Determining inclination and pitch for autostereoscopic displays

Abstract

The invention provides a system and a method. And a processor for capturing one or more images of the displayed test pattern by generating and displaying the test pattern on the autostereoscopic display, and determining a second phase at a second position in the image by determining a first phase at a first position in the image, and determining a tilt of the optical element based on a difference between the first phase and the second phase to determine a tilt and an optional pitch distance of the autostereoscopic display. Advantageously, the first position and the second position are horizontally and vertically offset from each other according to an assumed value of the tilt. This allows inclination measurements to be less susceptible to assumed pitch distance errors. Specifically, the inclination can be determined first, which is largely independent of the pitch distance, and then the pitch distance can be determined from the determined inclination. As a result, the inclination and the optional pitch distance can be determined more accurately and / or more quickly.

Description

Technical Field

[0001] The invention relates to a system and method for determining the tilt and optionally the pitch distance of an autostereoscopic display. The invention also relates to a computer readable medium comprising instructions arranged to cause a processor system to perform the method. Background Art

[0002] Display devices such as televisions, tablets, and smartphones increasingly include 3D displays to provide users with depth perception when viewing content on such devices. Autostereoscopic displays provide stereoscopic depth perception without requiring the viewer to wear polarized, color-filtered, or shutter glasses. To this end, an autostereoscopic display includes optical components, such as an array of optical elements, that enable the display to emit a viewing cone from each given point on the 3D display, wherein the viewing cone includes at least a left view and a right view of the scene. This enables the viewer to see a different image with each eye when positioned accordingly.

[0003] Certain types of autostereoscopic displays (sometimes specifically referred to as 'auto-multiview' displays) provide a viewer with a series of views of a scene represented by 3D image data in what is commonly referred to as a viewing cone. This allows the viewer to assume multiple positions in the viewing cone, for example, to experience motion parallax, while still obtaining a stereoscopic perception of the scene. Some displays can emit such a series of views in each of a series of repeating viewing cones.

[0004] US6064424 describes an embodiment of an autostereoscopic display in which an array of parallel lenticular elements covers the display, wherein the lenticular elements are tilted relative to the columns of display pixels. The tilt is said to cause the reduction in display resolution experienced to be shared between both horizontal and vertical resolution.

[0005] In order to display content on an autostereoscopic display having an array of optical elements, an output image may be generated by the autostereoscopic display or a device connected thereto based on the 3D image data. This may involve an "interleaving", "weaving" or "interdigitation" step, wherein for each display element of the display, it is determined that the image data from the view to be displayed by the display element. Such interleaving typically takes into account the type of optical element array and its configuration in the display, which may include the inclination of the optical elements relative to the display panel and the pitch distance between the optical elements. The inclination may be expressed as or with respect to the angle of the main longitudinal axis of the optical element and the column direction of the display element array, but may also be expressed in a different way, for example with respect to the row direction of the display element array.

[0006] Although an autostereoscopic display can be designed to have a certain tilt and pitch distance, manufacturing tolerances may cause the actual values ​​of the tilt and / or pitch distance to deviate from the nominal values ​​selected during the design phase. It is therefore desirable to be able to measure the tilt and pitch distance of an autostereoscopic display so that the staggering can be adapted to their actual values.

[0007] Can be obtained from https: / / arxiv.org / abs / 1606.07166 The paper "3D Display Calibration by Visual Pattern Analysis" by Hwang et al., which was obtained, describes a display calibration method. In this method, a pattern image is displayed on the panel, and a camera takes pictures of it twice at different positions. Then, based on a quantitative model, display parameters including pitch and tilt angle are determined from the pattern observed in the captured images.

[0008] Unfortunately, the measurement accuracy achieved by Hwang et al., at least for tilt, is insufficient for high-resolution autostereoscopic displays.

[0009] It is an object of the present invention to be able to measure at least the tilt and optionally the pitch distance of an autostereoscopic display in a more accurate manner. Summary of the invention

[0010] The following aspects of the invention relate to an autostereoscopic display, wherein the autostereoscopic display comprises:

[0011] - a display panel comprising an array of display elements; and

[0012] - an array of elongated optical elements for redirecting light emitted by the display elements into mutually different directions, the optical elements being arranged substantially parallel to each other at a pitch distance and oriented with their main longitudinal axes at an inclination relative to the array of display elements;

[0013] According to a first aspect of the present invention, there is provided a method for determining the tilt of an autostereoscopic display. The method comprises:

[0014] - assigning a phase to each display element based on the estimated value of the pitch distance and the estimated value of the tilt, wherein the phase indicates the direction in which light emitted by the respective display element is redirected;

[0015] - based on the assigned phases, generating display data, the display data comprising uniquely identifiable image content for each phase in a set of assigned phases;

[0016] - outputting the display data to the autostereoscopic display for display;

[0017] - capturing one or more images of the display panel while the display data is displayed by the autostereoscopic display;

[0018] - determining the tilt by analyzing the one or more captured images, wherein the analyzing of the one or more captured images comprises:

[0019] - at a first position on the display panel, determining a first phase based on uniquely identifiable image content shown at the first position;

[0020] - determining a second phase at a second position on the display panel based on uniquely identifiable image content shown at the second position, wherein the first position and the second position are horizontally and vertically offset from each other according to the estimated value of the tilt; and

[0021] - determining a tilt of the optical element based on a difference between the first phase and the second phase.

[0022] According to another aspect of the invention, there is provided a transitory or non-transitory computer-readable medium, the medium comprising data representing instructions arranged to cause a processor system to perform the method.

[0023] According to another aspect of the present invention, a system is provided for determining the tilt of an autostereoscopic display. The system comprises:

[0024] - a display output interface to said autostereoscopic display;

[0025] - a camera interface to a camera positioned to capture an image of a display panel of the autostereoscopic display;

[0026] - a processing subsystem, the processing subsystem being configured to:

[0027] - assigning a phase to each display element based on the estimated value of the pitch distance and the estimated value of the tilt, wherein the phase indicates the direction in which light emitted by the respective display element is redirected;

[0028] - based on the assigned phases, generating display data, the display data comprising uniquely identifiable image content for each phase in a set of assigned phases;

[0029] - outputting the display data to the autostereoscopic display for display via the display output interface;

[0030] - capturing, via the camera interface, one or more images of the display panel while the display data is displayed by the autostereoscopic display;

[0031] - determining the inclination by analyzing the one or more captured images, wherein the analyzing of the one or more captured images comprises:

[0032] - at a first position on the display panel, determining a first phase based on uniquely identifiable image content shown at the first position;

[0033] - at a second position on the display panel, determining a second phase based on uniquely identifiable image content shown at the second position, wherein the first position and the second position are horizontally and vertically offset from each other according to the estimated value of the tilt; and

[0034] - determining a tilt of the optical element based on a difference between the first phase and the second phase.

[0035] The above measures relate to characterizing an autostereoscopic display comprising a display panel, such as an LCD, OLED or microLED panel. Stacked on top of the display panel, i.e. above the light emitting side of the display panel, an array of elongated optical elements may be arranged for redirecting light emitted by display elements of the display panel into mutually different directions. The optical elements may be arranged substantially parallel to each other at a pitch distance and oriented with their main longitudinal axes at an inclination relative to the array of display elements. An autostereoscopic display of the type described in this paragraph may be known per se. For example, US6064424 describes an embodiment of such a display.

[0036] It may be necessary to determine the inclination and optional pitch distance of such an autostereoscopic display. The above measures utilize initial estimates of the inclination and pitch distance to be able to determine the actual value of the inclination and the actual value of the optional pitch distance in a more accurate manner. The initial estimates may be, for example, nominal values ​​of the inclination and pitch distance obtained from manufacturing specifications. Since the actual values ​​of the inclination and pitch distance are likely to deviate from the initial estimates, a test pattern is generated and shown on the display. The test pattern includes uniquely identifiable image content for at least some phases on which the display can be addressed. In order to generate the test pattern, estimates of the inclination and pitch distance may be used so as to be able to determine the phase to which the display element corresponds, thereby assigning the corresponding uniquely identifiable image content to the corresponding display element. Then, the phase may be measured at at least two locations (i.e., positions) on the screen by capturing one or more images of the light-emitting side of the display and by analyzing the captured images so as to identify uniquely identifiable image content at two locations. As known per se, the phase difference at two positions may indicate the difference between the actual values ​​of the inclination and pitch distance and the estimated values ​​of the inclination and pitch distance. Conventionally, the estimates of the tilt and pitch distances may be corrected based on the differences, for example, in an iterative process, so that the estimates of the tilt and pitch distances converge from their initial estimates to an approximation of their actual values.

[0037] Disadvantageously, any phase difference observed at two locations on the screen may be due to a mismatch in tilt, i.e., due to a mismatch between the estimated and actual values ​​of tilt, or due to a mismatch in pitch distance, or both. As a result, it may not be immediately apparent whether the estimate of tilt should be corrected, the estimate of pitch distance, or both. This may result in the determination of tilt and pitch distance being less accurate than expected, or the determination being (much) slower to converge when iteratively determined.

[0038] The above measures involve measuring the phase at two or more different positions on the screen, which can be offset from each other horizontally and vertically according to the estimated value of the inclination. Thus, the position where the phase is measured is located on a line that is tilted according to the estimated value of the inclination. The horizontal and vertical offsets of the position can correspond exactly to the estimated value of the inclination, but may also correspond approximately, for example, within its range. The phase difference measured at two or more different positions on the screen can then be used to correct the estimated value of the inclination, rather than simultaneously correcting the estimated values ​​of the inclination and the pitch distance. This allows the inclination measurement to be decoupled from the pitch measurement at least to a certain extent. Specifically, the inclination can be determined first, which is largely independent of the pitch distance, and then the pitch distance can be determined based on the determined inclination. In this way, the inclination and the optional pitch distance can be determined more accurately and in a fast (faster) manner when determined in an iterative manner.

[0039] Exemplary experiments show that an order of magnitude improvement in accuracy is achieved compared to the method of Hwang et al., "3D Display Calibration by Visual Pattern Analysis." This makes the claimed system and method particularly suitable for high-resolution displays, such as 4K and 8K displays and higher resolution displays.

[0040] Optionally, the first phase and the second phase are each determined based on uniquely identifiable image content in a corresponding measurement area at a corresponding position on the display panel. In addition to determining the phase only at a selected position on the screen, the phase can also be determined in a measurement area defined around the selected position, for example based on an average or majority selection of uniquely identifiable image content in the corresponding measurement area. In this way, the phase can be determined more reliably than if the phase measurement was based on a single position only.

[0041] Optionally, the first position and the second position are vertically positioned at the upper half and the lower half of the display panel, respectively, preferably at the upper third and the lower third of the display panel, and more preferably at the upper quarter and the lower quarter of the display panel. Since the phase error caused by the error in the estimated value of the inclination and the pitch distance accumulates horizontally (e.g., from the first column to the last column of the display panel) and vertically (e.g., from the first row to the last row of the display panel), a larger error can be expected when the positions where the phase is measured are vertically spaced apart. By appropriately spacing the positions apart, the sensitivity to the error can be increased, thereby increasing the accuracy of determining the inclination.

[0042] Optionally, the first position and the second position are horizontally located in the left and right halves of the display panel, preferably, in the left third and right third of the display panel, and more preferably, in the left and right quarters of the display panel. Although the positions described in the previous paragraph are very suitable for inclinations between vertical and 45 degrees or up to the diagonal of the display, these positions may not be well suited for inclinations beyond this range and up to the horizontal. For such inclinations, different positions along the horizontal axis may be preferred, such as the positions on the left and right sides of the display panel described above.

[0043] Optionally, the inclination is iteratively determined by:

[0044] - If the difference between the first phase and the second phase exceeds a threshold:

[0045] adjusting the estimate of the tilt based on the difference;

[0046] repositioning the first position and / or the second position to adjust the offset to the estimated value of the adjusted tilt; and

[0047] re-determining the first phase and / or the second phase at the repositioned first position and / or second position;

[0048] - if the difference between the first phase and the second phase is below a threshold, outputting the estimate of the inclination as the determined inclination.

[0049] Optionally, the method includes, and the processing subsystem is further configured to, at one or more intermediate positions between the first position and the second position, determine one or more intermediate phases based on uniquely identifiable image content shown at the one or more intermediate positions, wherein the difference is a difference measurement applied to the first phase, the second phase, and the one or more intermediate phases. The accuracy of determining the tilt can be further improved by measuring the phase at more than two positions (e.g., three or more positions) on the screen. The above content relates to the following: For an autostereoscopic display with a repeating cone, the observed zero difference between the first phase and the second phase does not guarantee that the estimated tilt and the actual tilt are the same, because only the phase modulo the pitch distance can be measured. Typically, when the phase difference is measured horizontally, it can be assumed that the phase difference is less than one pitch distance, for example due to manufacturing requirements (e.g., the accuracy required for bonding). However, when the phase difference is determined between vertically offset positions, the phase difference may exceed the phase difference represented by one pitch distance. In this case, it may be advantageous to measure the phase at an intermediate position along the line from the first position to the second position. That is, when the estimated tilt matches the actual tilt, the same phase should be observed at all three positions. Therefore, a phase mismatch at all three positions may indicate an error in the estimate of the tilt. Furthermore, by selecting the third position asymmetrically between the first and second positions, i.e. not directly in the middle of the two positions, it is possible to avoid detecting a homodyne in cases where the actual phase difference is 2x the pitch distance. Preferably, the third position is located at a fraction n / d of the distance between the two positions, where d is still large even if all common factors in n and d have been removed. Optionally, more than three positions may be used to further improve the accuracy of determining the value of the tilt.

[0050] Optionally, the method includes, and the processing subsystem is further configured to determine the pitch distance based on the determined inclination. After determining the inclination, the pitch distance can be determined in a known manner using the determined inclination. That is, when generating a test pattern for determining the pitch difference, the determined inclination can be used in the phase calculation. In this way, the observed phase difference can be mainly due to the difference between the estimated value and the actual value of the pitch distance, rather than or to a lesser extent due to the difference between the estimated value and the actual value of the inclination. In this way, the pitch distance can be determined more accurately and, if determined iteratively, more quickly.

[0051] Optionally, determining the pitch distance includes:

[0052] - reallocating a phase for each display element based on the estimated value of the pitch distance and the determined tilt;

[0053] - based on the reallocated phases, generating further display data, the further display data comprising uniquely identifiable image content for each phase of a set of reallocated phases;

[0054] - outputting the further display data to the autostereoscopic display for display;

[0055] - capturing one or more further images of the display panel while the display data is displayed by the autostereoscopic display;

[0056] - determining the pitch distance of the optical element by analyzing the one or more further captured images, wherein the analyzing of the one or more further captured images comprises:

[0057] - at a first further position on the display panel, determining a first further phase based on a uniquely identifiable image content shown at the first further position;

[0058] - at a second further position on the display panel, determining a second further phase based on a uniquely identifiable image content shown at the second further position, wherein the second further position is offset from the first further position;

[0059] - determining a pitch distance of the optical element based on a difference between the first further phase and the second further phase.

[0060] Optionally, the offset between the first further position and the second further position differs horizontally from the inclination.

[0061] Optionally, the uniquely identifiable image content comprises a different grey scale and / or a different colour for each of the group of assigned phases.

[0062] Optionally, the method comprises, and the processing subsystem is further configured to, obtain the estimate of the tilt and / or the estimate of the pitch distance from a target specification for manufacturing an autostereoscopic display.

[0063] Optionally, the array of elongated optical elements is a lenticular lens sheet.

[0064] It will be appreciated by those skilled in the art that two or more of the above-mentioned embodiments, implementations, and / or alternative aspects of the invention may be combined in any way deemed useful.

[0065] Those skilled in the art may make modifications and variations to any system, any computer-implemented method, or any computer-readable medium based on the present description, which modifications and variations correspond to the described modifications and variations of another of the entities described. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which:

[0067] Figure 1 A 3D display is shown, the 3D display comprising a display panel and an array of optical elements configured to emit a series of views in each of a series of viewing cones;

[0068] Figure 2 shows a cross section of an array of optical elements;

[0069] Figure 3 The optical element array is shown to be tilted at an angle θ° relative to the display panel;

[0070] Figure 4 A system for determining the tilt of an autostereoscopic display is shown;

[0071] Figure 5 The deviation between the nominal value used to illustrate the pitch distance and the actual value affects the determination of the inclination;

[0072] Figure 6 shows determining the inclination using a measurement area shifted horizontally and vertically according to a nominal value of the inclination;

[0073] Figure 7 A method for determining the tilt of an autostereoscopic display is shown;

[0074] Figure 8 A computer readable medium containing data is shown.

[0075] It should be noted that the figures are purely diagrammatic and not drawn to scale.In the figures, elements corresponding to elements already described may have the same reference numerals.

[0076] List of reference numbers and abbreviations

[0077] The following list of reference numbers is provided to facilitate explanation of the drawings and should not be construed as limiting the claims.

[0078] 0-5 Views

[0079] 10-12 Vision cone

[0080] 20 Cone Series

[0081] 30 Stereo viewing position

[0082] 120 processor system

[0083] 122 Interlaced display data

[0084] 140 3D Display

[0085] 150 Display Panel

[0086] 160 Optical Element Array

[0087] 162 substrate

[0088] 164 microlenses

[0089] 200 System for determining the tilt of an autostereoscopic display

[0090] 220 Processing Subsystem

[0091] 240 camera interface

[0092] 250 Camera

[0093] 252 Camera Data

[0094] 260 Display output interface

[0095] 262 interlaced display data

[0096] 300,301 measurement window

[0097] 310 An inclined line passing through the center of the first measurement window

[0098] 312 inclined line passing through the center of the second measurement window

[0099] 314 center line

[0100] 400 Method for determining the tilt of an autostereoscopic display

[0101] 410 Assigning phase to display element

[0102] 420 Generate interlaced display data

[0103] 430 Display data is output to the display

[0104] 440 Capture Image

[0105] 450 Determines the tilt by analyzing the captured image

[0106] 452 Determine the first phase at the first position

[0107] 454 Determine the second phase at the second position

[0108] 456Determine the tilt based on the phase difference

[0109] 500 Computer readable medium

[0110] 510 Non-transient data DETAILED DESCRIPTION

[0111] Figure 1 A 3D display 140 is shown in the form of an autostereoscopic 3D display, which is configured to enable stereoscopic viewing of content displayed thereon without requiring the user to wear glasses. To enable stereoscopic viewing, the 3D display 140 includes a display panel 150, which typically includes an array of light emitting or light modulating elements. Elements of this type may also be referred to elsewhere as 'display elements'. The 3D display 140 is further shown to include an array of optical elements 160 for redirecting light generated by the display panel 150 into different directions. Although Figure 1 Although not explicitly shown in the figure, the optical element array 160 may include or consist of an array of elongated optical elements (such as lenticular elements). The display panel 150 may be appropriately arranged and cooperate with the optical element array 160 so that a series of views 0-5 are emitted from the 3D display 140 in the form of a cone 11, which is repeated, resulting in a series of cones 20 being emitted. In this regard, it is noted that for ease of illustration, Figure 1 The series of views is shown to include six views 0-5, and the 3D display 140 is shown to emit views 0-5 in the viewing cone 11 and two adjacent viewing cones 10, 12. However, it will be understood that the series of views may consist of any number of views, such as 2, 5, 10, 20, 30, etc., and that the repetition of the viewing cones may continue beyond the adjacent viewing cones 10, 12.

[0112] The series of views 0-5 may show a series of images. Thus, a viewer may perceive a corresponding one of the series of images when viewing one of the series of views 0-5. In terms of image content, the series of images may correspond to a camera facing a scene and in front of the scene and moving from left to right relative to the scene. In this way, a viewer at a viewing position 30 within the viewing cone 11 may perceive two different views. Figure 2 , 3 , and thereby a stereoscopic viewing of the scene can be obtained. It should be noted that a series of views may include partial views, or may be entirely composed of partial views.

[0113] It should be noted that the 3D display of the above configuration and the way of processing a series of images for display as a series of views are known per se. For example, US 6,064,424 discloses an autostereoscopic display device having a lenticular element and discusses the relationship between the display element and the lenticular element. US 6,064,424 also discloses that the lenticular elements can be arranged substantially in parallel at a pitch distance p and oriented with their main longitudinal axes at an inclination angle s relative to the display element array. The pitch distance (also referred to as 'pitch' elsewhere) and the inclination angle (also referred to as 'inclination' elsewhere) represent parameters characterizing the optical design of the 3D display 140. The inclination can be defined in a variety of ways, for example relative to the column direction of the display element array or relative to the row direction of the display element array.

[0114] Figure 2 1 shows a cross section of an optical element array 160. In this embodiment, the optical element array 160 is formed by a lenticular sheet including a substrate 162 having a profiled surface defining an array of lenticular elements. Each lenticular element 164 may be an elongated cylindrical lens element, wherein the optical element array is a one-dimensional array formed by parallel arranged lenticular elements. Figure 2 A cross section of the array 160 is shown parallel to the rows of the pixel grid of the display panel. It should be noted that such an optical element array 160 is known per se. It should also be noted that the optical element array 160 may also take any other suitable form, such as a plurality of multi-faceted lens elements, a two-dimensional array, etc. Figure 2 The pitch distance is further illustrated, where the symbol is 'w'. The pitch distance is often expressed in terms of the number of pixels or sub-pixels. The value of the pitch distance can be selected based on the size of the underlying pixels for a particular nominal viewing distance.

[0115] Figure 3 The optical element array is shown tilted relative to the display panel at a tilt angle of 0°. Note that the tilt angle can be defined in degrees, radians, or any other quantity, such as related to the number of horizontal and vertical display elements traversed by the optical element, which has an inverse tangent relationship to the tilt angle expressed in radians. In general, the tilt can be related to the angle at which the optical element is arranged relative to the pixel grid. Pitch and tilt together can be used to determine for each sub-pixel its phase relative to the lens, i.e., through which portion of the lens the underlying pixel grid is viewed by the viewer. As Figure 2As illustrated, phase can be defined, for example, to represent the horizontal position of a corresponding display element relative to an optical element that redirects light emitted by the corresponding display element, e.g., assuming a value of 0.0 all the way through the left side of the lens, a value of 0.5 at the center of the lens, and a value of 1.0 to the right of the lens, with all phase values ​​being between the two, understanding that the exact phase also depends on the viewing distance, lateral position, and the distance between the optical element array and the sub-pixel below.

[0116] The phase of a sub-pixel can determine the direction in which its light is focused by the lens, so the image content of the sub-pixel should be selected to match that direction. From the viewer's perspective, the viewer should see an image corresponding to his / her viewing direction across the entire screen. In other words, the viewer should observe image content of the same phase across the entire screen. The phase can be determined based on pitch and tilt. However, if the value of the pitch or tilt used for rendering deviates from the actual values ​​of the pitch and tilt, the viewer may not see a consistent image in which image content intended for different phases / directions becomes visible at different locations across the screen. Therefore, it is desirable to be able to characterize the tilt and optional pitch distance of an autostereoscopic display in an accurate manner.

[0117] In short, a system and method for determining the inclination and optional pitch distance of an autostereoscopic display is described below. For this purpose, the system and method generate and display a test pattern on the autostereoscopic display, capture one or more images of the displayed test pattern, and determine the inclination by determining a first phase at a first position in one or more captured images, determining a second phase at a second position in one or more captured images, and determining the inclination of an optical element based on the difference between the first phase and the second phase. Advantageously, the first position and the second position are horizontally and vertically offset from each other according to an assumed value of the inclination. This allows the inclination measurement to be less susceptible to the influence of the assumed pitch distance error. Specifically, the inclination can be determined first, which is largely independent of the pitch distance, and then the pitch distance can be determined based on the determined inclination. Thus, the inclination and the optional pitch distance can be determined more accurately and / or faster in an iterative process.

[0118] Figure 4A system 200 is shown for determining the tilt of an autostereoscopic display 140. The autostereoscopic display 140 may be, for example, of the type described elsewhere in this specification. The system 200 may include a display output interface 260 to the autostereoscopic display 140 and a camera interface 240 to a camera 250 positioned to capture an image of a display panel of the autostereoscopic display. The system 200 may also include a processing subsystem 220 configured to assign a phase to each display element based on an estimate of the pitch distance and an estimate of the tilt, generate display data 262 via a display output interface 260, the display data including uniquely identifiable image content for each phase in a set of assigned phases, output the display data 262 to the autostereoscopic display 140 via a camera interface for display, and when the display data is displayed by the autostereoscopic display, capture one or more images 252 of the display panel, and determine the tilt by analyzing the one or more captured images, wherein the analysis of the one or more captured images includes: determining a first phase at a first position on the display panel based on uniquely identifiable image content shown at the first position; determining a second phase at a second position on the display panel based on uniquely identifiable image content shown at the second position; and determining the tilt of the optical element based on a difference between the first phase and the second phase. Here, the first position and the second position can be horizontally and vertically offset from each other based on the estimate of the tilt, which may be advantageous for reasons as described in reference to Figures 5 and 6 Explained.

[0119] Figure 5The deviation between the nominal and actual values ​​of the pitch is used to illustrate that it affects the determination of the tilt. As has been explained elsewhere, it may be necessary to be able to characterize the tilt and optional pitch distance of an autostereoscopic display in an accurate manner. Such a characterization may, for example, involve rendering image content that looks different for all phases or at least a subset of phases, for example by changing the color as described in Jurk, Silvio & Kuhlmey, Mathias & Duckstein, Bernd & de la Barré, René. (2016). Electronic correction of misalignments between optical grid and pixel panel on autostereoscopic displays, or by using image content that is specific to a specific phase and changes over time. It may be preferred to be able to measure the phase locally in multiple areas that are sufficiently spaced. The phase measurements in these areas can then be compared to determine whether the phase changes on the screen and if so, how it changes, which indicates whether the values ​​of the tilt and pitch distance used to render the image content match the actual optics, that is, whether they match the actual values ​​of the tilt and pitch distance. For example, if the phase observed in a small area on the left side of the screen is the same as the phase observed on the right side of the screen, this can indicate that the estimate of the pitch distance is correct, or at least within a small range of the actual value of the pitch distance.

[0120] To characterize the pitch distance, a horizontal offset between the measurement regions may be used, since the difference between the actual pitch distance and an initially estimated pitch distance (which may be an assumed pitch distance, e.g., based on manufacturing or design specifications) results in a horizontal and non-constant deviation of the phase from its assumed value; the phase deviation may be spatially varying. For example, for an autostereoscopic display designed to have a pitch distance of 5 sub-pixels, but where the actual pitch distance differs from the designed pitch distance by 1%, say 5.01, after 500 sub-pixels, the phase may have cycled a full additional cycle of 5 sub-pixels, having gone through the entire range of phases. This phase deviation may be the same for each line, so a horizontal phase deviation pattern may appear. If the deviation is in tilt rather than pitch distance, a similar phase deviation pattern may appear, but now in the vertical direction. Therefore, it may be preferred to measure the phase at a horizontally offset position so that deviations in pitch distance can be characterized, while it may be preferred to measure the phase at a vertically offset position so that deviations in tilt can be characterized.

[0121] Continue to refer Figure 5, which shows the light emitting side of the autostereoscopic display 140, showing two measurement areas 300, 301, which are vertically offset and cover most of the height of the screen to obtain accuracy. The diagonal lines 310, 312 each represent an elongated optical element (e.g., a lens) that is tilted relative to the display panel. The left line 310 runs through the middle of the upper measurement area 300, while the right line 312 runs through the middle of the lower measurement area 301. The double arrows represent the horizontal distance between the elongated optical elements. For reference, a dashed line ('center line') with the same tilt is shown running through the center of the display panel. For example, if the phase in the two measurement areas 300, 301 is the same, this may mean that the distance between the elongated optical elements (the width of the double arrow) is an exact multiple of the pitch distance, and this multiple corresponds to the elongated optical element between the left line 300 and the right line 301. Changes in the pitch distance (e.g. due to the distance between consecutive elongated optical elements expanding or contracting around the center line) may cause the phase difference to no longer be an exact multiple of the pitch distance. In this case, any phase difference observed between the two measurement regions 300, 301 may be due to a mismatch in tilt or a mismatch in pitch distance.

[0122] Figure 6 The determination of the inclination using measurement areas that are offset horizontally and vertically according to a nominal value of the inclination is shown. The figure can be further explained as follows. As explained elsewhere, it can be more advantageous to decouple the measurement of the inclination from the measurement of the pitch distance. Advantageously, such a decoupling can be obtained when at least two measurement areas 300, 301 are positioned along an approximate direction of the inclination. This approximate direction can be referred to elsewhere as an initial estimate of the inclination and can be obtained, for example, from manufacturing or design specifications. In this way, the measurement areas 300, 301 can be positioned along a value (such as the initial estimate of the inclination) at said initial estimate of the inclination. Figure 6 By offsetting the measurement areas 300, 301, phase measurements can be obtained from the same optical element or the same group of optical elements, or almost the same optical elements if the deviation between the initial estimate of the inclination and the actual value of the inclination is large. When the measurement areas 300, 301 are positioned along such a line, a deviation of the pitch distance from its actual value may not lead to a (significant) phase difference between the top and bottom measurements. On the contrary, the phase difference measured between the two measurement areas may be only or mainly due to the deviation of the inclination from its actual value. In this way, the inclination measurement can be decoupled from the pitch measurement, because after first determining the inclination in the manner described above, the pitch distance can be determined, for example in a known manner.

[0123] As reference Figure 6 As described, there are various alternatives for measuring the inclination. For example, the measurement area can be taken as Figure 6Other shapes other than the rectangular shape shown in . In specific alternative embodiments, the measurement area may be circular, elliptical, etc. Another embodiment is that the size of the measurement area may be different. For example, the size of the measurement area may be such that the phase can be observed at multiple positions within the measurement area, and the observed phases can then be combined into one value, for example, by averaging or majority selection. However, the size may also be relatively small, so that the phase is only observed at a single measurement position. Yet another embodiment is that more than two measurement areas may be used, and the measurement areas may be located on the aforementioned tilt line. The relative distance between the measurement areas may be selected to be asymmetric and / or non-equidistant. For example, the third measurement area may be located at a fraction n / d of the distance between the other two measurement areas, where d is still large even if all common factors in n and d have been removed, and where the distance between the measurement areas is large enough to accurately measure different phases in each measurement area. In other embodiments, more than three measurement areas may be used to further improve the accuracy of determining the value of the tilt.

[0124] In general, the tilt can be determined iteratively, for example, if the difference between the first phase and the second phase exceeds a threshold, the estimated value of the tilt is adjusted based on the difference, the first position and / or the second position is relocated to adjust the offset to the adjusted estimated value of the tilt, and the first phase and / or the second phase is re-determined at the relocated first position and / or the second position. If the difference between the first phase and the second phase is below a threshold, the estimated value of the tilt can be output as the determined tilt.

[0125] With further reference to the test pattern shown on the autostereoscopic display, it is noted that the test pattern may take the form of a single image that may include uniquely identifiable image content for each phase of a set of assigned phases at corresponding locations on the display panel. However, alternatively, the test pattern may be a spatiotemporal or temporal test pattern in which the uniquely identifiable image content for the corresponding phases is distributed over different images. In such a (spatial) temporal test pattern, one image may include a uniquely identifiable test pattern for one phase, while other phases may not be uniquely identifiable, and another image may include a uniquely identifiable test pattern for another phase, while again other phases may not be uniquely identifiable. For example, a first image may include white image content for phase zero and black image content for all other phases, while a second image may include white image content for phase one and black image content for all other phases, while a third image may include white image content for phase two and black image content for all other phases, and so on. It will be appreciated that such a (spatial) temporal test pattern may also allow the systems and methods described in this specification to determine which phase is visible at a corresponding location on the display panel from a camera position.

[0126] Figure 7A method 400 of determining the tilt of an autostereoscopic display is shown. The method 400 may include: in a step entitled "Assigning phases to display elements", assigning 410 a phase to each display element based on an estimate of the pitch distance and an estimate of the tilt; in a step entitled "Generating interlaced display data", based on the assigned phases, generating 420 display data including uniquely identifiable image content for each phase of a set of assigned phases; in a step entitled "Outputting display data for display", outputting 430 the display data to the autostereoscopic display for display; and in a step entitled "Capturing images", capturing 440 one or more images of a display panel while the autostereoscopic display displays the display data. The method 400 may further include: in a step entitled "Determining the Tilt by Analyzing the Captured Images", determining 450 the tilt by analyzing the one or more captured images, wherein the analyzing of the one or more captured images includes: in a sub-step entitled "Determining a First Phase at a First Position", determining 452 a first phase at a first position on the display panel based on uniquely identifiable image content shown at the first position; in a sub-step entitled "Determining a Second Phase at a Second Position", determining 454 a second phase at a second position on the display panel based on uniquely identifiable image content shown at the second position, wherein the first position and the second position are horizontally and vertically offset from each other according to the estimated value of the tilt; and in a sub-step entitled "Determining the Tilt Based on Phase Difference", determining 456 the tilt of the optical element based on the difference between the first phase and the second phase. It will be understood that the steps of the method may be performed in any suitable order, such as consecutively, simultaneously, or a combination of both, but where applicable, subject to a necessary specific order, such as according to an input / output relationship.

[0127] In general, each entity described in this specification can be implemented as a device or apparatus, or implemented in a device or apparatus. The device or apparatus may include one or more (micro) processors that execute appropriate software. The processor of the corresponding entity may be embodied by one or more of these (micro) processors. The software implementing the functions of the corresponding entity may have been downloaded and / or stored in one or more corresponding memories, for example, volatile memory (such as RAM) or non-volatile memory (such as Flash). Alternatively, the processor of the corresponding entity may be implemented in a device or apparatus in the form of programmable logic (for example, a field programmable gate array (FPGA)). Any input and / or output interface may be implemented by the corresponding interface of the device or apparatus. Each functional unit of the corresponding entity may be implemented in the form of a circuit or circuit system. The corresponding entity may also be implemented in a distributed manner, for example involving different devices or apparatuses.

[0128] It should be noted that any method described in this specification, such as any method described in any claim, can be implemented on a computer as a computer-implemented method, dedicated hardware, or a combination of both. Instructions for a computer (such as executable code) can be stored on a computer-readable medium 500, such as Figure 8 As shown, for example, in the form of a series of machine-readable physical marks 510 and / or a series of elements having different electrical (e.g., magnetic) or optical properties or values. The executable code can be stored in a temporary or non-temporary manner. Examples of computer-readable media include memory devices, optical storage devices, integrated circuits, etc. Figure 8 An embodiment of a storage device 500 is shown.

[0129] Examples, embodiments or optional features, whether or not indicated as non-limiting, should not be construed as limiting the invention as claimed.

[0130] It should be noted that the embodiments mentioned above illustrate rather than limit the present invention, and those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference numerals placed in brackets should not be interpreted as limiting the claims. The use of the verb "comprise" and its variations does not exclude the presence of elements or stages other than those stated in the claims. The "one" or "an" in front of an element does not exclude the presence of multiple such elements. When before a column of elements or a group of elements, a statement such as "at least one of ..." indicates that all elements or any subset of elements are selected from the column or group. For example, the statement "at least one of A, B, and C" should be understood to include only A, only B, only C, both A and B, both A and C, both B and C, or all A, B, and C. The present invention can be implemented by means of hardware including several different elements and by means of appropriately programmed computers. In the device claims that list several devices, several of these devices can be implemented by the same hardware item. The fact that some measures are recorded in mutually different dependent claims does not indicate that the combination of these measures cannot be used to benefit.

Claims

1. A method (400) for determining a tilt of an autostereoscopic display, the autostereoscopic display comprising: - a display panel comprising an array of display elements; as well as - an array of elongated optical elements for redirecting light emitted by the display elements into mutually different directions, the optical elements being arranged substantially parallel to each other at a pitch distance and oriented with a main longitudinal axis of the optical element at an inclination relative to the array of display elements; The method comprises: - assigning (410) a phase to each display element based on the estimated value of the pitch distance and the estimated value of the tilt, wherein the phase indicates the direction in which light emitted by the respective display element is redirected; - based on the assigned phases, generating (420) display data, the display data comprising uniquely identifiable image content for each phase in a set of assigned phases; - outputting (430) the display data to the autostereoscopic display for display; - capturing (440) one or more images of the display panel while the display data is displayed by the autostereoscopic display; - determining (450) the tilt by analyzing the one or more captured images, wherein the analyzing of the one or more captured images comprises: - determining (452) a first phase at a first location on the display panel based on uniquely identifiable image content shown at the first location; - determining (454) a second phase at a second location on the display panel based on uniquely identifiable image content shown at the second location, wherein the first location and the second location are horizontally and vertically offset from each other according to the estimated value of the tilt; and - determining (456) a tilt of the optical element based on a difference between the first phase and the second phase.

2. The method (400) of claim 1, wherein the first phase and the second phase are each determined based on uniquely identifiable image content in a corresponding measurement area at a corresponding position on the display panel.

3. The method (400) of claim 2, wherein the first phase and the second phase are each determined based on a selection of an average or a majority of uniquely identifiable image content in the respective measurement area.

4. The method (400) according to any one of claims 1 to 3, wherein the first position and the second position are respectively located at: - the upper half and the lower half of the display panel, preferably located in the upper third and the lower third of the display panel, more preferably located in the upper quarter and the lower quarter of the display panel; or - The left half and the right half of the display panel, preferably located in the left third and the right third of the display panel, more preferably located in the left quarter and the right quarter of the display panel.

5. The method (400) according to any one of claims 1 to 4, wherein the inclination is iteratively determined by: - If the difference between the first phase and the second phase exceeds a threshold: adjusting the estimate of the tilt based on the difference; repositioning the first position and / or the second position to adjust the offset to an estimated value of the adjusted tilt; and re-determining the first phase and / or the second phase at the relocated first position and / or second position; - if the difference between the first phase and the second phase is below a threshold, outputting the estimate of the inclination as the determined inclination.

6. The method (400) of claim 5, further comprising: At one or more intermediate positions between the first position and the second position, one or more intermediate phases are determined based on uniquely identifiable image content shown at the one or more intermediate positions, wherein the difference is a difference measurement applied to the first phase, the second phase and the one or more intermediate phases.

7. The method (400) of claim 6, wherein the one or more intermediate positions are asymmetrically located between the first position and the second position.

8. The method (400) according to any one of claims 1 to 7, further comprising determining the pitch distance based on the determined inclination.

9. The method (400) of claim 8, wherein determining the pitch distance comprises: - reallocating a phase for each display element based on the estimated value of the pitch distance and the determined tilt; - based on the reallocated phases, generating further display data, the further display data comprising uniquely identifiable image content for each phase of a set of reallocated phases; - outputting the further display data to the autostereoscopic display for display; - capturing one or more further images of the display panel while the display data is displayed by the autostereoscopic display; - determining the pitch distance of the optical element by analyzing the one or more further captured images, wherein the analyzing of the one or more further captured images comprises: - at a first further position on the display panel, determining a first further phase based on a uniquely identifiable image content shown at the first further position; - at a second further position on the display panel, determining a second further phase based on a uniquely identifiable image content shown at the second further position, wherein the second further position is offset from the first further position; - determining a pitch distance of the optical element based on a difference between the first further phase and the second further phase.

10. The method (400) of claim 9, wherein the offset between the first further position and the second further position is horizontally different from the inclination.

11. The method (400) of any one of claims 1 to 10, wherein the uniquely identifiable image content comprises a different grayscale and / or a different color for each of the group of assigned phases.

12. The method (400) according to any one of claims 1 to 11, further comprising obtaining the estimate of the tilt and / or the estimate of the pitch distance from a target specification for manufacturing the autostereoscopic display.

13. The method (400) of any one of claims 1 to 12, wherein the array of elongated optical elements is a lenticular lens sheet.

14. A transitory or non-transitory computer-readable medium (500) comprising data (510) representing instructions arranged to cause a processor system to perform a method according to any one of claims 1 to 13.

15. A system (200) for determining the tilt of an autostereoscopic display (140), the autostereoscopic display comprising: - a display panel (150), the display panel comprising an array of display elements; as well as - an array (160) of elongated optical elements for redirecting light emitted by the display elements into mutually different directions, the optical elements being arranged substantially parallel to each other at a pitch distance and oriented with their main longitudinal axes at an inclination relative to the array of display elements; The system comprises: - a display output interface (260) to said autostereoscopic display; - a camera interface (240) to a camera positioned to capture an image of a display panel of the autostereoscopic display; - a processing subsystem (220), the processing subsystem being configured to: - assigning a phase to each display element based on the estimated value of the pitch distance and the estimated value of the tilt, wherein the phase indicates the direction in which light emitted by the respective display element is redirected; - based on the assigned phases, generating display data, the display data comprising uniquely identifiable image content for each phase in a set of assigned phases; - outputting the display data (262) to the autostereoscopic display for display via the display output interface; - capturing, via the camera interface, one or more images of the display panel while the display data is displayed by the autostereoscopic display (252); - determining the inclination by analyzing the one or more captured images, wherein the analyzing of the one or more captured images comprises: - at a first position (300) on the display panel, determining a first phase based on uniquely identifiable image content shown at the first position; - at a second position (301) on the display panel, determining a second phase based on uniquely identifiable image content shown at the second position, wherein the first position and the second position are horizontally and vertically offset from each other according to the estimated value of the tilt; and - determining a tilt of the optical element based on a difference between the first phase and the second phase.

Images