WO2005083557A1

WO2005083557A1 - Multi-screen display and method of updating screen image data for e.g. video wall

Info

Publication number: WO2005083557A1
Application number: PCT/GB2005/000683
Authority: WO
Inventors: Timothy Martin Coker
Original assignee: Inputpearl Limited
Priority date: 2004-02-24
Filing date: 2005-02-24
Publication date: 2005-09-09
Also published as: GB0404087D0

Abstract

Disclosed is a display having a plurality of pixel arrays for displaying an image in a series of frames, each frame of a pixel arrag being displayed during a frame period. The display also has a plurality of driver means, each for control ling a respective pixel array by addressing pixels in the respective pixel array. Each driver means is arranged to address as required a first subset of pixels in a said pixel array during a first part of said frame period, and to address a s required a second subset of pixels in a said pixel array during a second part of said frame period. The driver means for a pixel array has a memory buffer cap ac by lower than the memory buffer capacity that would be required to address a11 of the pixels in the array of a frame at the same time.

Description

MULTI-SCREEN DISPLAY AND METHOD OF UPDATING SCREEN IMAGE DATA FOR E.G.VIDEO WALL

The present invention relates to a display. Particularly, but not necessarily exclusively, it relates to a large display such as may be used in public places for displaying a moving or fixed image. Large screens are used for a variety of applications. For example, screens may be installed in a sports stadium to show video or television pictures or images, or to display appropriate information such as match or event statistics. Such screens may also be employed at outdoor events such as rock concerts or festivals to display moving images to large audiences. Screens may be temporarily rigged on a stage or mounted on a truck, for example. Such screens may also be used as advertising hoardings or billboards. Such displays may be implemented using a number of different technologies. In some circumstances, it is possible to use projection to display images onto a large screen, e.g. in the same way as in a cinema or movie theatre. However, such technology generally is only of use where the ambient light levels are low. It is also possible to construct large screen displays using arrays of conventional television monitors or displays, e.g. cathode ray tubes, which screens are sometimes referred to as "video walls" . Such screens are usually not very bright and so such technology also tends only to be of use where the ambient light levels are low. Furthermore, there are inevitably gaps between the monitors or displays, and this significantly detracts from the overall appearance and picture quality of the screen. There are known large display screens.^' A large liquid crystal display (LCD) is disclosed in WO 03/016989. This display is made up of an arrangement of modules. Each module provides a number of liquid crystal pixels. Each pixel modulates and transmits light from a light source disposed behind the pixel . By appropriate control of the state of each pixel, an image can be displayed. Typically, each pixel is made up of red, green and blue sub-pixels to provide a full colour image. The state of each sub-pixel is controlled by a driver means¹ that addresses each sub-pixel to control the amount of light from the light source that each sub-pixel absorbs. Also known are large display screens that use light-emitting diode (LED) pixels. Such displays differ fundamentally from LCDs in that the light is emitted by and not transmitted by the pixels. Thus, LED displays do not have light sources that are independent of the pixels. Again, typically, each pixel is made up of red, green and blue sub-pixels to provide a full colour image. The brightness of each sub-pixel is modulated by altering the electrical drive to each sub-pixel. Known displays display images (particularly moving images) as a series of frames. Each frame is displayed for a frame period and all of the pixels are addressed (or are at least addressable) by a respective driver means during that frame period. In a general aspect, the inventors have realised that it is possible to address different subsets of pixels at different times during the frame period. This can give rise to efficiency savings in terms of the capacity of the driver means used to address the pixels. Preferably, in a first aspect, the present invention provides a method of operating a display, the display having: a plurality of pixel arrays for displaying an image ; and a plurality of driver means, each for controlling a respective pixel array by addressing pixels in the respective pixel array, wherein an image is displayed as a series of frames and each frame is displayed for a frame period, wherein for each pixel array the method includes the steps of : said driver means addressing as required a first subset of pixels in said pixel array during a first part of said frame period; and said driver means addressing as required a second subset of pixels in said pixel array during a second part of said frame period. In another aspect, the present invention provides a display having: a plurality of pixel arrays for displaying an image in a series of frames, each frame being for display for a frame period; and a plurality of driver means, each for controlling a respective pixel array by addressing pixels in the respective pixel array, wherein the driver means is arranged to address as required a first subset of pixels in said pixel array during a first part of said frame period, and to address as required a second subset of pixels in said pixel array during a second part of said frame period. Using the invention, it is possible to address one subset of pixels separately from another subset of pixels in the same pixel array, using the same driver means. Preferred and/or optional features will now be set out.' These are applicable either to the first or to the second aspect unless the context demands otherwise. The features set out below may be applied to the first and/or second aspects independently or in any combination. Preferably, the display is arranged so that it is possible to address all of the pixels in the first and second subsets of pixels at least once during the frame period. However, it may be the case that, for a particular image to be displayed, some of the pixels in the first and/or second subset need not be addressed in a particular frame period. Typically, this depends on the type of pixels that are used in the display. Some types of pixels need to be addressed only in order to change their state. Other types of pixels need to be addressed in order either to change their state or in order to maintain their state. The pixels may be any suitable type of addressable pixels that are capable of modulating light (e.g. either emitted or transmitted) in order to display an image. For example, the pixels may be light-emitting diode (LED) pixels. However, it is preferred that the pixels are liquid crystal (LC) pixels. In that case, the display typically includes at least one light source, the light source providing light for variable modulation and transmission by the pixels. The pixel array may include one or more further subsets of pixels, so that there are three or more subsets of pixels. These subsets of pixels may be addressable by the driver means at different times during the frame period. The arrangement of pixels into subsets within the pixel array need not be fixed. For example, the selection of pixels for the first subset may be altered by suitable control of the driver means. The ability to change the subsets of pixels in this way can be a useful tool in adjusting the display in order to avoid or remove observable artefacts that may be unintentionally included in the displayed image. Such artefacts may, for example, be included by a particular selection of pixels for one of the subsets . Preferably, the invention allows the driver means to address the first subset of pixels and then, having completed the addressing of the first subset of pixels, to address the second subset of pixels. In this way, it may only be necessary for the driver means to have the capacity that is necessary to address the largest of the subsets (having the largest number of pixels) . Preferably, therefore, the driver means has a capacity lower than the capacity that would be required to address all of the pixels in the array at the same time. Put another way, the driver means may have a capacity for storing information relating to the required states of the pixels that is less than the capacity that would be required for storing information relating to all of the pixels at the same time. In this way, driver means of lower capacity than would normally be required may be used, leading to an efficiency saving. Preferably, each pixel has two or more sub-pixels.

In that case it is typical that each sub-pixel requires addressing at least once during the frame period (depending on the type of pixels or sub-pixels, as discussed above) . More preferably, each pixel has at least one red sub-pixel, at least one green sub-pixel and at least one blue sub-pixel. Typically, some or all of the sub-pixels are individually addressable by the driver means . In effect, each sub-pixel may be addressed as though it were a pixel, in terms of forming subsets of pixels in the pixel array for addressing by the driver means. Each sub-pixel array may be addressable by a respective driver means. For example, the display may include a driver means for the red sub-pixels, a driver means for the green sub-pixels and a driver means for the blue sub- pixels . Preferably, the display is a modular display, formed of an arrangement of display modules. Each module may include one or preferably more of the pixel arrays . Preferably, the display is a large screen display. The screen may have an area of more than 3 m², more than 5 m² or more than 10 m². Preferably, the screen has an area of at least 15 m². Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 shows schematically how video data is distributed to modules and pixel arrays in an embodiment of the invention. Fig. 2 shows schematically how a module controller separates the video data into subsets before passing to a driver card in an embodiment of the invention. Fig. 3 shows further schematic detail of how the driver card updates the separate pixel subsets in an embodiment of the invention. Fig. 4 shows an outline timing diagram for a driver card illustrating a problem to be addressed by an embodiment of the invention. Fig. 5 shows an outline timing diagram for a driver card operating according to an embodiment of the invention. Fig. 6 shows schematically an alternate embodiment that allows for random and/or dynamic choice of pixel/data subset. In the preferred embodiments of the invention, a display system (or display screen) is formed from an array of modules. The array of modules is controlled by a system controller (not shown) , the system controller sending image data (also referred to as -video data) to each module for display. Fig. 1 shows the schematic layout of part of a display module according to an embodiment of the invention. The module has a module controller 14, a pixel driver 15 and a pixel array 16. In this example, the pixels are liquid crystal pixels and so the pixel driver is an LCD driver and the pixel array is an LCD. For reasons of clarity only one pixel array and pixel driver card are shown, although actual embodiments may include more than one of each. Fig. 1 illustrates how video data is passed to the pixel arrays within a module. In this figure video data 11 is passed to the module controller 14 from a PC or similar means which generates data for all modules in the screen. This link can be a standard data link such as RS485, but there are several alternatives known to those skilled in the art. The module controller 14 manipulates this video data as necessary, for example where the module has more than one LCD driver card, the module controller will separate out the data for each card. The appropriate data 12 is then passed to the LCD driver card

15. This link between cards is generally very short and simple cabling can be used rather than a full communications protocol such as RS485. The LCD driver card 15 then uses the video data 12 to generate pixel drive waveforms 13 which are then passed to the actual LCD 16. Again known forms of interconnect can be used for this link. Fig. 2 shows how a module controller card 25 receives video data 21 and separates out the data for the two or more pixel subsets 22a and 22b (only 2 subsets are shown in this diagram by way of example) . These data subsets are conceptually sent to the driver card 26 separately, typically in separate time intervals (in a form of time division multiplexing) , but other ways to achieve the same result will be apparent to those skilled in the art . The driver card uses the data sent to it by the controller card to derive the appropriate drive waveforms 23 for the pixels 24. In the preferred embodiment, the drive waveforms are in fact time varying electrical signals for the liquid crystal pixels, and as such the driver card is constantly driving the pixels (as opposed to the controller card which only has to send data to the driver card at discrete times during each frame) . In this way the fact that the data is sent to the driver card in distinct subsets is not apparent in the way that the pixels are driven, and therefore is not generally apparent to an observer of the display either. For this reason only one set of waveforms 23 is shown in Fig. 2. Fig. 3 shows further detail of how the driver card uses the pixel subset data. Video data 31 is sent from the controller card (not shown) to the LCD driver card 32, where it is initially stored in buffer 37. Driver means

33 and 36 use this video data to generate the appropriate drive waveforms 38 for the individual pixels. In this case, and only by way of example, the driver card is shown driving two subsets of pixels 34 and 35, each of two pixels. Driver means 33 and 36 are functionally identical, as one would expect, and there will, in general, be one means for each pixel or sub-pixel to be driven. The driver means is implemented using standard logic elements such as flip-flops, counters, logic gates and output buffers; these would be further implemented using an FPGA or other configurable logic device such as a CPLD, or possibly as a custom ASIC. The actual details of the driver means will depend on the type of pixel being driven and the method employed, but these will be well known to those appropriately skilled. At the appropriate time, the driver card will need to update the video data a particular pixel is displaying. In general this will occur once every frame period, but not necessarily at the same time within this frame period for each pixel. When an update for a particular pixel occurs, the data which the driver means is using to derive the drive waveform needs to be renewed. This is done by passing the appropriate data from the buffer 37 to the driver means 33 or 36. In prior art driver cards, where all the pixels are updated simultaneously, this would require all the pixel data to be stored in the buffer. According to the invention, however, a first subset of pixels 34 are driven by a first subset of driver means 33; at the moment where this subset is updated, the appropriate data is passed to the driver means 33 from the buffer 37. It is implicit that there is then a delay before the second subset of pixels 35 need to be updated. During this time the data for the second subset of pixels is transmitted to the driver card 32 from the module controller, in this way the buffer means 37 need only be large enough to store the largest data subset rather than an entire frames worth of data. During different parts of the frame period, the buffer addresses different subsets of the driver means.

This is shown diagrammatically in that datapath 39 from buffer means 37 goes to both subsets of driver means 33 and 36. In order for this to work correctly, some additional functionality, such as a de-multiplexer (not shown) , is needed on the driver card 32 to ensure that the buffer means sends data to the correct subset of driver means on the driver card at the correct time. However this additional functionality is generally small in comparison to the saving that can be made in reducing the size of the buffer. In one embodiment, the buffer 37 can be a simple serial-to-parallel converting shift register. In alternate embodiments, the buffer can be implemented as memory or possible a FIFO. Fig. 4 shows an outline timing diagram for one frame period (with time in the horizontal direction) , illustrating the problem to be addressed by the preferred embodiment of the invention. During a first part 41 of the frame period, the entire set of video data is passed to the driver card. At time 42 the entire pixel array is updated, substantially simultaneously. Provided period 42 is short enough, all pixels in the array can be updated every frame, but the data passed to the driver card during this period needs to be stored on the driver card until the update time 42. Fig. 5 shows an equivalent timing diagram to that shown in Fig. 4 but according to an embodiment of the invention. In this example, the pixels are split into 2 subsets; during a first period 51 within the frame the data^' for the first subset of pixels is sent to the driver card. At time 52 this subset of pixels is updated. Subsequently during period 53 the data for the second subset of pixels, comprising the remainder of the pixels in the array, .is passed to the driver card and this second subset of pixels is updated at time 54. Provided the sum of periods 51 and 53 is less than the frame period, all pixels in the array will be correctly updated every frame . In simpler embodiments, where the buffer is a shift register, the definitions of periods 51 and 53 is somewhat arbitrary and a simple extension is to include a

3^rd period and 3^rd update time, however the simplest embodiment is for two subsets only, each comprising exactly one half of all of the pixels that are to be driven by this particular card. In more sophisticated embodiments, the data sent during any one such period can be terminated with a coded bit pattern, in this way the number and size of the data/pixel subsets can be altered dynamically. Additional logic on the driver card will identify the bit pattern which will determine the amount of data in that particular data subset . Subsequently the correct subset of pixel driver means can then be updated at the appropriate time. These embodiments are variations on a theme wherein the ordering of the pixel data as it is passed to the driver card is not varied. In other words it is hardwired into the card design that, for example, the 43^rd datum to be passed to the driver card is intended for the 43^rd pixel; this will be so regardless of which data subset this particular datum ends up in. However, where the buffer is implemented as memory, the order in which the data is read out can be divorced from the order which it is read in; this is especially so if the memory is dual port memory. Fig. 6 shows a schematic view of an alternative embodiment of the invention. In Fig. 6, video data 61 is passed to driver card 62 by module controller means (not shown) . Within the card the data is stored in memory 68, under the control of an input address counter 67. The read out of the data from the memory to the driver means

63 or 66, which drive pixel subsets 64 and 65 respectively, is controlled by the addresses in the look- up table 69 (an additional counter will be needed of course) . In this way the data subsets can be randomly chosen from within the data passed to the driver card according to the entries in the look up table. In an extension to this embodiment, the actual look up table can be passed to the driver means dynamically, as additional data appended or prepended to the video data (again some coding of the data will be needed plus additional circuitry on the driver card) . Thus the selection of data/pixel subsets can be chosen dynamically, and ultimately can be optimised for each frame. The above embodiments have been described by way of example. Modifications of these embodiments, further embodiments and modifications thereof will be apparent to the skilled person on reading this disclosure and as such are within the scope of the invention.

Claims

1. A method of operating a display, the display having : a plurality of pixel arrays for displaying an image ; and a plurality of driver means, each for controlling a respective pixel array by addressing pixels in the respective pixel array, wherein an image is displayed as a series of frames and each frame is displayed for a frame period, wherein for each pixel array the method includes the steps of : said driver means addressing as required a first subset of pixels in said pixel array during a first part of said frame period; and said driver means addressing as required a second subset of pixels in said pixel array during a second part of said frame period, wherein the driver means has a capacity lower than the capacity that would be required to address all of the pixels in the array at the same time.

2. A method according to claim 1 wherein the display is arranged so that it is possible to address all of the pixels in the first and second subsets of pixels at least once during the frame period.

3. A method according to claim 1 or claim 2 wherein the pixel array includes one or more further subsets of pixels, so that there are three or more subsets of pixels that are addressed as required by the driver means at different times during the frame period.

4. A method according to any one of claims 1 to 3 wherein the selection of pixels for one or more of the subsets is altered by suitable control of the driver means .

5. A method according to any one of claims 1 to 4 wherein the driver means has a capacity for storing information relating to the required states of the pixels that is less than the capacity that would be required for storing information relating to all of the pixels at the same time.

6. A method according to any one of claims 1 to 5 wherein each pixel has at least one red sub-pixel, at least one green sub-pixel and at least one blue sub-pixel

7. A method according to claim 6 wherein each sub- pixel array is addressed as required by a respective driver means .

8. A display having: a plurality of pixel arrays for displaying an image in a series of frames, each frame being for display for a frame period; and a plurality of driver means, each for controlling a respective pixel array by addressing pixels in the respective pixel array, wherein the driver means is arranged to address as required a first subset of pixels in said pixel array during a first part of said frame period, and to address as required a second subset of pixels in said pixel array during a second part of said frame period, the driver means having a capacity lower than the capacity that would be required to address all of the pixels in the array at the same time.

9. A display according to claim 9 wherein the display is arranged so that it is possible to address all of the pixels in the first and second subsets of pixels at least once during the frame period.

10. A display according to claim 8 or claim 9 wherein the pixels are liquid crystal pixels.

11. A display according to any one of claims 8 to 10 wherein the driver means has a capacity for storing information relating to the required states of the pixels that is less than the capacity that would be required for storing information relating to all of the pixels at the same time.

12. A display according to any one of claims 9 to 11 wherein each pixel has at least one red sub-pixel, at least one green sub-pixel and at least one blue sub-pixel

13. A display according to claim 12 wherein each sub- pixel array is addressable by a respective driver means.

14. A display according to any one of claims 9 to 13 wherein the display is a modular display, formed of an arrangement of display modules .