Reducing crosstalk in glasses-free 3D display devices

Abstract

The present invention relates to a lenticular device comprising an array of elongated lenticular elements arranged parallel to each other, wherein an interference structure exists at the interface between two adjacent lenticular elements. The interference structure can extinguish light passing through it by destructive interference. Depending on the lens shape (convex or concave lenticular element), the interference structure is located on the valleys (in the case of a convex lenticular element) or the ridges (in the case of a concave lenticular element). The interference structure solves the problem that the lens shape is imperfect in the valleys and ridges (because valleys and ridges are not infinitely sharp, but are actually somewhat rounded). This imperfection causes crosstalk when the lens is applied to a naked-eye stereoscopic display device. The interference structure solves this problem and reduces crosstalk.

Description

Technical Field

[0001] The present invention relates to a lenticular device and a naked-eye stereoscopic display including such a lenticular device. The present invention also relates to a method for reducing crosstalk in a naked-eye stereoscopic display device.

Background Art

[0002] A naked-eye stereoscopic display having a lenticular lens enables a viewer to perceive a three-dimensional image 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.

[0003] A lenticular lens is composed of semi-cylindrical microlenses (lenticulas) arranged parallel to each other. In a naked-eye stereoscopic display, the lenticular lens is provided on an array of (sub) pixels, and each lenticula is associated with a specific arrangement of (sub) pixels. By appropriately controlling these (sub) pixels, the naked-eye stereoscopic display can simultaneously direct the left-eye image to the viewer's left eye and the right-eye image to the viewer's right eye. The resulting stereoscopic image can then appear to be in front of and / or behind the display. In this setting, an eye tracker is often used to ensure that light is accurately directed to each eye.

[0004] However, in conventional naked-eye stereoscopic display devices, light that reaches an unintended eye still exists at a small but significant rate. The effect is that there is a ghost image of the right-eye image in the left-eye image and vice versa. Therefore, the viewer will experience a degraded stereoscopic image. This phenomenon is known as "crosstalk".

[0005] To date, much effort has been made to reduce, or even completely eliminate, crosstalk in this type of display. For example, it is possible to identify the pixels that contribute the most to crosstalk and then correct the output of those pixels in a specific way. However, this has undesirable side effects such as a decrease in resolution and / or display intensity. It also requires valuable processor capacity. Other solutions focus on improving eye-tracking accuracy or reducing latency in the eye tracker.

[0006] A specific cause of crosstalk is the imperfect shape of the lenticular lens. For example, valleys between adjacent convex lenticulars that are slightly rounded or even flat at their deepest points allow light from (sub)pixels to pass through these valleys without being refracted, or to refract the light in the wrong direction. However, efforts to improve the "sharpness" of the valleys have not yielded satisfactory results so far. For concave lenticulars, a similar problem can arise if the steep ridges between adjacent concave lenticulars are slightly rounded rather than razor-sharp. [Overview of the Initiative]

[0007] Therefore, an object of the present invention is to find a solution to the occurrence of crosstalk, in particular a solution that does not exhibit one or more of the aforementioned side effects. In particular, an object of the present invention is to address crosstalk caused by imperfections in lenticular lenses, such as rounded or flat valleys. Another object is to provide a solution that is less complex than those known in the art.

[0008] More generally, the objective of the present invention is to improve the viewing experience for viewers of glasses-free 3D displays.

[0009] It has been found that one or more of these objectives can be achieved by applying specific modifications to the lenticular lenses of naked-eye stereoscopic displays.

[0010] Therefore, the present invention is - Extending in the x-direction and the y-direction perpendicular to the x-direction, - A lenticular device (1) having a profile surface (2) having a profile in the z direction perpendicular to the profile surface (2), The profile surface (2) defines an array of elongated lenticular elements (3) that have a lenticular length in the y direction and are arranged parallel to each other. The lenticular device (1) relates to a profile surface (2) which includes an interference structure (8) at the interface between two adjacent lenticular elements (3), wherein the interference structure (8) can extinguish light passing through the interference structure (8) by destructive interference.

[0011] The present invention further comprises a naked-eye stereoscopic display device (10), - A display panel (7) having an array of display pixel elements for generating a display output, - The present invention further relates to a naked-eye stereoscopic display device (10) comprising a lenticular device (1) as described above, wherein the lenticular device (1) is a lenticular lens provided on a display panel (7).

[0012] The present invention further relates to a method for reducing crosstalk in a glasses-free stereoscopic display device, including the use of destructive optical interference. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic perspective view of a conventional lenticular device. [Figure 2] This is a schematic cross-sectional view of an ideal lenticular device. [Figure 3] This is a schematic cross-sectional view of a conventional lenticular device. [Figure 4] This is a schematic enlarged view of the cross-sectional view in Figure 3. [Figure 5] This is a microscopic image of a portion of a conventional lenticular microscope. [Figure 6] This is a schematic cross-sectional view of the lenticular device according to the present invention. [Modes for carrying out the invention]

[0014] The elements in the figures are shown for simplification and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the figures may be exaggerated relative to others to help improve understanding of the various exemplary embodiments of the invention. For example, the relative dimensions of different components of the naked-eye stereoscopic display device cannot be derived from the drawings. This relates, for example, to the dimensions of the interference structure relative to the dimensions of the lenticular elements, or to the slope of the surfaces of lenticular elements that come into contact with adjacent lenticular elements (defining valleys or ridges). It also cannot be derived how the different dimensions of the interference structure itself relate to each other (e.g., ridge height, ridge width, and valley width).

[0015] Furthermore, terms such as “first,” “second,” etc., in this specification and claims are generally used to distinguish similar elements, if any, and are not necessarily used to describe a sequential or chronological order.

[0016] In the context of this invention, the term “viewer” means a person who consumes, specifically, can see, the content presented by the naked-eye stereoscopic display device. Throughout this text, references to the viewer are made by masculine words such as “he,” “him,” or “his.” This is solely for the purpose of conciseness and clarity, and it is understood that feminine words such as “she” and “her” are equally applicable.

[0017] In the context of this invention, the term "crosstalk" refers to a physical, observable, and measurable phenomenon in a naked-eye stereoscopic display that occurs when a display output generated for one eye is also experienced by another eye.

[0018] In the context of the present invention, the term "interference" means a range of phenomena related to the superposition of visible light waves. A specific phenomenon, which is the extinction of light when one wave cancels out another when the two waves have a phase difference of 1 / 2λ, is called "destructive interference".

[0019] The lenticular device according to the present invention is an object including a profile surface, that is, a surface having a surface relief or profiling.

[0020] For the purpose of clearly explaining the present invention, an x - direction, a y - direction, and a z - direction are defined with respect to the lenticular device according to the present invention. Here, the y - direction is a direction perpendicular to the x - direction, and the z - direction is a direction perpendicular to the plane (x, y plane) defined by the x - direction and the y - direction. The surface of the lenticular device extends in the x - direction and the y - direction as a whole, regardless of the surface relief extending in the z - direction.

[0021] The profile surface has an elongated shape in the y - direction and is formed as an array of lenticular elements that define the 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 each other. Here, the parallel arrangement of the lenticular elements means that no other profile - surface elements of equivalent dimensions (i.e., dimensions equivalent to those of the lenticular elements, for example, dimensions within one digit) exist between adjacent lenticular elements. When lined up on an array of display pixel elements, such an array of lenticular elements is a known means for directing the outputs from different pixel elements in different directions so that a stereoscopic image can be displayed to the viewer. The lenticular elements also have a lenticular width in addition to the lenticular length. This term is defined as the distance between two edges on both sides of the lenticular element at any location along the y - direction measured in the x - direction.

[0022] The lenticular length of the lenticular element is typically the same as the distance between two opposing edges of the array of lenticular elements, which is strongly related to the dimensions of the autostereoscopic display device for which the lenticular device is intended. For example, the lenticular length is in the range of 5 to 100 cm, or in the range of 20 to 80 cm.

[0023] The lenticular width of the lenticular element is usually in the range of 80 to 500 μm, and all the lenticular elements in the array typically have the same lenticular width.

[0024] Regarding the description of the lenticular device of the present invention, the expression that the lenticular elements are "arranged" is used only to describe a specific appearance or look in which a plurality of lenticular elements are grouped together, rather than a configuration of separate parts, since the plurality of lenticular elements are not arranged as separate objects. The lenticular device according to the present invention consists, in principle, of one single part, and as a result, all the different lenticular elements are parts of the same piece of material. Optionally, the lenticular lens comprises a coating and / or a casing.

[0025] Figure 1 is a schematic perspective view of a known lenticular device (1) in the art. It includes a profile surface (2) that defines an array of elongated lenticular elements (3). The above surface extends in the x-direction and the y-direction, while the profiling extends in the z-direction. Two adjacent lenticular elements (3) together define a valley (4) that is between both adjacent lenticular elements (3).

[0026] Figure 2 is a schematic cross-sectional view of an ideal version of the lenticular device (1) in Figure 1. The cross-section lies in the x,z plane, according to the x and z directions defined in Figure 1. This figure shows how light rays (6, 6a) emitted by the display panel (7) are refracted by the lenticular elements (3). This lenticular device is ideal in that the valley (4) between the two lenticular elements (3) is infinitely sharp and therefore does not allow light to pass through without refraction. Nor does it refract light in the wrong direction. This is shown by the light ray (6a) that enters the lenticular device from below the valley (4) and is still refracted by each lenticular element (3). This means that this lenticular device does not exhibit crosstalk, which is the result of valleys with rounded valleys or valleys with flat bottoms. However, to date, such an ideal lenticular device has not yet been provided and therefore it remains merely a theoretical possibility.

[0027] Figure 3 is a schematic cross-sectional view of a realistic version of the lenticular device (1) of Figure 1, obtained when the best conventional efforts are made to manufacture the lenticular device. The cross-section lies in the x,z plane, according to the x and z directions defined in Figure 1. However, Figure 3 shows how such conventional manufacturing efforts result in an imperfect lenticular lens, because it allows light rays (6a) emitted by the display panel (7) and entering the lenticular device from below the valley (4) to pass through the valley (4) without being refracted. Thus, viewers of naked-eye stereoscopic display devices with such lenticular devices may experience considerable crosstalk.

[0028] Figure 4 is a schematic enlarged view of the valley (4) in Figure 3 in the same x, z plane, showing how the light ray (6) is refracted by the lenticular element (3) and how the light ray (6a) passes through the valley (4) without being refracted.

[0029] Figure 5 shows 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 profile plane (2) of the lenticular element (3) is visible, as are the valleys (4) on either side of it. The bottom of the valleys (4) is flat, and its shape may cause substantial crosstalk to be experienced by viewers of naked-eye stereoscopic displays with such lenticular devices.

[0030] In the lenticular lens of the present invention, destructive interference is used to eliminate the display output transmitted by the lens between two adjacent lenticular elements. Otherwise, this display output would cause crosstalk if the lenticular lens is part of a naked-eye stereoscopic display device. The above elimination is achieved by providing the lenticular lens (or a mold from which a lenticular lens can be obtained) with an interference structure between two adjacent lenticular elements that can perform such destructive interference. This means that all surfaces between two adjacent lenticular elements (i.e., surfaces that are not part of the two adjacent lenticular elements themselves) are, in principle, capable of quenching light passing through the surface by destructive interference.

[0031] Figure 6 is also a schematic enlarged view of the valley (4) shown in Figure 3 (in the same x, z plane), but differs in that, according to the present invention, an interference structure (8) is provided in the valley (4). The diagram illustrates how a light ray (6a) travels through the flat portion of the valley (4) and through the interference structure (8). In this way, the light ray (6a) is extinguished by the interference structure (8) and cannot contribute to any crosstalk.

[0032] Interference structures are typically formed by relief structures that include structural features having a relief height in the z direction. The preferred value of the relief height varies depending on the desired wavelength to be extinguished and on the difference in refractive index between the lenticular lens material and the medium surrounding the interference structure (e.g., air or liquid crystal medium). In order to truly produce the required interference, the structural features must have appropriate dimensions. The concept of interference structures and the design options for interference structures to achieve specific desired interference of electromagnetic radiation are well known to those skilled in the art. One example is the extinguishing of visible light, as applied in this invention. Therefore, those skilled in the art will know how to arrive at structural features with appropriate dimensions through routine experiments and calculations according to standard optical theory. Furthermore, those skilled in the art will be able to do so without inventive effort.

[0033] Such a relief structure is a surface relief of the profile surface (2) of the lenticular device (1). This means that the relief structure is superimposed on (part of) the profile surface.

[0034] For example, the structural feature may have a relief height in the range of 400–4,000 nm, particularly in the range of 600–3,000 nm. Alternatively, it may be in the range of 450–2,000 nm, or 550–2,500 nm, particularly in the range of 500–1,500 nm, or 700–1,800 nm. Since a particular relief height is effective in extinguishing light of only one wavelength (or a small band of wavelengths around the central wavelength), different structural features with different relief heights may exist so that the relief structure can extinguish light of various wavelengths.

[0035] The structural features of the relief structure (which functions as an interference structure) are typically elongated in the y-direction. They may extend, for example, along the entire lenticular length of the lenticular element.

[0036] Alternatively, the interference structure may be formed by multiple domains with different refractive indices within the lens material of the lenticular device, and as a result, an actual relief structure with relief height in the z direction may not be present. Those skilled in the art will know how to achieve this type of interference structure for the purpose of light extinction according to the present invention through routine experiments and calculations in accordance with standard optical theory. Furthermore, those skilled in the art will be able to do so without inventive effort.

[0037] The parallel arrangement of lenticular elements should be understood as an arrangement in which adjacent lenticular elements are located side by side. In certain embodiments, adjacent lenticular elements may be provided intentionally separated from each other beyond the separation resulting from the manufacturing of the imperfect lenticular lens as described above. As a result, a relatively large (x-direction) flat surface is obtained between the two lenticular elements. However, given that there are no other profile surface elements of equivalent dimensions between adjacent lenticular elements, these lenticular elements are still adjacent to each other. Furthermore, despite the intentional separation between adjacent lenticular elements, these lenticular elements are still considered to be arranged side by side.

[0038] In the case of a convex lenticular element, the valley between two adjacent lenticular elements is more like a flat area at a lower position than a V-shape. In the case of a concave lenticular element, the ridge between two adjacent lenticular elements is more like a flat area at a higher position than a sharp ridge.

[0039] Such a flat surface has a width extending in the x-direction and a length extending in the y-direction, where 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. Typically, it is 9% or less, for example, in the range of 1-5% or 2-7%.

[0040] If a lenticular apparatus having such an arrangement is prepared by engraving lenticular elements onto a flat surface of a plate, then the flat surface between two adjacent lenticular elements corresponds in that case to a surface that has not been treated by engraving.

[0041] Such flat surfaces are unthinkable in conventional lenticular devices for naked-eye stereoscopic displays due to the enormous amount of crosstalk they generate. However, in this invention, this crosstalk can be neutralized simply by extending the interference structure across the entire flat surface. In other words, lens designs with flat surfaces between lenticular elements, which may be desirable for certain reasons, should not be rejected outright as unfeasible due to the associated crosstalk.

[0042] Therefore, in one embodiment, the profile surface (2) includes a flat surface region between the two lenticular elements (3), the flat surface region extends in the x and y directions, and the interference structure is located on the flat surface region.

[0043] The lenticular elements in the lenticular device of the present invention typically have either a convex (circular) or concave (hollow) shape, meaning that such a lenticular device typically includes only one of these types of lenticular elements.

[0044] The interface between two adjacent lenticular elements is indicated by a sharp change in the slope of the profile plane within a cross-sectional plane defined by the x and z directions (i.e., the x, z plane). If the lenticular elements have a convex shape, the interface between the two lenticular elements can be considered as a valley (usually a V-shaped valley) extending in the y direction of the profile plane. In that case, the interference structure exists in the valley between the two adjacent lenticular elements.

[0045] When lenticular elements have a concave shape, the interface between two lenticular elements can be considered as a ridge (usually a sharp ridge) extending in the y-direction on the profile plane. In this case, the interference structure is located on the ridge between two adjacent lenticular elements, typically at the top of the ridge, for example, in the highest region in the z-direction.

[0046] The lenticular device of the present invention is often a lenticular lens, for example, a device that can refract light as it passes through the lens. In such cases, it is composed of a transparent material (at least transparent to the wavelength of visible light) that can function as a lenticular lens.

[0047] However, the lenticular apparatus of the present invention does not necessarily have to be a lenticular lens. It may also be made of an opaque material. This is often the case when the lenticular apparatus is designed to act as a lenticular mold for the manufacture of lenticular lenses. Such a manufacturing process includes, for example, contacting a profile surface with a fluid curable resin, and then curing the curable resin to obtain a solid transparent lens material.

[0048] Such lenticular molds, despite the fact that they typically cannot function as lenses (due to being opaque materials), still fall within the scope of the present invention because they possess the same lenticular surface as a true lenticular lens (corresponding only in negative relief). Such lenticular devices of the present invention can, in principle, be made from any material suitable for acting as a mold in the molding process.

[0049] Therefore, in one embodiment, the lenticular apparatus of the present invention is a mold for preparing a lenticular lens. Such a mold includes an interference structure, which, when transferred to the lenticular lens in opposite relief by a molding process, provides the lenticular lens with an interference structure that can extinguish light passing through the interference structure by destructive interference.

[0050] Therefore, the lenticular element of the apparatus of the present invention may not function as a lenticular lens in some examples, but in practice, it has the same profile as a true lenticular lens, i.e., when the apparatus is made of an opaque material. In such cases, the shape of the lenticular element can be identified with the shape of a true lenticular lens.

[0051] The profile surface of the lenticular device (1) according to the present invention may be a faceted surface. This means that the profile surface (2) is composed of different planar facets that are at angles to each other. In principle, such a faceted surface does not have curved surfaces. The image shown in Figure 5 includes, for example, a lenticular element (3) having a faceted surface.

[0052] The minimum number of facets for a particular lenticular element is 2. This corresponds to a prism-shaped lenticular element. The number of facets for a lenticular element may be greater, for example, in the range of 3 to 20 or 5 to 16. In particular, the number may be 5, 7, 9, 11, 13, 15, or 17.

[0053] If the profile surface is a faceted surface, the interface between two facets can also produce crosstalk. This can occur if the interface is not perfectly sharp and includes a curved region. To resolve this, such an interface may include an interference structure that can extinguish light passing through the interference structure by destructive interference. Such an interference structure may have the same properties as an interference structure located in the valley or ridge between two adjacent lenticular elements, as described above.

[0054] Furthermore, other types of lenses with lens defects, particularly lenses with sharp surface features on their profile lens surface, such as Fresnel lenses, can also benefit from such interference structures.

[0055] Another type of lens that can benefit from interference structures is the distributed refractive index lens, commonly known as a GRIN lens. In these lenses, particularly voltage-driven GRIN liquid crystal lenses, sharp transitions between different regions with different refractive indices are rarely achieved.

[0056] The present invention further comprises a naked-eye stereoscopic display device (10), - A display panel (7) having an array of display pixel elements for generating a display output, - The present invention relates to a naked-eye stereoscopic display device (10) that includes a lenticular device (1) as described above, which is a lenticular lens.

[0057] The array of display pixel elements in the display panel (7) is typically lined with a lenticular lens such that the lenticular lens covers at least a portion of the array. The lenticular elements (3) of the lenticular device (1) allow the display outputs from different display pixel elements to be directed in different spatial directions within the field of view of the naked-eye stereoscopic display device (10) in order to enable the display of a stereoscopic image composed of a left-eye image and a right-eye image.

[0058] The present invention further relates to a method for reducing crosstalk in a naked-eye stereoscopic display device, which involves the use of the phenomenon of destructive interference of light. In particular, the method may include the use of an interference structure that causes crosstalk and can extinguish light passing through the interference structure by destructive interference.

[0059] The same considerations as those detailed above regarding the interference structure in the lenticular device according to the present invention apply to all the features and characteristics of such interference structures.

Claims

1. A lenticular apparatus (1) having a profile surface (2), wherein the profile surface (2) is - Extending in the x-direction and the y-direction perpendicular to the x-direction, - Having a profile in the z direction perpendicular to the profile surface (2), The profile surface (2) defines an array of elongated lenticular elements (3) having a lenticular length in the y direction and arranged parallel to each other. The lenticular device (1) includes an interference structure (8) at the interface between two adjacent lenticular elements (3) on the profile surface (2), wherein the interference structure (8) can extinguish light passing through the interference structure (8) by destructive interference.

2. The lenticular device (1) according to claim 1, wherein the interference structure (8) is formed by a relief structure that includes a structural feature having a relief height in the z direction.

3. The lenticular apparatus (1) according to claim 2, wherein the aforementioned structural features have a relief height in the range of 500 to 2,500 nm.

4. The lenticular apparatus (1) according to claim 2 or 3, wherein the structural features have a length in the y-direction in the range of 1 to 1,000 μm and a width in the x-direction in the range of 1 to 50 μm.

5. The lenticular device (1) according to any one of claims 2 to 4, wherein the relief structure includes different structural features having different relief heights in the z direction so that the relief structure can extinguish light of various wavelengths.

6. The lenticular device (1) according to claim 1, wherein the interference structure (8) is formed by a plurality of domains having different refractive indices within the lens material of the lenticular device.

7. The lenticular apparatus (1) according to any one of claims 1 to 6, wherein the profile surface (2) defines a flat surface region between two lenticular elements (3), the flat surface region having a width extending in the x direction and a length extending in the y direction, the width being at least 1% of the lenticular width, the interference structure (8) is located on the flat surface region, and the lenticular width is defined as the distance between the two edges on both sides of the lenticular element at any location along the y direction, measured in the x direction.

8. The lenticular device (1) according to any one of claims 1 to 7, wherein the lenticular element (3) is convex, and the interference structure (8) is located in the valley between the two lenticular elements (3).

9. The lenticular device (1) according to any one of claims 1 to 7, wherein the lenticular element (3) is concave, and the interference structure (8) is located on the ridge between the two lenticular elements.

10. The lenticular apparatus (1) is a mold for manufacturing a lenticular lens, the mold includes an interference structure, the interference structure (8) is provided to the lenticular lens, the interference structure (8) being transferred to the lenticular lens material in opposite relief by a molding process, thereby causing light passing through the interference structure (8) to be extinguished by destructive interference, according to any one of claims 1 to 9.

11. The lenticular device (1) according to any one of claims 1 to 10, wherein the lenticular element (3) is faceted such that the profile surface (2) is composed of different planar facets having angles to each other.

12. The lenticular device (1) according to claim 11, wherein the lenticular element (3) is prism-shaped, and each lenticular element (3) has two facets.

13. The lenticular device (1) according to claim 11 or 12, wherein the interface between two facets of the lenticular element (3) includes a further interference structure, the further interference structure is capable of quenching light passing through it by destructive interference.

14. The lenticular device (1) is a lenticular lens, as described in any one of claims 1 to 13.

15. A naked-eye stereoscopic display device (10), - A display panel (7) having an array of display pixel elements for generating a display output, A lenticular device (1) according to claim 14, provided on the display panel (7), wherein the lenticular element (3) can direct the display outputs from different display pixel elements in different spatial directions within the field of view of the naked-eye stereoscopic display device (10) in order to enable the display of a stereoscopic image composed of a left-eye image and a right-eye image.

16. A method for reducing crosstalk in a glasses-free stereoscopic display device, including the use of destructive interference of light.

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