Week 10: Hologram Projector

Holograms & Pepper’s Ghost

Ever been to Disneyworld? Have you been on the Haunted Mansion ride? Throughout that ride, ghosts appear in the rooms before you (and -spoiler- sometimes, in the ghost-mobile with you). Perhaps you’ve been to or have heard of concerts where a dead performer takes the stage again via ‘hologram’? These are all achieved by an illusion called ‘Pepper’s Ghost’. This is the same effect that teleprompters use too by the way. Through reflection and transparent screens, one can ‘project’ the illusion of an object (etc) in space somewhere else. I’m interested in these kinds of effects for data visualization and for public archaeology uses. In this exercise, I show you how you can build a ‘holographic projector’ that uses the Pepper’s Ghost illusion and your smartphone to project a digital 3d model into the space above your phone.

Here’s a version from a previous student:

Materials

  • plastic A4 (8.5" x 11") sheets. You can get these at Michaels fairly cheaply (where the intended use is to cover photographs in a frame). Alternatively, you can use a couple of CD jewel-cases
  • Ruler and pencil
  • Craft knife or scissors
  • Clear tape
  • Smartphone or tablet
  • Computer with presentation software (PowerPoint, Keynote, or similar)
  • 3d object model files (either made by you, or downloaded from Sketchfab.com or similar)

Step 1: Make the Pyramid Reflector

Cutting the Pyramid Pieces

  1. Create the template: Draw a trapezoid on paper with these dimensions:
    • Top edge: 1 inch or 2.5 cm
    • Bottom edge: 3.5 inches or 9 cm
    • Height: 2.75 inches or 7 cm
    • Side angles: approximately 45 degrees

The key element is that the angles are consistent; the actual size can be a bit smaller or larger depending on what you’re working with (eg, here’s a template from the Ontario Science Centre.)

  1. Cut 4 identical pieces:

    • Use the template to trace 4 trapezoids on your plastic sheets
    • Cut carefully with a craft knife for clean edges
    • If using CD cases, remove the covers and cut the clear plastic parts

  2. Assemble the pyramid:

    • Tape the 4 pieces together along the edges to form an inverted pyramid
    • The small ends should meet at the top, large ends form the base
    • Ensure all joints are secure and the pyramid sits flat

Step 2: Create the Hologram Content

Download or Create Your 3D Model

  1. Source your model:

    • Visit Sketchfab.com and download a cultural heritage 3D model
    • Or use poly.cam to create your own 3D model
    • Choose models with interesting details that will look good spinning

  2. Record the model animation:

    • Open your 3D model in a viewer or 3D software
    • Start screen recording on your computer
    • Slowly rotate the model 360 degrees (about 10-15 seconds)
    • Save the video file

Step 3: Create the Multi-View Video

Using PowerPoint or Keynote

  1. Set up your slide:

    • Create a new presentation with a black background
    • Insert your recorded video into the center of the slide
    • Resize the video to about 1/4 of the slide size

  2. Create the four-way mirror effect:

    • Bottom video: Place your original video at the bottom center
    • Top video: Duplicate the video, flip it vertically, place at top center
    • Left video: Duplicate again, rotate 90° counter-clockwise, place on left
    • Right video: Duplicate again, rotate 90° clockwise, place on right

  3. Positioning is crucial:

    • The bottom edge for all four videos should be oriented toward the center of the screen
    • Leave a square gap in the middle (about 1 inch square on screen)
    • The videos should form a + or X pattern
    • Ensure all videos are synchronized

  4. Export the final video:

    • Play the slide in presentation mode
    • Record your screen while the presentation plays (on a mac, cmd+5 can take a screencapture movie; on Windows I think it’s windows key+G)
    • Save this recording and put it on your phone

Step 4: Illusion Time!

Setup and Viewing

  1. Prepare your phone:

    • Transfer the final video to your smartphone
    • Set screen brightness to maximum
    • Disable auto-lock/sleep mode

  2. Position everything:

    • Place your phone flat on a table, screen facing up
    • Play the video in full-screen mode
    • Carefully place the pyramid over the center of the screen
    • The pyramid’s small base should cover the central square area (ie, the pyramid is upside-down)

  3. Optimize the viewing:

    • Dim the room lights for best effect
    • View from the sides of the pyramid
    • The 3D model should appear to “float” above your phone!

Troubleshooting Tips

  • Blurry reflection: Clean the plastic surfaces thoroughly
  • Image not centered: Adjust pyramid position on screen
  • Dim hologram: Increase phone brightness and reduce ambient lighting
  • Distorted image: Check that all video orientations are correct

How It Works

This creates a Pepper’s Ghost illusion where each face of the pyramid reflects one of the four video angles, creating the appearance of a 3D floating object when viewed from the correct angle.

Variations to Try

  • Use different 3D models (animals, artifacts, geometric shapes)
  • Create videos with multiple objects
  • Experiment with colored backgrounds
  • Try different pyramid sizes for tablets vs phones

Ta da! You now have a working hologram projector that creates 3D illusions for cultural heritage materials.

Question for you: is it worth it? How does interacting in space differ or create meaningful differences than interacting with a screen? Facebook and other companies are spending a lot of money on vr, augmented reality, or ’extended’ reality. Where does this fit on that spectrum, and what would enhance the experience?

Incidentally, I’m building a system right now that sits on top of a 30" monitor laid flat. I have coded an application that automatically takes a window on your computer and arranges it four-fold for projection onto a pyramid. I envision something like what this student at OCAD built combined with a 3d print of an archaeological site, where GIS data is projected in real-time onto the print. We’ll see how it goes.

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