Patent Publication Number: US-2007103583-A1

Title: Display wall comprising multiple displays and method of operation thereof

Description:
PRIORITY REFERENCE TO PRIOR APPLICATIONS  
      This application claims benefit of and incorporates by reference U.S. patent application Ser. No. 60/728,917, entitled “Method for Alignment of Multiple Rear Projection Displays for Display Wall Application,” filed on Oct. 21, 2005, by inventor William Burnett. 
    
    
     TECHNICAL FIELD  
      This invention relates generally to displays, and more particularly, but not exclusively, provides a display wall comprising multiple displays and a method of operation thereof.  
     BACKGROUND  
      A display wall (e.g., a wall of tiled displays) is an excellent construction method for applications that requires high resolution and large display area because the resolution and the display area can be partitioned into cost effective smaller display modules. A display wall is also an excellent method for handling multiple, high resolution video inputs since they can be partitioned and handled separately by different display modules or a group of display modules. Further, there is no requirement for a high power central processor to handle and process very high resolution video data streams.  
      However, a display wall usually has gaps in between displays if displays are made out of liquid crystal displays (LCDs), Plasma or cathode ray tubes (CRTs). By their construction, it is very hard to eliminate display bezel or borders. LCD and Plasma technology have driver electronics beyond the active display area that forms a non-display border. A CRT requires an evacuated vacuum to work and the glass envelope also forms a non-display border.  
      Currently, only projection technology offers a solution where a mullion (gap between displays) can be minimized to 1.0 mm or less. Most projection light source include a single lamp that approximates a point source, so the color temperature across a single display is very uniform, much better than LCD or Plasma. The projection optics, however, exhibits fairly large brightness differences from the center of a display to its borders. Commercial products typically have 20% to 25% brightness fall off as a marketing specification. Along the display border of a singular display, the brightness fall off is subject to projection optical design limitations and component tolerances and the brightness can be different from one region (e.g. comer) to another region (e.g. the center of one side). While the brightness non-uniformity for a singular display is accepted in the marketplace, when displays are tiled together, display brightness differences between two adjacent displays can become accented and conspicuous.  
      The human visual system is more sensitive to rapid changes within a small visual angle to the same changes across a wider visual angle. Average brightness across displays can be different by as much as 10-20%. If the border across displays varies by more than 5%, the discontinuity can be discerned.  
      Conventionally, along the border between two displays, the brightness variation can be very different from display to display, as much as 20%. Along the border between displays, the brightness discontinuity can therefore be picked out easily by the human visual system. The key to minimize the brightness discontinuity across displays within a video wall is to match the brightness at display borders to within 5%, and the average brightness across displays to within 10-20%  
      Current methods for display wall geometry and color alignment are manual or semiautomatic, time consuming to install and readjust. The alignment difficulties increases total system cost and slowed their adoption.  
      One solution to the deficiencies mentioned above is to have multiple projectors with overlapping borders. However, overlapping display borders requires one contiguous large screen that is difficult to transport. Mechanical structures for modular screens also interfere with the overlapping requirement.  
      Accordingly, a new display wall and method of operation are required to overcome the above deficiencies.  
     SUMMARY  
      Embodiments of the present invention overcome the above-mentioned deficiencies by adjusting border brightness and brightness uniformity in each light engine of each display module of a display wall. In addition, each screen of each module is held in place via pins that are outside the light path of the light engines, thereby minimizing the mullion.  
      In an embodiment, a display wall comprises a plurality of display modules and a fixture having ribs and pins. Each module has a screen and a light engine capable of projecting an image onto a screen of the module. The pins hold the plurality of screens in place via the screens&#39; perimeters.  
      In an embodiment, a display wall comprises a plurality of display modules; a camera, and a processor. Each module has a screen and a light engine that projects an image onto the screen. The camera images a screen of a display module and at least a portion of a screen of an adjacent module. The processor, which is communicatively coupled to the camera and at least one light engine, adjusts brightness of the at least one light engine such that a projected image from the at least one engine matches brightness of the at least a portion of a screen of an adjacent module within about 5%.  
      In an embodiment, a method of adjust brightness comprises: displaying images on screens of the display wall; imaging the screens; determining brightness of border areas of the screens; and matching brightness of border areas in a screen to within about 5% of border areas of an adjacent screen.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.  
       FIG. 1A  and  FIG. 1B  are diagrams illustrating a top and rear view of a display wall according to an embodiment of the invention;  
       FIG. 2  is a diagram illustrating a perspective view of the display wall of  FIG. 1 ;  
       FIG. 3  is a diagram illustrating a fixture of the display wall;  
       FIG. 4  is a diagram illustrating a field of view of a camera of the display wall;  
       FIG. 5  is a diagram illustrating fields of views from multiple cameras of the display wall;  
       FIG. 6  is a flowchart illustrating a method of adjusting brightness of the display wall;  
       FIG. 7  is a block diagram illustrating a circuit for adjusting brightness of the display wall;  
       FIG. 8  is a diagram illustrating a display wall according to another embodiment of the invention;  
       FIG. 9  is a diagram illustrating a field of view of a camera of the display wall of  FIG. 8 ;  
       FIG. 10  is a block diagram illustrating a circuit for adjusting brightness of the display wall of  FIG. 8 ;  
       FIG. 11  is a block diagram illustrating a display wall according to another embodiment of the invention;  
       FIG. 12  is a block diagram illustrating a circuit for adjusting brightness of the display wall of  FIG. 11 ; and  
       FIG. 13A  and  FIG. 13B  are graphs showing brightness variation before and after adjustment.  
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS  
      The following description is provided to enable any person having ordinary skill in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the embodiments will be readily apparent to those skilled in the art, and the principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles, features and teachings disclosed herein.  
       FIG. 1A  and  FIG. 1B  are diagrams illustrating a top and rear view of a display wall  100  according to an embodiment of the invention. The display wall  100  comprises a plurality (e.g., 4) of displays linked together via a fixture  140  comprising ribs and pins  150 , as will be discussed in further detail in conjunction with  FIG. 3  below. Each display includes a mirror  110  that reflects an image from a light engine  200  ( FIG. 2 ) onto a screen  130 . The optical projection paths are shown by the solid lines  120 . As such, the fixture  140  is outside of the projection path, as will be discussed in further detail below.  
       FIG. 2  is a diagram illustrating a perspective view of the display wall  100 . The light engine  200  projects an image on to a mirror, which reflects the image onto the screen  130 . Multiple screens are linked together via the fixture  140 . In addition, a camera mounted to the fixture  140  images the screen  130  for each display in the display wall  100 . The screen  130  will reflect sufficient light back toward the camera  210  for the system to discern brightness and geometry features. The field of view extends beyond one projection display module so the neighboring display&#39;s borders are visible. There are gaps in between mechanical attachment fixtures so the camera can capture most of the borders. Since the border area of multiple displays is visible in one camera, a feedback control system coupled to the camera  210  and light engine  200  bring the brightness uniformity of adjacent display borders to within 5%. The screen brightness changes gradually from the brightest spot on screen to the dimmest spot on screen.  
       FIG. 3  is a diagram illustrating a fixture  140  of the display wall. The fixture  140  comprises a plurality of ribs and pins  150 . In an embodiment, the pins  150  are conical, triangular, or pyramidal in shape such that a tip (e.g., head) of the pin  150  holds in place the screen  130 , thereby minimizing the mullion between displays while not blocking the projection of an image. The pins  150  hold the screen  130  in place by its perimeter, thereby minimizing the mullion.  
      The pins  150  that are visible to the camera  210  have, in one embodiment, a feature or features embedded on their surfaces for identification. These can be, but are not limited to, fiducial markings, bar code markings, three dimensional bar code markings, holographic markings, or other types of markings that can contain information that the camera or sensors can decode. This information might contain, but is not limited to, the serial number of the display, the calibration between the pin and the projected image for each individual display, and other information that might make alignment easier.  
      In an embodiment, the fixture  140  includes 2 pins and 2 reference holes per side, for multiple unit precision stacking. Pin and hold technique includes tab/slot, tapered pin/taped hole, 2 slots and a biscuit. Alignment features are placed in a region that is visible to the camera  210  in the adjacent display (e.g., see viewing area  410  of  FIG. 4 ) but not in the light path of that display&#39;s projection system.  
      As such, as disclosed in U.S. patent application Ser. No. 11/164,814, entitled “Image Adaptation System and Method,” which is hereby incorporated by reference, a vision system can be used in the alignment of the projection display module so the display geometry of each module can be controlled to within a fraction of a display pixel. With this embodiment, optical path design that projects the image all the way to the edges of the display surface within a fraction of a display pixel can be implemented. The modules forming the display wall  100  can be aligned using the camera  210  during manufacture, and/or during installation, and/or after installation (e.g., when powering on each day or at other intervals).  
       FIG. 5  is a diagram illustrating fields of views from multiple cameras of the display wall  100 . Each camera  210  has a field of view that extends slightly outwards from the screen  130  (e.g., about 5% of the area covered by a field of view includes an adjoining screen).  
       FIG. 6  is a flowchart illustrating a method  600  of adjusting brightness of the display wall  100 . First, border brightness of a first display (e.g., display A of  FIG. 5 ) and its neighbors (e.g., displays B and C) are checked ( 610 ). In an embodiment, only the borders having adjacent screens are checked, e.g., for screen A, only the right and bottom borders need to be checked. A border can include about 5% of area of a screen in one embodiment. Next, on a region by region basis, border brightness of the first display is lowered ( 620 ) to within about 5% of a neighbor&#39;s brightness if the brightness of the first display is higher than a neighbor&#39;s. In an embodiment, a region includes an entire border facing a neighbor. In another embodiment, a region includes a subdivision of a border (e.g., ⅛ of a border). Next, the border brightness adjustments are repeated ( 630 ) for the other screens in the display wall. Brightness uniformity adjustments are then performed ( 640 ,  650 ) for the first screen and other screens in the display wall. The adjustments are done by imaging each the screens and then applying an inverse function to each of the screens. For example, a brightness topography is shown in  FIG. 13A . The inverse of this can be applied to a screen, thereby generating a relatively uniform screen brightness. The method  600  then ends. The inverse can be stored in a regional scaling coefficient table  740  ( FIG. 7 ) (one per each screen) generated during manufacture of the display wall  100 , during installation of the display  100 , and/or after installation (e.g., at intervals, such as power on). In an embodiment, the method  600  can be applied to display walls comprising any number of displays.  
       FIG. 7  is a block diagram illustrating a circuit  700  for adjusting brightness of the display wall  100 . Each module of the display wall  100  can include the circuit  700 , which executes the method  600 . The circuit  700  comprises a microcontroller (also referred to as a processor)  710  communicatively coupled to the camera  210 , the light engine  200 , and the regional coefficient table  740 . During operation, the microcontroller  710  receives video  720  from a source and brightness data from the camera  210  that images the screen  130 . The microcontroller then adjusts border brightness of the video  720  as described above and then adjusts brightness of the entire video using the regional scaling coefficient table  740  as described above, to generate modified video output  750 , which is sent to the light engine  200  for projection on the screen  130 .  
      In an embodiment of the invention, the table  740  can also include coefficients for adjusting the border region brightness, i.e., the results of brightness adjustment can be applied to the video output  750 , then the screen  130  imaged, then the inverse of the entire screen  130  brightness can be stored in the table  740 . Alternatively, the coefficients for adjusting border brightness can be stored in the table  740  and then the inverse for the remaining region of the screen  130  brightness can be stored also in the table  740 .  
       FIG. 8  is a diagram illustrating a display wall  800  according to another embodiment of the invention. The display  800  is substantially similar to the display wall  100  except that a camera  810  images the entire display wall  800  (e.g., 4 screens) instead of a single screen  130 . The camera  810  includes a wide angle lens that can be used for the brightness adjustment of 4 displays. This camera  810  can be installed either on a production line, or be added during the construction of a display wall  800 . For a single mirror reflection projection design, the light engine  200  is placed near the front of the display  800  and can block some  910  ( FIG. 9 ) of the video information to this camera  810 . This camera  810  can clearly see the border areas of the four displays as well as the neighboring displays as shown in  FIG. 9  and can still capture the border brightness image need for uniformity adjustment. At display wall construction time, the video output of this camera  810  can be connected through a video distributor to the four displays for brightness uniformity correction. Further, since this camera  810  covers the neighboring displays beyond the four displays, this construction method can be used to assemble very large display walls beyond 2×2.  
       FIG. 10  is a block diagram illustrating a circuit  1000  for adjusting brightness of the display wall  800 . The circuit  1000  is similar to the circuit  700  except that a single camera  810  images more than one display of the display wall, thereby necessitating the need for the video distributor  1020 , which distributes video data pertaining to the displays to the appropriate controllers  1040 .  
       FIG. 11  is a block diagram illustrating a display wall  1100  according to another embodiment of the invention. The display wall  1100  is substantially similar to the display wall  800  except that photodiodes  1110  are used in place of the camera  810 . The photodiodes  1110  are placed in between mechanical attachment fixtures of two adjacent displays. These photodiodes  1110  are sensitive to border brightness of both displays, and by turning on one display at a time, can provide border brightness data needed for brightness uniformity matching. Note that since these photodiodes  1110  are used for relative measurement, there is no requirement that their light transfer characteristics must be matched. As shown in  FIG. 10 , by strategically placing the photo diodes on only two sides, it is sufficient for the brightness correction of a display wall  1100  with many displays in both vertical and horizontal directions. Note that the photodiodes  1110  are not to scale and do not obstruct a significant amount of light reflected onto the displays of the display wall  1100 .  
       FIG. 12  is a block diagram illustrating a circuit  1200  for adjusting brightness of the display wall  1100 . The circuit is substantially similar to the circuit  1000 , however, as photodiodes  1110  are used in place of a camera  810 , border brightness data is fed via an amplifier  1220  to a microcontroller  1240 . After the border brightness is adjusted, the rest of the method  600  can be applied using a regional coefficient table generated either by design, or at the time where individual display module was put together in production.  
       FIG. 13A  and  FIG. 13B  are graphs showing brightness variation before and after adjustment. Specifically,  FIG. 13A  shows the brightness distribution data of a single display before uniformity correction.  FIG. 13B  shows the brightness distribution data of two side-by-side displays after applying uniformity correction for both regional and border areas, e.g., via the method  600 .  
      The foregoing description of the illustrated embodiments of the present invention is by way of example only, and other variations and modifications of the above-described embodiments and methods are possible in light of the foregoing teaching. For example, display walls can comprise more than the 4 displays illustrated. Further, components of this invention may be implemented using a programmed general purpose digital computer, using application specific integrated circuits, or using a network of interconnected conventional components and circuits. Connections may be wired, wireless, modem, etc. The embodiments described herein are not intended to be exhaustive or limiting. The present invention is limited only by the following claims.