EPI

How To Set Up A Video Wall


How to set up a video wall

By Tom Hrabak, DSCE, DSDE,

Sr. Technical Sales Mgr., Philips Signage Solutions, North America, operated by Envision Peripherals Inc.

As a first timer, there are a few basic things to know when setting up a video wall for your business. Most often it’s the installer who provides the details you’ll need to efficiently be up and running. However, there’s one particular area that remains fuzzy and unknown and can be problematic for you.

Here’s the issue: In some cases, an extension is required to be placed between the engine and displays of their new video walls (as shown in Fig. 1). It’s important to know that a PC has the capability of sending both a PC signal or a video signal, while a media player can only send a video signal. In a multiscreen array or video wall, half the displays may show they are receiving a video signal; the other half may show they are receiving a PC signal. That’s when you start having problems.

Here’s the situation: An embedded software protocol in each display or screen, called EDID, for Extended Display Identification Data, allows the video wall displays and PC engine or player to correctly talk to each other. Each display needs to know precisely whether or not it’s receiving a PC or video signal so it can properly react to it and display the right format. When a signal is sent to one single display, that display may accurately identify the correct signal format. But once that signal is sent to multiple displays or is daisy-chained to the rest of the video wall, it may be converted to a wrong signal or not sent altogether.

Also, a wrong signal can be sent if the player has multiple display outputs and each output is not able to clearly define what signal type or format needs to be sent to each display.

The problem is that, when the EDID information isn’t accurately received at the graphics card that’s in the PC for all the displays or screens, the graphics card software is befuddled and doesn’t quite know the type of signal to send. The graphics card’s EDID may think it’s connected to a peripheral device such as an extender (HDMI, etc.) or switch instead of multiple monitors for a video wall or any other type of multiscreen array — and as a result, it could send out a video signal instead of a PC signal to one or more displays.

What does this mean on the big screen?

If the communication between player and video wall isn’t being correctly performed, those problems manifest themselves in two main ways. Since monitors may react differently to a PC signal versus a video signal, color differences among the displays in a video wall can occasionally be among the foremost differences. Plus, there can also be a synchronization issue because of differences in the two signals due to the way they are conveyed to each display.

If the sync signal is conveyed differently, then the display receives it differently. Consequently, there’s a chance that the image arriving on a signage display could be misaligned from one display to another, depending on whether the graphics card recognizes a monitor as a monitor or as a peripheral device, thereby resulting in a display receiving a video signal instead of a PC signal or vice versa.

A misalignment of a video signal between monitors has a potential to result in two major issues: content and/or color. For content, being misaligned from one display to the next normally presents itself in the form of a letter in a word, a person’s arm or an object, as examples, not being lined up from one monitor to the next.

The shifting that could occur in content could be a fraction of an inch or more, resulting in a complete misalignment between two or more displays. This difference can be quite noticeable to the customer looking at the content. For color misalignment, the end result could be a color shift between displays where a specific color — a shade of green as an example — may not be the same shade on the next monitor. Performing a color calibration could help in most cases; however, it is also possible that the difference in color space between a video signal and PC signal could be enough to prevent a color calibration from being effective.

The bits and bytes behind the issue

This issue may present itself when a video signal extender, such as an HDMI extender, is placed between the engine and the monitor or video wall. For example, the project owner has a PC with a built-in four-port HDMI output graphics card. Signals coming out via HDMI are then converted to RJ45 so they can extend to 150 feet. In effect, an extender line is put on each of the four HDMI lines to get to the monitor. At the monitor or display end, there’s an RJ45 receiver that converts the signal back to HDMI and then connects to the monitor (as shown in Fig. 1).

At this point, if the EDID protocol information is not necessarily received at the graphics card for all displays on the video wall, the graphics card may be confused. In its circuitry, it may not think it’s correctly connected to a display, and as a result, it tries to send out a video signal instead of a PC signal or vice versa.

The key is to ensure that all monitors receive the same video signal format, all PC signal or all video signal. One way to ensure that this happens for any multiscreen array is to ensure that the video signal extender allows for full EDID pass-through from the monitor and does not override the monitor’s EDID information in favor for the extender EDID info.

Again, this can be seen when the graphics card sees an HDMI extender or switch or generic display instead of the specific monitor model connected to it. Second, the PC or media player should also be checked to ensure it is set to send the same resolution to all monitors connected to it.  As an example: 1920-by-1080 (PC) versus 1080i (video).

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