### Help Me, Obi Wan

General Kenobi, years ago you served my father in the Clone Wars. Now he begs you to help him in his struggle to explain what a hologram is, and isn’t.

I only watched a few minutes of CNN’s election coverage before becoming ill (figuratively) and switching off the TV, so I missed where he called their camera trick a hologram. But it wasn’t, and several people caught it.

So what happened?

CNN focused more than 35 high-definition cameras on Yellin to get multiple views from Grant Park in Chicago for the look of a 3-D holographic image Tuesday. That made it appear as if Yellin was in the studio talking with CNN anchor Wolf Blitzer.

That’s a camera trick, but not a hologram.

Unfortunately, some of the criticism misses the mark. Uh, Wolf, That CNN Election Image Wasn’t a Hologram

A hologram is a photographic image that is three-dimensional and appears to have depth. They work by creating an image composed of two superimposed pictures of the same object, but seen from different points.

No, but I think I can see how the writer got from what a hologram actually is to this explanation. A hologram is a comparison of an image with some reference light, not the comparison of two images. Some of the light bounces off of the target and then interferes with the reference beam (and I think this interference pattern is the “superimposed” reference), and you record the interference pattern on the film. That pattern has all the information of the object, and when you pass a reference beam through the film (or off the surface, if it’s a reflection hologram) you’ll see a 3-D image.

The CNN image wasn’t 3-D. It looked something that was 3-D on the TV screen, but like everything else on the screen, the image was 2-D.

How Holograms Work

CNN’s Hologram. Real or Fake? calls the CNN technique a tomogram, which I don’t think is right. Tomography gives you 2-D slices of a 3-D object, and that’s not what’s happening here.

CNN’s “Holograms” Aren’t Holograms, So Cut It Out doesn’t attempt an explanation of holography, and is content to note that

It was movie magic, folks, similar to what we all remember from The Matrix. Given that it was done live without a hitch, it was extremely way cool. But it wasn’t a hologram, and no amount of wishing will make it so.

Zapperz, in Not A Hologram, has linked to an article that lists other instances of people misusing “hologram”