Abstract:
A system for displaying images in auto-stereoscopic format, the system includes an illumination source that produces light in at least two bands in synchronization with frame sequential stereo image data; a single spatial light modulator that is driven by the frame sequential stereo image data and that receives the two bands of light from the illumination source; and a real-time eye tracking device that monitors positions of eyes of a user so that viewing is not interrupted by movement of the eyes of the user; wherein the user views the two bands of light sequentially on only the single spatial display which projects a three-dimensional image to the viewer.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates generally to the field of display systems that project images in auto-stereoscopic format and, more particularly, to such display systems having only a single display for projecting auto-stereoscopic format and/or having one or more fresnel lenses for projecting auto-stereoscopic format.  
       BACKGROUND OF THE INVENTION  
       [0002]     Currently, there is a need in the display industry for displaying images in three-dimensional format. One method for displaying three-dimensional images is to provide two images respectively onto two viewing screens, and a beam splitter merges the images provided from the two screens. This method is described European Patent Specification EP 0 602 934 B1 (hereinafter the &#39;934 reference). In this patent specification, two light sources each include a plurality of individual light portions so that any portion of the light source may be illuminated at any time. The two screens respectively receive the light from the two light sources which images are viewed through a beam splitter. Lenses near the screens form images of the sources in a viewing region from which an observer perceives a three-dimensional image, when a stereo image pair is displayed upon the screens.  
         [0003]     The &#39;934 reference forms an auto-stereoscopic image whose optical position is near to the observer, and in fact, the optical position is located at the actual distance of the screens. This limits the useful volume of 3-D space, which may be comfortably viewed by the observer. U.S. Pat. No. 6,351,280 discloses an auto-stereoscopic display system that is based upon a liquid crystal display (LCD) system that incorporates two sub-arrays such that every other line of the LCD panel includes a micro-patterned half-wave retarder. The act of illuminating the LCD with a source comprised of two vertical bands of light, with each band configured in a manner such that they produce a light that is orthogonal linearly polarized, and by forming an image in space of the two bands, a stereoscopic image may be viewed from the position of the spatial image of the bands, when the two LCD sub-arrays are driven with proper stereo image pair data. A disadvantage of this approach includes the loss of inherent resolution of the LCD due to the spatial multiplexing of the sub arrays. Also, the optical position for accommodation is at the real image plane, that is, at the location of the LCD.  
         [0004]     The technical literature also describes various lenses useful for displaying three-dimensional images. One such paper entitled An Auto-stereoscopic Display Providing Comfortable Viewing Conditions and A High Degree of Tele-presence by Klaus Hopf discloses several lenses useful for displaying three-dimensional images. This paper teaches that fresnel lenses are not useful in forming the distant virtual images for the purpose of displaying three-dimensional images.  
         [0005]     Although the method disclosed by Hopf is satisfactory, the cost of providing two screens is costly and, in some instances, is undesirable because of the space required for two displays. Still further, it is desirable to use fresnel lenses due to the cost and ease of manufacturing.  
         [0006]     Lenticular and barrier-screen auto-stereoscopic displays are very well known in the art. These have an inherent disadvantage in providing a lower spatial resolution than is available in the spatial light modulator that is the principal component of this type of auto-stereoscopic display.  
         [0007]     Consequently, a need exists for displaying comfortably viewable auto-stereoscopic images onto only one screen and/or using fresnel lenses for displaying three-dimensional images. There also exists a need for a full resolution display for auto-stereoscopic images.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, the invention resides in a system for displaying images in auto-stereoscopic format, the system comprising (a) an illumination source that produces light in at least two bands in synchronization with frame sequential stereo image data; (b) a single spatial light modulator that is driven by the frame sequential stereo image data and that receives the two bands of light from the illumination source; and (c) a real-time eye tracking device that monitors positions of eyes of a user so that viewing is not interrupted by movement of the eyes of the user; wherein the user views the single spatial display which projects a three-dimensional image to the viewer when the single spatial display is illuminated sequentially by the two bands of light.  
         [0009]     These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.  
       ADVANTAGEOUS EFFECT OF THE INVENTION  
       [0010]     The present invention has the advantage of displaying comfortably viewable images onto only one screen and/or using fresnel lenses in displaying three-dimensional images. It further provides the full spatial resolution of the spatial light modulator. Yet another advantage is robust viewer eye tracking and non-mechanical servo action to provide a large range of viewing positions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is an illustration of the system of the present invention; and  
         [0012]      FIG. 2  is an illustration an alternative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     Before discussing the present invention, it is instructive to note that spatial resolution is defined as the number of pixels per linear dimension of the spatial light modulator.  
         [0014]     Referring to  FIG. 1 , there is shown an illustration of the auto-stereoscopic system  10  of the present invention. A computer  20  stores images that are transmitted to a liquid crystal display (LCD)  30 . A light source  40  for visibly illuminating the LCD  30  includes a plurality of light emitting diodes (LEDs) or any other suitable lighting source, such as organic LEDs, fluorescent and the like, arranged in a panel array. The diodes are partitioned into a plurality of bands  50  in which each band  50  is lit individually so that the bands  50  may be illuminated in any predetermined manner. The panel array  40  projects light through two fresnel lenses  60   a  and  60   b  positioned back-to-back adjacent the LCD  30 , and through the LCD  30 , or any suitable transmissive spatial light modulator. Preferred spatial light modulators include active matrix liquid crystal display panels, particularly those with fast response. One such display is available through Samsung of South Korea that includes a response time of 8 ms. The fresnel lenses  60   a  and  60   b  form a real image in space of the bands  50 . The real image in space of the bands  50  as used herein is referred to as viewing pupils  100 L and  100 R. The transmissive LCD  30  together with optical films  51  or  52  function as a weak diffuser and provide a smearing effect that reduces the imaging of discrete dots from, for example, an LED array which may form light source  40  at the position of the viewing pupils  100 L and  100 R.  
         [0015]     It is instructive to note that, when two distinct bands  50  of the panel  40  are sequentially illuminated, two discrete images will be sequentially produced upon the LCD  30 . Images selected for display are reproduced alternately (i.e., continuously and sequentially) for the left and right eyes of the viewer. Light produced by the lighting array panel  40  illuminates the LCD  30  coordinated with the plurality of images thus producing a stereoscopic image that may be viewed when a users eyes are positioned at the viewing pupils  100 L and  100 R. It is instructive to note that these images can be either coordinated still images or coordinated motion images. For example, the computer  20  will send an image to the LCD  30  that is intended only for the left eye. The panel array  40  will then be turned on in a manner that will illuminate only the left eye. The fresnel lenses  60   a  and  60   b  send the illumination through the LCD  30 , and form an image of the selectively illuminated light source  40  at the left viewing pupil  100 L. The viewers left eye, when placed at the location of the left viewing pupil  100 L will see only the left eye image of a stereo pair. Upon the same being completed for the right eye only, the human visual system combines these two sequential images into a stereoscopic image. Each eye is presented with an image having the full spatial resolution inherent in the LCDs spatial light modulator. It is instructive to recall that when thinking of the operation of an old time View master, film was used to display mages that were offset from one another in accordance with the spacing of the human eyes. Illumination that was provided from a light source was passed through the offset frames of film, and was viewed as distant virtual images by action of the eyepieces. The film images include a stereo pair and so the viewer perceives a three-dimensional effect. The present invention provides illumination of information to the viewer&#39;s eyes alternately at a frame rate that is imperceptible to the human visual system thus producing a three-dimensional effect.  
         [0016]     A third fresnel lens  70  is positioned on the opposite side of the LCD  30  from the other two fresnel lenses  60   a  and  60   b  for forming a distant virtual image of LCD  30  thus improving the depth volume of the viewer. In addition, the third fresnel lens  70  provides comfortable stereoscopic viewing. An eye tracker  80  is positioned in a location so that the users eye can be monitored in real time. The eye tracker  80  continuously locates the user&#39;s eyes so that, when the user moves their head, the system of the present invention can adjust to the changing position of the user&#39;s eyes by properly adjusting the illumination thus ensuring the coinciding of viewing pupils  100 L and  100 R with the user&#39;s eyes. More specifically, the bands  50  on the panel are adjusted to remain in registration with the user&#39;s eyes in accordance with the information received from the eye tracker  80 . A processor  90  in the computer  20  coordinates the information from the eye tracker  80  to any corresponding change for which bands  50  are illuminated. Preferably, the eye tracker  80  is as disclosed in U.S. Pat. No. 6,459,446 issued on Oct. 1, 2002 to Philip Harman, which is herein incorporated by reference.  
         [0017]     A diffusing element that can be activated electrically  110  switches from a transmissive mode to diffusing mode. Examples of such switchable elements include polymer dispersed liquid crystal (PDLC) elements that are well known in the art. Such elements are used as privacy glass and can be coated on plastic. Suitable PDLC element material is available from, for example SwitchLite Division of Pulp Studio, Inc. 3211 South La Cienega Blvd. Los Angeles, Calif. 90016. Other examples of switchable diffuser elements, e.g. smectic liquid crystal layers, and the like are also useful for the purposes of the invention. When in the transmissive state, the liquid crystal display produces auto-stereoscopic images viewable from pupils  100 L and  100 R, and when in the scattering state, the liquid crystal display produces ordinary two-dimensional images with ordinary LCD panel view ability.  
         [0018]     Referring to  FIG. 2 , there is shown an alternative embodiment of the present invention. The alternative embodiment includes two LCDs  30  positioned substantially ninety degrees from each other. A computer  20  stores and transmits frame information (images) to each individual LCD  30 . Fresnel lenses  60   a  and  60   b  are positioned adjacent each LCD  30  for the purpose of forming viewing pupils  100 L and  100 R, as described hereinabove, from two light sources or panel arrays  40  respectively positioned adjacent the two LCDS  30  for projecting light through the LCDs  30 . The light projected through each LCD  30  is directed onto a beam splitter  120  for coordinating the projection of the light passing through each LCD  30  in a manner in which the human visual system creates the perception of a three-dimensional image when the user&#39;s eyes are at the viewing pupils  100 L and  100 R.  
         [0019]     For example, the computer  20  will send images individually to each of the LCD  30  in a manner such that one image from one LCD  30  is intended for the left eye and one image from the other LCD  30  is intended for the right eye only. The two panel arrays  40  will then be turned on in a manner that will provide from one panel array  40  the illumination for the left eye only, and from the other panel array  40  the illumination for the right eye only. The fresnel lenses  60   a  and  60   b , positioned adjacent the two LCDs  30 , forming viewing pupils  100 L and  100 R, send the right and left illumination through each LCD  30 . The beam splitter  120  combines the left eye information and the right eye information that is displayed by the LCD panels; wherein the human visual system perceives combines these two images into a single stereoscopic image. As before, the third fresnel lens  70  produces distant virtual images thus enabling comfortable viewing of stereoscopic images over a large perceived volume of space.  
         [0020]     As discussed above, an eye tracker  80  is positioned in a convenient location for facilitating locating the position of the user&#39;s eyes.  
         [0021]     The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention.  
       PARTS LIST  
       [0022]      10  auto-stereoscopic system  
         [0023]      20  computer  
         [0024]      30  liquid crystal display (LCD)  
         [0025]      40  light source/panel array  
         [0026]      50  bands  
         [0027]      51  optional film/diffuser  
         [0028]      52  optional film/diffuser  
         [0029]      60   a  fresnel lens  
         [0030]      60   b  fresnel lens  
         [0031]      70  third fresnel lens  
         [0032]      80  eye tracker  
         [0033]      90  processor  
         [0034]      100 L left viewing pupil  
         [0035]      100 R right viewing pupil  
         [0036]      110  electrically activatable diffuser  
         [0037]      120  beam splitter