Patent Description:
PRIOR ART <FIG> shows the pixel structure of a striped liquid crystal display (LCD <NUM>), which is well known in the art. When a first and second display layers are stacked, moiré interference is produced. The interference is caused by interactions between the color filters within the layers when projected onto the viewer's retina. For example, when green color filters overlap, light is transmitted making for a comparative bright patch. When a green filter is over say a red filter, not as much light will be transmitted making for a dark region. Since the rear and front display layers have slightly different sizes when projected onto the retina, the pixels will slowly change from being in phase to out of phase. This has the effect of producing dark and bright bands otherwise known as moire interference.

There are several approaches to removing moiré interference in an MLD system. Most approaches rely on removing unwanted frequency components by spatial filtering. This can be accomplished with either a diffuser type system whereby an element with a refractive index of~<NUM> has random surface perturbations, or a diffraction type system. The performance of these systems in terms of visual aesthetics (e.g., how blurry the image looks; how much residual moiré is left; the effect on polarization; and cost, etc.) depend greatly on the system configuration. An example of a system utilizing a diffuser or a micro-lens array as a light spreader so that light points from adjacent pixels of the rear most display layer overlap is described in <CIT>. Furthermore, <CIT> discloses a multi-layered display device having a moiré vanishing element that acts as a spatial filter with a cut-off frequency of twice the pixel pitch so that a picture displayed on a display unit behind the moiré vanishing element becomes "out of focus".

Current multi-layered display (MLD) systems utilize diffusive optics to blur the rear most display layer. While commercially successful, this approach suffers from the following limitations: (a) the rear most image is inherently blurry - there is a trade-off between reducing moiré interference and the clarity of the rear most image display layer; (b) the diffusing element utilizes a specialized diffuser pattern, which is difficult to obtain; (c) the diffusing element sits between polarizers and both the film substrate and stiffener substrate must be free of any birefringence; and (d) the diffusing element requires a separate stiffener component (usually glass) which adds weight and expense to the final display system. As a result, diffusive type systems do not provide an ideal solution to reducing moiré interference in MLD systems, especially as those systems have reduced form factors.

In a diffraction type system of the prior art, to prevent interference from the color filters, several copies of an image are required, wherein the number of copies is defined as the rounded ratio of the width of the pixel to the width of the sub-pixel. However, while the diffraction grating is configured to generate copies of the image properly, moiré interference from the black matrix masking associated with electronic traces to each pixel is not alleviated.

Further, a disadvantage of the diffraction type system solution is that multiple orders are difficult to generate simultaneously, since this requires multiple periods PRIOR ART <FIG> shows the efficiencies of various blazed gratings for a diffraction type system implemented to reduce moiré interference. As can be seen from PRIOR ART <FIG>, phase gratings with simple repeating structures are only efficient at producing zero and first order diffraction simultaneously. Higher orders, including second order and third order copies, are not shown to be generated simultaneously with the first order.

What is desired is an MLD system that addresses the moiré interference due to overlapping black matrix masking from multiple display layers.

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:.

The invention is directed to a display device as recited in appended independent claim <NUM> and to a method for treating moire interference in a display as recited in appended independent claim <NUM>. Other aspects of the invention are recited in the appended dependent claims.

Reference will now be made in detail to the various embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. While described in conjunction with these embodiments, it will be understood that they are not intended to limit the disclosure to these embodiments. On the contrary, the disclosure is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the disclosure as defined by the appended claims. Furthermore, in the following detailed description of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be understood that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present disclosure.

Flowcharts of examples of methods for reducing moiré interference in a multi-layered display system are described, according to embodiments of the present invention. Although specific steps are disclosed in the flowcharts, such steps are exemplary. That is, embodiments of the present invention are well-suited to performing various other steps or variations of the steps recited in the flowcharts.

Accordingly, embodiments of the present invention provide for MLD systems that include a diffractive element configured to reduce moiré interference, in accordance with embodiments of the present disclosure. Specifically, the diffractive element is configured to minimize the effect of moiré interference due to the black mask patterns on overlapping display layers, and operates by convolution to generate multiple copies of the black mask pattern of a rearward display, wherein the copies each have substantially equal energy (e.g., luminance). In addition, the copies are generated and located within footprint of a corresponding pixel. It should be appreciated that when multiple copies of the mask pattern are constructed by convolution, the same number of copies of the color filter arrays are also made at the same spacing, thus concurrently removing the moiré interference pattern that would otherwise be generated by the color filters.

<FIG> is a block diagram of a multi-layered display system <NUM> including a diffraction element layer <NUM> configured to minimize the moiré interference contributions of a rearward display layer, in accordance with one embodiment of the present disclosure.

As shown in <FIG>, the MLD system <NUM> includes multiple display screens, wherein each screen is selectively transparent with the ability to display images. For instance, MLD system <NUM> includes a first display screen <NUM> and a second display screen <NUM>. The first display screen <NUM> is located nearer to the front <NUM> of the MLD system <NUM> than the second display screen <NUM>. In addition, the front <NUM> of the MLD system <NUM> closest to a viewer, as is shown in <FIG>.

For the sake of clarity and to aid understanding of the present invention, the MLD system <NUM> and associated display screens <NUM> and <NUM> (at least partially and selectively transparent) are shown in simplified, schematic form in the drawings, such that elements not essential to illustrate the present invention are omitted from the drawings to aid understanding. For example, the MLD system <NUM> may include one or more of the following items: one or more polarizers associated with one or more display screens, refractor to increase viewing angles, a rear light source (e.g., polarized backlight source), light guide, mirrors, glass substrates, etc. In one embodiment, the MLD system <NUM> does not include a diffuser type element.

It should be apparent to one skilled in the art that a number of alternative display technologies may be utilized in place of the LCD screens. Furthermore, although <FIG> shows a single screen <NUM> in front of the rear display layer <NUM>, for the sake of clarity and convenience, any number of additional (at least partially transparent) imaging screens may be incorporated. Although the rear display screen <NUM> may also be an LCD screen, it will be apparent that alternative, non-transparent display technologies may be employed.

In particular, the first display screen <NUM> includes a mask pattern, or black mask pattern, that is associated with pixels in the display <NUM>. For instance, the black mask pattern is used, for example, to hide electronic traces sending signals to the pixel components. A unit of the black mask pattern is associated with each pixel, and is further described in relation to <FIG>. In addition, the second display screen <NUM> includes the same or an identical mask pattern, that is associated with pixels in the second display screen <NUM>.

Embodiments of the present invention are configured to minimize and reduce the effect of moiré interference due to the overlapping of the black mask patterns from the first display screen <NUM> and the second, rear display screen <NUM>. In particular, MLD system <NUM> also includes a diffraction element that is configured to convolve the mask pattern of the second display screen <NUM> into one or more viewable and/or virtual copies (e.g., by the viewer) in order to minimize moiré interference with the mask pattern of the first display screen <NUM>.

In one embodiment, the diffraction element <NUM> is nearer to the front <NUM> of the MLD system <NUM> than the first display screen <NUM> and the second display screen <NUM>. In an example not according to the invention, the diffraction element <NUM> is located between the first display screen <NUM> and the second display screen <NUM>. For instance, the diffraction element <NUM> may be located adjacent to a polarizer component.

For purposes of illustration, <FIG> is a diagram of an exemplary pixel <NUM> of a representative display screen (e.g., screens <NUM> and <NUM>) illustrating one or more vertical portions of a black mask pattern that are repeatable in the horizontal direction <NUM>, and one or more horizontal portions of a black mask pattern that are repeatable in the vertical direction <NUM>, in accordance with one embodiment of the present disclosure. As shown in <FIG>, pixel <NUM> includes a red filter portion <NUM>, a green filter portion <NUM>, and a blue filter portion <NUM>, each of which corresponds to a sub-pixel. For instance, red filter portion <NUM> corresponds to the red sub-pixel, the green filter portion <NUM> corresponds to the green sub-pixel, and the blue sub-pixel portion <NUM> corresponds to the blue sub-pixel. By varying the luminance of each of the color filter portions of corresponding sub-pixels, a resulting color for the pixel is generated.

More particularly, the black mask pattern for the pixel <NUM> includes vertical portions <NUM> and the horizontal portions <NUM>. The unit size of the black mask pattern associated with pixel <NUM> is repeatable for each pixel in a corresponding display screen (e.g., <NUM> and <NUM> of <FIG>).

The black mask pattern for the pixel <NUM> can be further broken down into sub-pixel components. For instance, each of the sub-pixels include horizontal and vertical portions of the black mask. Taking the red sub-pixel as a representative sample, the vertical portion <NUM> includes a left vertical side <NUM>-L and a right vertical side <NUM>-R that flanks the red sub-pixel. Further, each vertical side is of width "W/<NUM>". The vertical side <NUM>-L and/or vertical side <NUM>-R are repeatable in the horizontal direction <NUM>. In addition, for the red sub-pixel the horizontal portion <NUM> includes a bottom <NUM>-B and a top <NUM>-T.

The black mask pattern for the red sub-pixel is repeatable for each of the green and blue sub-pixels. For example, the horizontal portion <NUM> includes the top <NUM>-T of each of the red, green, and blue sub-pixels. Though a separation or gap is shown between the vertical sides (e.g., <NUM>-R and <NUM>-L) of adjoining sub-pixels, this is illustrated purely for clarity. In embodiments, there is minimal or no separation between vertical sides of adjoining sub-pixels. As such, the horizontal portion <NUM> is one continuous sub-pattern joining the tops of the red, green, and blue sub-pixels, and joining the bottoms of the red, green, and blue sub-pixels. A height of the horizontal portion <NUM> of a pixel <NUM> is labeled "H". The horizontal portion <NUM> is repeatable in the vertical direction <NUM>, and is used to determine the physical characteristics and functionality of the diffraction element used to reduce moiré interference from the horizontal portions <NUM> of the black mask pattern in the vertical direction <NUM>.

Further, the vertical sides <NUM>-R and <NUM>-R of two adjoining sub-pixels have minimal or no separation. For example, the vertical side <NUM>-R of the green sub-pixel is located adjacent to the vertical side <NUM>-L of the blue sub-pixel. The resulting width of both vertical sides <NUM>-R and <NUM>-L of the green and blue sub-pixels, respectively, is labeled as "W". The combination of the vertical sides <NUM>-R and <NUM>-L is repeatable in the horizontal direction <NUM> and is used to determine the physical characteristics and functionality of the diffraction element used to reduce moiré interference from the vertical portions <NUM> of the black mask pattern in the horizontal direction <NUM>.

In general, the diffraction element is configured to minimize moiré interference due to portions of the black mask pattern that are repeatable in various directions. Each portion corresponding to a particular direction is treated by a resulting solution/component of the diffraction element. By combining one or more resulting solutions/components, the diffraction element is able to reduce moiré interference from the black mask pattern in multiple directions.

For example, one component of a diffraction grating for use with a multi-layered display system is disclosed, wherein the diffraction grating has a number of orders in the horizontal direction that is based on dividing the pixel width by the vertical black matrix width, and wherein the orders are of substantially equal energy. Further, another component of the diffraction grating has a number of orders in the vertical direction that is based on dividing the sub-pixel height by the vertical black matrix height, wherein the orders are of substantially equal energy. In the multi-layered display system, the pixels are part of a display layer that is behind the diffraction grating with respect to the viewer.

For purposes of discussion, the horizontal direction <NUM> is chosen to illustrate the functionality of one component of the diffraction element. In particular, the diffraction element is configured to minimize moiré interference due to the vertical portions of the black mask pattern that is repeatable in the horizontal direction.

In general, the mask pattern includes a first portion that is repeatable in a first direction. For example, the first portion may be the vertical portion <NUM> that is repeatable in the horizontal direction <NUM>. In addition, the first portion may also be the horizontal portion <NUM> that is repeatable in the vertical direction <NUM>.

The diffraction element is configured to convolve the first portion of the mask pattern in the corresponding first direction. In particular, the diffraction element is configured to convolve the vertical portion <NUM> in the horizontal direction <NUM>. The number of viewable copies is based on dividing a width of the pixel by a width of the first portion. In one embodiment, the width of the first portion that is repeatable in the horizontal direction is "W", and corresponds to both a right vertical side <NUM>-R and a left vertical side <NUM>-L associated with adjoining sub-pixels.

In one embodiment, the number of viewable copies completely covers the pixel <NUM> in the horizontal direction <NUM>. That is, the spacing between the one or more viewable copies is the width of the first portion (e.g., "W"). In that manner, the diffraction element convolves the first portion of the black mask pattern to cover the pixel, at least in the horizontal direction. In one embodiment, the resulting pixel intensity after convolving using the diffraction element is reduced in proportion to the width of first portion (e.g., "W") of the black mask pattern, so that the combined color of the sub-pixels is not hidden. As such, the black mask pattern from the rear display (e.g., second display <NUM>) is now a uniform structure, such that no repeating patterns are produced at the display level. This is accomplished without blurring out the information shown by the rear display.

In one embodiment, the number of copies comprises multiple orders beyond the variable two. For instance, the number of copies comprises four, such that that there are <NUM> copies (e.g., two for each order). Other embodiments are well suited to generating three orders, or orders greater than four.

<FIG> is an illustration of the diffracted orders generated through a transmission grating or diffraction element <NUM>, in accordance with one embodiment of the present disclosure. For example, as incident light hits the diffraction element <NUM>, orders of convolved images are created. The <NUM>-order image is not diffracted. The first ordered image includes a positive (+<NUM>) ordered image and a negative (-<NUM>) ordered image. The second ordered image includes a positive (+<NUM>) ordered image and a negative (-<NUM>) ordered image. The same is true for each order, including the Nth order, which includes a positive (+N) ordered image and a negative (-N) ordered image.

In one embodiment, the one or more viewable copies of the first portion of the black mask pattern for the pixel <NUM> is generated within a footprint of the pixel, in one embodiment. That is, the copies are viewable within the footprint of the pixel, wherein the footprint is defined as the outer edges of the pixel <NUM>, and includes the outer surface <NUM> (of horizontal portion <NUM>) and the outer surface <NUM> (of the vertical portion <NUM>). In another embodiment, the viewable copies are generated mostly within a footprint of the pixel.

<FIG> is an illustration of an image <NUM> of a display system with just green sub-pixels high-lighted, in accordance with one embodiment of the present disclosure. For example, in <FIG> image <NUM> is associated with a 5x6 matrix of pixels of a display screen. Outline <NUM> shows a red sub-pixel that is blackened (e.g., not energized), a green sub-pixel that is high-lighted as "white", and a blue sub-pixel that is blackened (or not energized). As discussed, the red sub-pixel and the blue sub-pixels are blackened out, or not considered for purposes of illustrating the reduction of moiré interference. In addition, the pixel in the second column and second row is completely blackened out, such that the green sub-pixel is also blackened. This image <NUM> is used to illustrate the effect of the diffraction element of embodiments of the present invention in reducing moiré interference, as compared to the diffraction type systems of the prior art, which are not effective in reducing moiré interference from the black mask pattern.

PRIOR ART <FIG> show a diffraction type system including a representative order-<NUM> image kernel and the resulting moiré interference pattern due to first portion (e.g., vertical portions) of the black mask regions. In particular, PRIOR ART <FIG> shows an order-<NUM> image filter kernel. This image filter kernel is designed to copy larger noise components of the pixels, and more specifically to copy the sub-pixels. As such, the green sub-pixel would be copied to the left over the red sub-pixel and to the right over a green sub-pixel. These copies would be made at spacings that are the size of the sub-pixels.

PRIOR ART <FIG> shows undesirable black mask regions that manifest as moiré interference when viewed through other display layers (e.g., a front display screen <NUM>). PRIOR ART <FIG> shows MTF (modulation transfer function) of order <NUM> in an image filter kernel. As shown in <FIG>, the effect of moiré interference is reduced, since the repeating vertical portions of adjoining sub-pixels is reduced (e.g., halved). However, the effect of moiré interference remains as evidenced by the lattice structure containing both vertical and horizontal elements. The horizontal elements exist because the component of the diffraction elements discussed only addresses the vertical portion that is repeatable in the horizontal direction.

Previous techniques (e.g., <FIG>) include using ray tracing of light rays or virtual images of lit objects when considering the effect of some subsequent lit element. The disadvantage of this technique is that the black mask still produces moiré interference for MLD systems.

On the other hand, embodiments of the present invention provide for the reverse of the above implementation. Specifically, copies of the black mask at the spacing that is the width of the black mask for the number of copies being made is the ratio of the width of the black matrix to the width of the pixel. This means that the black mask is spread over the width of the pixel, and concurrently the sub-pixel is spread over the width of the pixel and only the width of the pixel. Thus, the system works without blurring. Previous techniques would not have considered the inverse system of embodiments of the present invention, since the situation needs to be explicitly and non reversibly inverted for the purposes of analysis - that is the sub-pixels changed from emitting colored light to black, and the black matrix changed to emitting light.

<FIG> is a flow diagram <NUM> illustrations steps in a method for minimizing moiré interference in an MLD system, in accordance with one embodiment of the present disclosure. In one embodiment, flow diagram is a method for manufacturing an MLD system or MLD display device that is capable of reducing moiré interference due to contributions from the black mask pattern on overlapping display screens. Specifically, the method of flow diagram <NUM> is configured to generate copies of the black mask pattern in order to reduce the effect from moiré interference.

At <NUM> of flow diagram <NUM>, the method includes providing a first display screen including a black mask pattern. As previously described in relation to <FIG>, a unit of the black mask pattern is associated with each pixel. For instance, the black mask pattern is used to hide electronic tracing elements used to energize corresponding pixels of a display screen.

At <NUM>, the method includes providing a second display screen, wherein the second display screen includes the same or an identical mask pattern. Additionally, the second display screen is located further from a front of said display device than the first display screen, and wherein the front of the display device is closest to a viewer.

At <NUM>, the method includes convolving the mask pattern of the second display screen into one or more viewable copies in order to minimize or reduce moiré interference due to overlapping mask patterns of the first and second display screens. More specifically, a first portion of the mask pattern is convolved in a first direction, wherein the first portion is repeatable in the first direction. The method further includes providing a diffraction element including a component that is configured to convolve the first portion of the black mask pattern in the first direction. It should be appreciated that when multiple copies of the mask pattern are constructed by convolution, the same number of copies of the color filter arrays are also made at the same spacing, thus concurrently removing the moiré interference pattern that would otherwise be generated by the color filters.

In a particular case, first portions of the black mask pattern are convolved in the horizontal direction, such that the number of orders associated with the copies is based on dividing the pixel width by the width of the first portion, such as the vertical portion of the black matrix pattern (e.g., "W" in <FIG>), previously described. Further, the copies or orders are of substantially equal energy (e.g., similar luminance values).

In another case, first portions of the black mask pattern are convolved in the vertical direction, such that that the number of orders associated with the copies is based on dividing the sub-pixel height by the height (e.g., "H" in <FIG>) of the horizontal portion of the black matrix height, wherein the orders are of substantially equal energy (e.g., similar luminance values). In one embodiment, separate components of the diffraction element generate copies in different directions (e.g., one component for the horizontal direction and another component for the vertical direction).

For purposes of illustration, <FIG> show a diffraction element that is configured to minimize the moiré interference due to the black mask regions including a representative image filter kernel, and resulting moiré interference pattern that has eliminated portions of the black mask region that is repeatable in the horizontal direction, in accordance with embodiments of the present disclosure. For instance, <FIG> illustrate the performance of a diffraction element described in relation to <FIG>, <FIG>, and <FIG>.

The system described in <FIG> is by way of illustration only, and the convolution performed by a component of the diffraction element is only occurring in the horizontal direction. Additional convolution would need to occur in the vertical direction, by another suitable component of the diffraction element, to render the luminance profile of the display layer flat.

In particular, <FIG> shows an image filter kernel 800A configured to minimize the moiré interference contributions of a rearward display layer, in accordance with one embodiment of the present disclosure. That is, the image filter kernel 800A represents the functionality of a corresponding diffraction element. As shown, the image filter kernel 800A includes fifteen delta functions in a line, spaced at the width "W" of the black matrix in the horizontal direction, as previously described.

<FIG> shows the resulting image 800B after applying the image filter kernel 800A, in accordance with one embodiment of the present disclosure. That is, the display image <NUM> is convolved using the image filter kernel 800A, and produces resulting image 800B. Note that the black mask in the horizontal direction has vanished in resulting image 800B. <FIG> shows the resulting MTF of the diffraction grating shown as kernel 800A, in accordance with one embodiment of the present disclosure. <FIG> shows exemplary MATLAB code for modeling the required image kernel 800A.

In one embodiment, the diffraction element/grating (e.g., represented as image filter kernel 800A) may modulate incident light via amplitude variation, phase variation or a combination of both.

In another embodiment, the diffraction element/grating (e.g., represented as image filter kernel 800A) may be originated by normal optical means such as producing interference patterns onto photo resist, developing the photo resist to reveal the desired profile and then making a metal master from the photo-resist by depositing a metal zinc.

In still another embodiment, the diffraction element/grating (e.g., represented as image filter kernel 800A) may be originated by e-beam writing a mask whereby electrons are used to ablate a thin aluminum film on glass or other transparent substrate, and that mask is applied on top of photo resist and the resist exposed using UV or other light. Again the photo resist may be developed and a metal master may be constructed by applying a metal such as zinc.

In another embodiment, the diffraction element/grating (e.g., represented as image filter kernel 800A) may be physically realized by hot embossing, cold embossing, or UV embossing onto transparent optical substrates such as, but not limited to, Cyclo Olefin Polymer, Polyethylene, Polypropylene, Polyester, Nylon, triacetate cellulose, Poly(methyl methacrylate) and polycarbonate. The finished film may have a transparent adhesive such as <NUM>TM Optically Clear Adhesive 8173D applied to the back for attachment to a glass stiffener, protective layer or touch screen.

In another embodiment, conversely, if not used with a touch screen, the diffraction element/grating (e.g., in a separate layer) may point towards the viewer, where the advantage in this configuration is that it acts as an anti glare coating to prevent unwanted reflections from being noticed in addition to the diffraction effect.

In another embodiment, the diffraction film on the diffraction element may be optimized to have features pointing towards the display layer, leaving an optically smooth surface towards the viewer for the purposes of a touch screen layer. This is primarily so that the oils from the viewer's fingers in such a situation do not contaminate the diffraction layer and render it useless.

In still another embodiment, the diffraction film on the diffraction element may be placed between display layers or on top of the top most display layer. Preferably, the film would be on the top most display layer when used with LCD panels to avoid birefringence problems.

In another embodiment, the surface features of the diffraction element may be constructed by any combination of sine waves of any amplitude, frequency or phase in the horizontal and vertical directions. In one embodiment, preferably these sine waves form a series, where the wave-number increases by some integer multiple of a base wavelength, that is expressed as Equation <NUM>, as follows: <MAT> In Equation <NUM>, the term "An" is defined as the amplitude of the sine-wave, and chi is the phase. The term "kn" is defined, as follows: kn = <NUM>*pi*n*lambda, where lambda is the base wavelength, and "n" is an integer. The base wavelength depends on the distance between the diffraction film and the target image layer.

In another embodiment, there is one element in the series for each copy of the black mask required.

In still another embodiment, the diffraction element/grating may be optimized for situations where there are no color filters, such as in an transparent OLED or monochrome display.

In another embodiment, the diffraction grating may also be optimized for red green and blue stripe patterns, delta patterns, bayer patterns, phosphor dots or any other pixelated configuration where there is a black mask or shadow mask between pixels.

In one embodiment, implementation of the image kernel (e.g., kernel 800A) using a diffraction grating considers three requirements when generating a diffraction element that reduces moiré interference due to black mask patterns, in accordance with one embodiment of the present disclosure. The first requirement is the number of orders, which is determined by the ratio of the black mask width to pixel width in the horizontal and vertical directions respectively, as previously described. The second requirement is the spacing between the diffraction element and the rear pixel display. The third requirement is the wavelength(s) of light that the color filters transmit.

<FIG> shows the implementation of a representative image filter kernel on a single pixel, wherein the image filter kernel is configured to minimize moiré interference due to black mask regions in a MLD system in consideration of the three requirements described previously, in accordance with one embodiment of the present disclosure.

The display system shows one pixel <NUM> on rear most layer or screen <NUM>. The pixel includes a red filter component <NUM>, a green filter component <NUM>, and a blue filter component <NUM>.

In addition, the display system includes an interfering or intervening layer, such as, the front display layer or screen <NUM>. The front display layer <NUM> and the rear display layer <NUM> are configured to display images.

The display system includes a top most diffraction element <NUM> that operates on the wavelength spectra transmission of color filters. In particular, the diffraction element is configured to reduce and/or minimize moiré interference due to the black matrix patterns on overlapping display screens/layers. That is, the diffraction element <NUM> is configured to generate copies of the black matrix pattern, such as, copying a first portion of the mask pattern in a first direction, wherein the first portion is repeatable in the first direction.

As shown in <FIG>, the diffractive element convolves the black matrix portion <NUM> of width "W" across the pixel <NUM>. In one embodiment, the copies are confined within a footprint of pixel <NUM>. For example, black matrix <NUM> is associated with a zero mode along dotted line <NUM>. Virtual copies of the portion <NUM> of black matrix are generated by the diffraction element along the solid lines. For instance, first order copies are generated along lines 951A and 951B; second order copies are generated along lines 952A and 952B; third order copies are generated along lines 953A and 953B; and fourth order copies are generated along lines 954A and 954B. As an illustration, a second-order virtual copy <NUM> is generated along line 952A. Additional orders may be generated using a different diffraction element. Also, lesser number of orders may be generated using a different diffraction element.

The diffraction angle associated with any virtual copy is defined in Equation <NUM>, below. In Equation <NUM>, the variable "h" is the distance between the diffractive element <NUM> and the rear display layer <NUM>. The variable "a" indicates the order of the virtual copy. For instance, for virtual copy <NUM>, the variable "n" is the value <NUM>.

In one embodiment, the required diffraction element/grating may be optimized for the requirements above via the following process, described below.

The process includes an operation configured to select candidate diffraction grating profile(s) to be tested. For example this may be a combination of first, second, up to n order gratings designed for the wavelength in mind. The candidates may be generated by optimization algorithms such as genetic, simulated annealing, or levenberg-marquardt in one embodiment. The design may be optimized for a single wavelength such as <NUM> as in the green spectrum in <FIG>, or the optimization algorithm may be modified to create an Pareto optimum for <NUM> or more given wavelengths.

The process includes an operation configured to create a model of the candidate grating profile. The candidate profile is modeled in a finite difference time domain simulation package (e.g., MEEP available at http://ab-initio. edu/wiki/index. The model includes a substantially collimated incident beam, and the computational cell of interest, defined between the light source and diffraction grating, and just beyond the diffraction grating. The far field can be extrapolated using Fourier transforms.

The process includes an operation configured to create a model of the candidate grating profile to be modeled using an augmented light field approach. In one embodiment, the model uses a numerical Wigner Distribution code, such as the code contained in <FIG>. The model generated by the Winger Distribution code <NUM> minimizes moiré interference due to black mask regions in an MLD system, in accordance with one embodiment of the present disclosure. The code <NUM> in <FIG> is available from the Camera Culture Group, Media Lab, Massachusetts Institute of Technology, and is subject to change.

The process further includes an operation configured to use the model to calculate the field density of the incident beam after passing through the diffraction grating.

The process further includes an operation configured to compare the strength of the incident beam after passing through the diffraction grating through the required angles of incidence. A good candidate would have most of its field strength at these angles and certainly would have no field strength beyond the maximum diffraction angle defined as the inverse tangent of the height divided by the pixel width. The process is further configured to assign a fitness measure to the candidate according to these criteria and proceed with algorithm to either stop or test new candidates.

A desirable, practical one dimensional profile of a calculated configuration of a diffraction element is shown in <FIG>. The side profile shown in <FIG> (where y is measured in mm with refractive index <NUM>), has an angular output that has a corresponding point spread function shown in <FIG>, after passing through the one dimensional profile representing the diffraction grating. The effect on the one dimensional image profile is shown in <FIG> where the top of the image profile has been flattened, while the low point of the image profile corresponding to a dark pixel is approximately <NUM>% of the top portion of the profile.

Thus, according to embodiments of the present disclosure, systems and methods are described providing for a diffraction grating for use with a multi-layered display system that is capable of reducing moiré interference due to black matrix patterns located on overlapping display screens.

While the foregoing disclosure sets forth various embodiments using specific block diagrams, flowcharts, and examples, each block diagram component, flowchart step, operation, and/or component described and/or illustrated herein may be implemented, individually and/or collectively, using a wide range of hardware, software, or firmware (or any combination thereof) configurations. In addition, any disclosure of components contained within other components should be considered as examples because many other architectures can be implemented to achieve the same functionality.

While various embodiments have been described and/or illustrated herein in the context of fully functional computing systems, one or more of these example embodiments may be distributed as a program product in a variety of forms, regardless of the particular type of computer-readable media used to actually carry out the distribution. The embodiments disclosed herein may also be implemented using software modules that perform certain tasks. These software modules may include script, batch, or other executable files that may be stored on a computer-readable storage medium or in a computing system. These software modules may configure a computing system to perform one or more of the example embodiments disclosed herein. Various functions described herein may be provided through a remote desktop environment or any other cloud-based computing environment.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as may be suited to the particular use contemplated.

Claim 1:
A display (<NUM>) device comprising:
a first display screen (<NUM>) comprising a mask pattern of a pixel (<NUM>);
a second display screen (<NUM>) comprising said mask pattern, wherein said second display screen (<NUM>) is located further from a front of said display (<NUM>) device than said first display screen (<NUM>), wherein said front of said display (<NUM>) device is closest to a viewer; and
a diffraction element (<NUM>) at a distance from the second display screen (<NUM>) and configured to convolve said mask pattern of said second display screen (<NUM>) into two or more viewable copies in order to minimize moire interference with said mask pattern of said first display screen (<NUM>),
wherein said mask pattern comprises a first portion (<NUM>) repeatable in a first direction, and wherein said diffraction element (<NUM>) is configured to copy said first portion (<NUM>) of said mask pattern in said first direction,
characterized in
that a number of said viewable copies is based on dividing a width of said pixel (<NUM>) by a width of said first portion (<NUM>), and the number of viewable copies completely covers said pixel (<NUM>) in said first direction.