Today I am going to show you how I created some simple spooky Halloween window projections. The first thing we need to do is determine the best location for us to projection map onto. We want to find a window that is large enough to showcase our projection content to be visible from far away. Additionally, it is helpful to choose a window that is easily accessible from the inside of the house. In my case the house I'm using to projection map has two windows upstairs that are large enough to be seen from the street. The window on the left measures 5 feet wide and 6 feet tall and the window on the right is 5 feet wide and 4 feet tall. Make sure you measure the dimensions of your windows since you will need this later to calculate the surface resolution.

In order to accomplish this projection design we are going to be using a technique called rear projection. Unlike you might see in a movie theater rear projection is when we place the projector behind the screen instead of in front of it. This however causes a couple of problems that we need to be aware of. Traditional projection screens are designed to not let any light through. This makes sense because when you do front projection we want all of the light that bounces off the screen to end up going back into the viewers eyes. Also, since the projectors beam has to pass though the material some brightness is lost. Thankfully, there are special screens made just for rear projection. And you can pick these up on many different online retailers. Unfortunately these can be expensive and bulky. Also, Rear projection screens normally come in a 16 x 9 aspect ratio and it is highly unlikely the the windows in our house are going to line up perfectly with a screen.

Because of this I decided to go with a different approach and used some white plastic tablecloths. This is the one time I went to amazon and purposefully looked for a cheap product that had negative reviews. I found this 4 pack of tablecloths that had complaints that it was too thin. While that would make a tablecloth bad for being used as a tablecloth it is good news for us if we want to use it for rear projection since more light will pass though. Also, thin tablecloths are great since they are cheap and easy to install and dispose of after you are done. I simply used Gaff tape to tape the corners of the tablecloth to the corners of the window making sure to pull it taught so it would not move and to remove any wrinkles. One of my windows was larger than the tablecloth was so I had to overlap them in the center. If possible get a tablecloth that is large enough to cover the entire window or else you might have a very faint seam in the middle.

Now it is time to tackle the system. I ended up using one projector for each window particularly because they were in different rooms of the house. If you have multiple small windows that are close to each other you might be able to get away with using one projector to cover multiple windows. I went ahead and I set up my projectors and connected them back to my computer using HDMI cables. Now that we have the projector set up it's time to think about content. Since I only had a couple of days to get everything up and running I decided to do a simple projection design. I used the MO2 plug-in with Final Cut Pro along with the Halloween objects pack to create three-dimensional Halloween shaped particles export of those with a transparent background. Next, I used Apple motion to create various backgrounds such as caustics, rain, and fog.

Now the fun part begins with the actual projection mapping process and getting to see content on our windows. Using the dimensions of the windows we wrote down earlier we need to calculate the surface resolution. We will do this by finding the ratio of the width to the height and multiplying a resolution of one axis by that ratio. I created a previous post on that so please check that out. Since this is a simple projection design I will be using Qlab. We need to create one surface per window that we want to projection map onto. Then, we will use the resolution we calculated before. Lastly we need to go through the projection mapping corner pinning to map the surface to the window. Check out the projection mapping basics article I created for QLab on instructions on how to do this in more detail.

Now let's go ahead and drop our projection content we created into cue lab. Since the backgrounds and particles were rendered out separately we are able to layer them within QLab. And with that we have created some simple spooky Halloween projections for our windows!