GB2415850A

GB2415850A - Multiple view directional display operable in two orientations.

Info

Publication number: GB2415850A
Application number: GB0414496A
Authority: GB
Inventors: Diana Ulrich Kean; Jonathan Mather; Robert Winlow; David James Montgomery; Heather Ann Stevenson
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2004-06-29
Filing date: 2004-06-29
Publication date: 2006-01-04
Also published as: GB0414496D0

Abstract

A multi view directional display, such as an autostereoscopic, tree dimensional (3D) display, can display an image in two orientations, for example landscape or portrait (Figure 1). The display to viewer distance, and angular separation between images making up a stereo pair, are equal in each orientation; thus, display orientation may be changed without a viewer having to change their position. The display uses square colour pixels 11, 11', 11'' having an equal pixel pitch, and an opaque parallax barrier 12 having correspondingly square transmissive apertures 13; by using square pixels and parallax optical elements - having symmetric lens focal properties - the display operates in different orientations. Several colour pixels may be combined to form a composite square white pixel (14, Figure 7(a)). A colour filter may be used as the parallax barrier, or the barrier may be switchable (Figures 12(a) and 12(c)).

Description

A Multiple-View Directional Display The present invention relates to a

multiple-view directional display, which displays two or more images such that each image is visible from a different direction. Thus, two observers who view the display from different directions will see different images to one another. Such a display may be used in, for example, an autostereoscopic 3-D display device or a dual view display device.

For many years conventional displays have been designed to be viewed by multiple users simultaneously. The display properties of the display are made such that viewers can see the same good image quality from different angles with respect to the display.

This is effective in applications where many users require the same information from the display - such as, for example, displays of departure information at airports and railway stations. However, there are many applications where it would be desirable for individual users to be able to see different information from the same display. For example, in a motor car the driver may wish to view satellite navigation data while a passenger may wish to view a film. These conflicting needs could be satisfied by providing two separate displays, but this would take up extra space and would increase the cost. Furthermore, if two separate displays were used in this example it would be possible for the driver to see the passenger's display, which would be distracting for the driver. As a further example, in a computer game for two or more players each player may wish to view the game from his or her own perspective. This is currently done by each player viewing the game on a separate display screen so that each player sees their own unique perspective on individual screens. However, providing a separate display screen for each player takes up a lot of space, and is not practical for portable games.

To solve these problems, multiple-view directional displays have been developed. One application of a multiple-view directional display is as a 'dual-view display', which can simultaneously display two or more different images, with each image being visible only in a specific direction - so an observer viewing the display device from one direction will see one image whereas an observer viewing the display device from another, different direction will see a different image. A display that can show different images to two or more users provides a considerable saving in space and cost compared with use of two or more separate displays.

A further application of a multiple view directional display is in producing a three- dimensional image. In normal vision, the two eyes of a human perceive views of the world from different perspectives, owing to their different location within the head.

These two perspectives are then used by the brain to assess the distance to the various objects in a scene. In order to build a display which will effectively show a three dimensional image, it is necessary to re-create this situation and supply a so-called "stereoscopic pair" of images, one image to each eye of the observer.

Three dimensional displays are classified into two types depending on the method used to supply the different views to the eyes. A stereoscopic display typically displays both images of a stereoscopic image pair over a wide viewing area. Each of the views is encoded, for instance by colour, polarization state, or time of display. The user is required to wear a filter system of glasses that separate the views and let each eye see only the view that is intended for it.

An autostereoscopic display displays a right-eye view and a left-eye view in different directions, so that each view is visible only from respective defined regions of space.

The region of space in which an image is visible across the whole of the display active area is termed a "viewing window". If the observer is situated such that their left eye is in the viewing window for the left eye image of a stereoscopic pair and their right eye is in the viewing window for the right-eye image of the pair, then a correct view will be seen by each eye of the observer and a three-dimensional image will be perceived. An autostereoscopic display requires no viewing aids to be worn by the observer.

An autostereoscopic display is similar in principle to a dual-view display. However, the two images displayed on an autostereoscopic display are the left-eye and right-eye images of a stereoscopic image pair, and so are not independent from one another.

Furthermore, the two images are displayed so as to be visible to a single observer, with one image being visible to each eye of the observer.

For a flat panel autostereoscopic display, the formation of the viewing windows is typically due to a combination of the picture element (or "pixel") structure of the image display unit of the autostereoscopic display and an optical element, generically termed a parallax optic. An example of a parallax optic is a parallax barrier, which is a screen with transmissive regions, often in the form of slits, separated by opaque regions. This screen can be set in front of or behind a spatial light modulator (SLM) having a two- dimensional array of picture elements to produce an autostereoscopic display.

Figure 16 is a plan view of a conventional multiple view directional device, in this case an autostereoscopic display. The directional display 100 consists of a spatial light modulator (SLM) 104 that constitutes an image display device, and a parallax barrier 105. The SLM of Figure 16 is in the form of a liquid crystal display (LCD) device having an active matrix thin film transistor (TFT) substrate 106, a counter-substrate 107, and a liquid crystal layer 108 disposed between the substrate and the counter substrate. The SLM is provided with addressing electrodes (not shown) which define a plurality of independently-addressable picture elements, and is also provided with alignment layers (not shown) for aligning the liquid crystal layer. Viewing angle enhancement films 109 and linear polarisers 110 are provided on the outer surface of each substrate 106, 107. Illumination 111 is supplied from a backlight (not shown).

The parallax barrier 105 comprises a substrate 112 with a parallax barrier aperture array 113 formed on its surface adjacent the SLM 104. The aperture array comprises vertically extending (that is, extending into the plane of the paper in Figure 16) transparent apertures 115 separated by opaque portions 114. An anti-reflection (AR) coating 116 is formed on the opposite surface of the parallax barrier substrate 112 (which forms the output surface of the display 100).

The pixels of the SLM 104 are arranged in rows and columns with the colurans extending into the plane of the paper in Figure 16. The pixel pitch (the distance from the centre of one pixel to the centre of an adjacent pixel) in the row or horizontal direction being p. The plane of the barrier aperture array 113 is spaced from the plane ofthe liquid crystal layer 108 by a distance s.

In use, the display device 100 forms a lefI-eye image in a left-eye viewing window 102 and a right-eye image in a right-eye viewing window 103, and an observer who positions their head such that their left and right eyes are coincident with the left-eye viewing window 102 and the right-eye viewing window 103 respectively will see a three-dimensional image. The left and right viewing windows 102, 103 are formed in a window plane 1 17 at the desired viewing distance from the display. The window plane is spaced from the plane of the aperture array 113 by a distance rO. The intended viewing distance of the display, measured perpendicularly from the front face of the display, is equal to rO minus the thickness of the parallax barrier substrate 112. The windows 102, 103 are contiguous in the window plane. The viewing distance of the display is the distance from the display at which the lateral separation e between the viewing window for the right eye image and the viewing window for the left eye image is equal to the average separation between the two eyes of a human.

The pitch of the slits 115 in the parallax barrier 105 is chosen to be close to an integer multiple of the pixel pitch of the SLM 104 so that groups of columns of pixels are associated with a specific slit of the parallax barrier. Fig. 16 shows a display device in which two pixel columns of the SLM 104 are associated with each transmissive slit 115 of the parallax barrier. [The figure was unclear, as adjacent pixel columns were heavily shaded and in the copy were hard to distinguish from the black inter-pixel areas!] Figure 16 shows an autostereoscopic 3-D display. A dual view (or multiple view) display is similar in principle to an autostereoscopic display, but displays two (or more) different images to two (or more) different observers. The image display layer is therefore driven to display two (or more) independent images interlaced with one another. The viewing windows of the images are arranged to have, at the intended viewing distance, a size that can accommodate both eyes of an observer. The separation between viewing windows is made such that an observer will see only one of the displayed images.

Many conventional 2-D displays are designed such that they can be used in more than one orientation. This enables the viewer to have the flexibility to pick whether the image - whether still or moving - is better displayed in a landscape orientation as in figure 1(a) or in a portrait orientation as in figure l(b). One example of such a display is the SLC-760 & C750 Zaurus (trade mark) personal digital assistant (PDA) from Sharp Corporation which has a rotatable, 2-D liquid crystal display which may be used in landscape or portrait mode (see press release available at http://sharp- world.com/corporate/nevs/030516.html - May 16th 2003). Also, for some applications, in particular mobile device handsets, the ability to use the display in more than one orientation enables a reduction in the number of displays required for that device and also increases the flexibility in the way that the display may be integrated into the functionality of the device.

Multiple view directional displays, such as autostereoscopic 3-D displays and dual or multiple view displays, have hitherto been designed to operate in only one orientation of the display. Many directional displays have the images distributed in only one plane, and on rotating such a display the image splitting effect is not rotated and will in most cases not produce the desired effect.

Figure 2 is a schematic diagram of a multiple view display such as the display 100 of figure 16 and having, as is conventional, a parallax optic disposed in front of a pixellated image display layer. The parallax optic is a simple parallax barrier aperture array having opaque strips 114 separated by transmissive apertures 115. The opaque stripes 114 of the barrier extend in the vertical direction, as shown in figure 2. Two interlaced images are displayed on the image display layer - one image (for example a left eye image in the case of an autostereoscopic display) is displayed on pixels columns Cl, C3, C5... and another image (a right eye image in the case of an autostereoscopic display) is displayed on pixels columns C2, C4, C6... (Figure 2 shows a full colour display in which pixels columns Cl, C4, C7... display a red image, pixel columns C2, C5, C8 display a green image and pixel columns C3, C6, C9... display a blue image, but this is not relevant to the general principle of operation of the display.) The vertical opaque stripes 114 of the parallax barrier provide horizontal separation of the two images displayed on the image display layer so that the left and right eyes of an observer each see a different image, owing to the opaque strips 114 of the parallax barrier obscuring different portions of the display for each eye. This can be used to produce a 3D image.

The display shown in figure 2 is intended to be viewed in a landscape orientation, in which the horizontal width w of the display is greater than its vertical height h. When the display is rotated about an axis perpendicular to the front face (or display face) of the display into a portrait mode it appears as shown in figure 3. The image display layer can again be addressed to display two interlaced images, with one image on pixel columns C'I, C'3 and the other image on the alternate pixel columns C'2, C'4 (the pixel columns C'l, C'2... in the portrait mode are not the same as the pixel columns C1, C2... of figure 2). However, the parallax barrier cannot provide horizontal separation of the two images in the portrait mode. This is because, in this orientation of the display, the opaque stripes 114 of the parallax barrier are now horizontal. Thus, the two eyes of an observer now see the same portions of the display, and the same portions of the display are obscured for both eyes, so an observer will no longer perceive a 3-D image.

Some 3-D displays, in particular displays having a lenticular barrier as the parallax optic, are designed to produce multiple horizontal views and multiple vertical views.

Examples of such displays are described in, for example, "Super-multiview three dimensional display system", by S.S. Kim et. al., SID 02 Digest, pl422-1423 which describes a 3-D display that generates eight views in the horizontal direction and three views in the vertical direction. Another such display is described in US patent No. 6 373 637. In general, these displays are provided with multiple views in the vertical direction in order to increase the viewing freedom for the observer, and they are optimised to do this for the display in a particular orientation. If such a display is rotated, for example from landscape orientation to portrait orientation, the viewing distance of the display would change substantially.

In a similar way, taking a simple parallax barrier design with vertical opaque stripes 114 and vertical transmissive apertures 115 as shown in figure 2 and combining it with a simple horizontal parallax barrier would result in a parallax barrier 3 as shown in figure 4(b), in which rectangular transmissive apertures 4 are arranged in a matrix of rows and columns. The remainder of the parallax barrier is opaque to light. A suitable pixellated image display layer I for use with the parallax barrier 3 of figure 4(b) is shown in figure 4(a), and this contains pixels P arranged in a matrix of rows and columns. (In this example the image display layer is again a full colour display layer, so that pixels in pixel columns Cl, C4... are red pixels, pixels in pixel columns C2, C5... are green pixels and pixels in pixel columns C3, C6... are blue pixels.) The parallax barrier 3 will provide horizontal separation of two interlaced images displayed on the image display layer with the display oriented in either a portrait mode as in figure 4(c) or a landscape mode as in figure 4(d).

If the horizontal pixel pitch in portrait mode is denoted as pi, and the horizontal pixel pitch in landscape mode is denoted as p2, as indicated in figure 4(a), the viewing distance of the display of figures 4(a)-4(d) can be calculated as follows using the distances and angles as marked in Fig. 5.

If the refractive index inside the panel is n, and the refractive index outside the refractive index is I (corresponding to air), then by Snell's law: n sin(x) = sin(y) (1) However, the angles are small, so if the eye separation is e, the horizontal pixel pitch is p, the viewing distance is r, the pixel-barrier separation is s, then equation (1) can be approximated as: np/2s = e/2r (2) giving: r = es/np (3) Since p2 is significantly, typically about three times, larger than pi for an LCD panel, then from equation (3), the viewing distance of the display in portrait mode (when pi is the horizontal pixel pitch) will be typically about three times greater than the viewing distance in landscape mode at obtained (when p2 is the horizontal pixel pitch). This means that, if an observer is located at the correct viewing distance for viewing the display when the display is in a landscape orientation, when the display is rotated into a portrait orientation the observer will no longer be at the correct viewing distance from the display, and the observer will experience discomfort when they look at the display.

In the case of a large display the viewer will have physically to move towards or away from the display when the display is rotated, to position themselves at the correct viewing distance for the new mode - this is inconvenient, and in some cases may not be possible. Alternatively, in the case of a small mobile display the viewer is required to change how they are holding the display so as to move the display further away from, or closer to, their eyes. However, the extent to which a viewer can move a display is limited by ergonomic issues such as the length of the viewer's arm or the maximum distance of the display from the viewer's eyes which still allows the viewer to resolve a displayed image.

Although the above discussion relates to a multiple view display having a parallax barrier as the parallax optic, the same relation between the horizontal pixel pitch and the viewing distance holds for a display having a lenticular barrier. The problems described above therefore occur also in the case of a display with a lenticular barrier.

A first aspect of the present invention provides a display operable as a multiple view directional display in a first orientation and operable as a multiple view directional display in a second orientation different from the first orientation, wherein the viewing distance of the display in the first orientation is substantially the same as the viewing distance of the display in the second orientation; and wherein the the angular separation between a first image and a second image displayed by the device in the first orientation is substantially equal to the angular separation between a first image and a second image displayed by the device in the second orientation. . 9 The reference to substantially the same viewing distance indicates that the viewing distance of the display in one orientation need not be exactly the same as the viewing distance of the display in another orientation, since the viewing windows create by a multiple view directional display have a finite extent in the direction normal to the display. This is true, for example, where the "viewpoint correction" technique of making pitch of the parallax barrier slightly less than an integer multiple of the pixel column pitch is used. Provided that the viewing windows generated by the display in one orientation overlap (in the direction normal to the display) the viewing windows generated by the display in another orientation, it is possible for a viewer to find a position at which their eyes are within the viewing windows generated by the display in both orientations, and in this case it can be said that the display has substantially the same viewing distance in one orientation as in the other orientation. The maximum tolerable variation in viewing distance of the display between one mode and the other mode will be dependent on the exact shape of the viewing windows and the location of the viewer within the viewing windows.

Since the angular separation between the two images and the viewing distance of the display do not significantly chance between the two orientations of the display, a viewer is able to view a display of the invention, without discomfort, from the same viewing distance whether the display is, for example, oriented horizontally (to give a landscape mode) or is oriented vertically (to give a portrait mode). The user does not need to change their viewing position when the orientation of the display changes, and this makes viewing the display much more convenient both for the case of a large, fixed display and for the case of a portable display. In the case of an autostereoscopic 3-D display, for example, the separation between the left eye window and the right eye window, at the viewing distance of the display, will not change significantly when the orientation of the display is changed. Thus, an observer who is correctly positioned to see a 3-D image (de, with their left and right eyes in the left eye image viewing window and the right eye image viewing window, respectively) with the display in, for example, a portrait mode orientation will remain correctly positioned to perceive a 3-D image when the display is put into landscape mode orientation. To switch a display from one display mode to another display mode it is simply necessary to rotate the display to the new orientation, re-address the image display to suit the new orientation, and (in the case of some embodiments described below) re-configure the parallax optic to suit the new orientation of the display. In some cases an image will need to be re- formatted to suit the changed aspect ratio of the display, for example where one image is to be displayed in both modes (although any image supplied to a display may need to reformatted if the aspect ratio of the image is not the same as the aspect ratio of the display). In general the interlacing pattern for the images will change on switching between landscape and portrait modes (owing to the driving of the TFT panel) regardless of the display aspect ratio.

The display may comprise an image display layer and a parallax optic disposed in an optical path through the image display layer.

The pitch of the image display layer along a first direction, and the effective pitch of the image display layer along second direction perpendicular to the first direction, may be selected such that the viewing distance of the display in the first orientation is substantially the same as the viewing distance of the display in the second orientation.

In addition, other parameters of the display may need to be selected appropriately so as ensure that the viewing distance and angular separation between two images are substantially the same for each orientation of the display. The relationship between viewing distance and view separation in the case of a practical display is generally more complicated than suggested by equation (3). A parallax barrier in a practical barrier contains a large number of apertures, and the pitch of the parallax barrier must be selected so that the viewer can see each pixel correctly. In the "viewpoint correction technique" the pitch of the parallax optic is set not to be an integral multiple of the pixel pitch, to prevent the formation of overlapping image regions. In a practical display the pixel pitch p and refractive index n are fixed, and the ratio r/e of the viewing distance to the view separation is determined by the separation s between the image display layer and the parallax optic. The particular value of the viewing distance r is determined by the viewpoint correction applied to the parallax optic.

The image display layer may be a pixellated image display.

The image display layer may comprise at least first pixels of a first colour and second pixels of a second colour, the width of a first pixel along the first direction being substantially equal to the width of a first pixel along the second direction and the width of a second pixel along the first direction being substantially equal to the width of a second pixel along the second direction.

The image display layer may comprise at least first pixels of a first colour and second pixels of a second colour arranged to form composite pixels, each composite pixel having at least one first pixel and at least one second pixel; wherein the width of a composite pixel along the first direction is substantially equal to the width of a composite pixel along the second direction.

The pitch of the parallax optic along the first direction may be substantially equal to the pitch of the parallax optic along the second direction.

The parallax optic may comprise a plurality of transmissive apertures.

The transmissive apertures may be arranged in columns extending along the first direction, with an aperture in one column being displaced along the first direction relative to an aperture in an adjacent column.

The parallax optic may be a colour filter barrier, whereby each aperture comprises at least first and second regions having different lighttransmissive properties.

The parallax optic may be a fixed parallax optic.

Alternatively the parallax optic may be switchable between an OFF state in which no parallax optic is defined and an ON state.

The parallax optic may be reconfigurable between a first ON state and a second ON state.

The parallax optic may further be switchable to an OFF state in which substantially no parallax optic is defined.

The display may comprise a first parallax optic switchable between an OFF state in which substantially no parallax optic is defined and a first ON state and a second parallax optic switchable between an OFF state in which substantially no parallax optic is defined and a second ON state.

The display may comprise an image display layer, a first parallax optic and a second parallax optic, the first and second parallax optics being disposed in an optical path through the image display layer; wherein the first parallax optic has a finite pitch in a first direction and the second parallax optic has a finite pitch in a second direction perpendicular to the first direction; and wherein the ratio of the separation between the first parallax optic and the image display layer to the pitch of the image display layer along the first direction is substantially equal to the ratio of the separation between the second parallax optic and the image display layer to the pitch of the image display layer along the second direction.

The first parallax optic and second parallax optic may be disposed on opposite sides of the image display layer.

The first parallax optic and second parallax optic may be disposed on the same side of the image display layer.

The or each parallax optic may comprise a liquid crystal material.

The or each parallax optic may comprise a liquid crystal layer and a patterned retarder disposed in an optical path through the display.

The or each parallax optic may comprise a first patterned retarder, a liquid crystal layer, and a second patterned retarder disposed in this order in an optical path through the display.

The or each patterned retarder may comprise a reactive mesogen layer.

The or each parallax optic may comprise a plurality of addressable liquid crystal regions disposed alternately with regions of fixed optical characteristics.

The or each parallax optic may comprise an addressable liquid crystal layer having regions of first alignment characteristics alternating with regions of second alignment characteristics.

The parallax optic may comprise an addressable layer, first addressing means for defining a first parallax optic in the addressable layer, and second addressing means for defining a second parallax optic in the addressable layer.

Rotation of the display about the normal to a display face of the display may transforms the display from the first orientation to the second orientation.

The first orientation may be at substantially 90 to the second orientation.

The first orientation may be a horizontal orientation and the second orientation may be a vertical orientation.

A second aspect of the present invention provides a multiple view directional display adapted to display four views, each view being displayed, in use, along a respective one of four different non-coplanar directions.

The display may comprise an image display layer having a plurality of first regions for displaying a first view, a plurality of second regions for displaying a second view, a plurality of third regions for displaying a third view, and a plurality of fourth regions for displaying a fourth view; and a parallax optic for displaying each view, in use, along the respective one of the four different non-coplanar directions. An element of the parallax optic may be associated with one first region

of the image display layer, with one second region of the image display layer, with one third region of the image display layer, and with one fourth region of the image display layer.

The image display layer may be a pixellated image display layer and each first region, each second region, each third region and each fourth region may comprise one or more pixels.

A first region and a second region may be disposed laterally adjacent to one another, a third region may be disposed above the first and second regions, and a fourth region may be disposed below the first and second regions and is disposed vertically below the third region.

A third aspect of the invention provides a dual view display device comprising a display according to the first or second aspect.

A fourth aspect of the invention provides an autostereoscopic display device comprising a display according to the first or second aspect.

Preferred embodiments of the present invention will now be described by way of illustrative example with reference to the accompanying figures in which: Figures l(a) and l(b) illustrate a landscape display mode and a portrait display mode of a display; Figure 2 is a schematic illustration of a conventional multiple-view display; Figure 3 illustrates the display of figure 2 after rotation by 90 from landscape mode is a schematic plan view of viewing windows produced by another conventional multiple- view directional display device; Figures 4(a) and 4(b) show the image display layer and parallax barrier of another multiple view display; Figures 4(c), 4(d) and 4(e) illustrate operation of the display of figures 4(a) and 4(b) in a portrait mode and in a landscape mode; Figure 5 illustrates the viewing distance of a multiple view display; Figures 6(a) and 6(b) show the image display layer and parallax barrier of multiple view display of the invention; Figures 6(c), 6(d) and 6(e) illustrate operation of the display of figures 6(a) and 6(b) in a portrait mode and in a landscape mode; Figures 7(a) and 7(b) show the image display layer and parallax barrier of another multiple view display of the invention; Figures 7(c), 7(d) and 7(e) illustrate operation of the display of figures 7(a) and 7(b) in a portrait mode and in a landscape mode; Figure 8(a) shows the parallax barrier of another multiple view display of the invention and 8(b) illustrates operation of the display in a landscape mode; Figure 9 is a schematic sectional view of a display according to a further embodiment of the present invention; Figures 10 is a schematic sectional view of a display according to a further embodiment of the present invention; Figure lI(a) and lI(b) illustrate operation of a display according to a further embodiment of the present invention in a 3-D mode and Figure lI(b) and 11(d) illustrate operation of the display in a 2-D mode; Figure 12(a), 12(b) and 12(c) are schematic sectional views of displays according to further embodiments of the present invention; Figure 13(a) shows a parallax barrier of a display according to a further embodiment of the present invention; Figures 13(b) to 13(d) illustrate manufacture ofthe parallax barrier of figure 13(a); Figure 14(a) is a schematic sectional view of a parallax barrier of a display according to a further embodiment of the present invention, and figure 14(b) illustrates operation of the parallax barrier; Figures 1 5(a) to 1 5(e) illustrate operation of the parallax barrier of figure 1 4(a); Figure 16 is a schematic plan view of a conventional multiple view directional display; Figure 17 is a schematic plan view showing a display according to a further embodiment of the present invention; Figures 18(a), 18(b) and 18(c) show the image display layer, the parallax barrier, and the superposition thereof of one embodiment of the display of figure 17; Figure 19(a) shows another image display layer for the display of figure 17, and figure 19(b) shows a suitable parallax barrier superposed thereover; Figure 20(a) shows a further image display layer suitable for the display of figure 17, and figure 20(b) shows a suitable parallax barrier superposed thereover; Figure 21(a) shows a further image display layer suitable for the display of figure 17, and figure 21(b) shows a suitable parallax barrier superposed thereover; Figure 22 shows a display according to figure 17 embodied using a colour filter barrier as the parallax optic; Figure 23(a) shows a further display according to figure 17; and Figure 23(b) shows the image display layer for a further display of figure 17, and figure 23(c) shows a suitable parallax barrier superposed thereover.

Like reference numerals denote like components throughout the drawings.

Embodiments of the invention will be described with reference to a display that may be operated either in a horizontal (or landscape) orientation or in a vertical (or portrait) orientation. The display is transformed from one orientation to the other by a rotation of substantially 90 about an axis that is perpendicular to a front (display) face of the display. However, the invention is not limited to a display operable in horizontal and vertical orientations.

Figure 6(a) illustrates a multiple view directional display according to a first embodiment of the present invention. Figure 6(a) is a schematic front view of the image display layer of the display, and figure 6(b) is a schematic front view of the parallax optic. Figures 6(c) and 6(d) are schematic front views of the display 9 in a landscape orientation and a portrait orientation respectively, and figure 6(e) shows the observer's orientation.

As indicated in figure 6(a), the image display layer 10 of the display of this embodiment is a pixellated image display layer comprising a plurality of pixels 11, 11', 11" arranged in a matrix of rows and columns. The display is a full colour display, so that each pixel is either a red pixel 11, a green pixel 11', or a blue pixel 11". In this embodiment, each colour pixel 1 1, I 1', 11 " is substantially square. Thus, the pixel pitch in the horizontal direction, Ph. is substantially equal to the pixel pitch in the vertical direction pv Considering equation (3), the pixel-barrier separation s and the refractive index n of the panel do not depend on the orientation of the display. Provided that the parallax barrier gives substantially the same angular separation between the two views in the two orientations so that the view separation at the intended viewing distance doers not vary significantly between the two orientations of the display, therefore, the viewing distance of the display 9 when the display is horizontally oriented to give the landscape mode shown in figure 6(c) is substantially equal to the viewing distance of the display 9 it is when oriented vertically to give the portrait mode shown in figure 6(d). This embodiment of the invention thus provides a multiple view, directional display that is operable in either a horizontal orientation or a vertical orientation, and that has substantially the same viewing distance in both orientations. A user of the display is therefore not required to change their position, relative to the display, when the display is rotated from the landscape mode to the portrait mode or vice versa. Furthermore, the separation (measured at the intended viewing distance) between the two views is substantially the same in one mode as in another, so that an observer who is correctly positioned to see a 3-D image (de, with their left and right eyes in the left eye image viewing window and the right eye image viewing window, respectively) with the display in, for example, a portrait mode orientation will remain correctly positioned to perceive a 3-D image when the display is put into landscape mode orientation.

Figure 6(b) illustrates a suitable parallax barrier 12 for this display. The parallax barrier 12 of figure 6(b) contains a plurality of transmissive apertures 13, which are arranged in a matrix of rows and columns. Each of the transmissive apertures 13 has a substantially square cross-section. The remainder of the parallax barrier 12 is opaque. The size and shape of the apertures and the relation between the pixel pitch and the pitch of the parallax barrier are not relevant to the general concept of this invention and will not be described here (although they might be relevant to the crosstalk of the display).

This embodiment is not limited to a parallax barrier as the parallax optic of the display.

It may alternatively be effected using, for example, a lenticular barrier having square- base lenses or hemi-spherical lenses. In such a parallax optic the lenses would be arranged in rows and columns, in a similar manner to the transmissive apertures 13 of the parallax barrier 12 of figure 6(b).

Where this embodiment is effected using a lenticular parallax optics, it is preferable that each lens is symmetric in its focal properties - that is, its focussing power in the vertical direction indicated in figure 6(b) is substantially equal to its focussing power in the horizontal direction indicated in figure 6(b). If the lens should be asymmetric in its focal properties then, if the viewing distance of the display in its horizontal orientation is equal to the viewing distance of the display in its vertical orientation, the separation between viewing windows would be different between the horizontal orientation of the display and the vertical orientation of the display. In the case of a dual-view display, this would have the effect of the viewer needing to move parallel to the plane of the display to remain in the viewing window of a particular image if the display were rotated. In the case of an auto-stereoscopic 3- D display this would result in the separation between the left-eye viewing window and the right-eye viewing window changing, and it is likely that the 3-D effect would disappear when the display was rotated. If any 3-D effect did remain, the eyes of the observer would not be correctly positioned in the left-eye and the right-eye viewing windows, and it is likely that any 3- D effect would be uncomfortable.

Figures 7(a) and 7(b) show the image display layer 10 and parallax optic 12 of a display according to a further embodiment of the present invention. The image display layer 10 of this embodiment again contains pixels 11, 11', 11" arranged in a matrix of rows and columns. For convenience, the space between adjacent pixels has been omitted from figure 7(a). The pixels are again colour pixels, and pixels 11 are red pixels, pixels 11' are green pixels and pixels 11" are blue pixels.

The image display layer 10 of this embodiment is arranged to provide a white pixel which is substantially square. A "white pixel" is a composite pixel and is composed of three colour pixels - one red pixel, one blue pixel and one green pixel. A "white pixel" is outlined in bold in the upper right-hand corner of figure 7(a). In order for a "white pixel" 14 to be substantially square, each of the colour pixels 11, 11', 11" is made rectangular with its extent in one direction being approximately three times its extent in the perpendicular direction so that three adjacent colour pixels produce generate a composite white pixel 14 that is substantially square.

The effective pitch of the pixel to be used in equation (3) is the pitch of the composite white pixel 14. In portrait mode the effective pixel pitch is 3xPl, whereas in landscape mode the (effective) pixel pitch is P2. By choosing the shape and arrangement of the pixel such that P2 = 3PI, the effective pixel pitch in the landscape mode is the same as the effective pixel pitch in the portrait mode.

Figure 7(b) shows a suitable parallax optic for this display. The parallax optic is shown as a parallax barrier 12 having transmissive apertures 13 that are substantially square.

The pitch of the barrier in the horizontal direction (with the barrier oriented as shown in figure 7(b)) is denoted as PL since this is the barrier pitch when the display is in a landscape orientation, and the pitch of the barrier in the vertical direction (with the barrier oriented as shown in figure 7(b)) is denoted as pp since this is the barrier pitch when the display is in a portrait orientation. In this embodiment PL is made approximately equal to pp. by making the barrier pitch approximately six times greater than pi, the pitch of the colour sub-pixels in landscape mode, and equal to approximately twice p2, the pitch of the coloured sub-pixels in landscape mode.

Figures 7(c) and 7(d) illustrate operation of the display 9 in landscape mode and portrait mode respectively, and figure 7(e) shows the orientation of an observer. In landscape mode two images are interlaced on alternate columns of pixels. In the case of an autostereoscopic 3-D display, for example, that a right-eye image is displayed on pixel columns Cl, C3, etc. and a left-eye image is displayed on pixel columns C2, C4, etc. In portrait mode, the images are displayed on alternating columns of white pixels 14, with each column of white pixels corresponding to three columns of colour pixels. Thus, a right-eye image is displayed on colour pixel columns CRT, CGI, CB1 (which make up a first column of white pixels), a left eye image is displayed on colour pixel columns CR2, CG2, CB2 (which make up a column C2 of white pixels) and so on.

The displays described above with reference to figures 6(a) to 7(d) may be varied in known ways. For example, the image display layer may contain four or more colour sub-pixels for each white pixel, according to the technique disclosed in co-pending patent application No. 0315171.9. The interlacing of the left-eye image and the right- eye image may be displaced by one pixel from one row to the next, to provide a greater viewing angle, as suggested in co-pending UK patent application No. 0315170.1. The colour sub-pixels for the left-eye image and the right-eye image may be split across two rows of pixels, as suggested in UK patent application No. 0228644.1. The pitch of the parallax optic may be slightly greater than the pitch of the colour pixels of the image display layer, as disclosed in UK patent application No. 0306516.6. The contents of these applications are hereby incorporated by reference.

Where the parallax optics of the above displays are embodied as parallax barriers, the parallax barriers may be embodied as fixed parallax barriers, for example by selectively exposing a photographic emulsion material to define transmissive apertures. Such parallax barriers are suitable for displays designed to operate primarily in a 3- dimensional mode, or a dual-view display mode, since the parallax barriers cannot be switched off to provide a conventional 2-D display. If it is desired to operate a display having a fixed parallax barrier, or other fixed parallax optic, in a conventional 2-D mode, the image display layer may be driven to display two identical images so that both views provided by the display are the same. An alternative method of obtaining a 2-D display mode with a fixed parallax barrier is to provide a switchable scatterer, such as a polymer dispersed liquid crystal material, in the optical path of light from the parallax optic to the observer. The effect of the parallax optic is removed when the scatterer is switched ON and a 2-D display mode is obtained. With the scatterer switched OFF, a directional display mode is obtained.

The embodiments described above may alternatively be embodied using a lenticular parallax barrier such as, for example, a micro-lens array. The micro-lens array may be a fixed micro-lens array, or it may be a micro-lens array that can be switched to give a 2- D mode of operation. A switchable micro-lens array may be provided, for example, by means of a switching liquid crystal layer in conjunction with a micro-lens array fabricated using polarization sensitive materials, such as liquid crystal materials, as disclosed in WO 03/015424.

Alternatively, the displays described above may be embodied using a colour filter barrier as the parallax optic. An example of a colour filter barrier 15 is shown in figure 8(a). The colour filter barrier comprises a plurality of transmissive apertures 16a, 16b, 16c, and the remainder of the colour filter barrier is opaque. Compared to the parallax barriers described above, in which the apertures 13 are transmissive to all visible wavelengths of light, the apertures 16a, 16b, 16c of the colour filter barrier of figure 8(a) are transmissive over only a narrow range of the visible spectrum. The aperture 16a is transmissive over a red region of the spectrum, the aperture 16b is transmissive over the blue region of the spectrum, and the aperture 1 6c is transmissive over the green region of the spectrum, as denoted by the letters "r", "b", "g" shown for the apertures of the colour filter barrier 15. The apertures 16a,16b,16c are arranged in groups of three apertures, with each group containing one "red" aperture 16a, one "blue" aperture 16b and one "green" aperture 16c. The colour filter barrier 15 of figure 8(a) is suitable for use with the image display layer shown in figure 7(a).

A display 9 having the colour filter barrier 15 of figure 8(a) as its parallax optic and having an image display layer 10 as shown in figure 7(a) is shown in landscape orientation in figure 8(b). Figure 8(b) shows this embodiment applied to an autostereoscopic display, and the colour sub-pixels in figure 8(b) are labelled with a R or L to denote whether they are displaying the right-eye image or the left-eye image.

The lower case letters in figure 8(b) denote the transmission range of the apertures of the colour filter barrier.

Use of a colour filter barrier can provide a brighter 3-D display, with lower cross talk.

("Cross talk" occurs when the left eye of the observer perceives the image intended for the right eye, and vice versa.) The use of colour filter barriers is described in more detail in co-pending UK patent application No. 0320367.6, which is hereby incorporated by reference.

It will be noted that, in the display shown in figure 8(b), the right-eye image and left- eye image are not displayed in columns of pixels. The images are displayed such that the interlacing is offset by one white pixel (that is by three columns of colour pixels) from one row to the next. The apertures in the colour filter barrier 15 are therefore not arranged in columns, but the apertures in one row are laterally offset relative to the rows above and below, in correspondence with the offset interlacing of the images. A colour filter barrier can, however, be applied to a display device in which the left-eye and right-eye images are displayed in columns of pixels as shown in, for example, the embodiments of figures 6(a) to 7(d).

A colour filter barrier is generally embodied as a fixed barrier, and so is suitable for use in a display that is required to operate primarily in a directional display mode. If it is desired to operate a display having a colour filter barrier as a parallax optic in a 2-D display mode, a switchable scatterer, such as a polymer dispersed liquid crystal cell, may be disposed in an optical path from the display to an observer to remove the effect of the parallax barrier. Alternatively, the two images displayed on the image display layer of the display may be the same, so that the same image is displayed to both eyes and the device is operated in a 2-D mode.

Figure 9 is a schematic plan view of a display 9 according to a further embodiment of the present invention. The display 9 has an image display layer 10, and a parallax optic 12 disposed in an optical path through the image display layer 10. The image display layer may, as shown in figure 9, be formed of a conventional liquid crystal layer 18 disposed between first and second linear polarisers 17, l9 A further linear polariser 22 is disposed before the parallax optic 12 (in use, the display 9 is illuminated by a backlight disposed such that the backlight and the image display layer are on opposite sides of the parallax optic; light from the backlight enters the display via the polariser 22. Other components, such as, for example, addressing electrodes for addressing the liquid crystal layer 18, alignment layers for aligning the liquid crystal material, and colour filters in the case of a colour display, do not form part of the invention and are not shown.

In this embodiment the parallax optic 12 is a switchable parallax optic that can be switched between a OFF state in which substantially no parallax optic is defined and an ON state. The figure shows one way in which such a switchable parallax optic may be defined. In this embodiment, the switchable parallax optic is formed by a patterned retarder 20 in combination with a switchable liquid crystal layer. The patterned retarder may be patterned such that one or more first regions 23 correspond to the desired transmissive apertures of a parallax barrier, and one or more second regions 24 correspond to desired opaque regions of the parallax barrier. The liquid crystal layer 21 is switchable between a first state, in which both regions 23, 24 of the patterned retarder have the same optical effect on light leaving the image display layer 10 so that no parallax barrier is defined. In another state of the liquid crystal layer, the first regions 23 define transmissive regions of the parallax barrier, and the second regions define opaque regions of the parallax barrier.

The patterned retarder 20 of the parallax barrier 12 is a half-waveplate retarder with a patterned optic axis. The optic axis in one region 23 of the patterned retarder is at 45 to the optic axis in another region 24 of the patterned retarder. For light of one input polarisation (from the switch LCD 21), both regions 23,24 of the patterned retarder will transmit. No parallax barrier is defined in the patterned retarder, and the display operates in a 2-D mode. If the polarization of light incident on the patterned retarder 20 is rotated by 45 , by switching the switch LCD 21, one region of the patterned retarder will transmit light polarised parallel to the transmission axis of the input polariser 19 of the image display layer 10 while another region of the patterned retarder will transmit light polarised perpendicular to the transmission axis of the input polariser 19 of the image display layer.

Hence, light from one region of the patterned retarder is blocked, while light from the other region of the patterned retarder is transmitted. A parallax barrier is defined, and the display operates in a directional display mode such as a 3-D display mode. The general principle of the patterned retarder 20 of figure 9 is described in UK patent application no. 0215059.7.

The embodiment of figure 9 may be used to provide any desired parallax barrier. For example, the first regions 23 and second regions 24 of the patterned retarder 20 may be arranged to provide a parallax barrier as shown in any of figures 6(b) or 7(b). This embodiment may therefore be used to provide a multiple view directional display that can be used in a landscape orientation or a portrait orientation, and that has substantially the same viewing direction in either orientation. Furthermore, the use of a switchable parallax optic means that the display is switchable between a 2-D mode of operation and a directional mode of operation.

Figure 10 is a schematic plan view of a display 9 according to a further embodiment of the present invention. The display again consists of an image display layer 10 and a parallax optic 12 disposed in an optical path through the image display layer 10. The parallax optic is, in this embodiment, a switchable parallax barrier.

The image display layer 10 comprises a liquid crystal layer 18 disposed between a first substrate 23 and a second substrate 25. Red, green and blue colour filters 24R, 24G, 24B are disposed between the liquid crystal layer 18 and one of the substrates. Other components, such as, for example, addressing electrodes for addressing the liquid crystal layer 18, aligurnent layers for aligning the liquid crystal material, and polarisers, do not form part of the invention and are not shown. Figure 10 shows an active matrix image display layer in which one of the addressing electrodes is constituted by a plurality of pixel electrodes each of which is controlled by an associated switching element, such as a thin film transistor (TFT), and the image display layer 10 may therefore be referred to as a "TFT panel". In use, the display is illuminated by a light provided above the image display layer (as the display is shown in figure 10).

Polarisers (not shown) are provided at the input to the image display layer, at the output of the image display layer (which also forms the /input to active parallax barrier), and at the output from the active parallax barrier.

The parallax barrier 12 is formed of strips 28 of a material having fixed optical properties, for example a resin. These strips extend into the plane of the paper in figure 10. The strips 28 extend parallel to one another, and are spaced from one another.

Strips 21 of a liquid crystal material are disposed between adjacent strips 28 of material of fixed optical properties. The strips 21 of liquid crystal material and strips 28 of material of fixed optical properties are disposed between two light-transmissive substrates 26, 27. In use, the strips 21 of liquid crystal material are addressed by suitable addressing means (not shown). Suitable addressing means may consist of, for example a first uniform electrode (not shown) disposed on one side of the layer of resin 28 and liquid crystal material 21 and a second uniform electrode (not shown) disposed on one side of the layer of resin 28 and liquid crystal material 21. A voltage can be applied simultaneously across all the liquid crystal regions 21 by applying a voltage between the two electrodes.

In order for the display 9 to operate in a 2-D mode, the strips 21 of liquid crystal material are switched so that the refractive index of the liquid crystal material matches the refractive index of the strips 28. There is no difference in optical properties between the strips 21 of liquid crystal material and the strips 28, and no parallax barrier is formed. In order to obtain a directional display mode, the strips 21 of liquid crystal material are switched so that they act as birefringent regions and form the light blocking regions of the parallax barrier. The strips 28 of material of fixed optical properties remain transmissive.

The embodiment of figure 10 may be applied to any of the displays described above with reference to figures 6(a) to 7(d). This embodiment may therefore be used to provide a multiple view directional display that can be used in a landscape orientation or a portrait orientation, and that has substantially the same viewing direction in either orientation. Furthermore, the use of a switchable parallax optic means that the display is switchable between a 2-D mode of operation and a 3-D mode of operation.

In the above embodiments, the precise size and shape of the apertures of the parallax barrier are not directly relevant to the principle of the invention, and so have not been described in detail. However, although the size and shape of the apertures of the parallax barrier do not affect the operation of the display in different orientations they do influence properties of the display such as the degree of crosstalk of the display.

Parameters such as the widths of the barrier apertures may be adjusted so that features of the display, such as the location of the centre of the viewing windows, show the least change upon rotation between the orientations.

If the parallax barriers shown in figures 6(b) and 7(b) are compared with a conventional parallax barrier such as that shown figure 2, it will be seen that the proportion of the area of these parallax barriers that is light-transmissive is smaller than the proportion of the area of a conventional parallax barrier that is light-transmissive. Effectively, the displays of the invention described above have both a landscapeorientation parallax barrier and a portrait orientation parallax barrier. The reduced brightness will be particularly noticeable in a display having a barrier that is switchable between a directional display mode and a 2-D display mode.

In order to compensate for the reduced brightness in a directional display mode, it is possible to increase the power supplied to the back light when the display is operating in a directional display mode, to provide greater light intensity to compensate for the reduced transmissive area of the parallax barrier. In this embodiment, therefore, switching from a 2-D display mode to a directional display mode would comprise switching ON the parallax barrier and also increasing the power supplied to the back light of the display. Alternatively, the decreased brightness in a directional display mode may be compensated for by adjusting the driving of the image display layer to provide brighter grey levels when the device is operating in a directional display mode.

In the case of a display that operates only in a directional display mode, the intensity of the backlight may be adjusted to provide any desired brightness of the display.

Figures 11 (a) to 11 (d) illustrate a further switchable parallax barrier suitable for use in a display of the present invention. Figures Il(b) and 11(d) are schematic plan views of the parallax barrier 12 in a directional display mode (in this case a 3-D mode) and a 2-D display mode respectively.

As shown in figures 11(b) and 11(d), the parallax barrier 12 comprises a liquid crystal layer 21 disposed between substrates 26, 27 provided with uniform electrodes (not shown). The liquid crystal layer 21 and substrate 26, 27 are disposed between a first polariser 17 and a second polariser 19. When no voltage is applied across the liquid crystal layer, one or more first regions 28 of the liquid crystal layer have a first alignment and one or more second regions 29 have a second alignment. In the embodiment of figure 11(b), the first regions 28 have a homeotropic alignment and, if the transmission axis of one linear polariser 17 is arranged orthogonal to the transmission axis of the other linear polariser 19, these regions will appear dark when the parallax optic is illuminated from behind. The regions 28 thus define the opaque regions of a parallax barrier.

If the first regions 28 of liquid crystal material extend in strips, the result will be a conventional parallax barrier having opaque stripes I separated by transmissive stripes 5 as shown in figure 11(a) which is a front view of the parallax barrier in the 3-D mode.

By choosing suitable sizes, shapes, and positions for the first regions 28 of liquid crystal material, however, this embodiment can produce a parallax barrier as shown in figure 6(b) or 7(b) When a voltage is applied across the liquid crystal layer, the liquid crystal alignment in the first regions 28 switches and adopts the same alignment as the alignment in the second liquid crystal region 29. The result, as shown in figure 11(d) is that the entire liquid crystal layer has a uniform alignment. In this embodiment, the entire liquid crystal layer has a planar liquid crystal alignment. No parallax barrier is defined, and the entire area of the parallax barrier is transmissive as shown in figure 11 (c) which is a front view of the parallax barrier in this mode.

The patterned alignment of the liquid crystal layer may be obtained in any convenient way, and many methods of obtaining a patterned aligned liquid crystal layer are known.

For example, the patterned alignment may be achieved by applying a photo alignment process to a suitable alignment layer (not shown). The photo alignment process may be bond-breaking, bond-making or involve reorientation of an alignment layer such as an azo alignment layer. Alternatively, methods such as grating alignment, or multiple rubbing of a suitable alignment layer, may be used.

As a further alternative, a screen printing technique may be used to deposit an alignment layer on selected regions of one of the substrates 26, 27, with the selected regions being determined by the screen. A second screen, that covers different areas of the substrate, may then be applied and a second alignment layer is deposited over different regions of the substrate. The alignment layers may then be cured and rubbed, to provide a patterned alignment layer that will produce the desired alignment of the liquid crystal layer.

As a yet further example, a first alignment layer may be deposited on one of the substrates 26, 27, and be cured and rubbed to define an alignment direction. Next a second, photo-imagable, alignment layer may be deposited over the first alignment layer. The second alignment layer may then be rubbed along an aligurnent direction that is different to the alignment direction of the first alignment layer. The photo- imagable alignment layer may then be selectively exposed and developed, using suitable development conditions, so that in some regions the photo- imagable alignment layer is retained but in other regions the photo- imagable alignment layer is removed to expose the underlying first alignment layer. This provides an alignment layer having regions of different alignment direction, and this can be used to generate the desired liquid crystal alignment.

As noted above, the use of a parallax barrier of the type shown in figures 6(b) or 7(b), has the potential disadvantage of reducing light throughput through the device, owing to the low transmissive area of the parallax barrier. A further preferred embodiment of the invention therefore provides a display having a parallax optic that can be configured in either a first ON state and a second ON state. One ON state provides a parallax barrier that is suitable when the display is in one orientation, and the second ON state provides a parallax barrier that is suitable when the display is in another orientation.

Thus, when the device is in one orientation (e.g. a landscape orientation) the parallax barrier is put into the first ON state, and when the display is rotated into another orientation (e.g. a portrait orientation) the parallax barrier is switched into its second ON state to provide a parallax barrier appropriate for the portrait orientation. In this embodiment, the display has only a landscape parallax barrier or a portrait parallax barrier, as appropriate for the orientation of the display, at any one time so that the transmissive area of the parallax barrier in either the portrait mode or the landscape mode is greater than the transmissive area of the parallax barrier of the embodiments of figure 6(a) to 7(d).

In a particularly preferred embodiment, the parallax optic is not only reconfigurable between a first ON state and a second ON state, but can also be switched to an OFF state in which substantially no parallax optic is defined. This allows the display to be switched to a 2-D display mode.

Figure 1 2(a) is a schematic plan view of a display 9 according to this embodiment of the present invention. The display 9 comprises an image display layer 10 and two parallax optics 12, 12' with each parallax optic 12, 12' being provided in the optical path through the image display layer 10. The image display layer contains a liquid crystal layer 18 disposed between first and second substrates 23, 25. This embodiment is a full-colour display, and the image display layer accordingly further comprises red, green and blue colour filters 24R, 24G, 24B. Other components, such as, for example, addressing electrodes for addressing the liquid crystal layer 18, alignment layers for aligning the liquid crystal material, and polarisers, do not form part of the invention and are not shown.

In this embodiment, each parallax optic 12, 12' is embodied as a switchable parallax barrier. Each parallax barrier 12, 12' is switchable between an OFF state in which it is uniformly transmissive over its entire area so that no parallax barrier is defined and an ON state.

The parallax barriers 12, 12' are arranged such that one parallax barrier 12 provides, in its ON state a parallax barrier for use when the device is in one orientation (e.g. a landscape orientation). The other parallax barrier 12' provides, in its ON state a parallax barrier that is suitable for use when the display is in another orientation (e.g. a portrait orientation).

Figure 12(b) is a schematic exploded illustration of the display 9 of figure 12(a) showing the two parallax optics 12, 12' and the image display layer 10 separated from one another for clarity of explanation. Both parallax optics 12, 12' are shown in their ON state in figure 12(b), again for clarity of explanation to show how the opaque regions and transmissive regions of each parallax optic are arranged. As shown in figure 12(b), each parallax optic 12, 12' has, in its respective ON state, lighttransmissive regions 5,5' that are stripe-shaped and that extend generally parallax to one another and are separated by opaque regions 1, 1'. However, the opaque regions I and transmissive regions 5 of one parallax optics 12 are substantially perpendicular to the opaque regions 1' and transmissive regions 5' of the other parallax optic 12'.

The display 9 is shown in figure 12(b) in its portrait mode orientation. In this mode, the first parallax barrier 12 would be switched OFF and the second parallax barrier 12' would be switched ON to define vertical opaque stripes 1'. If the device is rotated into its landscape mode orientation, the second parallax barrier is switched ON - and, owing to the rotation of the device, the opaque strips of this parallax optic will now be oriented vertically. The second parallax barrier 12' is switched OFF when the device is rotated into its landscape mode.

if both parallax barriers 12, 12' are switched OFF, the display 9 will operate as a conventional 2-D display, irrespective of whether it is oriented in portrait mode or landscape mode.

In figure 12(b), both parallax optics 12, 12' are shown in their respective ON state, for clarity of explanation. It is, however, preferable that the device is not operated with both parallax barriers switched ON simultaneously- although this is possible, the display would then suffer from the problem of a low intensity in the 3-D mode as explained above. It is preferable that only one or other of the parallax optics is switched ON at any one time.

In the display of figure 12(a) and 12(b), one parallax optic 12 has been placed behind the image display layer 10 and the other parallax optic 12' has been disposed in front of the image display layer 10. (The notation "behind" and "in front" refer to the display as perceived by an observer.) This embodiment is not limited to this arrangement, however, and it would be possible for both parallax optics 12, 12' to be disposed on the same side of the display. For example, both parallax optics 12, 12' may be disposed behind the image display layer, as shown in schematic plan view in figure 12(c).

Alternatively, both parallax optics 12, 12' may be provided in front of the image display layer 10.

Any suitable switchable parallax optic may be used in this embodiment. For example, the switchable parallax optics shown in figures 9, 10 and l l(a) to l l(d) may be used.

A further advantage of the embodiments of figures 12(a) to 12(c) is that these embodiments are not limited to an image display layer that has square pixels or that has square composite pixels. Where the parallax optics are parallax barriers, for example, the two parallax barriers may be arranged so that the pixel-barrier separation for one barrier is not equal to the pixel-barrier separation for the second barrier - so that the term "s" in equation (3) is no longer a constant. The embodiment of figures 12(a) to 12(c) can provide a constant viewing distance provided that sp/pp sips, where sp is the pixel-barrier separation for the parallax barrier used in the portrait mode, pp is the pixel pitch in the portrait mode, so is the pixel-barrier separation for the parallax barrier used in the landscape mode, and pi is the pixel pitch in the landscape mode (in a case where the separation between views, e, is approximately the same in one mode as in the other).

(It should be noted that, if the two parallax barrier are arranged at the same distance from, but on opposite sides of, the image display layer so that sp = s', then it is necessary for the image display layer to have square pixels or square composite pixels as in earlier embodiments.) It should be noted that a parallax barrier of the type shown in figure 6(b) or 7(b) may be embodied as a switchable parallax barrier using, for example, any of the methods shown in figures 9, 10 and ll(a) to 11(d). This has the advantage that the embodiments of figure 6(a) to 7(d) may be embodied as displays that can be switched to give a 2-D display, although the problem of low intensity when operated in a directional display mode may occur as explained above.

In the embodiments of figures 12(a) to 12(c), each parallax optic 12, 12' and the image display layer 10 is provided with its own separate pair of substrates. It would, however, be possible for a substrate to be common to, for example, the image display layer 10 and to one of the parallax optics or, if both parallax optics are disposed on the same side of the image display layer, for a substrate to be common to both parallax optics.

In a further embodiment of the present invention the two switchable parallax optics are defined in a single addressable layer. This embodiment is illustrated with reference to figures 13(a) to 13(d). In the described example the addressable layer is a liquid crystal layer, but the embodiment is not necessarily limited to this.

As shown in figure 13(a), the addressable layer is provided with two independently addressable sets of electrodes 28, 29. One set of electrodes 28 defines a parallax barrier in the addressable layer that is suitable for use when the display is in one orientation (e.g. a landscape mode orientation). The second set 29 of electrodes defines a parallax barrier that is suitable for use when the display is in another orientation (e.g. portrait mode orientation). As is shown in figure 13(a), each set of electrodes 28, 29 consists of a series of stripe electrodes 28a,28b,28c;29a,29b,29c that extend parallel to one another, with the electrodes of one set being substantially perpendicular to the electrodes of the other set.

The parallax optic of this embodiment may be embodied by disposing one set of electrodes - for example, the "landscape electrodes" 28a,28b,28c... over a substrate 30. This is shown in figure 13(b).

An electrically insulating layer 31 is then disposed over the landscape electrodes 28a,28b,28c...so that the landscape electrodes are completely covered. The upper surface of the barrier layer is deposited so as to be, or is made, substantially flat as shown in figure 13(c).

The second set of electrodes - in this example the "portrait electrodes" 29a,29b,29c...- are then deposited over the barrier layer. They are insulated from the landscape electrodes 28a,28b,28c by the insulating barrier layer 31. This is shown in figure 13(d).

A second substrate with two independently addressable sets of crossed electrodes as shown in figure 13(a) is prepared in a similar manner. The two substrates are then assembled, with a layer of addressable material, such as a liquid crystal material, disposed between one substrate and the other substrate. When this parallax barrier is incorporated in a multiple view directional display, the addressable layer is addressed using either the landscape electrode 28 or the portrait electrode 29 as appropriate.

When the display is in its landscape orientation, for example, the landscape electrode 28 is energised to define a parallax barrier in the addressable layer that is suitable for the landscape orientation of the device, and the portrait electrode 29 is OFF. When the device is rotated into its portrait mode, the landscape electrode 28 is switched off, and the portrait electrode 29 is energised to define a parallax barrier that is suitable for use in the portrait mode of the display.

In this embodiment the pixel-barrier separation does not vary between the portrait mode and the landscape mode, since the parallax barrier is defined in the layer 31 in both modes. It is therefore necessary for the image display layer to have square pixels or square composite pixels in order to obtain the same viewing distance in one mode as in the other.

The parallax barrier described in figures 13(a) to 13(d) is switchable between two ON modes, and is also switchable to an OFF mode in which no parallax barrier is defined in the addressable layer. The parallax barrier is therefore suitable for incorporation in a display that is desired to be switchable between a directional mode and a 2-D mode of operation.

Figure 14(a) shows a further parallax barrier 12 that is configurable in one or other of two different ON states.

The parallax optic 12 of figure 14(a) is again a parallax barrier. it comprises a first linear polariser 31 having its transmission axis arranged at 45 to a reference direction.

The next layer is a patterned reactive mesogen layer 32, and next to this is a liquid crystal layer 33 of the Frederick's type having a thickness of >/2 where)\ is the design wavelength of the display. Typically, )\= 550nm, since 550nm is approximately in the centre of the visible wavelength range. (A Frederick's type liquid crystal layer, or FRED liquid crystal layers, is a simple planar type untwisted liquid crystal layer.) The liquid crystal layer 33 is followed by a second patterned reactive mesogen layer 34, and then by a second linear polariser 35 that has its transmission axis oriented at -45 to the reference direction. Finally, the parallax barrier 12 comprises a switchable scattering layer 36.

The switchable scattering layer 36 is provided at the output side of the parallax barrier 12 - that is, in use, light enters the parallax barrier via the first polariser 31, and leaves via the switchable scatterer layer 36. As a result, if the switchable scattering layer 36 is switched ON to scatter light leaving the parallax barrier 12, any parallax barrier defined in the liquid crystal layer 33 is removed by the scattering layer 36. When the scattering layer 36 is switched ON therefore, the parallax barrier 12 is switched OFF and has a uniform transmissivity over its entire area.

Each RM layer 32, 34 is patterned into four different areas. The optic axis of the reactive mesogen layer varies between the areas. In the first RM layer, 32, the first areas have an optic axis at 67.5 to the reference direction, the second areas have an optic axis at 0 to the reference direction, the third areas have a reference direction at 22.5 to the reference direction, and the fourth areas have a reference direction at 45 to the reference direction. In the second RM layer 34, the first areas have their optic axis at 22.5 to the reference direction, the second regions have their reference direction at 135 to the reference direction, the third regions have their optic axis at 22.5 to the reference direction and the fourth regions have their optic axis at 45 to the reference direction.

The liquid crystal layer 33 is switchable, and has an optic axis arranged at 45 to the reference direction. The liquid crystal layer 33 is, in use, switched between a state in which it acts as a halfwave plate and a homeotropic state. The RM layers act as phase retarders.

When the scattering layer 36 is switched OFF, the liquid crystal layer contains one set of regions (the regions 4) that are always opaque, and one set of regions (the regions 2) that are always transparent. It also contains one set of regions (the regions 1) that are transmissive when the liquid crystal layer 33 is switched ON but is opaque when the liquid crystal layer 33 is switched OFF; finally, it contains one set of regions (the regions 3) that are opaque when the liquid crystal layer 33 is switched ON but that are transmissive when the liquid crystal layer 33 is switched OFF. It is therefore possible to define a portrait mode parallax barrier or a landscape mode parallax barrier in the liquid crystal layer 33.

Figure 15(a) shows one of each region 1-4 arranged in a 2 x 2 matrix. When the switchable scatterer is OFF but the liquid crystal layer 33 is ON, regions 3 and 4 are opaque and regions I and 2 are transmissive. This allows a first parallax barrier, having vertically extending opaque and transmissive strips to be defined as shown schematically in figure 15(b). If, however, the liquid crystal layer 33 is switched OFF, regions I and 4 are now opaque and regions 2 and 3 are now transmissive. This allows a parallax barrier having horizontally extending opaque regions and horizontally extending transmissive regions to be defined as shown in figure 15(c). Thus, the parallax barrier of this embodiment is again configurable between a first ON state and a second ON state.

If the switchable scattering layer 36 is switched ON, all regions of the liquid crystal layer 33 are then light-transmissive, as shown in figure 15(a). This enables the display to be switched to a 2-D display.

Figure 15(d) illustrates one possible arrangement of the regions 1, 2, 3 and 4 in the liquid crystal layer. The regions I and the regions 2 are arranged in columns, and the regions 3 and the regions 4 are also arranged in columns. The regions I and the regions 4 are arranged in rows, as are the regions 2 and the regions 3. If the liquid crystal layer is switched so that regions 3 and 4 are black and regions I and 2 are transmissive, a parallax barrier with vertical opaque regions and vertical transmissive regions (vertical refers to the orientation shown in figure 1 5(d)) is obtained. If the liquid crystal layer is switched so that regions I and 2 are black and regions 3 and 4 are transmissive, a parallax barrier with horizontal opaque regions and horizontal transmissive regions (horizontal again refers to the orientation shown in figure 15(d)) is obtained. Thus, the liquid crystal is can be switched to provide either a parallax barrier having horizontally- extending transmissive and opaque regions or to provide a parallax barrier having vertically extending transmissive and opaque regions.

Finally, figure 15(e) shows the required states of the regions 1-4 of the liquid crystal layer 33 in a 2-D mode, a portrait mode and a landscape mode.

The switchable scattering layer 36 may be omitted from the parallax barrier of this embodiment. If the scattering layer 36 is omitted, the parallax barrier cannot then be switched to provide a 2-D mode of operation (although a display could be operated in a 2-D mode by displaying two identical images so that each eye of an observer sees the same image).

In this embodiment, the two parallax barriers defined in the addressable layer may have their width and pitch selected independently from one another. The parallax barrier of this embodiment may therefore be used with any image display layer, and by suitably configuring the two parallax barriers it is possible to ensure that the viewing distance of the display in the landscape orientation is substantially the same as the viewing distance of the display in the portrait orientation. With the regions 1 to 4 dimensioned as shown in figure lS(d), for example, one parallax barrier has a pitch approximately three times as great as the pitch of the other parallax barrier.

The switchable scattering layer 36 may be, for example, a polymer dispersed liquid crystal layer.

The displays described above may be provided with other known features such as, for example, "observer tracking". It is known to monitor the position of the eyes of a viewer, and to adjust the assignment of data to the pixels of the image display layer 10 in order to take account of the movement of the viewer. This may be done particularly when the viewer would otherwise start to move into a region where they would receive cross talk or secondary images. Monitoring the position of the observer's eyes, and adjusting the assignment of data to the image display layer accordingly, may be carried out using any suitable observer tracking technique.

As an alternative, rather than adjusting the assignment of data to the pixels of the image display layer 10 in order to take account of movement of an observer, it is possible, in embodiments in which the parallax barrier is defined in an addressable layer, to adjust the parallax barrier in order to take account of the movement of the observer. In this embodiment, the parallax barrier is adjusted so that the positions of the viewing windows of the two images displayed on the image display layer 10 are changed so as to follow the position of the observer's eyes. The position of a parallax barrier may be adjusted by, for example, if the electrode strips that define the barrier in the addressable layer are each formed of a plurality of independently addressable electrode strips. It is then possible to switch OFF one strip at, for example, the left side of an opaque region of the parallax barrier while switching ON one electrode strip at the right side of the opaque region of that parallax barrier. This is repeated for each opaque strip of the parallax barrier so that the position of the parallax barrier in effect moves to the right, and thus alters the position of the viewing regions of the two images displayed on the image display layer.

When the display is rotated from one orientation to another orientation, for example from landscape mode to portrait mode, the viewing angle characteristics of the display may be changed. If the display used has uniform viewing angle characteristics, then the quality of the displayed image will be largely unaffected by rotation of the display from one orientation to another. However, if the viewing angle characteristics are non- uniform, as may be the case for a simple twisted-nematic liquid crystal display that does not have complex viewing angle compensation films, the quality of a displayed image may vary considerably between the landscape mode and the portrait mode of operation of the display. This is likely to be a problem especially for a dual-view display, since a dual-view display tends to be operated at larger viewing angles than an auto- stereoscopic display. One way in which this disadvantage may be overcome is to use a different gray-scale mapping for the display in each orientation. This allows best use to be made of the transmission-voltage characteristics of the display for each orientation of the display.

In the embodiments described above, the parallax barrier has been external to the image display device. This places a limit on the minimum separation between the parallax barrier and the image display layer, and this means that the maximum angular separation between the two viewing windows may be too low. If it is desired to increase the angular separation between the two viewing windows, it is possible to dispose the parallax barrier within one of the substrates of the image display device, according to the teaching of co-pending UK patent application No. 0320358.5.

In the embodiments described above, the image display device has comprised a liquid crystal layer. The invention is not, however, limited to a display having a liquid crystal image display layer. Any suitable image display layer may be used. The image display layer may be a transmissive layer that is illuminated by a suitable backlight, or it may be an emissive layer such as an OLED layer, a plasma panel layer, or a cathode ray tube.

The invention may be applied to front barrier displays and to rear barrier displays.

The invention has been described above with reference to displays that are intended to operate in a landscape mode or in a portrait mode. The invention is not, however, limited to these two specific display modes. The invention may be applied to any display that is intended to be viewed in two, or more, different orientations. Figure 17 is a schematic plan view of a further multiple view directional

display 120 of the present invention. The display 120 can display four independent views, with each view being displayed along a respective one of four different, non-coplanar directions.

Each view is displayed in a direction that is inclined with respect to the display face of the display 120, so that each view is visible to a respective observer 122. When the directions in which the views are displayed are projected onto the display face of the display 120, each projected direction is at approximately 90 to an adjacent projected direction. Figure 17 shows the viewing window of each view with an angular extent, as seen in front view, of approximately 90 but the embodiment is not limited to this - the viewing windows may have different angular extents from one another. The viewing direction of an image is defined as the central direction of the viewing window for that image. Each of the images has approximately the same viewing distance as the other images.

As will be described below, the views are not all displayed in the same orientation. For example, views 2 and 4 may be displayed in one orientation, for example portrait orientation, and views I and 3 may be displayed in a different orientation, for example landscape orientations. If the display is rotated by 90 about its normal axis, a view that was display in portrait mode in one orientation of the display will be displayed in landscape mode in the new orientation, and vice-versa.

The display 120 of figure 17 may be used in, for example, a horizontal table top interactive game with the display disposed on a table 121 such that its display face is horizontal. Each observer 122 may be a participant in the game, with different participants being provided with different information about the situation of the game.

Another application of the display 120 of figure 17 is in teaching - one of the observers 122 may be a teacher and the remaining observers may be pupils. The display 120 may also be of use in business meetings and conferences. In these applications, the display would operate as a "dual view" display, with each observer seeing a view that could be controlled independently from the view displayed to other observers.

A display of the type shown in figure 17 may also be used as a 3dimensional multiple view display, and in this case it may be used with its display face vertical as for a conventional display or with its display face horizontal. In this case, the positions 122 shown in figure 17 would represent the position of the eye of an observer, rather than the position of the observer. Thus, for example, view I and view 2 might be, respectively, the right-eye view and left-eye view displayed to an observer from a first viewpoint, and view 3 and view 4 would be, respectively, the right-eye view and left- eye view displayed from a viewpoint above the first viewpoint. Thus, the display 120 could display independent autostereoscopic 3-D images from two separate viewpoints.

This can provide a vertical "look around" effect, in which one observer can see either a first 3-D view or a second 3-D view from a viewpoint above or below the first 3-D view. (For this application the orientation of the display would need to be changed from that shown in figure 17. The display would need to be stood on one of the bottom corners so that the two images of each stereoscopic image pair were displayed at the same vertical height. Alternatively, the pixel assignment shown in figure 18(a) would need to be changed so that two of the images were displayed at one height and the other two of the images were displayed at a different height.) Alternatively, views 1 and 2 may provide a 3-D view to one observer and views 3 and 4 may provide a 3-D view to a second observer, thus providing a combined 3D, dual viewing mode.

The embodiment of figure 17 has been described below with reference to a display that display exactly four views. However, this embodiment can be applied to a display that can display five or more views.

Figures 18(a) to 18(c) show one way in which the display 120 can display four views along four separate directions. Figure 18(a) shows how the images are displayed on an image display layer 125, and it can be seen that the image display layer has first to fourth regions for displaying the first to fourth views. In the embodiment of figure 1 8(a) the image display layer is a pixellated image display layer, and figure 1 8(a)shows how the four views are assigned to pixels. In the embodiment of figure 1 8(a) each views is displayed on two pixels 124a- 124h, and each pixel is labelled with a "l", "2", "3", or "4" to indicate which of views I to 4 is displayed by that pixel. As can be seen in figure 18(a) two views (views 2 and 3) are displayed side by side on one row of pixels. One view (view I) is displayed on a row of pixels about the row on which views 2 and 3 are displayed, and the fourth view, view 4, is displayed on the row of pixels below the row of pixels on which views 2 and 3 are displayed. Views I and 4 are displayed on the same columns of pixels as one another. Furthermore, the pixel columns on which views I and 4 are displayed are the left-hand column on which view 3 is displayed and the right-hand column on which view 2 is displayed, so as to yield the "cruciform" group of pixels shown in figure 18(a).

The image display layer may be any suitable pixellated image display layer. It may be a transmissive display layer, such as a pixellated liquid crystal display layer, illuminated by a suitable backlight, an emissive display layer, such as an OLED (organic electroluminescent devices) or PDP array, or any other display, with a regular well- defined pixel arrangement.

It should be noted that figure 18(a) shows each view being displayed on only a single row of pixels, and on two columns of pixels. The invention is not limited to this, and each view may be displayed on more than one row of pixels and/or on more than two columns of pixels, provided that the "cruciform" group of figure 1 8(a) is provided.

In the case of a full colour display, each pixel 124a-124h shown in figure 18(a) may be made up of red, green and blue sub-pixels 124R, 124G and 124B as shown in the inset to figure 18(a).

Figure 18(b) shows a suitable parallax optic 126 for use with the image display layer of figure 18(a). In this embodiment the parallax optic is a parallax barrier that comprises a transmissive aperture 127. The transmissive aperture 127 of the parallax barrier has substantially the same shape as, but is slightly smaller than, two laterally adjacent pixels of the image display layer 125. The parallax barrier is generally similar to the parallax barrier of, for example, figure 6(b) and may be thought of a superposition- of one parallax barrier having opaque strips that extend horizontally in figure 18(b) and another parallax barrier having opaque strips that extend vertically in figure 18(b) Figure 18(c) shows the parallax barrier 126 of figure 18(b) superposed over the image display layer 125 of figure 18(a). The aperture 127 of the parallax barrier 126 is associated with the region that displays the first view (de, with the two pixels 124a, 124b), with the region that display the second view (pixels 124c,124d), with the region that display the third view (pixels 124e,124f), and with the region that display the fourth view (pixels 124g,124h). The aperture 127 of the parallax barrier is positioned approximately centrally over the cruciform group of pixels shown in figure 18(a). In a case where the parallax barrier 126 is disposed between the image display layer 125 and observers, an observer viewing the display from the left (as the display is shown in figure 18(c) will perceive view 3 but will not see views 1, 2 or 4 since these will be blocked by the opaque regions of the parallax barrier. Conversely an observer viewing the display from the right-hand side will perceive only image 2. Similarly, an observer viewing the display from the top edge will perceive only image 4, whereas an observer viewing the display from the bottom edge will perceive only image 1.

It will be noted that views I and 4 will be seen in landscape mode, since the two pixels on which views I and 4 are displayed are arranged laterally with respect to the respective observers. Views 2 and 3, however, will be displayed in portrait mode since the two pixels on which image 2, or image 3, are displayed are arranged one above the other when seen by the observer to whom view 2, or view 3, is directed. Thus, the display 120 of this embodiment displays images in two different modes simultaneously.

Figure 18(a) shows one element of the image display layer 125 of the display 120.

Figure 19(a) shows one way in which pixels of an image display layer may be assigned to the four views in order to define a plurality of the cruciform pixel group of figure 18(a). The arrangement of figure 19(a) may be thought of as obtained by interlacing the cruciform pixel group of figure 18(a) such that the two pixels assigned to view 1 of one element are on the same row as, and adjacent to, the pixels assigned to view 4 of another element. Thus, every other row of pixels in figure 19(a) is assigned to views 2- and 3, and the intervening rows of pixels are assigned to views 1 and 4.

Figure 19(b) illustrates a suitable parallax barrier 126 disposed in front of the image display layer 125 of figure l9(a). The parallax barrier comprises an array of apertures 127. The apertures are positioned such that, when the parallax barrier is disposed over the image display layer 125, each aperture 127 is disposed over the centre of one of the cruciform pixel groups defined in the pixel arrangement of figure l9(a).

Figure 20(a) shows another way in which pixels 124 of an image display layer 125 may be assigned to the four views. In this arrangement, each row of pixels displays all four of the views. This arrangement may be considered as interlacing the cruciform pixel groups of figure 18(a) such that the upper row of one pixel group is defined on the same pixel row as the second row of pixels of an adjacent cruciform pixel group. One of the cruciform pixel groups of figure 18(a) has been highlighted in figure 20(a).

Figure 20(b) shows the image display layer 125 of figure 20(a) with a parallax barrier disposed thereover. The positions of the apertures 127 of the parallax barrier are again chosen so that, when the parallax barrier is disposed over the image display layer 125, the centre of each aperture of the parallax barrier coincides with the centre of one of the cruciform pixel arrangements of figure 18(a).

Figures l 9(a) to 20(b) show two possible assignments of the pixels of the image display layer among the four images that incorporate the "unit cell" of figure 18(a), and the corresponding parallax barrier, but the invention is not limited to these cruciform interlacings. Other cruciform interlacings may be used.

The assignment of the pixels between the images may be chosen in dependence on the particular intended application of the display. For example if barrier visibility is a problem the pixel assignment shown in figure 20(a) may be better because the barrier apertures 127 are not arranged in vertical or horizontal lines, as can be seen in figure 20(b). In figure 20(b) the apertures 127 of the parallax barrier are arranged in lines that are inclined with respect to the horizontal or vertical, and the human eye may not tend to see such lines as much as the vertical and horizontal lines in figure l9(b). Another possible assignment of the pixels of the image display layer is a random or semi- random arrangements of the "unit cell" of figure 18(a) and this may further reduce the visibility of the parallax barrier, and may also improve privacy between views (since secondary viewing windows would not be formed correctly as they would show a mixture of all the pixels at different parts of the display - so that a view would be visible only in its intended viewing direction). Privacy would be helpful in applications such as games playing, for example.

In figure 19(a) and 20(a), each pixel 124 may, in the case of a full colour display, consist of a red pixel, a blue pixel and a green pixel as shown in the inset to figure 18(a). Furthemmore, as explained above with reference to figure 18(a), figures 19(a) and 20(a) show each view arranged on only a single row of pixels, but the invention is not limited to this.

It will be noted that both figures 19(b) and 20(b) show that an observer who views the display along the nommal to the display face will see a mixture of views 2 and 3.

The display 120 may, as explained above, be used as a dual view display in which case views 1, 2, 3 and 4 may be independent from one another. Alternatively, as also explained above, it may be used to provide two 3-D autostereoscopic views, in which case the four views will include the left-eye image and right-eye images of two independent stereoscopic image pairs. The two image pairs may represent one image from two different viewpoints, or they may represent two different images so as provide a combined 3D and dual view mode.

The invention is not limited to use with a parallax barrier as a parallax optic. A display according to this embodiment of the invention may comprise other forms of parallax optic such as, for example, a lenticular array. The display of this embodiment may use a multiple parallax barrier system, in which two or more parallax barriers are provided, as described for the embodiment of, for example, figure 12(a).

The parallax optic may be a fixed parallax optic. Alternatively, the parallax optic may be an active parallax optic, that can be switched between an ON state and an OFF state.

For example, where the parallax optic is a parallax barrier this may be embodied as a liquid crystal layer that can be switched between an ON state in which an array of transmissive apertures are defined in the liquid crystal layer and the remainder of the liquid crystal layer is nontransmissive and an OFF state in which the liquid crystal layer is uniformly light-transmissive. This enables the display to be switched to a conventional 2-D display mode, by switching the parallax barrier OFF and re- addressing the display to display a single image in conventional manner.

The display 120 of this embodiment may be addressed in a time sequential manner in order to improve the resolution of the display and/or the brightness of the displayed views.

As may be seen from figure 18(a), 19(a) and 20(a), a display of the present invention may use a conventional pixellated image display layer in which rectangular pixels are arranged in rows and columns. These embodiments of the invention may therefore be used with any conventional liquid crystal display panel, and do not require a special display panel. Similarly a conventional parallax barrier containing a regular array of rectangular apertures (or other suitable conventional parallax optic) may be used, and the invention does not require a specialized parallax optic. A further advantage is that the interlacing pattern of the four views is relatively simple to reproduce.

The interlacing of the views shown in figures 18(a), 19(a) and 20(a) does not require any pixels of the image display layer to be kept permanently dark. Each pixel of the image display layer is assigned to one of the four views. This maximises the brightness of the display, and ensures that one quarter of the possible output intensity of the display is put into each of the four views.

Furthermore, as noted above, the panel 120 has a natural orientation with respect to the four observers 122 shown in figure 17, since the side edges of the display are vertical and the top and bottom edges of the display are horizontal. Two of the observers see a view in landscape mode, and two observers see a view in portrait mode. By rotating the display by 90 , the view seen by one observer would change from portrait mode to landscape mode (or vice versa).

Figure 21(a) shows a further image display layer 125 suitable for use in the display 120 of this embodiment of the present invention. The image display layer 125 is again a pixellated image display layer, with the four views being assigned amongst the pixels.

As shown in figure 21(a), the four views are assigned to groups of four pixels arranged at the ends of the four arms of a cross (+). The pixels are shaded in figure 21(a) to indicate to which image they are assigned, with the four images being indicated respectively by uniform shading, diagonal line shading, vertical line shading, and dot shading. Thus, this assignment of pixels again leads to a cruciform group of pixels, with the group containing a pixel assigned to each view. This assignment of pixels is repeated over the image display layer as shown in figure 21 (a).

One suitable parallax optic for use with the image display layer 125 of figure 21(a) is indicated in the figure. In this embodiment the parallax optic is a parallax barrier that contains a first set of opaque regions 126a that extend in one direction (laterally in figure 21(a), and a set of second opaque regions 126b that are crossed with the regions of the first set. The opaque regions of the first set are indicated with a full outline in figure 21(a), and the opaque regions 126(b) of the second set are indicated with a broken outline in figure 21(a). This parallax barrier is again similar to the parallax barrier of, for example, figure 6(b) and can be considered as the superposition of two convention parallax barriers whose opaque regions extend along directions that are crossed with one another.

Figure 21(b) shows the parallax barrier 126 produced by the two sets of opaque regions 126a, 126b superposed over the image display layer 125. As can be seen, the two sets of opaque regions generate a plurality of transmissive apertures 127 that are generally rectangular in shape. The widths of the opaque regions 126a, 126b are chosen so that the spacing between adjacent transmissive apertures 127 corresponds approximately to the spacing between the crucifomm groups of pixels 124. As a result, each transmissive aperture 127 of the parallax barrier is associated with one of the cruciform groups of pixels so that, as explained previously, the four views are displayed in four different directions, and each of the observers 122 in figure 21(b) will see a different one of the four views. The view which each observer 122 will see is indicated in figure 21(b), by a region of the appropriate shading adjacent to the observer.

In this embodiment, the area 128 of the image display layer at the centre of a cruciform group of pixels is not assigned to display an image. As a result, an observer who views the display along the nommal of the display will see a black display. This reduces the possibility that an observer will inadvertently see two images simultaneously or, in the case of an autostereoscopic display, will inadvertently see the left eye image in the right eye or vice versa. The black display also provides privacy, as it makes it more difficult for an observer to see a view that is not intended for them.

This embodiment of the invention may be implemented on a conventional liquid crystal display panel or other pixellated display means. To do this, the pixel at the centre of a crucifomm group must be driven to give a pemmanently black display, to provide the no- display region 128. Altematively, this embodiment may be implemented on a custom liquid crystal panel, or other custom image display means, in which addressable pixels are not provided at the centres of the crucifomm groups.

In figures 21(a) and 21(b) each image has been shown as assigned to a single pixel, so that each cruciform group of pixels comprises just four pixels. To obtain a full colour display, each pixel shown in figure 21(a) may comprise three colour sub-pixels, such as a red sub-pixel, a blue subpixel and a green sub-pixel as shown in the inset to figure 18(a). Furthermore, each image may be displayed on two or more pixels, and is not limited to each image being displayed on only one pixel.

Figure 22 shows a further embodiment of the display 120 of figure 17. In this embodiment the four views are assigned to the pixels of the image display layer 125 in- the manner shown in figure 18(a). In this embodiment the image display layer is a full colour image display layer, so that the pixels are either red pixels 124R, blue pixels 124B or green pixels 124G. Each view is assigned to a composite pixel 124 made up of a red pixel, a blue pixel and a green pixel. For simplicity, each view is shown as assigned to only one composite pixel 124, but otherwise the assignment of views among the pixels is similar to that shown in figure 18(a). Two views are assigned to two laterally adjacent pixels, one view is assigned to a pixel in the row above, and the other view is assigned to a pixel in the row below. Each colour sub-pixel in figure 22 is numbered "1", "2", "3" or "4" to indicate which view is assigned to that sub-pixel.

Each colour sub-pixel is also shaded in figure 22 to indicate whether it is a red pixel (diagonal line shading), a blue sub-pixel (uniform shading) or a green sub-pixel (vertical line shading).

In this embodiment the parallax optic is a colour filter barrier. The colour filter barrier contains apertures 127 arranged generally as shown in the parallax barrier in the embodiment of figure 19(b). However, as shown in the inset to figure 22, each aperture 127 contains regions of different light transmission properties. In this embodiment, each aperture 127 in the colour filter barrier contains a first region 127r that transmits red light and substantially blocks blue light and green light, a region 127b that transmits blue light while substantially blocking red light and green light, and a region 127g that transmits green light while substantially blocking red light and blue light. The positions of the apertures of the colour filter barrier are indicated in outline in figure 22.

It will be seen that the embodiment of figure 22 operates in the manner described in relation to figure 18(c) above, for red light, green light and blue light. The red- transmissive portion 127r of an aperture 127 of the colour filter barrier is positioned laterally between a red pixel assigned to view 2 and a red pixel assigned to view 3, and is positioned vertically between a red pixel assigned to view 4 and a red pixel assigned to view 1. Similarly, the portion 127B of an aperture in the colour filter barrier that transmits only blue light is positioned laterally between a blue pixel assigned to image 2 and a blue pixel assigned to image 3, and is positioned vertically between a blue pixel assigned to image 4 and a blue pixel assigned to image 1. The portion of a colour filter- barrier that transmits in the green region of the spectrum is positioned laterally between a green pixel that is assigned to image 2 and a green pixel assigned to image 3, and is positioned vertically between a green pixel assigned to image I and a green pixel assigned to image 4. Thus, the images 1, 2, 3 and 4 are directed in four different directions, as in the embodiment of figure 18(c).

Compared with the embodiments of figures 18(c), 19(b) and 20(b), the embodiment of figure 22 has the potential advantage that an observer viewing the display along the normal to the display face will perceive a dark display. This is because each portion of an aperture of the colour filter barrier is not positioned directly over a pixel that emits light that is transmitted by that portion of the aperture. A portion of the colour filter that transmits red light, for example, is positioned partially adjacent to a blue pixel and partially adjacent to a green pixel, so that all light incident at normal incidence on the aperture of the colour filter barrier is blocked. This embodiment therefore provides a display that provides a dark display when viewed along the display normal without requiring to hold pixels permanently black, or without requiring a custom image display layer.

Further details of a colour filter barrier are contained in co-pending UK patent application No. 0320367.6, to which attention is directed.

Figures 23(a) to 23(c) show a further embodiment of the present invention. In this embodiment the four images are assigned to the pixels using a simple horizontal and vertical interlacing, as shown in figure 23(a). This parallax optic in this embodiment is a parallax barrier having a rectangular transmissive aperture 127. This display is simple to implement, but has the potential disadvantage that the four views are directed towards the comers of the display, rather than to the edges of the display. The embodiment of figure 23(a) uses simple interlacing of the four images, and the display therefore requires simple well-known addressing techniques. (As in other embodiments, each pixel shown in figure 23(a) may be made up of three colour-sub- pixels as shown in the inset to figure 23(a), to provide a full colour display.

* In order to retain the advantages of the simple addressing provided by the simple horizontal and vertical interlacing of figure 23(a), it is possible to implement this embodiment using an image display layer in which the pixel columns are inclined with respect to the edges of the display. This image display layer is shown in figure 23(b), which shows the pixel columns 128 and the non-display areas 129 between adjacent pixel columns extend inclined with respect to the side edges, and with respect to the top and bottom edges, of the image display layer 125. When this image display layer is incorporated in a display, using a parallax barrier in which the side edges of the apertures 127 of the parallax barrier extend parallel to, or perpendicular to the pixel columns, the result is that the four views are directed to the centres of the four edges of the display, as shown in figure 23(c). This allows the viewers to observe the display from the normal orientations shown in figure 17, rather than having to view the display from its corners. However, this embodiment will generally require a custom image display panel in which the pixel columns extend inclined with respect to the edges of the image display panel.

The invention has been described above with particular reference to a parallax barrier having rectangular apertures. However, where a parallax barrier is used as the parallax optic the apertures are not limited to being rectangular but may be circular, square, or any particular shape that is useful. Non-rectangular apertures may be in particular be preferable for a display of the type shown in figure 17 which displays five or more views.

The edges of the apertures in the parallax barrier may be "softened" (apodised) to reduce crosstalk further, as described in UK patent application Nos. 9616281.3 and 99173 1 8.9.

Claims

CLAIMS: 1. A display operable as a multiple view directional display in a

first orientation and operable as a multiple view directional display in a second orientation different from the first orientation, wherein the viewing distance of the display in the first orientation is substantially the same as the viewing distance of the display in the second orientation; wherein the angular separation between a first image and a second image displayed by the device in the first orientation is substantially equal to the angular separation between a first image and a second image displayed by the device in the second orientation.
2. A display as claimed in claim I and comprising an image display layer and a parallax optic disposed in an optical path through the image display layer.
3. A display as claimed in claim 2 wherein the effective pitch of the image display layer along a first direction and the effective pitch of the image display layer along a second direction perpendicular to the first direction are selected such that the viewing distance of the display in the first orientation is substantially the same as the viewing distance of the display in the second orientation.
4. A display as claimed in claim 2 or 3 wherein the image display layer is a pixellated image display.
5. A display as claimed in claim 4 wherein the image display layer comprises at least first pixels of a first colour and second pixels of a second colour, the width of a first pixel along the first direction being substantially equal to the width of a first pixel along the second direction and the width of a second pixel along the first direction being substantially equal to the width of a second pixel along the second direction.
6. A display as claimed in claim 4 wherein the image display layer comprises at least first pixels of a first colour and second pixels of a second colour arranged to form composite pixels, each composite pixel having at least one first pixel and at least one second pixel; wherein the width of a composite pixel along the first direction is substantially equal to the width of a composite pixel along the second direction.
7. A display as claimed in claim 5 or 6 wherein the pitch of the parallax optic along the first direction is substantially equal to the pitch of the parallax optic along the second direction.
8. A display as claimed in claim 7 wherein the parallax optic comprises a plurality of transmissive apertures.
9. A display as claimed in claim 8 wherein the parallax optic is a colour filter barrier, whereby each aperture comprises at least first and second regions having different light-transmissive properties.
10. A display as claimed in any of claims 2 to 9 wherein the parallax optic is a fixed parallax optic.
11. A display as claimed in any of claims 2 to 9 wherein the parallax optic is switchable between an OFF state in which no parallax optic is defined and an ON state.
12. A display as claimed in any of claims 2 to 10 wherein the parallax optic is reconfigurable between a first ON state and a second ON state.
13. A display as claimed in claim 12, wherein the parallax optic is further switchable to an OFF state in which substantially no parallax optic is defined.
14. A display as claimed in claim I and comprising an image display layer, a first parallax optic and a second parallax optic, the first and second parallax optics being disposed in an optical path through the image display layer; wherein the first parallax optic has a finite pitch in a first direction and the second parallax optic has a finite pitch in a second direction perpendicular to the first direction; and wherein the ratio of the separation between the first parallax optic and the image display layer to the pitch of the image display layer along the first direction is substantially equal to the ratio of the separation between the second parallax optic and the image display layer to the pitch of the image display layer along the second direction.
15. A display as claimed in claim 12 or 14 wherein the display comprises a first parallax optic switchable between an OFF state in which substantially no parallax optic is defined and a first ON state and a second parallax optic switchable between an OFF state in which substantially no parallax optic is defined and a second ON state.
16. A display as claimed in claim 15 wherein the first parallax optic and second- parallax optic are disposed on opposite sides of the image display layer.
17. A display as claimed in claim 15 wherein the first parallax optic and second parallax optic are disposed on the same side of the image display layer.
18. A display as claimed in any of claims 12 to 17 wherein the or each parallax optic comprises a liquid crystal material.
19. A display as claimed in claim 18 wherein the or each parallax optic comprises a liquid crystal layer and a patterned retarder disposed in an optical path through the display.
20. A display as claimed in claim 18 wherein the or each parallax optic comprisies a first patterned retarder, a liquid crystal layer, and a second patterned retarder disposed in this order in an optical path through the display.
21. A display as claimed in claim 19 or 20 wherein the or each patterned retarder comprises a reactive mesogen layer.
22. A display as claimed in claim 18 wherein the or each parallax optic comprises a plurality of addressable liquid crystal regions disposed alternately with regions of fixed optical characteristics.
23. A display as claimed in claim 18 wherein the or each parallax optic comprises an addressable liquid crystal layer having regions of first alignment characteristics alternating with regions of second alignment characteristics.
24. A display as claimed in claim 13, or in any of claims 14 and 18 to 21 when dependent directly or indirectly from claim 13, wherein the parallax optic comprises an addressable layer, first addressing means for defining a first parallax optic in the addressable layer, and second addressing means for defining a second parallax optic in the addressable layer.
25. A display as claimed in any preceding claim wherein the rotation of the display about the normal to a display face of the display transforms the display from the first orientation to the second orientation.
26. A display as claimed in any preceding claim wherein the first orientation is at substantially 90 to the second orientation.
27. A display as claimed in claim 26 wherein the first orientation is a horizontal orientation and the second orientation is a vertical orientation.
28. A multiple view directional display adapted to display four views, each view being displayed, in use, along a respective one of four different non-coplanar directions.
29. A display as claimed in claim 28 and comprising an image display layer having a plurality of first regions for displaying a first view, a plurality of second regions for displaying a second view, a plurality of third regions for displaying a third view, and a plurality of fourth regions for displaying a fourth view; and a parallax optic for displaying each view, in use, along the respective one of the four different noncoplanar directions.
30. A display as claimed in claim 29 wherein an element of the parallax optic is associated with one first region of the image display layer, with one second region of the image display layer, with one third region of the image display layer, and with one fourth region of the image display layer.
31. A display as claimed in claim 29 or 30 wherein the image display layer is a pixellated image display layer and each first region, each second region, each third region and each fourth region comprises one or more pixels.
32. A display as claimed in claim 29, 30 or 31 wherein a first region and a second- region are disposed laterally adjacent to one another, a third region is disposed above the first and second regions, and a fourth region is disposed below the first and second regions and is disposed vertically below the third region.
33. A dual view display device comprising a display as defined in any of claims 1 to 32.
34. An autostereoscopic display device comprising a display as defined in any of claims I to 32.