AUTOSTEREOSCOPIC DISPLAY APPARATUS

Abstract: An autostereoscopic display apparatus comprising a display panel (10) operating in conjunction with optical director means (15), for example a lenticular sheet overlying the display panel, the panel comprising a plasma addressed electro-optic type of matrix display panel facilitating an increase in the number of display elements (12) in a row thereby enabling multiple views of higher resolution to be attained.

Description: DESCRIPTION AUTOSTEREOSCOPIC DISPLAY APPARATUS The present invention relates to an autostereoscopic display apparatus comprising a matrix display panel having an array of display elements arranged in rows and columns, and optical director means through which the display panel output is directed and comprising a plurality of optical director elements for directing the outputs of respective columns of display elements associated with each optical director element in mutually different angular directions. Examples of such autostereoscopic display apparatus are described in the paper by C. van Berkel et al entitled "Multiview 3D - LCD" presented at The IS & T/SPIE Symposium on Electronic Imaging, San Jose in January 1996, and published in SPIE Proceedings Vol. 2653, in the paper entitled "3-D Displays for Video telephone Applications" by D. Sheat et al in Eurodisplay 1993 and in GB-A-2196166. In these examples the matrix display panel comprises a matrix LC (liquid crystal) display panel, having rows and columns of display elements, which acts as a spatial light modulator and the optical director means comprises a lenticular sheet, whose lenticules, compπsing (semi) cylindrical lens elements, extend in the column direction of the display panel with each lenticule overlying a respective group of two, or more, adjacent columns of display elements and extending parallel with the display element columns. The matrix LC display panel is of a conventional form, comprising regularly spaced rows and columns of display elements, as used in other types of display applications, e.g. computer display screens. In an arrangement in which each lenticule is associated with two columns of display elements, the display panel is arranged to display two 2D sub-images vertically interleaved, with alternate columns of display elements displaying the two images, and the display elements in each column provide a vertical slice of the respective 2D (sub) image. The lenticular sheet directs these two slices, and corresponding slices from the display element columns associated with the other lenticules, to the left and right eyes respectively of a viewer in front of the sheet so that the viewer perceives a single stereoscopic image. In other, multi-view, arrangements, in which each lenticule is associated with a group of more than two adjacent display elements in the row direction and corresponding columns of display elements in each group are arranged appropriately to provide a vertical slice from a respective 2-D (sub-) image, then as a viewer moves his or her head a series of successive, different, stereoscopic views are perceived creating, for example, a look-around impression. A parallax barrier screen, comprising an array of slits, can be used instead of a lenticular sheet as a view determining screen. In using an LC matrix display panel having a given number of display elements in a row, to provide a plurality of views in the 3D display, horizontal display resolution is necessarily sacrificed. For example, with a display panel having an array of 800 columns and 600 rows of display elements (each comprising three, red, green and blue, sub-elements forming a colour triplet in the case of a colour panel), then for a four view system providing three stereo pairs (at a fixed viewing distance) the resulting display would have a resolution of only 200 in the horizontal (row) direction and 600 in the vertical (column) direction for each view. Thus, the stereoscopic images as seen by the viewer each have a comparatively high vertical resolution but only a comparatively small horizontal resolution. The substantial difference between vertical and horizontal resolution capabilities is, of course, undesirable. TFT (thin film transistor) active matrix LC display panels are typically used. Such panels offer good display quality and, for example, VGA (640 x 480), SVGA (800x600) and XGA (1024x768) compatible resolutions but the inability to provide appropriately high resolution displays and the consequent need to trade off the number of views provided against resolution has, however, been a limiting factor in the use and popularity of such autostereoscopic display apparatus. It is an object of the present invention to provide an improved autostereoscopic display apparatus. According to the present invention, an autostereoscopic display apparatus of the kind described in the opening paragraph is characterised in that the matrix display panel comprises a plasma addressed electro-optic matrix display panel. Plasma addressed electro-optic display panels, and particularly plasma addressed LC display panels, commonly known as PALC panels, have been developed over recent years as an alternative to TFT type active matrix display panels and with similar resolutions to those provided by TFT panels for use particularly as display screens in computer monitors, workstations, and TV display applications for which purposes they have the advantage over TFT display panels of offering larger display areas. The invention stems from a recognition that, because of the manner of its construction, this type of display panel has the capability of providing a comparatively much higher horizontal resolution, with its horizontal resolution greatly exceeding its vertical resolution and the ratio of horizontal resolution to vertical resolution being significantly greater than that of a conventional TFT matrix display panel, usually 4:3. A display panel having such a resolution potential is eminently suited to autostereoscopic display applications, particularly in the multiple view kind, where a display output with a high horizontal resolution is very desirable. In a TFT display panel, the horizontal resolution capability is limited due to the nature of its construction. The display elements are defined by electrodes on a plate arranged in rows and columns. Each electrode is connected to an adjacent TFT and each TFT is connected to a respective one of a set of row (scan) address conductors and to a respective one of a set of column (data) address conductors, with the row conductors extending in gaps between adjacent rows of display element electrodes and the column conductors extending in gaps between adjacent columns and display element electrodes. The construction of a PALC panel is very different. In this, a series of parallel, plasma-containing, channels extending in the row direction are used which underlie a layer of LC material. A set of parallel, transparent, conductors extending in the column direction is carried on a separate plate on the opposite side of the LC layer from the channels. A display element is defined at the cross-over regions between the spaced column conductors and the channels whose height (i.e. dimension in the column direction) is determined by the width of a channel and whose width (i.e. dimension in the row direction) is determined by the width of the column conductor. The spacing between adjacent display elements in a row is determined by the spacing between adjacent column conductors. Unlike a TFT display panel, it is the vertical resolution of a PALC panel which is limiting because of the need to provide the channels. The horizontal resolution of a PALC panel is, however, not limited in this way. The width of the individual display elements can be reduced by reducing the width of the column conductors and so the number of display elements in a row, and hence horizontal resolution, can be increased very simply and conveniently by reducing the width and pitch of the column conductors. This extra horizontal resolution possibility can be used to considerable benefit in an autostereoscopic display apparatus. It is envisaged that the number of display elements in a row could be increased such that a ratio of the number of display elements in a row (horizontal resolution) to the number of display elements in a column (vertical resolution) of up to around 10:1 may be achieved in contrast to a ratio of only 4:3 in a standard TFT panel. Further advantages are obtained in using a plasma addressed display panel. When using TFT panels unwanted display artifacts are experienced due to the presence of black matrix material extending in the gaps between columns of display elements. These vertical strips of black matrix material are imaged by the lenticular sheet which a viewer perceives as vertical black bands between adjacent 2D views. In a plasma addressed display panel, the display elements in a row can be closely packed with a comparatively small gap between adjacent display elements so that display artifacts due to the presence of any black matrix in these gaps becomes less noticeable. Moreover, the physically larger display area of a plasma addressed display panel compared with a TFT panel with a similar number of rows is beneficial for direct viewing autostereoscopic display purposes because the display provided fills more of the user's field of view. In order to provide an increased number of display elements in a row, it is necessary only to modify the substrate of an existing plasma addressed display panel which carries the column address conductors. Conveniently, the channel carrying substrate, defining the number of rows, of existing kinds of plasma addressed display panels can be utilised. Thus, channel substrates from known panels providing, for example, 600 or 800 rows can be employed. Preferably the ratio of the number of display elements in a row to the number of display elements in a column, determined by the number of column conductors and the number of channels respectively, is selected so as to be at least 2:1. For greatest benefit however, a higher ratio is desirably used. A ratio of 8:3, 12:3, 16:3 or 20:3 would enable 2, 3, 4 or 5 view systems with display resolutions comparable to those from a standard TFT display panel operating in monoscopic mode. In a particularly preferred embodiment, the ratio is selected to be around 28:3 which enables a seven view system to be achieved. Using a channel substrate from a standard plasma addressed panel having, for example, 600 rows, then display element arrays of 5600 by 600 or 4000 by 600 can provide 7 and 5 views respectively whilst maintaining for each view a resolution of 800 x 600 (a 4:3 ratio). For multi-colour display, each display element is preferably sub-divided to form a plurality of sub-elements providing respective and different colours, for example, a triplet comprising red, green and blue sub-elements arranged alongside one another in the row direction for a full colour display. An embodiment of autostereoscopic display apparatus in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a schematic perspective view of the apparatus; Figure 2 is a schematic block diagram of a display device comprising a plasma - addressed electro-optic matrix display panel used in the apparatus; Figure 3 is a perspective view of a part of the display panel of the display device illustrating its construction; and Figure 4 is a plan schematic view of the apparatus operating, for example, to provide four views. It should be understood that the Figures are merely schematic and are not drawn to scale. In particular, certain dimensions may have been exaggerated whilst other have been reduced. The same reference numerals are used throughout the drawings to indicate the same or similar parts. Referring to Figure 1 , the apparatus comprises a matrix display device acting as a spatial light modulator and comprising a display panel 10 having a planar array of individually addressable, regularly-spaced and similarly-sized, display elements 12 arranged in aligned rows and columns perpendicularly to one another. The display elements are shown schematically with only a comparatively few in each row and column for simplicity. The display panel 10 is illuminated by a light source 14 which can be of any suitable kind and in this example comprises a planar back-light co-extensive with the area ofthe display element array. Light incident on the panel is modulated by the individual display elements by the application of appropriate drive voltages thereto so as to produce the desired display output. Overlying the output side of the display panel 10, there is provided optical director means which in this embodiment comprises a lenticular sheet 15 having an array of elongate, parallel, lenticules 66. The lenticules 16 comprise optically cylindrically converging lenticules, for example formed as convex cylindrical lenses or graded refractive index cylindrical lenses, which extend parallel to the display element columns and serve, in known manner, to provide separate images, generated in the display element array of the panel 10 in a vertically interleaved fashion, to the two eyes of a viewer facing the side of the sheet 15 remote from the panel 10 so as to produce a stereoscopic display. Autostereoscopic display apparatus using lenticular sheets in conjunction with matrix display panels are well known and it is not thought necessary to describe here in detail their operation. Examples of such apparatus and their operation are described in the aforementioned papers by C. van Berkel et al and by D. Sheat et al, and in GB-A-21296166 to which reference is invited. Each lenticule 16 may overlie a respective group of two, three, or more, adjacent columns of display elements, to provide a corresponding number of views. The matrix display panel 10 comprises, in accordance with the invention, a plasma addressed matrix display panel. The construction, fabrication and operation of typical plasma addressed matrix display devices have been described in, for example, US Patent Application Serial No. 08/384090 (PHA 60090), US-A-4896149, EP-A-623838, and EP-A-628944 to which reference is also invited. An example of such a display panel, a PALC panel, will be briefly described with reference to Figure 2, which is a schematic block diagram of the example panel and its associated drive circuitry, and Figure 3, which is a perspective, part sectional view of a portion of the panel. The display panel 10, comprising the row and column array of display elements 12, includes sets of row and column address conductors, 20 and 18, extending in the row and column directions respectively, which at their intersections define the array of display elements. The array of display elements is driven by associated row and column drive circuits 22 and 24. The row drive circuit 22 applies, via connection lines 26, scan signals, comprising voltage pulses, to each row address conductor 20 in sequence to select each row of display elements, one at a time, in turn. The column drive circuit 24 applies data signals, comprising analogue voltages derived by sampling at column positions successive lines of an input video signal representing an image to be displayed, to the column address conductors 18, via connection lines 25, for a selected row such that the display elements 12 in a selected row are driven according to the level of their respective applied data signals to produce a required display output. All rows are driven in turn in this manner in a display field period the operation being repeated in subsequent field periods. A timing and control circuit 32 co-ordinates the functions of the row and column drive circuits 22 and 24 to this end. Referring to Figure 3, which shows a portion of the display panel containing parts of three column conductors 18 and four row conductors 20, the display panel 10 comprises a pair of substrates 34 and 36 of transparent insulating material, such as glass, between which a layer of liquid crystal material 42 is sandwiched. The substrate 34 carries the set of column address conductors 18 in the form of narrow, parallel, strips of transparent conductive material such as ITO. An array of colour filters (not shown) can be provided on the substrate 34 overlying the conductors 18 for a colour display. In this case each display element is effectively composed of three display sub- elements, providing red, green and blue outputs respectively, with each sub- element being associated with, and defined by, a different column conductor. The second substrate 36 comprises a series of parallel, elongated etched channels 44 extending in the row direction, perpendicularly to the conductors 18, each of which crosses all the conductors 18 and constitutes a row address conductor 20. The channels are sealed at their ends and are closed by a thin transparent dielectric sheet 45, e.g. of glass, extending over the surface of the substrate 36 and separating the channels from the LC layer 42. A capacitive LC display element, or display sub-element in the case of a colour display, is defined at each intersection between the column conductors 18 and the channels 44. Each channel 44 contains a low pressure ionisable gas, typically below 1 Atm., such as helium and/or neon and optionally with a small percentage of argon, and is provided on its surface with spaced first and second electrodes 30 and 31 extending along its length which are energisable to ionise the gas and create a plasma. The panel operates in a manner similar to that of a TFT active matrix LC display panel except that the TFTs associated with the display elements in a row are in effect replaced a plasma channel acting as a row switch for selective addressing of a row of display elements. The first electrode 30 is typically grounded and is commonly called the cathode. The second electrode 31 , the anode, is supplied with a selection pulse signal from the row drive circuit 24 which is positive relative to the cathode electrode, and sufficient to cause electrons to be emitted from the cathode 30 to ionize the gas. In operation, all but one of the row plasma channels are in the de- ionised or non-conducting state. The plasma of the one ionised selected channel is conducting and, in effect, establishes a reference potential on the adjacent side of a row of display elements of the LC layer 42, causing each LC display element 12 in the row to charge up according to the applied column potential of the data signal. After such addressing the ionised channel is turned off, isolating the LC display element charge and storing the data voltage for a field period. When the next row of data appears on the column conductors 18, only the succeeding plasma channel row is ionised to store the data voltages in the succeeding row of LC display elements, and so on. The attenuation of each LC display element 12 to incident light is a function of the stored voltage across the display element. As will be appreciated, in this kind of display panel the widths of the column conductors 18 and the channels 44 at their cross-overs determine the dimensions of the individual display elements 12, or display sub-elements in the case of a colour display in which each display element is divided into a plurality of colour sub-elements. Typically, the display elements, or sub- elements, are of rectangular shape with their width, in the row direction, determined by the width of the deposited ITO strips constituting the column conductors 18 and their height determined by the width of the channels 44. The provision of plasma channels introduces a limiting factor on the pitch of the rows of display elements due to the physical constraints in forming the channels, for example, by etching, and the dimensional requirements of the channels, with their electrodes, in achieving plasma generation. Thus the minimum height of the display elements and the resolution in the vertical direction obtained in the display produced are constrained. Typically, the channel pitch is around 300μm, the channels having a width at the top of around 270//m and a channel to channel spacing of around 30A/ΠΓI. The same constraints do not apply to the column conductors 18. The width of the ITO strips and their spacing can readily be reduced so as to increase the number, m, of display elements per row and thus the horizontal resolution. The number of display element columns, m, can, therefore, greatly exceed the number of display element rows, n. Heretofore, the ratio of m:n in PALC panels has generally corresponded to the ratios found typically in other flat panel displays such as TFT display panels which is around 4:3 (i.e. 640:480; 800:600; 1024:768). The ability to have an increased number, m, of display elements in a row, and thus a higher m:n ratio, offers a significant advantage in autostereoscopic display apparatus. Taking, for example, a known apparatus using a TFT display panel having an array of 800 (m) by 600 (n) display elements, then, when operated, for example, as a four view system providing three stereo pairs (at a fixed viewing distance) in which the panel displays the four views vertically interleaved with each column of display elements displaying a vertical slice from a respective view and with every fourth column displaying a vertical slice of one view, the resulting display has a resolution of only 200 in the horizontal (m) direction and 600 in the vertical (column) direction for each view. Thus, the stereoscopic images seen by viewer have a comparatively high vertical resolution but only a comparatively small horizontal resolution. In using instead a PALC panel with the same number of rows, n, but having a m:n ratio of 16:3, i.e. a 3200 x 600 array of display elements, similarly to provide a four view system, then the resulting display would have a resolution of 800 horizontal and 600 vertical. This is equivalent to the display resolution obtained from a corresponding TFT panel in monoscopic operation. In the case of a full colour display panel being used, in which each display element is divided into three sub-elements, forming a colour triplet, arranged alongside one another in the row direction, each sub-element being associated with a different column conductor and providing a respective one of the three primary colours, there would then be 9 600 sub-elements in a row, compared with 2400 in the TFT panel. The operation of a four view display apparatus is depicted schematically in Figure 4. Each lenticule 16 of the lenticular sheet overlies a respective group of four adjacent display element columns such that four vertical strips, each representing a vertical slice of a respective 2D view, are presented to a viewer. The numbers 1 to 4 denote the vertical slices of the corresponding views. The other lenticules provide similar strips. Thus, with a viewer's eyes situated as shown, the viewer will see a stereoscopic image composed of views 2 and 3. By moving sideways, the viewer will see 2 other stereoscopic images, composed of views 1 and 2, and views 3 and 4. If only two views are to be provided by the panel, constituting one stereoscopic image, then the ratio m:n need only be increased to 8:3, i.e. 1600 display elements in a row to obtain the same kind of resolution display as from the TFT panel in monoscopic operation. Preferably, the advantage offered by using a PALC display panel is utilised to greater benefit to provide higher numbers of views. In a particularly preferred embodiment, seven views are provided using a display panel having a 28:3 array, i.e. 5600 by 600 display elements. For other numbers of views, the ratio is selected accordingly, i.e. 12:3 (2400 x 600), or 20:3 (4000 x 600) for 3 and 5 view systems respectively. The increase in the number of display elements provided in each row is preferably such that the ratio m:n is at least 2:1. It is not essential that the usual ratio, 4:3, be increased merely in direct proportion to the number of views required. While most display standards conform to an m:n ratio of 4:3, at least one, the EWS/SXGA standard, differs in this respect. The increase in the number m is likely to be limited by the need to define the gap between adjacent column conductors 18. However, it is envisaged that an increase in the ratio of the number, m, of display elements in a row to the number, n, of display elements in a column up to around 10:1 can be achieved. For a panel with a given channel width and pitch, then increasing the number of display elements in a row by providing more column conductors of less width has the effect of altering the shape of the display elements (or colour sub- elements) such that they become more elongated in the vertical direction and this is another factor to be taken in account. It will be appreciated that the increase in the number of display elements in each row entails only modification to the structure on the upper substrate 34 of a standard form of PALC display panel to increase the number of column conductors 18 provided. The lower substrate 36, with the channels 44, conveniently can be the same as that used in the standard form. Of course, the number of rows, n, need not be 600. Using a lower substrate from a PALC display panel conforming to the XGA standard, for example, the number of rows, n, would be around 768. In this case, the number of columns, m, of display elements can be correspondingly increased according to the above- mentioned m:n ratios for 2 to 7 view systems. A display panel having the same number of rows as in a standard form is preferable for convenience and simplification of manufacture but, of course, display panels having a different number of rows to those used in standard forms could also be used. As in a TFT panel, the display elements may be bordered by black matrix material. Even so, the effects due to imaging by the lenticules of the vertical strips of black matrix extending between adjacent display element columns is less noticeable by a viewer as the space between adjacent columns is comparatively small. The layer of liquid crystal material in the above-described embodiment may comprise a twisted nematic LC material, in which case polarising layers are provided at the input and output sides of the panel in known manner. The panel 10 may employ electro-optic materials of different types. For example, if it uses such material that changes the polarisation state of incident light rays, panel 10 is positioned between a pair of light polarising layers, which co¬ operate with the panel to change the luminance of light propagating through them. The use of a scattering liquid crystal cell as the electro-optic material would not require the use of polarising filters, however. All such materials or layers of materials which attenuate transmitted in response to the voltage across it are referred to herein as electro-optic materials. LC materials are presently the most common example, but it will be understood that the invention is not limited thereto. For a projection display apparatus, full colour images can be achieved instead of using a colour filter within the panel by using three separate monochrome panels 10, each of which controls one primary colour. In such projection apparatus, the image outputs of the three panels are combined, in known manner, before being projected by a projection lens onto the rear of a diffuser projection screen. The lenticular sheet is provided over the front side of the screen, i.e. the side facing the viewer, with the lenticules overlying the enlarged image of the display element array produced in the screen. Forms of optical director means other than a lenticular sheet can be used as a view determining screen, for example a microlens screen, a parallax barrier having slits which extend in the column direction and are aligned with respective columns of display elements, or a holographic element. The above described apparatus is of simple and basic form. It will be appreciated, however, that the invention can be applied to other kinds of autostereoscopic display apparatus employing a matrix display device as a spatial light modulator, for example, the kind of apparatus which uses an array of light sources that are sequentially illuminated in synchronisation with display information being applied to the display panel and in which an additional lenticular sheet or parallax barrier is disposed before the display panel. From the foregoing it will be appreciated that an autostereoscopic display apparatus is disclosed comprising a display panel operating in conjunction with optical director means, for example a lenticular sheet overlying the display panel, the panel comprising a plasma addressed electro-optic type of matrix display panel facilitating an increase in the number of display elements in a row thereby enabling multiple views of higher resolution to be attained. From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the field of autostereoscopic display apparatus and component parts thereof and which may be used instead of or in addition to features already described herein.

Claims: CLAIMS 1. An autostereoscopic display apparatus comprising a matrix display panel having an array of display elements arranged in rows and columns, and optical director means through which the display panel output is directed and comprising a plurality of optical director elements for directing the outputs of respective columns of display elements associated with each optical director element in mutually different angular directions, characterised in that the matrix display panel comprises a plasma addressed electro-optic matrix display panel. 2. An autostereoscopic display apparatus according to Claim 1 , characterised in that the ratio of the number of display elements in a row to the number of display elements in a column is at least 2:1. 3. An autostereoscopic display apparatus according to Claim 2, characterised in that said ratio is at least 18:3. 4. An autostereoscopic display apparatus according to Claim 2, characterised in that said ratio is around 28:3. 5. An autostereoscopic display apparatus according to any one of the preceding claims, characterised in that each display element comprises a plurality of display sub-elements providing respective and different colour outputs. 6. An autostereoscopic display apparatus according to any one of the preceding claims characterised in that the display elements comprise liquid crystal display elements. 7. An autostereoscopic display apparatus according to any one of the preceding claims, characterised in that the optical director means comprises an array of lenticular elements.

Inventors: BATTERSBY STEPHEN JOHN, BATTERSBY, STEPHEN, JOHN
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1997
Main classification: G02B27
IPC codes: G02B27, G02F1, G09F9, G09G3, H04N13