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    What is a Video Wall?     What is a Data Wall?     What is a Media Wall?      
           
    For the sake of this definition, Video Wall, Data Wall, and Media Wall will all be referred to as a Video Wall. The scope of this page is to introduce the concept and technology for some types of video walls.

A video wall is any large electronic display of an image or images being displayed in a presentation format. Typically multiple display devices are tiled together as close as possible in a matrix to create a single logical screen (The Video Wall). Then with special Video Processor devices, an image is scaled across the logical screen or multiple images are spread out over the logical screen or a combination of both in the case of picture in picture. This is all without respect for the individual display devices physical boundaries.

The individual display devices can be anything from the smallest (4" diagonal) direct view LCD screens to very large (120" diagonal) front or rear projection devices depending on the ultimate size of video wall being created by the matrix. LED walls use individual discrete light emitting diodes from .5mm each to create each pixel.  For a discussion on Direct View LCD/Plasma displays and Video Wall Cubes, scroll to the bottom of this page to "Which Display Device to Use?.

The rest of this article will focus on building video walls with matrices of complete display devices and not LED technology.

The reason for creating large logical displays in this fashion is that you can assemble a single logical display area that is brighter, larger, higher resolution and has inherent redundancy unlike any other method of image display.

The human brain has the ability through your eyes to see and comprehend multiple changing messages through images all happening in real time by scanning each image in some rotation. It is for this reason that video walls can uniquely present many pieces of information to multiple people at the same time in the same place.

An example of a single image being scaled or spread across a 3 wide x 2 high matrix of  50" rear projection "cubes" is shown below.

     
    Media Wall      
     

Below is an example of multiple images being scaled across a 3x3 array of 67" rear projection cubes.

     
         
     

Below is an example of a 4x4 matrix of 17" LCD panels showing up-scaling (launch image in the 2x2 in the center) and down-scaling (12 displays around the perimeter)

     
    Media Wall      
     

Equally as important as the devices that make up the video wall itself are the electronics that drive the video wall, or so called Video Processor. The Job of this piece of hardware and software is to take all the source images to be viewed, convert them to a common format, size and place them across the video wall matrix as above. Below is a Image flow diagram that shows the importance of the processor in creating a video wall.

     
   

Image Sources                 Processing/Image Control              Video Wall Matrix

 
  

 

 

 

 

     
    Below is a logic diagram showing various image sources (DVD, Camera, Computer), the processor (VP-1000 in this case), and the display matrix (4x3 array). Included in this is the signal type for each source and the processor converting each to a format compatible with the display devices (RGBHV). Also shown is the software that is running on the processor and on computers being viewed (RGB Import). If you look at the image on each source icon you will see it appear on the video wall in a different scale, size and quantity.

     
         
     

The above descriptions, examples and pictures apply to video wall applications typically used in public display venues, command and control rooms, operation centers, situation rooms, traffic monitoring rooms, emergency operation centers, etc. There are many other applications for video walls and it is beyond the scope of this article to identify and describe them all.

Which Display Device to Use?

We are asked this question daily. When selecting a display device technology to build a matrix of displays to create a "Large Video Wall", designers are faced with basically 2 different display technologies, Video Wall rear projection cubes or Direct View LCD/Plasma screens.

Direct View LCD or Plasma displays:

On the outset it makes logical and fiscal sense to just go down to the local home electronics reseller (Costco, Best Buy, Etc.) and buy enough inexpensive LCD displays to create a large display matrix and hang them on the wall, Video Wall done... Not so fast.

There are some long and short term problems with this method:

1) Direct view LCD's/Plasma displays each have a border or bezel around each one and when you tile these together to create an array, you create gaps in the overall image that creates what the industry referrers to as mullions and transoms which is fine for windows in a building but causes problems when viewing images or data on a video wall. The human brain does not like to have information distorted in this way, (its hard to look at).

Doing this destroys the aspect ratio of the images as shown below with various shapes:

Using video wall cubes with their ~1mm mullions you would see something more like this with the same data:

Actual installations come out looking like this:

Although video processors that drive these walls can compensate for the width of the mullions, you are losing data in the gap of the mullion and although may be acceptable for some images, it is not for numerical data or mapping functions. This is a major compromise in the overall looks of the project when all is said and done and the end user will have to decide if they can live with this flaw.

2) What is not as obvious is that consumer grade LCD's and plasma displays are made, sold and discontinued from production in a very short life cycles, generally between 1 year and 3 months. This is because of a cost and competitive marketplace that demands that manufactures are constantly churning the product mix to have the latest and greatest being offered. This works fine if you have an application with a single display that fails in 2 years for example, no problem, buy a new one, and toss the old one. It will cost less to buy a new unit, than fix the old one. Manufactures know this and so there is no motivation for them to provide service parts and cost effective support for these devices long term, and so they don't. Even with long warranties, generally there is a stipulation that if the failed item is not repairable, then they have the option to replace with a similar item.

This doesn't work when that failed LCD is in a tightly spaced array because inevitably the replacement unit will not be the same physical size, nor have the same optical characteristics (colors wont match). This will require replacement of the entire array if 1 unit fails with new product which can wipe out any savings by using this technology instead of video wall cubes which cost more day one but are made for this purpose. Even if you accept the above risks, because of budget cycles there may be monies available day 1 to do it right with video wall cubes but there wont be down the line to do a complete replacement. Generally there is some reasonable funds available for repairs, which is the case with video wall cubes.

3) The human eye is extremely critical of very small color temperature, brightness and hue difference between closely spaced displays placed in this fashion. Since direct view LCD's were never made for this application they generally don't have the necessary color and geometry adjustment in them to match the neighboring display perfectly. This may be more of an issue over time as each device ages and therefore its color output changes, making the problem worse with age.

4) Since direct view displays were never designed for this function, cooling and their long term life expectancy can be an issue as well (and may void any warranty).

5) Image retention issues, Plasma displays will prematurely burn into their phosphor any image displayed that is static in very short time periods, rendering the display destroyed and not covered under warranty.  LCD's all suffer from some form of TIR or temporary image retention with static images. The term for this varies but it is a function of the technology and manufactures exclude this as a failure, but the end user wont because it is visible but not necessarily permanent.

6) If a unit fails and assuming a repair can be done, it wont be in the field. These devices are made to be repaired at a service facility not at the customers site. Which brings up how do you pack it to be shipped for repair? Its not a simple put it in a box and send it because of its size, shape and fragility. Manufactures shipping packaging is very specialized and difficult to obtain as most of it is made overseas. And even it when using manufactures packing materials damage is rather common.

7) Direct view display devices when mounted in an array are generally installed starting with the bottom row to the top row, and when one fails on anything but the bottom row, all units above it need to be removed to get access to the failed unit. We are aware of no front access mounting system that maintains small gaps between individual displays and allows for removal of any 1 display only.

8) The weight of an array of direct view display devices in aggregate is more than most commercial building walls are able to support safely. An example would be a 4x3 array of 57" LCD's with mounting hardware would weigh approximately 1620 Lbs. Most commercial building walls were never meant to have this kind of weight being cantilevered off of them and if the wall were to fail it could be lethal especially in an earthquake area. The cost to retrofit the building walls will have to be considered in any design such as this, as without this it would be considered negligent.

9) All the above issues don't generally arise when these devices are used for their intended design application which is for occasional television use. They were not designed and don't function well when being used in a group as a video wall array. There are "Commercial" versions of LCD's available which help to mitigate "some" of the above problems, but they are not optimal and will cost many times what the consumer counterparts do and will always be another form of compromise as the actual LCD panel itself comes from the same factory as the consumer model. So at its core suffers from the same planned obsolescence issues mentioned above.

Video Wall Cube devices:

Rear projection video wall cubes, although they cost more day 1, are designed and purpose built for this function and address the above issues, and their designs have been refined over many years. Certain tier 1 manufactures of these devices design and build them with high image quality day 1 and adjustments for the long term. 

Field serviceability is a part of the overall design and can easily be performed in the field by dealer or end user  personnel. Making spare parts available for time horizons in the 7 year range is quite common with many going longer.

In summary, these systems are made for incorporation into an overall installation design that if done correctly will look good on day 1 and for years to come. Selection of a qualified dealer to do the design and installation, or support the end user in doing the installation is recommended.

In a traditional rear projection video wall cube, the light source comes from a specially designed short arc lamp similar to These. The light then passes through a DLP or LCD apparatus that filters out the white light and only shows the colors that are in the image that is to be displayed. After a series of lenses and mirrors the image is shown on the back side (rear projection) screen that you look at the front of.

In addition to short arc lamp illuminated Video Wall cubes, there are LED illuminated Video Wall Cubes. Using LED's for illumination alleviates the need for color wheels in the light path and adds significant cost to the display. Although doing this theoretically reduces the cost to operate (no purchasing of lamps), the brightness will fade over the life of the LED illumination module. These devices have only been commercially available since mid 2010 and their long term reliability and cost savings over a long service life is as yet undetermined.

Narrow Mullion LCD displays.

Introduced in early 2010, narrow mullion LCD's are commercial grade direct view displays purpose built for use in creating video wall matrices. This scheme is a hybrid between typical LCD's and Video Wall Cubes, although the mullions are not as small as cubes can provide (~1mm), they are small enough for some applications where some mullion can be tolerated. As of early 2011 mullions on 46" is 7.3mm and on 55" displays it is 5.7mm.

Below are 2 examples of narrow mullion LCD's:

46" LCD running at 1366x768 with 7.3mm mullions above, this overall array is 80.76" wide x 45.66" high

55" LCD running 1920x1080 with 5.7mm mullions above, this overall array is 96" wide x 53.8" high.

Although narrow mullion LCD's are an attractive solution they still suffer a number of problems stated above for long term support and longevity.

     
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