When I crossed over from the television broadcast domain to the live events market a few years back, there was a fairly steep learning curve regarding all the lighting, staging and video equipment required to produce shows. With LED walls in particular, I figured that you simply connect a video signal to the LED wall, and presto — I-Mag images appear on the wall behind the lead singer. Well, not so fast, Sparky.
It turns out that an important video processing gadget is required between the input video signal and the LED wall — the LED digitizer. Regardless of the LED tile manufacturer or the electronic specifications of the little LED elements themselves, some form of digitizer is required. With minor variations, all digitizers perform the same basic functions. In layman’s terms, they translate video into pixels.
Inputs and Outputs
On the input side, some digitizers accept only one video format (e.g., SDI), while others accept a variety of video formats, including our favorite flavors: analog RGB, SD-SDI, HD-SDI and DVI. If the digitizer only takes a single input, you’ll need a scaler (such as Barco’s ImagePRO) to convert your format to the digitizer’s preferred input format.
Once accomplished, you can take just about any video device (such as DVDs, standard definition or high-definition cameras, media servers, PCs, etc.) and display its image on an LED wall via the digitizer. Typically, only one signal can be routed to a wall at a time, but certain advanced digitizers often allow you to switch or mix between inputs and even display multiple inputs simultaneously.
On the output side, digitizers send data to an LED wall instead of video. Depending on the manufacturer, some digitizers connect to a single wall only, while others can drive multiple walls — with separate output banks that can drive both new generation and older (legacy) LED tiles simultaneously.
Typically, coax cables are used to connect data from the digitizer to the walls. However, when multiple walls are used around an arena, the distance from digitizer to wall often exceeds the “signal loss” specs of the cable itself. For those cases, most rental and staging companies will be prepared to use fiber-optic transmitters and receivers to extend the signal over very long distances.
The Magic Inside
Your typical LED wall on stage isn’t a solid sheet of electronics. Instead, the wall is composed of multiple small tiles (or modules) fitted together with precision and rigidly supported by a frame — with both power and data running between each individual tile. Depending on the set designer’s creative concept, LED walls can be formed into squares, rectangles, strips or “slivers” of video, or even built into a checkerboard. And when you see a curved LED wall, it’s still composed of small square modules, but the frame that supports the tiles is the actual curved element.
Internally, a great deal of image manipulation wizardry occurs between the digitizer’s input and output stages. Essentially, the digitizer performs three major functions: scaling, mapping and image processing. To help you visualize this functionality, think of the digitizer’s internal electronics as a canvas of pixels on which the user defines and lays out their tiles.
Scaling
With this canvas in mind, scaling is the process of reducing or enlarging an input signal to fit a selected output resolution. When you adjust your PC’s desktop resolution to that of your LCD monitor (e.g., 1280 x 1024; or 800 x 600), you’re effectively scaling.
As you know from experience, some resolutions look better than others, and it’s the same when scaling to an LED wall. The best quality image is achieved when no scaling is required — that is, when the video content matches the LED wall’s exact pixel dimensions with a 1:1 ratio. However, content designers don’t always know the final size and shape of the target LED wall, so scaling is required much of the time, and each digitizer performs the task with ease.
Mapping and Processing
The next key function that the digitizer performs is mapping, which enables users to place an input video signal on the digitizer’s canvas, and select which portion of the signal to route to the wall. Similar to “cropping” in PhotoShop, this is the manner in which video is mapped to LED walls of all sizes and shapes. With more advanced digitizers, multiple inputs can be placed on a single electronic canvas and routed to different walls simultaneously.
The last important role of the digitizer is image processing, which includes all the visual adjustments required to make the image look its best. These adjustments include brightness, contrast, sharpness, hue, saturation, detail enhancement and noise reduction. Often, a few “special effects” are thrown in for good measure — such as freeze, image strobe, monochrome and negative video. All combined, the video engineer uses these adjustments to ensure that colors are true on the LED wall, with proper brightness and contrast. In multiple LED wall installations especially, these adjustments are also used to match colors across all walls on the stage.
Creative Apps
Well, this is all fine and dandy for sending video to standalone, rectangular walls, but LEDs are now manufactured in bar-shaped and circular modules, and they’re even woven into curtains. This flexibility enables set designers to create even more surprising structures out of LEDs. I distinctly remember two remarkable applications — a thousand-foot pathway of LED strips that snaked across the ceiling at the Detroit Auto Show, and Rascal Flatts’ “mothership” stage design used with the 2006-2007 “Me and My Gang” tour, where the checkerboard configuration of the flat LED tiles was curved, creating a semi-circular immersive environment on stage.
Mapping video to these non-rectangular wacky shapes typically can’t be performed with the digitizer’s on-board controls, so specialized software applications have been designed for this purpose. Programs such as Barco’s Director Toolset are PC-based apps that control the digitizer with far more latitude and creative mapping capabilities than can be done with the digitizer alone. A bit more training is required to use these apps, but the results are accurate and spectacular.
Always In-between
LEDs are usually rated by their pixel pitch — that is, the space between the individual LED elements themselves. An LED tile with a 4 millimeter pitch is virtually photo-realistic, as the tightly-packed LED elements resolve into a smooth, seamless image to the viewer.
A tile with a 20 millimeter pitch, on the other hand, would look awful inside a retail store, but actually looks pretty good when seen from the fast lane on the Interstate (on one of those new digital billboards).
Regardless of the application, the pixel pitch or the shape of the wall, there’s always a digitizer in-between the source video and the LED wall.
It’s not quite as simple as it looks, Sparky.
