Introduction: Decorating Your Snow With Anamorphic Projections

About: A lowly geologist who likes to build stuff.
Some people feel that a blanket of fresh snow is enough to get their Christmas spirits up. Well those scrooges don't live in my house; I would hang tiny Christmas ornaments on my ornaments if I could. 

It occurred to me that a fresh blanket of snow creates magnificent blank canvas, ready to be decorated. But how does one apply the colors to create the art without ruining the canvas by walking on it. Renting a crane and hanging from a tether in the style of Mission Impossible may provide some entertainment for your neighbors, but not much else I suspect.

I used a digital projector located in an upstairs bedroom to create images on the snow below. People regularly stop in front of my house while the show is playing. I think they are mostly curious as to the source of light. I wanted to create some anamorphic 3D perspective wizardry with the images in the style of Julian Beever's amazing chalk art. "Greasetatoo" has a great instructible on how to achieve this visual illusion and I have largely applied his methods to the medium of digital projection and video. This was  a really fun project which forced me to learn about perspective, anamorphic art and video animation.

See the video below to see the entire show, or at the very least skip to 45 seconds to see the whole yard crumble away.  At 124 seconds I look up to reveal the position of the projector, and the remainder of the movie is merely to illustrate how deformed the images need to be to trick your eyes from the vantage point in the street.

Step 1: STEP 1: Requirements

For this project you will need:
  1. Computer (a recent model with decent video card is advisable)
  2. Digital Projector (> 1000 lumens) 
  3. Drawing software, I used Corel Draw (Gimp is available for free)
  4. Movie software, I used Adobe After Effects (Imovie or MS Movie Maker for free)
  5. Some snow, the fresher the better: Check out the sad sad probability map for the US... Living in Winnipeg has to have SOME advantages.
Given enough time and experience you can largely make up for less than state of the art software. The quality of your projector, however, is going to have a direct impact on the quality of the final product. The model I use is a ≈1000$ consumer model (Optoma HD20) which has 1700 lumens, 4000:1 contrast and 1080p resolution. This is more than enough power and quality; you may be surprised how well your old office projector will work. Fresh snow provides great reflectance; and depending on the placement of streetlights, you could impress with less than 1000 lumens. You can also reduce the size of projection (by zooming or moving your projector closer to the target) to gain some precious brightness.

Step 2: STEP 2: Gain Some Perspective

I was attempting to create anamorphic art: basically deforming the image on the surface to create the impression that it is present in three dimension. In this case, the still images are meant to appear as they are standing up. The illusion is not as striking as I wished (see the Lego Terracotta Warriors by Planet Streetpainting above to see what is possible). Again I would like to direct you to Greasetatoo's great instructable:

To produce the maximum effect (and for future attempts):

   1. Longer distance in the viewing direction to amplify the effect by:
        A. Setting the projector on its side and
        B. Projecting across the street: this will change the keystone in your favor (the projector produces a rectangular shaped image that appears as a trapezoid (or keystone) with the narrow end nearest the projector (see the plan view).
    2. The use of shadows.
    2. Get someone with actual artistic talent to produce images that will pop.

Step 3: STEP 3: Living Off the Grid

This is the stage where you setup your grid that will allow you to deform your images and videos so that they appear in 3D from a single point of view in the street (Vantage Point). My computer and projector were setup in the upstairs bedroom. You should correct the keystone effect as much as possible using the functions directly on your projector (the goal is to maximize the length closest to your house). Once set, leave it. It is also a good idea to use the same computer that will be used for the projection for this step, because you may run into output resolution (aspect ratio) issues when switching between computers. 
  1. Create a grid in Corel Draw (or any drafting software that has a perspective function). You can try to match the aspect ratio of your projector (16 by 9) (red grid above). 
  2. Make a copy of the grid.
  3. Use the "perspective" function of  your software to deform one of the grids so that the short edge is towards the vantage point (in the street) (yellow grid above). 
  4. I'm sure that there is a mathematical function that will provide the shape you need to stretch the grid to. I needed the exercise more than the mental gymnastics, so I used the stair method instead. The stair method involves making incremental changes to the perspective of the grid and using the stairs to exit your house and stand on the "vantage point" to test the validity of your grid (5 to 20 times). I drew a pink square on the road with chalk to indicate the "vantage point" (anamorphic chalk art; no?). If you have a friend who understands what you are trying to do, then you can try the window yelling method (self explanatory). If there is any confusion during this process, you will inevitably go back to the stair method.
  5. How do you know if the deformation is perfect? When the grid looks square from the vantage point with all the cells being equal dimension throughout. The human brain is not very well adapted for judging this sort of thing; for this reason, even the Pros use a digital camera with a grid on it. See the video below to see what I mean. Basically, the squares are perfect and the same size from top to bottom. 
  6. The result is surprisingly extreme: the squares near the vantage point are about 20 times smaller than those furthest away.

Step 4: STEP 4: Deform the Images

At this step you will deform the chosen image to fit the grid you've created. 
  1. Import your image into Corel Draw;
  2. Use the "Trace Bitmap" function to transform the image into a vector drawing (careful, you likely have the original Bitmap hiding behind the vector version; and Corel Draw will not let you use the perspective function if it is in your group).
  3. Rotate the vector image so that the portion you want closest to the viewer to be at the narrow edge of your deformed grid.
  4. Re-size the Image to fit snugly within the square grid.
  5. Use the "Group" function to group the image with the square grid.
  6. Drag the new Group on top of the deformed grid.
  7. Select the new Group and use the "Add Perspective" function.
  8. Drag the corners of the group (image+square grid) to match the corners of the deformed grid so that all the squares are lined up. 
  9. Ungroup your image and export as a JPEG or whatever file format you want to use in your projection show.

Step 5: STEP 5: Create a Movie

I used Adobe After Effects 7.0 to create effects between the images. There are tons of great tutorials videos available online for this software, so I wont go into too much detail.
  1. I used a "Crumble" effect to transition between the images and to create the illusion that the yard was crumbling away to reveal the Jib Jab video below.
  2. In both cases I played with the gravity direction to match the direction the viewer should experience.
  3. I also tilted the layer representing my yard which crumbles down to match the deformed grid I created earlier. This provided a nice sense of depth.  
  4. I created a snow layer by using the "CC Particle System II" effect.
  5. The elf video was produced by using the JIBJAB Ecard website I filmed the computer screen with the camera held upside down. 
You can also string the images together in a free presentation software with some fancy slide transitions.

It is difficult to explain to my kids why they cant play in the front yard; "Santa wont come if you wreck his landing strip" seems to have done the trick.

Happy Holidays. 
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