GB2405543A

GB2405543A - Multiple view directional display having means for imaging parallax optic or display.

Info

Publication number: GB2405543A
Application number: GB0320362A
Authority: GB
Inventors: David James Montgomery; Jonathan Mather; Adrian Marc Simon Jacobs; Grant Bourhill; Graham Roger Jones
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2003-08-30
Filing date: 2003-08-30
Publication date: 2005-03-02
Also published as: JP4404311B2; CN1607418A; KR20050022954A; CN1306317C; JP2005078091A; GB0320362D0; KR100651099B1

Abstract

A multiple view directional display, suitable for an autostereoscopic or dual view system, comprises a parallax optic 3, a pixellated image display layer 4 such as a liquid crystal display ( LCD) and an imaging means 29. Imaging means 29 may be an lenticular screen, formed from holographic optical elements, or any convergent diffractive or refractive microstructures, such as fresnel lenses. Imaging means or lenticular 29 forms an image 30 of the parallax optic 3 or the display layer 4. The image may be formed so that the separation S' between the image and either the display layer 4 or the parallax optic 3 is less than the separation S between the display layer 4 and parallax barrier, as shown in Figure 5. In a further embodiment the image separation S' may be greater than the parallax to display separation S, as shown in Figure 7(G). These different arrangements allow the angular separation between viewing windows 13, 14 to be increased or decreased. Alternatively, the image produced may have a pitch equal to that of the parallax barrier or display element. The device may comprise a substrate with parallax optic and lens array on either side.

Description

A multiple-view directional display The present invention relates to a

multiple-view directional display. Such a directional display is able to display two or more images simultaneously, with each image being displayed in a different direction. The invention also relates to a dual- view display and an autostereoscopic display that incorporates a multiple- view directional display.

The general principle of a multiple-view direction display is described by Starkes in "Ins. J. Virtual Reality" Vol. 1 No. 2 (1995), and is shown in Figure 1 which is a schematic sectional plan view of a conventional multiple view directional display 1.

The display 1 of figure 1 comprises an image display device 2 and a parallax optic 3.

The image display device 2 comprises a pixellated image display layer 4 disposed between first and second light-transmissive substrates 5,6. The pixellated display layer 4 may be, for example a liquid crystal layer, and is addressable by any conventional technique to display two or more interlaced images. Figure 1 shows two images displayed on the display layer 4, with the two images displayed on alternate columns of pixels; one image is displayed on pixel columns Cl, C3, C5 and a second image is displayed on pixel columns C2, C4, C6. (The pixel columns extend into the plane of the paper.) The image display device is illuminated by light 7 from a light source (not shown). The light source may be any suitable light source such as, for example, a diffused source having low spatial coherence. Components 8 and 9 are linear polarisers.

The parallax optic 3 of the multiple-view directional display 1 acts to separate the two or more images displayed on the image display layer 4 so that each image is displayed in a different direction. In Figure 1 the parallax optic is formed by a parallax barrier that comprises a plurality of transparent slits 10 separated by opaque regions 11. The transparent slits 10 extend parallel to the columns of pixels (and so extend perpendicular to the plane of the paper in Figure l). The parallax barrier may be mounted on a transparent substrate 12, to provide physical support.

Because of the image separation effect of the parallax barrier, two viewing windows 13, 14 are set up as shown in figure l. In the first viewing window 13, the image displayed

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on pixel columns C1, C3, C5 is visible but the image displayed on the pixel columns C2, C4, C6 is not visible since the opaque regions 11 of the parallax barrier block light from passing through those pixel columns in the direction of the first viewing window; conversely, in the second viewing window 14 the image displayed on pixel columns C2, C4, C6 is visible, but the image displayed on pixel columns C1, C3, C5 is not visible since the opaque regions 11 of the parallax barrier 3 block light from passing through those pixel columns in the direction of the second viewing window.

Figure 1 illustrates a multiple-view directional display incorporated in an auto- stereoscopic display. In use, an observer would position themselves so that their right eye was coincident with the second viewing window 14 and so that that their left eye was coincident with the first viewing window 13 - and the viewing windows are therefore referred to as a "right viewing window" and a "left viewing window" in figure 1. A stereoscopic image pair would be displayed on the image display device 1, with a right-eye image being displayed on pixel columns C2, C4, C6 and a left-eye image being displayed on pixels C1, C3, C5. An observer positioned with their left and right eyes coincident with the left and right viewing windows respectively would therefore see the left-eye image in their left eye and the right-eye image in their right eye and so would perceive a three-dimensional image.

The parallax optic of the display 1 of Figure 1 is a parallax barrier, consisting of transparent strips separated by opaque regions. Other types of parallax optics are known. For example, it is also known to use a lenticular array as a parallax optic - a lenticular array typically comprises columnar lenses, which act to direct images from different regions of the pixellated image display layer 4 in different directions and thereby obtain the directional effect.

A multiple view directional display may alternatively be incorporated in a "dual-view" display. A dual-view display is intended to display one image to one observer and to display a different image to another observer. As an example, a dual-view display in a motor car might display a map to the driver of the car and display a television programme or film to a passenger. The principle of a dual-view display is generally l similar to the principle of an autostereoscopic display, but the two images displayed on the image display layer of a dual-view display would be independent images rather than the left-eye and right-eye images of a stereoscopic image pair. Furthermore, since the two images displayed by a dual-view display are intended to be seen by different observers, the view angle separation V (which is the angular separation between the centres of the viewing windows for the two images) is, for a given viewing distance generally required to be greater for a dual-view display than for an autostereoscopic display.

The view angle separation V is the angular separation between the centres of the viewing windows for the two images and so is the angle through which a viewer needs to move in order to move between two different views on the display. For a multiple view display having a parallax barrier as the parallax optic, the view angle separation V, expressed in radians, is approximately given by: V=np/s (1) where n is the refractive index of the material separating the parallax barrier 3 and the image display layer 4 (in Figure 1, n is the refractive index of the rear transparent substrate 5 of the image display device), p is the pixel pitch of the image display layer, and s is the separation distance between the parallax barrier 3 and the image display layer 4. For a given image quality (resolution), the pixel pitch p is generally fixed. The substrates of a directional display 1 are generally made of glass, and the refractive index n of glass typically does not vary much for most commercially relevant glasses.

One approach to increasing the view angle separation would be to reduce the thickness of the rear substrate 5 of the image display device and thereby reduce the separation between the parallax optic 3 and the image display layer 4. However, the thickness of the substrate 5 cannot be reduced significantly below 0.5mm, as otherwise it becomes prone to damage, difficult to manufacture, and unable to provide sufficient structural support. Thus, there are substantial difficulties in reducing the thickness of the rear substrate 5 to a thickness that can produce a substantial increase in the view angle. l

There are also cases in which it is desired to reduce the view angle separation. For example where a display is intended to be viewed at a large viewing distance the view angle separation of the display may be greater than the desired view angle separation.

Conventionally the view angle separation is reduced by using thick substrates so as to increase s, but this significantly increases the weight of the display.

A first aspect of the present invention provides multiple-view directional display comprising; a parallax optic; a pixellated image display layer; and an imaging means for imaging one of the parallax optic and the image display layer so that the separation between the image of the one of the parallax optic and the image display layer and the other of the parallax optic and the image display layer is less than the separation between the parallax optic and the image display layer thereby increasing the angular separation between two viewing windows generated by the display.

In a display of the present invention, the view angle separation is determined by the distance between, on the one hand, the image of one of the parallax optic and the image display layer and, on the other hand, the other of the parallax and the image display layer which has not been imaged. By making this distance less than the separation between the parallax optic and the image display layer, the view angle separation may be increased. The invention does not require the thickness of any of the substrates of the display to be reduced, so that thick, structurally robust substrates may be used.

There have been a number of prior art displays that incorporate an imaging means.

However, in none of the prior art displays has an imaging means been used to image the parallax optic or the image display panel in order to increase the view angle separation.

Figure 2A is a schematic plan view of a prior art directional display IS described in EP- A-O 597 629 and incorporating an imaging means LSI. In this prior display, two interlaced images are displayed on a pixellated display panel 16, and the images are separated by a parallax optic LS2. The display is illuminated by a switched illuminator 18, and light from the illuminator is focused by the imaging means LSI onto a diffuser s 17, and is modulated by the pixellated display panel 16 as it passes from the imaging means LS1 to the diffuser. Thus, in this prior art display, the imaging means LS1 generates a greatly reduced image of the switched illuminator 18 on the pixel plane.

The purpose is to ensure that the light from all points on the extended illuminator is properly passed through the pixels and the parallax optic LS2. The imaging means LS1 does not contribute to an increased view angle separation.

Figure 2B shows a further prior art display 15' described in EP-A-O 597 629. This corresponds generally to the display of figure 2A, except that the pixellated display panel 16 is disposed between the switched illuminator 18 and the imaging means LS1.

In this display, the imaging means LS1 re-images the illuminator onto the diffuser plane which with a time-sequential display synchronized with changing illuminators gives a full resolution 3-D display. Lens array LS2 is the image splitter.

Figure 3 shows a further prior art autostereoscopic display, as described in EP-A-O 656 555. The display is illuminated by an autostereoscopic projection unit 20 having an arTay of movable illuminators. The image is projected onto a double lenticular screen 21. The two lenticular arTays 22, 23 of the screen 21 have different focal lengths, and the lenticular screen 21 changes the view angle separation of the projected image. In this prior art display, the first lenticular screen generates an image of the switched illuminator 18. Such a prior art display is only suitable for projection-type displays where the components of the display are disparate, and not suitable for smaller, integral desktop' or 'direct view' types of display.

Figure 4 is a schematic plan view of a further prior art directional display 24 of the type described by Yamamoto et al in "Reduction of the Thickness of Lenticular Stereoscopic Display Using Full Colour LED Panel", Proc. SPIE Vol. 4660, p236 (2002). The display 24 is an autostereoscopic display, in which two lens arrays 25, 26 are placed in front of a very large poster-size LED display 27. The display 27 has a large pitch and a short viewing distance, and so would ordinarily be unsuitable for its use as an autostereoscopic display for large screen poster/advertiscmcnt style applications since l the separation between views at the intended (long) viewing distance would be greater than the average separation between the two eyes of a human being. To reduce the view angle separation, the first lenticular barrier 25 dc-magnifies the pixels of the display panel 27 to form an image of the display having a much smaller pixel pitch. The second lenticular sheet 26 separates two interlaced views displayed on the LED panel but, owing to the reduced pixel pitch of the imaged LED panel, the view angle separation is low so that the two images may comfortably be viewed by the left eye and right eye of an observer.

US 2002/000096 discloses a volumetric 3-dimensional display that uses multiple light sources. Each light source is provided with a light beam scanning means, such as a mirror, and a micro-lens element. The moving images of the light sources create a 3- dimensional image in space between the viewer and the display.

Park et al disclose, in "Analysis of viewing parameters for two display methods based on integral photography", Applied Optics Vol. 40 No. 29 pS217 (2001), an autostereoscopic display operating on the principle of integral imaging. This principle involves small image areas on a display being imaged by a lens array (one lens to each area) lo an image plane between the view and the display. Integral imaging can be considered to be a multiple-view display with a high number of views, where the separation between views is much less than the human eye separation. The lens array can be considered as a parallax optic, although the lenses focus the pixel planes areas to an image plane between the observer and the display, rather than into the observer's plane. The position of this image, however does not affect the viewing angle of the display.

JP-I() 206 795 discloses an autostereoscopic display in which a lenticular lens array is used as a parallax optic to provide angular separation between two displayed views.

The display further comprises a parallax barrier that limits the light passing through the lens array, and thereby reduces cross-talk and helps in formation of the viewing windows. The barrier and lens array are roughly in the same plane. The lens array is the image splitter and the barrier reduces the crosstalk of the system by restricting light l l through the lenses. The lens does not reimage the barrier or pixels (except as a normal lenticular would image the pixels into the view plane) .

US-A-6 304 288 discloses a tracked autostereoscopic display system that has two lenticular barriers, one in front of the image display panel and one behind the image display panel. The display is illuminated by a light source array, and the lenticular barrier behind the image display panel focuses the light source elements into the pixel plane. The lenticular barrier in front of the image display panel provides angular separation between two images displayed on the image display panel.

US-A-6 061 179 discloses a display that is switchable between a 2-D display mode and a 3-D display mode. In one embodiment, the display comprises a single mask and a single lenticular barrier, and switching between the display modes is effected by moving the lenticular barrier towards or away from the mask.

US-A-5 682 215 discloses a liquid crystal display panel containing intracell lenses.

These are provided to improve the brightness of the display panel, by redirecting the light that would otherwise be incident on an opaque component such as a gate or source line.

EP-A-I 089 115 discloses a liquid crystal cell provided with external micro-lenses. The display is not a directional display, and the microlenses are not provided to separate views. Rather the display is a reflective display for use in a projection display.

A second aspect of the present invention provides a multiple-view directional display comprising: a parallax optic; a pixellatcd image display layer; and an imaging means for imaging the parallax optic so that the separation between the image of the parallax optic and the image display layer is less than or is greater than the separation between the parallax optic and the image display layer, thereby increasing or decreasing, respectively, the angular separation between two viewing windows generated by the display.

A third aspect of the present invention provides a multiple-view directional display comprising: a parallax optic; a pixellated image display layer; and an imaging means for imaging one of the parallax optic and the image display layer such that the image of the parallax optic or the image display layer has a pitch substantially equal to the pitch of the parallax optic or image display layer.

A display according to the second or third aspects of the invention may be used either to decrease or increase the view angle separation. In particular, it allows the view angle separation to be decreased, in the case of a display intended to be viewed by an observer a long way from the display, without the need to use thick glass substrates. These aspects of the invention may also be used to increase the view angle separation in an application where a display would not otherwise produce sufficient angular separation at a given viewing distance.

In a display according to the third aspect, the imaging means is arranged to produce an image of the parallax optic or the image display layer having a pitch substantially equal to the pitch of the parallax optic or the image display layer. In the prior art display 24 of Figure 4 the pitch of the image of the pixellated display layer is deliberately made smaller than the pitch of the display layer to reduce the view angle separation.

However, if the pitch of the image of the parallax optic (or image display layer) is significantly different to the pitch of the parallax optic (or image display layer) viewing properties of the display, such as the resolution, are altered. It is therefore desirable that the pitch of the image of the parallax optic (or image display layer) is the same as or similar to the pitch of the parallax optic (or image display layer), since this allows the invention to be effected with minimum modification to other components of the display.

The imaging means of a display according to the first or second aspects may be arranged to produce an image of the parallax optic or the image display layer having a pitch substantially equal to the pitch of the parallax optic or image display layer.

The imaging means of a display according to the third aspect may form, in use, an image of the parallax optic or image display layer such that the separation between the image of the one of the parallax optic and the image display layer and the other of the parallax optic and the image display layer is less than or greater than the separation between the parallax optic and the image display layer thereby increasing or decreasing, respectively, the angular separation between two viewing windows generated by the display.

The parallax optic may be disposed behind the image display image, and the imaging means may be disposed between the parallax optic and the image display layer and may form, in use, an image of the parallax optic. Alternatively, the image display layer may be disposed behind the parallax optic, and the imaging means may be disposed between the image display layer and the parallax optic and may form, in use, an image of the image display layer.

The terms "behind" and "in front of" as used herein refer to the order of components as seen by a person observing the display from an intended viewing position of the display.

The imaging means may be arranged to produce an image of an element of the parallax optic or of a pixel of the image display layer having a width substantially equal to the width of the element of the parallax optic or the pixel of the image display layer. The imaging means may be arranged to produce unit magnification of the parallax optic or image display layer.

Alternatively, the imaging means may be arranged to produce an image of an element of the parallax optic or of a pixel of the image display layer having a width greater than the width of the element of the parallax optic or the pixel of the image display layer. The imaging means may be arranged to produce an image of an element of the parallax optic or a pixel of the image display layer having a width that is substantially an integral multiple of the width of the element of the parallax optic or the pixel of the image display layer. The imaging means may be arranged to produce non-unit magnification (greater than unit magnification) of the parallax optic or image display layer.

Alternatively, the imaging means may be arranged to produce an image of an element of the parallax optic or of a pixel of the image display layer having a width smaller than the pitch of the parallax optic or the image display layer. It may be arranged to produce an image of an element of the parallax optic or a pixel of the image display layer having a width that is substantially equal to the width of the element of the parallax optic or the pixel of the image display layer divided by an integer. The imaging means may be arranged to produce non-unit magnification (less than unit magnification or demagnification) of the parallax optic or image display layer.

The display may comprise blocking means for blocking the image of one or more elements of the parallax optic. The blocking means can be arranged to suppress, for example, generation of secondary viewing windows.

The blocking means comprises a plurality of opaque regions extending between the imaging means and the one of the parallax optic and the image display layer. The opaque regions allow an element of the imaging means to form an image of a corresponding element of the parallax optic or the image display layer, but block the light path between an element of the imaging means and other elements of the parallax optic or the image display layer.

The imaging means may have a variable focal length, and the display may have a controller for controlling the focal length of the imaging means.

The display may comprise a diffuser layer, the diffuser layer being positioned so as to be substantially coincident with the plane of the image of the parallax optic or the image of the image display layer.

The display may further comprise first tracking means for determining a distance between the display and an observer wherein the controller receives, in use, an output from the tracking means and thereby controls the focal length of the imaging means on the basis of the distance between the display and the observer.

The imaging means may have a variable focal length and a variable magnification, and the display may have a controller for controlling the focal length and magnification of the imaging means.

The display may further comprise a diffuser layer. Providing a diffuser layer in a display having a variable focal length imaging means may be used to provide a display in which the size, at the diffuser, of the image of the elements of the parallax optic or the size of pixels of the image display layer may be controlled, by controlling the position at which the image is formed. This allows the effective size of the image of the elements of the parallax optic, or of the image of the pixels, to be controllably varied.

The imaging means may comprise a lens arTay.

The imaging means may comprise first and second disableable lens arrays, the first lens array being laterally displaced with respect to the second lens array; and the display may comprise a controller for enabling either the first lens arTay or the second lens arTay while disabling the other of the first and second lens arTays.

The imaging means may be laterally moveable with respect to the one of the parallax optic and the image display layer.

The display may comprise second tracking means for determining the lateral position of an observer relative to the display. The controller may receive, in use, an output from the second tracking means. The lateral position of the imaging means relative to the one of the parallax optic and image display layer may be controlled on the basis of an output from the second tracking means.

The imaging means may be fixed relative to the one of the parallax optic and the image display layer and may be moveable with respect to the other of the parallax optic and the image display layer. Relative movement may be possible in a lateral direction and/or a longitudinal direction. The relative movement may be controlled on the basis of an observer tracking device that tracks lateral and/or longitudinal movement of an l l observer relative to the display. In this embodiment, the position of the imaging means is fixed relative to the component that it images. In an embodiment where the imaging means images the parallax optic, for example, the position of the image of the parallax optic relative to the image display layer may be controlled by moving the imaging means and parallax optic, together, relative to the image display layer.

The display may further comprise means for identifying an observer of the display.

The imaging means may be adapted to produce an image of the parallax optic or image display there that is laterally offset relative to the image display layer or the parallax optic whereby the display displays, in use, first and second images such that the angular extent of the first image is different from the angular extent of the second image.

The imaging means may be an asymmetric imaging means. This is another way in which first and second images of different angular extent may be formed.

Each clement of the imaging means may comprise a first portion having a first focal length and a second portion having a second focal length different from the first focal length. This produces two image of the parallax optic or image display layer, and so leads to first and second images of different angular extent.

The imaging means may be arranged such that the image of the parallax optic or image display layer is a virtual image.

The parallax optic or image display layer may cooperate with the imaging means to produce an image of the parallax optic or image display layer having a non-uniform pitch.

A fourth aspect of the present invention provides an optical device comprising a light- transmissive substrate having a parallax optic associated with one face of the substrate and a lens array associated with the other face of the substrate. The parallax optic may be formed on or adjacent the one face of the substrate. The lens array may be formed on or adjacent the other face of the substrate. The substrate, the parallax optic and the lens array may be formed as an integral unit.

Preferred embodiments of the present invention will be described by way of illustrative examples, with reference to the accompanying figures in which; Figure I is a schematic plan view of a prior art multiple-view directional display; Figures 2A and 2B show further prior art directional displays; Figure 3 shows a further prior art directional display; Figure 4 shows a further prior art directional display; Figure 5 is a schematic plan view of a directional display according to a first embodiment of the present invention; Figure 6 illustrates a modification of the display of figure 5; Figures 7A to 7I are schematic plan views of directional displays according to further embodiments of the invention; Figure 8A is a schematic plan view of display according to a further embodiment of the present invention and having a variable focal length imaging means; Figure 8B and 8C are schematic plan views of directional displays according to further embodiments of the invention; Figure 9A is a schematic plan view of a display according to a further embodiment of the present invention and having a multiple lens system; Figure 9B is a schematic plan view of a display according to a further embodiment of the present invention and having two separately controllable lens arrays; Figure 9C is a schematic plan view of a display according to a further embodiment of the present invention and having a laterally movable parallax barrier or imaging system; Figure 9D is a schematic plan view of a display according to a funkier embodiment of the present invention and having a movable parallax barrier and imaging system; Figure 10 is a schematic plan view of a display according to a further embodiment of the present invention; Figure 11 is a schematic plan view of a display according to a further embodiment of the present invention; Figure 12 is a schematic plan view of a displayaccording to a further embodiment of the present invention; Figures 13A and 13B are schematic plan views of a display according to a further embodiment of the present invention; and Figure 14 is a schematic plan view of a display according to a further embodiment of the present invention.

Like reference denote like components throughout the description and drawings.

Figure S is a plan view of a multiple-view directional display 28 according to a first embodiment of the present invention. The display 28 comprises an image display device 2 containing a pixellated image display layer 4 such as, for example, an active matrix TFT liquid crystal display layer disposed between first and second light- transmissive substrates S. 6. The display device 28 is illuminated by light 7 from a light source (not shown) disposed behind the display, and the image display layer may be any transmissive display layer; in this embodiment the image display layer 4 is a liquid crystal layer, and the display device 2 therefore comprises first and second polarisers 8, 9 disposed one on each side of the image display layer. The image display element 2 will further comprise addressing means such as pixel electrodes, switching elements etc for addressing the pixels of the liquid crystal layer, but these may be entirely conventional and so have been omitted from figure 5.

The display 28 further comprises a parallax optic 3 disposed behind the image display element 2. In this embodiment the parallax optic 3 is a parallax barrier having light- transmissive slits 10 that extend into the plane of the paper in figure 5, separated by opaque portions 11. In operation, drive means (not shown) drive the pixellated display layer 4 to display two interlaced images and this is indicated in figure 5 by every other column of pixels Cl, C3, C5 being shaded in grey to denote one image while other columns of pixels C2, C4, C6 are left unshaded to denote another image (the pixel columns extend into the plane of the paper in Figure 5). This is intended to indicate that one image is displayed on pixel columns Cl, C3, CS and a second image is displayed on the other pixel columns C2, C4, C6. The parallax barrier 3 causes angular separation of the two images displayed on the image display layer 4, so that two viewing windows are formed as shown in figure 5. The image displayed on pixel columns C1, C3, C5 is visible in the viewing window 13, and this window is therefore shaded in grey. The other image, displayed on pixel columns C2, C4, C6, is visible in the right viewing window 14.

The construction of the display 28 is thus far conventional.

The parallax barrier 3 is disposed between a first light-transmissive substrate i2 and a second light-transmissive substrate 12'.

A display device according to the present invention further comprises an imaging means for forming an image of one of the parallax optic 3 or the image display layer 4. Where the invention is applied to a rear barrier display, in which the parallax optic is disposed behind the image display element 2, as is the case in figure 5, the imaging means is disposed between the parallax optic 3 and the image display layer 4 and forms an image of the parallax optic 3. The imaging means is constituted by a lenticular lens array 29 in figure 5, and this forms an image 30 of the parallax barrier 3. Each lens of the lenticular lens array 29 extends substantially parallel to the pixel columns Cl...C6 of the image display layer 4.

Although figure 5 shows a lenticular lens array as the imaging means, the invention is not limited to this specific type of imaging means. In principle, any convergent diffractive or refractive micro-structures (for example, Fresnel lenses) could be used in place of normal Icnscs. The imaging means could also be formed using holographic optical elements.

In the absence of the imaging means, the view angle separation achieved by the display 28 of figure 5 would be determined by the pitch p of the pixels of the image display layer 4, the separation s between the image display layer 4 and the parallax optic 3, and the refractive index of the material separating the image display layer 4 and the parallax optic 3. According to the invention, the image 3() of the parallax optic is formed such that the separation between the image display layer 4 and the image 30 of the parallax optic, indicated as s' in figure 5, is less than the separation between the image display layer 4 and the parallax optic 3:that is, s' < s. The view angle separation in the display of figure 5 is determined by the separation between the image 30 of the parallax optic and the image display layer, according to: V = np/s' (2) where n is the refractive index of the material separating the image display layer 4 and the image 30 of the parallax optic (so in figure 5, n is the refractive index of the substrate 5) and where p is the pixel pitch of the image display 4.

The thickness of the substrate 5 does not affect the view angle separation as given by equation (2). The substrate 5 may therefore be relatively thick, so as to provide adequate structural strength.

The position of the image 30 of the parallax optic is determined by the focal length of the lenses of the lenticular lens arTay (or more generally, by the imaging power of the imaging means), and by the separation between the parallax optic 3 and the lenticular lens array (or, more generally, between the parallax optic and the imaging means). The separation between the imaging means and the parallax optic is determined by the thickness of the substrate 12' separating the parallax optic 3 and the imaging means.

The image 30 of the parallax optic may therefore be arranged to lie in any desired plane perpendicular to the axis of the display by choosing the imaging power of the imaging means, and the separation between the imaging means and the parallax optic, accordingly.

It will be appreciated that the first light-transmissive substrate 12 shown in figure 5 is not necessary to the operation of the display and can be omitted. The parallax optic 3, second light-transmissive substrate 12' and lens array 29 are preferably manufactured as an integral unit. l

Figure 6 shows a schematic plan view of a display 28' according to a further embodiment of the present invention. This embodiment is generally similar to the embodiment of figure 5, and the detailed description of the embodiment will not be repeated.

In the display 28' of figure 6, the imaging power of the imaging means (constituted by lenticular lens array 29) and the thickness of the substrates 12', 5 separating the parallax optic 3 and the image display layer 4 are chosen so that the image 30 of the parallax optic is not formed within the display 28' but is formed between the display and the observer. The view separation in this embodiment is again determined by the separation between the image 30 of the parallax optic and the image display layer 4, again indicated as s'. Provided that the image 30 of the parallax optic is located such that s' < s, where s is the distance between the image display layer 4 and the parallax optic 3, the embodiment of figure 6 will obtain an increased view angle separation.

Alternatively, if the image 30 of the parallax optic is located such that s' > s, this embodiment can provide a reduced view angle separation. This is of use where a display is used in an application with a large intended viewing distance and so which require a small view angle separation, since the invention avoids the prior art use of very thick, heavy glass substrates.

In the displays of figures 5 and 6, the imaging means is arranged so that the pitch of the image of the parallax optic is equal or substantially equal to the pitch of the parallax optic - thus, in the image 30 of the parallax optic, the pitch b' between apertures 10' of the image 30 of the parallax optic is substantially equal to the original pitch b of the parallax optic 3. Furthermore, the width of an image of element of the parallax optic is approximately equal to the width of the element - so, in figures 5 and 6 the width w' of an image 10' of a barrier slit is approximately equal to the width w of a transmissive slit of the parallax barrier. The invention is not, however, limited to a display in which the image of the parallax optic (or the image of the image display layer, in embodiments in which the imaging means forms an image of the image display layer) is not significantly magnified compared with the original parallax optic (or image display layer). I;igure 7A is a plan view of a further display device 28" according to the present l l l invention, in which the image of the parallax optic is magnified (in this case, by greater than one) compared to the original parallax optic.

The display device 28" of figure 7A corresponds generally to the display device 28 of figure 5, and will therefore not be described in detail. In the display device 28", however, the imaging means which in this embodiment is again a lenticular lens array 29 images the parallax optic 3 such that the images of the elements of the parallax optic are magnified compared to the original elements. The magnification is obtained by using a lens array 29 having a focal length such that the distance between the lens array and the image 30 of the parallax optic is greater than the distance between the parallax optic and the lens array. This is shown in figure 7A for a display where the parallax optic is a parallax barrier 3 having transmissive slits 10 separated by opaque regions 11, although this embodiment of the invention is not limited to this particular form of the parallax optic.

In more detail, the width w' of the image 10' of a transmissive slit 10 of the parallax barrier is greater than the width w of the transmissive slit 10 in the original parallax barrier 3. The pitch b' of the image 30 of the parallax barrier is, however, equal or approximately equal to the pitch b of the original parallax barrier 3 because each lens segment images its particular aperture. The pitch of the lens array is preferably the same as the pitch b of the parallax barrier.

In a particularly preferred embodiment, the width w' of the image 10' of a slit of the parallax barrier is approximately equal to an integral multiple of the width w of a transmissive slit 10 of the parallax barrier 3. In figure 7A the width w' of the image 10' of the transmissive slits in the image 30 of the parallax barrier is approximately double the width w ot the transmissive slits 10 in the parallax barrier 3, but any approximately integral multiple could be used. Making the width w' of the image 10' of the transmissive slits an integral multiple of the width w of the transmissive slits 10 of the parallax barrier means that secondary viewing windows 31 do not overlap with the primary viewing windows 13, 14. An observer can therefore view the display 28" without experiencing cross-talk. Making the width w' of the image 10' of a t transmissive slit greater than, but not equal to an integral multiple of, the width w of a transmissive slit 10 of the parallax barrier 3 could result in cross-talk. For example, if the secondary window formed by the left-eye image (in the case of an autostereoscopic display) overlapped the primary viewing window for the right-eye image, an observer would experience some cross- talk as their right eye would see a mixture of the left-eye and right-eye images In some applications, however, non-integral magnification of the width of the transmissive slits can be used, provided that the cross-talk is kept down to an acceptable level.

Figure 7B is a schematic plan view of a further display 28". This is again generally similar to the displays of figures 5 and 7A, and will therefore not be described in detail.

The imaging means of the display 28" of figure 7B, which is again a lenticular lens array 29, produces an image 30 of the parallax optic of the display. The parallax optic is again a parallax barrier 3. The lenticular lens array produces an image 30 of the parallax barrier in which the width w' of the images 10' of the transmissive slits is less that the width w of the transmissive slits. Furthermore, the pitch of the image of the parallax barrier b' is less than the pitch b of the parallax barrier 3. That is, w' < w and b' < b, and both the slit width and barrier pitch are reduced by the same amount.

In figure 7B the width w' of the images 10 of the transmissive slits of the parallax barrier 3 is approximately one half of the width w of the slits lO of the parallax barrier 3.

Making the width w' of the images to' of the transmissive slits less than the width w of the transmissive slits 10 of the parallax barrier means that the spatial extent of the images of the transmissive slits in the parallax barrier 3 is reduced, which would increase the brightness of the display if the width of the pixels of the image display layer 4 arc small - if the slit is wider than the pixel aperture light is lost in the black mark of the display layer, so reducing the width w' of the images of the slits lO allows l more light through a pixel. Also, a smaller pixel aperture and barrier slit lead, in general, to reduced cross-talk. Furthermore, if the width w of the images 10' of the transmissive slits is made small, the divergence of the light is increased and the viewing angle range of the display is made greater.

While using an imaging means that produces an image of the parallax optic with a magnification of less than one provides the above advantages, a significant disadvantage is that, since the pitch b' of the image 30 of the parallax barrier is also reduced, secondary windows that overlap the primary windows are produced, and this will lead to cross-talk. In figure 7B, for example, the image lO'a of one transmissive slit 10 of the parallax barrier gives rise to a primary viewing window denoted by A. An adjacent image lO'b of a transmissive slit 10 of the parallax barrier gives rise to a secondary viewing window denoted by B. As can be seen in figure 7B, the two viewing windows overlap, and an observer situated in the region of overlap will experience cross-talk.

Figure 7C is a schematic plan view of a display device 32 according to a further embodiment of the present invention. The display of figure 7C corresponds generally to the display of 7B and, in particular, the imaging means (in this embodiment a lenticular lens array 29) produces a magnification of approximately one half, so that the width of an image of an element of the parallax optic is approximately one half the width of an element of the parallax optic. In figure 7C the parallax optic is shown as a parallax barrier having transmissive slits 10 and opaque portions 11; the width w' of an image 10' of a transmissive slit, in the image 30 of the parallax bander, is approximately one half of the width w of a transmissive slit 10 of the parallax banier 3. The components of the display of figure 7C that correspond to the display 28" of figure 7B will not be described again.

The display 32 of figure 7C further comprises blocking means for blocking the image of one or more elements of the parallax optic. In the display 32 of figure 7C, the blocking means blocks every alternate image of a transmissive slit 10 of the parallax banier 3.

Thus, the image 30 of the parallax bander consists of transmissive regions 10' having a l l width w' approximately equal to one half the width w of the transmissive regions 10 of the parallax barrier, but with the pitch b' of the image 30 of the parallax barrier being equal or approximately equal to the pitch b of the parallax barrier itself (w' low, b b). Because the images 10' of the slits have a smaller width than the slits 10 of the parallax barrier, the advantages of improved brightness and improved viewing angle described above with reference to figure 7B also apply to the display 32 of figure 7C.

However, because the pitch of the images 10' of the transrnissive slits 10 is equal or approximately equal to the pitch of the transmissive slits 10 of the parallax barrier, the secondary viewing windows are eliminated and only the primary viewing windows 13, 14 remain. The cross-talk present in the images displayed by the display 28" of figure 7B has been eliminated. The display 32 of figure 7C is therefore particularly suited for use as an autostereoscopic display, with the primary windows 13, 14 corresponding to the left-eye and right-eye viewing windows.

In figure 7C the blocking means comprises the combination of a patterned polariser 33 and a patterned half-wave retarder 34. The direction of shading in the patterned polariser 33 and the polarisers 8, 9 indicates the direction of the transmission axis of the polarisers which, in this embodiment, are linear polarisers. It will be seen that the elements of the patterned polariser 33 are arranged with their transmission axis being alternately parallel to or at 90" to the transmission axis of the rear polariser 8 of the image display element 2. That is, the region 33A of the patterned polariser that is behind transmissive slit 10A has its transmission axis parallel to the transmission axis of the rear polariser 8, the region 33B that covers slit lOB of the parallax barrier has its transmission axis at 90 to the transmission axis of the rear polariser 8, and so on.

The patterned halt:wave retarder 34 consists of regions 34A, 34C that provide half- wave retardation alternating with regions 34B that have zero retardation. Each region 34A, 34B, 34C of the patterned retarder 34 corresponds generally to one lens of the lenticular lens array. Light passing through the central slit IOB of the parallax barrier 3 in figure 7C can pass through the central section of the rear polariser 8 - it passes through a part of the patterned p:'lariser having its transmission axis at +45 , the light passes through a region ol zero retardation, and is then incident on the polariser 8 which has its transmission axis at +45 . However, light coming through the upper or lower slit IDA, lOC of Figure 7C is polarised at -45 by the upper or lower element 33A, 33C of the patterned polariser, passes through a region of zero retardation and so is then blocked by the polariser 8 which has its transmission at +45 . Thus, every alternate image of a slit of the parallax barrier is blocked.

Figure 7D shows a further display 32' according to the present invention. This is generally similar to the display of figure 7C, and only the differences between the two displays will be described.

The display 32' of figure 7D again comprises a blocking means for blocking the images of selected elements of the parallax optic. The parallax optic is again a parallax barrier, and as a result of the blocking means the image 30 of the parallax barrier comprises images 10' of the slits 10 of the parallax barrier that have a width of approximately one half of the width of the slits of the parallax barrier, but that have a pitch that is the same, or approximately the same, as the pitch of the parallax barrier. In the embodiment of figure 7D, however, the images 10' of the transparent slits are positioned such that no primary windows are generated, and that left and right secondary windows 35, 36 are generated. The left and right secondary windows are separated by a dark area 37 in which no image is visible. The display 32' of figure 7D is therefore particularly suitable for use in a dual-view display, which is intended to display two independent images to two different observers. When the display 32' is used as a dual-view display, one observer would be positioned in the left secondary window 36 and would see one image, and a second observer positioned in the right secondary window 35 would see a different image. The presence of the central dark area prevents an observer from inadvertently seeing the incorrect image if they move or turn their head.

The blocking means in the display 32' of figure 7D are again formed by a patterned linear polariser 33 in which different regions have orthogonal transmission axes, and a patterned half-wave retarder 34. The patterned linear polariser 33 is placed in the path of light through the transmissive slits 10 of the parallax barrier, and the patterned half wave retarder is placed adjacent to the polariser 8. The blocking means operates in a similar manner to the blocking means of Figure 7C.

Figure 7E is a schematic plan view of a further display 28"' according to the present invention. This embodiment generally corresponds to the display 28"' of figure 7B; in particular, the imaging means (in this embodiment a lenticular lens array 29) produces an image of the parallax optic in which the width of a parallax element, and the pitch of the parallax optic, are reduced by approximately one half. The display 28"' of figure 7E is generally similar to the display 28" of figure 7B, and only the differences will be described here.

In the display 28"' of figure 7E, the parallax optic is a parallax barrier 3 having transmissive slits 10 separated by opaque portions 11. In this embodiment, the slits width and pitch of the parallax barrier are chosen to provide the desired width of the image 10' of the slit and the desired pitch b' in the image 30 of the parallax barrier. In the case shown in figure 7E where the lenticular lens array 29 creates an image having a magnification of approximately one half, the width w of a slit of the parallax barrier 3 is therefore made approximately twice as great as the desired slit width. This ensures that the width w' of an image 10' of the slit in the image 30 of the parallax barrier will have the desired width. Similarly, the pitch of the parallax barrier 3 is made approximately twice as great as desired, so that the pitch b' of the image 30 of the parallax barrier is equal to the desired pitch. As a result, the prevention of secondary viewing windows is suppressed and cross-talk is prevented. However, since the width w' of the images 10' of the slits in the image 30 of the parallax barrier have a reduced width, the advantages of increased brightness and high light divergence are retained.

Figure 7F shows a display 60 according to a further embodiment of the present invention. The display 60 of figure 7F corresponds generally to the display 28" of figure 7B, and only the differences will be described. The display 60 of figure 7F comprises opaque "flanges" 57 that extend between the parallax optic 3 and the imaging means 29". The flanges extend substantially parallel to the axis of the display, and extend over substantially the entire vertical height ol the display (that is, they extend into the plane of the paper in figure 7F). The distance d between adjacent flanges 57 is equal to the pitch of the imaging means 29'.

The flanges 57 are arranged so that each element 29a, 29b, 29c of the imaging means can form an image of only one corresponding element lea, 10b, 10c of the parallax optic 3. In figure 7F, the parallax optic 3 is shown as a parallax barrier having transmissive apertures 10a, lOb, lOc, and the imaging means is shown as a lens array having lens elements 29a, 29b, 29c. The central lens element 29b shown in Figure 7F, for example, is able to form an image of the central transmissive aperture 10b of the parallax barrier, as indicated in the figure. However, the central lens 29b of the lens array is not able to form images of the upper or lower apertures lea, 10c of the parallax barrier, since the flanges 57 prevent light passing through the upper or lower apertures lea, 10c of the parallax optic from reaching the central lens 29b of the lens array.

Similarly, the upper lens element 29a of the lens array can form an image only of the upper slit lOa of the parallax barrier, and the lower lens 29c of the lens array can form an image only of the lower slit lOc of the parallax barrier.

In consequence, in the image 30 of the parallax barrier the image 10' of each transmissive slit IOa, lOb, 10c is reduced in width by the magnification of the lens array (in figure 7F the lens array provides a magnification of approximately one half, but the embodiment can be applied to any magnification of less than 1. However, the advantages given above in connection with the display of figure 7B are therefore obtained. However, the presence of the opaque flanges 57 means that the pitch of the image of the parallax barrier is equal or approximately equal to the pitch b of the original parallax barrier 3. The generation of secondary windows is therefore prevented, and cross-talk is reduced. Since there are no secondary viewing windows, the display is dark outside the primary viewing zone and this may be advantageous where the invention is applied to a security screen. The flanges 57 accordingly act as blocking means that block each element of the imaging means from forming an image of more than one element of the parallax optic. They achieve the same result as the patterned polariser 33 and patterned half-wave retarder 34 of the embodiment of figure 7C.

The substrate 12' may be formed from several sections of glass, with an opaque layer disposed between each section so as to form the flanges. Alternatively, deep cuts may be made in a substrate, and each cut filled with an opaque material to form a flange 57.

Figure 7G shows a display 62 according to a further embodiment of the present invention. The display 62 of figure 7G corresponds generally to the display 28 of figure and the display 28" of figure 7A, and only the differences will be described. In the figure 7G embodiment, the imaging means 29 comprises weak convergent lenses that do not image the parallax barrier 3 in front of the imaging means 29 but instead produce a virtual image 30 of the parallax barrier 3 behind the imaging means 29, with a separation s' between the parallax barrier image 30 and display layer 4 that is greater than the separation s between the actual parallax barrier 3 and display layer 4. This results in a narrower view angle separation than would be produced with the actual parallax barrier 3 and display layer 4 in the absence of the imaging means 29.

Figure 7H shows a display 63 according to a further embodiment of the present invention. The display 63 of figure 7H corresponds generally to the display 62 of figure 7G, and only the differences will be described. In the figure 7H embodiment, the imaging means 29 comprises divergent lenses that produce a virtual image 30 of the parallax barrier 3 behind the imaging means 29, and in this embodiment also in front of the parallax barrier 3, with a separation s' between the parallax barrier image 30 and display layer 4 that is less than the separation s between the actual parallax barrier 3 and display layer 4. This results in a wider view angle separation than would be produced with the actual parallax barrier 3 and display layer 4 in the absence of the imaging means 29.

Figure 7I shows a display 64 according to a further embodiment of the present invention. The display 64 of figure 7I corresponds generally to the display 63 of figure 7H, and only the differences will be described. In the figure 7I embodiment, the imaging means 29 are disposed adjacent the image display layer 4 on the front face of the light-transmissive substrate 5, rather than on the front face of the light-transmissive substrate 12'. The imaging means 29 comprises divergent lenses that produce a virtual image 30 of the parallax barrier 3 behind the imaging means 29, and in this embodiment also in front of the parallax barrier 3 and inside the light- transmissive substrate 5. The separation s' between the parallax barrier image 30 and display layer 4 is less than the separation s between the actual parallax barrier 3 and display layer 4. This results in a wider view angle separation than would be produced with the actual parallax barrier 3 and display layer 4 in the absence of the imaging means 29. Weak convergent lenses could also be used in the imaging means 29. The imaging means 29 can also be formed integrally with the image display layer 4; for example the imaging means may be formed from microstructures within the pixel plane itself. Figure 8A is a plan view of a display according to a further embodiment of

the present invention. The display 38 of figure 8A corresponds generally to the display 28 of figure 5, and only the differences will be described.

In the display 38 of figure 8A, the imaging means (which in this embodiment forms an image of the parallax optic) has a variable focal length. The focal length of the imaging means is controlled by a controller 40. It is therefore possible to control the position of the image of the parallax barrier and thereby control the separation between the image display layer 4 and the image of the parallax barrier. This enables the view angle separation of the display to be controlled. For example, if the focal length is set so the image of the parallax barrier is formed in one position 30a, the separation between the image and the image display layer 4 is relatively low, and a wide view angle is therefore obtained - which is desirable for a display operating as a dualview display where the images are intended to be viewed by different observers. Conversely, if the image of the parallax barrier is formed at another position 30b, the separation between the image of the parallax barrier and the image display layer 4 is greater (although still less the separation between the parallax barrier and the image display layer), leading to a lower view angle than when the image of the parallax barrier is at the first position 30a - and this may be appropriate for a display intended to be used as an autostereoscopic display, where the view angle must be chosen such that the image separation corresponds to the separation between the eyes of a human being. By suitably controlling the focal length of the imaging means, therefore, it is possible to alter the view angle of the display 38.

This allows the view angle to be adjusted to suit a particular application and, in particular, allows the display to be switched between a dual-view display mode and an autostereoscopic display mode. It is also possible to switch the display between a rear- barrier mode, in which the image of the parallax optic is disposed behind the image display layer 4, and a front-barrier mode in which the image of the parallax optic is disposed in front of the image display layer 4.

Any suitable imaging means having a variable focal length may be used in the display 38 of figure 8A. For example, modal liquid crystal lenses, pixellated liquid crystal lenses, or micro-lens structures filled with liquid crystal may be used. In each case, the focal length of these lenses varies with the applied voltage across the liquid crystal lens.

In this case the controller 40 would control the voltage applied across the lens array.

Thus, the focal length of the imaging means may be controlled simply by controlling the magnitude of the voltage applied across the lenses using the controller 40.

Figure 8B is a schematic plan view of a further display 38' according to the present invention. The display 38' of figure 8B is generally similar to the display 38 of figure 8A, and only the differences will be described here.

The display 38' of figure 8B is further provided with tracking means 41 for determining the longitudinal distance between the display and an observer. The controller 40 for controlling the focal length of the imaging means receives, as input, an output signal from the tracking means 41 indicative of the longitudinal distance between the display and the observer. The controller 40 is therefore able to vary the focal length of the imaging means, and thus vary the position of the image 30 of the parallax optic, on the basis of the longitudinal distance between the observer and the display. When the display is used in an autostereoscopic mode, the view angle separation can be varied on the basis of the longitudinal distance between the display 38' and an observer, and this enables the separation between the left and right viewing windows to be kept equal to the separation between the eyes of the observer. In contrast, a conventional autostereoscopic display is intended to be viewed by an observer at a fixed distance from the display, and the view angle separation is set so that the left-eye and right-eye images are correctly spaced for an observer at that distance. However, if the observer moves towards or away from the display the lateral separation between the viewing windows decreases or increases, and thus ceases to be equal to the separation between the eyes of the observer.

Figure 8C is a schematic plan view of a display device 38" according to a further embodiment of the present invention. In this embodiment, the imaging means is again a variable focal length imaging means, and its focal length is controlled by a suitable controller 40.

In the display 38" of figure 8C, the parallax optic is a parallax barrier 3. The variable focal length imaging means 39 is arranged such that it can create an image of the parallax barrier in the plane of the image display layer 4. Furthermore, the width and pitch of the parallax barrier, and the magnification produced by the imaging means 39, are arranged such that the image of the parallax barrier 30 has no imaged black areas in the plane of the image display layer 4 or behind the plane of the image display layer 4, as indicated schematically in figure 8C. (In Figure 8C the parallax barrier has a 2:1 black area: transmissive slit ratio and the image of the parallax barrier at position 30C is magnified by approximately a factor of 3.) The parallax barrier 3 has therefore effectively been disabled, and a two-dimensional display mode may be obtained. This display device may therefore be switched between a three- dimensional display mode and a two-dimensional display mode by controlling the imaging means to provide the appropriate image of the parallax barrier 3. When the image of the parallax barrier provides imaged black areas behind the pixel plane, as shown at 30B in figure 8C, a three-dimensional display mode will result as shown in figures 5 or 6.

The display device 38" of figure 8C may further be switched between different three- dimensional display modes. For example, the focal length of the lens array 39 may be controlled to give either a dual-view display mode or an autostereoscopic display mode as explained with reference to figure 8B above, as well as a 2-D display mode (although this may require a more complex optical system such as, for example, the optical system shown in Figure 9A).

Figure 9A is a plan view of a display device 42 according to a further embodiment of the present invention. This embodiment generally corresponds to the display device 28 of figure 5, and only the differences will be described.

The display device 42 of figure 9A comprises an imaging means formed of multiple layers of lenses. In figure 9A three layers 43, 44 and 45 are shown, with each layer constituting a lenticular lens array. Two of the layers comprises lenses having a variable focal length, and these are the central lens 44 and one other lens layer (in figure 9A the central lens layer and the right hand lens layer 44, 45 are controllable). The lenses having variable focal length may be a liquid crystal lens, as described above in relation to the display of figure 8A. The focal lengths of the variable focal length lens layers 44,45 are controlled independently of one another by a suitable controller (not shown). This embodiment allows independent control of the focal length and magnification of the imaging means. The display 42 may therefore be switched between two-dimensional and three-dimensional display modes, and/or between different three-dimensional display modes, as described with reference to figures 8A to 8C above.

Since the embodiment of Figure 9A provides independent control over both the focal length and the magnification of the imaging means, it is possible to ensure that the pitch of the image of the parallax optic (or image display layer) is always equal to the pitch of the parallax optic (or image display layer), regardless of the position of the image. In contrast, in the embodiments of 8A, 8B and 8C in which only the focal length of the imaging means can be controlled it is possible that, in practice, varying the focal length of the imaging means results in an accompanying change in the magnification of the imaging means in which case the pitch of the image of the parallax optic (or image display layer) varies slightly with the position of the image. This can give rise to the formation of secondary windows for some positions of the image of the parallax optic (or image display layer); these secondary windows may be eliminated using, for example, the techniques of Figures 7C, 7D or 7F.

Figure 9B shows a display 43 according to a further embodiment of the present invention. The display 46 of this embodiment is intended to allow tracking of an observer who is moving laterally with respect to the display.

The imaging means of the display 46 comprise two disableable lens arrays 47, 48, one disposed behind the other. The two lens arrays 47, 48 have the same pitch but are offset laterally with respect to one another in figure 9B by approximately one eighth of the pitch. The focal lengths of the two lens arrays are approximately the same, so that the arrays 47, 48 produce respective images 30A, 30B of the parallax optic 3 that are in the same longitudinal position but arc laterally offset by one quarter of the pitch with respect to one another. (In figure 9B the two images of the parallax optic 30A, 30B are shown as longitudinally offset, but this is just for clarity of drawing - preferably, the two images 30A, 30B lie in the same plane).

The two lens arrays 47, 48 are independently controllable by means of a controller 40.

In particular, the controller 40 may enable either one or the other of the lens arrays 47, 48 and disable the other array.

The display 46 further comprises a tracking means 41 for tracking the lateral position of an observer relative to the display. The controller 40 receives, as an input, an output signal from the tracking means 41 that provides information as to the lateral position of the observer. Depending on the lateral position of the observer relative to the display, the controller 40 may select either one or the other of the lens arrays 47, 48. Since the images 30A, 30B of the parallax optic produced by the two lens arrays are laterally offset by one quarter of the pitch, the viewing windows generated by the lens array 47 are angularly displaced from the viewing windows produced by the lens array 48. In figure 9B, the positions of the centres of the primary viewing windows produced by the lens array 47 are shown in full lines, and the positions of the centres of the viewing windows produced by the lens array 48 are shown in broken lines.

Thus, by switching from one lens array to the other, it is possible to displace the viewing windows laterally, to follow the movement of an observer.

One method of providing the switchable lens arrays 47, 48 will now be described. In this method, each lens array consists of liquid crystal lenses 47a, 48a disposed in a transmissive substrate 47b, 48b such as for example glass. If the refractive index of a lens 47a, 48b is matched to the refractive index of the surrounding substrate 47b, 48b, the lens is effectively disabled and produces no lensing effect, whereas if the refractive index of the liquid crystal material of the lens 47a, 48a is different from the refractive index of the respective substrate 47b, 48b then the tensing effect is produced. Thus, by applying a suitable voltage across the liquid crystal material of the lenses 47a, 48a and thereby controlling their refractive index, it is possible to select one of the lens arrays while disabling the other lens array.

In an alternative embodiment (not shown), the lens arrays 47, 48 are not controllable.

In this embodiment, one lens array is arranged such that the liquid crystal material is index-matched to the surrounding substrate for light of one polarization and the other lens array 48 is arranged so that the refractive index of the lens array is index-matched to the surrounding substrate for light having an orthogonal polarization state. In this case one or other of the lens arrays may be selected by controlling a suitable polarization switch (not shown) that controls the polarization of the light incident on the lens array.

Figure 9C shows a further display 49 according to the present invention. This display 49 is again able to vary the angular position of the viewing windows to follow, for example, lateral movement of an observer.

In the display of figure 9C, the imaging means, here shown as a conventional lenticular lens array 29, is arranged to be laterally movable with respect to the parallax optic. In figure 9C the imaging means is shown as being mechanically movable, but it will be possible for the parallax barrier to be laterally movable in addition to or instead of the imaging means. By varying the lateral position of the imaging means relative to the parallax optic, the lateral position of the images of the elements of the parallax optic are also varied. Where the parallax optic is a parallax barrier, for example, varying the lateral position of the imaging means relative to the parallax barrier will cause the lateral position of the images 10' of the transmissive slits 10 of the parallax barrier to change. As explained with relation to figure 9B, this will in turn change the angular position of the viewing windows generated by the display 49.

Controller 40 receives, as input, an output signal from a tracker 41 that tracks the lateral position of an observer relative to the display 49. The lateral position of the imaging means, relative to the parallax barrier, is controlled by controller 40 on the basis of the input from the tracker 41 so as to vary the angular position of the viewing windows to follow the lateral movement of an observer.

The remaining components of the display 49 correspond to those of the display 28 of figure 5 and will not be described further.

In a modification of this embodiment, the parallax barrier 3 is embodied as a spatial light modulator such as, for example, a liquid crystal panel. In this embodiment, lateral movement of the parallax barrier is simulated by re-addressing the spatial light modulator so that the lateral positions of the transmissive slits of the parallax barrier move laterally.

Figure 9D is a plan view of a further multiple view directional display 49' of the present invention. The display 49' corresponds generally to the display 49 of Figure 9C, and features of the display 49' that are in common with the display 49 of Figure 9C will be described again.

In the display of figure 9D, the position of the imaging means, here shown as a conventional lenticular lens array 29, is fixed with respect to the parallax optic 3, here shown as a parallax barrier. This may be effected by mounting the imaging means on one of the substrates 12' of the parallax optic. The imaging means and parallax optic are movable, together, with respect to the image display device 2. In figure 9D the imaging means and parallax optic are shown as being mechanically movable, but it will be possible for the image display device to be movable in addition to or instead of the imaging means.

The imaging means 29 and parallax optic 3 may together be movable laterally and/or longitudinally with respect to the image display device 2. By varying the lateral position of the imaging means and the parallax optic relative to the image display device, the lateral position of the images of the elements of the parallax optic are also varied. As explained with relation to figure 9B, this will in turn change the angular position of the viewing windows generated by the display 49', thus allowing the display to track an observer moving laterally with respect to the display.

By varying the longitudinal position of the imaging means and the parallax optic relative to the image display device, the longitudinal position of the images of the elements of the parallax optic are also varied. As explained with relation to figure 8B, this will in turn change the view angle separation of the viewing windows generated by the display 49', thus allowing the display to track an observer moving longitudinally with respect lo the display. The display can provide a constant lateral separation between viewing windows regardless of the longitudinal distance between the display and an observer.

The lateral and/or longitudinal movement of the imaging means and the parallax optic relative to the image display device is controlled by a controller 40. Where the imaging means and the parallax optic can move in both lateral and longitudinal directions relative to the display, the controller 40 preferably controls the lateral movement and longitudinal movement independently from one another.

The controller 40 may receive, as input, an output signal from an observer tracking device 41 that tracks the longitudinal and/or lateral position of an observer relative to the display 49'. The controller 40 is able to control the longitudinal and/or lateral position of the imaging means and the parallax optic relative to the image display device on the basis of the output from the observer tracking device 41.

Figure 10 is a plan view of a further display 28"" of the present invention. In this embodiment, the present invention is applied to a front-barrier display, in which the parallax optic is disposed in front of the pixellated display layer, rather than an image of the parallax optic.

In figure 1O, the parallax optic is shown as a parallax barrier 3 having light-transmissive slits to separated by opaque regions 11. The imaging means is shown as a lenticular lens array, having a pitch that is substantially equal to the pixel pitch, or an integral multiple of the pixel pitch, of the pixellated display layer 4. The lenticular lens array 29 forms an image of the image display layer 4 such that the longitudinal separation s' between the parallax barrier 3 and the image 30 of the image display layer 4 is less than the longitudinal separation s between the parallax barrier 3 and the image display layer 4. The view angle separation is therefore increased, as explained above with reference to figure 5.

The remaining components of the display 28"" of figure 10 correspond generally to those of the display 28 of figure 5, and their description will therefore not be repeated here. It should be noted however, that the image display layer 4 of this embodiment may be either a transmissive image display layer illuminated by a backlight (not shown) or an emissive display layer such as a plasma or organic light-emitting device (OLED) display layer.

ln the display of figure lO, the image 30 of the image display layer is formed within the display, the lenticular lens array has a fixed focal length, and produces a magnification of approximately 1. In principle, however, the embodiments of figures 6 - 9C may all be applied in a frontbarrier display of the type shown in figure to (although in practice there may be difficulties in embodying the displays of Figures 7C and 7D as front battier displays since the primary image may overlap with the secondary image of an opposing pixel).

In the display of figuec IO, the image 30 of the image display layer is formed with a pitch that is substantially the same as the pitch of the image display layer 4. It would also be possible to arrange for the lens array 29 to have a different pitch to the image display layer 4, either larger or smaller. If the pitch of the lens array 29 is arranged to have a larger pitch, then the resulting pitch of the image 30 of the image display layer will be larger than the pitch of the image display layer 4, resulting in a further increase in the view angle separation.

Figure II shows a display 50 according to a further embodiment of the invention.

Features of the display 50 that are in common with the display 28 of figure 5 will not be described again.

In this embodiment, the imaging means comprises a lens array 51. The lenses 52 of the lens array are not formed with their flat surface perpendicular to the axis of the display.

Instead, the lenses 52 are mounted on micro-structures 53, so that the flat surfaces of the lenses 52 are at an angle to the longitudinal axis to the display.

The focal length of the lenses 52 is arranged such that they produce images of the elements of the parallax optic (in this case images 10' of the transmissive slits 10 of the parallax barrier 3) that are coincident with the pixels 54 of the pixellated display layer 4.

That is, the images 10' of the transmissive slits are in the plane of the pixellated display layer 4, and coincide or substantially coincide with the display area of the pixels 54 of the image display layer 4.

The images 10' of the slits 10 lie at an angle to the plane of the image display layer 4, as shown schematically in figure II. This is a consequence of the lenses 52 being mounted on the microstructures 53. As a result, the display 50 can provide good quality viewing windows at relatively large angles from the normal axis to the display.

Aberrations that typically occur at wide viewing angles in a conventional display are eliminated or reduced significantly in the display 50 of figure 11. The images 10' of the slits are locussed at the plane of the image display layer since there arc two lenses for each barrier slit. If the images 10' of the slits were in front of, or behind, the image display layer there would in general be twice as many images of the slits and the 3-D viewing windows could be swamped.

The embodiment of figure 11 may also be embodied in a front-barrier display in which the parallax optic is disposed in front of the image display layer 4.

In the above-described embodiments, the cone angle of view described by the vignetting of the lens rays will determine the maximum viewing angle that can be seen. These lines are marked on the figures relating to the embodiments. Notably, in the case of magnified images where the image sizes are greater than the original slit widths, the cone angle is also reduced. This is part of the rationale behind the embodiment described above with reference to figure 7D.

Figure 12 is a plan view of a display 55 according to a further embodiment of the present invention. Features of the display 55 that are in common with the display 28 of figure S will not be described again.

In this embodiment, a diffuser layer 56 is disposed within one of the substrates of the image display device 2. In figure 12 the diffuser layer 56 is shown as disposed within the first substrate 5, which is accordingly formed of two substrates 5a, 5b with the diffuser layer sandwiched there between, but the diffuser layer 56 could alternatively be provided within the second substrate 6 of the image display element.

The diffuser layer is positioned substantially perpendicular to the axis of the display.

The display 55 of figure 12 is a rear-barrier display, in which the imaging means (in figure 12 a lenticular lens array 29) forms an image 30 of the parallax optic. In this embodiment, the diffuser layer is positioned such that the image 30 of the parallax optic is substantially coincident with the diffuser layer. The image 30 of the parallax optic and the diffuser layer 56 are shown as longitudinally separated in figure 12, but this is for clarity of explanation, and it is preferable that the diffuser layer is positioned such that the image 30 of the parallax optic is coincident with the plane of the diffuser layer. r

The cone angle of the display depends on the divergence angle of the light focussed in the focus plane, and beyond this angle there will be vignetting. Providing the diffuser layer 56 improves the viewing angle of the display.

The diffuser layer 56 of figure 12 may be applied to any of the embodiments described above in which the imaging means produces an image of the parallax optic, and has a fixed imaging power so that the position of the image of the parallax optic is fixed, where the image of the parallax optic is formed within the display. The embodiment of figure 12 may also be applied to the front-barrier embodiments in which the imaging means produces an image of the image display layer 4, provided that the imaging power of the imaging means is fixed so that the position of the image of the image display layer is also fixed.

The diffuser layer of figure 12 may also be applied to a display that is switchable between a 3-D mode and 2-D mode. For example the diffuser layer 56 could be incorporated in a display of the type shown in figure 8C that is operable in a 3-D or dual view display mode and a 2-D display mode. The diffuser layer would be positioned so as to be coincident with the image of the parallax optic in the 3-D or dual view display mode, and an increased viewing angle would be obtained in the 3-D or dual view display mode. In the 2-D mode the image of the parallax barrier would be formed well away from the diffuser layer so that the diffuser layer becomes a uniform backlight in the 2-D display mode.

Figure 13A is a schematic plan view of a further multiple-view directional display 58 according to the present invention. The display 58 corresponds generally to the display of figure 12, and features in common to both displays will not be described again.

In the display 58 of figure 13A the imaging means 29 has a variable focal length and may be, for example, a lens array having a variable focal length as shown in figure 13A.

The parallax optic 3 and the imaging means 29 are arranged to provide an image of the parallax optic in which the image of the elements of the parallax optic are small. Where the parallax optic is a parallax barrier, for example, a parallax barrier having relatively narrow slits may be used. Additionally or alternatively, an imaging means with a magnification of less than one may be used, so that images of the slits 10' in the image of the parallax barrier arc narrower than the slits 10 in the parallax barrier, as described with reference to Figures 7B to 7E above.

The focal length of the imaging means is controllable using a suitable controller (not shown) to vary the position of the image 30 of the parallax optic. It is thus possible for the image 30 of the parallax optic to be formed behind the diffuser, or in the plane of the diffuser. Thus, by controlling the position of the image 30 of the parallax optic it is possible to change the size of the image of the elements of the parallax optic at the diffuser and thereby vary the effective size of the image of the elements of the parallax optic - thus producing a display in which the effective size of the elements of the parallax optic is controllable. The view angle separation is constant regardless of the effective size of the elements of the parallax optic and is determined by the separation between the diffuser layer and the image display layer.

The display 58 of Figure 13A may also be operable in a 2-D display mode, by controlling the focal length of the imaging means so that the image of the parallax optic is formed far from the diffuser layer 56, so that the diffuser layer acts as uniform backlight.

The display 58 of Figure 13A may also be operable in a 2-D display mode if the imaging means 29 is disableable. By disabling the imaging means, no image of the parallax barrier is formed. Light from the parallax barrier 3 is diffused by the diffuser layer 56 and a 2-D display mode is again obtained, as shown in Figure 13B. A disableable imaging means of this embodiment may be constituted by, for example, a disableablc lens array 47,48 of the embodiment of figure 9B.

The embodiments of figures 12 and 13 may also be applied to a frontbarrier display in which the parallax optic is disposed in front of the image display layer 4.

In the embodiments of figures 8A to 13, the pitch of the image of the parallax optic (or image of the image display layer) is equal orsubstantially equal to the pitch of the parallax optic (or image display layer).

The embodiments of figure 8B, 9B, 9C and 9D that incorporate an observer tracker may further be provided with means for identifying a user of the display. For example the display may have a tracking/identification device 26 that can track the position of a user's eyes and can also identify a user. For example, the tracking device 41 of figure 8B, 9B, 9C or 9D may comprise an iris sensor and/or a fingerprint sensor that contains information about the iris or fingerprint pattern of authoriscd users of the display.

When a person attempts to activate the apparatus, the tracking device 41 determines whether the person is an authorised user of the system, and will allow the system to be activated only by an authorised user. The tracking device 41 may further store information about the display mode most often used by each authorised user - and when the system is activated, the tracking device 41 would preferably instruct the controller to drive the display in the user's favourite display mode.

In the displays described above, the substrates, polarisers, parallax barrier, and lens arrays may be made of any suitable materials. The image display layer 4 may, in principle be any pixellated display layer. In embodiments where the image display layer is disposed in front oi the parallax optic any transmissive image display layer may be used, and in embodiments where the image display layer is disposed behind the parallax optic any transmissive or emissive image display layer may be used.

Depending on the nature of the image display layer 4, the polarisers 8, 9 of the image display device 2 may be unnecessary.

The present invention may also be used to obtain asymmetric viewing windows - that is, to provide a display in which the angular extent of the one viewing window is not equal to the angular extent of another viewing window. This can be done by use of an imaging system that produces an image of the parallax optic that is laterally offset relative to the image display layer, or that produces an image of the image display layer that is laterally offset relative to the parallax optic. This may be achieved by suitable lateral alignment of the imaging means.

Production of asymmetric viewing windows is described in co-pending UK patent application (Marks & Clerk reference: P52815GB). One technique disclosed in this co-pending application for obtaining asymmetric viewing windows is to use a parallax barrier that is substantially misaligned relative to the image display layer. It is known to make the pitch of the parallax barrier to be slightly less than the pitch of a pixellated image display panel, in order to provide "viewpoint correction", and in such a display there will be some small misalignment between the apertures of the parallax barrier and the pixels (or pixel columns) of the image display panel. In the above co- pending application, however, the misalignment between the parallax barrier and the image display layer is significantly greater than in known displays. For example, in the centre of the display, an aperture of the parallax barrier is typically displaced by around 20 from the correctly-aligned position. The effect of this misalignment is to make one viewing window small, and hence produce viewing windows having different angular extents to one another.

By suitable lateral position of the imaging means in the embodiments described above of the present invention, it is possible to produce an image of the parallax optic that is substantially misaligned relative to the image display layer (or to produce an image of the image display layer that is substantially misaligned relative to the parallax optic) and thereby produce asymmetric viewing windows in the manner taught in copending UK Patent Application No. The embodiment of Figure 9C can provide a display that can be controlled to provide either symmetric viewing windows or asymmetric viewing windows. If the lens array is correctly aligned with the parallax optic, the image of the parallax optic will be aligned with the image display layer, and symmetric viewing windows will be obtained. By laterally moving the lens array relative to the parallax optic, it is possible to create an image of the parallax optic that is severely misaligned with respect to the image display layer thereby producing asymmetric viewing windows. This also applies to the front barrier modification of Figure 9C.

Figure 14 shows a multiple-view directional display 59 of the present invention that can produce asymmetric viewing windows. The display 59 corresponds generally to the display 28 of figure 5, and only the differences between the display of figure 14 and the display of figure 5 will be described here.

In the display 59 of figure 14, the imaging means is asymmetric, in that the imaging power is not constant over each element of the imaging means. In the specific imaging means shown in Figure 14, the imaging means is a lens array 29 having asymmetric lenses. Each lens contains a portion 29a having a long focal length and a portion 29b having a short focal length. As a consequence, the lens array 29 produces two images of the parallax barrier. A first image 30a of the parallax barrier is produced by the portions 29a of the lenses of the lens array that have a long focal length. The second image 30b of the parallax barrier is formed by the portions 29b of the lenses of the lens array that have a short focal length, and the second image 30b of the parallax barrier therefore lies between the first image 30a of the parallax barrier and the lens array 29.

The two images 30a, 30b of the parallax barrier are laterally aligned with respect to one another. Furthermore, the two images have substantially the same size as one another.

Two images are displayed in interlaced manner on the image display layer, and Figure 14 shows the left eye image displayed on pixel columns Cl,C3,C5 and the right eye image displayed on pixel columns C2,C4,C6. A pixel column that displays the left-eye image is illuminated with light that has passed through the short focal length regions 29b of the lenses, whereas a pixel column that displays the right-eye image is illuminated with light that has passed through the long focal length regions 29a of the lenses. The separation between the image display layer 4 and the image of the parallax barrier therefore differs between the lcit eye image and the right eye image. The separation for the left eye image (SL) iS equal to the separation between the short focal length image 30b of the parallax barrier and the image display layer 4, but the separation (SR) for the right eye image is the separation between the long focal length image 30a of the parallax barrier and the image display layer 4, so that SL > SR. The viewing window 14 for the right eye image therefore has a greater angular extent than the viewing window 13 for the left eye image.

The embodiment of figure 14 may also be applied to a display in which the imaging means forms an image of the image display layer.

The above embodiments are described as incorporating a parallax barrier of standard form in which the slits are arranged repeated uniformly across the barrier. Co-pending UK patent application nos. 0228644.1, 0306516.6 and 0315170.1 disclose displays in which the parallax barrier is of a non-standard form. For example, co-pending application no. 0306516.6 discloses a parallax barrier in which the slits are arranged in repeating groups spaced apart by an inter-group separation, with the slits in each group being spaced apart by an intra-group separation smaller than the inter-group separation.

Such non-standard parallax barriers can be incorporated into an embodiment of the present invention by ensuring that the parallax optic and the imaging means cooperate to produce an image of the parallax optic is of the desired non-standard form. This can be achieved by: (a) having a parallax optic 3 of the non-standard design in combination with a uniform lens array 29 as described above; (b) having a standard parallax optic 3 as described above in combination with a non-standard lens array 29; the non-standard lens array 29 can be appropriately patterned with lenses that are not necessarily cylindrical, not necessarily straight or can involve opaque patches in the lens plane; or (c) having both a non-standard parallax optic 3 and non-standard lens array 29.

Claims

J

CLAIMS: 1. A multiple-view directional display comprising: a parallax optic; a pixellated image display layer; and an imaging means for imaging one of the parallax optic and the image display layer so that the separation between the image of the one of the parallax optic and the image display layer and the other of the parallax optic and the image display layer is less than the separation between the parallax optic and the image display layer thereby increasing the angular separation between two viewing windows generated by the display.
2. A multiple-view directional display comprising: a parallax optic; a pixellated image display layer; and an imaging means for imaging the parallax optic so that the separation between the image of the parallax optic and the image display layer is less than or is greater than the separation between the parallax optic and the image display layer thereby increasing or deceasing, respectively, the angular separation between two viewing windows generated by the display.
3. A multiple-view directional display comprising: a parallax optic; a pixellated image display layer; and an imaging means for imaging one of the parallax optic and the image display layer such that the image of the parallax optic or the image display layer has a pitch substantially equal to the pitch of the parallax optic or image display layer.
4. A display as claimed in claim 1 or 2 wherein the imaging means is arranged to produce an image of the parallax optic or the image display layer having a pitch substantially equal to the pitch of the parallax optic or image display layer.
5. A display as claimed in claim 3 wherein the imaging means forms, in use, an image of the parallax optic or image display layer such that the separation between the image of the one of the parallax optic and the image display layer and the other of the parallax optic and the image display layer is less than or greater than the separation between the parallax optic and the image display layer thereby increasing or decreasing, respectively, the angular separation between two viewing windows generated by the display.
6. A display as claimed in any of claims 1 to 5 wherein the parallax optic is disposed behind the image display image, and wherein the imaging means is disposed between the parallax optic and the image display layer and forms, in use, an image of the parallax optic.
7. A display as claimed in any of claims 1 to 5 wherein the image display layer is disposed behind the parallax optic, and wherein the imaging means is disposed between the image display layer and the parallax optic and forms, in use, an image of the image display layer.
8. A display as claimed in any of claims I to 7 wherein the imaging means is arranged to produce an image of an element of the parallax optic or of a pixel of the image display layer having a width substantially equal to the width of the element of the parallax optic or the pixel of the image display layer.
9. A display as claimed in any of claims 1 to 7 wherein the imaging means is arranged to produce an image of an element of the parallax optic or of a pixel of the image display layer having a width greater than the width of the element of the parallax optic or the pixel of the image display layer.
10. A display as claimed in claim 9 wherein the imaging means is arranged to produce an image of an clement of the parallax optic or a pixel of the image display layer having a width that is substantially an integral multiple of the width of the element of the parallax optic or the pixel of the image display layer.
11. A display as claimed in any of claims 1 to 7 wherein the imaging means is arTangcd to produce an image of an element of the parallax optic or of a pixel of the image display layer having a width smaller than the width of the parallax optic or the image display layer.
12. A display as claimed in claim 11 wherein the imaging means is arranged to produce an image of an element of the parallax optic or a pixel of the image display layer having a width that is substantially equal to the width of the element of the parallax optic or the pixel of the image display layer divided by an integer.
13. A display as claimed in claim 11 or 12 and further comprising blocking means for blocking the image of one or more elements of the parallax optic.
14. A display as claimed in claim 13 wherein the blocking means comprises a plurality of opaque regions extending between the imaging means and the one of the parallax optic and the image display layer.
15. A display as claimed in any preceding claim and comprising a diffuser layer, the diffuser layer being positioned so as to be substantially coincident with the plane of the image of the parallax optic or the image of the image display layer.
16. A display as claimed in any of claims l to 14 wherein the imaging means has a variable focal length.
17. A display as claimed in claim 16 and having a controller for controlling the focal length of the imaging means.
18. A display as claimed in claim 17 and further comprising first tracking means for determining a distance between the display and an observer wherein the controller receives, in use, an output from the tracking means and thereby controls the focal length of the imaging means on the basis of the distance between the display and the observer.
19. A display as claimed in any of claims l to 14 wherein the imaging means has a variable focal length and a variable magnification.
20. A display as claimed in claim 19 and having a controller for controlling the focal length and magnification of the imaging means.
21. A display as claimed in any of claims 16 to 20 and further comprising a diffuser layer.
22. A display as claimed in any preceding claim wherein the imaging means comprises a lens array.
23. A display as claimed in any of claims 1 to 15 wherein the imaging means comprises first and second disableable lens arrays, the first lens array being laterally displaced with respect to the second lens array; and wherein the display comprises a controller for enabling either the first lens array or the second lens array while disabling the other of the first and second lens arrays.
24. A display as claimed in any preceding claim wherein the imaging means is laterally moveable with respect to the one of the parallax optic and the image display layer.
25. A display as claimed in claim 23 or 24 and comprising second tracking means for determining the lateral position of an observer relative to the display.
26. A display as claimed in claim 25 when dependent directly or indirectly from claim 23 wherein the controller receives, in use, an output from the second tracking means.
27. A display as claimed in claim 25 when dependent from claim 24 wherein the lateral position of the imaging means relative to the one of the parallax optic and image display layer is controlled on the basis of an output from the second tracking means.
28. A display as claimed in any of claims 18 to 27 and further comprising means for identifying an observer of the display.
29. A display as claimed in any of claims 1 to 15 wherein the imaging means is fixed relative to the one of the parallax optic and the image display layer and is moveable with respect to the other of the parallax optic and the image display layer.
30. A display as claimed in any of claims I to 22 wherein the imaging means is adapted to produce an image of the parallax optic or image display layer that is laterally offset relative to the image display layer or the parallax optic whereby the display displays, in use, first and second images such that the angular extent of the first image is different from the angular extent of the second image.
31. A display as claimed in any of claims 1 to 22 wherein the imaging means is an asymmetric Imaging means.
32. A display as claimed in claim 31 wherein each element of the imaging means comprising a first portion having a first focal length and a second portion having a second focal length different from the first focal length.
33. A display as claimed in any preceding claim wherein the imaging means is arranged such that the image of the parallax optic or image display layer is a virtual image.
34. A display as claimed in any preceding claim wherein the parallax optic or image display layer cooperates with the imaging means to produce an image of the parallax optic or image display layer having a non- uniform pitch.
35. An optical device comprising a light-transmissive substrate having a parallax optic associated with one face of the substrate and a lens array associated with the other face of the substrate.
36. An optical device as claimed in claim 35, wherein the parallax optic is formed on or adjacent the one face of the substrate.
37. An optical device as claimed in claim 35 or 36, wherein the lens array is formed on or adjacent the other face of the substrate.
38. An optical device as claimed in claim 35, 36 or 37, wherein the substrate, the parallax optic and the lens array are formed as an integral unit.