Media Servers and Digital Lighting was a quick introduction to “convergence” and the technologies involved in using digital media for stage lighting. Current lighting trends include the use of arrays of fixtures such as RGB LED units to replay images and effects, using Pixel Mapping. This article looks at the basics of pixel mapping and asks if it is possible to re create some of these effects on a budget.

What is Pixel Mapping, exactly?

Pixel Mapping (in the World of Lampie) is the use of software to map and replay media such as bitmaps or video on an array (AKA grid or raster) of lighting fixtures. The fixtures could be anything; moving spots, PAR cans, Birdies but the use of colour mixing LED kit (inc Pixeline, Versa Tube or Color Web) is a common and appealing technique. You effectively get a low resolution screen to display your goodies, made from “pixels” of red, green and blue LEDs. In this article, we will refer back to the RGB LED model as it’s easy to understand.

Displaying the image on the screen is the job of the pixel mapper. Professional lighting media servers have mapping functions, pixel mapping software (like PixelDrive or the Arkaos Pixel Mapper) is available to run on a laptop and some lighting consoles can cope with a degree of mapping all on their own.

Pixel Mapping isn’t projecting media content using a projecter and firing it from the lighting console. The main brief of mapping is to turn your array of “simple” fixtures into a giant telly. The “screen” doesn’t have to be rectangular or even one complete surface – using pixel mapping, you could create some great effects with a long single strip of RGB LEDS or play a huge image across a number of different elements.

How does pixel mapping work?

The pixel mapper treats each fixture as an individual pixel and sends the correct information (usually colour and intensity) to the array.

Lighting fixtures are still commonly controlled using different implementations of DMX. With our LED “pixels” using up at least 3 DMX channels, you can see how even a small surface can use up hundreds of DMX addresses. Some control systems and media servers have their own proprietory network protocol to talk to each other, but talking to the fixtures themselves requires a standardised approach. Currently, the most common control signals are sent using ARTNet, the open source protocol for sending mulitple DMX universes. This can be split down at the surface or go straight into a proprietory control box for the LED sytem.

Pixel mapping is only an interface tool. It lets you create complex effects the easy wasy – with digital media. It certainly beats programming a 1000 step chase of complex RGB levels. It doesn’t have to be a full colour “screen” of LEDs. There is no reason why you can’t send the output to dimmers connected to a grid of PARS.

What information does a pixel mapper need?

Take the simplest system – a 3 x 3 grid of PARs (yes, you can’t display hi res video on this but it’s a good starting point). The pixel mapper needs to know that your array or grid is 3 pixels by 3 pixels – 9 PARs in a square.

The system also needs to know that PAR 1 (DMX dimmer A/001 for example) is top left and that the number runs from Left to Right, Top to Bottom. This means when media pixel 1 is ON, the correct PAR (Top Left) fades up.

If we had a 3 x 3 grid of RGB leds, it would need to know that DMX 0/001 was Red, Top Left; 0/002 Green, Top Left etc. When media pixel 1 needed to be Yellow, it would send 100% ish to 0/001 and 0/002. (If you are wondering what 0/ is, it’s just the numbering system we are using to identify DMX universes this time. The first ARTnet DMX universe is 0)

So, the pixel mapper needs to know the number of fixtures and the shape of the surface plus the positioning (ie. DMX addresses) of the fixtures. Media server pixel mapping software can have the fixture personalities of particular instruments to help with the DMX channels. The personalities are handy for the quick set up of large arrays using common fixtures such as Color Web or Pixeline. In our examples, we’ll just think in terms of a few simple RGB elements.

Pitch or Offset

Many products and layouts have a set pixel “pitch”. This is the distance between each pixel, vertically and horizontally, and is important when mapping onto surfaces where the pixels/fixtures aren’t jammed up tight together.

Mapping a screen image onto a surface with a wide pitch, the image ends up stretched all over. Digital media usually has a 1:1 pixel pitch ( the horizontal pitch is the same as the vertical). If your fixtures were 300mm apart sideways but 1m up/down from each other, the resulting image is stretched and squashed all over the place. Distortion of media might be a nice effect but only if you intended it to happen.

Some mapping layouts consist of a number of different “bits” of surface, spread apart from each other across stage. Getting an entire image to work across all the surfaces requires the actual positions of each piece being entered into the pixel mapper. Getting the heights and offsets correct, in the mapper as well as in the rig, can be time consuming. The final effect is worth it.

Content for Pixel Mapping

The suitability of content for pixel mapping depends on the arrays they will be replayed on. A really low resolution grid like our 9 PARs isn’t going to look much with an XGA full colour image across it. Although it is not always necessary to create media content at exactly the right resolution, understanding how the images will actually look is important. Great effects can be created with a low resolution array and some carefully chosen higher res media but think of the result of 16 million colours on those 9 PAR Cans. A bit of a dimmy, flashy mess. I don’t recommend trying to get those colours using scrollers – heh, heh!

Pixel Mapping on the cheap

We bet that you want ways to experiment with pixel mapping without going the expense of full on media servers or Grand MA’s. Quite a few cheap lighting control software has some form of pixel mapping function including the OSL favourite – Cham Sys MagicQ PC (some tutorials on pixel mapping the Cham Sys are in the pipeline). The onboard array control on the Cham Sys is similar in nature to the system on the Grand MA – creation of grids, applying fixtures and mapping images, text and other effects to them. The MagicQ also has the facility to preview the resulting output in a window, so you can see the result.

Previewing your pixel mapping is ideal when you are looking for a cheap solution to experiment with this kind of digital lighting. Even if with some free pixel mapping software, the chances of being able to set up a vast array of real RGB LEDs to work with are slim. Even getting hold of 9 working PAR cans is a struggle in some places

What cheap pixel mapping options are there?

I have done some hunting around on behalf of the On Stage Lighting readers. Many of the software mappers have free trials but some genuinely free pixel mapping software is .Matrix, a project developed by a student from Tulsa. Although not in current active development, .Matrix maps Quicktime files to an LED Matrix,.outputs ArtNet ArtNet and developer Landy Bible, tells us that current features are stable and show ready:

“.Matrix is stable in my experience, and none of my users have reported any problems with it.
The biggest problem that anybody wanting to use .Matrix will have is getting it working the first time. It relies on Java and Quicktime to do its magic, and Quicktime doesn’t always like to play nice with Java. Typically, reinstalling Quicktime after Java is installed will correct the problem. “

Landy also says that he has currently put extra features on hold ( more I/O devices like the Enttec Pro USB DMX) but hints that if enough people are interested, he would continue working on the software. So, why not download it and let us know how you get on.

On Stage Lighting readers always want to know how they can learn this kind of technology without huge budgets. Do you have experience of any free/cheap solutions for pixel mapping? Tell us about your experiences in the comments box.

If this has helped you, consider buying me a beer and CLICK HERE to donate a few bucks to On Stage Lighting (why should I donate?). Thanks, - Rob

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On Stage Lighting has a ton of stuff like this. You may also like:

• Media Servers and Digital Stage Lighting
• RDM DMX – A Guide to the Basics
• Lighting Desk Basics – Beginner’s Guide to a Stage Light Control – 1
• Gobos – A Guide To Choosing And Using A Gobo
• PAR 64 Bulbs – A Guide to PAR 64 Lamp Sizes
• ChamSys MagicQ PC – Free Lighting Control Software

Rob is a freelance LD and Programmer working the the UK events industry. He is also the Editor of On Stage Lighting

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