By Paul Bray in Technology March 17, 2022 0

Video walls are the public face of AV, from mainstays of the meeting room and shopping mall to nerve centres of control rooms and windows on to virtual worlds. But what’s required to create one of these modern marvels? Paul Bray reveals what goes on behind the scenes.

A video wall is any display composed of more than one display panel, from a basic 2×2 in a meeting room to the entire facade of a building or the animated touchline board of a sports stadium.

The display area itself generally uses one of three technologies: LCD, direct view LED or rear projection cubes. Rear projection is bulky, energy-hungry and expensive, and its total demise has been predicted for years. It retains a role, however, in critical environments such as control rooms, where its longevity, very high reliability and lack of ‘burn-in’ (where a static image leaves a permanent stain on the display surface) continue to recommend it.

LCD has been the mainstay of video walls for some years, beloved by users for its clear, detailed images, and by accountants for its modest price. Its main drawback has always been the borders (or bezels) around each panel. These have shrunk over the years to a few millimetres, but they still give the video wall a slight grid or chequerboard effect, which can be unsightly for images and irritating when reading text or (especially) figures.

LED has long been popular for outdoor installations for its high brightness. But it was expensive, and the image could appear grainy when viewed close up because the pixel pitch (distance between pixels) was wider than on LCD panels. Now the price is falling and pixel pitches are narrowing, especially with new microLED technology. Neither has quite achieved parity with LCD, but LED’s other advantages – including high brightness and contrast, longevity (up to three times LCD) and lower energy consumption – are seeing the pendulum begin to swing in its favour.

An interesting LED variant that is gaining in popularity is mesh LED, according to Thomas Fenton, senior business development manager at Peerless-AV. Typically, mesh LED is 5mm+ strips of LED configured to give a full image from the front but to be transparent from behind – for example in a window, where people inside can see out, but anyone looking from outside only sees an image.

LED quirks One quirk of LED is that colours and brightness are not always uniform between manufacturers, or even between batches from the same manufacturer. “With LED, spare panels and parts should always be part of the solution set,” advises John Sheehan, global vice-president for visual product marketing at Mood Media. “Typically we recommend five to ten per cent, manufactured during the same production run as the rest of the panels. Should an LED panel fail, it can be easily removed from the wall and replaced with a spare.”

Such ease of maintenance should be a function of the intrinsic design. “Being able to access the inside of an LED video wall from the front and the back, as well as motorised extraction for the quick and safe removal of parts, can minimise potential disruption, enabling an engineer to safely swap out an LED module in less than a minute,” says Piet Vanhuyse, marketing director for large video walls at Barco.

During installation, all the panels of a video wall must be fine-tuned so that they appear to the viewer as a single, uniform display, and advances in technology are helping to reduce the time and cost of this. “With optical seam compensation, for example, you can take a picture with a camera within the video wall and an algorithm can calibrate and steer the LEDs at the edge of the wall to get a perfect picture,” says Vanhuyse.

Enabling viewers to interact with the video wall is becoming increasingly common, which requires extra hardware. “A touch screen overlay can allow users to annotate, select or move items on the screen,” says Nick Shaw, sales and marketing director at integrator, ADXBA. “To achieve this, infrared is fired across the surface of the video wall, and when a finger intercepts the beam it’s interpreted as a touch.”

“Interactive overlays are product specific, so it’s important to ensure you choose a compatible LED display if this functionality is needed,” adds Roy Martin from the technical division at Northamber/AVM.

“Another option, which has become more popular due to Covid measures, is gesture-based technology,” says Shaw. “Here, a camera is mounted at the top of the screen to monitor body movements and gestures. This data is fed back to a media server or computer running software that interprets the movement and manipulates the content accordingly.”

While most video walls still conform to the traditional flat, rectangular shape, there is a growing vogue for curves, contours and three-dimensional shapes. Limited curvature is just about possible with conventional LCD panels.

“LCD displays are rigid with no flexibility,” says Shaw. “Gradual curves can be created by mounting the screens at a slight angle to each other, but these angles need to be kept very small to avoid exacerbating the divisions already introduced by the bezels and creating a facet where the screens connect.”

With LED, however, designers can be more imaginative. “LEDs are essentially single pixels that are mounted on surfaces,” explains Vanhuyse. “Therefore, unlike LCD panels or rear projection cubes, LED panels aren’t restricted to a rectangular shape, and since the early 2000s they’ve also become a lot smaller, opening up a host of creative solutions.”

“Most standard LED panels are still quite rigid, but because they don’t have bezels it’s easier to avoid facets when they’re mounted at a gradual angle,” says Shaw. “And an increasing number of LED displays have a mechanism on the back that allows you to release a section on either side of the panel and move this inwards or outwards to create the illusion of curvature.”

Completely flexible LED tiles are also available, although these are still relatively niche. “Here the rigid panel is replaced by a flexible piece of rubber with a membrane behind it, into which the LEDs are embedded,” explains Shaw. “These are attached to a framework of almost any shape using magnets, and are most likely to be used in the events industry for creative applications.”

Hardware aside, the prerequisite of a successful video wall is content. This is the province of the content management system (CMS), which creates a template of the wall, enabling users to produce content that precisely matches its format.

“A powerful digital signage CMS will help users of any skill level to create content that’s repeatable, visually appealing and professionally presented,” says Jordan Feil, marketing director of Navori Labs. “The best CMS solutions offer a web-based user interface, typically coded in HTML5, that simplifies the essential tasks of uploading, scheduling and storing content, and easily placing and arranging that content on a video wall. Content synchronisation heightens the visual experience by aligning how immersive content presents across several screens and media players.”

Advanced CMS needed for curves Shaped and contoured video walls rely heavily on advanced CMS, adds Feil. “This enables designers to more easily map pixels in creative ways, create canvases in custom shapes, sizes and resolutions, and position different content zones as desired.”

Getting the content onto the video wall can be achieved in various ways, depending on the application. “In a control room, you’ll want flexibility to dynamically change between multiple video streams on one large canvas,” says Martin Lienau, product manager for large format displays at Sharp NEC Display Solutions. “Therefore each LCD display has a modular and integrated controller (single-board computer) which is managed centrally from the distribution software. For LED this is similar, but the controller manages many pixel cards.

“For retail signage, the easiest way of distributing content for LCD displays is via daisy-chaining, where a single source is looped through the whole canvas and each display takes a portion of the signal.”

In the latter case, a signal distribution system crops the appropriate portion of the image and scales across the display, explains Art Weeks, director of product management at ZeeVee. So if you have a 2×2 video wall, one-quarter of each whole image will appear on each display. “An LED system is a bit different, in that it can have one or more controllers that direct the pixels where to go over a certain segment of the video wall.”

For example, the 220x18ft video wall in Las Vegas’s Westgate Resort & Casino is broken into seven segments, each 3840 pixels wide by about 2200 pixels tall, and powered by seven controllers.

“In an LED system, the controller can also be fed by other information from multiple sources. At Westgate, there are two sources feeding each controller, from a variety of inputs including DirecTV receivers, media players and other content creation devices, which enable individual images or multi-views to be displayed. It could also receive scrolling ticker information, for example, to be displayed simultaneously.”

The playout devices generally download and store content locally, so it is not streaming and is therefore not at the mercy of glitches in the broadband connection, according to Sheehan.

“Distribution of content to the media players is controlled by the CMS. Most clients set predetermined content download windows, typically during the night, when their other systems aren’t using their bandwidth.”

In future, local playout devices may no longer be necessary. “The growing adoption of centralised, AV-over-IP content delivery means you no longer need media players on the back of every device, you only need the decoder on the back of the display,” says Michael DiBella, director of commercial product marketing at Crestron. “That will bring significant cost savings, not only in the hardware but in deployment time and in reducing potential points of failure.”

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