AUTOSTEREOSCOPIC DISPLAY DEVICE AND DRIVING METHOD

Abstract

An autostereoscopic display uses a beam control system and a pixelated spatial light modulator. Different display modes are provided for the displayed image as a whole or for image portions. These different modes provide different relationships between angular view resolution, spatial resolution and temporal resolution. The different modes make use of different amounts of beam spread produced by the beam control system.

Claims

1. An autostereoscopic display, comprising: an image generation system, the image generation system comprising: a backlight; a beam control system; and a pixelated spatial light modulator; and a controller circuit wherein the controller circuit is arranged to control the image generation system in dependence on the image to be displayed, wherein the beam control system is arranged to adjust an output beam spread, wherein the image generation system is arranged to produce a beam-controlled modulated light output, wherein the beam-controlled modulated output defines an image to be displayed, the image comprising views for a plurality of different viewing locations, wherein the controller is arranged to provide at least two display output modes, each of which generates at least two views: a first display output mode in which a portion or all of the displayed image has a first angular view resolution; a second display output mode in which a portion or all of the displayed image has a second angular view resolution larger than the first angular view resolution and the beam control system produces a smaller output beam spread than in the first display output mode.

2. The display as claimed in claim 1, wherein the beam control system comprises an array of beam control regions arranged in spatial groups, wherein when a group is in the first output mode, the beam control regions in the group are each directed to multiple viewing locations at the same time; wherein when a group is in the second output mode, the beam control regions in the group are each directed to an individual viewing location.

3. The display as claimed in claim 2, wherein when a group is in the second output mode, a first part of the group directed to a first viewing location, and a second part of the group directed to a second, different viewing location.

4. The display as claimed in claim 2, wherein the controller is arranged to provide sequential frames, each of which comprises sequential sub-frames, wherein the first mode comprises controlling at least one beam control region to be in the first output mode for a first and a next sub-frame and directed to the same multiple viewing locations in the first and next sub-frames; wherein the second mode comprises controlling at least one beam control region to be in the second output mode directed to a first viewing location for a first sub-frame and then in the second output mode directed to a second, different viewing location for a next sub-frame.

5. The display as claimed in claim 1, wherein the beam control system comprises an array of beam control regions, wherein first regions of the displayed image have at least one beam control region in the first output mode and second regions of the displayed image have at least one beam control region in the second output mode, at the same time, and depending on the image content.

6. The display as claimed in claim 2, wherein each group comprises two regions.

7. The display as claimed in claim 1, wherein the first output mode is applied to the whole displayed image or the second output mode is applied to the whole displayed image, wherein the second output mode is for displaying a smaller number of views than the first output mode.

8. The display as claimed in claim 1, wherein the controller is arranged to select between the at least two autostereoscopic display output modes based on one or more of: the depth range of a portion or all of the image to be displayed; the amount of motion in a portion or all of the image to be displayed; visual saliency information in respect of a portion of the image to be displayed; contrast information relating to a portion or all of the image to be displayed.

9. The display as claimed in claim 1, wherein the beam control system comprises an array of electrowetting optical cells.

10. A method of controlling an autostereoscopic display, the autostereoscopic display comprising an image generation system, the image generation system comprising a backlight, a beam control system and a pixelated spatial light modulator, the method comprising: controlling the beam control system to adjust at least an output beam spread, providing two autostereoscopic display output modes, each of which generates at least two views: a first display output mode in which a portion or all of the displayed image has a first angular view resolution; a second display output mode in which a portion or all of the displayed image has a second angular view resolution larger than the first angular view resolution and the beam control system is controlled to provide a smaller output beam spread than in the first display output mode.

11. The method as claimed in claim 10 wherein the beam control system comprises an array of beam control regions arranged in spatial groups, further comprising: in the first output mode, directing the beam control regions in the group to multiple viewing locations at the same time; and in the second output mode, directing each beam control region in the group to an individual viewing location.

12. The method as claimed in claim 11, further comprising in the second output mode controlling all beam control regions in the group to be in the second output mode, wherein a first part of the group is directed to a first viewing location and a second part of the group directed to a second, different viewing location.

13. The method as claimed in claim 11, further comprising: providing sequential frames each of which comprises sequential sub-frames, in the first mode controlling at least one beam control region to be in the first output mode for a first and next sub-frame image and directed to the same multiple viewing locations in the first and next sub-frames; in the second mode controlling at least one beam control region to be in the second output mode directed to a first viewing location for a first sub-frame then in the second output mode directed to a second, different viewing location for a next sub-frame.

14. The method as claimed in claim 10, wherein the beam control system comprises an array of beam control regions, further comprising: providing first regions of the displayed image with beam control regions or groups of beam control regions in the first output mode; providing second regions of the displayed image with beam control regions or groups of beam control regions in the second output mode, at the same time; and depending on the image content.

15. The method as claimed in claim 10, wherein the controller is arranged to select between the at least two autostereoscopic display output modes based on one or more of: the depth range of a portion or all of the image to be displayed; the amount of motion in a portion or all of the image to be displayed; visual saliency information in respect of a portion of the image to be displayed; or contrast information relating to a portion or all of the image to be displayed.

16. The method as claimed in claim 10, wherein the beam control system comprises an array of beam control regions, further comprising: providing first regions of the displayed image with beam control regions or groups of beam control regions in the first output mode; and applying the first output mode or the second output mode to the whole displayed image, wherein the second output mode comprises displaying a smaller number of views than the first output mode

Description

BRIEF DESCRIPTION OF THE FIGURES

[0077] Embodiments of the invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

[0078] FIG. 1 is a schematic perspective view of a known autostereoscopic display device;

[0079] FIG. 2 is a schematic cross sectional view of the display device shown in FIG. 1;

[0080] FIG. 3 shows the principle of operation of an electrowetting cell;

[0081] FIG. 4 shows how image rendering can be used to change how the autostereoscopic effect is presented;

[0082] FIG. 5 shows a display device in accordance with an example of the invention;

[0083] FIG. 6 shows a first approach which makes use of control of the beam width, to provide a selectable trade off between spatial resolution and angular view resolution;

[0084] FIG. 7 shows control of the beam width with temporal multiplexing of a single beam control region;

[0085] FIG. 8 is used to show how temporal, spatial and angular view resolutions can all be controlled;

[0086] FIG. 9 shows a disparity map and the ray space;

[0087] FIG. 10 shows the use of adjustable beam profiles applied to the ray space of FIG. 9;

[0088] FIG. 11 shows a first alternative possible implementation of the required beam control function;

[0089] FIG. 12 shows a second alternative possible implementation of the required beam control function; and

[0090] FIG. 13 shows a third alternative possible implementation of the required beam control function.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0091] The invention provides an autostereoscopic display which uses a beam control system and a pixelated spatial light modulator. Different display modes are provided for the displayed image as a whole or for image portions. These different modes provide different relationships between angular view resolution, spatial resolution and temporal resolution. The different modes make use of different amounts of beam spread produced by the beam control system.

[0092] FIG. 5 shows a display device in accordance with an example of the invention. FIG. 5(a) shows the device and FIGS. 5(b) and 5(c) illustrate schematically two possible conceptual implementations.

[0093] The display comprises 30 a backlight for producing a collimated light output. The backlight should preferably be thin and low cost. Collimated backlights are known for various applications, for example for controlling the direction from which a view can be seen in gaze tracking applications, privacy panels and enhanced brightness panels.

[0094] One known design for such a collimated backlight is a light generating component which extracts all of its light in the form of an array of thin light emitting stripes spaced at around the pitch of a lenticular lens that is also part of the backlight. The lenticular lens array collimates the light coming from the array of thin light emitting stripes. Such a backlight can be formed from a series of emissive elements, such as lines of LEDs or OLED stripes.

[0095] Edge lit waveguides for backlighting and front-lighting of displays are also known, and these are less expensive and more robust. An edge lit waveguide comprises a slab of material with a top face and a bottom face. Light is coupled in from a light source at one or two edges, and at the top or bottom of the waveguide several out-coupling structures are placed to allow light to escape from the slab of waveguide material In the slab, total internal reflection at the borders keeps the light confined while the light propagates. The edges of the slab are typically used to couple in light and the small out-coupling structures locally couple light out of the waveguide. The out-coupling structures can be designed to produce a collimated output.

[0096] An image generation system 32 includes the backlight and further comprises a beam control system 34 and a pixelated spatial light modulator 36. FIG. 5 shows the spatial light modulator after the beam control system but they may be the other way around.

[0097] The spatial lighting modulator comprises a transmissive display panel for modulating the light passing through, such as an LCD panel.

[0098] A controller 40 controls the image generation system 32 (i.e. the beam control system, the backlight and the spatial light modulator) in dependence on the image to be displayed which is received at input 42 from an image source (not shown). In some implementations, the backlight may also be controlled as part of the beam control function, such as the polarization of the backlight output, or the parts of a segmented backlight which are made to emit. Thus, the beam control function may be allocated differently as between a backlight and a further beam control system. Indeed, the backlight may itself incorporate fully the beam control function, so that the functionality of units 30 and 34 are in one component.

[0099] In one example which is based on the use of electrowetting cells, the beam control system comprises a segmented system, having an array of beam control regions, wherein each beam steering region is independently controllable to adjust an output beam spread and optionally also direction. The electrowetting cells may take the form as shown in FIG. 3. In this case, the backlight output can be constant, so that the backlight is only turned on and off. In other examples discussed below, the beam control system may not be segmented and it may operate at the level of the whole display.

[0100] The autostereoscopic display has a beam steering function to create views, and additionally in accordance with the invention there is also beam control for controlling a beam spread. The beam steering function needs to direct the light output from different sub-pixels to different view locations. This may be a static function or a dynamic function. For example, in a partially static version, the beam steering function for creating views can be provided by a fixed array of lenses of other beam directing components. In this case, the view forming function is non-controllable, and the electrically controllable function of the beam control system is limited to the beam spread/width.

[0101] This partially static version is shown in FIG. 5(b), in which beam controlling regions 37 are provided over a lens surface, so that the beam controlling regions only need to change the beam spread to implement the different modes. The beam spread may be controlled globally so that a segmented system is not needed.

[0102] In a dynamic version, the beam direction as well as the beam spread/width can both be controlled electrically. FIG. 5(c) shows an example of segmented beam controlling regions 37 over a planar substrate, with each beam controlling region able to adjust the beam direction (for view forming) and the beam spread angle.

[0103] In a segmented beam control system, there may be one sub-pixel of the spatial light modulator associated with each individual beam control region 37 (e.g. electrowetting cell), or else the beam control regions may each cover multiple sub-pixels, for example one full colour pixel, or even a small sub-array of full pixels. Furthermore, the beam control regions 37 may operate on columns of pixels or columns of sub-pixels instead of operating on individual sub-pixels or pixels. This would for example allow steering of the output beam only in the horizontal direction, which is similar conceptually to the operation of a lenticular lens.

[0104] The type of beam control approach used will determine if a pixelated structure is used or if a striped structure is used. A pixelated structure will for example be used for an electrowetting beam steering implementation.

[0105] The image to be displayed is formed by the combination of the outputs of all of the beam control regions. The image to be displayed may comprise multiple views so that autostereoscopic images can be provided to at least two different viewing locations.

[0106] The controller 40 is adapted to provide at least two autostereoscopic display output modes. These modes can be applied to the whole image to be displayed or they can be applied to different image portions.

[0107] A first display output mode has a first angular view resolution. A second display output mode has a larger angular view resolution and the associated beam control regions produce a smaller output beam spread to be more focused to a smaller number of views. This approach enables the amount of angular view resolution to be offset against other parameters.

[0108] Multiplexing angular information in the light coming from a display panel inherently reduces the resolution along some of the light field dimensions (such as space, time, colour or polarization) to gain angular view resolution. For example, angular view resolution can be traded against spatial resolution or temporal resolution.

[0109] With regard to temporal resolution, flicker is visually disturbing so time sequential operation should be limited to keep all sub-frames within maximally 1/50 s=20 ms or preferably less than 1/200 s=5 ms. Blue phase liquid crystal is reported to have a 1 ms switching speed so this gives the possibility for 5 to 20 sub-frames. This is not enough for a high quality single cone autostereoscopic display, at least not without eye tracking so that temporal multiplexing alone is not suitable for autostereoscopic displays producing multiple autostereoscopic viewing directions.

[0110] Spatial resolution is very important and should be at least 1080p or even higher to be considered sufficient. However often footage is blurry due to limited depth of field, motion blur and camera lens quality.

[0111] Spatiotemporally multiplexed electrowetting displays are able to make good use of available technology and are able to benefit from improvements in spatial resolution and switching speed, for instance as a result of increased frame rates due to oxide TFT developments.

[0112] This invention makes use of multiplexing schemes, for example including spatiotemporal multiplexing, which are controlled based on the characteristic of the content and/or viewing conditions. Examples which make clear the potential advantages of control of the multiplexing scheme are:

[0113] an object that does not move or only slowly moves can be rendered using less sub-frames.

[0114] an object that has a narrow depth range can be rendered using less and broader views.

[0115] an object that is blurred can be rendered with less pixels.

[0116] Different multiplexing approaches are implemented by enabling control of the beam width based on the image content either locally or globally.

[0117] FIG. 6 shows a first approach which makes use of control of the beam width, to provide a selectable trade off between spatial resolution and angular view resolution. For this purpose, the beam control regions are arranged in spatial groups. FIG. 6 shows the most simple grouping, in which each group is a pair of adjacent beam control regions, and a corresponding pair of adjacent sub-pixels x1 and x2. The upper arc 50 indicates the angular view ranges v1 and v2. The envelopes 52 are intensity profiles.

[0118] FIG. 6(a) shows a first output mode. The beam control regions in the group are each directed to multiple viewing locations, in particular to views v1 and v2. Thus, image data A is provided to sub-pixel x1 and image data B is provided to sub-pixel x2. Both sub-pixels present their information in both views. This gives a large spatial resolution, since both sub-pixels are visible in each view. In this mode mode the outputs have the same beam shape and direction.

[0119] FIG. 6(b) shows a second output mode. The beam control regions in the group are directed to individual and different viewing locations, in particular sub-pixel x1 is directed to v2 and sub-pixel x2 is directed to view v1. Thus, image data A is provided only to view v2 and image data B is provided only to view v1. This gives a large angular view resolution, since views v1 and v2 display different views within the overall displayed image. In this mode, the beams form adjacent views.

[0120] Thus, FIG. 6(a) gives more spatial resolution, and FIG. 6(b) gives more angular view resolution. In FIG. 6(a) the intensity profile comprises view ranges v1 and v2 thus having less angular view resolution, however both sub-pixels are visible from both view ranges, thus providing more spatial resolution. In FIG. 6(b) there is more angular view resolution and less spatial resolution by the same argument.

[0121] FIG. 6(c) is an abstract representation of the spatial mode of FIG. 6(a) and FIG. 6(d) is an abstract representation of the angular view mode of FIG. 6(b). It shows the views and the pixel locations to which the image data A and B are provided. For example, FIG. 6(c) shows that image data A is provided to both views by sub-pixel x1. FIG. 6(d) shows that image data B is provided only to view v1. Note that the square in FIG. 6(d) is filled (rather than leaving the top left and bottom right blank) for ease of representation in 3D (in FIG. 8). It shows view allocation, namely that each view only has one pixel data spread over the two positions.

[0122] The combined profile of the two beams is similar in both modes.

[0123] One method to decide which mode to use involves obtaining four luminance or colour values and placing them in a 2×2 matrix. In the high spatial resolution mode of FIG. 6(a), only the average of each column can be represented in each sub-pixel, while in the high angular view resolution mode of FIG. 6(b) only the average of each row as represented in FIG. 6(d) can be represented.

[0124] This generally gives two different errors. Because the combined beam profile is similar, the decision as to which mode to use can be made locally based on a simple error metric that—for each mode—measures the colour or luminance difference for both involved views at both involved spatial locations. This gives an error for each mode (ε1 and ε2). The balance for spatial and angular view resolution can then be set by a threshold (λ) that chooses to select for the second mode when λε1>ε2. To always select the mode that gives the lowest error λ=1.

[0125] Considering the example of FIG. 6, the input data has values for each position (x) and view (v) combination, such that each combination gives rise to a particular input value:

[0126] If we define the input I(xi,vj) as “Iij” in a selected colorspace, then in the first mode corresponding to FIGS. 6(a) and (c):

[0127] The colour for A (IA) is the average of I11 and I12.

[0128] The colour for B (IB) is the average of I21 and I22.

[0129] The error that is made for the first mode is:

ε1=d(I11,IA)+d(I12,IA)+d(I21,IB)+d(I22,IB).

[0130] For the second mode, corresponding to FIG. 6(b) and FIG. 6(d):

[0131] The colour for A (I′A) is the average of I11 and I21.

[0132] The colour for B (I′B) is the average of I12 and I22.

[0133] The error that is made for the second mode is:

ε2=d(I11,I′A)+d(I21,I′A)+d(I12,I′B)+d(I22,I′B).

[0134] A computation of the average of the colours and the distance between colours depends on the colour space. With RGB and YCbCr it might be a regular per-component averaging operation and a sum-of-absolute-differences operation (SAD) or sum of squared differences operation (SSD) to compute errors. Computation in linear light (RGB without gamma) with regular averaging and L.sub.2 error may also be used (L.sub.2 error is a geometric distance of two vectors, sometimes also known as the “2-norm distance”).

[0135] This scheme can be extended to groups of multiple cells that form multiple adjacent views. The number of combinations (modes) will increase rapidly. The above scheme can be generalized to any situation where:

[0136] beams of two or more nearby cells are adjacent such that they can be merged to a single broad beam (by applying the same voltages on both cells). This increases the spatial resolution because all cells are now visible from all view points, but lowers the angular view resolution;

[0137] beams of two or more nearby cells are overlapping such that they could be split in two or more narrow beams (by applying different voltages to both cells) that together form the original beam shape. This decreases the spatial resolution because only one cell is now visible for each view point, but it increases the angular view resolution.

[0138] Instead of having fixed sets of pairs of cells with two modes per pair, this problem can thus also be put in a form that can be optimized by a suitable method such as a semi-global method (e.g. dynamic programming) or a global method (e.g. belief propagation).

[0139] The implementation above is based on trading spatial resolution with angular view resolution. An approach which makes use of temporal multiplexing uses multiple sub-frames (e.g. 2 or 3 sub-frames). This gives more error terms and more possibilities.

[0140] FIG. 7 shows control of the beam width with temporal multiplexing of a single beam control region (e.g. an electrowetting cell). The same references are used as in FIG. 6.

[0141] FIG. 7(a) shows a first output mode. The beam control region is directed to multiple viewing locations, in particular to views v1 and v2. Thus, image data A is provided to the sub-pixel in a first sub-frame and image data B is provided to the sub-pixel in a second sub-frame. The sub-pixel presents its information in both views in both sub-frames. This gives a large spatial resolution, since the sub-pixel is visible in each view. In this mode the outputs have the same beam shape and direction.

[0142] FIG. 7(b) shows the second output mode. The beam control region is directed to one viewing location v2 with image data A in the first sub-frame, and is directed to viewing location v1 with the image data B in the second sub-frame. This gives a large angular view resolution, since views v1 and v2 display different views within the overall displayed image. In this mode, the beams form adjacent views.

[0143] Thus, FIG. 7(a) gives more spatial temporal resolution but less angular view resolution, and FIG. 7(b) gives more angular view resolution but less temporal resolution (since each view is only updated every frame). FIGS. 7(c) and 7(d) are again abstract representations of FIGS. 7(a) and (b).

[0144] In the first mode the beam control region cell has the same beam profile in both sub-frames whereas in the second mode the beam control region has adjacent beam profiles in the sub-frames that combine to form the beam profile of the first mode.

[0145] FIG. 8 is used to show how temporal, spatial and angular view resolutions can all be controlled. It shows various multiplexing options with a set of two nearby beam control regions cells over two sequential (or at least close in time) sub-frames.

[0146] FIG. 8 is essentially a combination of the abstract representations in FIGS. 6 and 7 but as a 3D block.

[0147] FIG. 8(a) shows spatial resolution sacrificed for angular and temporal resolution. At any time, different data is provided to the different views, similar to FIG. 6(b).

[0148] FIG. 8(b) shows angular view resolution sacrificed for spatial and temporal resolution. At any time, the same data is provided to both views by each sub-pixel, similar to FIG. 6(a).

[0149] FIG. 8(c) shows temporal resolution sacrificed for view and spatial resolution. Each sub-pixel provides the same image data for both sub-frames, similar to FIG. 7(d).

[0150] FIG. 8(d) shows one possible mixed solution where for the first spatial position, angular view resolution is sacrificed for temporal resolution, while for the other spatial position, the opposite sub-mode is chosen.

[0151] The example above requires decision making for each pair of beam control regions, or even for all cells independently but taking other cells into account. Although this local adaption is preferred, there are benefits if the adaption is made on a global (per-frame) level.

[0152] One reason to use global adaption is that there may be limited processing power available or part of the rendering chain is implemented in ASIC and cannot be adapted. In one mode more views could be rendered at a lower spatial resolution in comparison to the other mode. The complexity for both modes would be similar.

[0153] The choice between global modes can be based on the depth range, amount of motion, a visual saliency map and/or a contrast map.

[0154] The input data has spatial positions and views. Instead of multiple views, this can be imagined to be a volume of samples in (x,y,v) space where v is for view position. To avoid the use of 3D representations, a common analytical approach is to take a slice that corresponds to a single scan line (y=c.). In FIG. 9, the above image shows the depth map and (x, y) space for a single scan line.

[0155] FIG. 9 (top part) shows a depth (otherwise known as disparity) map for a single scan line.

[0156] A, B, C and D are planes at constant disparity.

[0157] FIG. 9 (bottom part) shows a ray space diagram, which plots the view position against the horizontal position along the selected scan line.

[0158] For objects on the screen (zero disparity, e.g. object A), the spatial position is the same for each view, hence the texture of such an object forms vertical lines in the view-direction in ray space, as shown.

[0159] For objects away from the screen (non-zero disparity), lines form in another direction. The slope of those lines relates directly to the disparity. Occlusion is also visible in ray space (object B is in front of object A).

[0160] Analysis of 3D display images, including the use of ray space diagrams, is presented in the article “Resampling, Antialiasing, and Compression in Multiview 3D displays” of Matthias Zwicker et. al., IEEE Signal Processing Magazine November 2007 pp. 88-96.

[0161] The image rendering may be optimized to create sharp depth edges and high dynamic range. This can be achieved by selecting the local beam profiles in dependence on depth jumps. When a light field such as shown in FIG. 9 is regularly quantized, some sub-pixels contribute partially to both sides of a depth jump, creating strong crosstalk.

[0162] With adjustable beam profiles, it becomes possible to create a semi-regular sampling by snapping sub-pixels to depth jumps.

[0163] FIG. 10 shows an adaptive sampling approach applied to the image of FIG. 9. In FIG. 10, groups of four pixels form four views. Thus, there are four regions 56 in each column. The height of each region 56 represents the view angle provided by the beam control system in respect of that pixel.

[0164] The positions of the views can be determined based on the image data. With regular view sampling such as in the left-most part of FIG. 10, each beam has the same width but different positions.

[0165] By optimizing the positions and widths of each of the beams, it becomes possible to have a better image quality (lower total error ε).

[0166] There are two examples in FIG. 10:

(i) Depth Jumps (A and B) with Different Texture on Either Side of the Jump.

[0167] This creates sharper depth edges, offering more depth effect from the occlusion cue and may reduce the number of beam control regions that are required to render a scene at a given quality. It avoids sub-pixels that span across a depth jump, and which would result in blur.

[0168] It can be seen that the different regions 56 again give different angular view resolutions, as represented by their height. The angular view resolutions are selected such that view boundaries coincide more closely with boundaries between image portions at different depths.

(ii) High Dynamic Range (C and D).

[0169] This is based on another effect of changing the beam profile, which is that it also changes the intensity. By having narrower beam profiles in bright regions, it becomes possible to produce a high dynamic range image (objects C and D in FIG. 10). When modeling edges, this effect also has to be taken into account. Consider that object C is a bright but small object (e.g. the sun or a light) and object D is a large but dim object (e.g. the sky or a wall). By choosing narrower beams for C and wider beams for D the available light output (and resolution) is distributed towards the brighter object.

[0170] It can again be seen that the different regions 56 again give different angular view resolutions. Different angular view resolutions are allocated in this case to different portions of an image such that narrower angular view resolutions are allocated to brighter image portions than neighboring darker image portions.

[0171] The example above makes use of electrowetting cells to provide beam direction and shaping. This enables each sub-pixel (or pixel) to have its own controllable view output direction. However, this approach requires two active matrices of equal resolution giving rise to double the typical cost and power consumption associated with these components.

[0172] Furthermore, the electrowetting cells currently have side walls of substantial thickness and height compared to the pitch of the cell. This reduces the aperture and thereby light output and viewing angle. There are alternative solutions for adaptive view forming arrangements:

1. LC Barrier

[0173] Liquid crystal barriers have a variable aperture width. A narrow aperture results in more view separation, less light output and lower spatial resolution. A broader aperture result in less view separation, more light output and more spatial resolution. LC barriers for example comprise 2D arrays of stripes to realize local adaptation. A single barrier may be used with the barrier formed by stripes or pixels of LC material. The beam width is determined by the number of stripes that are transparent at any time (the slit width). The beam position is determined by which stripes are transparent (the slit position). Both can be controlled. Light output and spatial resolution increases when more stripes are made transparent. View resolution increases when fewer stripes are made transparent.

2. Sub-Pixel Area Driving

[0174] A display (e.g. AMLCD or AMOLED) can be provided with sub-pixel areas, i.e. each color sub-pixel comprises a set of independently addressable regions, but to which the same image data is applied. The active matrix cell that is associated with the sub-pixel can have an addressing line, a data line and at least one “view width” line. The “view width” line determines how many of the sub-pixel areas are activated. For example, different subsets of these sub-pixel areas may be activated for consecutive sub-frames. The areas are positioned such that they occupy adjacent view positions (e.g. preferably side-by-side instead of top-down). This means they can be used to selectively control the view width, i.e. the beam angle at the output.

3. Emitter Stripes

[0175] WO 2005/011293 A1 of the current applicant discloses the use of a backlight having light emitting stripes (e.g. OLED).

[0176] FIG. 11 shows an image from WO 2005/011293. The backlight 60 is an OLED backlight which has electrodes 62 in the form of alternating thick and thin stripes. A conventional display panel 64 is provided over the backlight. The backlight implements switching between 2D and 3D modes.

[0177] The backlight stripes are separated by slightly more than the rendering pitch. Instead of single stripes there can be a set of closely packed stripes, where each pack has a pitch slightly larger than the lenticular pitch. By varying the number of stripes or more generally the intensity profile over the stripes within each pack, it becomes possible to change the beam profile of each view.

[0178] One potential issue might be that the central stripes are used more often and reach end-of-life earlier. This can be circumvented by regularly or occasionally changing which stripe is central, possibly based on an aging model.

[0179] If the backlight that is entirely covered by emitter lines, light steering is possible. This enables left and right stereo views to be projected to the eyes of one or multiple viewers, or allows a head-tracked multi-view system. Time-sequential generation of views and viewing distance adjustment are also possible. This type of backlight can be used to implement the invention.

4. Partially Birefringent Waveguide

[0180] WO 2005/031412 of the current applicant discloses an autostereoscopic display having a backlight in the form of a waveguide with structures separated by a pitch that is slightly larger than the rendering pitch.

[0181] FIG. 12 shows the display. The backlight comprises a waveguide slab 70 which has light out-coupling structures 72 provided on the top face. It is edge lit by a light source 73. The out-coupling structures comprise projections into the waveguide. The top face of the slab of waveguide material is provided with a coating 74 which fills the projections and optionally also provides a layer over the top. The coating has a refractive index higher than the refractive index of the slab of waveguide material so that the light out-coupling structures allow the escape of light.

[0182] The light out-coupling structures 72 each comprise a column spanning from the top edge to the bottom edge in order to form stripes of illumination. A display panel 76, in the form of an LCD panel, is provided over the backlight.

[0183] The width of the out coupling structures can for example be controlled to achieve the required control of the beam width by using polarized light and birefringence. Each line of out-coupling structures can be formed by a pair of adjacent lines with structures that are constructed from birefringent material. The light source 73 can then be controlled to output polarized light that refracts on either one of the two lines, or unpolarized light that refracts on both.

[0184] One implementation of such a light source is to have two sets of light sources with orthogonal polarizers. In one mode there are sets of two sub-frames with alternate polarizations. In the other mode both polarizations are used.

5. LC Prisms on Top of Lenticular

[0185] WO 2009/044334 of the current applicant disclosed the use of a switchable birefringent prism array on top of a 3D lenticular display to increase the number of views in a time-sequential manner.

[0186] FIG. 13 shows the structure used in WO 2009/044334. There is a switchable view deflecting layer 80 in combination with a lenticular lens array 82. The view deflecting layer has different beam steering functions for different incident polarization. This structure can be used, with weakly-diverging birefringent lenses, to implement the beam control required. In one mode the prisms play no role and the display effectively has good view separation. In another mode the prisms partially diverge the light to create less view separation. Local adaptation is possible with an array of electrodes.

6. Diffractive Optical Elements (DOEs)

[0187] Diffractive optical elements can be incorporated into a waveguide structure to generate autostereoscopic displays. Birefringent DOEs can be used to control beam shapes with polarized light sources. Alternatives might be light sources with different wavelengths (e.g. narrow-band and broad-band red, green and blue emitters), or emitters at different positions.

[0188] There are further possible beam control implementations. Multiple switchable lenses or LC graded refractive index lenses may be used, for example of the type as disclosed in WO 2007/072289 of the current applicant. The beam control system may alternatively be based on MEMS devices or electrophoretic prisms.

[0189] The controller 40 can be implemented in numerous ways, with software and/or hardware and/or firmware, to perform the various functions required. A processor is one example of a controller which employs one or more microprocessors that may be programmed using software (e.g., microcode) to perform the required functions. A controller may however be implemented with or without employing a processor, and also may be implemented as a combination of dedicated hardware to perform some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) to perform other functions.

[0190] Examples of controller components that may be employed in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0191] In various implementations, a processor or controller may be associated with one or more storage media such as volatile and non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when executed on one or more processors and/or controllers, perform at the required functions. Various storage media may be fixed within a processor or controller or may be transportable, such that the one or more programs stored thereon can be loaded into a processor or controller.

[0192] The control method will in practice be implemented by software. Thus, there may be provided a computer program comprises code means adapted to perform the method of the invention when the method is run on a computer. The computer is essentially the display driver. It processes an input image to determine how best to control the image generation system.

[0193] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. 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. Any reference signs in the claims should not be construed as limiting the scope.