Abstract:
An apparatus including an autostereoscopic image selection device and an overcoat opaque material applied to the autostereoscopic image selection device. The autostereoscopic image selection device and overcoat opaque material operate together to provide a self-locating aperture in association with the autostereoscopic selection device. The associated method entails applying an opaque overcoat material to an image selection device comprising a plurality of lenticules and removing selected portions of the opaque overcoat material from the image selection device. The applying and removing operate together with the image selection device to reduce a numerical aperture for at least one lenticule.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present design relates generally to the art of autostereoscopic displays, and more specifically to enhanced techniques for flat panel monitor devices that improve optical quality, and increase the depth of the image and the number and quality of the viewing zones. 
         [0003]    2. Description of the Related Art 
         [0004]    Today&#39;s stereoscopic display manufacturers seek to continually improve the image quality associated with the presentation of three-dimensional (3-D) content. One current autostereoscopic flat panel monitor device that exhibits improved image quality uses refractive optic techniques for image selection. Refractive optic designs typically include lenticular screens and Winnek slanted lenses. Another current flat panel monitor design relies on raster barrier techniques for image selection. In both designs, columns of images consisting of stripes made up of perspective views form a repeating pattern on the autostereoscopic display. Refractive optic techniques involve associating each column of images with a cylindrical lenticule. Raster barrier techniques associate each column of images with an aperture slit of a raster barrier. 
         [0005]    Autostereoscopic display designs have been the subject of several prior disclosures. Reference is made to the work of, for example, Okoshi in “Three-Dimensional Imaging Techniques”, Academic Press, New York, 1976. 
         [0006]    An alternate technology currently available for use in flat panel monitor device designs employs a “fly eye lens” technique for image selection. This technique involves a number of related miniature spherical lenses refracting light rays in both the vertical and the horizontal direction. 
         [0007]    As noted, refractive optic autostereoscopic display techniques employ parallel rows of cylindrical lenticules, while raster barrier autostereoscopic display techniques employ parallel rows of slits. Both techniques produce a parallax effect only in the horizontal direction, unlike the “fly&#39;s eye lens” that produces parallax effects in both the vertical and horizontal directions. Accordingly, the refractive and raster barrier techniques involve horizontal parallax exclusively. Refractive and raster barrier designs can produce images with lower resolution requirements since they selectively use image information in the horizontal direction only, rather than in both the vertical and the horizontal directions. 
         [0008]    In practice, designs employing lenticular autostereoscopic screens have drawbacks because they reduce the overall effective display sharpness. In particular, autostereoscopic displays that employ a lenticular screen for image selection tend to have shortcomings with regard to the sharpness of the image having high parallax values. Such shortcomings are particularly apparent with regard to images including objects appearing off the plane of the screen or very deep into the screen. Further issues with lenticular screens can occur when a multiplicity of non-primary viewing zones exist, particularly with respect to the sharpness of those non-primary viewing zones. 
         [0009]    In practice, designs employing raster barrier displays reduce the overall display brightness and introduce undesirable visible pattern noise. In fact, raster barrier autostereoscopic screens turn out to be so dim, typically losing 80 or 90 percent of the light when rendering multi-perspective images, that they may not be commercially viable when used with currently available flat panel displays. 
         [0010]    Refractive screens employing “fly eye lens” designs have not been deployed into the marketplace to any extent but have been shown experimentally in laboratories. They have low resolution when employed in connection with a flat panel monitor device. 
         [0011]    Autostereoscopic displays using either lenticular screen, raster barrier, or “fly eye lens” techniques are difficult to manufacture due to the tight dimensional and alignment tolerances required when used with the underlying flat panel monitor device electronic display. 
         [0012]    Based on the foregoing, it would be advantageous to provide a flat panel display for use in viewing stereoscopic image content that overcomes the foregoing drawbacks present in previously known designs. 
       SUMMARY OF THE INVENTION 
       [0013]    According to one aspect of the present design, there is provided an apparatus comprising an autostereoscopic image selection device and an overcoat opaque material applied to the autostereoscopic image selection device. The autostereoscopic image selection device and overcoat opaque material operate together to provide a self-locating aperture in association with the autostereoscopic selection device. 
         [0014]    According to a second aspect of the present design, there is provided a method for providing an enhanced image selection device. The method comprises applying an opaque overcoat material to an image selection device comprising a plurality of lenticules and removing selected portions of the opaque overcoat material from the image selection device. The applying and removing operate together with the image selection device to reduce a numerical aperture for at least one lenticule. 
         [0015]    These and other advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which: 
           [0017]      FIGS. 1A ,  1 B, and  1 C are diagrammatic representations of refractive autostereoscopic lens sheets; 
           [0018]      FIG. 2  is a ray diagram illustrating the optics of an individual lenticule and consequent spherical aberration; 
           [0019]      FIG. 3  show the optics of a lenticular screen, and the curvature of field resultant from the simple optics employed; 
           [0020]      FIG. 4  illustrates a ray tracing of a cross-section of a lenticular screen, highlighting the issue of adjacent viewing zones. 
           [0021]      FIG. 5  is a lenticular screen with the over coating as applied in the present design as a manufacturing step in the embodiment described; 
           [0022]      FIG. 6  shows a lenticular screen in the final stage of manufacturing in that the overcoat has been buffed to produce the aperture-corrected lenticular screen in accordance with the present design; 
           [0023]      FIG. 7  illustrates a lenticular screen with a ray diagram showing the improvement of aperture correction with regard to spherical aberration; 
           [0024]      FIG. 8  illustrates a lenticular screen whose lenticules exhibit curvature of field, showing the aperture correction that is the subject of the present invention; and 
           [0025]      FIG. 9  is a ray trace diagram of the cross-section of a lenticular screen, illustrating how the aperture correction produces an improvement in the optical quality of off-axis viewing zones. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    The following description and the drawings illustrate specific embodiments sufficiently to enable those skilled in the art to practice the system and method described. Other embodiments may incorporate structural, logical, process and other changes. Examples merely typify possible variations. Individual components and functions are generally optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. 
         [0027]    The present design combines the virtues of both refractive or lenticular autostereoscopic displays and raster barrier displays. The technique described herein vastly improves the image quality of an autostereoscopic display using refractive lenticular optics, with only a minor reduction in light output. 
       Lenticular Screens 
       [0028]    Autostereoscopic display technology has been applied to flat panel displays with some success. There are two major variants—one using refractive optics for image selection and the other using raster barriers. In both cases, columns of images consisting of stripes made up of perspective views form a repeating pattern on the display. Each column is associated with a cylindrical lenticule or with an aperture slit of a raster barrier. In addition to the refractive and raster barrier techniques, which are essentially optically interchangeable, another technique—the “fly&#39;s eye lens”—has also been employed. The fly&#39;s eye lens includes a number of miniature spherical lenses that refract in both the vertical and the horizontal direction. 
         [0029]    A lenticular screen that includes parallel rows of cylindrical lenticules, or the raster barrier having parallel rows of slits, produce their effect only in the horizontal direction, unlike the fly&#39;s eye lens that works in both the vertical and horizontal directions. Accordingly, these techniques involve the use of horizontal parallax exclusively. Because of this restriction, there is the ability to produce a sharper image because the image information is used selectively only in the horizontal direction, rather than in both the vertical and the horizontal. 
         [0030]    Standard Lenticular Screens 
         [0031]    In  FIG. 1A , a typical lenticular screen  101  is shown with a subject lenticule  102 , and the pitch of the screen P is given at point  103 . Display surface  104  is shown. The display surface  104  can be any type of display, including but not limited to hard copy or electronic. For the most part the display surface  104  can be either a self-illuminated or rear-illuminated display. The design presented herein results in a reduction in brightness, and thus self-illuminated or rear-illuminated displays can benefit from the present design. Even though the technique can be applied to a hard copy that is not rear-illuminated, the present technique can be applied to rear-illuminated hard copy or electronic displays such as plasma panels, liquid crystal displays, light-emitting diodes, or similar displays that either modulate or emit light. 
         [0032]      FIG. 1B  is a Winnek slanted lens sheet is shown that is highly similar to the screen of  FIG. 1A . The difference here is that the lenticules are slanted to the horizontal. Instead of the boundary between lenticules being parallel to the vertical edge of the display, the lenticules are slanted at some angle. The lens sheet  105  is shown with individual lenticule  106  having pitch P  107 , with display  108  as shown. The advantage to this type of display has been discussed in, for example, U.S. Pat. No. 3,409,351. The major advantage to the Winnek tipping of the lens sheet is to eliminate pattern noise and color banding or moiré, and to also equalize the resolution in the vertical and the horizontal direction. 
         [0033]    Fly&#39;s Eye 
         [0034]      FIG. 1C  shows a fly&#39;s eye lens sheet  109  with an individual circular lens element  110 . The fly&#39;s eye lens sheet  109  has a pitch P  111  equal in both the vertical and the horizontal directions, with the display surface  112  oriented as shown. Fly&#39;s eye lenticular screens have not been widely accepted in the marketplace but laboratory experiments have demonstrated their performance. Fly&#39;s eye lenticular screens are generally difficult to manufacture and also have low resolution when used with a flat panel display. However, they do have interesting properties insofar as they closely resemble holography in terms of their physics and end effect for the viewer. 
         [0035]    Raster Barriers 
         [0036]    Other designs attempted include the raster barrier display, consisting of a series of zebra-like slits or Ronchi-grating-like slits, with the slits going in the vertical direction. These raster barriers produce an autostereoscopic display having a greater parallax budget before image breakdown occurs. 
         [0037]    “Parallax budget” is defined as the useful range of parallax within the display. In-screen parallax is assigned positive values and off-screen parallax is assigned negative values. The greater the absolute value of the parallax, the deeper the appearance of image points associated with those values. Image points with large values of parallax, such as in the autostereoscopic displays discussed herein, tend to lose sharpness or take on unfortunate artifacts such as image doubling. The range of parallax values, or the parallax budget, that can be well represented by the display before image breakdown is a principal quantitative measurement that directly relates to stereoscopic image depth. 
         [0038]    Raster barrier designs also have increased and sharper viewing zones. The increased parallax budget is important because parallax information is important in a stereoscopic display. Because raster barrier displays can have a larger parallax budget, the image can appear to be deeper, because parallax is the principal stereoscopic depth cue. 
         [0039]    In addition, raster barrier displays can also have a greater number of viewing zones. The reason for the greater number of viewing zones, optically, is that raster barrier displays use slit optics rather than refractive optics and have, in effect, a great deal of depth of focus because the image-forming rays are more nearly parallel as a result of the tiny aperture involved. 
         [0040]    The disadvantage of the raster barrier is the dimness, or lack of brightness. In fact, raster barriers are so extremely dim that they may not be commercially viable. Raster barriers require an extremely bright underlying display, and both the commonly used plasma panels and liquid crystal displays lack sufficient brightness to make a satisfactory raster barrier autostereoscopic display. One of the hallmarks of a good display, and one of the most important things about an electronic display, is brightness, and display manufacturers have had a challenge to meet the brightness requirements for a flat panel display. Given the additional brightness limitations of a raster barrier, the quest for a display that meets illumination specifications becomes nearly hopeless, because raster barrier displays for multi-view or stereoscopic imaging typically waste 80 or 90 percent of the light originally transmitted. 
         [0041]    Although raster barrier displays may appear easier to manufacture, in point of fact they are not necessarily easier to manufacture than lenticular displays. Both displays have challenges with regard to dimensional tolerances and alignment with regard to the underlying electronic display. 
       Parallax Issues 
       [0042]    Autostereoscopic displays, especially those using lens sheets for image selection, tend to have shortcomings with regard to the sharpness of images having high parallax values, especially with regard to images with objects appearing off the plane of the screen or that go very deep into the plane of the screen. In other words, the parallax budget is limited. Such displays also have issues with both a multiplicity of non-primary viewing zones and the sharpness of those non-primary viewing zones. 
         [0043]    Lenticular displays have associated with them, behind each vertical-going lenticule, a column of image information broken up into stripes of perspective views. When viewing an autostereoscopic image image selection takes place at the plane of the screen. The functioning of lenticular screens and their optical characteristics are described in detail in the Okoshi publication. One publication discussing the aberrational correction of photographic optics is Photographic Optics by Arthur Cox, 1974, Focal Press, London, 15th edition. 
         [0044]    The accompanying figures showing ray diagrams work to serve as explanation for what is happening optically in  FIGS. 1A ,  1 B, and  1 C. In the case of  FIGS. 1A and 1B , cylindrical lenticules are employed, so the cross-section surface is assumed to be perpendicular to the intersection of the lenticule boundaries. In the case of  FIG. 1A , the cross section is a horizontal plane passed through the lenticules. In the case of  FIG. 1B , the cross section is a plane passing through the lenticules, but at an angle to account for the Winnek tip angle—so that the plane that passes through the lenticules is perpendicular to the boundary of intersection of the lenticules, as shown in  FIG. 1B . In the case of  FIG. 1C , the cross-section could be made at any angle, because the fly&#39;s eye lenses at point  109  are sections of a sphere rather than a cylinder. 
         [0045]    From  FIG. 2 , a cross-section of a lens sheet  201  is shown and an individual lenticule  202  is called out. Pitch P  203  represents the width of a lenticule. Display surface  204  is shown, representing a flat panel display that could be a plasma display screen, a liquid crystal display screen, a light-emitting diode display screen, or any other suitable flat panel display. Curved surface of the lenticule  205  is shown, and rays  206 A and  206 B are emitted from the display screen  204  after having been refracted by the individual lenticule  202 . The arrows are pointing toward the eyes of the observer because the surface produces pixels illuminated in various ways depending upon the display type. Rays  207 A and  207 B are parallel, but these rays come from the central area of the lens rather than from the boundary edges, and the double-headed arrows indicate the rays. Point  208  is the location where the outermost or boundary rays cross or are in sharp focus, and point  209  is where the central rays  207 A and  207 B cross—namely, behind the plane of the display surface. Point  208 , representing boundary or outermost rays crossing, is in front of the plane of the display surface. 
         [0046]    The drawings assume that the rays are monochromatic—that is, the rays are for a single wavelength. Illustrated here is a non-ideal lens having spherical aberration. With reference to  FIG. 2 , several of the classical aberrations will be described. Those aberrations can be improved by stopping down the lens or by adding an aperture. The present design reduces the numerical aperture (and hence the area of the available lens surface) to improve correction of the aberrations. The present design also can improve the depth of field. 
         [0047]    Multiple perspective views required for viewing the image are included within the column P. When looking at a normal display there is no refractive lens sheet, forcing each eye to see individual image points, which produces the stereoscopic effect. In the case of a normal display, there is but a single image point on the display where the eyes converge and focus. However, because of the autostereoscopic display&#39;s selection device—the lens sheet—the perspective views incorporated within pitch P  203  are refracted to different locations and seen by the eyes, and the combination of these separate perspectives forms the stereoscopic image. 
         [0048]    In the case of lens sheets used for autostereoscopic displays, such lens sheets are single-element devices. In order to achieve good correction (namely, a significant reduction in aberration), lens systems require a complex system of lens elements. These elements have different dispersions and different indices of refraction to compensate for the dispersive properties of light and to produce a decently corrected image. 
         [0049]    Simple lens sheets represent an optical system that cannot possibly provide high-quality correction and reduction of aberration. Aberration correction would be a departure from the lenses&#39; ability to produce single, small, clean image points of objects in space. A good overall optical design must produce an image that is sharp and has as high a contrast as possible coming from the display surface. So, in a sense, the optics for this design more nearly resemble the optics of a projector than a camera. The entity or measurement of interest is termed “depth of focus.” Depth of focus is the range of acceptable focus that can be sharply resolved with respect to the display plane  204  in the case of  FIG. 2 . 
         [0050]    Note that in the case of lens sheet  201 , parallel rays that emerge from the display, namely rays  206 A and  206 B, have a point of sharp focus at point  209 . Rays emerging not from the boundary edges of the lenticules but from the center come to sharp focus at  208 . Accordingly, this condition, which has been described as “spherical aberration,” cannot produce perfectly sharp images. 
         [0051]    Looking at  FIG. 3 , note lens sheet  301  has an individual lenticule  302  and pitch P  303 . The display surface is shown as surface  304 . In this case curvature of field is illustrated. Once again, the subject light is monochromatic light. The on-axial parallel rays that enter the lens at its very boundary are denoted as rays  306 A and  306 B. Rays  306 A and  306 B come to sharp focus at point  308 . Rays  307 A and  307 B enter at the same points of the lens, but are viewed off-axially, and these are denoted by double-headed arrows (whereas  306 A and  306 B are denoted by single-headed arrows) and come to a sharp focal point  309 . Focal point  309  lies on surface  310  that, in the case of a lenticular sheet, is a cylindrical surface with a curvature of fixed radius. If a fly&#39;s eye lens is employed rather than a cylindrical surface, the depiction would be a section of a sphere, as denoted by surface  310 . And as noted above, the present drawings can serve for either cylindrical lenticules or for a fly&#39;s eye lens. 
         [0052]    In the case of  FIG. 3 , the aberration curvature of field limits the effective depth of focus at the image plane  304 , because points  308  and  309  are at different distances. This is a condition that is difficult to cure using a single element. The cure advocated herein and that will be described below is one of aperture correction, in which the lenticules are actually stopped down to have a numerically higher aperture and less available area. 
         [0053]    In  FIG. 4 , lens sheet  401  is shown with individual lenticule  402  having pitch P  403 , with a display surface  404 . The curvature  405  of the lenticule is shown. The concern is with the observer seeing the adjacent perspective views. When viewing a lenticular autostereoscopic display, the progression or continuum of views can be seen within a viewing zone. In space, some reasonable distance from the display, the eyes of the observer can see a stereoscopic image over a relatively limited angle of view. The angle of view may be as narrow as a few degrees, or as great as several tens of degrees. Once the observer moves to the side, a so-called “flip” occurs, and the rays that heretofore had been associated with the central viewing zone move to adjacent viewing zones. 
         [0054]    An individual viewing an autostereoscopic display sees a primary viewing zone, secondary viewing zone, tertiary viewing zone, and so forth. The primary viewing zone—if the display has been properly set up—is on-axis, and is of a certain specifiable angular extent. When the observer moves laterally, he or she sees the columns refracted by the lenticules. These columns are now not directly under the lenticules and on-axis, but instead are the secondary, tertiary, and so forth, columns (which in fact are image columns under other lenticules). The images of the secondary, tertiary, and so forth, columns should be sharp and well corrected. The present design addresses making this improvement using aperture correction. 
         [0055]    Regarding raster barriers, autostereoscopic displays using raster barriers tend to have sharper images and more image “pop.” That means that the image can apparently emerge further from the screen, and actually go deeper into the screen, without the image breaking down because of aberration defects. In addition, these raster barrier displays have sharper secondary, tertiary, and so forth, viewing zones—and indeed have more of these auxiliary viewing zones, which is an advantage of some significance. 
         [0056]    Raster barriers and lenticular screens are optically interchangeable so one can be swapped for the other for a given underlying display. A raster barrier display has narrow openings, or slits. A raster barrier looks like a zebra-stripe grating or a Ronchi grating, and despite the fact that these displays have certain virtues, they have very low brightness for a panoramagram-type display with a multiplicity of perspective views, and also a noticeable pattern noise. Viewing images using a raster barrier resembles looking through a grating, which indeed one is. 
         [0057]    With regard to  FIG. 4 , the familiar elements are shown. Lens sheet  401  is shown, the individual lenticule  402  is presented, width  403  is the width of the lenticule given by pitch P, display surface  404  is shown, and curvature  405  is the curvature of the individual lenticule. Of interest is how the image is formed by the adjacent column. Rays  406 A and  406 B are seen, and once again only monochromatic rays are assumed and are indicated with single-headed arrows, forming sharp focus at point  408 . This case assumes the lens is a perfect lens, and aberration is not a consideration. The concern is with depth of field. When viewing a secondary viewing zone, rays  407 A and  407 B illustrate what is happening. These rays have double-headed arrows. The rays cross at  409  in lenticule  402 , which is a secondary lenticule with regard to the specific rays. In this case sharp focus is not maintained. With regard to tertiary and lenticules that are even further away, focus will be even worse. 
       Aperture Corrected Design 
       [0058]    In the present design, a material is coated on top of the lenticules and then is removed by buffing.  FIG. 5  shows a section of a lens sheet  501 , with individual lenticule  502 . The lenticule pitch P  503 , where display surface  504  is shown. Curve  505  represents the curved surface of a lenticule. Opaque material  506  is applied to the surface. The opaque material can be a waxy material, or another appropriate masking material, including but not limited to INX pigments or other waxy materials. 
         [0059]    The material is then buffed, as shown in  FIG. 6 .  FIG. 6  shows the corresponding lens sheet identical to that shown as lens sheet  501 . Individual lenticule  602  is shown, with pitch P  603 , where display surface  604  is shown. Curvature  605  is the curvature of the lens sheet, or the very top surface, while material  606  represents the remaining aperture material. 
         [0060]    Once the material  506  has been applied as shown in  FIG. 5 , depending upon the type of opaque material employed, after a passage of time (which may be very rapid, or may take time for the material to set), the material may be manually buffed or wiped way with a polishing or wiping cloth, or the rubbing, buffing, or polishing performed by a machine. By applying the proper pressure the top surfaces are revealed, forming a reduced section of a cylinder in the case of a lens sheet, or a circle in the case of a fly&#39;s eye lens. The result is an aperture reduction. 
         [0061]    Lens apertures can be placed at various points in a lens system. They can be placed in front of a simple lens, or behind a simple lens, or they can be placed—probably most efficaciously—within a complex lens system at or near the optical center of the lens. In this case, several issues exist with regard to manufacturing a lens sheet of this type with aperture correction. One is that the optical center of the lens, or the radius of the lens, lies within the lens sheet, so it is difficult or impossible to place an aperture there. An aperture could be placed in other ways, but many of the other ways are difficult, costly, and/or impractical. Placement of an aperture at the display screen causes a loss of pixels and resolution and results in a poor quality picture with pattern noise. 
         [0062]    The best place to place the aperture is at the surface of the lens, as described with the aid of  FIGS. 5 and 6 . This approach is self-locating. Because there are frequently tens of thousands of individual lenticules in such a display, it would be virtually impossible to find a way to manufacture an aperture sheet that could be located in intimate juxtaposition with the lenticules and provide the advantages described herein. Various materials can be used. 
         [0063]    The benefits of the reduction are shown with respect to  FIGS. 7 ,  8 , and  9 .  FIG. 7  shows lens sheet  701  with individual lenticule  702  whose pitch P  703  is presented together with display surface  704 . The top surface  705  of the lens is shown. The aperture-reducing material  710  is shown. In this case there is a reduction of spherical aberration because the outer rays touch the aperture. Rays  706 A and  706 B (single-headed arrows) form a point of sharp focus at point  708 . Rays  707 A and  707 B, indicated by double-headed arrows, form a point of sharp focus  709 . The rays here are more nearly parallel, the focus spot is a tighter, smaller spot, and focus is improved. 
         [0064]    In  FIG. 8  an improvement in curvature of field is shown, because lens sheet  801  with individual lenticule  802 , given pitch P  803  and display surface  804 , now has a narrower angle at the focus point. This can be illustrated by looking at the parallel rays  806 A and  806 B that come to focus at point  808 . The on-axial rays  806 A and  806 B are indicated by single-headed arrows. Rays  807 A and  807 B, which are indicated by double-headed arrows, come to a focal point  809  on curve  810 . The rays are now more nearly parallel, or form a focus point at a less steep angle. Accordingly, the curvature of field becomes less of a problem because the image points are tighter and smaller as they cross the image-forming surface  804 . 
         [0065]      FIG. 9  presents the operation of secondary and tertiary viewing zones. Lens sheet  901  is shown, including individual lenticule  902 , where pitch P  903  is illustrated with display surface  904 . Curvature  905  is the curvature of the lenticule and opaque material  910  has been applied to reduce the aperture. Rays  906 A and  906 B are on-axial parallel rays that are out at the edge of the aperture, illustrated by single-headed arrows. Rays  906 A and  906 B come to focal point  908 . Rays  907 A and  907 B are non-axial points that are refracted and form image point  909  in lenticule  902 . Rays  907 A and  907 B are illustrated with double-headed arrows. An observer seeing the non-primary viewing zone sees a sharper image because the rays are more nearly parallel and the focus spot is a tighter, smaller point. Thus by using the opaque material, the present design improves the depth of field (or the depth of focus, more properly) of the lens elements. This improvement in depth of focus helps both non-primary viewing zone viewing and correction of both spherical aberration and curvature of field. 
         [0066]    The result of this is a lens sheet that has one significant reduction in quality, namely brightness. Such a design is typically less bright than a normal lens sheet, but likely far brighter than a raster barrier display. The modern flat panel displays can be extremely bright, so a small sacrifice in brightness—even a loss of half or a third of the brightness—still produces a reasonably bright display. But the end result now is an image with much greater “pop.” Off-screen effects before any image breakdown are noticeably improved, larger values of parallax can hold up, and the parallax budget of the display has been greatly expanded. The benefit is a highly enhanced stereoscopic effect. 
         [0067]    In addition, the secondary and tertiary viewing zones have vastly improved sharpness. And, indeed, there will be more of them because the image-forming rays as shown in  FIG. 9  are more nearly parallel. 
         [0068]    The present design lens sheet configuration may reduce overall brightness. This method will be less bright than a normal lens sheet, but may be far brighter than current raster barrier display designs. Today&#39;s flat panel monitor devices can be extremely bright, so the reduction in brightness associated with the present design may still display a reasonably bright image. In contrast, the present design can render images with a very much greater “pop” or a more pleasing overall effect. In addition, the present design can improve the off-screen effects before any image breakdown occurs and allow larger values of parallax to be realized. The parallax budget of an autostereoscopic display according to the present design can be greatly expanded and produce what is known as a deep stereoscopic effect. The secondary and tertiary viewing zones may yield images with improved sharpness and may provide additional off-axis viewing zones resulting from the image-forming rays as illustrated in  FIG. 9  become nearly parallel. 
         [0069]    What has been shown will be appreciated by a worker with ordinary skill in the art as having produced an aperture reduction that produces a consequential improvement in image quality. This aperture reduction has been achieved without requiring precision location of a multiplicity of apertures, because it is essentially self-locating in terms of its manufacturing process. In addition, there is a vast improvement in image quality for the primary, secondary, tertiary, and other viewing zones. And, indeed, additional viewing zones are now possible that can be viewed and enjoyed, and that have enhanced quality. In other words, the overall stereoscopic effect is vastly extended and improved. 
         [0070]    The design presented herein and the specific aspects illustrated are meant not to be limiting, but may include alternate components while still incorporating the teachings and benefits of the invention. While the invention has thus been described in connection with specific embodiments thereof, it will be understood that the invention is capable of further modifications. This application is intended to cover any variations, uses or adaptations of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within known and customary practice within the art to which the invention pertains. 
         [0071]    The foregoing description of specific embodiments reveals the general nature of the disclosure sufficiently that others can, by applying current knowledge, readily modify and/or adapt the system and method for various applications without departing from the general concept. Therefore, such adaptations and modifications are within the meaning and range of equivalents of the disclosed embodiments. The phraseology or terminology employed herein is for the purpose of description and not of limitation.