In the past, using multiple projectors and syncing them for a projection mapping show required special hardware, software and expertise that was beyond the budget and skills of a typical home user. However, I have discovered a practical and less expensive method that can work for a lot of people. Now, don’t get me wrong. There is still extra expense and extra work involved compared to setting up a single projector system, but not an insurmountable amount.
But before I begin, it’s important to point out that even though I have successfully set up and tested a multi-projector setup, I still only use one projector on my house. For my situation, one projector works best. In fact, I think one projector will work best on most houses I have seen. But there definitely are situations where using multiple projectors makes sense. For instance, a long, ranch style house could benefit from multiple projectors, or a very large house. If you need help deciding whether to use multiple projectors, we are happy to advise you. Just contact us and send us photos of your house so we can evaluate.
Now, onto the tutorial:
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The HDMI Video Wall Processor
You have probably seen businesses that have a wall with multiple TVs lined up on it, as shown below:
One video is playing spread across all of the TVs. It’s a cool effect made possible by the use of a video wall processor like the small unit pictured below:
This processor takes one HDMI video source and splits it into multiple HDMI sources that provide a signal for each TV. The idea for our projection mapping application is to set up multiple projectors just as you would set up multiple TVs. You are simply replacing the TVs with projectors. As you can see in the above photo, there is one HDMI input and 4 HDMI outputs. Plug your computer or media player into the HDMI input and then plug your projectors into the numbered HDMI outputs. Using all 4 of the outputs is not required. Just use as many as you need. There are multiple modes available where you can select the number of projectors you are using and how you want them arranged. (Typically, you will want to use the 2×2 mode as that divides the screen up into 4 equal parts, each with a 16:9 aspect ratio)
You can spend a lot of money on one of these video wall processors, but pricing has come way down recently, especially on units without a lot of bells and whistles. I purchased mine for about $150, but there are even less expensive ones available.
HDMI Connections
Of course, you will want to position your projectors a good distance apart to cover different parts of your house and you will need to connect them via HDMI. Unfortunately, HDMI cables don’t work well if they are too long. 15 feet is about the maximum length that will work reliably. To get HDMI connectivity over longer distances, there are a few options.
This wireless HDMI transmitter/receiver kit pictured below, can work for distances up to 30 feet.
Wireless connectivity not only depends on the distance between transmitter and receiver, but also on how well radio signals work in your area. If you have radio interference or you need an even longer distance, you’ll need a hard wired solution. We recommend using these HDMI repeaters:
The repeaters boost the HDMI signal so that it can be transmitted through a standard network cable for distances up to 196 feet. Network cables are available in varying lengths. This 50′ outdoor cable pictured below will work for many applications
Power Extension Cords
Since multiple projectors are often used on larger buildings and properties, you may need longer extension cords to provide power. If your cord run is long, you may run into electrical trouble because your equipment is not getting enough electricity. The solution is to use a heavier gauge, or thicker extension cord. Gauges are identified by a number and the higher the number, the thinner the cable. Common extension cord gauges are: 16 gauge (thin), 14 gauge (medium), and 12 gauge (thick). For runs over 100 feet, 12 gauge is recommended.
Minimizing The Seams
Just like the edges of the TVs in a video wall create seams, you will have seams between your projected images. Unfortunately, getting the edges to align perfectly and seamlessly will be virtually impossible. Your goal will be to get them aligned close enough to be acceptable. On the positive side, there are some strategies you can employ to minimize alignment problems.
The architecture of a house usually provides natural breaks where you can hide the seams. For example, if you need to cover one large flat wall with multiple projectors, try to use the edges of windows or doors or a downspout to disguise the seam.
Another strategy would be to dedicate each projector to an area that already has well defined boundaries. For example, you may want to dedicate one projector to cover your garage area and another to cover the entryway.
Drawing Your Map
The process of drawing your map with this multi-projector setup is virtually the same as with a single projector. First draw one map for each projector following our tutorial here.
Once you have your maps done you can send them to us and we will put them together into one master map for you, or you can use Photoshop or a similar program to do it yourself.
Typically, your map images will each be 1920 x 1080 pixels. If yours are not, enlarge or reduce them to fit that size
Create a blank image that is 3840 x 2160 pixels and copy and paste each map into the new image as a new layer. Visualize your setup just like the TVs on the wall arranged in a 2 x 2 format. The illustration below shows how mapping for each projector will be arranged on your multi-projector map. Move each layer to the appropriate position. Alignment must be exact.
In this example, 3 projectors would be used. You could potentially add a 4th projector or subtract one to only use 2 projectors. The unused areas will remain blank and that is just fine. Leaving areas blank will not diminish the quality of your final show.
Save that image and send it to us. We will create a test video you can use to check the alignment. Keep in mind that your video wall processor must be set to 2×2 mode for this to work properly.
Video Resolution
To get the highest quality images, it is best to use a 4K resolution video (3840 x 2160 pixels) as the source input for the video wall processor. That way, when the image gets split up for each projector, the output will still be fairly high quality at 1080p (1920 x 1080). If you use a lower resolution source video, the quality of the final images will be inferior.
The media players we recommend can output 4K which is perfect for this application.
Normally, we render our videos at 1080p, but when we see that you have a multi-projector setup, we will render yours in 4K.