House Projection Mapping
How do you do projection mapping on a house?
Whether it’s your aim to create digital decorations for Halloween or you want to design Christmas video mapping and other holiday projections, this article will guide you step-by-step through the process of 3d projection mapping a house or building.
It will help you decide what kind of projector you might need, what software to use as well as more tips and advice.
Projectors & Equipment
As a starting point, check out my kit list for house projection mapping.
In there I’ve given all the details of the hardware, software and other accessories involved in my house projection shows.
I use a 2200 lumen short throw projector. “Short throw” means that it has a lens which produces a larger image at much shorter distances away from the projection surface – in our case, the house – compared to a ‘standard’ lens.
Should I Use a Short Throw Projector?
The advantage of using a short throw projector is that you can project from fairly close to the house; you are not forced to have the projector at the end of the garden or even across the street.
A projector’s lens will have a throw ratio.
Throw Ratio = Throw Distance / Image Width
To calculate the ideal throw ratio for your projector, you need to decide:
- The distance you want to place your projector away from the house (Throw Distance)
- The width of the area you want to cover with projection on your house (Image Width)
Make sure your units are the same for both measurements. In other words, if you want to project from 10 metres from your house, make sure the Image Width is also in metres.
Plug your numbers into the formula above and you will end up with the ideal throw ratio for the lens of the projector you need.
How Bright Does the Projector Need to be?
I use a 2200 lumen projector and I found that to be bright enough.
However, it’s worth saying that my house projection show took place in a rural area where there was no competing light whatsoever.
In an urban environment, extraneous light can come from sources like street lamps or your neighbours’ yard lights.
If you are dealing with ambient light that you can’t eliminate, you might need to opt for a brighter projector.
Be aware that when a projector claims to be a certain number of lumens, it doesn’t always perform to those specifications. Read reviews of a projector model’s real-world performance when it comes to brightness.
As a rule of thumb, more expensive projectors from reputable manufacturers will output brightness closer to the promised lumen rating.
Mac or PC?
As far as I’m concerned, you can achieve good results with both.
Check the minimum system requirements for the software you intend to use, be it After Effects or other software, and make sure your machine is up to the task.
The laptop or computer you intend to use for animating and projection mapping needs to be fairly high performing by way of memory, processor, internal drive and graphics card.
Unless you want your laptop hooked up to your projector for the duration of the show (not recommended outdoors) you will need a media player.
This is a small piece of hardware that connects to your projector. You load it up with media and it sends a display output signal to the projector in place of a laptop.
You can set it to loop or shuffle through your media files as needed.
See the media player I use here.
In order to select an appropriate cable to connect your projector to your laptop or machine, you must check
- The display outputs from your laptop/computer
- The available inputs in the back of your projector
Either physically look at the ports in both machines to find this information. Or look in their manuals.
HDMI is a very common signal for transferring HD video and audio.
Remember that cables can be either male or female, so make sure to check you are buying the right kind.
The other pieces of equipment you are likely to need are
- An extension cable so you can run power to your projector and laptop over a large distance.
- A sturdy table onto which you put the projector. Remember, a wobbly table results in wobbly projections!
What is the Best Way to Projection Map a House?
There are at least two approaches to projection mapping a house.
With one method, you fix your projector in position and design all your animations and video content from the projector’s point of view.
The other method, which I call the neutral or ‘orthographic’ method, involves designing neutral content, without a point of view. This video content can then be mapped on to the house from any projector position.
- Fewer steps to follow
- More intuitive
- Very little flexibility to move the projector
- Best audience viewpoint is behind the projector
- Additional projectors require their own video content
- Requires more time outside
- Not true ‘mapping’
- Flexibility to project from anywhere
- Unobscured audience viewpoint that does not have to be behind the projector
- Use the same video content for multiple projectors
- Very little time spent outside
- A few more steps to follow
- Less intuitive
So Which Method is Best?
It’s probably obvious that I prefer the Orthographic Method!
Creating a Guide
The first step involves creating a guide over which we can design our video content.
This guide must be free from perspective or any ‘point of view’.
To do this, we take lots of reference photos of the house during the day (20-30 should be enough).
Then we feed these photos into photogrammetry software in order to generate a 3d reconstruction of our house.
I use Meshroom, which is free. It can be used on Windows or Linux and requires a Nvidia GPU.
If you are on PC or Linux but don’t have a Nvidia GPU, there are other free options available like 3DF Zephyr Free.
If you are on a Mac you can try Regard3D.
Then we clean up our model and straighten it up in a 3d application like Blender, which is also free.
We then export a front-on view of our house model and take that in to Adobe After Effects. In there we create outlines of our house by using masks and the Stroke Effect.
Animating Video Content & Using Free Footage
After Effects can feel very intimidating at first, but once you have the basics under your belt, you can very quickly start to design unique animations of your own.
The tutorial above will help you get to grips with creating lights and shadows on your house.
It also shows you how to import free footage and remove green screen backgrounds using Keylight.
You will also learn simple animation basics like keyframing position and other layer attributes.
Where can I find free video animations & green screen footage?
I’ve put a list together of all the best places I’ve found to find free videos and green screen footage online.
Free Video Footage for House Projection Mapping
Find free footage, stock video and green screen animations online.
Preparing for Mapping
Once you’ve saved out your animation, there are a few steps you need to follow to prepare the file and make it ready for projection mapping in After Effects.
This involves splitting up the content into sections relating to the different parts of the house.
How do I know which sections get mapped separately?
The rule of thumb is that you map separately anything that doesn’t exist on the same plane.
For example, if you have a part of your house that is slightly set back from another part, those two sections get mapped independently and need to be separated.
As another example, if you have a porch that juts forward, that also needs to be split out from the main part of the house and mapped on its own.
Projection Mapping the House
If you have blinds or curtains in the windows of your house, make sure you close them. You also might want to put white paper in the windows to catch the projections.
Anything between the projector and the house will cast a shadow. This includes garden furniture, pot plants and trees and should be moved out of the way if possible.
Set up a table for your projector to stand on and make sure it’s sturdy.
How far does the projector need to be from the house?
You can calculate how far away the projector needs to be to cast an image over the whole house using the throw ratio of the projector’s lens.
Here is a handy projection calculator tool for doing this calculation. Just enter the make and model of your projector.
Personally, I make a guess where the projector will need to be and then move it closer or further away from the house as needed once the projector is casting an image.
Once it has got fairly dark, plug the projector into power, connect it to your laptop, turn it on and focus the image on the house.
Make sure your projector is set up as a secondary, external display and is not mirroring your screen.
Mapping the house
Once again, I’ve listed all the house projection mapping kit I’ve used.
The first thing you need to do is set your projector as your output display.
By applying the Corner Pin Effect in After Effects, pull the corner points so that the content maps correctly on to the house.
Mask out sections of content that are being cast where they shouldn’t be.
Once you’re happy with your mapping, export the video file with all the mapping applied. That way you can play your video file from an external media player connected to your projector. It will look correct on the house without the need for After Effects or even for the laptop at all.
From this point on, one thing is very important: the projector must not move. If the projector does move, you will have to go back and adjust your corner pinning again.
Copy your exported video to a USB. Then plug that USB into the back of the media player and connect the media player to power.
If you want to have audio with your show, the media player will likely come with cables which you can run out of the media player into a speaker or an FM transmitter.
Set up the media player, typically using a remote control. Don’t forget to set the media player to loop continuously if that’s what you want it to do.
At this point you can leave your projector in place or stay with it if you are concerned about security.
If you are DIY-minded, you could create secure, weatherproof housing for your projector.
Now I hope you feel like you’ve got a solid beginner’s knowledge of how to projection map a house.
I’ve aimed to cover just the foundational principles so that you can now advance your skills in After Effects and create more elaborate, unique animations of your own.