GB2276057A - Video test signal equipment - Google Patents

Abstract

A video test signal for testing video apparatus defines a substantially rectangular test image including a first test pattern along first and second opposite edges of the image for testing display characteristics at each of a plurality of respective positions along the first and second edges, and a second test pattern along third and fourth opposite edges of the image for testing display characteristics at each of a plurality of respective positions along the third and fourth edges. A preferred example of a test image includes a set of nested areas of different luminance and/or chrominance values extending from each corner of the image towards its centre. The test signal is particularly useful in aligning individual display units in a wide wall display, and to minimise the luminance/colour mismatch between adjoining screens. <IMAGE>

Description

TESTING VIDEO EQUIPMENT The invention relates to methods and apparatus for testing video equipment and a video test signal for use therewith.

As with other types of technology, it is desirable to test the performance and set-up of video equipment. In the case of video equipment for use in broadcast and professional applications, a series of rigorous tests have been established. For example, a number of standard video test signals can be applied in order to test the equipment. The conventional test signals take the form of full-field images. Examples of such images are vertical colour bar images, pulse and bar images, pedestal (grey scale) images, modulated staircase (e.g. 5-step) images, and multiburst (frequency response) images.

The conventional test signal patterns are designed for setting up the parameters of an individual video display unit used in isolation in accordance with a standard and they are generally very effective for this purpose. In normal use, however, a video display unit set up using the conventional test patterns is not used with another video display unit where the exact set-up of each video display unit is critical. Accordingly, slight differences from the standard go unnoticed. However, problems can be encountered with the conventional test signals when testing the set-up and mutual alignment of individual video display units in applications where a plurality of video display units are arranged in close proximity to one another as is the case, for example, with a video wall.

In a conventional video wall a plurality of video display units are arranged 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.

Considerable difficulties can be encountered in setting up the various display parameters, such as geometric alignment, luminance, contrast and colour balance of the individual display units so that the complete picture is faithfully reproduced on the array of individual video display units.

As is generally known, disturbing effects can be experienced, for example, at a television retailer where different television receivers on display are set up differently. Even small geometric misalignments, differences in colour balance, etc. on the individual television receivers can be very noticeable to a viewer.

Misalignments, colour differences etc. can be even more noticeable in the case of a video wall where the individual video display units display different parts of the same image.

Moreover, it is also well known that the display parameters of an individual display-unit can change with time, as a result of temperature changes, ageing of the unit and so on. The changes vary from unit to unit. Accordingly, even if the display parameters of a plurality of video display units in an array were initially matched well, with time the individual video display units can drift out of alignment such that it is necessary to readjust them in order that the display parameters may be matched once more.

Accordingly, it is an object of the invention to mitigate the problems of setting up a plurality of video display devices.

In accordance with a first aspect of the present invention, there is provided a video test signal for testing video apparatus, the video test signal defining a substantially rectangular test image, the substantially rectangular test image including a first test pattern defined along first and second opposite edges of the image for testing a plurality of display characteristics at each of a plurality of respective positions along the first and second edges, and a second test pattern defined along third and fourth opposite edges of the image for testing a plurality of display characteristics at each of a plurality of respective positions along the third and fourth edges.

A video test signal in accordance with the invention facilitates the setting up of the individual video display units in sn array of such units. In particular, by providing a video test signal which defines a test image having corresponding test patterns along opposite edges, there is then a correspondence between the test patterns on adjacent video display units in both the vertical and horizontal directions within such an array of units. This means that a comparison of the display of different display parameters on adjacent display units may be made directly on immediately adjacent display regions.

Preferably, the test image includes, adjacent each corner thereof, a test region having the same colour and/or luminance value.

By arranging that a region adjacent to each corner of the test image has the same display parameters, the mutual alignment of the display parameters of four video display units meeting at their respective corners is facilitated. Progressively setting-up adjacent display units enables matching of the display parameters of each video display unit in an array of such units.

Also, the first test pattern preferably comprises a first sequence of test regions with respective display characteristics, and the second test pattern comprises a second sequence of test regions with respective display characteristics. By providing distinct test regions aligned as a result of the first sequence on the first and third edges and as a result of the second sequence on the second and fourth edges, the set-up of the display parameters of video display units in an array can be facilitated by the comparison of corresponding regions on adjacent video display units in the horizontal and vertical directions. The same sequence of test regions may be provided in the first and second test patterns.

In a preferred embodiment of the invention, the first test pattern includes the first sequence of test regions twice, the first time in one order and the second time in the reverse order, and the second test pattern includes the second test sequence twice, the first time in one order and the second time in the reverse order.

Preferably, at least in the region of the edges of the test image, the test image is symmetrical about first and second orthogonal image axes which are substantially parallel to a respective pair of the sides of the test image. This helps in setting up the colorimetric parameters of the display device along the whole edge of the image.

Each sequence of test regions preferably comprises a predetermined sequence of blocks of different luminance and/or chrominance values extending from each corner of the image along an edge of the image. Preferably each block extends in a direction substantially perpendicular to the edge of the image along which it is aligned up to a diagonal extending between the corners of the image.

This arrangement maximises the length of the lines between adjacent display regions in directions parallel to edges of the image. This helps in setting up the geometric parameters of the display devices.

In a preferred video test signal in accordance with the invention, the test image comprises, extending from each corner thereof towards the centre thereof, a set of nested areas of different luminance and/or chrominance values comprising a first area adjacent the corner and a sequence of bounding areas, the first of which is adjacent to and partially surrounds the first area and the remaining ones of which are adjacent to and partially surround a respective other bounding area.

In a first preferred example of a video test signal the first area is rectangular and the bounding areas are L-shaped. In a second preferred example of video test signal, the first area is a quarter of a circle or ellipse and the bounding areas are arc shaped. In a further example of a video test signal according to the invention, the first and second test patterns are defined by a plurality of diagonal test areas.

In addition to the basic test patterns described above, the video test signal can include a substantially rectilinear grid defined on the basic test patterns.

The video test signal preferably corresponds to a video frame for display on a video display unit.

The invention also provides a compound video test signal for testing an array of video display units, the compound test signal defining a compound test image comprising an array of test images corresponding to the test image defined by a video test signal as defined above. The use of a compound test signal enables the testing of circuitry for splitting a video image such as is provided for controlling a conventional video wall.

The invention further provides a video system comprising a plurality of video display units, test signal generation means for generating a video test signal as defined above for defining a test image, means for displaying the test image by each of the plurality of video display units and means for adjusting the display parameters of the video display units.

The invention further provides a method of setting up a plurality of video display units comprising displaying test image derived from a video test signal as defined above on each of the video display units, and adjusting the display parameters of the individual video display units until the display characteristics of the video display units are matched.

The invention will be described hereinafter, by way of example only, 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 a conventional video display apparatus comprising an array of projection video display units; Figure 5 is a schematic representation of the display of an image on a video wall comprising a plurality of individual video display units; Figure 6 is a monochrome representation of a conventional test image;; Figure 7 illustrates the luminance values of respective bars of the test image of Figure 6; Figure 8 represents the display of a test image as illustrated in Figure 6 on a plurality of video display units in a video wall; Figure 9 is a monochrome representation of a first example of a test image derived from a video test signal in accordance with the invention; Figure 10 represents the display of the test image of Figure 9 on a plurality of video display units in a video wall; Figure 11 is a monochrome representation of a second example of a test image derived from a video test signal in accordance with the invention; Figure 12 is a monochrome representation of a third example of a test image derived from a video test signal in accordance with the invention;; Figure 13 is a monochrome representation of a fourth example of a test signal derived from a video test signal in accordance with the invention; Figure 14 is an example of a simplified test image for a video test signal in accordance with the invention; and Figure 15 is a monochrome representation of a compound test image derived from a compound test signal.

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 of video display units 14. In the present example 16 video display units are shown in an array of 4 x 4 units. However, the array of video display units may comprise any number of units in an m x n array, where m and n are integers which may be the same or different. Also, the array need not be rectangular, and can be shaped (e.g. L-shaped) for a particular application. 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 is mounted on a plinth 20 to support the array above the ground. The plinth 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 normal viewing direction for the apparatus. 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 V 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 switch 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 they receive 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 V is a 625 line signal and each video display unit is able to resolve 625 line video) then the effect of the video switch 24 and the individual video control units 26(0,0) - 26(3,3) is, in normal operation, 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.

In normal operation, the video switch 24 also causes 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 32 which decodes the received signal format for processing. Typically, the decoder 32 converts the received signal from composite to component form. 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. Each field of input video data is stored in each of the 16 frame stores.

The video data from the frame stores FS(O,O) - FS(3,3) are 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) - 14(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. In the present case, as there are 16 video display units, the data that are read out from the frame stores for each of the video display units correspond generally to 1/16th of the information stored in each frame store, at least in normal operation for the display of a complete image over the 16 video display units.

The video data read out from the frame store for a particular video display unit correspond 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 from the frame store FS(O,O) corresponding generally to the top left hand 16th of the input video image is read out.

In practice, the data read out will not correspond exactly to the top left hand 16th of the input video image to take account of the margin areas between individual display units, the degree of overscanning of the cathode ray tube required and corrections for nonlinearity. 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. Alternatively, or in addition, the alignment can be performed by the control circuitry of the individual video display units. The control of the alignment can be carried out by the user using controls on the video display units, or using a remote controller to allow the displayed image to be viewed as changes are made.

Although the normal operation of the video switch 24 is described above, where 1/16th of the input image is directed to each video display unit, conventional video walls are operable in many different modes. Thus, for example, the input image may be displayed on only a sub-set of the video display devices. It could, for example be displayed on each of the video display units by selective reading of the data from the frame stores.

For testing purposes during the setting up of the display parameters of the individual display units, as will be described later, the mode of operation where the whole of a single input image is displayed on each of the video display units within the wall can be used. Alternatively a compound test signal could be generated and this signal could be split by the control circuity 24 before being passed to the individual video display units.

Figure 4 is a schematic front view of a further example of a conventional video wall 40 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 although it does not extend right to the edge of the monitor. This is because the front projection screen is held in the apparatus by a bezel. When the monitors are assembled in an array as illustrated in Figure 4, 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. The control electronics can be substantially the same as that illustrated in Figure 3.

Figure 5 represents, in schematic terms, the display of a single input image II on a video wall such as the video wall 40 of Figure 4. In normal operation, each of the 16 video display units 15(0,0) - 15(3,3) in the video wall displays a respective 16th of the input video image on its screen 12(0,0) - 12(3,3).

With such an array of sub-images, the setting up of the individual video display units is very critical in order that the reproduced image is as faithful to the original input image as possible. It will be appreciated that a very slight inaccuracy in the geometric parameters of adjacent video display units could cause misalignments of the lines which should be continuous across the boundaries between individual video display screens. Likewise, even small differences in the luminance, contrast or colour reproduction of adjacent video display units will be very noticeable. Thus, the parameters of the video display units which need to be set up include their geometry and, their colorimetry (i.e., their luminance and contrast and colour settings). Controls for adjusting these parameters are typically provided on each video display unit and/or on a remote control unit.However, they could be provided centrally, for example at a control console.

In order that the display quality can be uniform across the whole of the video display wall, each image on the individual display unit must match every adjoining unit at least along the adjoining edges and preferably, of course, over the whole image. In order to provide such adjustment, a test pattern is required that exercises the variable parameters of the video display units. For example, testing the colorimetry requires a test signal which traverses the operating range of the video display unit from black to white.

Conventionally, for setting up an individual video display unit, some form of grey scale or colour bar test signal is used which contains illuminance level varying from black to white, either linearly or in steps. Typically, a series of grey scale bars of varying luminosity is used as illustrated in Figure 6. The different degrees of shading represent different luminosity values.

Figure 6 is a schematic representation of a set of bars 0 to 5 of increasing luminosity. Bars 0, 1, 2, 3, 4, and 5 are, respectively, 0%, 20%, 40%, 60%, 80%, and 100% luminosity bars as illustrated in Figure 7. In other words, bar 0 is the black level for the video display unit and bar 5 is the white level for the video display unit, with bars 1 - 4 representing stepped transitions in grey scale between those values. It will be appreciated by those skilled in the art that the choice of six bars in the present example is merely for purposes of illustration, and that other numbers of bars are also used in conventional test signals. Moreover, the bars, may, in addition to the grey scale, also contain colour information. Thus, for example, eight bars 0 to 7 may be used to display the colours black, blue, red, magenta, green, cyan, yellow and white.In many applications, however, monochrome test patterns are sufficient for setting up the colour balance of a video display unit, as incorrect colour balance causes easily noticeable changes in hue.

However, conventional test signals such as the example shown in Figure 6 are designed for setting up a single video display unit.

If such a signal is applied individually to each unit in a video wall, the result is as shown in Figure 8. Thus, matching of the variable parameters can be achieved across the horizontal boundaries HB1, HB2, and HB3. However, the matching of the variable display parameters cannot be tested across the vertical boundaries VB1, VB2 and VB3 as there is no continuity across these boundaries. The invention seeks to overcome these problems.

Figure 9 is a schematic representation of a first example of a test image corresponding to a test signal in accordance with the invention. This example of a video test signal defines a substantially rectangular image having an upper horizontal edge UHE, a lower horizontal edge LHE parallel to the upper horizontal edge, and a left-hand vertical edge LVE and right-hand vertical edge perpendicular to the horizontal edges. The video test image illustrated in Figure 9 includes a set of nested areas AO - A5 of different luminance values extending from each corner of the image towards its centre. A first area AO is defined adjacent each corner.

A sequence of bounding areas Al - A5 then extend towards the centre of the image C. The first bounding area Al is adjacent to and surrounds the first area AO and the remaining bounding areas (A2 - A5) are adjacent and surround a respective other bounding area (Al - A4).

As illustrated in Figure 9. the first area AO is substantially rectangular and the bounding areas (Al - A5) are Lshaped. The areas AO - A5 define, along each edge of the test image, a test pattern comprising a sequence of test regions with respective display characteristics. The different shading in the respective areas illustrate different display characteristics (in this case luminosity). The particular test pattern used in this example repeats, along each edge of. the image, a sequence of test regions (A), the first time in one order (AO - A5) and the second time in the reverse order (A5 - AO).

In this example the video test image is symmetrical about a vertical axis VA which is parallel to and centrally located between the left-hand and right-hand vertical edges, LVE and RVE. It is also symmetrical about a horizontal axis which is symmetrical about a horizontal axis which is parallel to and central located between the upper and lower horizontal edges, UHE and LHE.

Thus, rather than a series of bars, the image corresponding for the preferred test signal of Figure 9 represents a series of areas which radiate from each of the corners of the video image. Areas AO, Al, A2, A3, A4 and A5 represent, respectively, areas having luminosity values at levels 0%, 20%, 40%, 60%, 80% and 100%. Other numbers of nested areas could be used. Also, the areas can additionally or alternatively provide a colour scale. Thus, for example eight nested areas AO, Al, A2, A3, A4, A5, A6 and A7 could provide a luminance and a colour scale with respective areas defining black, blue, red, magenta, green, cyan, yellow and white. In contrast to the test signal of Figure 6, however1 the video test signal of Figure 9 enables a plurality of display characteristics to be tested along each edge of the image.

Figure 10 represents the application of the test signal of Figure 9 to each video display unit in a 4 by 4 video wall. It can be seen that a good comparison of the display parameter adjustment of adjacent video display units can easily be made in both the horizontal and vertical directions due to the juxtaposition of like test areas on those adjacent units. In particular, it will be noted that as the same colour or grey scale (luminosity) value is located in all four corners of each individual image, the set-up of four video display units which meet at each corner can readily be compared.

As well as enabling the comparison of colour, luminance and contrast settings of adjacent display units in the vertical and horizontal directions (note that, as mentioned above, even a monochrome test signal can be used for testing correct colour balance), the video test signal of Figure 9 also facilitates the comparison and alignment of the geometric parameters of adjacent video display units. Even small differences in the geometric alignment of the adjacent video display units will be apparent from a mismatch between the adjacent test areas of the test signal pattern.

Figure 11 is a monochrome representation of a third example of a test image for a video test signal in accordance with the invention in which, rather than a combination of a rectangular area AO and a set of L-shaped areas radiating from each corner, the test image includes a first area formed by a quarter of a circle CAO in each corner of the image, with a series of arc-shaped areas CA1 - CA4 radiating towards the centre C of the image and a central area CA5.

As with the example of Figure 9, the shading of the areas represents different display characteristics (colour and/or luminance values).

A substantially rectilinear grid RG can be superimposed on the test pattern of circles to aid the mutual geometric alignment of adjacent video display units. When four video display units meet at their respective corners, the four quarter circles on the adjacent units should join to form a complete circle. The creation of circular patterns across the boundaries between the video display units provides a good test of the geometric alignment of the units. The human eye is very sensitive to even small distortions in circular features. The use of circular patterns in the corners of the images with the same colour and/or luminance at each said corner and an overlying grid provides a particular effective test of the geometric alignment of the units.The different colour and/or luminance parameters of the respective colour areas provides a good test of the colorimetric alignment of the units.

Figures 12 and 13 illustrate two further examples of test images derived from video test signals in accordance with the invention. As in the earlier Figures, the different shading of respective areas represent different display parameters (colour and/or luminance values). It will be appreciated the test image of Figure 12 provides, close to each horizontal edge, a first matching test pattern and close to each vertical edge, a second matching test pattern; likewise the test image of Figure 13. The examples of test image patterns shown in Figures 12 and 13 provide an overall pattern of diamond shapes when displayed on the array of video display units.

Once again, the test pattern along each edge of a video display unit should align with the counterpart pattern on the adjacent edge of an adjacent video display unit, with the same display parameter (colour and/or luminance) in each corner of the image.

Preferably, the test signal pattern defines a video frame comprised of two fields of interlaced video. It can be generated electronically by a general purpose video signal generator, or by a dedicated generator. The generator could, for example, be a solid state storage device with appropriate addressing means for outputting the video test signal. The video test signal could also be captured by a video camera, scanner or the like from a test card. The generated video test signal could be directly applied for display, or could be stored on a conventional video tape recorder, or other suitable storage means for later use. Thus the test signal can be stored as an electrical signal, a magnetic signal or as an optical signal on appropriate recording media, and be reproduced as an electrical signal for generating the test image.In particular, the test signal pattern could be stored internally to the control circuitry 26 of each of the video display units and be output onto the screens of the display units in a test mode. In this case in the test mode of the video display units, although the individual video display units are arranged to use the internally generated test signals, the control circuitry 24 is used to generate synchronisation signals for synchronising the display of the test images. Suitable video image memory and control circuitry, as well known in the art, could be provided for this purpose. Alternatively, the video test signal can be applied via the control electronics 24, 26 illustrated in Figures 2 and 3 for display on the individual video display units of the video wall. In this case, it is possible to test the overall operation of the video wall system.

The method of testing the individual video display units of the video wall includes the steps of: - displaying a video test signal in accordance with the invention on each of the video display units of the video wall; - adjusting the display parameters of the individual display units until the desired uniformity of display is achieved over the video wall.

Although in examples described above, the test signal is representative of a pattern which tests many display parameters of the video display unit, the test signal pattern may be chosen to only test selected display parameters of each video display unit. Thus, for example, Figure 14 illustrates a simplified test pattern which merely includes areas with two different luminance values for testing the colorimetric and geometric alignment of the video display unit.

In the above described method of testing video display units in an array of such units, an individual test signal is applied to each video display unit for generating a test image. Alternatively, however, a compound test signal could be applied to the control circuitry 24, which compound test signal is then split to generate a plurality of test signals for application to respective video display units in the array of those units. Figure 15 illustrates such a compound test image which can be generated from a compound test signal.Then, using the approach illustrated in Figure 5, this compound test signal would be split by the control circuitry 24 into sub-images as represented by the vertical dot dash lines VS and the horizontal dot dash lines HS in Figure 15 and then applied to the control circuitry 26 for display on the screens of the units in the array of such units. It will be appreciated that the compound test signal is not limited to the generation of a compound image as illustrated in Figure 15, but could be applied to the generation of any of the test images discussed above, or indeed any test signal having the characteristics necessary in accordance with the invention.

As with the individual test signals, the compound test signal can be generated electronically by a general purpose signal generator, or by a dedicated generator and could be applied directly as a video input VI to the control circuitry 24, or could be provided from an intermediate video storage means. Alternatively, the compound video signal could be generated internally to the control circuitry 24.

The use of a compound test signal enables not only the individual display units to be tested, but also the control circuitry 24.

In the above described embodiments, a static test signal is applied to the video display units. However, the test signal applied to the video display units could be arranged to be changed at discrete intervals so that the display parameters displayed in each of the test areas could be changed. Thus, for example, where a grey scale is displayed in respective test areas, the grey scale values displayed in any particular area could be arranged to cycle from white to black or vice versa, or in a random sequence. The changes applied to one video display unit will simultaneously be applied to the other video display units in the array. Thus, it is possible to compare different colorimetric values over the whole edge of the display units and also to test dynamic characteristics of the video display units.Such a dynamic test operation is preferably performed using a compound test signal which is split before being applied to the individual video display units so that the timing of the changes is synchronised. The changing test signal can be provided in any appropriate manner, for example by recording a sequence of test signals on a video tape and then replaying the video tape at the input VI of the control circuitry 24.

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, although in the examples described above the pattern of test areas is symmetrical about the horizontal and vertical axis, this need not be the case. However, the video test signal should generate a test image which, when displayed on a first video display unit, and on video display units surrounding that first video display unit in an array of such units, has a pattern of test areas along the edges of the first video display unit aligned with the pattern of test areas along the adjacent edges of the surrounding video display units. If the same display parameters (colour and/or luminance) are displayed in each corner of each image, this provides a particularly effective method of adjusting the colorimetric parameters of four adjacent video display unit as the same colorimetric values should be displayed on each of those units.

Although, in the examples described above, a stepped transition between test areas is provided, the video test signal could be arranged to generate a sawtooth or sliding change in display parameters. In such a case, however, it is preferred that a grid is displayed on the basic test pattern to aid the geometric alignment of the video display units. Indeed, although the superposition of a rectilinear grid is only shown for the example of Figure 12, such a grid could be included in any other example of the invention.

Also, although in the examples described above, the luminosity of adjacent display areas increases sequentially from white to black, so that black is displayed in the corner of each image (with the exception of Figure 13), this need not be the case. The display parameters (colour and/or luminance) can be provided in any sequence along the edges of the video display units. In particular, it is not necessary that black or white be displayed in the corners of the test image. Any colour and/or luminosity value could be displayed there.

However, as explained above, the same colour should, preferably, be displayed in each corner of the test image.

Although, in the above examples, the sequence of test areas is displayed twice along each edge of the test images with the order being reversed, this need not be the case. Any number of repetitions of the sequence of test areas can be provided along each edge of the test image as long as the test image, when displayed adjacent further examples of the same test image, enables the correct alignment of corresponding test areas to be provided.

It will appreciated that the invention is not limited to the specific images described above. Thus, for example, instead of circular test areas as illustrated in Figure 11, ellipsoidal test areas could be generated. In the examples shown in Figures 12 and 13, diamond shaped areas which subtend 900 at each corner of those diamond shaped areas could be employed rather than the particular shape shown.

Indeed, many other modifications and/or alternatives to the specific examples herein can be envisaged.

It will also be appreciated that although the invention illustrates video test signals for producing test images in standard definition television format, it will be appreciated that such test areas could be provided in proportions of high definition television or in any other proportion as required for the particular video display units to be tested. The invention is not limited to the display of interlaced television images, but is equally applicable to other raster-scanned applications, for example computer generated images, whether interlaced or not.

Although a video test signal in accordance with the invention is specifically designed for setting-up individual video display units in an array of video display units such as a video wall, it will be appreciated that it could be used for setting up video display units in any situations where video display units are to be viewed in close proximity, for example in a television studio control room. Indeed, a video test signal in accordance with the invention could be used for setting up a single video display unit. It will be appreciated that the invention is applicable to the testing of video display units in any video technology, whether that be CRT based, display panel based or indeed any other video display technology.

Claims (24)

1. A video test signal for testing video apparatus, the video test signal defining a substantially rectangular test image1 the substantially rectangular test image including a first test pattern defined along first and second opposite edges of the image for testing a plurality of display characteristics at each of a plurality of respective positions along the first and second edges, and a second test pattern defined along third and fourth opposite edges of the image for testing a plurality of display characteristics at each of a plurality of respective positions along the third and fourth edges.

2. A video test signal according to claim 1 in which the test image includes, adjacent each corner thereof, a test region having the same colour and/or luminance value.

3. A video test signal according to claim 1 or claim 2, wherein the first test pattern comprises a first sequence of test regions with respective display characteristics, and the second test pattern comprises a second sequence of test regions with respective display characteristics.

4. A video test signal according to claim 3, wherein the first test pattern includes the first sequence of test regions twice, the first time in one order and the second time in the reverse order and the second test pattern includes the second test sequence twice, the first time in one order and the second time in the reverse order.

5. A video test signal according to any one of the preceding claims wherein, at least in the region of the edges of the test image, the test image is symmetrical about first and second orthogonal image axes substantially parallel to a respective pair of sides of the test image.

6. A video test signal according to any one of claims 3 to 5, wherein each sequence of test regions comprises a predetermined sequence of blocks of different luminance and/or chrominance values extending from each corner of the test image along an edge of the test image.

7. A video test signal according to claim 6 wherein each block extends in a direction substantially perpendicular to the edge of the test image along which the test pattern is aligned up to a diagonal extending between the corners of the test image.

8. A video test signal according to any one of the preceding claims wherein the test image comprises, extending from each corner thereof towards the centre thereof, a set of nested areas of different luminance and/or chrominance values comprising a first area adjacent the corner and a sequence of bounding areas, the first of which is adjacent to and partially surrounds the first area and the remaining ones of which are adjacent to and partially surround a respective other bounding area.

9. A video test signal according to claim 8 wherein the first area is substantially rectangular and the bounding areas are L-shaped.

10. A video test signal according to claim 8 wherein the first area is formed by a quarter of a circle or ellipse and the bounding areas are arc shaped.

11. A video test signal according to any one of claims 1 to 6 wherein the first and second test patterns are defined by a plurality of diagonal test areas.

12. A video test signal according to any one of the preceding claims wherein the substantially rectangular image comprises a substantially rectilinear grid pattern.

13. A video test signal according to any one of claims 1 to 12 which corresponds to a video frame.

14. A compound video test signal for testing an array of video display units, the compound test signal defining a compound test image comprising an array of test images corresponding to the test image defined by a video test signal according to any one of claims 1 to 13.

15. A video system comprising a plurality of video display units test signal generation means for generating a video test signal according to any one of claims 1 to 13 for defining a test image, means for displaying the test image by each of the plurality of video display units and means for adjusting the display parameters of the video display units.

16. A video system according to claim 15 comprising video control means for distributing a video test signal according to any one of claims 1 to 13 for display of the test image by each of the video display units.

17. A video system according to claim 15 wherein the test signal generation means is integral in each video display unit, the video system comprising video control means supplying synchronising signals to each video display unit to synchronise the display of the test image by each video display unit.

18. A video system comprising a plurality of video display units, compound test signal generating means for generating a compound video test signal according to claim 14 for defining a compound image, means for splitting the compound test signal into constituent test signals, each of which defines a test image corresponding to the test image defined by a video test signal according to any one of claims 1 to 13 and for applying the constituent test signals to respective video display units for display of the test images and means for adjusting the display parameters of the video display units.

19. A method of setting up a plurality of video display units comprising displaying test image derived from a video test signal according to any one of claims 1 to 13 on each of the video display units. and adjusting the display parameters of the individual video display units until the display characteristics of the video display units are matched.

20. A method setting up a plurality of video display units comprising displaying test images derived from a compound video test signal according to claim 14 on each of the video display units, and adjusting the display parameters of the individual video display units until the display characteristics of the video display units are matched.

21. A method according to claim 19 or 20 comprising sequentially applying test images having different display parameters.

22. A video test signal for testing video apparatus substantially as hereinbefore described with reference to the accompanying drawings.

23. A video system substantially as hereinbefore described with reference to the accompanying drawings.

24. A method of setting up a plurality of video display units substantially as hereinbefore described with reference to the accompanying drawings.