Abstract:
A system for auto-stereoscopic presentation of stereo-image pairs that uses volumetric imaging elements so that a viewer may experience a 3-D illusion that appears to be located in a space free of system components. A reflecting optical element produces a real image of part of the auto-stereoscopic imaging system, in a position that is indicative of where a viewer must place their eyes in order to see the 2-D stereo images so that stereopsis may occur, and a 3-D image perceived. A viewer can clearly see where to place there eyes, and without any actual physical elements of the imaging system in, or around, the region where the 3-D image is perceived to be, allowing the viewer to touch the images being observed. Furthermore, in such a system, real objects may be located along side the 3-D images, further enhancing the stereoscopic 3-D illusion by providing additional depth cues.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is related to, and claims priority from, U.S. Provisional Patent application No. 60/641,947 filed on Jan. 7, 2005, by Robert E. Andrews entitled “Auto-Stereoscopic Volumetric Imaging System”, the contents of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to auto-stereoscopic imaging systems and methods, and more particularly to auto-stereoscopic imaging systems and methods that employ volumetric imaging components.  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention provides a system and method for auto-stereoscopic presentation of images.  
         [0004]     Stereoscopy is a well-known process in which a viewer perceives a three-dimension (3D) object when shown a stereo pair of two-dimensional (2-D) images of the object. In particular, when a viewer is presented with one 2-D image corresponding to a left eye view of the object and another 2-D image corresponding to a right eye view of the same object, the viewer&#39;s brain merges the images to produce a 3-D perception of the scene. This phenomena is sometimes called stereopsis and is part of the mental process in visual perception by which an observer discerns the depth or distance of objects from the observer.  
         [0005]     Generally, stereoscopy may be accomplished one of three general methods in which each eye receives image information of the same subject from two slightly different viewpoints.  
         [0006]     In a first general method for stereoscopy, a single 2-D image, or anaglyph, contains all the information for both 2-D stereo views. The left and the right stereo images, however, are encoded with some optically separable quality, and the viewer wears glasses that ensure that each eye receives only the correct view. For instance, in viewing simple color anaglyph images, in which the left and right eye stereo pairs are encoded as different colors, the viewer wears glasses with color filters that ensure that each eye only sees one of the stereo pairs. Similarly, to view polarized anaglyphs, in which the left and right eye images are encoded in orthogonal polarizations, glasses with appropriate polarization filters are used to separate the images and ensure that each eye only sees one of the stereo pairs.  
         [0007]     In the second general method for stereoscopy, a single screen presents the 2-D stereo pairs sequentially in time. The viewer wears glasses that have shutters synchronized to the presentation of the images, so that each eye only sees the appropriate stereo image.  
         [0008]     Stereoscopic systems based on both these first two methods have two major drawbacks. Firstly, the viewer has to wear special stereo glasses. Secondly, each eye only sees an image that has half the maximum intensity the display screen is capable of providing.  
         [0009]     A third general method of presenting stereo images is by use of auto-stereoscopic imaging systems. These are optical projection systems that display both of the stereo 2-D images simultaneously, either on separate displays, or on separate parts of a single display. An optical system relays each image such that, when a viewer places their eyes at certain predetermined locations, each eye only sees one of the stereo pairs, and stereopsis occurs. Head mounted displays, such as the early Virtual Reality (VR) helmets in which two small display monitors, about an inch wide, were place in front of each eye are an example of an auto-stereoscopic imaging system.  
         [0010]     Auto-stereoscopic viewing systems have the advantage of not requiring the viewer to wear special glasses. Furthermore, an auto-stereoscopic system in which a separated screen displays each image, allows each eye to see an image at the full screen brightness so that the 3-D image is perceived to be twice as bright as an image on a single screen.  
         [0011]     Auto-stereoscopic stereo image viewing systems, however, do have the disadvantage that the viewer&#39;s eyes have to be located at particular locations in space. This may require the use of additional, cumbersome equipment as in the example of the VR viewing helmet.  
         [0012]     A further drawback of typical implementations of all these general methods of presenting stereo images is that the 3-D object appears to be located in the same space as some the optical elements used to create the illusion. This collocation of the stereoscope components and the illusion prevents the viewer from attempting to touch the object of the illusion.  
       SUMMARY OF THE INVENTION  
       [0013]     Briefly described, the present invention provides a system, apparatus and method for auto-stereoscopic presentation of stereo-image pairs that uses volumetric imaging elements and processes so that a viewer may experience a 3-D illusion that appears to be located in a space free of system components.  
         [0014]     In a preferred embodiment, the auto-stereoscopic stereo, volumetric imaging system (also known as a volumetric imager) includes a large format reflecting optical element that produces a real image of a reflecting prism and a relay lens that are part of the auto-stereoscopic volumetric imaging system. The real images of the prism and relay lens are projected to positions that are indicative of where a viewer must place their eyes in order to see the 2-D stereo images so that stereopsis may occur, and a 3-D image may be perceived. To a viewer using the system, the stereo image pairs that are observed auto-stereoscopically, for instance, may appear to be on the real image of the reflecting prism.  
         [0015]     One advantage of such a system is that the viewer can clearly see where to place their eyes, and yet there are no actual physical elements of the auto stereoscopic, volumetric imaging system in, or around, the region where the 3-D image is perceived to be. This allows 3-D viewing in which the viewer may attempt to touch the images being observed. Furthermore, in such a system, real objects may be located along side the 3-D images, further enhancing the stereoscopic 3-D illusion by providing additional depth cues.  
         [0016]     In a preferred embodiment of the invention the large format optical element is a section of a sphere, whose concave reflective surface has an arc length greater than ¾ of a meter and whose radius of curvature is larger than 1 meter.  
         [0017]     These and other features of the invention will be more fully understood by references to the following drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is an isometric drawing showing a schematic representation of an auto-stereoscopic volumetric imaging system in accordance with one embodiment of the present invention.  
         [0019]      FIG. 2  is a drawing showing a plan view of a schematic representation of an auto-stereoscopic volumetric imaging system in accordance with one embodiment of the present invention.  
         [0020]      FIG. 3  is a drawing showing a plan view of the principal optical elements of an auto-stereoscopic imaging system in accordance with one embodiment of the present invention.  
         [0021]      FIG. 4A  is a drawing showing a pseudo-sagittal view of one-half of the principal stereoscopic optical elements of an auto-stereoscopic, volumetric imaging system in accordance with one embodiment of the present invention.  
         [0022]      FIG. 4B  is a drawing showing a sagittal view of the principal optical elements for creating a locating real image of an auto-stereoscopic, volumetric imaging system in accordance with one embodiment of the present invention.  
         [0023]      FIG. 5  is a drawing showing a pseudo-sagittal view of the principal optical elements of an auto-stereoscopic, volumetric imaging system in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0024]     The present invention relates to a method, system and apparatus for auto-stereoscopic volumetric imaging. In a preferred embodiment, the invention incorporates volumetric viewing elements so that a viewer may have a virtual object to guide the viewer as to where to place their eyes in order to perceive the 3-D illusion. In addition, the volumetric imaging elements allow the perceived location of the 3-D illusion to be in a space that does not contain any elements of the auto-stereoscopic system. This allows volumetric imaging in which other real objects may be co-located with the perceived three-dimensional object, heightening the illusion by adding real depth cues. This auto-stereoscopic, volumetric imaging arrangement also allows a user to interact virtually with the perceived three-dimensional object by observing their hands or fingers attempt to touch, feel or hold the virtual object or its surface.  
         [0025]     A preferred embodiment of the present invention will now be described in greater detail by reference to the accompanying drawings in which, as far as possible, like numbers represent like elements.  
         [0026]      FIG. 1  is an isometric drawing showing a schematic representation of an auto-stereoscopic, volumetric imaging system in accordance with one embodiment of the present invention. The system includes an optical cabinet  11 , a digital fusion module having a reflecting prism  14 , a left-eye image display  15 A, a right-eye image display  15 B and a relay lens  13 ; and an image delivery system having a large format reflecting optical element  12 . The relay lens  13  is preferably an achromatic lens such as, but not limited to, a doublet achromatic lens.  
         [0027]     The image delivery system produces a real prism image  24  of the prism  14 , primarily by means of the reflection imaging properties of the large format optical element  12 . The large format optical element may be, but is not limited to, a concave reflecting element such as a mirror having a concave reflecting surface that is spherical or part of an oblate spheroid. In one preferred embodiment, the large format optical element  12  is an aluminized, front surface mirror having a diameter of 760 mm and a focal length of 1350 mm. For good imaging performance, the front, optical reflecting surface of the large format optical element  12  preferably has ½ wavelength surface smoothness at 560 nm.  
         [0028]     The focal properties, position and alignment of the relay lens  13 , the prism  14  and the image displays  15 A and  15 B may be selected so that a left display-image  20 A and a right display-image  20 B over-lap in space, in the approximate region of the rear of the real prism image  24 . In a preferred embodiment of the invention, the left and right display images  20 A and  20 B are real images. The degree of overlap of the relayed, real images  20 A and  2 B may be varied from completely where they completely overlap each other and are effectively collocated in space, to any suitable degree of horizontal separation that approximately matches the eye separation of the user. A the normal, adult eye separation is about 62 mm, a separation capability in the range from about 10 mm to about 80 should cover most potential users of the system.  
         [0029]     These left and right display-images  20 A and  20 B may be viewed by a human eye having the pupil located within the optimal viewing regions  26 A and  26 B, which may be arranged to coincide with some part of the real image of the prism. A pupil placed within optimal viewing region  26 A will, however, only see the left-image  20  A of image display  15 A. Similarly, a pupil placed within optimal viewing region  26 B will, however, only see the right-image  20 B of image display  15 B.  
         [0030]     In a further embodiment of the invention, the left and right display-images  20 A and  20 B may not be co-planer but one may be displaced further from the viewer eyes than then the other so as to accommodate for a viewer having different focusing capabilities in each of their eyes. The variation in the location of the left and right display-images  20  A and  20  B may be accomplished, for instance, by varying the location or the angle of the reflecting surfaces of the prism  14 , or the positions of the image displays  15  A or  15  B relative to the reflecting surfaces, or some combination thereof.  
         [0031]     In addition, the focal properties, position and alignment of the optical elements may be selected so that the optimal viewing region  26 A and  26 B are separated by approximately the average distance between pupils in an adult human. As a result, if image displays  15 A and  15 B simultaneously display corresponding stereo images, an adult human with their pupils located within the optimal viewing regions may experience stereopsis, and may experience the illusion of seeing a virtual three-dimension object.  
         [0032]     Because the optimal viewing regions  26 A and  26 B are collocated with a part of the real prism image  24 , a person has a clear indication of where to place their eyes in order to use the auto-stereoscopic viewing system of this invention, without there being any physical parts of the viewing system in the vicinity of the perceived three-dimensional objects seen by that person.  
         [0033]     One of ordinary skill in the art will appreciate that the method and system of this invention is not limited to having the front surfaces of the real prism image  24  collocated with the optimal viewing regions  26 A and  26 B, but that as long as any identifiable portion of the real image of an object is located a predetermined distance from at least one of optimal viewing regions, the system may function. For instance, the system may be arranged so that by placing one&#39;s nose at the apex of the real prism image, one&#39;s eyes would be correctly located to view the images so as to produce stereopsis.  
         [0034]      FIG. 2  is a drawing showing a plan view of a schematic representation of an auto-stereoscopic imaging system in accordance with one embodiment of the present invention. In  FIG. 2 , the schematic is drawn as though the upper surface of optical cabinet  11  is transparent so as to simplify the representation of the images displays  15 A and  15 B, the reflecting prism  14  and the transfer lens  13 . One of ordinary skill in the art will readily appreciate that although the optical cabinet may have a transparent glass top, in a preferred embodiment the upper surface may be an opaque surface.  
         [0035]      FIG. 2  shows a user  30  placing their face effectively touching the real prism image  24  so that their eyes are collocated at the optimal viewing locations  26 A and  26 B.  
         [0036]     Optimal viewing location  26 A is a location in space from where a viewer, looking in the required direction, will see an image  20 A of the object  16 A that is being displayed on display screen  15 A. The image  20 A, which is preferably a real image, is formed by the combined imaging properties of a facet of reflecting prism  14 , the transfer lens  13  and the large format reflecting optical element  12 .  
         [0037]     Similarly, optimal viewing location  26 B is a location in space from where a viewer, looking in the required direction, will see an image  20 B of the object  16 A that is being displayed on of display screen  15 B, as imaged by one facet of the reflecting prism  14 , the transfer lens  13  and the large format reflecting optical element  12 .  
         [0038]     As the optimal viewing locations  26 A and  26 B are separated by approximately the same separation as an average viewers eyes, an average viewer positioned as shown in  FIG. 2 , will see only the relayed image  20 A of the image displayed on display screen  15 A with their left eye, and only the relayed image  20 B displayed on display screen  15 B with their right eye. Both relayed images  20 A and  20 B may, however, appear to be collocated, or to be separated by a horizontal displacement relative to each other so that stereopsis occurs when a user views them.  
         [0039]     An image server  32  is a device capable of storing and distributing images. The images server may be, but not limited to, a personal computer having appropriate storage devices and running appropriate software.  
         [0040]     If the image server  32  delivers appropriately matched stereo images to image displays  15 A and  15 B, a viewer with their eyes located at optimal viewing regions  26 A and  26 B may experience stereopsis. This may occur although the relayed images  20 A and  20 B are horizontally displaced relative to each other because each relayed image is only seen with one eye. The user&#39;s brain effectively collocates the images with the result that the user experiences the illusion of seeing a virtual three dimensional image.  
         [0041]     The stereo images delivered by image server  32  may be still images, or they may be a sequence of images in the form of a video or any combination thereof. Video images may include the external surfaces of objects as in the case of video camera feeds or the interior structures in the case of penetrating imaging such as, for example, x-ray, MRI, PET or other such imaging technologies. One of ordinary skill in the art will realize that the stereo image pairs may be produced or manipulated by any suitable image production or manipulation means including, but not limited to any suitable digital or analogue computer enhancement, manipulation, processing or generation method.  
         [0042]      FIG. 3  is a drawing showing a plan view of the principal optical elements of an auto-stereoscopic imaging system in accordance with one embodiment of the present invention.  
         [0043]     Large format reflecting optical element  12 , which may have an inner reflecting surface that is part of a sphere or an oblate spheroid, is shown as having a principle radius of curvature R, centered at location R. Such a surface has a focal point F such that F is half of R.  
         [0044]     Object  16 A is the surface of the display screen  15 A (not shown in  FIG. 3 ). Object  16 A is imaged as image  20 A by a reflection off one facet of reflecting prism  14  and the combined imaging properties of transfer lens  13  and the large format reflecting optical element  12 . The image  20 A is best viewed by a human observer having the pupil of an eye located within the optimal viewing location  26 A.  
         [0045]     Similarly, object  16 B is the surface of the display screen  15 B (not shown in  FIG. 3 ). Object  16 B is imaged as image  20 B by a reflection off one facet of reflecting prism  14  and the combined imaging properties of transfer lens  13  and the large format reflecting optical element  12 . The image  20 B is best viewed by a human observer having the pupil of an eye located within the optimal viewing location  26 B.  
         [0046]     It is well-known that an object placed at the center of curvature of a spherical mirror will produce a real image, also at the center of curvature and having unit magnification. Similarly, it is well known that placing an object between the center of curvature and the focal point of a spherical mirror will result in a real image located a corresponding distance beyond the radius of curvature and having a corresponding magnification.  
         [0047]     By careful selection of the principal radius of curvature of the large format reflecting optical element  12 , the focal length and position of the transfer lens  13 , the position of the reflecting prism  14  and the position of the display images  16 A and  16 B on the display screens  15 A and  15 B, the optimal viewing locations  26 A and  26 B can be collocated with part of the real image of the prism  24 .  
         [0048]      FIG. 4A  is a drawing showing a pseudo-sagittal view of the principal stereoscopic optical elements of an auto-stereoscopic, volumetric imaging system in accordance with one embodiment of the present invention.  
         [0049]     The effect of reflecting prism  14  is represented unfolded, i.e., the line joining prism surface  14  to objects  16  A&amp; B would, in reality, be normal to the page but is shown here folded back onto the page, hence the view is only a pseudo-sagittal representation.  
         [0050]     One objective of showing the pseudo-sagittal view of  FIG. 4A  is to show how the display images  16 A and  16 B are projected from beneath the normal to the large format reflecting element  12 , represented by the line joining R and F, to above it, as images  20 A and  20 B, which are best viewed by a pupil place at optimal viewing regions  26 A and  26 B. In this way, the images  20 A and  20 B may be located above the optical cabinet (not shown in  FIG. 4 ), in a region free of any components of the auto-stereoscopic imaging system. The images  20 A and  20 B may be collocated in space or they may have some degree of lateral or horizontal separation or displacement relative to each other. This horizontal displacement allows a user to view the images in a more relaxed manner and achieve stereopsis.  
         [0051]      FIG. 4B  is a drawing showing a sagittal view of the principal optical elements for creating a locating real image of an auto-stereoscopic, volumetric imaging system in accordance with one embodiment of the present invention.  
         [0052]     One objective of showing the view of  4 B is to illustrate how real images of the transfer lens  13  and the reflecting prism  14  are produced by the large format reflecting element  12 . In particular, by placing the transfer lens  13  and the reflecting prism  14  beneath the normal to the large format reflecting element  12  and between the radius of curvature R and the focal point F, an enlarged, real prism image  24 , and an enlarged, real transfer lens image  22  are produced above the normal, R-F, of the large format reflecting element  12 .  
         [0053]      FIG. 5  is a drawing showing a view of all the principal optical elements of an auto-stereoscopic, volumetric imaging system in accordance with one embodiment of the present invention.  FIG. 5  is essentially a combination of  FIGS. 4A and 4B , and illustrates the collocation of the regions of optimal viewing  26 A and  26 B with the front surfaces of the real prism image  24 .  
         [0054]     In further embodiments of the invention, the large format reflecting optical element  12  may be a spherical mirror and may have a radius of curvature greater than 1 meter or larger. In many applications, the radius of curvature of the large format reflecting optical element  12  may be greater than 2 meters and may even exceed 3 or 4 meters.  
         [0055]     In a further embodiment of the invention, the relay optic  13  may consist of two separate achromatic, optical refracting elements, each being used to relay either the image from the left-eye image display  15 A or the right-eye image display  15 B.  
         [0056]     In another embodiment of the invention, the angle between the reflecting surfaces of the prism  14  may be varied to effect horizontal displacement of the images  20 A and  20 B relative to each other. The reflecting surfaces, for instance, may be two independent flat mirrors capable of independent angular adjustment with respect to each other.  
         [0057]     In a further embodiment of the invention the positions of the image displays  15 A and  15  B relative to the reflecting surfaces of the prism  14  may be variable so that the relative position of the images  20 A and  20 B relative to the optimal viewing locations  26 A and  26 B may be varied.  
         [0058]     Although the invention has been described in language specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed invention