GB2414848A

GB2414848A - A driving method for a multiple view directional display

Info

Publication number: GB2414848A
Application number: GB0412209A
Authority: GB
Inventors: Harry G Walton
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2004-06-02
Filing date: 2004-06-02
Publication date: 2005-12-07
Also published as: JP2005346077A; GB0412209D0; JP4610415B2

Abstract

A method of driving a multiple view directional display comprises supplying image data such that the image data for a pixel identify an intended viewing direction of that pixel. The image data for a pixel contain information that identifies an intended viewing direction of that pixel, for example by identifying the intended observer. In a one example, image data for a pixel include a brightness identification field (37) and an observer identification field (39). The invention makes it straightforward for pixels of a display to be reassigned from one image to another, since this can be done just by changing the input image data. It is not necessary to pre-set the driving circuitry to operate in a particular way, since the driving circuitry can identify, from the input image data for a pixel, to which image that pixel relates.

Description

1 241 4848 A Driving Method for a Multiple View Directional Display The

present invention relates to a method of driving a multiple-view directional display. A multiple-view directional display is able to display 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 as, for example, an autostereoscopic display device or a dual view display device.

For many years conventional display devices have been designed to be viewed by multiple users simultaneously. The display properties of the display device 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 display devices, 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 if the driver moved his or her head, which would be distracting for the driver.

As a further example, each player in a computer game for two or more players 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 costly, 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 advantage of a multiple-view directional display is the ability to preclude the users from seeing each other's views. This is desirable in applications requiring security such as banking or sales transactions, for example using an automatic teller machine (ATM), as well as in the above example of computer games.

A further application of a multiple view directional display is in producing a three- dimensional display. 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 display a three dimensional image, it is necessary to recreate 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 view 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.

The operation of a dual-view display will be explained with reference to figure 1.

Figure 1 is a schematic plan view of a dual view display 1, comprising a multiplicity of columns of display pixels 2 (the pixel columns extend into the plane of figure 1).

The pixels 2 shown in figure 2 are denoted by either a or b for reasons that are explained below.

Figure 1 shows a first observer 3 and a second observer 5. The observers 3,5 are spaced from the front face of the display 1, and are laterally separated from one another. The first observer 3 is positioned on one side of the normal to the front face of the display 1, and the second observer 5 is positioned on the other side of the normal to the front face of the display 1. Owing to the relative spatial locations of the display and the observers 3, 5, the first observer 3 views the display 1 at a first viewing angle 01 along a first approximate line of sight indicated by 7 in figure 1.

The second observer 5 views the display 1 at a second viewing angle 02, along a second approximate line of sight indicated by 9 in figure 1. The first and second lines of sight 7,9 are on opposite sides of the normal to the front face of the display 1.

The dual view display 1 is so constructed as to have an optical performance that varies according to viewing angle. When the display is viewed by the first observer 3 along the first line of sight 7, the first observer is caused to see a first image 11.

Similarly, when the display is viewed by the second observer 5 along the second line of sight 9, the second observer is caused to see a second image 13. The first and second images are controllable independently from one another. 1 1

A method of achieving the display of two independent images along the lines of sight 7,9 will now be described with reference to figure 2.

Figure 2 shows an example of brightness vs. applied voltage characteristic curves of a pixel of a liquid crystal display. Liquid crystal displays are well known to exhibit a variation of brightness with viewing angle, and figure 2 shows a first brightness vs. voltage characteristic 15 that arises when a pixel is viewed at angle 81 to the normal of the pixel. In accordance with the first brightness vs. voltage characteristic IS, application of a voltage of level V1 results in the pixel displaying approximately full brightness as viewed at angle 01, and application of voltage of level V2 results in the pixel displaying approximately minimal brightness as viewed at angle 01. (For brevity, the term 'voltage of level V1" will henceforth generally be shortened to "voltage V1", and so on.) Application to the pixel of a voltage having a level that is intermediate between voltage V1 and voltage V2 results in the pixel, as viewed at angle 81, displaying a brightness that is intermediate between the full brightness obtained by application of voltage V1 and the minimal brightness obtained by application of voltage V2. The characteristic 15 is shown for simplicity with a linear relationship between brightness and applied voltage for voltages between V1 and V2, but in practice many liquid crystal materials have a brightness vs. applied voltage characteristic that provides a non-linear variation in brightness with applied voltage.

Figure 2 further shows a second brightness vs. applied voltage characteristic 17 that is obtained when the same pixel is viewed at an angle 82 which is on the opposite side of the normal to the pixel from 01. In accordance with the second brightness vs. voltage characteristic 17, application of a voltage V3 results in the pixel displaying approximately full brightness when viewed at angle 02, and application of a voltage V4 results in the pixel displaying approximately minimal brightness when viewed at angle 02. Application to the pixel of a voltage having a level that is intermediate between voltage V3 and voltage V4 results in the pixel, as viewed at angle 02, displaying a brightness that is intermediate between the minimal brightness obtained by application of voltage V3 and the full brightness obtained by application of voltage V4. In this example, the voltages are ordered V4 > V3 > V2 > V 1. l

With reference to figure 2, one method of driving the display 1 of figure 1 as a dual view display can now be understood. All pixels of the display in pixels denoted by a are supplied with individual voltages that are in the range from V1 to V2. When viewed by the first observer 3 at a viewing angle 01, each of the pixels a will, in accordance with the first brightness vs. applied voltage characteristic 15 of Figure 2, therefore be observed by the first observer to display individual brightness levels lying in the range between full brightness and minimal brightness, with the precise brightness of an individual pixel as viewed by the first observer depending on the precise voltage (in the range V1 to V2) applied to the pixel. As far as the second observer 5 is concemed, however, application of voltages in the range V1 to V2 to pixels a will cause these pixels to appear at minimal brightness level to the second observer 5. This is because the brightness of the pixels as seen by the second observer 5 is detemmined by the second brightness vs. applied voltage characteristic 17 of Figure 2 - and application of a voltage in the range from V1 to V2 produces a minimal brightness level in the second brightness vs. applied voltage characteristic 17.

Conversely, however, all pixels denoted by b in the display 1 of figure 1 are supplied with individual voltages in a range V3 to V4. When the display is viewed by the second observer 5 at the viewing angle 02, each of the pixels in pixel columns b will, in accordance with the second brightness vs. applied voltage characteristic 17 of Figure 2, be observed by the second observer 5 to have individual brightness levels lying in the range between full brightness and minimal brightness with the precise brightness of an individual pixel as observed by the second observer 5 depending on the precise voltage (in the range V3 to V4) applied to the pixel. The first observer 3 will, however, observe all pixels b at the minimal brightness level. This is because the brightness of the pixels as seen by the first observer 3 is determined by the first brightness vs. applied voltage characteristic 15 of Figure 2 - and application of a voltage in the range from V3 to V4 produces the minimal brightness level in the first brightness vs. applied voltage characteristic 15. Thus, the pixels a and the pixels b do not differ in their construction, and the two directional images are obtained by driving the pixels either in the voltage range V1 to V2 or in the voltage range V3 to V4. l

In summary therefore, application of voltages in the range from Vl to V2 to pixels a will allow any desired image to be displayed to the first observer 3 on these pixels.

The second observer 5 will observe a uniformly dark background arising from pixels a. Simultaneously, however, application of voltages in range V3 to V4 to pixels b will allow any desired image to be displayed for the second observer 5 on pixels b, whilst the first observer 3 merely observes a uniformly dark background arising from pixels b. Thus, two independent images may be displayed simultaneously on display 1, with the image being interlaced on the image display layer (for example, the first and second images may be displayed on odd-numbered and even-numbered pixel columns respectively. The images may be still images or they may be video images.

An autostereoscopic display is similar in principle to the dual view display described above. However, the two images displayed on an autostereoscopic display are not independent images but are the left-eye and right-eye images of a stereoscopic image pair, and the two images are not displayed to different observers but are displayed to the left eye and right eye of an observer.

In order to drive a multiple view display of the type described in figures 1 and 2, the input data is arranged in a predetermined order to ensure that a pixel that is intended to form part of an image for viewing by the first observer 3 is addressed with a voltage in the range from V1 to V2 and that a pixel that is intended to form part of an image for viewing by the second observer 5 is addressed with a voltage in the range from V3 to V4. For example the input data may be arranged so that every odd- numbered input bit relates to a pixel for viewing by the first observer 3 and every even-numbered input bit relates to a pixel for viewing by the second observer 5. The driving circuitry of the display would be designed to operate on the basis that an odd- numbered pixel related to the first observer and so would convert a brightness level specified for an odd-numbered pixel into the corresponding voltage in the range from V1 to V2. Similarly, the driving circuitry would assume that an even-numbered pixel related to the second observer and so would convert a brightness level specified for an even- numbered pixel into the corresponding voltage in the range from V3 to V4.

Other types of multiple view directional display are known that contain a parallax optic (such as a parallax barrier or a lens array) to provide angular separation between two displayed images. In these displays two image are displayed simultaneously, usually interlaced between adjacent columns of pixels, and the parallax optic ensures that one image is displayed only in one direction and the other image is displayed only in a different direction. It is known to provide such displays with two separate analogue inputs, one input for each image.

The present invention provides a method of driving a multiple view directional display comprising the step of supplying, to the display, image data for a selected pixel of the display; wherein the image data for the pixel identify an intended viewing direction of the selected pixel.

A prior art multiple view directional display has a fixed configuration, in that the pixels of the display are assigned to either a first image or to a second image and the driving circuit is designed accordingly. However, it is sometimes desired to alter the configuration of a multiple view directional display by altering the assignment of the pixels to the two images. For example this might be done to alter the relative extents of the two images, as described in co-pending UK patent application No. 0320365.0.

It might be thought that this could be done simply by changing the input data.

However, altering the pixel-to-image assignment of a conventional multiple view display would also require that the driving circuit is redesigned since, to use the example given above, it would no longer be the case that all odd-numbered-bits related to an image for viewing by the first observer (and needed a driving voltage in the range V1 to V2) and that all even-numbered-bits related to an image for viewing by the second observer (and so needed a driving voltage in the range V3 to V4).

In the present invention, the input image data for a pixel identifies the intended viewing direction of the pixel. It is therefore not necessary to pre-set the driving circuitry to operate in a particular way (such as treating all odd-numbered pixel as relating to one image and treating all even-numbered pixels as relating to a second image). The driving circuitry can identify, from the input image data for a pixel, whether that pixel relates to a first image 11 or a second image 13 and can select a voltage in the range V1 to V2 or a voltage in the range V3 to V4, as appropriate, for each pixel. It is therefore straightforward to re- configure the display, since this can be done just by changing the input image data. There is no need to redesign the driving circuit.

The image data for the selected pixel of the display may contain information for identifying an intended viewing direction of the selected pixel. For example, the image data for a selected pixel may contain observer information that identifies the intended viewing direction of the selected pixel by identifying the observer to whom the pixel is intended to be displayed.

The method may further comprise applying a voltage to the selected pixel of the display on the basis of the image data for the selected pixel.

The image data may be digital data.

The method may comprise supplying, as image data, a sequence of data words, each data word relating to a respective pixel of the display.

Each data word may contain information for identifying an intended viewing direction of the respective pixel. For example, each data word may contain observer information that identifies the intended viewing direction of the respective pixel by specifying the observer to whom the pixel is intended to be displayed.

Each data word may comprise brightness information for identifying a desired brightness of the respective pixel.

The method may comprise the step of applying digital-to-analogue conversion to the display data to derive a voltage to be applied to the pixel or the respective pixel.

The digital-to-analogue conversion may comprise determining a range for a voltage to be applied to the pixel or the respective pixel on the basis of the observer information for the pixel or the respective pixel. It may further comprise selecting a voltage within the determined voltage range on the basis of the brightness information.

The information for identifying an intended viewing direction of a pixel may be observer information for identifying an intended observer of the pixel.

Preferred embodiments of the present invention will now be described by way of illustrative example with reference to the accompanying figures in which: Figure 1 is a schematic plan view of a conventional dual view display; Figure 2 is a schematic illustration of typical brightness versus applied voltage characteristic curves for the dual view display of figure 1; Figure 3 is a schematic illustration of a driving method of the invention; Figure 4 is a schematic illustration of driving voltages applied by a driving method of the invention; Figures 5 and 6 are further schematic illustrations of a driving method of the invention; and Figures 7, 8 and 9 illustrate driving circuits suitable for effecting a driving method of the present invention.

Preferred embodiments of the invention will be described with reference to driving a dual view display to display a first image to a first observer and a second image to a second observer. The invention is not however limited to this specific application.

Figure 3 illustrates an embodiment of the driving method of this invention. Figure 3 shows a dual view display 21 which has an image display layer 23. A plurality of pixel regions 25 are defined in the image display layer 23, and these pixels 25 are arranged in a matrix. A plurality of row electrodes 27 and a plurality of pixel electrodes 29 are provided, and each pixel region 25 is at the intersection of a respective row electrode 27 and a respective column electrode 29. The analogue voltages applied to row electrodes 27 are controlled by a row driver circuit 31. The analogue voltages applied to the column electrodes 29 are controlled by display driver circuit 33.

In this example the image display layer is a liquid crystal layer. The liquid crystal layer is typically incorporated in a liquid crystal panel, and any suitable liquid crystal panel may be used. Other components of the liquid crystal panel such as transparent substrate and polarising plates are not shown. The liquid crystal layer 23 may, for example, be of the super-twisted nematic type or may be of the active matrix twisted nematic type. The concept of matrix addressed liquid crystal displays is well known and it will be understood that the application of appropriate analogue voltage waveforms to row and column electrodes allows control of the voltages applied to individual pixels. For example, the liquid crystal layer may be actively addressed via pixel electrodes (not shown) disposed on one side of the liquid crystal layer and a common electrode disposed on the opposite side of the liquid crystal layer, and in this case the row electrodes control switching elements (not shown) to selectively connect a pixel electrode to, or isolate it from, the respective column electrode.

Image data are supplied to the dual view display along a bus line 35. In this embodiment the bus line 35 is a digital data bus line and the dual view display 21 receives digital image data 43. The data bus line 35 may be serial or parallel in nature. The digital image data 43 are input to the display driver circuit 33 via the bus line 35. The display driver circuit 33 has the function of performing digital-to- analogue conversion of the digital image data 43. The analogue voltages resulting from the digital-to-analogue conversion process will typically be supplied to pixels 25 in sequential fashion. For example, a first analogue voltage arising from digital-to- analogue conversion by the display driver 33 of a first data word 41 of the input image data 43 may be applied to a first pixel of the display, a second analogue voltage arising from digital-to-analogue conversion by the display driver 33 of a second data word 37 of the input image data 43 may be applied to a second pixel of the display, and so on. In this manner, all pixels 25 of the display 21 are addressed so as to form images on the display. This process is then periodically repeated so as to refresh or change the displayed images. Again, such a driving technique is well-known.

According to the invention, the image data for a pixel supplied to the display identify an intended viewing direction of the pixel, and this is conveniently done by including information identifying an intended viewing direction of a pixel in the image data for that pixel. For example, the image data for a pixel may specify the observer to whom the pixel is intended to be displayed and thereby identify the intended viewing direction of the pixel.

In the preferred method illustrated in figure 3 the digital image data 43 comprise a sequence of distinct image data words 41. In accordance with this invention, an individual data word 41 comprises information about the intended viewing direction of the pixel to which that word relates. In the preferred embodiment of figure 3, an individual data word 41 comprises information about the intended observer of the pixel to which that word relates so that a data word 41 for a pixel comprises information about the desired brightness of the pixel (in brightness data field 37) and information about the intended viewing direction of the pixel (in observer

identification field 39).

The combined action of the observer identification field 39 and the brightness data field 37 will now be explained by reference to figure 4, using an example where the observer identification field 39 is a 1-bit field and the brightness identification field is a 2-bit field. Thus in this example there are two possible values for the observer identification field (binary logic value "O" or binary logic value "1") so that the observer field may denote either of two observers (such as the first and second observers 3,5 of figure 1). The brightness identification field can denote four brightness levels, as "00", "01", "10" and "11" (where "00" denotes binary logic value "O" followed by binary logic value "O", and so on) and it will be assumed that these are the minimum brightness level, two intermediate brightness levels and the maximum brightness level.

The horizontal axis of figure 4 shows the eight possible digital data words comprising a 1-bit observer identification field 39 and a 2-bit brightness identification field 37.

The vertical axis of figure 4 shows the analogue voltage level arising from digital-to- analogue conversion of the eight possible digital data words.

Referring again to the explanation of dual view operation given with reference to figures 1 and 2, the purpose of observer identification field 39 in an input data word can now be understood. It will be assumed that a value of"O" in the observer identification field 39 denotes the first observer 3 in figure 1 and that a value of"1" in the observer identification field denotes the second observer S in figure 1. In the case that the observer identification field 39 in an input data word has a value '0', therefore, the display driver 33 causes a voltage in the range V1 to V2 to be applied to the corresponding pixel 25 of the dual view display 21. The voltage level within the range from V1 to V2 is determined by the brightness identification field 37. If the brightness data field in the data word 41 has some e-bit digital value, the first observer 3 will then observe the pixel as having one amongst 2n possible brightness levels. The second observer 5 will, however, observe said pixel as being in a minimal brightness state, regardless of the value of the brightness identification field 37.

Conversely, in the case that observer identification field 39 of an input data word has a value '1', the display driver circuit 33 causes a voltage in the range V3 to V4 to be applied to the corresponding pixel 25 of dual view display device 21. The voltage level within the range from V3 to V4 is determined by the brightness identification field 37 of the data word. The second observer 5 will now observe the pixel as having one of 2n possible brightness levels, as determined by the brightness identification field. The first observer 3 will observe the pixel as being in a minimal brightness state, regardless of the value of the brightness identification field 37. That is, selection of the voltage to be applied to a pixel may be thought of as a two-stage process. A voltage range is chosen on the basis of information about the intended observer for the pixel (in this example on the basis of the observer identification field). Then, a voltage within the chosen voltage range is selected on the basis of brightness information for the pixel (in this example on the basis of the brightness identification field). (It should be noted that the reference to a two-stage process is for illustration only, and that determination of the driving voltage need not involve two identifiably distinct steps.) Thus, as an example, the digital-to- analogue conversion of data word '001' results in analogue voltage V5 where V1 < V5 < V2. The first logic value "O" is the observer identification field and identifies that the pixel is intended for display to the first observer, and so the voltage range V1 to V2 is selected. The brightness identification field 37 has the value "01", and identifies an intermediate brightness level. Similarly, digital-to- analogue conversion of data word '101' results in analogue voltage V6 where V3 < V6 < V4. The first logic value "1" is the observer identification field and identifies that the pixel is intended for display to the second observer 5, and so the voltage range V3 to V4 is selected.The brightness identification field 37 has the value "01", and again identifies an intermediate brightness level.

Figure 4 shows the analogue voltage levels corresponding to all eight possible digital data words comprising a 1-bit observer identification field 39 and a 2-bit brightness identification field 37. It will be clear that in all instances when the observer identification field 39 has the digital value '0', the resultant analogue voltage has a value in the range V1 to V2. Equally, in all instances when the observer identification field 39 has the digital value '1', the resultant analogue voltage has a value in the range V3 to V4.

The present invention thus provides a simple way of ensuring that each pixel of the display 21 is supplied with a voltage in the correct voltage range so that the image displayed on that pixel is visible in the intended viewing direction. Since a data word 41 identifies the intended viewing direction of the pixel to which that word relates, the display driver circuit 33 is able to select the appropriate voltage range - V1 to V2 or V3 to V4 - according to the intended viewing direction. It is not necessary to pre- design the display driver circuit to, for example, select the voltage range V1 to V2 for odd-numbered data words and select the voltage range V3 to V4 for even-numbered data words.

Figures 5 and 6 illustrate an advantage of the invention. Figure 5 shows the images 11,13 displayed on a dual view display 76 comprising four pixels 70,71,72, 73. The dual view display receives input image digital data 43, comprising a sequence of four 3-bit image data words 70a-73a. The 1st bit of each data word constitutes the observer identification field and the 2n and 3 bit constitutes the brightness data field. The first image data word 70a corresponds to the first pixel 70, the second image data word 71 a corresponds to the second pixel 71, etc. The display driver circuit (not shown in figure 5) performs digital-to-analogue conversion of the first data word 70a ("001") and applies an analogue voltage to the first pixel 70. The display driver circuit next performs digital-to-analogue conversion of second data word 71a ("110") and applies a resulting analogue voltage to the second pixel 71. This procedure is similarly repeated for the third data word 72a ("101") and pixel 72, and for the fourth data word 73a ("010") and the fourth pixel 73.

The image 11 is the image observed by a first observer (for example the first observer 3 of figure 1) of dual view display 76. The image 13 is the image observed by a second observer (for example the second observer 5 of figure 1) of dual view display 76.

The nature of images 11 and 13 in figure 5 can be understood as follows. Since the first data word 70a ("001") has an observer identification field with the bit value '0', an analogue voltage in the range V1 to V2 is accordingly applied to pixel 70 as a result of the digital-to-analogue conversion performed on the first data word 70a by the display driver circuit of the dual view display 76. The exact voltage level within the range is determined by the brightness identification field of the first data word 70a. Thus, the first observer sees the first pixel 70 as having a brightness level appropriate to the data ('01') present in the brightness identification field of the first data word 70a (as indicated by shading of the first pixel 70 in image 11 of figure 5).

Since the voltage applied to the first pixel 70 is in the range V1 to V2, the second observer however observes the first pixel 70 as having the minimal brightness level (as indicated by full shading of the first pixel 70 in image 13 of figure 5), regardless of the status of the brightness identification field.

Similarly, since the second data word 71a ("110"), has an observer identification field of "1", an analogue voltage in the range V3 to V4 is accordingly applied to the second pixel 71 as a result of the digital-toanalogue conversion performed on data word 71 a by the display driver circuit of the dual view display 76. The exact voltage level within the range is determined by the brightness identification field of the second data word 71a. Thus, the second observer sees the second pixel 71 as having a brightness level appropriate to the data ("10") present in the brightness identification field of the second data word 71a (as indicated by shading of the second pixel 71 in image 13 of figure 5). Since the voltage applied to the second pixel 71 is in the range V3 to V4, the first observer however observes the first pixel 71 as having the minimal brightness level (as indicated by full shading of the second pixel 71 in image 11 of figure 5), regardless of the status of the brightness identification field.

It will be understood from above description that the first observer will observe an image (11) generated by all those pixels 70,73 for which the observer identification field in the corresponding data word 70a,73a has the value "0". All pixels 71,72 for which the observer identification field in the corresponding data word 71a,71a has value "1", have minimal brightness for the first observer, and form essentially a featureless dark background. It is therefore possible to define the first and fourth pixels 70, 73 of image 11 as comprising a f tat intended image since the relative brightness level of these pixels is visible to the first observer. It is also possible to define the second and third pixels 71, 72 of image 11 as comprising a first background, since these pixels appear uniformly of minimal brightness to the first observer.

Similarly it is possible to define the second and third pixels 71, 72 of image 13 as forming a second intended image, since the relative brightness level of these pixels is visible to the second observer. It is also possible to define the first and fourth pixels 70, 73 of image 13 as comprising a second background, since these pixels appear uniformly of minimal brightness to the second observer.

In the example of figure 5, an equal number of pixels (2 in each case) are used to form the intended image for each observer. As explained above, however, the invention makes it straightforward to re-configure the display areas allotted to the two images.

This can be seen in figure 6.

Figure 6 again shows a dual view display having four pixels 83-86 arranged in a 2x2 matrix. The image 11 shows the display as it would be seen by one observer (such as the first observer 3 of figure 1) and the image 13 shows the display as it would be seen by another observer (such as the second observer 5 of figure 1). In figure 6 the first, second and third pixels 83,84,85 form a first intended image, and only the fourth pixel 86 forms a second intended image. The data word 83a, 84a, 85a corresponding to the first, second and third pixels 83,84,85 each have a "O" in their observer identification field, and only the data word 86a corresponding to the fourth pixel 86 has a "1" in its observer identification field. Thus, the first image is generated by three pixels 83-85, and only one pixel 86 forms a dark background in the first image.

Conversely, the second image is generated by only one pixel 86 and three pixels 83-

form a dark background in the second image.

It is a feature of this invention that first observer and second observer need not view intended images of equal pixel number.

This invention is not limited to use with a display having an image display layer that has brightness vs. applied voltage characteristic curves of the form of figure 2. For example the first background and/or the second background defined above need not be comprised of pixels in a minimal brightness state, but may be comprised of pixels in some other brightness state, depending on the precise form of the brightness vs applied voltage characteristics of the liquid crystal layer. The characteristic curve 17 is preferably substantially flat for voltages between V1 and V2, and the characteristic curve 15 is preferably substantially flat for voltages between V3 and V4, so as to provide a constant brightness background for both viewing directions.

This invention is not limited to only two observers, and may be applied to a multiple view display with more than two intended observers. In the case of a multiple view display designed to generate 4 intended images for 4 observers, for example, an observer identification field of at least 2 bits is required. (A dual view display that can display three (or more) images to three (or more) different observers can be obtained by using a material with a more intricately varying brightness/voltage characteristic than that shown in the two-observer example of figure 2 - a material that undergoes more than a single high-to-low brightness transition as the applied voltage is varied (as observed from at least one viewing angle) is required in the case of more than two observers.) This invention is not limited by precise nature or architecture of circuits, such as display driver 33. The display driver circuits may, for example be integrated circuits formed on a silicon wafer (i.e. silicon chips) for possible bonding to a display substrate. Alternatively all or part of display driver circuits may be formed directly on a display substrate using, for example, polysilicon or continuous grain silicon.

Examples of display driver circuits suitable for carrying out digital-toanalogue conversion of digital image data that includes a brightness data field and an observer identification field, in accordance with the driving method of this invention, will now be described.

Figure 7 shows a digital-to-analogue conversion circuit 100 designed to supply voltage to a pixel 113 (represented as a capacitance) via a unitygain buffer amplifier 111. The digital-to-analogue converter comprises a resistor string 103 of resistors 103a-103e arranged in series. The action of digital-to-analogue converters incorporating a resistor string is well known, though not in conjunction with the observer identification field technique of this invention.

The resistor string 103 is connected to the input of buffer amplifier 111 via switches 105,106,107,108. One end of each of these switches is connected to the junction between two adjacent resistors of the resistor string - one terminal of the switch 105 is connected to the junction of the first resistor 103a and the second resistor 103b of the resistor string, for example - and the second terminal of each of the switches 105108 is connected to the input of the buffer amplifier 111.

The digital-to-analogue conversion circuit 100 receives digital brightness identification field data ('BIF)' on a brightness data bus 115. The status (i.e. open or closed) of the switches 105,106,107,108 connected between the resistor string 103 and the input to the buffer amplifier 111 is set according to digital data present in brightness identification field, by a digital logic circuit (not shown) acting on the

brightness identification field data.

One end of the resistor string 103 is connectable to either a voltage source V1 via a first switch 117 or to a voltage source V3 by a second switch 123. The other end of the resistor string 103 is connectable either to a voltage source V4 via a third switch 121 or to a voltage source V2 by a fourth switch 119.

The digital-to-analogue conversion circuit 100 receives observer identification field (OIF) digital data on a bit-line 130. The input from the bit line 130 is used to control the second and third switches 123,121 that connect the ends of the resistor string 103 to the voltage sources V3 and V4. The input from the bit line 130 is also used, after passing through an inverter 118, to control the first and fourth switches 117,119 that connect the ends of the resistor string 103 to the voltage sources V1 and V2. In the event that OIF has logic value '0' the output from the inverter 118 is logic value "1" and the first and fourth switches 117 and 119 are closed but the second and third switches 123,121 are open. As a result, the resistor string 103 is connected or pinned' between voltage V1 and voltage V2. Consequently, the analogue voltage applied to the pixel 113 is then constrained to lie in the range V1 to V2 (with the precise value of the applied analogue voltage dictated by the status of the switches 105-108 connected between the resistor string 103 and the unity-gain buffer amplifier 111).

Similarly, in the event that OIF has logic value '1' the first and fourth switches 117, 119 are open (since the output from the inverter 118 is logic value "0") whereas the second and third switches 123,121 are closed. Thus, the analogue voltage applied to the pixel 113 is then constrained to lie in the range V3 to V4 (again with the precise value of the applied analogue voltage dictated by the status of the switches 105-108 connected between the resistor string 103 and the unity-gain buffer amplifier 111).

It will be clear from the above explanation that the digital-to analogue conversion circuit 100 performs the function of restricting the voltage applied to the pixel 113 to a chosen range (either the range V1 to V2 or the range V3 to V4), on the basis of digital data contained in the observer identification field. Multiple pixels may be addressed in similar manner to that shown in figure 7 by, for example, multiplexing the output of digital-to-analogue conversion circuit 100 using a shift register multiplex circuit (not shown).

Figure 8 shows another digital-to-analogue conversion circuit 140 that can be used to implement the method of the invention. The digital-to- analogue conversion circuit is again designed to supply an analogue voltage to a pixel 146 (again represented as a capacitance) via a unity gain buffer amplifier 145. The digital-to-analogue conversion circuit 140 operates on the same general principle as the conversion circuit of figure 7, but it comprises two resistor strings 142,144.

One end of the first resistor string 142 is connected to a voltage source V2 by a first switch 160, and the other end of the first resistor string 142 is connected to a voltage source V1 by a second switch 161. The first resistor string 142 is connected to the input of the buffer amplifier 145 via switches 150, 151, 152, 153 each connected at one end to the junction between two adjacent resistors of the resistor string, and by a third switch 165 arranged in series with the switches 150, 151, 152, 153. One end of the second resistor string 144 is connected to a voltage source V3 by a fourth switch 163, and the other end of the second resistor string 144 is connected to a voltage source V4 by a fifth switch 164. The second resistor string 144 is connected to the input of the buffer amplifier 145 via switches 154, 155, 156, 157 each connected at one end to the junction between two adjacent resistors of the second resistor string 144, and by a sixth switch 165 arranged in series with the switches 150, 151, 152, 153.

The digital-to-analogue conversion circuit 140 receives digital brightness identification field data ('BIF)' on a brightness data bus 148. The status (i.e. open or closed) of the switches 150-153 connected between the first resistor string 142 and the input to the buffer amplifier 145, and the status of the switches 154-157 connected between the second resistor string 144 and the input to the buffer amplifier 145, are set according to digital data present in the brightness identification field, by a digital logic circuit (not shown) acting on the brightness identification field data.

The digital-to-analogue conversion circuit 140 also receives input digital observer identification field (OIF) data along an OIF bus line 149. The OIF bus line 149 controls, via an inverter 158, the first, second and third switches 160,161,165 of the first resistor string 142, and also controls the fourth, fifth and six switches 163,164,166 of the second resistor string 144.

By comparison with figure 7, operation of the conversion circuit of figure 8 will be clearly understood. In the event that the OIF data has value logic value 'O' the output from the inverter 158 is logic value "1", and the first, second and third switches 160,161 and 165 are closed. The first resistor string 142 is then pinned between voltages V1 and V2, and an analogue voltage in the range from V1 to V2 is accordingly applied to pixel 146 via the third switch 165 (with the precise value of the applied analogue voltage dictated by the status of the switches 150-153 connected between the first resistor string 142 and the third switch 165). At the same time the fourth, fifth and six switches 163,164,166 are open, so that the second resistor string 144 is isolated from the voltages sources V3,V4 and from the input to the buffer amplifier 145.

Similarly, in the event that the OIF data has logic value '1', the fourth, fifth and sixth switches 163,164 and 166 are closed. The second resistor string 144 is then pinned between voltages V3 and V4, and an analogue voltage in the range from V3 to V4 is accordingly applied to pixel 146 via the sixth switch 166 (with the precise value of the applied analogue voltage dictated by the status of the switches 154-157 connected between the second resistor string 144 and the sixth switch 166). At the same time the output from the inverter 158 is logic value "0" and the first, second and third switches 161,162,165 are open, so that the first resistor string 142 is isolated from the voltages sources V1,V2 and from the input to the buffer amplifier 145.

The embodiments of figures 7 and 8 use switches that are closed by logic state "1" and are opened by logic state "0". These embodiments are not limited to this, however, and could alternatively be implemented using switches that are closed by logic state "0" and opened by logic state "1", by suitably repositioning the inverter 118,158.

The circuit of figure 8 has the advantage that the two resistor strings 142,144 are not constrained to be identical and therefore two distinct sets of analogue voltages (or equivalently distinct gamma correction) can be applied to the pixel 146 according to status of the OIF data. This embodiment may be of particular benefit where the liquid crystal layer has brightness vs. applied voltage characteristic curves 15,17 for the two intended viewing positions that are not mirror images of one another.

Figure 9 shows a further example of a digital-to-analogue conversion circuit 170 that is designed to supply an analogue voltage to a pixel 173 (again represented as a capacitance) via a unity gain buffer amplifier 172. The digital-to-analogue conversion circuit 170 comprises a switched capacitor array 171. Such switched capacitor digital-to-analogue conversion circuits are well-known.

The capacitor array 171 comprises a plurality of capacitors 174-177 connected in parallel to one another. One end of each capacitor is connected to the input to the buffer amplifier 172 and also is connectable, via a first switch 180, to a point A. Point A may be connected to a voltage source V1 via a second switch 190 or to a voltage source V3 via a third switch 194. The other end of each capacitor 174-177 is connected, via respective switches 184-187, either to point A or to a point B. Point B may be connected to a voltage source V2 via a fourth switch 192 or to a voltage source V4 via a fifth switch 196.

The digital-to-analogue conversion circuit 170 receives input digital observer identification field data (OIF) along an OIF bus line 178. The OIF bus line 178 controls, via an inverter 179, the status of the second and fourth switches 190,192, and also controls the status of the third and fifth switches 194,196.

The first switch 180 is controlled by a clock signal up. During a first time period, the first switch 180 is closed and switches 184,185,186,187 are set so as to connect both plates of all capacitors 174-177 to point A. During this time period point A is connected to voltage source V1 or to voltage source V3, dependent on whether the OIF data received at the OIF bus line 178 is "0" or "1". Thus, during this first time period voltage V1 or voltage V3 is applied to both plates of all capacitors of the capacitor array.

During a second time period, switch 180 is open. At the start of the second time period the switches 184,185,186,187 are set so as to connect the lower plate of each individual capacitor either (1) to point A and so to the voltage source V1 (if the OIF data is "0") or to the voltage source V3 (if the OIF data is "1 ") or (2) to point B and so to the voltage source V2 (if the OIF data is "0") or to the voltage source V4 (if the OIF data is "1"). The status of the individual switches 184,185, 186,187 during the second time period is dictated by a logic circuit (not shown) acting on digital brightness identification data input via a BDF bus line 181.

As will be well understood by those familiar with switched capacitor circuit design, the above action will causes sharing of electrical charge amongst capacitors during the second time period. The output analogue voltage of the digital-to-analogue converter 170, that is applied to pixel 173 via the buffer amplifier 172, will lie in a voltage range of either from V1 to V2 ( if the OIF data field is "0") or from V3-to-V4 (if the OIF data field is "1". The precise value of the output analogue voltage, within the range selected by the OIF data field, will be determined by the brightness

identification data field.

The embodiment of figure 9 uses switches that are closed by logic state "1" and are opened by logic state "0". The embodiment is not limited to this, however, and could alternatively be implemented using switches that are closed by logic state "0" and opened by logic state "1", by suitably repositioning the inverter 179.

It would be possible to modify the conversion circuit of figure 9 to include two separate capacitor arrays, one array for providing an output voltage in the range from V1 to V2 and one array for providing an output voltage in the range from V3 to V4.

The two capacitor arrays would not be constrained to be identical and therefore two distinct sets of analogue voltages (or equivalently distinct gamma correction) could be applied to the pixel 173 according to status of the OIF data.

The present invention has been described with reference to a multiple view directional display in which two images are displayed in different viewing directions by choosing the magnitude of the voltages applied to the pixels appropriately. The invention may, however, in principle be applied to a multiple view directional display in which a parallax optic is used to produce viewing angle separation between two different displayed images. In particular, multiple view directional displays that have a parallax optic that can be reconfigured are known. For example, the parallax optic may be a series of opaque and transparent regions defined on an addressable liquid crystal display panel to form a parallax barrier, so that the opaque and transparent regions of the barrier can be reconfigured if desired. If the parallax optic of a multiple view directional display is reconfigured the assignment of pixels of the image display layer between the two images must also be changed, and the present invention provides a simple way of achieving this.

The invention has been described above with reference to embodiments in which the image data for a pixel identify the intended viewing direction of the pixel by identifying the intended observer. The invention is not limited to this, however, and the intended viewing direction of a pixel may be identified in other ways. For example the invention may be applied to a 3-D display which displays two images - a left eye image and a right eye image that together constitute a stereoscopic image pair.

In this case, the image data for a pixel could identify the intended viewing direction of the pixel by including information as to whether the pixel was for the left eye image or the right eye image. A pixel that was identified as being for the left eye image would be displayed to the left eye of the observer, and a pixel that was identified as being for the right eye image would be displayed to the right eye of the observer. In the embodiment of figure 3, for example, the observer identification field would be replaced by a field that identifies whether a pixel is for the left eye image or the right eye Image.

Claims

Claims 1. A method of driving a multiple view directional display

comprising the step of supplying, to the display, image data for a selected pixel of the display; wherein the image data for the pixel identify an intended viewing direction of the selected pixel.
2. A method as claimed in claim 1 wherein the image data for the selected pixel of the display contain information for identifying an intended viewing direction of the selected pixel.
3. A method as claimed in claim 1 or 2 and further comprising applying a voltage to the selected pixel of the display on the basis of the display data for the selected pixel.
4. A method as claimed in claim 1, 2 or 3 wherein the image data are digital data.
5. A method as claimed in claim 4 and comprising supplying, as image data, a sequence of data words, each data word relating to a respective pixel of the display.
6. A method as claimed in claim 5 wherein each data word contains information for identifying an intended viewing direction of the respective pixel.
7. A method as claimed in claim 5 or 6 wherein each data word comprises brightness information for identifying a desired brightness of the respective pixel.
8. A method as claimed in any of claims 4 to 7 and comprising the step of applying digital-to-analogue conversion to the image data to derive a voltage to be applied to the pixel or the respective pixel.
9. A method as claimed in claim 8 wherein the digital-to-analogue conversion step comprises determining a range for a voltage to be applied to the pixel or the respective pixel on the basis of the information for the pixel or the respective pixel.
10. A method as claimed in claim 9 when dependent directly or indirectly from claim 7 wherein the digital-to-analogue conversion step further comprises selecting a voltage within the determined voltage range on the basis of the brightness information.
11. A method as claimed in any of claims 2 to 10 wherein the information for identifying an intended viewing direction of a pixel is observer information for identifying an intended observer of the pixel.