This is a question that is asked almost daily. When I ask questions about the project, I learn that even the most basic understanding of the capabilities of video wall controllers is absent. This is clearly not because the designer is misunderstanding the application, but rather it is a case of not fully understanding the topology of video wall controllers in general.
Part of this problem is that the term “video wall controller” is a very broad category.
There are three distinct applications for video wall controllers. One application is for traditional LCD multi-display walls. The second application is for a direct-view LED display. The third application is for multiple edge-blended projectors used to create a large video display.
In each of these cases, the most basic function of a video wall controller is to divide an image into multiple independent parts so that a segment of the total image can be sent separately to multiple display devices. This is the primary function of any video wall controller. Once this function is accomplished, each individual segment of the image can be processed independently. This processing might include adjustments for color and brightness (gamma curve), and image adjustment such as cropping to account for a display’s bezel size, and in the case of projection walls, edge-blending to create a seamless image across multiple, independently projected source images. Finally, the last function of a video wall controller can be to allow multiple sources to be displayed within the video wall simultaneously. This might be done by tiling many source images across a video wall, or by creating a picture-in-picture layout.
When dealing with direct-view LED displays, one of the common misconceptions is that a “special” video wall controller is required. It is true that some video wall controllers may also contain LED driver circuitry. However, typically, it is never a good idea to select “jack-of-all-trades” devices. This is because, like the saying goes, it is the “master-of-none”. Instead, I recommend that we let the LED manufacturer provide the LED driver to perfectly match their devices, and use a separate video wall controller to manage the video image.
To better understand LED technology, we must agree that an LED is not a video display device. It is simple semiconductor. We ought to think of an LED as a solid-state light bulb. LEDs are single color devices. Multicolor LEDs can display different colors dependent on the mixing of multiple emitters inside the semiconductor to create each color. In the case of an RGB LED (sometimes called tricolor), there resides within a miniature control unit. This control unit directs the flow of current to each of the red, green and blue emitters according to a signal received from a driver device. Depending on the type of LED semiconductor, and its on-board control unit, a specific driver is always required to make the LED do its job. Therefore, it is wise to select a driver circuit that is perfectly matched to the specific semiconductors used by the LED manufacturer.
Once we have the appropriate driver circuitry for the LED device, we can consider the LED display as a “video device” and feed it with a standard video signal.
We now have LCD displays, video projectors and direct-view LED cabinets all on a level playing field. The next step is to determine
exactly how the source content is to be displayed on the video wall. Here, there are three categories of content. The first is a single source image spread across the entire video wall canvas. The next type is two or more source images where each source image is wholly contained within a single display device. Next, we have two or more source images spread across the video wall, where one or more of those source images spans across multiple display devices. Each of these three categories require a different kind of processing.
The first type of displayed content requires the simplest video wall controller. A single input is simply divided into segments matching the size and shape of the component displays. Adjustments can be made to account for the thickness of the display’s bezels so that from a distance, the whole image looks just like you are looking out of a multipaned window.
Some people choose to use on-board matrix capabilities that are built-in to some digital signage displays. This is seldom a good solution. The key to successfully blowing-up a source image to a much larger size is the quality of the up-scaling engine. High quality scaling engines cost a lot of money. Do you truly believe that a display manufacturer could sell many displays if the price tag included a high-priced scaling engine? Certainly not in today’s buying environment.
Instead, we can choose a cost-effective single-source, multiple output video wall processor that will handle just the tasks that we need for this application. These controllers are perfect for digital signage, and for large video spaces where the objective is to deliver a large video image economically. A good choice for this kind of processor would be the Datapath Fx4 or the Digibird VRC controllers. One note here. The Datapath Fx4 controller can handle displays mounted in either portrait or landscape orientation. The Digibird VRC can handle displays mounted in 45-degree increments, so that controller can be used for designer video walls. Digibird also offers a VRC-360 controller that supports displays mounted in 1-degree increments, so that any display layout that you could imagine is supported. Bothe the Digibird VRC and the Datapath Fx4 can take a 4K UHD source input and will support any number of output displays by daisy-chaining controllers, four outputs per controller.
The second type of displayed content is the tiled display, where each of multiple source images occupies only the area of a single display device. Here, if the content is static, you don’t even need a video wall controller. Just run the source devices directly into each display input. Using several inexpensive media players, like the Vivitek NovoDS, will allow you to schedule and display content to each independent display, over the network. A system design like this may be much more attractive than the added cost of a multi-source video wall controller. And, you’ll realize that since the source image is not being blown-up, no scaling is required.
In my next article, we’ll look at the third, and most complex type of displayed content – multiple sources spread out across the video wall, spanning across multiple displays.