GB2405518A

GB2405518A - Multiple view display

Info

Publication number: GB2405518A
Application number: GB0320361A
Authority: GB
Inventors: Heather Stevenson; Emma Walton; Diana Kean
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2003-08-30
Filing date: 2003-08-30
Publication date: 2005-03-02
Also published as: GB0320361D0

Abstract

A multiple view display is provided for displaying two or more views in respective different viewing directions. The display comprises a liquid crystal device (20-28) with two or more sets of pixels having different configurations and different asymmetric viewing angle properties. A driving arrangement (29) drives the sets of pixels appropriately so that the pixels of a first set display an image which is viewable in a first viewing direction and the pixels of a second set display a further image which is viewable in a different direction. Preferably, the pixels appear dark or black when viewed in other viewing directions.

Description

24055 1 8

MULTIPLE VIEW DISPLAY

The present invention relates to a multiple view display. Such a display may be used to display two or more views containing images which are substantially different from each other. Such displays allow different viewers to see different images which may be unrelated to each other.

Figure 1 of the accompanying drawings illustrates the concept of a multiple view i display which, in this example, comprises a dual view display. Viewers 1 and 2 located - in viewing regions 1 and 2 view a dual view display 10. The display 10 has discrete viewing regions in which substantially different images may be displayed. For example, viewer 1 may be watching a film while viewer 2 may be reading a map. Such an example is applicable, for instance, to a display for automotive use so that a driver may see navigation information while a passenger simultaneously sees the film.

Figure 2 of the accompanying drawings illustrates another example of the use of a dual view display l O. In this case, the display is mounted in the plane of a desk or counter 11 so that viewers 1 and 2 on opposite sides of the desk or counter may view different images. Similarly, Figure 3 illustrates a horizontally oriented multi-view display which, in this case, displays four unrelated images to viewers 1 to 4 on the four sides of the display.

The viewing angle properties of the twisted nematic (TN) liquid crystal (LC) mode are well known and the viewing angle properties of such a liquid crystal display (LCD) are disclosed in P. Yeh and C. Gu, "Optics of Liquid Crystal Displays", John Wiley and Sons Inc., 1999, chapter 9. These properties are generally relatively uniform in the horizontal viewing angle direction but are asymmetric in the vertical viewing angle direction. Techniques for optimising the viewing angle properties of LCDs to allow the same image to be viewed from a wide range of angles are known.

A multiple view video display is disclosed in JP 06-236152. In this example, use is made of lenticular lenses to generate different viewing regions.

JP 08-101367 discloses a dual layer autostereoscopic display. One layer displays spatially multiplexed images behind another layer which acts as a direction control layer to direct the images into dificrcnt viewing regions for autostereoscopic viewing.

The directional viewing properties of TN and guest-host (GH) LCDs are disclosed in JP 2-146087, JP 60-211418, JP 60-211420, JP 60-211428 and in Okada et al, IEEE Transactions on Electron Devices, Vol. 45, No. 7, 1988, pp 1445-1452 "Possibility of Stereoscopic Displays by Using a Viewing Angle Dependence of Twisted Nematic Liquid Crystal Cells". These documents disclose spatially multiplexing two images on an LCD with the pixels for displaying one of the images having a different alignment from the pixels for displaying the other image. These documents refer to autostereoscopic or stereoscopic displays for displaying related images to provide a 3D display.

These documents disclose arrangements in which the pixels for displaying one image are of the same configuration as the pixels for displaying the other image. However, the pixels for one image are effectively rotated or are effectively mirror images of the pixels for the other image being displayed.

The concept "of different configurations" when applied to liquid crystal display (LCD) pixels (picture elements) is defined to mean that the pixels differ in respect of any one or any combination of: pretilt at either or both liquid crystal substrate interfaces; bulk liquid crystal director orientation; liquid crystal thickness; director twist; doping of the liquid crystal material with chiral additives, dyes or polymeric materials; polariser transmission axis orientation; azimuthal and/or zenithal anchoring strength; retardation layer magnitude and/or optic axis orientation; compensation layer effect; liquid crystal material; and driving scheme, but excludes cases where one pixel is a rotation or mirror image of the other pixel.

The concept "of different LC modes" when applied to liquid crystal display pixels is defined to mean that the pixels differ in respect of any one or any combination of: pretilt at either or both liquid crystal substrate interfaces; bulk liquid crystal director orientation; liquid crystal thickness; director twist; azimuthal and/or zenithal anchoring strength; polariser transmission axis orientation where the polarisers are disposed within the liquid crystal cell; retardation or compensation effect where the retarders or compensators are disposed within the liquid crystal cell; liquid crystal material; and doping of the liquid crystal material with chiral additives, dyes or polymeric materials, but excludes eases where one pixel is a rotation or mirror image of the other pixel.

According to a first aspect of the invention, there is provided a multiple view display comprising: a liquid crystal device comprising first pixels, which have a first configuration with first asymmetric viewing angle properties, and second pixels, which have a second configuration different from the first configuration with second asymmetric viewing properties oriented differently from the first asymmetric viewing properties; and a driving arrangement for driving the first pixels for displaying a first image in a first viewing direction and for driving the second pixels for displaying a second image in a second viewing direction different from the first direction.

The first and second images may be viewable in a third viewing direction between the first and second directions.

According to a second aspect of the invention, there is provided a multiple view display comprising: a liquid crystal device comprising first pixels, which have a first configuration with first asymmetric viewing angle properties, and second pixels, which have a second configuration different from the first configuration, and a driving arrangement for driving the first pixels for displaying a first image in first and second viewing directions and for driving the second pixels for displaying a second image in the second viewing direction.

The first pixels may be spatially interspersed with the second pixels.

The first and second images may be unrelated to each other.

The first and second directions may be in a plane which is orthogonal to a display surface of the device and contains directions of maximum viewing angle asymmetry of the first and second properties. The first and second directions may be on opposite sides of a normal to the display surface. The first and second directions may be asymmetric about the normal.

The angle between the first and second directions may be greater than substantially 10 . i The first pixels may be arranged to provide a first contrast ratio greater than one in the first direction and a contrast ratio substantially equal to one in the second direction and the second pixels may be arranged to provide a second contrast ratio greater than one in the second direction and a contrast ratio substantially equal to one in the first direction.

The first and second pixels may be arranged to appear black in the second and first directions, respectively.

The first and second asymmetric viewing properties may be oriented in substantially opposite directions.

The device may comprise sets of pixels with the pixels of each set being the same colour and being of a different colour from the pixels of the other sets. The device may comprise a liquid crystal layer having different thicknesses at the pixels of different colours. The device may comprise a patterned retarder with regions of different retardations being optically aligned with the pixels of different colours. The regions of different retardations may contain dyes of the different colours for acting as colour filters.

The first and second pixels may have first and second liquid crystal modes, respectively, which are different from each other. At least one of the first and second modes may be one of twisted nematic, hybrid aligned nematic, twisted vertically aligned nematic, Freedericksz, vertically aligned nematic and pi-cell.

The first and second pixels may have different liquid crystal director twists in the absence of an applied field. The different twists may have different magnitudes. The different twists may have different twist senses. One of the different twists may be 0".

The first and second pixels may have different liquid crystal director pre-tilts at at least one liquid crystal substrate interface. The different pre-tilts may have different magnitudes. The different pretilts may have different directions.

The first and second pixels may have different bulk liquid crystal director orientations.

The first and second pixels may have different surface anchoring strengths at at least one liquid crystal substrate interface.

The first and second pixels may have different liquid crystal materials.

At least one of the first and second pixels may have a liquid crystal material containing at least one of a chiral dopant, a polymer network and a dye.

The first and second pixels may have liquid crystal layers of different thicknesses.

The first pixels may have first polarisers whose transmission axes are oriented at a first angle with respect to liquid crystal optic axes of the first pixels and the second pixels may have second polarisers whose transmission axes are orientated at a second angle different from the first angle with respect to the liquid crystal optic axes of the second pixels.

The first and second pixels may have first and second retarders of different retardations.

The first and second pixels may have first and second compensation layers providing different compensation effects.

The driving arrangement may be arranged to drive the first and second pixels with different voltage ranges.

The device may comprise a parallax barrier.

The device may comprise a transmission mode device.

The display may comprise a further liquid crystal device arranged to be viewable through and to operate time-sequentially with the firstmentioned device.

It is thus possible to provide a multiple view display which makes use of asymmetrical viewing angle properties of pixels of different configurations to allow unrelated images to be viewed in different viewing regions. Each image may be viewable in its respective viewing direction while substantially not being viewable in any other viewing direction. Alternatively, one or more images may be viewable only in their respective viewing directions but two or more images may be simultaneously viewable in one or more other viewing directions. It is unnecessary to use any parallax generating optic such as a parallax barrier or lenticular screen, although it is possible to use such a parallax optic, for example so as to improve display contrast ratio. It is further possible for those pixels which are displaying an image for viewing in a different viewing direction to appear dark or substantially black in the viewing directions of other image pixels.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which; Figures 1-3 arc diagrams illustrating uses of a multiple-view display; Figure 4 is a cross-sectional diagram of display constituting an embodiment of the invention; Figure 5 is an exploded diagram illustrating the orientation of components of the display of Figure 4; Figures 6 and 7 describe the luminance in transmission against voltage for a device configuration; Figure 8 describes the variation of luminance ratio with voltage; Figure 9 is an exploded diagram illustrating the orientation of components of a display; Figures 10 and l l describe the luminance in transmission against voltage for a device configuration; Figure 12 describes the variation of luminance ratio with voltage; Figure 13 shows dual view display usage; Figure 14 describes the use of polymer walls to separate different LC materials; Figure is describes the operation of a dual display with a central crosstalk region; Figure 16 describes the operation of a dual display with the use of a central crosstalk region; Figures 17 and 18 describe the use of four device configurations; Figure 19 describes the variation of viewing angle with respect to orientation to the panel; Figure 20 describes the variation in grey level with colour for the TN mode; Figure 21 describes the corrected grey levels for different colours for the TN mode; Figure 22 describes the use of variable liquid crystal layer thickness for colour compensation; Figure 23 describes the use of in-cell retarders for colour compensation; Figure 24 describes a method of forming a pixellated retarder; and Figure 25 shows the use of a parallax barrier.

Figure 4 illustrates a dual view thin film transistor (TFT) active matrix LCD for directing images 1 and 2, which may be unrelated, in two views into viewing regions 1 and 2 for viewers 1 and 2, respectively as illustrated in Figures 1 and 2. The display comprises a front linear polariser 20 attached to or formed on the outer surface of a substrate 21. The substrate 21 may be made of glass or any suitable transparent nonbirefringent material of sufficient stability. The substrate 21 carries on its inner surface a transparent electrode 22, for example made of indium tin oxide (ITO). The electrode 22 acts as a counter-electrode for the active matrix and uniformly covers the whole active area of the display 10. An aligning surface such as alignment layer 23, for example of rubbed polyimide, is formed on the electrode 22.

A second substrate 27 carries a rear linear polariser 28 and a TFT and electrode layer 26. The electrodes of the layer 26 are patterned so as to define pixels (picture elements). Such TFT and electrode arrangements are known and will not be described further. An aligning surface such as alignment layer 25, for example of rubbed polyimide, is formed on the layer 26.

The substrates 21 and 27 are formed with the layers 22, 23, 25 and 26 and are brought together with the alignment layers 23 and 25 facing each other so as to define a liquid crystal cell with a liquid crystal layer 24 therebetween. The liquid crystal of the layer 24 is a nematic liquid crystal. The polarisers 20 and 28 may be formed or provided before or after the liquid crystal cell is formed. The layer 26 includes or is connected to a driving arrangement illustrated at 29 for providing the appropriate signals to address the individual pixels with voltages defining greyscales. The arrangement 29 may be formed entirely or partly of external components for providing the appropriate driving schemes for the first and second images which are to be displayed. Alternatively, the arrangement 29 may be integrated on the panel for example, using continuous grain shcon.

The LCD is pixellated so as to provide first and second sets of pixels 101 and 102 for displaying the images 1 and 2 for viewing in different directions. The pixels 101 and 102 are spatially multiplexed or interspersed with each other so that each image is visible from its viewing direction across the whole display surface of the display. For example, the pixels 101 and 102 may be arranged in a chequerboard pattern or as alternating vertical strips of one or more columns of pixels.

The pixels 101 are of a first configuration whereas the pixels 102 are of a second configuration different from the first configuration. The different configurations may be characterized by differences in any one or more of the following features: pre-tilt at one or both surfaces of the liquid crystal layer 24; bulk liquid crystal director orientation in the layer 24; thickness of the layer 24; twist in the absence of an applied field; doping of the liquid crystal layer 24; orientation of the transmission axis in either or both of the polarisers 20 and 28; azimuthal and/or zenithal anchoring of the liquid crystal substrate interfaces at the alignment layers 23 and 25; retarders and/or compensation films (not shown in Figure 4); the material of the liquid crystal layer 24; and driving schemes such as voltage ranges provided by the driving arrangement 29.

In embodiments where the pre-tilts differ for the pixels 101 and 102, either or both of the alignment layers 23 and 25 may be appropriately patterned so as to provide different pre-tilts for the pixels 101 and 102. The pretilts may be different in respect of magnitude or direction or both.

Where the bulk liquid crystal director orientation is different between the pixels 101 and 102, the alignment layers 23 and 25 may be patterned so as to provide different pretilts and/or alignment directions at the liquid crystal layer surfaces. The combination of pretilt characteristics and alignment directions determine the liquid crystal director orientation in the bulk of the liquid crystal layer 24.

The thicknesses of the liquid crystal layer 24 at the pixels 101 and 102 may be different from each other. This is described in more detail hereinafter.

Where the twist differs between the pixels lot and 102, there may be a difference in the angle of twist and/or in the sense of the twist between the pixels, ie clockwise or anticlockwise, in the absence of an applied field between the electrodes 22 and 26 AISO, there may be zero twist, for example in the pixels lot, and a non zero twist in the pixels 102 in the absence of an applied field between the electrodes 22 and 26.

The liquid crystal of the layer 24 may include chiral dopants. Differences in thickness and alignment directions between the pixels 101 and 102 together with the effect of such chiral dopants affect the bulk director orientation in the layer 24, for example constraining it to form a twisted structure with a predetermined handedness and pitch.

The LC layer 24 may also include dopants such as dyes or polymer materials to enhance the viewing characteristics of the LCD.

The polariser 20 and/or the polariser 28 may be patterned such that the transmission axes of the polariser regions of the pixels 101 with respect to the optic axis of the layer 24 of the pixel may be different from that for the pixels 102.

By providing differences in the anchoring strengths of the liquid crystal directors at the interface between either or both alignment layers 23 and 25 and the adjacent liquid crystal material of the layer 24, the switching properties of the liquid crystal material in the presence of an applied voltage may be made different between the pixels 101 and 102.

Although not shown in Figure 4, retarders and/or compensation films may be provided for either or both of the pixels 101 or 102. For example, patterned retarders and/or compensation films may be used with a different retardation or compensation effect between the pixels 101 and 102.

As described in more detail hereinafter, different liquid crystal materials may be used for the pixels 101 and 102. By using different materials, the birefringence, elastic constants, and dielectric constants may be appropriately selected and may be different for the pixels 101 and 102. i Differences in liquid crystal director structure and anchoring may be combined with differences in dielectric and elastic constants so that different voltage ranges are used for the pixels 101 and 102. The driving arrangement 29 thus provides the appropriate driving schemes, such as different voltage ranges, in order to optimise the image qualities of the first and second images in their respective viewing regions while minimising the contrast ratio in other viewing regions and making the pixels appear relatively dark or black in the other regions.

Figure 5 illustrates diagrammatically in an exploded view the polarisers 20 and 28 and the layers 23 to 25 for a specific embodiment of the display 10 shown in Figure 4 using the twisted vertically aligned nematic (TVAN) liquid crystal mode. Figure 5 also illustrates the vertical direction for normal orientation of the display 10 as illustrated in Figure 1 and the horizontal direction. The vertical upward reference direction is referred to as 0 and the horizontal right direction as 90 . The various directions illustrated for the components shown in Figure 5 are referred to the upward vertical 0 direction.

The front polariser 20 has a transmission axis 30 oriented at +180 relative to the upward vertical direction. The alignment layer 23 has a patterned alignment direction with an alignment direction 33a for the pixels 101 oriented at +90 to the upward vertical direction and an alignment direction 33b for the pixels 102 oriented at +70 to the upward vertical direction. The alignment layer 25 is also patterned with an alignment direction 35a oriented at +180 to the upward vertical direction for the pixels 101 and an alignment direction 35b oriented at 0 to the upward vertical direction for the pixels 102. The polariser 28 has a transmission axis 38 oriented at +90 to the upward vertical direction. Thus, the polarisers 20 and 28 are uniform and unpatterned.

In a specific example of the display illustrated in Figures 4 and 5, the liquid crystal layer 24 has a thickness of 3.7 micrometres in the regions 34a of the pixels 101 and a thickness 4.0 micrometres in the regions 34b of the pixels 102. The liquid crystal is of the type known as MJ97174 available from Merck UK.

The patterned alignment layers 23 and 25 may be formed by multiple rubbing techniques, for example as disclosed in "3D display systems hardware research at Sharp Laboratories of Europe; an update", Harrold et al see Sharp technical journal, issue number 74, August l 999.

A material such as polyimide P12555 available from Dupont UK, is coated onto a substrate, for example by spin coating. The layer is appropriately cured, for example by heat treatment, and is then rubbed uniformly so as to define a certain alignment direction and pretilt when ultimately brought into contact with the liquid crystal material. A photoresist, such as S1865 available from Shipley UK, is coated on the rubbed polyimide layer. The photoresist is exposed to ultraviolet radiation through a suitable mask such that regions corresponding to, for example, the pixels 101 are exposed whereas the other regions corresponding to the pixels 102 are unexposed. The resist is developed so that the regions of the alignment layer for one of the sets of pixels is protected by the photoresist whereas the regions for the other pixels are exposed. A further rubbing operation is then performed in a different direction from the first rubbing operation and with a different rubbing strength so as to produce a different alignment direction and pretilt. The photoresist is then removed so as to provide two sets of regions for the pixels 101 and 102 with different alignment directions and pretilts.

Alternatively, a photoalignmcnt technique may be used in place of the rubbing technique. For example, a first uniform exposure may be followed by a second patterned exposure for altering the alignment direction and pretilt of the first exposure.

Photoalignment may be by bond breaking, bond making or by exploiting photo re- orientable materials such as azo dyes.

As an alternative, a combination of rubbing and photoalignment may be used to define the alignment directions and pretilts of the patterned alignment layers.

As a further possibility, microstructured alignment surfaces of the type disclosed in GB 2384318 may be provided.

Other techniques such as photolithography and embossing of polymers may also be used, for example simultaneously to provide the microstructured aligning surface and to form a step in the thickness of the polymer layer between pixels 101 and 102 of the different sets. Such a technique may be used to provide pixels of different liquid crystal layer thicknesses without requiring any extra processing steps beyond the formation of the aligning layers.

The display of Figures 4 and 5 is of the normally black type in that the pixels 101 and 102 appear maximally dark or "black" in their respective viewing directions in the absence of an applied field between the electrodes 22 and 26. In this case, the liquid crystal layer 24 is aligned substantially homeotropically. When a voltage is applied across the liquid crystal layer of any of the pixels 101 and 102, light is transmitted in the viewing direction of the pixel. The transfer functions of the pixels 101 and 102 are illustrated in Figures 6 and 7, respectively, as luminance in transmission against applied voltage for viewing directions of -30 and +60 to the normal to the display surface in a horizontal plane. The driving arrangement 29 supplies voltages in a range for producing greyscale in the +60 direction and these pixels 101 appear substantially black in the -30 direction. Conversely, the driving arrangement 29 supplies voltages for selecting grey levels in the -30 viewing direction for the pixels 102 and these pixels appear substantially black in the +60 viewing direction.

Figure 8 illustrates the luminance ratio against applied voltage for the pixels 101 and, in particular, illustrates the ratio of the luminance for the image viewed from +60 divided by the luminance of the black state at _30U. This ratio is very high and, for example, exceeds 100 even up to 25% transmission.

Figure 9 illustrates another embodiment of the display shown in Figure 4 with the pixels lOl operating in the Freedericksz or untwisted planar aligned nematic mode and the pixels 102 operating in the twisted nematic mode. The front polariser 20 has a transmission axis oriented at +180 to the upward vertical direction. The alignment layer 23 is patterned with regions corresponding to the pixel 101 having an alignment direction 33a oriented at +45 to the upward vertical direction and regions corresponding to the pixels 102 having an alignment direction 33b oriented at +90 to the upward vertical direction. The alignment layer 25 is similarly patterned with regions corresponding to the pixels 101 having an alignment direction 35a oriented at +45 to the upward vertical direction and regions corresponding to the pixels 102 having an alignment direction 35b oriented at +180 to the upward vertical direction. The polariser 28 is uniform and has a transmission axis 38 oriented at +90 to the upward vertical direction. The liquid crystal layer 24 is of uniform thickness, for example 2 micrometres, and may comprise the material known as E7 available from Merck UK.

The display illustrated in Figures 4 and 9 operates in the normally white mode. In the absence of an applied voltage between the electrodes 22 and 26, the liquid crystal layer 24 is aligned with a planar untwisted alignment for the pixels 101 and with a planar 90 twist for the pixels 102. The liquid crystal layer 24 thus rotates the direction of polarisation of light passing therethrough by 90 . When a voltage is applied between the electrodes 22 and 26 for any of the pixels 101 and 102, the pixel transmits light and provides greyscale in accordance with the applied voltage. The transfer functions of the pixels 101 and 102 are illustrated in Figures 10 and 11, respectively, as luminance in transmission against applied voltage at viewing angles of +60 and -30 . The driving arrangement 29 supplies voltages to the pixels 101 in a voltage range such that a greyscale image is displayed so as to be viewable in the -30 direction but these pixels appear substantially black in the +60 direction. Conversely, the driving arrangement 29 supplies voltages to the pixels 102 for displaying a greyscale image in the +60 direction and these pixels appear substantially black in the - 30 viewing direction. The luminance ratios (as defined hercinbefore) for the Freedericksz pixels 101 and for the twisted nematic (TN) pixels 102 are illustrated in Figure 12, which indicates that the luminance ratio is very high and is, for example, at least 200 over 20% transmission for both types of pixels.

Figure 13 illustrates diagrammatically a display 10 in which the liquid crystal layer 24 is of different thicknesses for the different pixels 101and 102. The different- thicknesses may be achieved by any suitable techniques, for example as disclosed herein. Figure 13 also illustrates the different viewing angle directions al and a2 in the horizontal plane relative to a normal to the display for the images displayed by the sets of pixels 101 and 102. In general, the viewing angles a' and at are required to be substantially larger than those which are conventionally used for autostereoscopic displays. For example, for a typical autostereoscopic display, the angle between viewing directions may be of the order of 10 . For displays displaying unrelated or non- stereoscopic images to two different viewers, the angular separation between the viewing directions is generally much larger than this and may be asymmetric (at is not equal to a2). For example, if the display 10 is used in the dashboard of a vehicle where the viewers may be of different heights and may therefore sit at different distances from the display, the viewing angles al and at may be of different magnitudes. It may also be possible to optimise operation of the display for variable viewing angles so as to be able to accommodate different viewer positions.

Patterned alignment or multi-domain arrangements of known type, for example as described hereinbefore, are incapable of providing optimised or even sufficient image quality with the relatively wide or large viewing angles required. The techniques disclosed herein permit this and also permit pixels to appear relatively black when viewed from the nonintended viewing directions of those pixels.

The combination of liquid crystal material and aligning surface has substantial influence on the eventual bulk liquid crystal director configuration. By providing different materials for the different pixels and using this to form the aligning surface, differences in anchoring strengths (zenithal and/or azimuthal) may be obtained and may result in a difference in the liquid crystal director structure and switching behaviour from one type of pixel 101 to another 102. This may be used to provide two or more sets of pixels in a single liquid crystal device such that each set displays a greyscale image in its viewing direction and appears dark or black in other viewing directions.

In order to provide pixels of different liquid crystal layer thicknesses, steps may be- formed on either or both substrate, for example photolithographically, by techniques such as embossing of suitable polymer materials, by etching glass substrates, or by any other suitable technique. Aligning surfaces may then be formed upon the stepped surfaces. Two stepped substrates or a stepped substrate and a uniform counter substrate may then be used to form a liquid crystal cell with different thicknesses of liquid crystal layer for the pixels 101 and 102.

In displays where different liquid crystal materials are used for the different pixels 101 and 102, it is necessary to provide an arrangement which confines each liquid crystal material and separates it from the or each other liquid crystal material. This may be achieved by forming polymer walls on either or both substrates, for example by means of photolithography of a highly binary resist material such as SUB available from MicroChem. Figure 14 illustrates an arrangement of this type in which polymer walls extend generally vertically in a serpentine path leaving fill holes 111 for a first liquid crystal material (LC1) and fill holes 112 for a second liquid crystal material (LC2).

For example, one of the liquid crystal materials LC1 may be chirally doped so as to define a certain twist sense whereas the other material LC2 may be undoped. This allows one twist sense to be preferentially selected in the case where the alignment conditions would otherwise be twist degenerate. Alternatively, different doping may be used for the different materials. One material may have positive dielectric anisotropy and the other material may have negative dielectric anisotropy. Liquid crystal materials with different birefringences and/or different elastic constants may be used.

Figure lS illustrates a dual view display 10 in which, in addition to the viewing regions for the viewers l and 2 in which substantially only a single respective view is visible, there is a "crosstalk region" 1 Is in which both of the images l and 2 are visible because of the overlap of viewing angle characteristics of the pixels lot and 102. In some applications, the crosstalk region llS is undesirable and the display 10 is designed or optirnised to minimise crosstalk. In some applications the crosstalk region may be i replaced by a black central region. However, in other applications, use may be made of - the crosstalk region 115. For example, for office presentations or for use with customers where a first person wishes to display information on a laptop or PC monitor to a second person, the first person (viewer 1) may view the display to from the crosstalk region as illustrated in Figure 16. The viewer 1 may therefore see the images l and 2 effectively superimposed on each other and, for this application, the display may be controlled or optimised to improve the superimposed images in the region 115, for example at the expense of image quality in the viewing region 1. The viewer 2 in the viewing region 2 substantially only sees the image intended for him or her. For example, where the viewer 1 is giving a demonstration, the image 1 may contain additional details with respect to the image 2 such as prompts for presentation or menu options to allow image data shown to the viewer 2 to be selected. The display 10 may also be controllable such that, when the demonstration has ended, the display may operate as a dual "discrete" view display or as a single view display of higher spatial resolution, for example optimised for normal incidence viewing.

In yet other applications, it may be desirable to make use of the viewing regions l and 2, where the images 1 and 2, respectively, only are visible to the viewers 1 and 2, respectively, and the crosstalk region 115 where both images may be seen simultaneously. An example of this is for multi player gain, where a player in the crosstalk region 115 sees all of the image data whereas players in the zones on either side can only see partial image data.

The displays described hereinbefore are of the type in which two images which are unrelated, for example by being non-stereoscopic, are displayed, for example for two viewers to see simultaneously different images from different viewing regions.

However, by optimization of viewing angle characteristics, crosstalk regions may be sufficiently reduced or substantially eliminated to allow displays providing more than two views to be displayed. For example, as illustrated diagrammatically in Figure 17, by using four different types of pixel configurations in the liquid crystal device, four different unrelated (or related) images may be directed to four viewing regions so that four viewers may see different images simultaneously displayed on the same device.

As an alternative and as illustrated in Figure 18, four device configurations 120 may be displayed by means of two liquid crystal devices 121 and 122 with the devices being stacked so that one device 122 is viewable through the other device 121. For example, the devices may be operated time-sequentially so that, in one time frame, one of the devices supplies images to two viewing regions and black to the other region whereas, in the second time frame, the liquid crystal device roles are reversed. Such an arrangement provides images with twice the spatial resolution (assuming that all images are displayed with the same spatial resolution) compared with the arrangement shown in Figure 17.

Suitable holograms may be used to eliminate or reduce crosstalk regions.

When a dual view display is looked at by a person, the size of the panel and the distance of the person from the panel both affect the angle which the extreme edges of the panel make with that person's eyes, as shown in Figure 19. In the case of a 8cm wide panel 130, the angular range over which the greyscale correction operates should be 23 to 25 but, for a 30cm wide panel 131, this increases to 16 to 41 . As the angular range increases, software image correction techniques may be used to prevent changes being observed at the extremes of the image.

Alternatively or additionally, patterning of the alignment layer may be optimised with position across the panel. This may be used, for example, to vary the angle or twist across the panel for each set of pixels 101 and 102, for example in opposite directions depending on the viewing directions which have been chosen. A variation in angle across the panel for one set of pixels may be achieved by exploitation of the effect of variation of the angle of photo alignment direction with exposure energy. For example, this may be achieved by means of a scanned ultraviolet source incident upon a photo alignment layer and by varying the ultraviolet flux as the beam is scanned across the surface so as to result in a change in angle across the surface. Other regions may be masked during this process. The ultraviolet source may be polarised. i

As an alternative, a variable amplitude mask may be used with a uniform ultraviolet exposure source. As a further alternative, a phase mask may be used for rotating the angle with which the alignment is formed across the panel, for example by means of differently oriented waveplates. This may be used with bond breaking or bond making photo alignment.

Alternatively different liquid crystal materials may be used across the panel so as to optimise image quality.

The grey level range used for the pixels 101 and the grey level range used for the pixels 102 may be optimised. For example, the optimization may be to provide the best image quality in the viewing direction in which each pixel is to display an image and to give the best grey level state, such as substantially black, for other viewing directions.

Where different voltage ranges are required for dual or multiple view display and/or for operating such a display in a single view normal incidence mode, the driving arrangement 29 is required to provide the appropriate voltage ranges.

A dual view display may be used as a single view or 2D display. When such a display is used for normal incidence viewing, the range of vertical and horizontal angles over which the single view is visible with good quality may be reduced as compared with a conventional single view type of display. In order to improve normal incidence viewing of a multiple view display, the different pixel sets may need to be driven differently because of the different configurations in order to improve or optimise the range over which a single image is viewable with acceptable quality.

Flexibility in tuning the required viewing angle characteristics over a limited range may be achieved by adjusting the angle for which an image is optimised by changing the grey-scalc range used until it is correct or optimum for that user. For example, where such a display is used in the dashboard of a vehicle, this may be done at the same time as a driver or passenger adjusts the seat and rear-view mirror. Alternatively, the position of the viewer or viewers in a vehicle may be located using suitable tracking i apparatus so that compensation for different viewing angles may be performed- automatically.

In applications where a single view is required to be visible in the multiple view viewing regions but not necessarily at normal incidence to the display, all of the sets of pixels may display the same image. This does not require any changes, for example to the voltages ranges used for the pixel sets. However, each viewer sees the same image with reduced spatial resolution as compared with embodiments in which all of the pixels are used to display the single image.

In order to be able to provide a full colour LCD, the effect of colour on the LC mode has to be taken into consideration when selecting the drive schemes for the first and second images. In a typical colour display, colour filters filter the light from respective sets of pixels. The colours may be red, green and blue or cyan, magenta and yellow.

Because of the dispersion of the liquid crystal layer 24, the optical properties of the liquid crystal mode used in the LCD vary with the wavelength of light. For example, Figure 20 illustrates the variation for the -30 and +30 viewing directions for red, green and blue pixels as intensity against grey level for the individual colours.

In order to produce a good colour dual view display, the effects of the dispersion of the liquid crystal mode on the grey scale curves may be overcome by performing careful mapping of grey levels individually for each of the colour components. Figure 21 illustrates the results of such a mapping procedure to allow the same grey level to be selected and displayed for each colour. Thus, the intensity of the image is the same for a given grey level irrespective oi which colour is displaying the image.

The colour mapping may be chosen in accordance with the application of the display.

For example, for some applications, it may be desirable to have a higher relative intensity of green light in either or both images relative to red and/or blue. The mapping may be selected in order to take account of such requirements.

Figure 22 illustrates an alternative dual view display for displaying colour images. The display of Figure 22 differs from that of Figure 4 in that colour filters 45 arc provided on the inner surface of the substrate 21 and the liquid crystal layer thickness 46 is different for different colour pixels.

The optical properties of the pixels are determined by the retardation of the liquid crystal layer 24 at the pixel. The retardation is the product of the birefringence and the thickness 46 of the liquid crystal layer 24. Thus, by varying the thickness of the layer 24 for the different colour pixels, each pixel can have its properties optimised or, at least, improved for the colour or range of colours which it is to display.

Alternatively, liquid crystal materials with different birefringence values may be used, for example separated by polymer walls as described hereinbefore. The retardation is matched to the wavelength of the respective colour pixel.

The display of Figure 22 has discrete stepped thicknesses for the pixels of different colours. In this particular example, this is achieved by forming polymer steps such as 47 on the TFT substrate 26, 27 with the alignment layer 25 being formed on top of the steps. Such steps may be formed on the other substrate beneath the alignment layer or on both substrates. The steps 47 may be formed by photolithographic processing of suitable resist materials. Alternatively, the steps 47 may be formed by screen printing of suitable polymer materials directly onto the or each substrate. In a further alternative, the colour filters 45 may have stepped thicknesses. In another example, the variation in liquid crystal layer thickness may be achieved using wedge-shaped structures of suitable gradient or similar structures without sharp edges so as to reduce the effects of any misalignment of the LC caused by the sharp edges of the steps.

Figure 23 illustrates another technique for compensating for the liquid crystal dispersion. In this display, a pixellated retarder 50 is provided. Each "pixel region" of the retarder provides an amount of retardation which substantially compensates for the dispersion effect of the liquid crystal of the associated pixel. In order to reduce parallax, the pixellated retarder 50 is disposed between the substrates 21 and 26, 27. In Figure 23, the retarder 15 is shown as being located on the TFT substrate 26, 27 but the i retarder could alternatively or additionally be located on the colour filter substrate 21.

Various techniques are available for making the pixellated retarder 50. Examples of such techniques are disclosed in van der Zande et al, Sid 03 Digest, "Technologies towards Patterned Optical Foils", pp 194-197. A specific example of a suitable technique is illustrated in Figure 24 and makes use of polymerisable liquid crystals such as reactive mesogens, an example of which is RMM 34 available from Merck UK.

A substrate 53 is prepared with an aligning surface such as an alignment layer 52 for aligning the optic axis of the reactive mesogen. The reactive mesogen is then coated on the alignment layer 52 by any suitable technique, such as spin coating. The reactive mesogen is of the type whose birefringence when unpolymerized varies with temperature and which is polymerised so as to fix the orientation of the optic axis upon exposure to light, such as ultraviolet light.

In order to form the regions of the retarder for a first colour, the layer 51 is exposed through a photomask 52 to ultraviolet radiation with the layer 51 being maintained at a suitable temperature for controlling its birefringence. The first regions are those which require the largest retardation and hence birefringence.

Following the first ultraviolet polymerization, the layer 51 is heated to a second temperature in order to provide the desired birefringence for second regions of the finished retarder. This is illustrated at 55 in Figure 24. The birefringence of the unpolymerised reactive mesogen is thus reduced to a desired value, after which the second regions for the next colour are exposed to ultraviolet radiation through a second photomask 56. The second regions are thus polymerized and their properties are fixed.

The temperature is then increased again as illustrated at 57 so as to reduce the birefringence of the remaining unpolymerized regions, which are polymerized by exposure to ultraviolet radiation through a third mask 58. The retarder is then effectively ready for use and may be removed from the substrate 53 and the alignment layer 52 for inclusion in a display device of the type shown in Figure 23. Alternatively, the retarder may be made directly on the TFT substrate as illustrated at 59 in Figure 24 with the alignment layer being formed on its upper surface, before being used with the upper substrate and its associated layers to form the liquid crystal cell.

It may also be possible to add suitable dyes to the polymerisable liquid crystal in order to form the colour filters for the display. In such cases, the retarder and colour filters can be made in a single layer so as to reduce the number of layers required in the display, which simplifies manufacture and reduces the number of alignment steps which are necessary.

The viewing angle characteristics of the polariser 20 and/or the polariser 28 may be chosen or optimised for non-normal incidence of light so as to improve performance and, in particular, image quality in the viewing regions of the display.

The voltages used for addressing the grey levels for the different views may be selected or optimised by techniques similar to gamma correction, which is well known in the technical field and which is described, for example, in "Frequently Asked Questions about Gamma" by Charles Poynton available at www.inforamp.net/poynton/. This may be done by first remapping the grey levels in the original image of each view to the grey levels which are visible from the viewing region for that view. The remapping may be to a single linear range or may be two or more ranges of intensity level.

Adjustments are then made in accordance with the appearance of the image from its viewing region so as to improve the appearance of the image. This may be performed by suitable gamma correction of the image data. This type of correction may not take the greyscales outside the existing greyscale range for that view. Any suitable gamma value may be used according to the effect which it is desired to achieve. For example a value of 2.2 may be used or a lower value of gamma correction may be used, such as 1.7. Applying gamma correction to images after they have been colour- corrected is unlikely to produce a good result. Gamma correction may therefore be applied to the colour correction curve or to the original image before colour correction.

Other image intensity adjustment techniques may be used, such as "histogram i equalization".

The grey level ranges of the pixels for the first and second viewing regions may be suitably chosen or optimised. For example, the grey level range may be chosen so as to give good image quality in the viewing region from which the image is to be viewed and to give the best grey level state when the pixel is viewed from the or each other viewing range.

The driving arrangement 29 is required to be capable of driving the pixels in accordance with the different drive schemes, such as voltage ranges as described hereinbefore, so that each pixel receives the appropriate voltages for the image which it is selected to display. In the case of displays which are also designed to allow a single view mode of operation, a further drive scheme, such as a further voltage range, may be used and the driving arrangement 29 must then also be capable of supplying the appropriate voltages to each pixel.

Although the embodiments described hereinbefore are based on TVAN, TN and Freedericksz liquid crystal modes, any liquid crystal mode which produces the appropriate asymmetric viewing angle may be used. For example, suitable smectic or ferroelectric liquid crystal modes may be used. Also, other twisted nematic modes may be used, such as the hybrid aligned nematic (HAN) mode or pi-cell mode. The TVAN mode is disclosed in EP 1103840 and has a substantially untwisted vertical structure with respect to the substrates below the threshold voltage for switching. Above this threshold voltage, this mode progressively switches to a more planar twisted structure, which is similar to that of the twisted nematic mode below its threshold voltage.

In the case of a multiple view display such as a dual view display as described hereinbefore, the images may be spatially multiplexed across the active area of the display device by allocating the appropriate sets of pixels to each image. For example, the images may be displayed as interlaced vertical strips or columns of pixels. In the case of video images, the field or frame rate is unchanged but the spatial resolution of each image is equal to the spatial resolution of the display device divided by the number of images which are being displayed, assuming that the pixels are substantially equally divided among the images.

Viewing angle compensation films are known and are disclosed, for example, in "Viewing angle compensators for liquid crystal displays based on layers with a positive birefringence" P.Van de Witte et al, Japan Journal of Applied Physics, vol. 39, pages 101-108, 2000. Such films are used to optimise the characteristics of the liquid crystal mode, for example the viewing angle characteristics and the black/white and grey level states. In known single view displays, such films are used to produce a viewing angle characteristic which is as uniform as possible with respect to vertical and horizontal directions and for optimising grey levels.

For the multiple view displays disclosed herein, the different requirements for greyscale viewing angle characteristics of the liquid crystal modes require different optimisations from the known arrangements and hence require different designs of viewing angle compensation films where such films are used. The requirements of such viewing angle compensation films are to optimise each image when viewed in its viewing direction and to make as black as possible the appearance of pixels displaying images for viewing in other directions.

More than one retarder layer may be used to improve the chromatic properties of the images. For example, two retarders may be used and each may be patterned or uniform.

Such retarders may be made from liquid crystal polymer or polymerisable liquid crystal, such as a reactive mesogen, and may be used inside the liquid crystal cell so as to reduce or eliminate parallax effects. Alternatively, a thin substrate may be used between a patterned retarder and the liquid crystal layer.

As an alternative, such a retarder may be external to the liquid crystal cell. As a further alternative, a uniform retarder may be laminated or fixed to the outside of the cell.

Patterned retarders may be made by any suitable technique and known examples of some techniques are disclosed in GB 2384318 and EP 0887692.

Another approach to prevent pixels from displaying an image in one viewing direction from appearing as white pixels in another viewing direction is the use of a parallax barrier 95 as illustrated in Figure 25. Such a barrier is arranged to restrict the viewing angles of the pixels such that substantially only those pixels intended to display an image to be visible in a viewing region are visible in that region, other pixels being obscured.

Parallax barriers may, for example, be made from an emulsion. However, conventional emulsions used for parallax barriers reduce the brightness of displays. An alternative may be to use a partially transmitting barrier for providing improved brightness and contrast. The parallax barrier may be made from a patterned retarder, for example as disclosed in British Patent Application No. 0215059.7. Where a switchable retarder is also used, the barrier may be switched off to provide a single view mode of operation with viewing at or near normal incidence.

The numbers of pixels used for the images of the different views do not have to be equal, although equal numbers are advantageous where the same spatial resolution is required for each image. Also, the distribution of pixels allocated for displaying the different views need not be uniform or alternating across the display device. For example, it may be desirable to provide a high resolution region for one of the views to display text with a small font size. Thus, an increased number of pixels at that regions

Claims

CLAIMS: 1. A multiple view display comprising: a liquid crystal device

comprising first pixels, which have a first configuration with first asymmetric viewing angle properties, and second pixels, which have a second configuration different from the first configuration with second asymmetric viewing properties oriented differently from the first asymmetric viewing properties; and a driving arrangement for driving the first pixels for displaying a first image in a first viewing direction and for driving the second pixels for displaying a second image in a second viewing direction different from the first direction.
2. A multiple view display as claimed in claim 1, in which the first and second images are viewable in a third viewing direction between the first and second directions.
3. A multiple view display comprising: a liquid crystal device comprising first pixels, which have a first configuration with first asymmetric viewing angle properties, and second pixels, which have a second configuration different from the first configuration; and a driving arrangement for driving the first pixels for displaying a first image in first and second viewing directions and for driving the second pixels for displaying a second image in the second viewing direction.
4. A display as claimed in any one of the preceding claims, in which the first pixels are spatially interspersed with the second pixels.
5. A display as claimed in any one of the preceding claims, in which the first and second images are unrelated to each other.
6. A display as claimed in any one of the preceding claims, in which the first and second directions are in a plane which is orthogonal to a display surface of the device and contains directions of maximum viewing angle asymmetry of the first and second properties.
7. A display as claimed in claim 6, in which the first and second directions are on opposite sides of a normal to the display surface.
8. A display as claimed in claim 7, in which the first and second directions are asymmetric about the normal.
9. A display as claimed in any one of the preceding claims, in which the angle between the first and second directions is greater than substantially 10 .
10. A display as claimed in claim 1 or 2 or in any one of claims 4 to 9 when- dependent on claim 1 or 2, in which the first pixels are arranged to provide a first contrast ratio greater than one in the first direction and a contrast ratio substantially equal to one in the second direction and the second pixels are arranged to provide a second contrast ratio greater than one in the second direction and a contrast ratio substantially equal to one in the first direction.
11. A display as claimed in claim 10, in which the first and second pixels are arranged to appear substantially black in the second and first directions, respectively.
12. A display as claimed in claim 1 or 2 or in any of the claims 4 to 11 when dependent on claim l or 2, in which the first and second asymmetric viewing properties are oriented in substantially opposite directions.
13. A display as claimed in any one of the preceding claims, in which the device comprises sets of pixels with the pixels of each set being the same colour and being of a different colour from the pixels of the other sets.
14. A display as claimed in claim 13 in which the device comprises a liquid crystal layer having different thicknesses at the pixels of different colours.
15. A display as claimed in claim 13 or 14, in which the device comprises a patterned retarder with regions of different retardations being optically aligned with the pixels of different colours.
16. A display as claimed in claim lS, in which the regions of different retardations contain dyes of the different colours for acting as colour filters.
17. A display as claimed in any one of the preceding claims, in which the first and second pixels have first and second liquid crystal modes, respectively, which are different from each other.
18. A display as claimed in claim 17, in which at least one of the first and second modes is one of twisted nematic, hybrid aligned nematic, twisted vertically aligned nematic, Freedericksz, vertically aligned nematic and pi-cell.
19. A display as claimed in claim 17 or 18, in which the first and second pixels have different liquid crystal director twists in the absence of an applied field.
20. A display as claimed in claim 19, in which the different twists have different magnitudes.
21. A display as claimed in claim 19 or 20, in which the different twists have different twist senses.
22. A display as claimed in any one of claims 19 to 21, in which one of the different twists is 0 .
23. A display as claimed in any one of claims 17 to 22, in which the first and second pixels have different liquid crystal director pretilts at at least one liquid crystal substrate interface.
24. A display as claimed in claim 23, in which the different pretilts have different magnitudes.
25. A display as claimed in claim 23 or 24, in which the different pretilts have different directions.
26. A display as claimed in any one of claims 17 to 25, in which the first and second pixels have different bulk liquid crystal director orientations.
27. A display as claimed in any one of claims 17 to 26, in which the first and second pixels have different surface anchoring strengths at at least one liquid crystal substrate interface.
28. A display as claimed in any one of claims 17 to 27, in which the first and second pixels have different liquid crystal materials.
29. A display as claimed in any one of claims 17 to 28, in which at least one of the first and second pixels has a liquid crystal material containing at least one of a chiral dopant, a polymer network and a dye.
30. A display as claimed in any one of claims 17 to 29, in which the first and second pixels have liquid crystal layers of different thicknesses.
31. A display as claimed in any one of the preceding claims, in which the first pixels have first polarisers whose transmission axes are oriented at a first angle with respect to liquid crystal optic axes of the first pixels and the second pixels have second polarisers whose transmission axes are oriented at a second angle different from the first angle with respect to liquid crystal optic axes of the second pixels.
32. A display as claimed in any one of the preceding claims, in which the first and second pixels have first and second retarders of different retardations.
33. A display as claimed in any one of the preceding claims, in which the first and second pixels have first and second compensation layers providing different compensation effects.
34. A display as claimed in any one of the preceding claims, in which the driving arrangement is arranged to drive the first and second pixels with different voltage ranges.
35. A display as claimed in any one of the preceding claims, in which the device comprises a parallax barrier.
36. A display as claimed in any one of the preceding claims, in which the device comprises a transmission mode device.
37. A display as claimed in any one of the preceding claims, comprising a further liquid crystal device arranged to be viewable through and to operate time-sequentially with the first-mentioned device.