Abstract:
A viewing system and method for producing at least one image for being perceived as three-dimensional, including at least one of: a provision for compensating the center-of-interest of the at least one image in such a manner as to reduce convergence-accommodation conflict; a provision for configuring the viewing system such that crosstalk produced by a stereo display is perceived as foreground and background blur instead of ghosting; and a provision for viewing the at least one image via automicrostereopsis.

Description:
CROSS-REFERENCE TO RELATED U.S. APPLICATIONS 
   This application claims priority from U.S. Provisional Patent Application Ser. No. 60/116,691, filed on Jan. 21, 1999. 

   FIELD OF THE INVENTION 
   The present invention generally relates to arrangements for three-dimensional imaging. 
   BACKGROUND OF THE INVENTION 
   Generally, a need has been recognized for what may be termed “kinder gentler stereo”. 
   In this context, “stereo” refers to a system for putting information on a two-dimensional, essentially flat screen surface (such as front and back projection “movie” screens, CRTs, LCDs, etc.) in a way that causes the observer to see an image in depth corresponding to the depth in the original scene. The scene could be a real scene captured by an appropriate camera system, a virtual scene generated by a computer, or a hybrid of these. 
   The term “kinder gentler” is provided as a contrast to what has been experienced with known conventional devices. Particularly, conventional stereo displays often involve various types of physical and mental discomfort, to varying degrees. One commonly encountered example of such discomfort is “virtual reality sickness”. Technical inconveniences have also been noted among known devices, such as specialized types of eyewear that must be worn and “viewing zones” that are often perceived to be bothersome. 
   At a basic level of the musculature of the human visual system, there is a well-known conflict, known as convergence-accommodation (sometimes termed “vergence-accommodation”, among other things) that makes it difficult to achieve the desired consistency among stimuli (or cues). That is, because the information is presented on a 2D “flat” screen surface, the eyes focus (i.e., accommodate) on that surface. However, the directions-of-gaze of the eyes have been found to converge not on the screen but onto a center-of-interest which generally exists someplace in front of or behind the screen at a distance corresponding to the virtual location of the point or region at the momentary center-of-interest. 
   The conflict between what the convergence muscles and the focusing muscles are each communicating to the brain about the scene&#39;s depth is thus a major disturbing conflict. A need has thus been recognized to overcome this and other conflicts of less severe nature. 
   SUMMARY OF THE INVENTION 
   As a significant departure from known devices, at least one presently preferred embodiment of the present invention involves a stereo display system, with corresponding scene capture or scene generating components, that is natural and undisturbing to view, that involves neither eyewear nor viewing zones, and does not induce the perceptual conflicts that underlie “virtual reality sickness” and other bothersome features of existing stereo displays. 
   These features are achieved, in accordance with at least one embodiment of the invention, by recognizing and incorporating in the image capture or image generation system, and in the display technology, a consistent set of the numerous stimuli that contribute to depth perception. 
   The aforementioned conflict between what the convergence muscles and the focusing muscles are each communicating to the brain about the scene&#39;s depth is believed to be overcome in connection with at least one presently preferred embodiment of the present invention. 
   In accordance with at least one presently preferred embodiment of the present invention, “center-of-interest correction” (or, alternatively, “center-of-interest compensation”) is contemplated. This may be carried out by optical or algorithmic means, or by a combination of the two. The left-right perspective disparity is adjusted to be zero (or near zero) at the center-of-interest. 
   Since the center-of-interest is generally subjective, it will typically be selected by a person. However, the present invention also broadly contemplates the possibility of selecting the center-of-interest by automatic means. 
   The selection of center-of-interest can preferably be accomplished by sliding the left-right perspective images over each other until they coincide at the center-of-interest. The images can then be suitably cropped so that the two fields-of-view coincide at the distance of the center-of-interest. Alternatively, the camera sensors (CCD&#39;s) could be shifted at the time of image capture. This would avoid the need to crop, such that picture area would not be lost, nor would the desirable constancy of aspect ratio be compromised. 
   In accordance with at least one presently preferred embodiment of the present invention, it is also recognized that it is possible to significantly decrease the disparities (corresponding to interocular separations between the real or virtual cameras generating the left and right eye views) needed to sufficiently stimulate binocular depth perception. The degree to which this is possible has been found to be quite surprising. Assuming, for mechanical convenience (as is often the case), that a human scale is employed for artificial cameras, then the standard of normal human interocular separation employed in that connection can be in the range of 60 to 65 mm. In this context, it has been found, in conjunction with at least one presently preferred embodiment of the present invention, that a 2 mm camera separation by comparison is usually completely sufficient, and even 1 mm is often adequate. This effect is to be termed “microstereopsis”. A proportionately scaled interocular reduction can, of course, also be enjoyed in connection with systems that are not originally built on the aforementioned human scale. 
   It has been found that the combination of center-of-interest correction and microstereopsis greatly minimizes the convergence-accommodation conflict. When consistently combined with other depth cues, this combination effectively achieves the desirable consequence, encountered in accordance with at least one embodiment of the present invention, that the viewer sees the scene in depth without experiencing the undesirable side effects (e.g., “virtual reality sickness”) that are normally regarded as a necessary accompaniment of 3D-stereoscopic displays. 
   In accordance with at least one presently preferred embodiment of the present invention, it is also recognized that the combination of center-of-interest correction and microstereopsis has the desirable side effect of enabling an entirely new class of stereoscopic display hardware paradigms, in view of a surprisingly effective utilization of “crosstalk” in accordance with at least one presently preferred embodiment of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention and its presently preferred embodiments will be better understood by way of reference to the detailed disclosure herebelow and the accompanying drawings, wherein: 
       FIG. 1   a  is a schematic representation of right and left human eyes showing their locations and viewing directions in relation to a flat display screen on which is rendered imagery that is perceived in three-dimensions by the human brain; 
       FIG. 1  is a schematic representation of the relative locations on the screen of  FIG. 1   a  at which are rendered right eye views and left eye views of objects at background distance, screen distance, and foreground distance from the viewer for the case of a conventional three-dimensional display; 
       FIG. 2  is a schematic representation of the relative locations on the screen of  FIG. 1   a  at which are rendered right eye views and left eye views of objects at background distance, screen distance, and foreground distance from the viewer for the case of a three-dimensional display utilizing “microstereopsis”; 
       FIG. 3  is a schematic demonstration of microstereopsis; and 
       FIG. 4  is a schematic representation of an autostereoscopic arrangement utilizing microstereopsis. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Three-dimensional imagery can be displayed a flat screen  001  with the arrangement illustrated in  FIG. 1   a . As shown, right eye  002  and left eye  003 , respectively, perceive screen points  007  and  008  along respective lines of sight  009  and  010 . Shutter, barrier, or other means not illustrated explicitly in  FIG. 0  are employed to prevent right eye  002  from perceiving screen point  007  intended for left eye  003 , and to prevent left eye  003  from perceiving screen point  008  intended for right eye  002 . Lines of sight  009  from right eye  002  and  010  from left eye  003  converge at virtual scene point  006  behind screen  001 . The human brain fuses separate right eye  002  and left eye  003  perceptions of screen points  007  and  008  into a single three-dimensional perception at virtual scene point  006 . The distance  012  between corresponding screen points  007  and  008  is called the “disparity”. 
   Conventional 3D displays use large on screen disparities, as illustrated in  FIG. 1 . As shown, the left eye and right eye views ( 100   a  and  100   b , respectively) of an object  100  in the foreground coincide to a greater degree than the left eye and right eye views ( 102   a  and  102   b , respectively) of an object  102  on the screen, and greater still than the left eye and right eye views ( 104   a  and  104   b , respectively) of an object  104  in the background. 
   It can thus be appreciated that, with the conventional arrangement shown in  FIG. 1 , conflict between focusing the eyes on the screen and converging the eyes on the foreground or background results in eye strain, fatigue and “virtual reality sickness”. The image looks “ghosted” (doubled) if it is viewed without special equipment that would otherwise direct the left eye&#39;s view to only the left eye and the right eye&#39;s view to only the right eye. 
   In contrast, the inventive concept of microstereopsis contemplates the use of an appropriately configured and of appropriately conducted processing to make the background and foreground disparities very small, and the on-screen disparity zero, as shown in  FIG. 2 . Particularly,  FIG. 2  illustrates that the left eye and right eye views ( 200   a  and  200   b , respectively) of an object  200  in the foreground almost completely coincide, as do the left eye and right eye views ( 204   a  and  204   b , respectively) of an object  204  in the background, while the left eye and right eye views ( 202   a  and  202   b , respectively) of an object  202  on the screen coincide virtually completely. 
   In accordance with the arrangement illustrated in  FIG. 2 , there is no discomfort with stereo viewing, and no ghosting with normal viewing. Perception with microstereopsis is soft and natural, like the perception of depth in the natural world. As in the natural world, depth perception with microstereopsis is enhanced by cues that complement binocular perspective disparity: mainly occlusion, shading and size familiarity with statically displayed images, and aided by motion parallax, interposition, and possible dynamic monocular depth perception (MDP) effect when the displayed image does not have to be constant in time, e.g., in video or movie images as opposed to still images. 
   Microstereopsis can be demonstrated using the type of off-the-shelf display equipment that is used to view left/right image pairs with strong binocular disparity, as shown in  FIG. 3 . Particularly, right eye views  300   b ,  302   b  and  304   b , corresponding to an object in the foreground, an object on the screen and an object in the background, respectively, combine with corresponding left eye views  300   a ,  302   a  and  304   a  (foreground, screen and background, respectively), to result in the type of imaging shown in diagram  306 . 
   There exist many arrangements, such as the one shown in  FIG. 3 , that can involve the use of some type of eyewear to select the left and right images at the left and right eyes. Although lenticular (tiny lens array) autostereoscopic (requiring no glasses) displays and the like (e.g. barrier-type displays) exist, they have inconvenient viewing zones and they reduce the horizontal resolution of the images. 
   Because the left and right microstereopsis images are almost identical, with microstereopsis it may be less important to completely select the left and right images at the left and right eyes than it is with strong binocular stereopsis; in other words, crosstalk between the left and right eye information channels, which is a serious defect for strong binocular stereopsis displays, may not be a significant worry with microstereopsis. 
   To expound on this point, crosstalk, in a stereo display, is the mixing of some information intended for the left-eye into the right-eye&#39;s view, and vice versa. The perceptual effect of crosstalk in conventional 3D-stereoscopic display systems is “ghosting”, a perceived image doubling due to each eye receiving some of the other eye&#39;s image, whereas a complete separation of these information streams is ultimately desired. 
   A requirement to eliminate ghosting, and thus to eliminate crosstalk, can severely restrict one&#39;s options in developing a stereo display. However, it has been recognized, with relation to at least one presently preferred embodiment of the present invention, that when center-of-interest correction is applied to microstereoptically captured or generated images, that is, when left-right on-screen image disparities are very small, crosstalk does exist, but is not perceived as the highly objectionable phenomenon of ghosting. Instead, the crosstalk will be perceived as the natural and acceptable phenomena of foreground and background blurring, almost identical with the blurring associated with the finite depth of field of camera lenses and human eye lenses. 
   Thus, at least one presently preferred embodiment of the present invention broadly contemplates 3D-stereoscopic display systems based on principles, and employing parameters, such that any crosstalk between left and right eye channels is perceived as foreground and background blur (comparable to the blur expected from lens depth-of-focus) rather than as ghosting. 
   When crosstalk is perceived as foreground and background blur (which is generally perceived as not being objectionable), in contrast with its perception as ghosting (which is generally perceived as being objectionable), this essentially enables an enormous new class of display system paradigms in which the left and right eye channels do not need to be completely separated. In other words, it would essentially be sufficient for some bias to exist, so that the right eye sees more right- than left-eye image, and vice versa for the left eye. 
   With this in mind, the auto-microstereoscopic display depicted schematically in  FIG. 4  is broadly contemplated in accordance with at least one presently preferred embodiment of the present invention. 
   As illustrated in  FIG. 4 , in accordance with a preferred embodiment of the present invention, a three-state electronically switched non-lambertian light source  400  may be provided. This could be embodied by a liquid crystal directional display or equivalent apparatus. 
   Three states will preferably be attainable by way of light source  400 , namely: state  402 , which is for viewing the left frame of a microstereoscopic image pair; state  404 , for viewing monoscopic images; and state  406 , for viewing the right frame of a microstereoscopic image pair. 
   As illustrated in the diagram  402   a , state  402  involves greater light source brightness when the eye is left of the screen center and less light source brightness when the eye is right of the screen center. In contrast, as shown in diagram  406   a , state  406  involves greater light source brightness when the eye is right of the screen center and less light source brightness when the eye is left of the screen center. In either case, it is preferably the case that the transition from the brighter to the less bright zones is gradual. 
   As opposed to the aforementioned “left” and “right” states  402  and  406 , the selectable monoscopic state  404  will preferably involve brightness that is always uniform across the screen (diagram  404   a ). 
   In accordance with an embodiment of the invention, a transmissive display panel  408  is preferably provided in which a toggling arrangement  410  serves to toggle between the left and right images provided by the light source, that is, between state  402  and state  406 . The rapidity of the toggling will preferably be governed by that which is appropriate for ensuring that the aggregate image (contributed to by the left and right images) is perceived as a 3-D image without the assistance of special eyewear. A conceivable rendering of such an aggregate image is indicated in  FIG. 4  at  412 . 
   The toggle rate will preferably be comparable to that encountered in current “strong stereo” time-multiplexed systems, e.g., greater than 60 Hz per eye (30 Hz overall) and preferably close to 120 Hz per eye (60 Hz overall). 
   It should be appreciated that, in accordance with the embodiment illustrated in  FIG. 4 , the light source  400  will preferably function in such a manner that, from essentially any viewing angle, the illumination appears constant over the full area of the light source whereby, however, the intensity of the illumination depends on the viewing angle. Thus, the right eye would see the right eye image ( 406   a ) more brightly than it sees the left eye image ( 402   a ), and the left eye would see the left eye image ( 402   a ) more brightly than it sees the right eye image ( 406   a ). 
   In recapitulation, one example of an embodiment of the present invention that could be implemented using existing liquid crystal display (LCD) technology, is a “non-lambertian angularly coded screen” (NLAC). A conceivable substitute for the LCD display is suspended particle display technology, or perhaps even reverse emulsion display technology. The NLAC embodiment involves a light source (behind the normally pixelated image display panel), or a filtering screen (in front of the display panel), that exhibits an electrically switchable angular nonuniformity such that, from any position, it looks brighter to the right eye than to the left eye during times when the right eye image is on the pixelated display, and it looks brighter to the left eye than to the right eye during times when the left eye image is on the pixelated display. If the right and left eye images, and the corresponding biases of the NLAC, are alternated rapidly, then depth should be perceived by any observer in any location from which the display is visible. This is in contrast to the situation with existing lenticular autostereoscopic displays (i.e., in which no eyewear needed), in which correct stereoscopy is achieved for observers in certain “sweet spot” zones, left-right reversed stereoscopy (or pseudoscopy) occurs for observers in other zones, and ghosting is seen by observers in still other zones. 
   An analogous, simulated, example carried out in experimentation involved a conventional LCD shutter eyewear-based 3D-stereoscopic display whose electronics were modified to make it function adjustably “imperfectly”, that is, so that there was (characteristically undesirable) crosstalk between the left and right eye images. The eyewear was adjusted so that crosstalk was perceived and stereoscopy was lost with a conventional stereoscopic image pair on the screen. This image pair was then be replaced by a center-of-interest adjusted microstereoptical image which, without further adjustment of the eyewear control, was perceived stereoscopically. 
   Thus, to achieve an autostereoscopic realization (i.e., no eyewear is involved), at least one presently preferred embodiment of the present invention contemplates an NLAC screen. A “static” analog might be the “privacy screen” material manufactured by 3M, commonly used to prevent bystanders from reading over a customer&#39;s shoulder at ATMs (automatic teller machines). The “privacy screens” available off the shelf are usually center-biased, but types are available with off-center bias, so that, for instance, a co-worker to one&#39;s right could read what is on one&#39;s computer monitor, but a customer to one&#39;s left sees only a black screen. In accordance with at least one embodiment of the present invention, it is contemplated that the property just described be electronically switchable between left and right bias. 
   At least one presently preferred embodiment of the present invention broadly contemplates, in addition to NLAC screens in general, any plausible principles that could be used to implement NLAC screens. Possibilities include (as mentioned) LCDs, suspended particle displays, and reverse emulsion displays. Other possibilities, to name just a few, include micromechanical “venetian blinds”, micromirror displays (as in the projectors manufactured by Texas Instruments), holographic optical elements, and coherently emitting displays in which diffraction and interference effects can be exploited in any conceivable way. 
   In experimentation, it was found that, in attaining microstereopsis, frames offset by camera shifts of only a few millimeters (down to 1 mm) can be viewed binocularly using the same viewing apparatus that is normally used with frame pairs whose perspectives are offset for 50–100 mm (normally 65 mm, the typical human interocular separation). The effect was a strong perception of depth with none of the sense of discomfort that usually accompanies binocular viewing of stereo pairs. 
   It was found that a practical bonus of microstereopsis is that the disparity between left and right eye images is so small that no doubling is visible when the display screen is viewed without the eyewear needed to see the stereo. That is, when the screen is viewed without glasses it looks like a normal 2D-display; when it is viewed with glasses it is seen in 3D-stereo, without conflict or discomfort. 
   If not otherwise stated herein, it may be assumed that all components and or processes described herein may, if appropriate be considered to be interchangeable with similar components and/or processes disclosed elsewhere herein, unless an express indication is made to the contrary. 
   If not otherwise stated herein, any and all patents, patent publications, articles and other printed publications discussed or mentioned herein are hereby incorporated by reference as if set forth in their entirety herein.