CA3022719A1

CA3022719A1 - Vision correction system and method, light field display and microlens array therefor

Info

Publication number: CA3022719A1
Application number: CA3022719A
Authority: CA
Inventors: Daniel Gotsch
Original assignee: Evolution Optiks Ltd
Current assignee: Evolution Optiks Ltd
Priority date: 2018-03-09
Filing date: 2018-10-31
Publication date: 2019-09-09
Also published as: CA2997883A1

Abstract

Described are various embodiments of a digital display device for use by a user having reduced visual acuity. In one embodiment, a digital display device is described to render an image for viewing by a viewer having reduced visual acuity. The device comprises a digital display medium comprising an array of pixels and operable to render a pixelated image accordingly; a microlens array disposed relative to said digital display so to align each said microlens with a corresponding set of said pixels to shape a light field emanating therefrom and thereby at least partially govern a projection thereof from said display medium toward the user; and a hardware processor operable on pixel data for the image to be displayed to output corrected image pixel data to be rendered as a function of a designated characteristic of said microlens array and a selected vision correction parameter related to the viewer's reduced visual acuity such that said processed image is rendered via said microlens array to at least partially compensate for the user's reduced visual acuity. A dimension of each said microlens is selected to minimize a spot size on the retina of the viewer produced by given pixels of said corresponding set of pixels.

Description

VISION CORRECTION SYSTEM AND METHOD, LIGHT FIELD DISPLAY AND MICROLENS ARRAY THEREFOR
FIELD OF THE DISCLOSURE
[001] The present disclosure relates to digital displays, and in particular, to a vision correction system and method, light field display and microlens array therefor.
BACKGROUND

[002] Individuals routinely wear corrective lenses to accommodate for reduced vision acuity in consuming images and/or information rendered, for example, on digital displays provided, for example, in day-to-day electronic devices such as smartphones, smart watches, electronic readers, tablets, laptop computers and the like, but also provided as part of vehicular dashboard displays and entertainment systems, to name a few examples. The use of bifocals or progresses corrective lenses is also commonplace for individuals suffering from near and far sightedness.

[003] The operating systems of current electronic devices having graphical displays offer certain "Accessibility" features built into the software of the device to attempt to provide users with reduced vision the ability to read and view content on the electronic device. Specifically, current accessibility options include the ability to invert images, increase the image size, adjust brightness and contrast settings, bold text, view the device display only in grey, and for those with legal blindness, the use of speech technology.
These techniques focus on the limited ability of software to manipulate display images through conventional image manipulation, with limited success.

[004] The use of 4D light field displays with lenslet arrays or parallax barriers to correct visual aberrations have since been proposed by Pamplona et al.
(PAMPLONA, V., OLIVEIRA, M., ALIAGA, D., AND RASKAR, R.2012. "Tailored displays to compensate for visual aberrations." ACM Trans. Graph. (SIGGRAPH) 31.).
Unfortunately, conventional light field displays as used by Pamplona et al.
are subject to a spatio-angular resolution trade-off; that is, an increased angular resolution decreases the spatial resolution. Hence, the viewer sees a sharp image but at the expense of a significantly lower resolution than that of the screen. To mitigate this effect, Huang et al.
(see, HUANG, F.-C., AND BARSKY, B. 2011. A framework for aberration compensated displays. Tech. Rep. UCB/EECS-2011-162, University of California, Berkeley, December; and HUANG, F.-C., LANMAN, D., BARSKY, B. A., AND RASKAR, R.
2012. Correcting for optical aberrations using multi layer displays. ACM
Trans. Graph.
(SiGGRAPH Asia) 31, 6, 185:1-185:12. proposed the use of multilayer display designs together with prefiltering. The combination of prefiltering and these particular optical setups, however, significantly reduces the contrast of the resulting image.

[005] Finally, in U.S. Patent Application Publication No. 2016/0042501 and Fu-Chung Huang, Gordon Wetzstein, Brian A. Barsky, and Ramesh Raskar. "Eyeglasses-free Display: Towards Correcting Visual Aberrations with Computational Light Field Displays". ACM Transaction on Graphics, xx:0, Aug. 2014, the entire contents of each of which are hereby incorporated herein by reference, the combination of viewer-adaptive pre-filtering with off-the-shelf parallax barriers has been proposed to increase contrast and resolution, at the expense however, of computation time and power.

[006] This background information is provided to reveal information believed by the applicant to be of possible relevance. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art.
SUMMARY

[007] The following presents a simplified summary of the general inventive concept(s) described herein to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to restrict key or critical elements of the invention or to delineate the scope of the invention beyond that which is explicitly or implicitly described by the following description and claims.
[0081 A need exists for a vision correction system and method, light field display and microlens array therefor, that overcome some of the drawbacks of known techniques, or at least, provide a useful alternative thereto. Some aspects of the disclosure provide embodiments of such systems, methods, displays and microlens arrays.
[009] In accordance with one aspect, there is provided a digital display device to render an image for viewing by a viewer having reduced visual acuity, the device comprising: a digital display medium comprising an array of pixels and operable to render a pixelated image accordingly; a microlens array disposed relative to said digital display so to align each said microlens with a corresponding set of said pixels to shape a light field emanating therefrom and thereby at least partially govern a projection thereof from said display medium toward the user; and a hardware processor operable on pixel data for the image to be displayed to output corrected image pixel data to be rendered as a function of a designated characteristic of said microlens array and a selected vision correction parameter related to the viewer's reduced visual acuity such that said processed image is rendered via said microlens array to at least partially compensate for the user's reduced visual acuity; wherein a dimension of each said microlens is selected to minimize a spot size on the retina of the viewer produced by given pixels of said corresponding set of pixels.
[0010] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 15 of said pixels.
[0011] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 10 of said pixels.
[0012] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 5 to about 10 of said pixels.
[0013] In one embodiment, the dimension of each said microlens is selected to minimize said spot size on the retina of the viewer produced by each of a set of constituent subpixels for each said corresponding set of pixels.
[0014] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 10 of said pixels.

toi6P-006-CAD2 [0015] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 5 to about 10 of said pixels.
[0016] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 10 to about 35 of said pixels.
[0017] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 15 to 25 of said pixels.
[0018] In one embodiment, the microlens array is disposed at a designated distance from said digital display that is shorter than a focal length of said microlens so to produce a divergent light field therefrom.
[0019] In one embodiment, the designated distance is selected such that said microlens focuses on a virtual image plane generated thereby.
[0020] In accordance with another aspect, there is provided a microlens array for use with a display medium comprising an array of pixels and operable to render a pixelated image accordingly to be viewed by a viewer having a reduced visual acuity, wherein the microlens array is dimensioned to be disposed relative to the digital display medium and comprises an array of microlenses, each one of which being disposed, when overlaid onto the digital display medium, to be centered over a corresponding set of the pixels to shape a light field emanating therefrom and thereby at least partially govern a projection thereof from said display medium toward the user, wherein a dimension of each said microlens is selected to minimize a spot size on the retina of the viewer produced by given pixels of said corresponding set of pixels.
[0021] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 15 of said pixels.
[0022] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 10 of said pixels.
[0023] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 5 to about 10 of said pixels.

[0024] In one embodiment, the dimension of each said microlens is selected to minimize said spot size on the retina of the viewer produced by each of a set of constituent subpixels for each said corresponding set of pixels.
[0025] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 10 of said pixels.
[0026] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 5 to about 10 of said pixels.
[0027] In one embodiment, a diameter of each said microlens is selected to correspond with a dimension of about 10 to about 35 of said pixels.
[0028] In one embodiment, the diameter of each said microlens is selected to correspond with a dimension of about 15 to 25 of said pixels.
[0029] Other aspects, features and/or advantages will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0030] Several embodiments of the present disclosure will be provided, by way of examples only, with reference to the appended drawings, wherein:
[0031] Figure 1 is a diagrammatical view of an electronic device having a digital display, in accordance with one embodiment;
[0032] Figures 2A and 2B are exploded and side views, respectively, of an assembly of a light field display for an electronic device, in accordance with one embodiment;
[0033] Figures 3A, 3B and 3C schematically illustrate normal vision, blurred vision, and corrected vision in accordance with one embodiment, respectively;

[0034] Figure 4 is a schematic diagram of a single light field pixel defined by a convex lenslet or microlens overlaying an underlying pixel array and disposed at or near its focus to produce a substantially collimated beam, in accordance with one embodiment;
[0035] Figure 5 is another schematic exploded view of an assembly of a light field .. display in which respective pixel subsets are aligned to emit light through a corresponding microlens or lenslet, in accordance with one embodiment;
[0036] Figure 6 is an exemplary diagram of a light field pattern that, when properly projected by a light field display, produces a corrected image exhibiting reduced blurring for a viewer having reduced visual acuity, in accordance with one embodiment;
[0037] Figures 7A and 7B are photographs of a Snellen chart, as illustratively viewed by a viewer with reduced acuity without image correction (blurry image in Figure 7A) and with image correction via a light field display (corrected image in Figure 7B), in accordance with one embodiment;
[0038] Figure 8 is a schematic diagram of a portion of hexagonal lenslet array disposed at an angle relative to an underlying pixel array and having an irregular pitch mismatch offset, in accordance with one embodiment;
[0039] Figures 9A to 9E are graphical plots illustrating a variation of a spot size on a user's retina as a function of a microlens pitch for set operating criteria, in accordance with different embodiments;
[0040] Figures 10A to 10E are graphical plots illustrating a variation of a spot size on a user's retina as a function of a microlens pitch for a set of exemplary operating criteria, in accordance with different embodiments;
[0041] Figures 11A and 11B are photographs as illustratively viewed by a viewer with reduced visual acuity without image correction (blurry image in Figure 11A) and with image correction via a light field display having an angularly mismatched lenslet array (corrected image in Figure 11B), in accordance with one embodiment;

[0042] Figures 12A and 12B are photographs as illustratively viewed by a viewer with reduced visual acuity without image correction (blurry image in Figure 12A) and with image correction via a light field display having an angularly mismatched lenslet array (corrected image in Figure 12B), in accordance with one embodiment;
[0043] Figures 13A to 13C are schematic diagrams of a substantially collimated, substantially converging or substantially diverging beams, respectively, produced from a convex lenslet or microlens overlaying an underlying pixel array and the associated change in spot size on a user's retina; and [0044] Figure 14 is a graphical plot illustrating the effect of beam divergence on the variation of a spot size on a user's retina as a function of a microlens pitch for set operating criteria, in accordance with different embodiments.
DETAILED DESCRIPTION
[0045] The systems and methods described herein provide, in accordance with different embodiments, different examples of a vision correction system and method, light field display and microlens array therefor. For instance, the devices, displays and methods described herein may allow a user's perception of an input image to be displayed, to be adjusted or altered using the light field display. For instance, in some examples, users who would otherwise require corrective eyewear such as glasses or contact lenses, or again bifocals, may consume images produced by such devices, displays and methods in clear or improved focus without the use of such eyewear. Other light field display applications, such as 3D displays and the like, may also benefit from the solutions described herein, and thus, should be considered to fall within the general scope and nature of the present disclosure.
[0046] For example, some of the herein-described embodiments described herein provide for digital display devices, or devices encompassing such displays, for use by users having reduced visual acuity, whereby images ultimately rendered by such devices can be dynamically processed to accommodate the user's reduced visual acuity so that they may consume rendered images without the use of corrective eyewear, as would otherwise be required. As noted above, embodiments are not to be limited as such as the notions and solutions described herein may also be applied to other technologies in which a user's perception of an input image to be displayed can be altered or adjusted via the light field display.
[0047] Generally, digital displays as considered herein will comprise a set of image rendering pixels and a light field shaping layer disposed at a preset distance therefrom so to controllably shape or influence a light field emanating therefrom. For instance, each light field shaping layer (i.e. microlens array) will be defined by an array of optical elements centered over a corresponding subset of the display's pixel array to optically .. influence a light field emanating therefrom and thereby govern a projection thereof from the display medium toward the user, for instance, providing some control over how each pixel or pixel group will be viewed by the viewer's eye(s). As will be further detailed below, arrayed optical elements may include, but are not limited to, lenslets, microlenses or other such diffractive optical elements that together form, for example, a lenslet array;
pinholes or like apertures or windows that together form, for example, a parallax or like barrier; concentrically patterned barriers, e.g. cut outs and/or windows, such as a to define a Fresnel zone plate or optical sieve, for example, and that together form a diffractive optical barrier (as described, for example, in Applicant's co-pending U.S.
Application Serial No. 15/910,908, the entire contents of which are hereby incorporated herein by reference; and/or a combination thereof, such as for example, a lenslet array whose respective lenses or lenslets are partially shadowed or barriered around a periphery thereof so to combine the refractive properties of the lenslet with some of the advantages provided by a pinhole barrier.
[0048] In operation, the display device will also generally invoke a hardware processor operable on image pixel data for an image to be displayed to output corrected image pixel data to be rendered as a function of a stored characteristic of the light field shaping layer (e.g. layer distance from display screen, distance between optical elements (pitch), absolute relative location of each pixel or subpixel to a corresponding optical element, properties of the optical elements (size, diffractive and/or refractive properties, etc.), or other such properties, and a selected vision correction or adjustment parameter

8 related to the user's reduced visual acuity or intended viewing experience.
While light field display characteristics will generally remain static for a given implementation (i.e. a given shaping layer will be used and set for each device irrespective of the user), image processing can, in some embodiments, be dynamically adjusted as a function of the user's visual acuity or intended application so to actively adjust a distance of the virtual image plane induced upon rendering the corrected/adjusted image pixel data via the static optical layer, for example, or otherwise actively adjust image processing parameters as may be considered, for example, when implementing a viewer-adaptive pre-filtering algorithm or like approach (e.g. compressive light field optimization), so to at least in part govern an image perceived by the user's eye(s) given pixel-specific light visible thereby through the layer.
100491 Accordingly, a given device may be adapted to compensate for different visual acuity levels and thus accommodate different users and/or uses. For instance, a particular device may be configured to implement and/or render an interactive graphical user interface (GUI) that incorporates a dynamic vision correction scaling function that dynamically adjusts one or more designated vision correction parameter(s) in real-time in response to a designated user interaction therewith via the GUI. For example, a dynamic vision correction scaling function may comprise a graphically rendered scaling function controlled by a (continuous or discrete) user slide motion or like operation, whereby the GUI can be configured to capture and translate a user's given slide motion operation to a corresponding adjustment to the designated vision correction parameter(s) scalable with a degree of the user's given slide motion operation. These and other examples are described in Applicant's co-pending U.S. Patent Application Serial No.
15/246,255, the entire contents of which are hereby incorporated herein by reference.
100501 With reference to Figure 1, and in accordance with one embodiment, a digital display device, generally referred to using the numeral 100, will now be described. In this example, the device 100 is generally depicted as a smartphone or the like, though other devices encompassing a graphical display may equally be considered, such as tablets, e-readers, watches, televisions, GPS devices, laptops, desktop computer monitors,

9 televisions, smart televisions, handheld video game consoles and controllers, vehicular dashboard and/or entertainment displays, and the like.
[0051] In the illustrated embodiment, the device 100 comprises a processing unit 110, a digital display 120, and internal memory 130. Display 120 can be an LCD
screen, a monitor, a plasma display panel, an LED or OLED screen, or any other type of digital display defined by a set of pixels for rendering a pixelated image or other like media or information. Internal memory 130 can be any form of electronic storage, including a disk drive, optical drive, read-only memory, random-access memory, or flash memory, to name a few examples. For illustrative purposes, memory 130 has stored in it vision correction application 140, though various methods and techniques may be implemented to provide computer-readable code and instructions for execution by the processing unit in order to process pixel data for an image to be rendered in producing corrected pixel data amenable to producing a corrected image accommodating the user's reduced visual acuity (e.g. stored and executable image correction application, tool, utility or engine, etc.). Other components of the electronic device 100 may optionally include, but are not limited to, one or more rear and/or front-facing camera(s) 150, an accelerometer 160 and/or other device positioning/orientation devices capable of determining the tilt and/or orientation of electronic device 100, and the like.
[0052] With reference to Figures 2A and 2B, the electronic device 100, such as that illustrated in Figure 1, is further shown to include a light field shaping layer 200 overlaid atop a display 120 thereof and spaced therefrom via a transparent spacer 310 or other such means as may be readily apparent to the skilled artisan. An optional transparent screen protector is also included atop the layer 200.
[0053] For the sake of illustration, the following embodiments will be described within the context of a light field shaping layer defined, at least in part, by a lenslet array comprising an array of microlenses (also interchangeably referred to herein as lenslets) that are each disposed at a distance from a corresponding subset of image rendering pixels in an underlying digital display. It will be appreciated that while a light field shaping layer may be manufactured and disposed as a digital screen overlay, other integrated concepts may also be considered, for example, where light field shaping elements are integrally formed or manufactured within a digital screen's integral components such as a textured or masked glass plate, beam-shaping light sources or like component. Accordingly, each lenslet will predictively shape light emanating from these pixel subsets to at least partially govern light rays being projected toward the user by the display device. As noted above, other light field shaping layers may also be considered herein without departing from the general scope and nature of the present disclosure, whereby light field shaping will be understood by the person of ordinary skill in the art to reference measures by which light, that would otherwise emanate indiscriminately (i.e.
io isotropic ally) from each pixel group, is deliberately controlled to define predictable light rays that can be traced between the user and the device's pixels through the shaping layer.
[0054] For greater clarity, a light field is generally defined as a vector function that describes the amount of light flowing in every direction through every point in space. In other words, anything that produces or reflects light has an associated light field. The embodiments described herein produce light fields from an object that are not "natural"
vector functions one would expect to observe from that object. This gives it the ability to emulate the "natural" light fields of objects that do not physically exist, such as a virtual display located far behind the light field display, which will be referred to now as the 'virtual image'.
[0055] To apply this technology to vision correction, consider first the normal ability of the lens in an eye, as schematically illustrated in Figure 3A, where, for normal vision, the image is to the right of the eye (C) and is projected through the lens (B) to the retina at the back of the eye (A). As comparatively shown in Figure 3B, the poor lens shape (F) in presbyopia causes the image to be focused past the retina (D) forming a blurry image on the retina (E). The dotted lines outline the path of a beam of light (G).
Naturally, other visual aberrations can and will have different impacts on image formation on the retina.
To address these aberrations, a light field display (K), in accordance with some embodiments, projects the correct sharp image (H) to the back of the retina for an eye with a lens which otherwise could not adjust sufficiently to produce a sharp image. The other two light field pixels (I) and (J) are drawn lightly, but would otherwise fill out the rest of the image.
[0056] As will be appreciated by the skilled artisan, a light field as seen in Figure 3C
cannot be produced with a 'normal' two-dimensional display because the pixels' light field emits light isotropically. Instead it is necessary to exercise tight control on the angle and origin of the light emitted, for example, using a microlens array or other light field shaping layer such as a parallax barrier, or combination thereof.
[0057] Following with the example of a microlens array, Figure 4 schematically illustrates a single light field pixel defined by a convex microlens (B) disposed at its focus from a corresponding subset pixels in an LCD display (C) to produce a substantially collimated beam of light emitted by these pixels, whereby the direction of the beam is controlled by the location of the pixel(s) relative to the microlens. The single light field pixel produces a beam similar to that shown in Figure 3C where the outside rays are lighter and the majority inside rays are darker. The LCD display (C) emits light which hits the microlens (B) and it results in a beam of substantially collimated light (A).
[0058] Accordingly, upon predictably aligning a particular microlens array with a pixel array, a designated "circle" of pixels will correspond with each microlens and be responsible for delivering light to the pupil through that lens. Figure 5 schematically illustrates an example of a light field display assembly in which a microlens array (A) sits above an LCD display on a cellphone (C) to have pixels (B) emit light through the microlens array. A ray-tracing algorithm can thus be used to produce a pattern to be displayed on the pixel array below the microlens in order to create the desired virtual image that will effectively correct for the viewer's reduced visual acuity.
Figure 6 provides an example of such a patter for the letter "Z".
[0059] As will be detailed further below, the separation between the microlens array and the pixel array as well as the pitch of the lenses can be selected as a function of various operating characteristics, such as the normal or average operating distance of the display.

[0060] Further, as producing a light field with angular resolution sufficient for accommodation correction over the full viewing 'zone' of a display would generally require an astronomical pixel density, instead, a correct light field can be produced, in some embodiments, only at the location of the user's pupils. To do so, the light field display can be paired with pupil tracking technology to track a location of the user's eyes/pupils relative to the display. The display can then compensate for the user's eye location and produce the correct virtual image, for example, in real time.
[0061] In some embodiments, the light field display can render dynamic images at over 30 frames per second on the hardware in a smartphone.
[0062] In some embodiments, the light field display can display a virtual image at optical infinity, meaning that any level of accommodation-based presbyopia (e.g. first order) can be corrected for.
[0063] In some further embodiments, the light field display can both push the image back and forward, thus allowing for selective image corrections for both hyperopia (far-.. sightedness) and myopia (nearsightedness).
[0064] In some embodiments, a display device as exemplified below can be configured to render a corrected image via the light field shaping layer that accommodates for the user's visual acuity. By adjusting the image correction in accordance with the user's actual predefined, set or selected visual acuity level, different users and visual acuity may be accommodated using a same device configuration.
That is, in one example, by adjusting corrective image pixel data to dynamically adjust a virtual image distance below/above the display as rendered via the light field shaping layer, different visual acuity levels may be accommodated.
[0065] As will be appreciated by the skilled artisan, different image processing .. techniques may be considered, such as those introduced above and taught by Pamplona and/or Huang, for example, which may also influence other light field parameters to achieve appropriate image correction, virtual image resolution, brightness and the like.

[0066] With reference to Figure 8, and in accordance with one embodiment, an microlens array configuration will now be described, in accordance with another embodiment, to provide light field shaping elements in a corrective light field implementation. In this embodiment, the microlens array 800 is defined by a hexagonal array of microlenses 802 disposed so to overlay a corresponding square pixel array 804.
In doing so, while each microlens 802 can be aligned with a designated subset of pixels to produce light field pixels as described above, the hexagonal-to-square array mismatch can alleviate certain periodic optical artifacts that may otherwise be manifested given the periodic nature of the optical elements and principles being relied upon to produce the to desired optical image corrections. Conversely, a square microlens array may be favoured when operating a digital display comprising a hexagonal pixel array.
[0067] In some embodiments, as illustrated in Figure 8, the microlens array 800 may further or alternatively overlaid at an angle 806 relative to the underlying pixel array, which can further or alternatively alleviate period optical artifacts.
[00681 In yet some further or alternative embodiments, a pitch ratio between the microlens array and pixel array may be deliberately selected to further or alternatively alleviate periodic optical artifacts. For example, a perfectly matched pitch ratio (i.e. an exact integer number of display pixels per microlens) is most likely to induce periodic optical artifacts, whereas a pitch ratio mismatch can help reduce such occurrences.
Accordingly, in some embodiments, the pitch ratio will be selected to define an irrational number, or at least, an irregular ratio, so to minimize periodic optical artifacts. For instance, a structural periodicity can be defined so to reduce the number of periodic occurrences within the dimensions of the display screen at hand, e.g. ideally selected so to define a structural period that is greater than the size of the display screen being used.
[0069] With reference to Figures 9A to 9E, different plots are shown illustrating the impact certain parameters may have on the performance of a light field display. In these particular examples, the spot size on a user's retina created by a given pixel (in microns), which generally dictates how many pixels can be projected onto the user's retina at one time, is plotted as a function of a microlens pitch (or diameter), as measured in pixels (i.e.

the number of pixels associated with each microlens). Generally, the ideal solution will be one that minimizes the spot size on the retina for given operating characteristics.
[0070] In the calculated examples, illustrated in accordance with certain exemplary embodiments, the ratio of the pupil width (taken as 1 to 3, or preferably 1.5 to 2 times an average pupil diameter to allow for some level of motion without imposing too high a threshold for pupil tracking accuracy capabilities) to the viewing/reading distance was taken be more or less equal to the ratio of the microlens pitch (diameter) to the microlens focal length, the later more or less dictating the distance of the microlens to the pixel array output surface for optimal operation. Furthermore, the viewing/reading distance may also be constrained by the type of application. For example, for a mobile phone display, the viewing distance may be between 30 to 40 cm, while for a digital display located within a vehicle (i.e. vehicular dashboard), the user may be constrained to be positioned at a distance of at least 65 cm or similar.
[0071] Furthermore, by matching the two ratios as described above, the pitch ratio (number of pixels per microlens) may then be found to be equal to: (pupil-diameter/viewing -di stance)* (focal-distance/pixel-size),In some embodiments, this equation was found to give increased image quality for values of 8 or more.
Similarly, in some embodiments, the effect of the periodic optical artifacts mentioned above were found to be minimized, in some embodiments, with the hexagonal microlens an-ay/square pixel array arrangement and a pitch ratio of 8 pixels per microlens or more.
[0072] To further refine computed results, in some embodiments, a subpixel coverage factor was taken into account, namely defining a percentage of the pixel area that is in fact represented by a subpixel light source, thus refining results to actual sub pixel spot size coverage on the user's retina. For instance, illustrated results were computed for a typical 4K phone display in which a subpixel coverage was set at 100% (Figure 9A), 35%
(Figure 9B) and 15% (Figure 9C). Similar results were also computed for an 8K
and 16K
display (Figure 9D and 9E, respectively), in each of which a subpixel coverage was set at 15%.

[0073] In each example, an average device viewing distance was set at 40cm, with a minimum user focal distance set at 6 meters (to define a maximum image correction range, i.e. the furthest a virtual image can be pushed back to accommodate reduced visual acuity in one example), as well as assuming an average eye depth of 25mm and pupil width of 5inm.
[0074] In some embodiments, an active percentage or fraction of each lens, i.e. a relative transparent area centered on each lens and otherwise circumscribed by a darkened or masked periphery, such as to combine the benefits of microlens beam shaping with parallax barrier effects, can also be taken into account to further refine optimizations.
[0075] Using any of these calculations, an appropriate microlens array may be selected, for example, based on an intended application (viewer distance), display screen technology (pixel size, subpixel coverage, pixel resolution), visual aberration correction, etc. For example, using the results of Figure 9B for a 4K screen having 35%
subpixel coverage, microlenses having a diameter corresponding to anywhere between about 5 and

10 pixels should produce optimal results (as compared to 10-15 pixels for 100%
subpixel coverage and 3-7 pixels for 15% subpixel coverage on a similarly defined 4K
screen; 3-10 pixels on an 8K screen; and 5-15 for a 16K screen). As smaller microlens diameters result in being able to optimally bring the microlens array closer to the display screen, these calculations may be used to seek out a smallest diameter possible without unduly limiting optimal retinal spot size formation. The optimized microlens diameter can also be used to select the microlens focus length as prescribed by the above-note ratios.
[0076] While the above-described embodiments are sufficient for providing high quality light-field corrected images. In some embodiments, it may be advantageous to further include additional parameters, such as the width of the light beam emerging from a microlens at the corneal surface and the width of the unlit edge of the beam as it focuses behind the retina.
[0077] With reference to Figures 10A to 10E, and in accordance with another exemplary embodiment, different plots are shown illustrating the impact certain parameters may have on the performance of a light field display. The spot size on a user's retina created by a given pixel (in microns) is again plotted as a function of a microlens pitch (or diameter), as measured in pixels. However, in this exemplary embodiment, the effect of both the width of the light beam emerging from a microlens at the corneal surface and the width of the unlit edge of the beam as it focuses behind the retina were incorporated. The illustrated results were again computed for a typical 4K
phone display in which subpixel coverage was set at 100% (Figure 10A), 35% (Figure 10B) and 15%
(Figure 10C). Similar results were also computed for an 8K and 16K display (Figure 10D
and 10E, respectively), in each of which a subpixel coverage was set at 15%.
However, herein the viewing distance was set to 65 cm and the pupil width to 4 mm (i.e.
for vehicular applications). The ideal microlens pitch is once more taken as one that minimizes the spot size on the retina for given operating characteristics.
[0078] Using any of these calculations, according to this embodiment, an appropriate microlens array may be selected, for example, based on an intended application (viewer distance), display screen technology (pixel size, subpixel coverage, pixel resolution), visual aberration correction, etc. For example, using the results of Figure 10B for a 4K
screen having 35% subpixel coverage, microlenses having a diameter corresponding to anywhere between about 17 to 22 pixels should produce optimal results (as compared to 30-35 pixels for 100% subpixel coverage and 10-12 pixels for 15% subpixel coverage on a similarly defined 4K screen; 15-20 pixels on an 8K screen; and 20-30 for a 16K screen).
[0079] Accordingly, the methods and approaches described herein allow for the non-trivial determination of optimal optical hardware characteristics that can be applied to a particular display device, user application, and/or other such characteristics.
DISPLAY # Resolution Pixel size Subpixel coverage (x %,y %) (x/y pixels) (microns) 1 3840x2160 31.5 (38,67) 2 3840x2160 72.0 (27,70) 3 1920x1080 8.1 (50,50) 4 2048 x1080 47.25 (23, 60) [0080] The skilled artisan will understand, based on the parameters disclosed above, that different combinations of microlens array/digital display may be available, depending on the application and applied minimum spot size. The table below lists an exemplary set of digital displays that have been used to demonstrate a working light field solution:
The table includes the display's resolution, the pixel size in microns and the subpixel coverage (in % both the x and y directions). Notably, display #1 is taken from the SonyTM
XperiaTM XZ Premium phone while the other displays are attainable from manufacturers or readily modified from other devices.
100811 Similarly, the table below lists some exemplary microlens array designs operable to be used with some or all the displays disclosed in the table above:
MLA # Manufacturer Focal length Pitch (mm) Viewing Geometry (mm) distance (cm) 1 Fraunhofer 43.0 0.521 65 hexagonal 2 Fraunhofer 65.0 1.000 65 hexagonal 3 Fraunhofer 43.0 0.600 65 hexagonal 4 Edmund Optics 15.3 0.500 30 square 5 RPC 3.5 0.125 30 square 6 Okotech 10.0 0.150 30 square 7 Okotech 7.0 0.200 30 square For each microlens array listed, indicated are the focal length (mm), the pitch of each individual microlenses (in mm), the expected optimal viewing distance (in cm) and its geometry (hexagonal or square). While using any combination of microlens array/display are operable to provide an functional light field, some combinations may provide higher perceived resolutions (smaller spot size on the user's retina), based on the parameters discussed above. For example, the Fraunhofer microlens arrays (#1, #2 and #3) were specifically designed to be used with display #1, based on the above-described optimization of the functional parameters affecting the spot size on the user's retina. In contrast, the Edmund Optics microlens array (#4) is a small microlens (10mm x 10mm) used for preliminary testing with a focal length best suited for a 30 cm viewing distance with the Z5 screen (display #1) while the RPC microlens array (#5) was used for a close-to-eye test, generally only a few centimeters from the eye. Finally, the Okotech 10mm (#6) and 7nun (#7) are off the shelf MLAs. Examples of such combinations of digital displays/microlens arrays from the above tables will be discussed below.

[0082] In order to demonstrate a working light field solution, and in accordance with one embodiment, the following test was set up. A camera was equipped with a simple lens, to simulate the lens in a human eye and the aperture was set to simulate a normal pupil diameter. These factors are generally controlled to adequately simulate the depth of focus of the human eye. The lens was focused to 50cm away and a phone was mounted 25cm away. This would approximate a user whose minimal seeing distance is 50 cm and is attempting to use a phone at 25cm.
[0083] With reading, glasses, +2.0 diopters would be necessary for the vision correction. A scaled Snellen chart was displayed on the cellphone and a picture was taken, as shown in Figure 7A. Using the same cellphone, but with a light field assembly in front that uses that cellphone's pixel array, a virtual image compensating for the lens focus is displayed. A picture was again taken, as shown in Figure 7B, showing a clear improvement.
[0084] Figures 11A and 11B provide another example or results achieved using an s exemplary embodiment, in which a color image was displayed on the LCD
display #1 (a SonyTM XperiaTM XZ Premium phone with a reported screen resolution of 3840x2160 pixels with 16:9 ratio and approximately 807 pixel-per-inch (ppi) density) without image correction (Figure 13A) and with image correction through a square fused silica microlens array set at a 2 degree angle relative to the screen's square pixel array and defined by microlenses #7 having a 7.0mm focus and 200i_im pitch. In this example, the camera lens was again focused at 50cm with the phone positioned 30cm away.
Another microlens array was used to produce similar results, and consisted of microlens array #6 haying microlenses with a 10.0mm focus and 150[,tm pitch.
[0085] Figures 12A and 12B provide yet another example or results achieved using an exemplary embodiment, in which a color image was displayed on the LCD
display of a SonyTM XperiaTM XZ Premium phone (display #1) without image correction (Figure 12A) and with image correction through a square fused silica microlens array set at a 2 degree angle relative to the screen's square pixel array and defined by microlens array #6 having microlenses with a 10.0mm focus and 150kim pitch. In this example, the camera lens was focused at 66cm with the phone positioned 40cm away.
[0086] While the two above examples were provided using off-the-shelf components, the Fraunhofer microlens arrays (#1, #2 and #3) described above were specifically .. designed, using the spot size minimization procedure described above, to be combined with display #1 (SonyTM XperiaTM XZ Premium phone) and were found to provide an improved resolution that substantially approaches the so called retina resolution.
[0087] In some embodiments, the microlens array and the digital display may be relatively positioned so that each microlens produces moderately convergent or divergent light beams. By adjusting the beam convergence/divergence by changing the relative position of the microlens and the display with respect to the microlens' focal length, the width of the spot size on the user's retina may be minimized as well. Figures 13A to 13C
schematically illustrates the effect using a different microlens focus has on the width of the spot size on the retina. Indeed, for a microlens with a pixel located on its focal plane, the emerging beam is collimated (parallel) and thus the width of the beam on the cornea is the width of the microlens. In contrast, if the focal plane is located instead in front/behind the pixel (e.g. pixel is further/closer than focal length), then the emerging beam converges/diverges and the width of the beam on the cornea will be smaller/greater than the width (or pitch) of the microlens. In Figure 13A, three collimated beams exiting microlens plane 1305 are shown, each associated with a single pixel from the display (not shown) as described above with respect to Figure 4. The rays from each beam are directed towards the cornea/crystallin plane 1308 and converge on focal plane 1315, which is located behind the retina plane 1318. The perceived spot size 1325 is the width of the region covered by the beams on the retina plane 1318. The associated virtual image portion covered by each beam, as perceived by the user, on the virtual image plane 1331 behind microlens 1305 is also shown for comparison. Similarly, Figures 13B and illustrates the perceived spot sizes 1337 and 1345, respectively, for the same configuration but with the microlens focused at the cornea (e.g. converging beam) or focused at the virtual image plane (e.g. diverging beam), respectively. For the diverging beam (Figure 11C), the resulting spot size 1345 is smaller than the spot sizes 1325 or 1337 for the collimated beam and the converging beam, respectively. This effect of beam divergence of the spot size is further illustrated in Figure 14. Starting with the same calculations used to generate Figure 10C, a beam divergence parameter was further added to measure the effect of increased beam divergence on the spot size on a user's retina .. created by a given pixel (in microns), herein again plotted as a function of a microlens pitch (or diameter), as measured in pixels. For comparison, plot 1405 is the same plot as the one shown in Figure 10C (e.g. perfectly collimated beam) while plot 1413 is a plot obtained using the same parameters but with an added increased beam divergence. The divergence of the beam emerging from the microlens may be quantified using, for example, the inverse distance from the microlens to the convergence point of the beam emanating from it. For a divergent beam (e.g. that converges "behind" the lens), this inverse distance parameter will be negative. Plot 1413 was obtained with a divergence parameter equal to the negative inverse distance to the virtual image plane, representing a microlens focused on the virtual image plane (same as seen in Figure 13C). We clearly see the resulting improvement on the minimum perceived spot size 1417 vs the original optimized value 1409, which shifts from a minimum value of about 3.3 microns to a minimum value of about 1.08 microns.
[0088] While the present disclosure describes various exemplary embodiments, the disclosure is not so limited. To the contrary, the disclosure is intended to cover various modifications and equivalent arrangements included within the general scope of the present disclosure.

Claims

What is claimed is:

1. A digital display device to render an image for viewing by a viewer having reduced visual acuity, the device comprising:
a digital display medium comprising an array of pixels and operable to render a pixelated image accordingly;
a microlens array disposed relative to said digital display so to align each said microlens with a corresponding set of said pixels to shape a light field emanating therefrom and thereby at least partially govern a projection thereof from said display medium toward the user; and a hardware processor operable on pixel data for the image to be displayed to output corrected image pixel data to be rendered as a function of a designated characteristic of said microlens array and a selected vision correction parameter related to the viewer's reduced visual acuity such that said processed image is rendered via said microlens array to at least partially compensate for the user's reduced visual acuity;
wherein a dimension of each said microlens is selected to minimize a spot size on the retina of the viewer produced by given pixels of said corresponding set of pixels.
2. The digital display device of claim 1, wherein a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 15 of said pixels.
3. The digital display device of claim 1, wherein a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 10 of said pixels.
4. The digital display device of claim 1, wherein a diameter of each said microlens is selected to correspond with a dimension of about 5 to about 10 of said pixels.

5. The digital display device of claim 1, wherein said dimension of each said microlens is selected to minimize said spot size on the retina of the viewer produced by each of a set of constituent subpixels for each said corresponding set of pixels.
6. The digital display device of claim 5, wherein a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 10 of said pixels.
7. The digital display device of claim 5, wherein a diameter of each said microlens is selected to correspond with a dimension of about 5 to about 10 of said pixels.
8. The digital display device of claim 1, wherein a diameter of each said microlens is selected to correspond with a dimension of about 10 to about 35 of said pixels.
9. The digital display device of claim 1, wherein a diameter of each said microlens is selected to correspond with a dimension of about 15 to 25 of said pixels.
10. The digital display device of any one of claims 1 to 9, wherein said microlens array is disposed at a designated distance from said digital display that is shorter than a focal length of said microlens so to produce a divergent light field therefrom.
11. The digital display device of claim 10, wherein said designated distance is selected such that said microlens focuses on a virtual image plane generated thereby.
12. A microlens array for use with a display medium comprising an array of pixels and operable to render a pixelated image accordingly to be viewed by a viewer having a reduced visual acuity, wherein the microlens array is dimensioned to be disposed relative to the digital display medium and comprises an array of microlenses, each one of which being disposed, when overlaid onto the digital display medium, to be centered over a corresponding set of the pixels to shape a light field emanating therefrom and thereby at least partially govern a projection thereof from said display medium toward the user, wherein a dimension of each said microlens is selected to minimize a spot size on the retina of the viewer produced by given pixels of said corresponding set of pixels.
13. The microlens array of claim 12, wherein a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 15 of said pixels.
14. The microlens array of claim 12, wherein a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 10 of said pixels.
15. The microlens array of claim 12, wherein a diameter of each said microlens is selected to correspond with a dimension of about 5 to about 10 of said pixels.
16. The microlens array of claim 12, wherein said dimension of each said microlens is selected to minimize said spot size on the retina of the viewer produced by each of a set of constituent subpixels for each said corresponding set of pixels.
17. The microlens array of claim 16, wherein a diameter of each said microlens is selected to correspond with a dimension of about 3 to about 10 of said pixels.
19. The microlens array of claim 16, wherein a diameter of each said microlens is selected to correspond with a dimension of about 5 to about 10 of said pixels.
20. The microlens array of claim 14, wherein a diameter of each said microlens is selected to correspond with a dimension of about 10 to about 35 of said pixels.
21. The digital display device of claim 14, wherein a diameter of each said microlens is selected to correspond with a dimension of about 15 to 25 of said pixels.