It's not pedantic because it has a material effect on what we're lead to believe this is. This is hacker news. A hacker knows (and cares about) the difference between a "3D hologram" and Pepper's Ghost illusion, and that distinction is important in understanding what has been achieved.

This is definitely a cool hack, but it does not involve 3-dimensional projection. This is a 2D image cast on to a 2D projection plane with no stereoscopic effect. That makes the term "3D hologram" a misnomer at best, and a gross misrepresentation at worst.

Because of this mislabeling, we're all sitting around talking about the inaccuracy of the title, rather than the fun part. That's the fault of the person who titled the article, not the person pointing it out.

The first thing he said is that it's cool. And he's right, it's not a hologram; some of us care about that, and would really like to see actual holograms. It's not an attempt to take away from the achievement here, rather a desire not to exaggerate it.

Down-voted your comment because you are confusing the truth with being pedantic.

This demo is neat. No question about it. I like when people play with ideas like this.

The demo isn't any more a hologram or 3D than if I took four LCD's, arranged them as the sides of a cube and turned down the lights. Other than not seeing through the LCD's, the images would be the same.

Again, as the person you are accusing of being pedantic said, this is no hologram and it isn't 3D in almost any imaginable way.

Notice how he moves from angle to angle quickly with the camera? That's because there are no volumetrics here. It's just a flat 2D image effectively seen through a 45 degree partial mirror.

It's a 2D image that appears to float in space. And it's cool.

Many, many years ago I thought about the idea of installing a screen spinning or translating (harder mechanically, easier imaging) at high speed in a vacuum chamber with transparent walls and then using lasers to project slices of a true 3D scene onto it. Challenging, but it would be really interesting to see how something like that works out.

It's not even "perceptually 3D" though. It's a 3D rendering projected in 2D.

How did you get a leap motion? What do you think of it?

Honestly, part of why I come here is for instant debunking of hype. So I appreciated it.

I loved how the public went crazy over a technology "invented" in 1873 and how people where like "finally holograms".

Holography entails the diffractive reconstruction of the wavefront corresponding to a 3-D scene, and optical holograms are generated using the coherent interference of light scattered from a 3-D scene with that from a second reference beam. Holography, by definition, necessitates scene reconstruction via diffraction. In the case of an electro-holographic display, diffraction patterns corresponding to 3-D scenes are computed and displayed on suitable light modulators to achieve wavefront reconstruction. This technology is still in its infancy, so you probably won't see anything truly holographic in the marketplace for some number of years.

As cool as this demonstration is, it's using a 19th-century technique -- "Pepper's Ghost" -- and cannot correctly be called holographic.

Here's work out of MIT depicting the true state-of-the-art in real-time electroholography: http://web.mit.edu/newsoffice/2011/video-holography-0124.htm....

Today's average 3D displays are "stereoscopic": they have 2 views, for the left and right eye. A real hologram shows the whole object, so multiple people can walk around it and see it from every angle at once.

But this isn't even stereoscopic. This is just a 2D image reflected on a piece of glass.

I think you need elements of light interference and diffraction for something to be a hologram.

It's essentially a way to "record" light the same way you can record sound in grooves or magnetic tape.

Well, like anything different tasks will call for different UI's. After looking at the OPs demo I could immediately see this being used with Radiology Imaging systems.

He moves the camera to another side across the edge in the video- it's far from seamless, it's exactly as you would expect- two images in perspective.

Correct.