include conical stereograms and cylindrical holograms. 
   In  FIGS. 3 and 4  image data used to create the 3-D image  2  or 3-D scene  8  composed of several 3-D subjects in a scene, is recorded by rendering or recording a 3-D scene from multiple viewpoints. Generally, a 2-D camera  6  will follow a circular path  7  above the 3-D image  2  or a 3-D scene  8 . In this embodiment, the camera  6  will always be oriented so that the camera  6  points at the center of the 3-D scene  8  that will be reproduced as appearing to straddle the flat in-table top display surface  1 . The camera  6  should be orthographic, i.e., placed at a radius of infinity. One position of the camera is shown in  FIG. 3 . In this embodiment, one recorded view per degree is adequate totaling 360 views total. This is illustrated in  FIG. 3 . Of course, the camera  6  can be a physical camera or a computer-graphic “camera” as is well-known in the field of computer graphics. 
   Once the image data is recorded and stored, the 3-D image  2  or the 3-D scene  8  may be recreated. See Prior Art  FIG. 15  for a diagram of a known image view recording arrangement. As shown in  FIG. 5 , a fast digital micromirror device (DMD) based 2-D digital DMD projector  9  capable of 10,000+ frames per second is illuminated using collimated illumination, enabling an image to form at any distance from the projector, up to several meters. 
   Significantly, in order to provide the flat in-table top display surface  1 , in this embodiment, a rotating element or assembly of elements will rotate and is located in the plane of the tabletop. Thus, the overall apparatus retains the look of a flat table. The important point to note is that the flat in-table top display surface  1  is flat and does not protrude. A viewable side of the flat rotating display surface is structured to be locatable flush within the surface plane of the table top and is structured to be a flat section of the flat table top. Alternatively, the flat rotating display surface can be inset below the surface of the rest of the table, changing the depth of the principal 3-D image location. 
   Thus, it is also possible for an embodiment of this invention to form a table by itself. Therefore, the fact that this embodiment is suitable for placement within a tabletop does not mean that another embodiment of the display may not stand alone as a flat surface or that the display may make up most or all of the “table” as a piece of furniture because this is also envisioned. 
   In the embodiment shown in  FIG. 5 , a rotatable inverted cake pan  11  holds two relay mirrors, a first relay mirror  12 , a second relay mirror  13 , an optional collimating layer  14 , and a unidirectional diffusing screen  15  as shown in  FIG. 5 . The DMD projector  9  illuminates the first relay mirror  12 , which sends light to the second relay mirror  13 , which in turn illuminates the collimating layer  14  and the unidirectional diffusing screen  15 . The relay mirrors ( 12 ,  13 ) and display surfaces ( 14 ,  15 ) are rotated together at frequency of thirty (30) revolutions per second, in synchrony with the sequence of 360 images projected from the stationary DMD projector  9 . For example in reference to  FIGS. 4 and 5 , recorded “image  0 ” is projected when the image surface comprised of the unidirectional diffuser  15  is oriented at 0 degrees during its rotation. “Image  90 ” is displayed at 90 degrees of rotation, and so on for all 360 images or slices of the total 3-D image  2  displayed in this embodiment. In this way, a flat in-table top display is created. The final diffusing layer may also be chosen to enable the viewer to move his head up and down within a specified viewing range of angles from the viewing surface, for example 45 degrees. 
   For optimum image quality, the present embodiment may create a display surface that is capable of casting a bundle of rays with a 2-D cross section that is pitched at an angle. This is illustrated in  FIG. 6A . For example, in this embodiment, a ray bundle  16  exiting the display surface is propagated at an angle around 45 degrees from the display surface is chosen to intersect with the likely viewing height of the viewer. However, any suitable viewing angle can be configured. When the flat in table top display surface  1  is oriented parallel to the floor and is rotated about the vertical axis, the bundle of rays  16  will sweep out a large hollow truncated conical volume as shown in  FIG. 8 . The trajectory of one pixel  17 , chosen from the overall bundle  16 , is shown in  FIGS. 7A and 7B . As the rotating cake pan  11  spins, the 2-D ray bundle sweeps out a truncated conical volume. The resultant conical volume is termed an “eye box”  18  herein and is illustrated in  FIG. 8 . 
   The motor  22  used to spin the image surface may use a belt drive or geared drive so that it can be placed alongside the image surface or elsewhere. 
   Another embodiment having a spinning TPO display surface is shown in  FIG. 9 . However, this embodiment does not use a spinning vertical cake pan  11  for example. Instead, the spinning display surface is comprised of three optical elements sandwiched together. Specifically, a light shaping diffuser  19  is located on the surface. A collimating grid  20  is located beneath the light shaping diffuser and is pitched at an angle, for example 45 degrees. Lastly, a unidirectional diffuser  21  is used as an imaging surface for the projector. It noted herein that in this embodiment that there are no relay mirrors. Instead, the stationary projector illuminates the “spinning sandwich” comprised of three optical elements which sweeps out a conical volume. The 3-D data is captured as before. 
   The concept of the image scan sequence is more specifically illustrated in  FIG. 10 . Using only four positions for purposes of illustration only, planes A and B are shown to depict the plane of ray bundle  16  projected at 0, 90, 180, and 270 degrees. 360 positions may be used for example, one at every degree, to display 360 images at rate of thirty revolutions per second. At this high rate of rotation, human persistence of vision combines the displayed images to form a 3-D image that is viewable from 360 degrees, i.e., a user or viewer can “walk around” the 3-D image  2 . 
   Another embodiment is shown at  FIG. 11  wherein the light-steering surface may be comprised of a diffractive optic such as a diffraction grating  23 . The diffraction grating  23  may be as simple as a standard linear grating that spins. One such system composed of a single frequency linear grating sandwiched between a Fresnel lens  24  and a louver  25  is shown in  FIG. 11 . The embodiment can also be made with a stationary display surface if the projection optic is capable of a circumferential scan. Alternatively, an alternative to use of a grating could also be use of an off axis Fresnel lens as shown in  FIG. 18 . 
   Of course, there are many ways to construct TPO displays using the principles taught herein. The specific embodiments we describe are only a few among the set of all possible constructions that fall within the scope of the claims. 
   Another embodiment is described in  FIGS. 12 and 13 .  FIG. 12  demonstrates an alternative rendering or recording method that could be used, and  FIG. 13  shows one possible projection system that would be used in conjunction with this system. The operation of this system is identical to that of the system in  FIG. 5 , however with modified optical properties. For example, instead of projecting collimated images from the display screen, the system of  FIG. 13  system scans an exit pupil in the viewing zone to create a similar “eyebox” as is described in  FIGS. 5 and 8 . However, the direction of the rays  16  emanating from the display surface in  FIG. 13  is different in this system because an exit pupil  26  is where the rays are directed. 
   The TPO systems described in this document can also be adapted for use in full-parallax 3-D displays. One or more of the relay mirrors inside the rotating inverted cakepan  11  of  FIG. 5  or  FIG. 11  could be made to rotate. The volume of rays swept out from such a system could fill a shape similar to a frustum, whereby the instantaneous ray bundles are “raster scanned” so that the “eyeboxes” are filled in a row by row manner. 
   While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.