Resolution for autostereoscopic video displays

The present invention relates generally to autostereoscopic displays, and, more particularly, to a video autostereoscopic display with significantly improved resolution.

Conventional autostereoscopic displays use arrays of lenses or parallax barriers or other view selectors to make a number of pixels of the display visible to one eye of a viewing person and to make a number of other pixels of the display visible to the other eye of the viewing person. By isolating the pixels of the display visible to each eye, the two components of a stereoscopic image can be presented on the display.

Since an ordinary viewer's eyes are side-by-side and aligned horizontally, the array of lenses makes pixels visible according to horizontal orientation. As a result, corresponding pixels for the left and right eyes are located in the same scanline and displaced from one another horizontally.

Each eye of the viewer therefore sees an image whose horizontal resolution is halved in an autostereoscopic displays having only two views. In most autostereoscopic displays, field of view is improved by having more than just two views. In attempts to provide greater perceived depths of projection, many more views—e.g., 24 views—are required within a relatively narrow space—e.g., 1 mm. A typical LCD display screen has a pixel density of about 200 pixels per inch, though some have densities approaching 300 pixels per inch. That's approximately 6 pixels per millimeter, i.e., about one quarter of the resolution required to provide 24 views in a 1 mm space.

Thus, conventional video display devices are incapable of providing enough views in a sufficiently small space to satisfy the demands of modern autostereoscopic images.

In accordance with the present invention, a single pixel of a video display can display respective individual pixels of multiple views. In other words, a video display can include more views for an autostereoscopic image than the physical pixels of the video display would ordinarily support.

To achieve multiple views with a single physical pixel, the physical pixel is time-multiplexed. In particular, the physical pixel displays a pixel of one view for a given time interval and a view multiplexer deflects the light from the physical pixel by a predetermined angle to make the pixel appear in a location corresponding to the pixel of the view. In another time interval, the physical pixel displays a pixel of a different view and the view multiplexer deflects light from the physical pixel by a different predetermined angle to make the pixel appear in a location corresponding to the pixel of the different view.

The view multiplexer includes a number of columnar prisms of birefringent material such that deflection of light passing through the columnar prisms is switchable between two different angles by controlling the polarity of the light passing through. Alternatively, the material of the columnar prisms varies its refraction index according to an electrical field of the columnar prisms. An example of such a material is liquid crystal. The controllability of the reflection angles provided by the columnar prisms enables control of the location at which a given pixel appears to be to a human viewer.

By synchronizing the location at which a given pixel appears to be and the particular view displayed by the pixel allows that pixel to display pixels of multiple views for respective fractions of a frame rate. Persistence of vision of the human viewer causes the one pixel of the one view that is visible to the viewer through the lenticular array to continue to be perceived for the entire frame.

Multiple view multiplexers can be stacked to provide a wider variety of cumulative deflection angles.

In addition, focus errors due to curvature of field of the individual lenticles of a lenticular array are reduced by configuring the lenticles to focus at an acceptable distance behind the target of focus, e.g., the pixels of the autostereoscopic display. The result is that, due to curvature of field, the lenticles will focus particularly well at moderate angles of viewing perspective and will still produce acceptable focus errors and even wider angles of viewing perspective.

FIG. 1 is a plan view of a viewer and an autostereoscopic display in accordance with the present invention.

FIG. 2 is a plan view of a portion of the autostereoscopic display of FIG. 1 in greater detail.

FIG. 3 is a plan view of a view multiplexer of the autostereoscopic display of FIGS. 1 and 2 in greater detail.

FIG. 4 is a timing diagram illustrating the time-multiplexing of a pixel using two (2) view multiplexers in accordance with the present invention.

FIG. 5 is a plan view of an alternative autostereoscopic display in accordance with the present invention.

FIG. 6 is a plan view of a portion of the autostereoscopic display of FIG. 5 in greater detail.

FIG. 7 is a plan view illustrating focus of the autostereoscopic display of FIGS. 5 and 6 .

FIG. 8 is a plan view of an alternative view multiplexer in accordance with the present invention.

FIGS. 9 and 10 are timing diagrams illustrating time-multiplexing of a pixel using the view multiplexer of FIG. 8 .

FIG. 11 is a plan view of the mask of FIG. 2 enlarged to illustrate locations of apparent pixels due to operation of view multiplexers of FIG. 2 .

In accordance with the present invention, a single pixel of a video display can display respective individual pixels of multiple views. In particular, a stereoscopic display 100 ( FIGS. 1 and 2 ) includes view multiplexers 204 A-B ( FIG. 2 ) that bend light from each of a number of pixels, such as pixels 216 A-F, such that each pixel appears to be at a slightly different location and represents a pixel of a different view for each of a number of multiple time intervals. For example, view multiplexers 204 A-B can cause pixel 216 A to be at any of locations 216 A 1 ( FIG. 11 ), 216 A 2 , 216 A 3 , and 216 A 4 . In this manner, each of pixels 216 A-F is time-multiplexed to represent pixels of respective multiple views of an autostereoscopic display.

In a manner described more completely below, view multiplexers 204 A-B combine to provide 4-to-1 multiplexing in this illustrative embodiment. View multiplexers 204 A-B bend light from pixels 216 A-F at predetermined, fractional view angles at predetermined time intervals. In this illustrative embodiment, lenticle 202 C is designed to provide a view angle increment of one degree, meaning that viewing perspectives through lenticle 202 C at which each of pixels 216 A-F is viewable through a mask 214 differ by one degree. To provide four (4) views from a single pixel, view multiplexers 204 A-B combine to deflect light at four (4), evenly spaced, fractional view angles, namely, 0 degrees, 0.25 degrees, 0.5 degrees, and 0.75 degrees in this illustrative embodiment; other angles can be used in other embodiments. It should be appreciated that a single view multiplexer can provide two (2) views from a single pixel, three (3) view multiplexers can be combined to provide up to eight (8) views from a single pixel, and numerous other combinations can be implemented to provide even more views from a single pixel. It should be further appreciated that a view multiplexer can sweep across a range of deflection angles to provide other numbers of views from a single pixel in the manner described below.

Display of four (4) views using a single one of pixels 216 A-F is shown in timing diagram 400 ( FIG. 4 ). As described more completely below, view multiplexer 204 A is switchable between deflecting light at 0.5 degrees or not deflecting light at all, and view multiplexer 204 B is switchable between deflecting light at 0.25 degrees or not deflecting light at all. View multiplexers 204 A-B switch at a rate of 120 Hz, and view multiplexer 204 B follows view multiplexer 204 As by a lag of one-half clock cycle as shown in timing diagram 400 .

Pixels 216 A-F have a refresh rate of 240 Hz. Initially in timing diagram 400 , view multiplexers 204 A-B are both off, i.e., not deflecting light, and pixel 216 A displays a pixel of view N for a single refresh cycle. If an eye of viewer 10 is aligned with pixel 216 A through mask 214 and lenticle 202 A, that eye will see view N of pixel 216 A at location 216 A 1 ( FIG. 11 ) and the pixel of view N will appear to occupy the entire width of lenticle 202 A ( FIG. 2 ). When pixel 216 A is displaying pixels of other views, the deflection of view multiplexers 204 A-B cause the eye to see flat black mask 214 . However, the persistence of vision causes viewer 10 to continue to see the pixel of view N at location 216 A 1 ( FIG. 11 ) for four (4) 240 Hz cycles.

In the next 240 Hz cycle ( FIG. 4 ), view multiplexer 204 A switches on. The cumulative deflection of view multiplexers 204 A-B is 0.5 degrees, and pixel 216 A appears to be at location 216 A 3 ( FIG. 11 ) and displays a pixel of view N+2 ( FIG. 4 ) for a single refresh cycle. If an eye of viewer 10 is 0.5 degrees from being aligned with pixel 216 A through mask 214 and lenticle 202 A, that eye will see view N+2 of pixel 216 A and the pixel of view N+2 will appear to occupy the entire width of lenticle 202 A. Mask 214 and the persistence of vision cause viewer 10 to continue to see the pixel of view N+2 at location 216 A 3 ( FIG. 11 ) for four (4) 240 Hz cycles as described above.

In the next 240 Hz cycle ( FIG. 4 ), view multiplexer 204 B switches on. The cumulative deflection of view multiplexers 204 A-B is 0.75 degrees, and pixel 216 A appears to be at location 216 A 4 ( FIG. 11 ) and displays a pixel of view N+3 ( FIG. 4 ) for a single refresh cycle. If an eye of viewer 10 is 0.75 degrees from being aligned with pixel 216 A through mask 214 and lenticle 202 A, that eye will see view N+3 of pixel 216 A and the pixel of view N+3 will appear to occupy the entire width of lenticle 202 A. Mask 214 and the persistence of vision cause viewer 10 to continue to see the pixel of view N+3 at location 216 A 4 ( FIG. 11 ) for four (4) 240 Hz cycles as described above.

In the next 240 Hz cycle ( FIG. 4 ), view multiplexer 204 A switches off The cumulative deflection of view multiplexers 204 A-B is 0.25 degrees, and pixel 216 A appears to be at location 216 A 2 ( FIG. 11 ) and displays a pixel of view N+1 ( FIG. 4 ) for a single refresh cycle. If an eye of viewer 10 is 0.25 degrees from being aligned with pixel 216 A through mask 214 and lenticle 202 A, that eye will see view N+1 of pixel 216 A and the pixel of view N+1 will appear to occupy the entire width of lenticle 202 A. Mask 214 and the persistence of vision cause viewer 10 to continue to see the pixel of view N+1 at location 216 A 2 ( FIG. 11 ) for four (4) 240 Hz cycles as described above.

In the next 240 Hz cycle ( FIG. 4 ), view multiplexer 204 B switches off. The cumulative deflection of view multiplexers 204 A-B is 0 degrees, and pixel 216 A again displays a pixel of view N and appears to be at location 216 A 1 ( FIG. 11 ) for a single refresh cycle. And, the four (4) cycle pattern of timing diagram 400 ( FIG. 4 ) repeats.

Thus, view multiplexers 204 A-B time-multiplex pixels 216 A-F such that each pixel can display a pixel of four (4) different views of autostereoscopic display 100 . It should be appreciated that, without lenticles 202 A-C, pixel 216 A would appear to a human viewer to be four (4) distinct pixels at locations 216 A 1 ( FIG. 11 ), 216 A 2 , 216 A 3 , and 216 A 4 . Thus, without a lenticular array or other view selector, view multiplexers 204 A-B cause a display to have an apparent resolution that is much more dense than the physical resolution of the display.

It should also be appreciated that there are alternatives to a lenticular array to ensure that a human viewer sees only one of the multiple views of an autostereoscopic image. For example, a parallax barrier can be used. In addition, using lasers rather than LCDs or LEDs as light sources allow the individual views displayed by a particular pixel to be only visible at locations to which the laser's light is directed.

As shown in FIG. 2 , autostereoscopic display 100 includes a number of lenticles 202 A-C of a lenticular array. In this illustrative embodiment, lenticles 202 A-C are designed to provide a relatively flat field in the manner described in co-pending U.S. patent application Ser. No. 12/901,478 for “Improved Perceived Image Depth for Autostereoscopic Displays” by Dr. Richard A. Muller on Oct. 8, 2010. Other approaches to minimize lenticle focus errors due to curvature of fields are described below.

View multiplexers 204 A-B are immediately behind the lenticular array in this illustrative embodiment. View multiplexers 204 A-B are described in more detail below in conjunction with FIG. 3 . Behind view multiplexers 204 A-B is a layer 206 of transparent material such as plastic, glass, or a gas such as air, a polarizer 208 , and a second layer 210 of transparent material.

Behind layer 210 is an array of color filters 212 A-F, each of which imparts a red, green, or blue hue to a respective one of pixels 216 A-F. Pixels 216 A-F are vertical pixels as described in co-pending U.S. patent application Ser. No. 12/868,038 for “Improved Resolution for Autostereoscopic Video Displays” by Dr. Richard A. Muller and filed Aug. 25, 2010.

Mask 214 is positioned between color filters 212 A-F and pixels 216 A-F and limits the perceived width of pixels 216 A-F to about one-quarter their actual width, leaving dark space between pixels 216 A-F for apparent pixels due to light deflection by operation of view multiplexers 204 A-B. In this illustrative embodiment, the field of focus of lenticles 202 A-C is at about mask 214 .

Pixels 216 A-F are positioned immediately behind mask 214 . Each of pixels 216 A-F is a single, independently controlled LCD sub-pixel, having its own independently controlled display intensity. The color of each of pixels 216 A-F is controlled by a respective one of color filters 212 A-F. Behind pixels 216 A-F is another layer 218 of transparent material and a polarizer 220 . Behind polarizer 220 is a light source (not shown) as is typical in conventional LCD displays. Polarizers 208 and 220 are similar to polarizers used in conventional LCD displays.

View multiplexer 204 A is shown in greater detail in FIG. 3 . Except as otherwise noted herein, view multiplexer 204 B is directly analogous to view multiplexer 204 A and the following description is also applicable to view multiplexer 204 B.

View multiplexer 204 A ( FIG. 3 ) is shown in cross-section view from above and includes triangular columns 304 A-C of birefringent material such as liquid crystal. Triangular columns 304 A-C are positioned between a layer 302 of transparent plastic or glass and a grooved layer 306 of transparent plastic or glass into which triangular grooves are made to provide space for triangular columns 304 A-C.

Behind layer 306 is a switch layer 310 of liquid crystal between electrode layers 308 and 312 . By selectively applying a charge to electrode layers 308 and 312 , polarization of light passing through switch layer 310 can be switched, e.g., between parallel and perpendicular orientations relative to the birefringent material in triangular columns 304 A-C.

The birefringent material, its orientation set at manufacture, and the size and shape of triangular columns 304 A-C are selected to provide one amount of light deflection with one polarization orientation of switch layer 310 and a different amount of deflection with the other polarization orientation of switch layer 310 . In effect, the birefringent material in triangular columns 304 A-C are prisms whose degree of light deflection vary according to the state of switch layer 310 .

In this illustrative embodiment, the birefringent material is selected to have one refraction index substantially equal to the refraction index of the transparent material of layers 302 and 306 , and therefore provides no deflection of light as shown by arrow 314 A, for one polarization orientation of switch layer 310 . In effect, the prisms of triangular columns 304 A-C disappear into layers 302 and 306 , and triangular columns 304 A-C and layers 302 and 306 appear to be a single, flat layer of transparent material. However, it should be appreciated that it is not necessary that the prisms provide a deflection of zero degrees to effectively disappear into layers 302 and 306 . As long as the prisms are controllable to provide one of at least two different angles of deflection, pixel 216 A can be made to appear in one of at least two different, perhaps overlapping, locations and thus serve the purpose of time-multiplexing of pixel 216 A.

For the other polarization orientation of switch layer 310 in this illustrative embodiment, the birefringent material, its orientation set at manufacture, and the size and shape of triangular columns 304 A-C in view multiplexer 204 A are selected to deflect light by 0.5 degrees as shown by arrow 314 B, and the birefringent material, its orientation set at manufacture, and the size and shape of triangular columns 304 A-C in view multiplexer 204 B are selected to deflect light by 0.25 degrees. In effect, the different refraction index of the birefringent material with this polarization orientation and the dimensions of triangular columns 304 A-C are prisms designed to reflect light by a predetermined desired angle, such as 0.5 degrees in view multiplexer 204 A and 0.25 degrees in view multiplexer 204 B in this illustrative embodiment.

As described above, autostereoscopic display 100 includes a number of lenticles 202 A-C that are designed to provide a relatively flat field in the manner described in the '478 Application. Another approach to reducing autostereoscopic image degradation due to curvature of field of conventional lenticles is illustrated by FIGS. 5 and 6 .

Viewers 10 ( FIG. 5 ) are viewing an autostereoscopic image displayed by autostereoscopic display 100 B from various viewing angles. Autostereoscopic display 100 B is an alternative embodiment to that of autostereoscopic display 100 and is directly analogous to autostereoscopic display 100 except as otherwise described herein. Autostereoscopic display 100 B does not include meniscus-cylinder lenticles but instead includes lenticles of a more conventional design, having a convex proximal surface and a flat distal surface.

An autostereoscopic image is best viewed in very good focus. In the case of autostereoscopic display 100 B, the focus target is mask 214 B. However, viewing angles that stray significantly from directly perpendicular to autostereoscopic display 100 B tend to be out of focus due to the curvature of field of some lenticles. This curvature of field is illustrated by curved line 502 , which represents the locus of foci of the lenticle at various angles of perspective. To reduce loss of focus over a wider range of viewing angles, the lenticular array of autostereo scopic display 100 B are focused slightly behind mask 214 B to provide loci of focus along curved line 504 .

A portion of autostereoscopic display 100 B is enlarged in FIG. 6 . Curved lines 502 and 504 are exaggerated to illustrate the focus errors therein.

Curved line 502 represents loci of focus provided by a lenticle in a typical conventional autostereoscopic display. Curved line 502 shows a very good focus, i.e., near zero focus error, for straight-on viewing angles, i.e., perpendicular to autostereoscopic display 100 B. At a wider viewing angles, curved line 502 shows a noticeable focus error 602 .

In this illustrative embodiment, lenticles of autostereoscopic display 100 B are designed to focus behind mask 214 B for straight-on viewing angles. As shown in FIG. 7 , curved line 504 is behind mask 214 B by an amount that, from viewing perspectives near perpendicular to mask 214 , the focus of lenticles of autostereoscopic display 100 B are blurred by a width 702 that is no more than the width of the gaps in mask 214 B. Such limited blurring does not affect the accuracy of the autostereoscopic image perceived by viewer 10 because nothing other than the intended pixel is viewable to viewer 10 through each lenticle. Thus, the focus error 604 ( FIG. 6 ) viewable at near perpendicular viewing angles is sufficiently small to not affect the perception of focus of viewer 10 .

At wider viewing perspectives, curved line 504 intersects mask 214 B to provide very good focus, yet no better than that perceivable by viewer 10 at near perpendicular viewing angles, and begins to blur at even wider viewing perspectives as curved line 504 is in front of mask 214 B. The quality of view as perceived by viewer 10 is preserved at these wider viewing perspectives up to a focus error 606 , beyond which the amount of blurring exceeds the width of gaps in mask 214 B.

In some embodiments, maintaining focus errors no wider than gaps in mask 214 B might allow for unacceptably large focus errors at wider angles of viewing perspective. Generally, best results are achieved by determining the width of blur over a range of viewing angles for which quality viewing is desired and selecting a lens and locus of foci whose width of blur is minimized over that range of viewing angles.

The result is that lenticles whose locus of foci are represented by curved line 504 provide a much wider range of acceptable viewing angles than do conventional lenticles.

As described briefly above, a single view multiplexer 804 (shown in cross section view in FIG. 8 ) can sweep across a range of deflection angles to provide a number of views from a single pixel.

View multiplexer 804 includes triangular columns 808 A-C of a material whose refraction index is controllable, e.g., by an electrical field. An example of such a material is liquid crystal. Triangular columns 808 A-C are positioned between a layer 606 of transparent plastic or glass and a grooved layer 810 of transparent plastic or glass into which triangular grooves are made to provide space for triangular columns 808 A-C.

In front of layer 806 is an electrode layer 802 . Behind layer 810 is an electrode layer 812 . By selectively applying a charge to electrode layers 802 and 812 , the refraction index of the material in triangular columns 808 A-C can be varied.

The material within triangular columns 808 A-C, its orientation set at manufacture, and the size and shape of triangular columns 808 A-C are selected to provide a desired range of deflection across the range of electrical fields that can be produced across electrode layers 802 and 812 . In effect, the material in triangular columns 808 A-C are prisms whose degree of light deflection vary according to the electrical field between electrode layers 802 and 812 .

In this illustrative embodiment, the desired range of deflection is 0.0-2.0 degrees, the material within triangular columns 808 A-C has a refraction index that varies from the refraction index of layers 806 and 810 to 0.1 above the refraction index of layers 806 and 810 , and triangular columns 808 A-C have a cross-sections that are right triangles with an angle 816 of 20 degrees.

Timing diagram 900 ( FIG. 9 ) illustrates the time-multiplexing of pixel 216 A using view multiplexer 804 . Timing diagram 900 shows an electrical field between electrode layers 802 and 812 , the corresponding angle of deflection of view multiplexer 804 , and various views displayed by pixel 216 A. The angle of deflection provided by view multiplexer 804 sweeps through a predetermined range, e.g., 0-2.0 degrees. Pixel 216 A displays pixels of views N through N+3 in a synchronized manner such that pixel 216 A displays a pixel of view N while view multiplexer 804 sweeps through deflection angles 0.0-0.5 degrees, displays a pixel of view N+1 while view multiplexer 804 sweeps through deflection angles 0.5-1.0 degrees, displays a pixel of view N+2 while view multiplexer 804 sweeps through deflection angles 1.0-1.5 degrees, and displays a pixel of view N+3 while view multiplexer 804 sweeps through deflection angles 1.5-2.0 degrees, after which view multiplexer 804 returns to provide a deflection of 0 degrees and pixel 216 A displays a pixel of the next frame of view N.

It should be appreciated that, while pixel 216 A is shown to time-mulitplex only four (4) views, pixel 216 A can time-multiplex many more views, limited only by the switching rate of pixel 216 A relative to a desired frame rate. In embodiments in which pixel 216 A is implemented using one or more LEDs, e.g., in very large signage, pixel 216 A can switch much more rapidly than an LCD pixel and can time-multiplex many more views. For example, some LEDs can switch at frequencies of 2.0 MHz. Accordingly, a single LED (or a cluster of red, green, and blue LEDs) can provide 300 or more views of single pixel, limited only by the optical quality of lenticles 202 A-C and the range of deflection angles and switching speed of view multiplexer 804 .

Timing diagram 1000 ( FIG. 10 ) shows an alternative manner in which view multiplexer 804 can time-multiplex pixels of multiple views shown by pixel 216 A. Once view multiplexer 804 sweeps through a range of deflection angles, e.g., 0-2.0 degrees, view multiplexer 804 sweeps back through the range in reverse direction, e.g., from 2.0 degrees to 0 degrees. In a synchronized manner, once pixel 216 A switches through pixels of views N, N+1, N+2, and N+3, pixel 216 A switches through pixels of a subsequent frame in reverse order, i.e., through views N+3, N+2, N+1, and N.

If should be appreciated that view multiplexer 804 can cycle through angles of deflection in other ways, including stepped patterns. In addition, multiple instances of view multiplexer 804 can be stacked as are view multiplexers 204 A-B ( FIG. 2 ) to provide greater ranges of cumulative deflection angles.

The above description is illustrative only and is not limiting. The present invention is defined solely by the claims which follow and their full range of equivalents. It is intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and substitute equivalents as fall within the true spirit and scope of the present invention.