A video wall is a special multi-monitor setup that consists of multiple computer monitors, video projectors, or television sets tiled together contiguously or overlapped in order to form one large screen. Typical display technologies include LCD panels, LED arrays, DLP tiles, and rear projection screens.
Screens specifically designed for use in video walls usually have narrow bezels in order to minimize mullion, the gap between active display areas, and are built with long-term serviceability in mind. Such screens often contain the hardware necessary to stack similar screens together, along with connections to daisy chain power, video, and command signals between screens. A command signal may, for example, power all screens in the video wall on or off, or calibrate the brightness of a single screen after bulb replacement.
Reasons for using a video wall instead of a single large screen can include the ability to customize tile layouts, greater screen area per unit cost, and greater pixel density per unit cost, due to the economics of manufacturing single screens which are unusual in shape, size, or resolution.
Video walls are sometimes found in control rooms, stadiums, and other large public venues, such as Oakland International Airport's baggage claim, where patrons are expected to observe the display at long distances. Video walls can also benefit smaller venues when patrons may view the screens both up close and at a distance, respectively necessitating both high pixel density and large size. For example, the 100-inch video wall located in the main lobby of the Lafayette Library and Learning Center has enough size for the distant passerby to view photos while also providing the nearby observer enough resolution to read about upcoming events.
Simple video walls can be driven from multi-monitor video cards, however more complex arrangements may require specialized video processors, specifically designed to manage and drive large video walls. There is also new software-centric video wall technology that uses ordinary PCs, displays and networking equipment.
The largest video wall as of 2013 is located at the backstretch of the Charlotte Motor Speedway motorsport track. Developed by Panasonic, it measures 200 by 80 feet (61 by 24 m) and uses LED technology. The Texas Motor Speedway will install in 2014 an even larger screen, measuring 218 by 125 feet (66 by 38 m).
Video wall controller
Video wall controller (sometimes called “processor”) is a device that forms an image and splits it into parts to be displayed on individual screens. Video wall controllers can be divided into groups:
- Hardware-based controllers.
- Software-based controllers.
Hardware-based controllers are electronic devices built for specific purpose. They usually are built on array of video processing chipsets and do not have operating system. The advantage of using hardware video wall controller is high performance and reliability. Disadvantages include high cost and the lack of flexibility.
The most simple example of video wall controller is single input multiple outputs scaler. It accepts one video input and splits the image into parts corresponding to displays in the video wall.
Most of professional video wall displays also have built-in controller. It allows to “stretch” image from one video input to the whole video wall. This type of displays has loop-through output (usually DVI) that allows to daisy-chain all displays and feed them with the same input. It is fairly simple method to build a video wall but it has some disadvantages. First of all, it is impossible to use full resolution of the video wall because the resolution cannot be bigger than resolution of input signal. It is also not possible to display multiple inputs in the same time.
Software-based controller is a computer running Windows or Linux operating system that has special multiple-output graphic cards and video capture cards. These controllers are usually built on industrial-grade chassis due to the reliability requirements of control rooms and situational centers. The advantage of software-based video wall controller is that it can launch applications like maps, VoIP client (to display IP cameras), SCADA clients, Digital Signage software. These applications can use full resolution of the video wall. That is why software-based controllers are widely used in control rooms and high-end Digital Signage.
The performance of the controller depends on the quality and functionality of graphic cards and management software. There are a number of multiple output graphic cards commercially available. Most of general purpose multi-output cards manufactured by AMD (Eyefinity technology) and NVidia (Mosaic technology) support up to 6-12 genlocked outputs. General purpose cards also do not have optimizations for displaying multiple video streams from capture cards. To achieve larger number of displays or high video input performance one needs to use specialized graphic cards (e.g. Datapath Limited, Matrox Graphics, Jupiter Systems).
Jason Leigh and others at the Electronic Visualization Laboratory, University of Illinois, Chicago, developed SAGE, the Scalable Adaptive Graphics Environment, allowing the seamless display of various networked applications over a large display wall (LDW) system. Different visualization applications such as 3D rendering, remote desktop, video streams, and 2D maps, stream their rendered pixels to a virtual high-resolution frame buffer on the LDW. Using a high-bandwidth network, remote visualization applications can feed the streams of the data into SAGE. The user interface of SAGE, which works as a separate display node, allows users to relocate and resize the visualization stream in a form of window, which can be found in a conventional graphical user interface. Depending on the location and size of the visualization stream window on the LDW, SAGE reroutes the stream to respective display nodes.
Chromium is an OpenGL system for interactive rendering on graphics clusters. By providing a modified OpenGL library, Chromium can run OpenGL-based applications on a LDW with minimal or no changes. One clear advantage of Chromium is utilizing each rendering cluster and achieving high resolution visualization over a LDW. Chromium streams OpenGL commands from the `app' node to other display nodes of a LDW. The modified OpenGL library in system handles transferring OpenGL commands to necessary nodes based on their viewport and tile coordinates.
David Hughes and others from SGI developed Media Fusion, an architecture designed to exploit the potential of a scalable shared memory and manage multiple visual streams of pixel data into 3D environments. It provides data management solution and interaction in immersive visualization environments. Its focus is streaming pixels across heterogeneous network over the Visual Area Network(VAN) similar to SAGE. However, it is designed for a small number of large displays. Since it relies on a relatively small resolution for the display, pixel data can be streamed under the fundamental limit of the network bandwidth.
The system displays high-resolution still images, HD videos, live HD video streams and PC applications. Multiple feeds can be displayed on the wall simultaneously and users can reposition and resize each feed in much the same way they move and resize windows on a PC desktop. Each feed can be scaled up for viewing on several monitors or the entire wall instantly depending upon the user’s discretion.
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