GB2274225A - Video display apparatus with an array of display units - Google Patents

Abstract

A video display apparatus 40 such as a video wall includes an array of display units 12 for displaying respective sub-areas of a video image, a video control arrangement (24, 26) for controlling the display of the respective sub-areas of the image on the respective display units and illumination elements 42 for illuminating interstitial regions between adjacent display units in order to reduce the grid-like effect which is apparent in conventional video walls and the like. Active illumination elements 42 can be provided, with the illumination of an element being controlled in dependence upon the brightness and/or colour of the video image as a whole or of at least an area of the input, video image corresponding at least generally to the interstitial region. The illumination element may be a fluorescent device and controllable liquid crystal Fig 7, or a controllable light source (Fig 8). Alternatively, illumination can be provided (Figure 9) from an additional display of the whole image via light guides. In an arrangement of projection displays, light guides (110, Fig 17; 126, Fig 18) transmit to the interstitial areas light generated in the normal overscanning of the projection screen and picked up by collecting surfaces (126). <IMAGE>

Description

VIDEO DISPLAY APPARATUS WITH AN ARRAY OF DISPLAY UNITS The invention relates to a video display apparatus for displaying a video image wherein the video display apparatus comprises an array of video display units for displaying respective sub-areas of the video image.

A familiar example of a video display apparatus of this type is a video wall made by arranging a plurality of video display units in a two-dimensional array or matrix. Typically, the individual video display units are cathode ray tube (CRT) monitors. However, it is also known to use CRT-based rear projection monitors. Video control means are provided for controlling the display of an input video image on the video display apparatus. The input video image is divided into different sub-areas so that individual sub-areas may be displayed on a respective one of the video display units. The complete picture is then observable on the complete array of video display units.

A problem with conventional video display apparatus of this type arises from the fact that the active display screens of individual video display units do not abut seamlessly to one another within the array. In the first place, the video wall is normally assembled by stacking the video display devices in their housings in a two-dimensional array. The fact that the active display screens of the video display units are mounted in their housings means that the screens are separated from one another. Where cathode ray tubes are used as the individual video display units, the active display areas of the screens are further separated from one another. Firstly, cathode ray tubes, as viewed from the front. are not rectangular.

Also, the active screen area of a CRT does not extend right to the edge of the tube. The result of this is that a margin or border area is formed around each sub-area of the image. Even with a rear projection monitor, although the border area is normally less than that for a conventional CRT monitor, there is still a border due to the front bezel for mounting the display screen in the projection monitor. A similar effect would be produced if, for example, liquid crystal displays were used as the individual video display units.

This is because the image area of such video display units is normally surrounded by circuitry to enable the rows and columns of liquid crystal elements in the display to be driven.

Accordingly, a problem which is found in known video display apparatus based on an array of individual video display units is that a grid formed from the margins or borders mentioned above interrupts the picture. Typically, the border or margin area is chosen to be relatively dark (i.e. grey or black). Then, when pictures are displayed which have a generally low level of illumination, the grid almost disappears. However, if brighter pictures are being displayed, the grid becomes intrusive. If another light colour were chosen for the grid, this would become very noticeable when the video image to be displayed is relatively dark, although it would mean that the grid would be less noticeable on bright scenes.

In accordance with the invention, therefore, there is provided a video display apparatus for displaying an input video image, the video display apparatus comprising an array of display units, each of which includes a screen for displaying a respective sub-area of the video image, video control means for controlling the display of the respective sub-areas of the input video image on the respective screens and means for illuminating interstitial regions between adjacent screens.

By illuminating the interstitial regions between the active screen areas of the display unit, the grid-like effect which is superimposed on the overall picture in conventional video walls and the like can be mitigated. By the screen of a video display device is meant a surface at which an image or picture can be viewed. This can be separate from an image generator as in, for example a rear projection video display unit, or can be integral with the image generation device as in a conventional CRT device or a liquid crystal display panel, etc.

By providing means whereby the intensity of illumination of a said interstitial region is, in use, dependent on an illumination intensity for at least an area of the input video image corresponding at least generally to the interstitial region, the overall appearance of a video wall or the like can be further improved.

Similarly, by providing means whereby the colour of the illumination of a said interstitial region is dependent on an illumination colour for at least an area of the input video image corresponding at least generally to the interstitial region, a further improvement is possible.

Rather than making the illumination of an individual interstitial region dependent upon the illumination of an area of the input image corresponding to the interstitial region, the illumination of each interstitial region can be made to be dependent upon the average illumination over the displayed image.

Preferably, the illumination means comprises active illumination means for illuminating an interstitial region, the video control means controlling the operation of the active illumination means in dependence on an area of the input video image corresponding at least generally to the interstitial region. In this manner, dynamic control of the illumination of the interstitial regions is possible.

The active illumination means can comprise at least one active illumination element located in a said interstitial region for illuminating that interstitial region. Alternatively, the active illumination means can comprise at least one active illumination element located remotely from a said interstitial region and light guide means for directing light from the active illumination element(s) to the interstitial region for illuminating that interstitial region.

The video control means can comprise an active illumination means controller which is responsive to the input video image to generate control signals for controlling the active illumination means for respective interstitial regions.

In a particularly effective embodiment, the active illumination element comprises a further video display device comprising a further screen for displaying the input video image and wherein the light guide means comprises, for respective interstitial regions. means for collecting light from a corresponding area of the further screen and for guiding said light to the interstitial region for illuminating that interstitial region.

The video control means can also be made to be responsive to ambient light conditions to determine the illumination of the interstitial regions.

The video display apparatus can comprise passive means for illuminating an interstitial region by directing light from a video display unit adjacent to the interstitial region for illuminating that interstitial region. Preferably, the passive illumination means is a light guide means forming part of the housing of a video display unit.

In one particular implementation, where the video display units are projection video display units, the passive illumination means comprises a light guide forming at least part of a structure extending at least partially around the edge of a projection screen of a projection video display unit, the light guide forming part of a structure for mounting the projection screen in the projection video display unit and, in use, collecting overscanned light within the projection video display unit and directing the light so collected to a front surface of the video projection display unit around the projection screen.

The invention also provides a projection video display unit for use in a video display apparatus as defined above, the projection video display unit comprising a projection screen and a light guide forming at least part of a structure extending at least partially around the edge of the projection screen, the light guide forming part of a structure for mounting the projection screen in the projection video display unit and, in use, collecting overscanned light within the projection video display unit and directing the light so collected to a front surface of the video projection display unit around the projection screen.

Alternatively, the display unit can be a cathode ray tube monitor or an active display panel such as a liquid crystal display panel.

The invention is described hereinafter with reference to the accompanying drawings in which: Figure 1 is a schematic front view of a conventional video display apparatus comprising an array of CRT video display units; Figure 2 is a schematic side view of the apparatus of Figure 1 illustrating, in block diagrammatic form, a video control structure; Figure 3 is a schematic block diagram illustrating in more detail the video control structure of Figure 2; Figure 4 is a schematic front view of an example of video display apparatus in accordance with the invention; Figure 5 is a schematic side view of the apparatus of Figure 4 illustrating, in block diagrammatic form, a video control structure; Figure 6 is a schematic block diagram of a first example of a video control structure for the apparatus of Figure 5;; Figure 7 is a schematic diagram of a first example of an illumination element for the apparatus of Figure 4; Figure 8 is a schematic diagram of a second example of an illumination element for the apparatus of Figure 4; Figure 9 is a schematic diagram of a second example of a video control structure for the apparatus of Figure 5; Figure 10 is a schematic diagram of parts of the video control structure of Figure 9; Figure 11 is a schematic diagram of further parts of the video control structure of Figure 9; Figure 12 is a schematic diagram of one of the parts illustrated in Figure 11; Figure 13 is a schematic front view of a conventional video display apparatus comprising an array of projection video display units; Figure 14 is a schematic side view of the apparatus of Figure 13 illustrating, in block diagrammatic form, a video control structure for the apparatus of Figure 13;; Figure 15 is a schematic plan view, in cross-section, of a projection video display unit; Figure 16 is a detail showing the conventional mounting of a screen in the projection video display unit of Figure 15; Figure 17 illustrates a first example of a mounting for a screen in a projection video display unit for an embodiment of the invention; and Figure 18 is a schematic illustration of a second example of a mounting for a screen in a projection video display unit for an embodiment of the invention.

Figure 1 is a schematic diagram of the front view of a video display apparatus in the form of a video wall 10 comprising a plurality (in the present example 16) video display units 14. As can be seen in Figure 1, the video display units 14(0,0) - 14(3,3) are stacked to form a video wall. Each of the video display units 14 illustrated in Figure 1 is a conventional cathode ray tube (CRT) monitor comprising a cathode ray tube having an active screen area 12 mounted in a housing 22. The individual monitors are stacked on top of one another and beside one another so that the active screen areas 12 form an array of active screen areas 12(0,0) - 12(3,3) which together are used for displaying a complete image.As the cathode ray tubes are mounted in their housings 22 and the active screen areas of the cathode ray tubes do not extend right to the edge of those tubes, each adjacent pair of active screen areas on the video display units is separated in the vertical direction by a non-active row 16 and in the horizontal direction by a non-active column 18 where no image is generated. The array of video display units can be mounted on a plinth 20 to support the array above the ground and which can also contain control electronics for separating an input video image into sub-images and to direct the sub-images of the input video image to the individual video display units.

Figure 2 is a schematic diagram illustrating a side view of the video display wall 10 of Figure 1. The arrow 21 represents the general viewing direction for the apparatus. It will be appreciated that the viewers will view the apparatus over a wide range of viewing angles. The video display units 14(0,0) - 14(3,3) are stacked such that the active screen areas 12(0,0) - 12(3,3) (hereinafter referred to simply as "the screens") face the viewing direction 21. Each of the video display units 14 comprises control circuitry 26 for controlling the display of video signals supplied at an input of the unit.Control circuitry 24, which can be housed in the plinth 20, is used to control the separation of input video signals VI received from a broadcast system, or from a video tape recorder, or the like, into separate channels 28 to be passed to the control circuitry 26(0,0) 26(3,3) for display on the screens 12 of the individual video display units 14.

Figure 3 illustrates in more detail the video control circuitry 24, 26 of the apparatus of Figure 2. The video control circuitry comprises a video splitter 24 for separating the video for sub-areas of an input video image into different channels for supply via the video channels 28 to the individual video control units 26(0,0) - 26(3,3) for controlling the display of video on the screens 12(0,0) - 12(3,3), respectively, of the video display units 14. The individual video control units 26(0,0) - 26(3,3) control the individual video display units 14(0,0) - 14(3,3) in a conventional manner to provide a display of video information on their screens 12(0,0) - 12(3,3).

If each of the individual video display units has a resolution for displaying substantially the whole video image (e.g., if the input video image VI is a 625 line signal and each video display unit is able to resolve 625 line video) then the effect of the video splitter 24 and the individual video control units 26(0,0) 26(3,3) is to cause each line of input video to be displayed on approximately four successive lines on the screen 12 of an individual video display unit 14. In this way, the screens of the four rows of individual video display units, that is screens 12(0,0) - 12(0,3); 12(1,0) - 12(1,3); 12(2,0) - 12(2,3); 12(3,0) - 12(3,3), will be able to display almost every line of the input video image. Interpolation of, for example, the edge-most of a group of four lines with the lines of an adjacent group of lines could be employed to smooth the resulting image.

The effect of the video splitter 24 is also to cause approximately one quarter of a row to be displayed on the screen of an individual video display unit. In other words, the screens of the four video display units in a row (e.g. 12(0,0) - 12(0,3)) together enable a complete row of video information to be displayed. The combination of the array of 16 video display unit screens 12(0,0) 12(3,3) enables the almost complete video image supplied at the input VI to be displayed.

In practice the whole image is not normally displayed on the individual active screen areas as the gaps between those screens provide breaks in the displayed image. In other words, the parts of the picture corresponding to the margins between the individual video display units (that is the rows 14 and columns 16) are not normally displayed so that the overall mapping of the displayed image as perceived on the array of video display units corresponds to that which would be achieved if the whole image were displayed on a single video display unit. It is important that an accurate mapping from the input video image onto the video display units is provided in order that, for example, diagonal lines across the image do not produce a stepped effect when displayed on the array.As long as a diagonal line matches up either side of the break formed by a margin region, the human viewer will not be too disturbed by this break and will see the line as a continuous entity.

Returning to Figure 3, the input video signal VI is input to a signal decoder 30 which decodes the received signal format for processing. Typically, the decoded input signal is then converted from composite to component form in a converter 32. The individual video components are then digitised in a digitiser 34 and the digitised video signals are stored in a plurality of frame stores (FS) 36.

One frame store FS is provided for each of the individual video display units in the array. In this case therefore, there are 16 frames stores FS(O,O) - FS(3,3). In practice, the individual frame stores FS(O,O) - FS(3,3) are implemented as a tandem pair of field stores so that a first field may be written into a first field store while a previous field is read out from the other field store. A controller 38 controls the writing of input video information to the frame stores and the reading of video data from those frame stores 36 by means of control paths, which are not shown in Figure 3 for reasons of clarity of illustration.One possibility is for each complete field of input video data to be stored in each of the 16 frame stores and then to cause selected parts of the video data from the frame stores FS(O,O) - FS(3,3) to be read out via respective video buses 28 to the control circuitry 26(0,0) - 26(3,3) of the video display units 14(0,0) - 12(3,3), respectively. Interpolation of the data read out (as mentioned above) can be provided at this stage in a conventional manner as will be apparent to one skilled in the art. Alternatively, interpolation can be performed on a received video image and selected parts of the video data only stored in each of the frame stores.

Either way, in the present example where there are 16 video display units, the data read out from the frame stores for each of the those video display units should correspond generally to 1/16th of a received video image.

The video data read out from the frame store for a particular video display unit corresponds to the position of that video display unit within the array. Thus, for example, for the active display screen 14(0,0) of the top left hand monitor 14, the portion of the video data corresponding generally to the top left hand 16th of the input video image is obtained from frame store FS(O,O). In practice, the data read out does not correspond exactly to the top 16th of the input video image. As will be apparent to one skilled in the art, the amount of data to be read out depends on the margin areas between individual display units, on the degree of over-scanning of the cathode ray tube required and on corrections for non-linearity.As is well known, the amount of a television image actually displayed on a CRT is normally somewhat less than the total area of the input video image. This is to avoid linearity effects and generally to avoid noise problems at the extremities of the image. The controller 38 controls the storage of data in the frame stores FS(O,O) - FS(3,3) and the reading of data from those frame stores. The exact control of the data read from those frame stores can be adjusted in a conventional manner for alignment purposes by means of an input keyboard 39 connected to the controller 38. The adjustment for alignment purposes can be performed additionally or alternatively on the individual monitors.

Figure 4 is a schematic front view of an embodiment of a video display apparatus in accordance with the invention. Figure 4 illustrates a video display apparatus 40 comprising an array of 16 video display units similar to that in Figure 1. However, in addition to the video display units 14 of Figure 1, illuminating elements 42 are provided for illuminating the grid formed by the interstitial regions forming the rows 16 and columns 18 between the screens (i.e.

the active screen areas) 12 of the individual video display units 14.

Various examples of illuminating elements 42 will be described hereinafter. The purpose of the illuminating elements 42 is to adjust the illumination of the grid to the changing illumination level of the display units screens in order to reduce the visual impact of the grid.

As shown in Figure 4, horizontal illuminating elements 42 (Y,X,H) are provided between vertically adjacent screens (e.g.

illumination element 42(0,O,H) between screens 12(0,0) and 12(1,0)).

Vertical illumination elements 42(Y,X,V) are provided between horizontally adjacent screens 12 (e.g. illumination element 42(0,O,V) between screens 12(0,0) and 12(0,1)).

Figure 5 is a schematic side view of the video display apparatus 40 of Figure 4 including a schematic representation, in block diagrammatic form, of a video control structure 24, 26, 28, 44 and 46.

Figure 6 illustrates in more detail the video control structure of Figure 5. The video control structure includes the control features 24, 26 and 28 corresponding to the like-numbered features of the apparatus of Figures 1-3, which operate as described with reference to Figure 3. In addition to the features 24, 26 and 28, the apparatus 40 of Figure 4 also comprises an illumination element control unit 44 which is connected to the video splitter 24.

The illumination level of an illumination element 42 can be controlled by the illumination element control unit 44 in various ways via control lines 46.

The illumination element control unit 44 can be arranged to control the level of illumination of all of the illumination elements 42 in accordance with an average level of illumination for the video image(s) being displayed on the screens of the array of video display units. Alternatively, the illumination element controller 44 can be arranged to control the level of illumination of an individual illumination element 42 in accordance with the illumination level of the input video image in an area corresponding to and/or adjacent to the interstitial region.

As well as determining a monochrome illumination level, if illumination elements providing selectable colours are provided, the illumination element control unit 44 can be arranged to determine colour and brightness values for controlling the illumination elements 42.

The arrangement illustrated in Figure 6 is intended to control the level of illumination of individual illumination elements 42 in accordance with the illumination level of the areas of the input video image corresponding generally to respective interstitial regions. An illumination element controller 48 receives the output of the digitiser 34 of the video splitter 24 illustrated in Figure 3. A plurality of registers 49 corresponding to the number of illumination elements for illuminating the interstitial regions is also provided.

In the present example, there are 24 illumination elements and two sets of 24 registers in the register block 49. The illumination element controller 48 operates the registers as accumulators for accumulating illumination values to be used for controlling the illumination elements. The illumination element controller 48 identifies pixels in the digitised image data from the digitiser 34 which relate to areas of the video image corresponding generally to respective illumination elements. The illumination levels of those pixels are used to accumulate an illumination value for an illumination element in the corresponding register. Illumination values are accumulated in one set of registers during the period in which a video image is stored in one set of 16 field stores of the frame stores 36 illustrated in Figure 3.The content of the registers is then used for controlling the illumination level of the illumination elements during the period in which the video data is read out from those field stores. The values stored in the registers 49 are processed by illumination element controller 48 into illumination control signals for controlling the illumination level of the individual illumination elements. Two sets of registers 49 are provided corresponding to a respective set of field stores of the frame stores 36 so that values can be accumulated in one set of registers as video data is written to one set of field stores simultaneously with the reading of the data accumulated for a previous field from the other set of registers as the video data is read from the other set of field stores.The registers can either be arranged to accumulate merely brightness values for controlling monochrome illumination elements or can, alternatively, be used to accumulate separate colour signals for controlling multi-colour illumination elements.

Figure 7 is a schematic diagram of an example of an active illumination element 42 for illuminating part of the grid. Figure 7 illustrates two vertically adjacent video display units comprising cathode ray tubes 13(Y,X) and 13(Y+1,X). Part of the structure 15 of the housings of each of the adjacent display units is also shown. The active display areas (i.e. the screens) of the cathode ray tubes 13(Y,X) and 13(Y+1,X) are represented by 12(Y,X) and 12(Y+1,X), respectively. Between these active display areas, there is an interstitial dead region 50 in which no illumination is provided in prior art video apparatus.

In this example of the invention an active illumination device 52 is provided. The active illumination device 52 can, for example, comprise an elongate fluorescent illumination device such as is used in liquid crystal display devices. An elongate liquid crystal display panel 54 providing a plurality of different grey levels is located in front of the illumination device 52. In the present example, the elongate fluorescent illuminating element is arranged to be illuminated permanently when the video display apparatus is in use.

The level of illumination perceived by a viewer viewing the video apparatus in the direction 21 is controlled by means of adjusting the transmission coefficient of the liquid crystal panel 54. The power for the fluorescent illuminating element and the control signals and power for the liquid crystal display are provided via the control lines 46(Y,X,H) from the illumination element controller 48 in accordance with the data stored for the element in question in the registers 49.

The elongate fluorescent illumination device and the elongate liquid crystal display panel are shaped and sized substantially to cover the interstitial dead region. A lens 56 is provided to the viewing side of the liquid crystal display panel 42 to spread the illumination from that panel to fill the interstitial area 50 between the active display screens 12(Y,X) and 12(Y+1,X).

It will be appreciated that Figure 7 illustrates only one possibility for illuminating the interstitial regions. For example, modifications may be made to the structure shown in Figure 7. For example, the liquid crystal display panel 54 could be omitted and the level of illumination of the fluorescent illumination device 52 varied directly instead. Alternatively, another form of illumination device could be provided. Also, the lens 56 could be omitted and an illumination element provided which, in itself, completely covers the interstitial area 50.

Figure 8 is a schematic diagram of a second example of an illumination element 42 for illuminating part of the grid. In this example, the interstitial region 50 is illuminated by means of light guided via a light guide 60 from an illumination device provided, for example, behind the video display unit to a lens structure 58 for spreading and projecting the illumination for illuminating the interstitial region 50. The elongate lens 58 is provided with a rearwardly extending portion for optically coupling the lens to the light guide 60. The light guide 60 can be formed from a plurality of individual optical fibres arranged side by side to form a ribbon where an elongate illumination device is, or a plurality of illumination devices are provided at the input to the optical fibres.

Alternatively, the light guide 60 could be arranged in a fan shape to spread light from a point source or a light source having a limited area, whereby the light may be spread along the length of the lens 58 which covers the interstitial region. An individual active illumination device 62(Y,X,H) can be provided for each interstitial region, the illumination of the individual illumination device 62(Y,X,H) being controlled via signals on a respective control line 46(Y,X,H) from the illumination element controller 48.

Figure 9 illustrates an alternative embodiment which avoids the need for the illumination element control unit 44. In the embodiment shown in Figure 9, a frame store 62 is connected to receive the output of the digitiser 34. A cathode ray tube monitor 64 is then arranged to receive each complete image stored in the frame store 62 and to display the image on its screen 12 CI. An optical collector and light guide arrangement 66 is provided for channelling light collected from the screen 12 CI and to direct this to the light guides 60 for respective interstitial regions.

Figure 10 illustrates an arrangement of collecting areas 68 for collecting illumination levels from the screen 12 CI of the monitor 64 for illuminating corresponding interstitial areas between the screens 12(0,0) - 12(3,3) of adjacent video display units in the array. For example, collecting areas 68(0,O,V) and 68(0,0,H) correspond to the interstitial areas covered by the elements 42(0,O,V) and 42(0,0,H) in Figure 4.

Figure 11 illustrates a light guide for channelling light from one of the areas 68 to the corresponding interstitial area. The light guide arrangement shown in Figure 11 comprises a lens 70 for collecting light from a corresponding area 68, a fan shaped light guide 72 for concentrating light from the lens 70, a bundle of optical fibres 74, preferably configured as a ribbon, a fan shaped light guide 76 for distributing the light from the bundle of optical fibres to be directed into an elongate lens 78 which is inserted into the interstitial region. The fan shaped light guide 76 can be used as the light guide 60 illustrated in Figure 8 and the elongate lens 78 as the elongate lens 58 shown in Figure 8.

Figure 12 is a schematic illustration of a fan shaped light guide which can be used to implement the fan shaped light guide 72 and 76. The light guide comprises a substantially triangular acrylic sheet which is scored substantially through the thickness thereof to define individual triangularly shaped light guides of square crosssection.

Figure 13 illustrates a further example of a conventional video wall 80 formed from a plurality of rear projection video monitors 15(0,0) - 15(3,3) stacked next to and above one another to define a four by four array of projection monitors. The active screen area 12(0,0) - 12(3,3) of such a rear projection monitor is proportionally larger compared to the front dimensions of the monitor than is the case with a conventional CRT monitor. However, in conventional projection CRT monitors1 the front projection screen is held in the apparatus by a metal bezel. When the monitors are assembled in an array as illustrated in 13, the mounting bezel, which is normally painted black, appears in the composite image as a black grid comprising horizontal lines 16 and vertical lines 18.As with the CRT video display wall, it is conventional when using video projection monitors to support the monitors on a plinth 20 which can be used to contain control electronics for separating the video signals for the respective monitors.

Figure 14 is a schematic diagram illustrating a side view of the video display wall 80 of Figure 13. The arrow 21 represents the normal viewing direction for the apparatus. The projection video display units 15 are stacked such that the active screen areas 12(0,0) - 12(3,3) face the viewing direction 21. Each of these display units comprises control circuitry and projection units (27) for projecting video images onto the screen at the front of the projection display unit. The control unit 24, which can be housed in the plinth 20 is used to control the separation of input video signals VI received from a broadcast system, or from a video tape recorder, or the like, into separate channels for display on the display screens 12 of the individual projection display units 15.

Figure 15 is a schematic plan view, in cross-section, of a typical conventional projection video display unit. Within the walls 106 of the display unit housing, the unit comprises three cathode ray tube projection monitors 82, 84 and 86 for projecting, respectively, one of the primary transmission colours red, green and blue. A light from the cathode ray tube projectors passes via a respective lens system 88, 90, 92 for focusing the projected light onto the active display area 12 of a screen 94 at the front of the device. The cathode ray tube projectors 82, 84 and 86 are controlled by control circuitry 96 in response to signals from a respective video bus 28.

The internal surfaces of the video projection unit, with the exception of the screen 94, are painted black to avoid undesired internal reflections.

Figure 16 illustrates the conventional arrangement for mounting the screen 94 on the front of the device. Conventionally, the screen, which is a two layer screen comprising an inner member 94I and an outer member 940 is held between first and second L-shaped members 100 and 102. These members 100 and 102, which are typically made of aluminium and are painted black, are held together by means of screws 104. The L-shaped members completely surround the edge of the screen. The assembly comprising the screen 94 and the L-shaped members 100 and 102, can then be slid onto the front of the wall 106 of the projection video display unit housing and secured thereto by means of screws 108.It will be appreciated, that with such an arrangement, the border area of the screen 12 at the edge of the front of the video display unit appears dark where the L-shaped metal members 100 and 102 are located. This border area could be illuminated in accordance with the invention by one of the types of arrangements described with reference to Figures 4 to 12.

Alternatively, however, Figure 17 illustrates one example of a mounting of the screen of a rear projection video display unit which enables the border area to be illuminated. Specifically, the screen 94 is held between a transparent light guide 110 which can be formed of an acrylic material and a wedge shaped member 112 which can be secured to the acrylic member by gluing, by means of screws, or by any other suitable means. The light guide 110 is shaped to enable light to be directed from within the body of the projection video display unit to the exterior thereof. The inner edge 120 of the light guide is directed such that it can collect light from the lens systems 88, 90 and 92 at the periphery of the housing of the video projection unit. The outer edge 122 of the light guide 100 is preferably formed as a lens for spreading light received within the light guide.The member 112 can be formed of a plastics material, or could be formed of metal. The member 112 is preferably of an opaque material and has a blackened surface 114 facing the interior of the video projection unit to avoid internal reflections. Likewise, a surface 116 of the light guide 110 is preferably also blackened to avoid internal refections within the projection monitor and to improve the light transmission characteristics of the light guide. An external surface 117 of the light guide is also coated to avoid leakage of light from the sides of the light guide 110.

The light guide 110 extends at least substantially, preferably completely, around the periphery of the screen 94 to form a frame therefor. A further wedge shaped member 118 is provided on the outside of the light guide 110. The wedge-shaped member 118, which can be secured to the light guide 110 by gluing, screwing or any other suitable manner, could be configured as a strengthening frame around the light guide 110. The structure comprising the screen 94, the transparent light guide 110 and the wedge shaped member 112 can be mounted on the end of the walls 106 of the housing of the video projection unit. The aforementioned assembly of the screen 94, the light guide 110 and the wedge 112 can be secured to the housing by means of screws 124.

Figure 18 illustrates a further example of means for mounting the screen 94 of a video projection unit in such a manner that light can be transmitted to the non-active screen area at the periphery of that screen. In particular, the screen 94 is bonded to a light guide 126 which can then be secured to the wall 106 of the housing of the video projection unit by means of screws 124. The light guide 126 is preferably provided with a wedge shaped member 128 corresponding to the wedge shaped member 118 of the arrangement of Figure 17. The internal and external surfaces 130 and 132 of the light guide are blackened or coated as required. The surface 120 provides the entry for light into the light guide 126. The light guide 126 extends substantially, preferably completely, around the periphery of the screen 94.

In both the examples shown in Figure 17 and Figure 18 the light guide is able to collect light for illuminating the periphery of the screen 94 without any significant modification to the remainder of the video projection apparatus. Specifically, because of the overscanning provided in typical video projection devices, significant stray light is provided at the periphery of the screen 94. This is collected by the collecting surface 120 of the light guides 110 or 126 in Figures 17 and 18 respectively. However, where the standard overscanning is insufficient to cover the surface 120 of the light guides 110 or 126, relatively minor corrections to the scanning or optics of the video projection device can be effected to increase the degree of overscanning.

As an alternative to mounting the wedge shaped members 118 and 128 on the light guides 110 and 126, respectively, these wedge shaped members could be formed as an integral part of the walls 106 of the video projection unit.

Although specific embodiments of the invention have been described hereinabove, it will be appreciated that many additions and/or modifications are possible within the scope of the invention.

For example, other means could be used to form the illumination elements for the interstitial regions. An illumination device could be located on the viewing side of the video display apparatus and arranged to project light in a controlled manner onto the interstitial regions to illuminate them.

As a further refinement, when active illumination elements are employed, the level of illumination of the grid could be adapted to take into account ambient light levels in the viewing area in combination with the video signal illumination levels. This would take account of the ambient light raising the dark level of the grid.

This could mean, for example, that at certain levels of ambient light illumination, the grid illumination may not be activated even when the picture has an average intensity greater than black. In such an embodiment, an ambient light sensor could be provided in the front wall of the video display apparatus (e.g. in the plinth 20) and could be connected to the illumination element control unit 44. The illumination element controller would then be made responsive to the ambient light level as well as to the video signal illumination level.

In the specific embodiments described above, the individual video display units are CRT or video projection monitors. However, the invention can also be applied where the individual video display units are implemented using other technology such as an active display panel (e.g. liquid crystal display).

Although in the above embodiments each of the video display devices comprises a screen mounted in a housing. in other embodiments, the screens and the associated control circuitry, etc., could be mounted directly in a supporting surface with apertures for the individual screens.

In some of the above embodiments, each active illumination element has been described as including a single illumination device.

However, it will be appreciated that each illumination device could be composed of a plurality of smaller illumination devices or device segments, with these being separately controlled.

In the specific embodiment illustrated in Figures 4 and 13, the video display apparatus comprises an array of 16 individual video display units. It will be appreciated, however, that the present invention is applicable where more or less individual display units are provided. For example it is equally applicable to an embodiment where an array of two by two, three by three, or indeed n by n display units is used. Moreover, the number of display units in the horizontal and vertical directions need not be the same, but the array could be provided by m by n units where and m and n are different integers. Also, the invention is not only applicable where rows and columns of display units are provided. It is also applicable where an array of display units is provided where the individual display units are arranged in another geometrical relationship.

Claims (18)

1. Video display apparatus for displaying an input video image, the video display apparatus comprising an array of display units, each of which includes a screen for displaying a respective sub-area of the video image, video control means for controlling the display of the respective sub-areas of the input video image on the respective screens and means for illuminating interstitial regions between adjacent screens.

2. Video display apparatus according to claim 1 wherein, in use, the intensity of illumination of a said interstitial region is dependent on an illumination intensity for at least an area of the input video image corresponding at least generally to the interstitial region.

3. Video display apparatus according to claim 1 or claim 2 wherein the colour of the illumination of a said interstitial region is dependent on an illumination colour for at least an area of the input video image corresponding at least generally to the interstitial region.

4. Video display apparatus according to claim 2 or claim 3 wherein the illumination of each interstitial region is dependent upon the average illumination over the displayed image.

5. Video display apparatus according to any one of claims 1 to 3 comprising active illumination means for illuminating an interstitial region, the video control means controlling the operation of the active illumination means in dependence upon an area of the input video image corresponding at least generally to the interstitial region.

6. Video display apparatus according to claim 5 wherein the active illumination means comprises at least one active illumination element located in a said interstitial region for illuminating that interstitial region.

7. Video display apparatus according to claim 5 wherein the active illumination means comprises at least one active illumination element located remotely from a said interstitial region and light guide means for directing light from the active illumination element(s) to the interstitial region for illuminating that interstitial region.

8. Video display apparatus according to any one of claims 5 to 7 wherein the video control means comprises an active illumination means controller which is responsive to the input video image to generate control signals for controlling the active illumination means for respective interstitial regions.

9. Video display apparatus according to claim 7 wherein the active illumination element comprises a further video display device comprising a further screen for displaying the input video image and wherein the light guide means comprises, for respective interstitial regions1 means for collecting light from a corresponding area of the further screen and for guiding said light to the interstitial region for illuminating that interstitial region.

10. Video display apparatus according to any one of claims 1 to 9 wherein the video control means is responsive to ambient light conditions to determine the illumination of the interstitial regions.

11. Video display apparatus according to any one of claims 1 to 3 comprising passive means for illuminating a said interstitial region by directing light from a video display unit adjacent to the interstitial region for illuminating that interstitial region.

12. Video display apparatus according to claim 11 wherein the passive illumination means is a light guide means forming part of the housing of a video display unit.

13. Video display apparatus according to claim 12 wherein the video display units are projection video display units and wherein the passive illumination means comprises a light guide forming at least part of a structure extending at least partially around the edge of a projection screen of a projection video display unit, the light guide forming part of a structure for mounting the projection screen in the projection video display unit and, in use, collecting overscanned light within the projection video display unit and directing the light so collected to a front surface of the video projection display unit around the projection screen.

14. A projection video display unit for use in an apparatus according to claim 13, the projection video display unit comprising a projection screen and a light guide forming at least part of a structure extending at least partially around the edge of the projection screen, the light guide forming part of a structure for mounting the projection screen in the projection video display unit and, in use, collecting overscanned light within the projection video display unit and directing the light so collected to a front surface of the video projection display unit around the projection screen.

15. Video display apparatus according to any one of claims 1 to 12 wherein a said display unit comprises a cathode ray tube.

16. Video display apparatus according to any one of claims 1 to 12 wherein a said display unit comprises an active display panel.

17. Video display apparatus substantially as hereinbefore described with reference to the accompanying drawings.

18. A projection video display unit substantially as hereinbefore described with reference to the accompanying drawings.