FIELD OF THE INVENTION

The invention relates to an autostereoscopic display comprising a display panel for providing a display output composed of pixels in an array and an optical stack comprising lenticular means arranged at a display side of the display panel. The invention also relates to the optical stack as such. The invention further relates to an electronic device comprising such autostereoscopic display. The invention also relates to a method of manufacturing such autostereoscopic display

BACKGROUND ART

3D displays, and in particular televisions equipped with 3D displays, are increasingly popular amongst consumers, as they provide a viewer with stereoscopic perception of depth. So- termed autostereoscopic displays provide said stereoscopic perception of depth without needing the viewer to wear polarized or shutter-based glasses. For that purpose, optical components are used, such as lenticular lens arrays (or in general lenticular means), which enable the display to emit a viewing cone from each given point on the 3D display, the viewing cone comprising at least a left view and a right view of a scene. This enables the viewer to see a different image with each eye when positioned accordingly within the viewing cone. Certain autostereoscopic displays, sometimes referred to as automultiscopic displays, provide multiple views of the same scene, rather than only a left and a right view. This allows the viewer to assume multiple positions in the viewing cone, i.e., move left-right in front of the display, while still obtaining a stereoscopic perception of the scene.

Examples of such autostereoscopic displays are described in a paper by C. van Berkel et al entitled "Multiview 3D - LCD" published in SPIE Proceedings Vol. 2653, 1996, pages 32 to 39 and in GB-A-2196166. In these examples the autostereoscopic display comprises a matrix LC (liquid crystal) display panel which has rows and columns of pixels (display elements) and which acts as a spatial light modulator to modulate light directed therethrough from a light source. The display panel can be of the kind used in other display applications, for example computer display screens for presenting display information in two dimensional form. A lenticular sheet, for example in the form of a molded or machined sheet of polymer material, overlies the output side of the display panel with its lenticular elements, comprising (semi) cylindrical lens elements, extending in the column direction with each lenticular element being associated with a respective group of two, or more, adjacent columns of display elements and extending in a plane that runs parallel with the display element columns. In an arrangement in which each lenticule is associated with two columns of display elements, the display panel is driven to display a composite image comprising two 2D sub-images vertically interleaved, with alternate columns of display elements displaying the two images, and the display elements in each column providing a vertical slice of the respective 2D (sub) image. The lenticular sheet directs these two slices, and corresponding slices from the display element columns associated with the other lenticules, to the left and right eyes respectively of a viewer in front of the sheet so that, with the sub-images having appropriate binocular disparity, the viewer perceives a single stereoscopic image. In other, multi-view, arrangements, in which each lenticule is associated with a group of more than two adjacent display elements in the row direction and corresponding columns of display elements in each group are arranged appropriately to provide a vertical slice from a respective 2-D (sub-) image, then as a viewer's head moves a series of successive, different, stereoscopic views are perceived for creating, for example, a look-around impression.

In view of the need for the lenticular elements to be accurately aligned with the display pixels, it is customary for the lenticular screen to be mounted over the display panel in a permanent manner so that the position of the lenticular elements is fixed in relation to the array of pixels.

Autostereoscopic displays of above kind may be used for various applications, for example in home or portable entertainment, medical imaging and computer-aided design (CAD).

Autostereoscopic displays are preferably designed in such a way that the structure of the pixels combined with the structure of the lenticular means and/or other optical elements does not result in viewer clearly noticing (repeating) patterns when viewing the autostereoscopic display.

An example of such a pattern is the so-termed banding effect. The banding effect is at least in part caused by the lenticular means in a manner as follows. As the sub-pixels (and thus the pixels) of the display panel are not entirely adjacent, there is an area between the sub-pixels that emits no or hardly any light. This area is known as black matrix or guard band(s). If a viewer moves along an autostereoscopic display, different sub-pixels are visible, together forming a view. However, also the guard bands between sub pixels are then seen in an alternating way, which causes said banding effect. Intuitively, banding may be understood as a moire effect of the interaction between a grid formed by the guard bands and a grid formed by the lenticular means.

INTRODUCTION OF THE INVENTION

The inventors have recognized that present designs and solutions for autostereoscopic displays are still unsatisfactory in that, when viewing the autostereoscopic display, the user can often clearly notice patterns such as those caused by the above-mentioned banding effect.

It is an object of the invention to reduce such noticeable patterns in autostereoscopic displays and/or to reduce the visibility of such noticeable patterns to the viewer.

A first aspect of the invention provides an autostereoscopic display comprising i) a display panel providing a display output composed of pixels in an array and ii) an optical stack arranged at a display side of the display panel, the optical stack comprising:

a lenticular means comprising a profiled surface, the profiled surface defining an array of lenticular elements for directing the outputs from respective groups of said pixels in mutually different directions so as to enable a stereoscopic image to be perceived; and

an anti-banding layer arranged for effecting a variation in the refraction of light along a periphery of each lenticular element.

Embodiments are defined in the dependent claims.

An optical stack in accordance with the first aspect of the invention comprises a lenticular means such as one known per se from the field of autostereoscopic displays. According to the present invention, the optical stack comprises an anti-banding layer which effects a variation in the refraction of light along a periphery of each lenticular element. Accordingly, the light which is (re)directed by the lenticular element is differently refracted along the periphery of the lenticular element. It has been found that such variation in refraction along the periphery of each lenticular element causes noticeable patterns such as those caused by the banding effect to be less visible to a viewer. Advantageously, the autostereoscopic display provides a better picture quality to the viewer.

In an embodiment, the anti-banding layer is arranged on the profiled surface of the lenticular means, the anti-banding layer comprises a main layer and an adhesive layer for adhering the anti-banding layer to the profiled surface, and the anti-banding layer is arranged such on the profiled surface that the adhesive layer adheres to a protruding portion of each of the lenticular elements while keeping clear of depressions between adjacent ones of the lenticular elements so as to form a gap between adjacent ones of the lenticular elements and the anti-banding layer.

Accordingly, the anti-banding layer is attached discontinuously to the lenticular means, namely by adhering to the protruding portion of each of the lenticular elements while keeping clear of the portion(s) bordering the depressions between adjacent ones of the lenticular elements. Such discontinuous attachment provides a first type of refraction at the interface between the anti-banding layer and the lenticular element, with the first type of refraction being determined by the refractive indexes of the lenticular element and the anti-banding layer, and a second type of refraction at the interface between the lenticular element and the gap, with the second type of refraction being determined by the refractive indexes of the lenticular element and the medium inside the gap, e.g., air. This embodiment provides an efficient way of effecting the variation in the refraction of light along the periphery of each lenticular element, namely by the aforementioned way of attaching the anti- banding layer discontinuously to the lenticular means. It may therefore not be needed to modify the optical properties of the anti-banding layer itself to effect said variation in the refraction of light.

A further advantage is that this type of discontinuous attachment may be conveniently realized by pressing the anti-banding layer onto the lenticular means with a pressing surface, since, upon such pressing, the anti-banding layer firstly attaches to the protruding portion of each lenticular element. The gaps between the anti-banding layer and the lenticular means may then be generated and/or maintained by controlling the pressing pressure with which the pressing surface presses the anti-banding layer onto the lenticular means, e.g., by limiting said pressure to a maximum value.

In a further embodiment, the anti-banding layer is arranged for effecting the variation in the refraction of light by being attached to a first portion of each lenticular element while keeping clear of a second portion of each lenticular element. This embodiment also establishes a discontinuous attachment of the anti-banding layer to each lenticular element, thereby providing an efficient way of effecting the variation in the refraction of light along a periphery of each lenticular element.

In a further embodiment, the first portion is a central portion centered around an optical axis of each lenticular element, and the second portion is a peripheral portion at a side of the central portion. The central portion of each lenticular element is typically a most protruding portion of the lenticular element. Accordingly, the discontinuous attachment may be conveniently realized by pressing the anti-banding layer onto the lenticular means with a pressing surface.

In a further embodiment, the anti-banding layer is arranged for effecting the variation in the refraction of light based on at least one of: a variation in material of the anti-banding layer, a variation in thickness of the anti-banding layer, the anti-banding layer being locally deformed, and the anti-banding layer being locally subjected to mechanical stress. In addition or alternatively to providing a discontinuous attachment of the anti-banding layer to the lenticular means, the anti- banding layer may itself be adapted to establish the variation in the refraction of light. The aforementioned arrangements are well suited to establish said variation in the refraction of light.

In a further embodiment, the optical stack further comprises a top layer arranged above the profiled surface so as to substantially avoid contact with the profiled surface, the top layer comprises a downward facing surface which faces the display panel, the anti-banding layer is arranged on the downward facing surface of the top layer, and the anti-banding layer comprises a main layer and an adhesive layer for adhering the anti-banding layer to the downwards facing surface. This embodiment provides an alternative way of including the anti-banding layer in the autostereoscopic display, namely by attaching it to a top layer of the autostereoscopic display, such as a protective top layer, rather than attaching it directly to the lenticular means.

A further aspect of the invention provides a method of attaching or applying an anti- banding layer to a lenticular means, wherein the lenticular means comprises a profiled surface, wherein the profiled surface defines an array of lenticular elements, wherein the anti-banding layer comprises a main layer and an adhesive layer for adhering the anti-banding layer to the profiled surface, and wherein the method comprises pressing the anti-banding layer onto the lenticular means with a pressing surface. Pressing the anti-banding layer onto the lenticular means with a pressing surface is a convenient way of discontinuously attaching the anti-banding layer to the lenticular means, as the anti-banding layer will first attach to a protruding portion of each lenticular element while initially keeping clear of depressions between adjacent ones of the lenticular elements.

In an embodiment, the method further comprises:

pressing the anti-banding layer with the adhesive layer onto the lenticular means with the pressing surface; and

during the pressing, controlling a pressing pressure so as to generate and/or maintain gaps between the anti-banding layer and the lenticular means at depressions in the profiled surface between adjacent ones of the lenticular elements.

By controlling the pressing pressure, it can be avoided that the anti-banding layer is seamlessly applied to the lenticular means, e.g., by expelling all air between the lenticular means and the anti-banding layer. This may otherwise occur if a too high pressure is applied when applying the anti-banding layer onto the lenticular means with the pressing surface.

In a further embodiment, the anti-banding layer is a flexible layer, and the method further comprises pressing the anti-banding layer with a substantially rigid, i.e., non-deformable, pressing surface onto the lenticular means. By using a non-deformable pressing surface, it can be avoided that a flexible anti-banding layer is seamlessly applied to the lenticular means, e.g., by expelling all air between the lenticular means and the anti-banding layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings, Fig. 1 shows an autostereoscopic display for enabling stereoscopic viewing of content displayed thereon without a need for the user to wear glasses;

Fig. 2a shows a cross-sectional view of an optical stack of the autostereoscopic display, the optical stack comprising an anti-banding layer and lenticular means;

Fig. 2b shows a zoomed-in view of the anti-banding layer and the lenticular means;

Fig. 3 shows a cross-sectional view of a further optical stack which may be arranged on the light generating portion of the autostereoscopic display; and

Fig. 4 shows a lenticular element and illustrates the anti-banding layer effecting a variation in the refractive index along a periphery of the lenticular element.

It should be noted that items which have the same reference numbers in different Figures, have the same structural features and the same functions, or are the same signals. Where the function and/or structure of such an item has been explained, there is no necessity for repeated explanation thereof in the detailed description.

DESCRIPTION OF THE INVENTION

Fig. 1 shows an autostereoscopic display 140 for enabling stereoscopic viewing of content displayed thereon without a need for the user to wear glasses. The autostereoscopic display 140 comprises a light generating portion 142 which is typically comprised of an array of light emitting or light modulating elements. For example, the light generating portion 142 may formed by a display panel such as an Liquid Crystal Display (LCD) panel or an Organic Light Emitting Display (OLED) panel, which are known per se. The autostereoscopic display 140 further comprises an optical stack 150 comprising lenticular means for redirecting light generated by the light generating portion 142 into different directions. The light generating portion 142 may be suitably arranged and cooperative with the lenticular means such that a series of, e.g., views 0-5 are emitted from the autostereoscopic display 140 in the form of a viewing cone 104 as well as repeated viewing cones 102, 106.

Fig. 1 further shows a display processor 120 being connected to the autostereoscopic display 140 for providing a series of images 122 to the autostereoscopic display 140. The autostereoscopic display 140 may be arranged for adjacently emitting said series of images 122 in the form of the series of views 0-5. Thus, the viewer will perceive, when viewing one of the series of views 0-5, a respective one of the series of images 122. The series of images 122 may correspond to a camera facing a scene comprised in 3D image data and moving from left to right in front of, and relative to, said scene. Hence, a viewer positioned 1 10 within the viewing cone 104 and perceiving two different ones 0, 1 of the series of views obtains stereoscopic viewing of said scene.

It is noted that autostereoscopic displays of the above configuration, and the manner of processing a series of images 122 for display as the series of views 104, are in itself known. For example, US 6,064,424 discloses an autostereoscopic display apparatus having a lenticular sheet as lenticular means 150 and discusses the relationship between display elements, i.e., light emitting or light modulating elements, and the lenticular elements of the lenticular sheet.

In the following, a reference to "on top", "upwards", etc. is to be understood as referring to a direction or surface of an layer which faces away from the light generating portion 142, i.e., towards a viewer. Moreover, a reference to "below", "downwards", etc. is to be understood as referring to a direction or surface of a layer which faces towards the light generating portion 142.

Fig. 2a shows a cross-sectional view of an optical stack 150 which may be arranged on the light generating portion 142 of the autostereoscopic display 140. The optical stack 150 typically comprises a spacing layer 160. The spacing layer 160 is an optically transparent layer for enabling light generated by the light generating portion 142, which is located beneath the spacing layer 160, to pass through the spacing layer substantially unhindered, i.e., without substantially redirecting or scattering the light. It is noted that such a spacing layer 160 is known per se, and is typically being used for spacing apart the lenticular means 170 from the light generating portion 142.

The optical stack 150 further comprises lenticular means 170, with the lenticular means

170 being arranged on top of the spacing layer 160, i.e., on an opposite side of the spacing layer 160 than the light generating portion 142. Alternatively, but less typically, the lenticular means 170 may be directly arranged on top of the light generating portion 142. In this particular example, the lenticular means 170 is constituted by a lenticular sheet comprising a profiled surface which faces upwards, the profiled surface defining an array of lenticular elements for directing the outputs from respective groups of said pixels in mutually different directions so as to enable a stereoscopic image to be perceived. Also, in this particular example, the array is a one-dimensional array formed by a series of cylindrical lens elements arranged in parallel. However, the lenticular means 170 may also take any other suitable form, e.g., comprising a plurality of multi-faceted lens elements, the array being a two- dimensional array, etc. It is noted that such lenticular means 170 are known per se.

It is noted that Fig. 2a shows a cross-section of the optical stack which is chosen to be substantially perpendicular to a length of the cylindrical elements. Thus, the cylindrical lens elements are shown to be cross-sectioned in parallel to the bases of the cylindrical lens elements.

The optical stack 150 further comprises an anti-banding layer 190 which is arranged on top of the lenticular means 170, i.e., at a side of the lenticular means which faces away from the light generating portion 142. In the example of Fig. 2a, the anti-banding layer 190 is constituted by a main layer 192 which is provided with an adhesive layer 194. The adhesive layer 194 is provided on a downward facing side of the main layer 192, i.e., a side of the main layer 192 which faces towards the lenticular means 170. The anti-banding layer 190 is shown to be attached to the lenticular means 170 at least in part using the adhering properties of the adhesive layer 194. Fig. 2a further shows an anti- reflective (AR) coating having been applied to an upward facing side of the anti-banding layer 190, i.e., a side which faces away from the lenticular means 170. Such an AR coating is optional.

Fig. 2b shows a zoomed-in view of the anti-banding layer 190 and the lenticular means 170. The zoomed-in view is indicated in Fig. 2a by a dashed rectangle INS. Consequently, Fig. 2b shows a portion of the lenticular means 170, the adhesive layer 194 and the main layer 192. As can be seen in Fig. 2b, the anti-banding layer 190 is attached such to the lenticular means 170 that a gap 180 is formed between the lenticular means 170 and the anti-banding layer 190. In particular, the gap 180 is formed by a depression between two adjacent ones the lenticular elements and the anti- banding layer 190 covering said depression so as to establish the gap 180. Although not visible in Fig. 2b, it will be appreciated that, in case the lenticular elements are elongated, the gap may extend along the elongated lenticular elements, i.e., may have a similar length. The gap 180 may also be described as follows. The lenticular elements of the lenticular means 170 form a 'wave'-like pattern along the cross-section shown in Figs. 2a and 2b. The anti-banding layer 190 is attached on top of the lenticular means 170 such that it adheres to, and thus makes contact with, the lenticular means 170 at a top of the 'wave'-like pattern, i.e., at a protruding portion of each lenticular element. At a same time, the anti-banding layer 190 does not adhere to, and thus does not make contact with the lenticular means 170 at a bottom of the 'wave'-like pattern, i.e. at the aforementioned depression between two adjacent lenticular elements. In other words, the adhesive layer 194 only adheres to, and thus makes contact with, each lenticular element along a portion of its periphery. Consequently, a gap 180 is formed at another portion of each lenticular element where the adhesive layer does not attach to the lenticular element. In yet other words, the lenticular means 170 may be considered to constitute a plurality of straight parallel ridges and intermediate hollows, with the anti-banding layer 190 being attached to the ridges by means of the adhesive layer 194 while covering the hollows so as to form a plurality of gaps 180.

The gap 180 may be an air gap 180, i.e., filled with air. The air gap 180 may constitute an air pocket, with the term air pocket generally referring to air being trapped between layers which are adjoined, e.g., in a bonding process. In general, such air pockets may be considered undesirable, i.e., it may be desirable to reduce their occurrence. Here, however, the gap 180 is provided on purpose. The gap may also be filled with another medium, e.g., another gas, liquid, polymer, etc.

In general, the adhesive layer 194 may be constituted by a deformable material, e.g., deformable glue, gel or other material which as adhering properties. As such, as is also shown in Fig. 2b, the adhesive layer 194 may deform to a certain degree when applying the anti-banding layer 190 to the lenticular means 170. This may ensure seamless contact between the lenticular means 170 and the anti-banding layer 190 at the aforementioned portions of contact. The adhesive layer 194 may comprise a delay-bond adhesive that may temporarily allow repositioning during application to correct placement errors. The adhesive layer 194 is substantially optically transparent in that it is able to pass through light. It is noted that this applies to all other layers of the optical stack 150, i.e., all are optically transparent. It is noted that the term optically transparent does not imply other optical properties. For example, while being optically transparent, they adhesive layer 194 may also be diffuse in that it may scatter the light passing through the adhesive layer 194.

It is noted that, in general, instead of an adhesive layer 194, alternative layers having similar functionality can be thought of by those skilled in art. For example, a substantially non- adhesive layer 194 may be provided, comprising, e.g., a deformable gel or other material without substantial adhering properties. Said layer may in general be a contact layer 194, i.e., having adhesive or non-adhesive properties. In the latter case, the anti-banding layer 190 may be affixed to the lenticular means 170 mechanically, e.g., at a side of the layer, or by being pressed against the lenticular means 170 by a transparent top layer arranged on top of the anti-banding layer 190.

The main layer 192 may constituted by a polymer film or a solid substrate such as glass. The anti-banding layer 190, i.e., the combination of main layer 192 and adhesive layer 194, may be constituted by self-adhesive (sticky) protective film, e.g., for covering and protecting a display screen, a window, a book cover, etc. Another example is polarizer foil or a polarizer layer as used in LCD panels. Such type of film is commercially available on sheets or rolls. Such a self-adhesive protective film may comprise an adhesive layer of water-based or oil-based glue. The protective film may be of vinyl (PVC), polyester, polypropylene, etc. The anti-banding layer 190 may also be constituted by a part of the optical stack of a LCD panel. For example, the lenticular means 170 may be integrated between a color filter layer and a polarizer layer of the LCD panel, with, e.g., the polarizer layer constituting the anti-banding layer 190. In general, the anti-banding layer 190 may have a thickness below the millimeter range, e.g., in an order of magnitude of 50, 100, or 200 micrometer. This is not a limitation, however, as other thicknesses are also conceivable.

In the example of Figs. 2a and 2b, the anti-banding layer 190 may be constituted by a self-adhesive protective film having a thickness of approximately 200 micrometer.

The main layer 192 may be a diffuse main layer 192. Here, the term diffuse refers to being optically transparent, yet being arranged for scattering light to a certain degree. As a result, the light generated by the light generating portion 142 is scattered, thereby providing a viewer with a less sharp impression of the image shown on the autostereoscopic display 140. Alternatively, the main layer 192 may be a substantially non-diffuse main layer 192, i.e., avoiding said scattering of light.

The anti-banding layer 190 may be applied as follows to the lenticular means 170. In general, the lenticular means 170 may have already have been applied, e.g., via the spacer layer 160, to the light generating portion 142. This may provide a stable basis onto which the anti-banding layer 190 may be applied in a controllable manner. For example, the anti-banding layer 190 may be applied to an, at least in part, already manufactured display panel of the autostereoscopic display 140. Alternatively, the optical stack 150 may have already been prefabricated before applying it to the light generation portion 142, e.g., an LCD panel. For example, the optical stack 150 may have been produced in a process in which the anti-banding layer 190 is attached to the lenticular means 170, with the optical stack 150 only thereafter being applied to the light generation portion 142.

In case the anti-banding layer 190 is a flexible layer, e.g., being a film such as the self- adhesive protective film, the anti-banding layer 190 may be applied by pressing the anti-banding layer 190 onto the lenticular means with a substantially rigid, i.e., non-deformable, pressing surface. The pressing surface may be a flat pressing surface, and may be provided by, e.g., a roll which is rolled over the anti-banding layer 190 so as to press the anti-banding layer 190 against the lenticular means 170. The pressure may be controlled so as to ensure that gaps 180 of the aforementioned type are generated between the anti-banding layer 190 and the lenticular means 170. Hence, it may be avoided that the anti-banding layer 190 is seamlessly applied to the lenticular means 170, and thus, e.g., expelling all air between the lenticular means 170 and the anti-banding layer. This may otherwise occur if the pressing surface is deformable and/or a too high pressure is applied when applying the anti-banding layer 190. In case the anti-banding layer 190 is a rigid layer such as the aforementioned solid glass substrate, the pressing surface may also be flexible or deformable.

Fig. 3 shows a cross-sectional view of a further optical stack 152 which may be arranged on the light generating portion 142 of the autostereoscopic display 140. Like the optical stack 150 of Figs. 2a and 2b, the optical stack 152 of Fig. 3 comprises a spacing layer 160 and lenticular means 170 arranged on top of the spacing layer 160. The optical stack 152 further comprises a top layer 200. The top layer 200 is optically transparent and may constitute a protective layer for protecting, e.g., the lenticular means 170 from damage. Moreover, the top layer 200 serves as a basis for the anti-banding layer 190 in that the anti-banding layer 190 is applied to the top layer 200. In particular, the adhesive layer 194 is applied to a downward facing side of the top layer 200, thereby attaching the anti-banding layer 190 in its entirety to the top layer 200. The top layer 200 is mechanically kept at a distance from the lenticular means 170, e.g., by being mechanically affixed at its periphery at said distance. As such, a gap 182 is formed between multiple or all of the lenticular elements of the lenticular means 170 and the anti-banding layer 190. The gap 182 may be an air gap 182.

It is noted that the lenticular means 170 may be oriented such that the profile surface faces away from the light generating portion 142, i.e., as is the case in Figs. 2a, 2b and 3. However, the lenticular means 170 may also be oriented such that the profile surface faces towards the light generating portion 142. It is noted that also in the latter case autostereoscopic viewing functionality can be provided, with those skilled in art being able to provide a suitable optical stack comprising the lenticular means 170. In this case, the anti-banding layer 190 may be applied in various ways. For example, the anti-banding layer 190 may be attached to the spacing layer 160 such that the adhesive layer 140 of the anti-banding layer 190 faces upwards, and the lenticular means 170 may be arranged on the anti-banding layer 190 with the profile surface facing downwards using, at least in part, the adhering properties of the adhesive layer 194. The contact between the anti-banding layer 190 and the profile surface may be similar as discussed in reference to Figs. 2a and 2b, e.g., the adhesive layer 194 may only adhere to each lenticular element along a portion of its periphery.

The inventors have determined an effect in an optical stack comprising the anti-banding layer. In recognition thereof, an anti-banding layer may be provided which is adhered to the lenticular means, and which, when adhered to the lenticular means, causes a variation in the refractive index at a periphery of each lenticular element. Here, the term periphery refers to the outer boundary of each lenticular element from which light from the light generating portion 142 is emitted or coupled out after being redirected inside the lenticular element. The variation may be achieved in different ways, as further explained in reference to the single lenticular element as shown in Fig. 4, being exemplary for a plurality or all of the lenticular elements of the lenticular means 170.

For example, the anti-banding layer may only be attached discontinuously to the lenticular means, e.g., as shown in Figs. 2a and 2b. The anti-banding layer may be applied to a first portion 175 of the lenticular element, thus effecting a first type of refraction at the interface between the anti-banding layer and the lenticular element at the first portion 175, with the first type of refraction being determined by the refractive indexes of the lenticular element, i.e., its material, and the anti- banding layer. Moreover, another portion 176, 177 of the lenticular element may be adjoining a gap such as an air gap, which may be formed by the anti-banding layer being attached discontinuously in an aforementioned manner. This effects a second type of refraction at the interface between the lenticular element and the gap, with the second type of refraction being determined by the refractive indexes of the lenticular element and the medium inside the gap, e.g., air. The gap may also be filled with another medium, e.g., another gas, liquid, polymer, etc. The medium may be suitably chosen according to refraction index and thus enable a tuning of the second type of refraction

The variation may be substantially symmetric with respect to an optical center axis 178 of the lenticular element, with, e.g., light being emitted from a center portion 175 of the periphery being subjected to the first type of refraction, and light being emitted from peripheral portions 176, 177 at either side of the center portion being subjected to the second type of refraction.

The aforementioned variation in refraction may also be obtained by an anti-banding layer which is substantially continuously applied to the lenticular means, but in itself comprises a variation of refractive index, e.g., due to material variations, or as a result of being locally deformed, subjected to mechanical stress, etc. For example, the thickness of an adhesive layer of the anti-banding layer may vary, e.g., being thicker at the depressions between adjacent lenticular elements and being thinner at the top of each lenticular element. Alternatively or additionally, the variation may be in an optical property other than refraction or refractive index. For example, the adhesive layer may be optically transparent yet diffuse to a certain degree. The degree of diffuseness may depend on a thickness of the adhesive layer. A variation in diffuseness may be obtained by the anti-banding layer being applied such to the lenticular means that the adhesive layer is thicker at the depressions between adjacent lenticular elements and thinner at the top of each lenticular elements. Other optical properties are equally conceivable. As an alternative to a continuous layer, the anti-banding layer may be constituted by a local coating applied to portions of each lenticular element.

Further embodiments of the invention are described in the following clauses. Clause 1. Autostereoscopic display comprising i) a display panel providing a display output composed of pixels in an array and ii) an optical stack arranged at a display side of the display panel, the optical stack comprising:

a lenticular means; and

an anti-banding layer.

Clause 2. Autostereoscopic display according to clause 1 , wherein:

the lenticular means comprises a profiled surface, the profiled surface defining an array of lenticular elements for directing the outputs from respective groups of said pixels in mutually different directions so as to enable a stereoscopic image to be perceived; and

the anti-banding layer is arranged on the profiled surface of the lenticular means, the anti-banding layer comprising a main layer and an adhesive layer for adhering the anti- banding layer to the profiled surface, wherein the anti-banding layer is arranged such on the profiled surface that the adhesive layer adheres to a protruding portion of each of the lenticular elements while keeping clear of depressions between adjacent ones of the lenticular elements so as to form a gap between adjacent ones of the lenticular elements and the anti-banding layer.

Clause 3. Autostereoscopic display according to clause 1 , wherein:

the lenticular means comprises a profiled surface, the profiled surface defining an array of lenticular elements for directing the outputs from respective groups of said pixels in mutually different directions so as to enable a stereoscopic image to be perceived;

the optical stack further comprises a top layer arranged above the profiled surface so as to substantially avoid contact with the profiled surface, the top layer comprising a downward facing surface; and

- the anti-banding layer is arranged on the downward facing surface of the top layer, the anti-banding layer comprising a main layer and an adhesive layer for adhering the anti- banding layer to the downwards facing surface.

Clause 4. Autostereoscopic display according to clause 1 , wherein the anti-banding layer arranged on or above the lenticular means according to Fig. 2a or Fig. 3.

Clause 5. Autostereoscopic display according to clause 1 , wherein: the lenticular means comprises a profiled surface, the profiled surface defining an array of lenticular elements for directing the outputs from respective groups of said pixels in mutually different directions so as to enable a stereoscopic image to be perceived;

the anti-banding layer is arranged on the profiled surface of the lenticular means, the anti-banding layer being arranged for effecting a variation in the refraction of light (or a variation in another optical property) at a periphery of each lenticular element.

Clause 6. Autostereoscopic display according to clause 5, wherein the anti-banding layer is arranged for effecting the variation in the refraction of light (or the variation in the other optical property) by being attached to a first portion of each lenticular element while keeping clear of a second portion of each lenticular element.

Clause 7. Autostereoscopic display according to clause 6, wherein the first portion is a central portion centered around an optical axis of each lens element, and wherein the second portion is a peripheral portion at a side of the central portion.

Clause 8. Autostereoscopic display according to clause 5, wherein the anti-banding layer is arranged for effecting the variation in the refraction of light (or the variation in the other optical property) based on at least one of: a variation in material of the anti-banding layer, a variation in thickness of the anti-banding layer, the anti-banding layer being locally deformed, and the anti- banding layer being locally subjected to mechanical stress.

Clause 9. Electronic device comprising the autostereoscopic display of according to any of clauses 1-8.

Clause 10. Optical stack according to any of clauses 1-8.

Clause 1 1. Method of attaching or applying an anti-banding filter to a lenticular means, the method comprising pressing the anti-banding layer onto the lenticular means with a pressing surface.

Clause 12. Method according to clause 1 1 , wherein the lenticular means comprises a profiled surface, the profiled surface defining an array of lenticular elements, wherein the anti-banding layer comprises a main layer and an adhesive layer for adhering the anti-banding layer to the profiled surface, and wherein the method comprises:

pressing the anti-banding layer with the adhesive layer onto the lenticular means with the pressing surface; and

during the pressing, controlling a pressing pressure so as to generate and/or maintain gaps between the anti-banding layer and the lenticular means at depressions in the profiled surface between adjacent ones of the lenticular elements.

Clause 13. Method according to clause 12, wherein the anti-banding layer is a flexible layer, and wherein the method further comprises pressing the anti-banding layer with a substantially rigid, i.e., non-deformable, pressing surface onto the lenticular means.

Clause 14. Method of manufacturing an optical stack, comprising the method according to any one of clauses 1 1-13.

Clause 15. Method of manufacturing an autostereoscopic display, comprising the method according to any one of clauses 1 1-14.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.