Crosstalk reduction in an autostereoscopic display device

Abstract

The invention relates to a lenticular device comprising an array of elongate lenticular elements that are arranged parallel to one another, wherein an interference structure is present at an interface between two neighboring lenticular elements. The interference structure is capable of causing light that passes through the interference structure to extinct by destructive interference. Depending on the lens shape (convex or concave lenticular elements), the interference structure is present in a valley (in case of convex lenticular elements) or on a ridge (in case of concave lenticular elements). The interference structure solves the problem that the lens shape is imperfect in valleys and at ridges, as they are in practice not infinity sharp but a bit rounded. This gives rise to crosstalk when the lens is applied in an autostereoscopic display device. The interference structure solves this problem and reduces the crosstalk.

Description

[0001] CROSSTALK REDUCTION IN AN AUTOSTEREOSCOPIC DISPLAY DEVICE

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a lenticular device and to an autostereoscopic display comprising such a lenticular device. The invention also relates to a method for reducing crosstalk in an autostereoscopic display device.

[0004] BACKGROUND

[0005] Autostereoscopic displays with a lenticular lens allow a viewer to perceive three-dimensional images without a dedicated eyewear device such as glasses or a headset. These displays are playing an increasingly important role in virtual reality and augmented reality applications.

[0006] A lenticular lens is composed of semi-cylindrical micro-lenses (lenticulars) that are arranged parallel to one another. In an autostereoscopic display, the lenticular lens is provided over an array of (sub-)pixels, each lenticular being associated with a particular arrangement of (sub-)pixels. By properly controlling these (sub)-pixels, the autostereoscopic display is capable of simultaneously directing a left eye image to a left eye of the viewer and a right eye image to a right eye of the viewer. The resulting stereoscopic image may then appear to be in front of the display and / or behind the display. In this set-up, an eye tracker is often used to ensure that light is more accurately directed to the respective eye.

[0007] Yet, in conventional autostereoscopic devices there is still a small but significant proportion of light that arrives at the eye for which it was not intended. The effect is that in the image for the left eye a ghost image of the right eye image is present and vice versa. The viewer thus experiences a compromised stereoscopic image. This phenomenon is known as ‘crosstalk’.

[0008] To date, many efforts have been deployed to reduce or even completely cancel crosstalk in this type of displays. For example, it is possible to identify the pixels that make the largest contribution to the crosstalk and to then modify their pixel output in a specific way. This however has undesired side-effects such as a reduced resolution and / or a reduced display intensity. Moreover, this requires valuable processor capacity. Other solutions are focused on improving eye tracking accuracy or on reducing latency in the eye tracker.

[0009] A particular cause of crosstalk is an imperfect shape of the lenticular lens. For example, valleys between neighboring convex lenticulars that are a bit rounded or even flat at their deepest point allow light of (sub-)pixels to pass through these valleys without being refracted, or they cause light to be refracted in a wrong direction. Efforts to improve the ‘sharpness’ of the valleys have however not yielded satisfactory results. For concave lenticulars, a similar problem may occur when the steep ridges between neighboring concave lenticulars are not razor sharp but a bit rounded.

[0010] SUMMARY OF THE INVENTION

[0011] It is therefore an object of the present invention to find a solution to the appearance of crosstalk, in particular one that does not exhibit one or more of the abovementioned side-effects. It is in particular an object to combat crosstalk that is caused by imperfections in the lenticular lens, such as rounded or flat valleys. It is also an object to provide a solution that is less complicated than solutions known in the art.

[0012] It is more generally an object of the present invention to improve the viewing experience of a viewer of an autostereoscopic display.

[0013] It has now been found that one or more of these objects can be reached by applying a certain modification to a lenticular lens of an autostereoscopic display.

[0014] Accordingly, the present invention relates to a lenticular device (1 ) having a profiled surface (2) which

[0015] - extends in an x-direction and in an y-direction perpendicular to the x-direction; and

[0016] - has a profiling in a z-direction perpendicular to the profiled surface (2), wherein the profiled surface (2) defines an array of elongate lenticular elements (3) which have a lenticular length in the y-direction and are arranged parallel to one another; wherein the profiled surface (2) comprises an interference structure (8) at an interface between two neighboring lenticular elements (3), which interference structure (8) is capable of causing light that passes through the interference structure (8) to extinct by destructive interference.

[0017] The present invention further relates to an autostereoscopic display device (10), comprising

[0018] - a display panel (7) having an array of display pixel elements for producing a display output;

[0019] - a lenticular device (1 ) as described hereabove, wherein the lenticular device (1 ) is a lenticular lens which is provided over the display panel (7).

[0020] The present invention further relates to a method for reducing crosstalk in an autostereoscopic display device, comprising the use of destructive light interference.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 schematically displays a perspective view of a conventional lenticular device.

[0023] Figure 2 schematically displays a cross-sectional view of an ideal lenticular device.

[0024] Figure 3 schematically displays a cross-sectional view of a conventional lenticular device.

[0025] Figure 4 schematically displays a close-up of the cross-sectional view of Figure 3.

[0026] Figure 5 displays a microscopic image of a portion of a conventional lenticular device.

[0027] Figure 6 schematically displays a cross-sectional view of a lenticular device according to the invention.

[0028] DETAILED DESCRIPTION OF THE INVENTION

[0029] Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in a figure may be exaggerated relative to other elements to help improve understanding of various exemplary embodiments of the present invention. For example, the relative dimensions of the different components of an autostereoscopic display device cannot be derived from the figures. This concerns for example the dimensions of the interference structure relative to those of the lenticular elements; or the steepness of surfaces of lenticular elements where neighboring lenticular elements meet (defining a valley or a ridge). Neither can it be derived how the different dimensions of the interference structure itself are related to one another (e.g. height of the ridges, width of the ridges, and width of the valleys).

[0030] Further, the terms “first”, “second”, and the like in the present description and claims, if any, are generally used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order.

[0031] In the context of the invention, by the term ‘viewer’ is meant a person who can consume, in particular view, content presented by an autostereoscopic display device. Throughout the text, references to the viewer will be made by male words like ‘he’, ‘him’ or ‘his’. This is only for the purpose of conciseness and clarity, and it is understood that female words like ‘she’, and ‘her’ equally apply.

[0032] In the context of the invention, by the term ‘crosstalk’ is meant the physical, observable and measurable phenomenon of an autostereoscopic display that occurs when display output generated for a particular eye is also experienced by the other eye.

[0033] In the context of the invention, by the term ‘interference’ is meant a range of phenomena associated with the superposition of waves of visible light. A particular phenomenon is the extinction of light when one wave cancels another wave when the two waves have a1 / 2 A phase difference, which is termed ‘destructive interference’.

[0034] A lenticular device according to the invention is an object that comprises a profiled surface, i.e. a surface with a surface relief or a profiling.

[0035] For the purpose of clearly describing the invention, an x-direction, an y-direction and a z-direction are defined for a lenticular device according to the invention. Herein, the y-direction is perpendicular to the x-direction and the z-direction is perpendicular to a plane defined by the x-direction and the y-direction (an x,y-plane). The surface of the lenticular device as a whole extends in the x-direction and the y-direction, irrespective of the surface relief that extends in the z-direction. The profiled surface is shaped as an array of lenticular elements that have an elongate shape in the y-direction, defining a lenticular length in the y-direction. The lenticular elements are arranged side-by-side in the x-direction and extend in the y-direction parallel to one another. Herein, by a side-by-side arrangement of lenticular elements is meant that other profiled surface elements of comparable dimensions (i.e. dimensions comparable to those of the lenticular elements, for example a dimension that is within one order of magnitude) are absent between neighboring lenticular elements. When lined on an array of display pixel elements, such an array of lenticular elements is a known means to direct the outputs from different pixel elements in mutually different directions so as to enable that a stereoscopic image is displayed to a viewer. Besides the lenticular length, the lenticular elements also have a lenticular width. This term is defined as the distance between two edges on either side of a lenticular element, anywhere along the y-direction, measured in the x-direction.

[0036] The lenticular length of the lenticular elements is typically similar to the distance between two opposing edges of the array of the lenticular elements, which is strongly related to the dimensions of an autostereoscopic display device for which the lenticular device is intended. For example, the lenticular length is in a range of 5-100 cm, or in a range of 20-80 cm.

[0037] The lenticular width of the lenticular elements is usually in a range of 80-500 pm, wherein all lenticular elements in an array typically have identical lenticular widths.

[0038] For the description of a lenticular device of the invention, the expression that lenticular elements are ‘arranged’ is merely used to describe a certain look or appearance of the lenticular elements together rather than a composition of separate parts, since the lenticular elements are not arranged as separate objects. The lenticular device according to the invention in principle consists of one single part, so that the different lenticular elements are all part of the same piece of material. Optionally, the lenticular lens is provided with a coating and / or a casing.

[0039] Figure 1 schematically displays a perspective view of a lenticular device (1 ) known in the art. It comprises a profiled surface (2) that defines an array of elongate lenticular elements (3). The surface extends in the x-direction and in the y-direction, while the profiling extends in the z-direction. Two neighboring lenticular elements (3) together define a valley (4) that is in between both neighboring lenticular elements (3).

[0040] Figure 2 schematically displays a cross-sectional view of an ideal version of the lenticular device (1 ) of Figure 1 . The cross-section is in an x,z-plane, in accordance with the x- and z-direction as defined in Figure 1 . The Figure shows how the light rays (6, 6a), emitted by the display panel (7), are refracted by the lenticular elements (3). The lenticular device is ideal in that the valley (4) between two lenticular elements (3) is infinitely sharp and therefore does not allow light to pass unrefracted. Neither does it cause light to be refracted in a wrong direction. This is illustrated by the light rays (6a), which enter the lenticular device from beneath the valley (4) and are still refracted by the respective lenticular element (3). This means that the lenticular device does not exhibit crosstalk that is the result of a round valley or a valley with a flat bottom. To date, such ideal lenticular device has however not yet been provided and it is therefore merely a theoretical possibility.

[0041] Figure 3 schematically displays a cross-sectional view of a realistic version of the lenticular device (1 ) of Figure 1 , obtained when best conventional efforts are made to manufacture a lenticular device. The cross-section is in an x,z-plane, in accordance with the x- and z-direction as defined in Figure 1 . Figure 3 however demonstrates how such conventional manufacturing efforts lead to an imperfect lenticular lens, as the light rays (6a) emitted by the display panel (7) that enter the lenticular device from beneath the valley (4) are allowed to pass the valley (4) without becoming refracted. A viewer of an autostereoscopic display device with such a lenticular device may therefore well experience crosstalk.

[0042] Figure 4 schematically displays a close-up of the valley (4) of Figure 3 in the same x,z-plane, illustrating how the light rays (6) are refracted by the lenticular element (3) and how the light rays (6a) pass the valley (4) without becoming refracted.

[0043] Figure 5 displays a microscopic image of a portion of a conventional lenticular device, recorded with a microscope (Olympus OLS4000 LEXT confocal laser scanning microscope). In the microscopic image, the profiled surface (2) of a lenticular element (3) is visible, just as the valleys (4) on either side of it. The bottom of the valleys (4) is flat, which shape may cause a viewer of an autostereoscopic display device with such a lenticular device to experience a substantial crosstalk.

[0044] In a lenticular lens of the present invention, destructive interference is used to eliminate display output that is transmitted by the lens between two neighboring lenticular elements. This display output would otherwise cause crosstalk in the event that the lenticular lens is part of an autostereoscopic display device. This is achieved by providing the lenticular lens (or a mold from which the lenticular lens may be obtained) with an interference structure between two neighboring lenticular elements that is capable of performing such destructive interference. This means that all of the surface between two neighboring lenticular elements (viz. surface that is not part of the two neighboring lenticular elements themselves) is in principle provided with the capability to extinct light that passes through the surface by destructive interference.

[0045] Figure 6 schematically displays also a close-up of the valley (4) as displayed Figure 3 (and in the same x,z-plane), but with the difference that an interference structure (8) is provided in the valley (4), in accordance with the present invention. It is illustrated how the light rays (6a) travel through the flat portion of the valley (4) and through the interference structure (8). In doing so, the light rays (6a) extinct due to the interference structure (8) and cannot contribute to any crosstalk.

[0046] The interference structure is typically formed by a relief structure comprising structural features with a relief height in the z-direction. A preferred value of the relief height depends on the desired wavelengths to extinct and on the difference in refractive index of lenticular lens material and of medium surrounding the interference structure (e.g. air or a liquid crystal medium). In order to truly effect the required interference, the structural features need to have appropriate dimensions. The concept of interference structures and the design options of interference structures to achieve a particular, desired, interference of electromagnetic radiation is well-known to the skilled person. One example thereof is the extinction of visible light, as applied in the present invention. A person skilled in the art will therefore know how to arrive at structural features with the appropriate dimensions by routine experimentation and calculations according to standard optical theory. He will also be able to do so without exerting an inventive effort.

[0047] Such relief structure is a surface relief of the profiled surface (2) of the lenticular device (1 ). This means that the relief structure is a structure that is superimposed upon (parts of) the profiled surface.

[0048] For example, the structural features have a relief height in a range of 400-4,000 nm, in particular in a range of 600-3,000 nm. It may also be in a range of 450-2,000 nm or in a range of 550-2,500 nm, in particular in a range of 500- 1 ,500 nm or in a range of 700-1 ,800 nm. Since a particular relief height is effective in the extinction of light of only one wavelength (or a small band of wavelengths around a central wavelength), different structural features with different relief heights may be present, so that the relief structure is capable of causing light of various wavelengths to extinct.

[0049] The structural features in the relief structure (functioning as interference structure) are usually elongated in the y-direction. They may for example extend along the entire lenticular length of the lenticular elements.

[0050] The interference structure may alternatively also be formed by multiple domains within lens material of the lenticular device that have different refractive indices, so that an actual relief structure with a relief height in the z-direction may be absent. A person skilled in the art will know how to arrive at this type of interference structure for the purpose of light extinction in accordance with the present invention by routine experimentation and calculations according to standard optical theory. He will also be able to do so without exerting an inventive effort.

[0051] The parallel arrangement of lenticular elements is to be understood as an arrangement wherein neighboring lenticular elements are lying side-by-side. In a particular embodiment, neighboring lenticular elements may be provided at an intentional separation from one another that exceeds the separation resulting from an imperfect lenticular lens manufacture as described above. The result is a flat surface of a relatively large width (x-direction) between two lenticular elements. Yet, given the absence of other profiled surface elements of comparable dimensions between neighboring lenticular elements, these lenticular elements are still neighboring one another. Also, despite the intended separation between to neighboring lenticular elements, these lenticular elements are still regarded as being arranged side-by-side.

[0052] In case of convex lenticular elements, a valley between two neighboring lenticular elements is then more like a low-lying plateau than like a V-shape. In case of concave lenticular elements, a ridge between two neighboring lenticular elements is more like a high-lying plateau than like a sharp ridge.

[0053] Such flat surface then has a width that extends in the x-direction and a length that extends in the y-direction, wherein the width is for example at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, at least 6%, at least 8% or at least 10% of the lenticular width. Usually, it is 9% or less, for example in a range of 1-5% or in a range of 2-7%.

[0054] When a lenticular device with such arrangement would have been prepared by engraving the lenticular elements in a flat surface of a plate, then the flat surface between two neighboring lenticular elements would correspond to surface that had not been treated by the engraving.

[0055] Such flat surface would be unthinkable in conventional lenticular devices for autostereoscopic display devices, because of the enormous amount of crosstalk that would result from them. With the present invention, however, this crosstalk can be neutralized by just extending the interference structure over the entire flat surface. In other words, a lens design with flat surfaces between lenticular elements, which for certain reasons may be desired, is not to be rejected beforehand as a viable option because of the crosstalk that is associated with it.

[0056] Thus, in an embodiment, the profiled surface (2) comprises a flat surface region between two lenticular elements (3), which flat surface region extends in the x-direction and the y-direction, and wherein the interference structure is present on the flat surface region.

[0057] The lenticular elements in a lenticular device of the invention typically have either a convex (round) shape or a concave (hollow) shape, meaning that such a lenticular device typically comprises only one of these types of lenticular elements.

[0058] The interface between two neighboring lenticular elements that are lying side-by-side is indicated by an abrupt change of the slope of the profiled surface in a cross-sectional plane defined by the x-direction and the z-direction ( / .e. the x,z-plane). In case the lenticular elements have a convex shape, then the interface between two lenticular elements can be regarded as a valley that extends in the y- direction of the profiled surface (usually a V-shaped valley). The interference structure is then present in a valley between two neighboring lenticular elements.

[0059] In case the lenticular elements have a concave shape, then the interface between two lenticular elements can be regarded as a ridge (usually a sharp ridge) that extends in the y-direction on the profiled surface. The interference structure is then present on a ridge between two neighboring lenticular elements, typically on top of the ridge, e.g. at its most elevated areas in the z-direction.

[0060] A lenticular device of the invention is often a lenticular lens, e.g. a device that is capable of refracting light when the light passes through the lens. In such case, it is made of a transparent material that allows it to function as a lenticular lens (transparent to at least the wavelengths of visible light).

[0061] A lenticular device of the invention is however not necessarily a lenticular lens. It may also be of a non-transparent material. This is often the case when the lenticular device is designed to act as a lenticular mold for the production of a lenticular lens. Such production process for example comprises contacting the profiled surface with a fluid curable resin followed by curing the curable resin to yield a solid and transparent lens material.

[0062] Despite the fact that such lenticular molds are usually not capable to act as a lens (because they are of a non-transparent material), they still fall within the scope of the present invention since they have the same lenticular surface as true lenticular lenses (only corresponding in negative relief thereto). Such lenticular device of the invention may in principle be made from any material that is suitable to act as a mold in a molding process.

[0063] Accordingly, in an embodiment, a lenticular device of the invention is a mold for preparing a lenticular lens. Such mold then comprises an interference structure, which, when transferred in opposite relief to a lenticular lens by a molding process, provides the lenticular lens with an interference structure that is capable of causing light that passes through the interference structure to extinct by destructive interference. Thus, the lenticular elements of a device of the invention may in some instances not function as a lenticular lens, yet indeed have the same profiling as a true lenticular lens, viz. in case the device is of a non-transparent material. In such case, the shape of the lenticular elements can be equated with the shape of a true lenticular lens.

[0064] The profiled surface of a lenticular device (1 ) according to the invention may be a facetted surface. This means that the profiled surface (2) is composed of different planar facets that have an angle with respect to one another. In principle, there are no curved surfaces in such facetted surface. The image displayed in Figure 5 for example comprises lenticular elements (3) that have a facetted surface.

[0065] The smallest number of facetted surfaces of a particular lenticular element is two. This corresponds to a lenticular element of a prismatic shape. The number of facets of a lenticular element may also be higher, for example in a range of 3-20 or in a range of 5-16. Their number is in particular 5, 7, 9, 11 , 13, 15 or 17.

[0066] When the profiled surface is a facetted surface, then an interface between two facets may also give rise to crosstalk. This may occur when the interface is not perfectly sharp but comprises a curved surface area. To solve this, such interface may comprise an interference structure capable of causing light that passes through the interference structure to extinct by destructive interference. Such interference structure may have the same characteristics as an interference structure that is positioned in a valley or on a ridge between two neighboring lenticular elements, as described hereabove.

[0067] Also other types of lenses with lens imperfections may benefit from such an interference structure, especially lenses with sharp surface features in their profiled lens surface, such as Fresnel lenses.

[0068] Another type of lenses that may benefit from an interference structure are graded index lenses, commonly known as GRIN lenses. With these lenses, in particular with voltage-driven GRIN liquid crystal lenses, sharp transitions between different domains with different refractive indices can hardly be realized.

[0069] The invention further relates to an autostereoscopic display device (10), comprising - a display panel (7) having an array of display pixel elements for producing a display output;

[0070] - a lenticular device (1 ) as described above, wherein the lenticular device (1 ) is a lenticular lens.

[0071] The array of display pixel elements of the display panel (7) is typically lined with the lenticular lens, so that the lenticular lens covers at least a part of the array. The lenticular elements (3) of the lenticular device (1 ) are capable of directing the display output from different display pixel elements to different spatial directions within a field of view of the autostereoscopic display device (10) to allow a display of an stereoscopic image that is composed of a left eye image and a right eye image.

[0072] The invention further relates to a method for reducing crosstalk in an autostereoscopic display device, comprising the use of the phenomenon of destructive interference of light. The method may in particular comprise the use of an interference structure that is capable of causing light that is responsible for the crosstalk and that passes through the interference structure, to extinct by destructive interference.

[0073] For all features and characteristics of such interference structure, the same considerations apply as those elaborated hereabove for the interference structure in a lenticular device according to the invention.

Claims

CLAIMS1 . Lenticular device (1 ) having a profiled surface (2) which- extends in an x-direction and in an y-direction perpendicular to the x-direction; and- has a profiling in a z-direction perpendicular to the profiled surface (2), wherein the profiled surface (2) defines an array of elongate lenticular elements (3) which have a lenticular length in the y-direction and which elongate lenticular elements (3) are arranged parallel to one another and side-by-side; wherein the profiled surface (2) comprises an interference structure (8) at an interface between two neighboring lenticular elements (3), which interference structure (8) is capable of causing light that passes through the interference structure (8) to extinct by destructive interference.

2. Lenticular device (1 ) according to claim 1 , wherein the interference structure (8) is formed by a relief structure comprising structural features with a relief height in the z-direction.

3. Lenticular device (1 ) according to claim 2, wherein the structural features have a relief height in a range of 500-2,500 nm.

4. Lenticular device (1 ) according to claim 2 or 3, wherein the structural features have a length in the y-direction that is in a range of 1-1 ,000 pm and a width in the x-direction that is in a range of 1-50 pm.

5. Lenticular device (1 ) according to any one claims 2-4, wherein the relief structure comprises different structural features with different relief heights in the z-direction, so that the relief structure is capable of causing light of various wavelengths to extinct.

6. Lenticular device (1 ) according to claim 1 , wherein the interference structure (8) is formed by multiple domains within lens material of the lenticular device that have different refractive indices.

7. Lenticular device (1 ) according to any one of claims 1 -6, wherein the profiled surface (2) defines a flat surface region between two lenticular elements (3), which flat surface region has a width that extends in the x-direction and a length that extends in the y-direction, wherein the width is at least 1% of the lenticular width and wherein the interference structure (8) is present on the flat surface region, wherein the lenticular width is defined as a distance between two edges on either side of a lenticular element, anywhere along the y-direction, measured in the x-direction.

8. Lenticular device (1 ) according to any one claims 1-7, wherein the lenticular elements (3) are of a convex shape and wherein the interference structure (8) is present in a valley between two lenticular elements (3).

9. Lenticular device (1 ) according to any one of claims 1 -7, wherein the lenticular elements (3) are of a concave shape and wherein the interference structure (8) is present on a ridge between two lenticular elements.

10. Lenticular device (1 ) according to any one claims 1-9, wherein the lenticular device (1 ) is a mold for preparing a lenticular lens and wherein the mold comprises an interference structure, which, when transferred in opposite relief to a lenticular lens material by a molding process, provides the lenticular lens with an interference structure (8) that is capable of causing light that passes through the interference structure (8) to extinct by destructive interference.11 . Lenticular device (1 ) according to any one of claims 1 -10, wherein the lenticular elements (3) are facetted in that the profiled surface (2) is composed of different planar facets that have an angle with respect to one another.

12. Lenticular device (1 ) according to claim 11 , wherein the lenticular elements (3) are of a prismatic shape, each lenticular element (3) comprising two facets.

13. Lenticular device (1 ) according to claim 11 or 12, wherein an interface between two facets of a lenticular element (3) comprises a further interference structure that is capable of causing light that passes through the further interference structure to extinct by destructive interference.

14. Lenticular device (1 ) according to any one of claims 1 -13, wherein the lenticular device (1 ) is a lenticular lens.

15. Autostereoscopic display device (10), comprising- a display panel (7) having an array of display pixel elements for producing a display output;- a lenticular device (1 ) as claimed in claim 14, which is provided over the display panel (7), the lenticular elements (3) being capable of directing the display output from different display pixel elements to different spatial directions within a field of view of the autostereoscopic display device (10) to allow a display of an stereoscopic image that is composed of a left eye image and a right eye image.

16. Method for reducing crosstalk in an autostereoscopic display device, comprising the use of destructive interference of light.

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