In case you missed it, Snoop Dog rapped with a virtual Tupac Sunday night at the Coachella music festival in Indio, California. (The real Tupac was killed in a drive-by shooting almost 16 years ago.)

People are calling it a hologram, but it really wasn’t. Holograms are 3D. The image of Tupac was only 2D, but, still, it was a cool effect.

Tupac was a digital creation that took about 4 months to create and cost somewhere in the range of $100,000 to $400,000, but the basic technology for making it appear that Tupac was stalking the stage has been around since the 1800′s.

It’s an old magician’s trick called “Pepper’s ghost,” after John Henry Pepper, who popularized the effect in the 1860s.

The gist is this: There’s a piece of glass angled between the stage and the audience, and the ghost is reflected on that glass.

It’s the same trick Disney uses to make it appear as if ghosts are dancing around the table in the ballroom at the Haunted Mansion, and it’s how the cartoon band Gorillaz was able to perform “live” at the MTV Europe Awards a few years ago.

If you want, you could create your own holographic Tupac. Here’s how.

1. Create a digital version of Tupac. If you can’t do that, then use a still picture or shoot a video of something against a black background. I was in a hurry, so I grabbed my little Conductor toy from “Conjunction Junction,” because it’s small, and I was too lazy to find something better.
2. Lay the picture flat on a table. If you shot a video with a smartphone or tablet, lie your gadget with the screen face up.
3. Lean a piece of glass over the picture or video at a 45-degree angle.
4. Position yourself directly in front of the glass so that you can’t see the picture or the screen. It’ll look as if the object is floating in space. If you’re careful, you can make it look like your Tupac or whatever is standing on a flat surface, like a stage or a boom box. (If you look closely at the picture on the right, you’ll see I wasn’t being careful, at all.)
5. Try to think of some clever way to use this trick in the real world, like, say, putting people who don’t really exist live on stage, or the floor of your garage.