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Using DMX Merge for Pixel Mapping

Vickie Claiborne • April 2020Video Digerati • April 8, 2020

Video content can be mapped beyond the screen and synched with lighting fixture colors and effects.

With today’s productions relying more and more on visual impact, the video and lighting elements of a show play huge roles in creating those wow moments that audiences remember. Prior to media servers, tying in lighting with the video required a lot of programming time to match colors and movement from a video across lighting fixtures in the rig. Now, media servers make that process much simpler and less time-consuming through the process of pixel-mapping. But there are some “gotchas” in the process of merging data together from two sources that are worth pointing out. So let’s take a closer look at the process of mapping the color values of a video image from a media server to the color channels of a lighting fixture via DMX, Art-Net and/or sACN.

Most media servers on the market today include pixel mapping as a function. I say “most” because the term “media server” is broad enough to mean anything from a simple one-output standalone video playback device used for digital signage to a very sophisticated video presentation management system. The type of media server I’m focusing on for this article is the type that allows the user to create a “pixel map” within the software that then converts the color data of an image overlaid onto the pixel map into DMX information that will be output to RGB LED fixtures (or fixtures with CMY based color mixing systems) via DMX, Art-Net or sACN.

This process starts with creating the pixel map in the media server, of course. Depending on the server you choose to work with, that process can range from easy to hair-pulling. But the end result is essentially the same: you create a layout of your fixtures by positioning them within the raster where your video image is to be displayed, and their location determines what color data those color channels in the lighting fixture will receive when merged back into the lighting network.

‡‡         Merging Color Information

Merging color information from a media server into a lighting system is a bit of a networking challenge. I’ve worked with a wide variety of servers and lighting consoles, and I can attest that they don’t all share the same approach. And they are not all simple to set up, either. In fact, because of the complexity of merging, there are now entirely stand-alone protocols with related convertor boxes available for the sole purpose of talking directly to the lighting fixtures from the media server and thus, eliminating the need for merging data back into the same system as the rest of the lighting rig. ArKaos’ KlingNet and the proprietary Kling Force LED control box are examples. The Kling Force LED is used to provide power and data to KlingNet-friendly lighting fixtures.

An advantage of using a completely different network for communicating directly to the light fixtures is that the programmer only has to select a piece of media, and the fixtures will display it. A downside of using this method, however, is that it requires an entirely separate network for transmitting the color information to the fixtures, so you need double the cables and extra hardware such as switches and convertor boxes to use it. Not to mention that KlingNet is a proprietary protocol, so you need an ArKaos media server as well.

If you’ve decided that you would prefer to use a non-proprietary data merging configuration instead, you have some options. Some consoles will handle merging directly within the console, such as the grandMA and Hog lighting consoles. This simplifies cabling, because if everything is already connected to an Ethernet-based (Art-Net or sACN) network, then the data is pumped out of the media server and directly back into the same network. If your lighting console of choice doesn’t give you the ability to input data back into it directly, then you are not out of luck. There are DMX merge boxes from companies such as Enttec (the Datagate MK2), for instance, that will do this job for you very nicely.

‡‡         Data Priority: LTP vs. HTP

Regardless of the way you configure merging your media server’s pixel mapping data back into your lighting system, you will need to consider priority. The priority of a piece of data in the system can be managed in two different ways: LTP and HTP. LTP, or Latest Takes Precedence, is commonly used in tracking values between cues. It is not the best choice for merging two sets of data to a single DMX channel, however. Instead, HTP, or Highest Takes Precedence, is the priority method that makes better sense. And in fact, without HTP, merging doesn’t work well at all. Why? Because using HTP, the DMX channel will only listen to the channel with the highest value.

So the key to merging is using HTP. On the lighting console, in order for the “higher” values of the information being received from the media server to become active, the color channels of the fixtures that are a part of the pixel map must be recorded at zero in the console. Often times, programmers will simply park/unpark those channels at zero, effectively enabling/disabling the data merge. (Savvy programmers make macros to do this so it’s only one button). And some consoles have built in features that allow the programmer to select channels directly in the network window and enable Art-Net/sACN input (such as the Hog 4).

If merging using an Art-Net/sACN network, there is a bit of configuring universe/subnet offsets that may also need to happen to make merging work the way it’s supposed to. Typically, the data coming from the media server need to be on a separate universe than the control data going to the media server. Then, in the console or the merging box, you point (map) that data back to the desired color channels on the fixtures. That part sounds like it would be hard, but it really isn’t. Even so, it also isn’t something you want to put off until you arrive on site to configure because, again, not all consoles and merging boxes use the same approach, and networking does have its own set of challenges related to configuring IP addresses and subnets.

‡‡         The End Result

In the end, merging data from a piece of content to a DMX channel of a lighting fixture isn’t new. But as consoles evolve, the interfaces for merging also evolve, making it even easier to map a piece of content not only to your LED wall but also to the fixtures that surround the screen at the same time. And mapping a moving image across a rig of lighting fixtures will produce organic lighting effects that not even the best effects engine can recreate. Learning to set this up is definitely worth the effort, so take the time to experiment with merging and start turning your LED or CMY wash fixtures into big moving pixels on your next gig!

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