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  • Writer's pictureAndrew Murchie

When is a hologram not a hologram?

Updated: Nov 13, 2020

Over the last 18 months I’ve been fortunate to have a chance to experience some amazing technologies and chat with experts in fields that will in all likelihood play some kind of role in our future. One area that has always held interest for me is holograms and I was fortunate to meet Dr Javid Khan from Holoxica, an expert in the field and I found out an amazing amount about the production and uses of real holograms and cutting edge lightfield displays.

Even as a youngster, well before I had my mind blown by Princess Leia’s mid-air holographic projection in Star Wars, I had a small collection of holograms that amazed me. I would often sit staring, completely mesmerised by these little artefacts. How could a flat 2D, metallic looking sheet display a 3-dimensional image? In fact, I’m still not sure how it does!

In the world of cutting edge visual displays there’s an awful lot of bandying about of the term “hologram” or “holographic” and a number of the real experts in this area can get somewhat frustrated with the misuse of the terminology (admittedly though this is somewhat amusing - the phrase "but that's not actually a hologram" does make me smile).

So when is a “hologram” not a “hologram”?

What is a hologram?

As an intro let’s be clear what an actual hologram is, then we might better understand what it isn’t. Wikipedia defines a hologram as “ A hologram is a real world recording of an interference pattern which uses diffraction to reproduce a 3D light field, resulting in an image which still has the depth, parallax, and other properties of the original scene.”

I’m not 100% sure this is accurate as my understanding of “a real world recording” would suggest that a hologram created completely virtually in software isn’t a hologram, and based on some of the marvellous digital holograms I’ve seen from Holoxica these are definitely holograms.

It looks like a hologram.

Professor Pepper's Holograms

The biggest culprits misusing the “h” word are typically those attempting to find a way to explain a well known illusion referred to as “Pepper’s Ghost”, which was pioneered in Victorian times and made famous by John Henry Pepper. This was a simple illusion, where a reflected image on a pane of glass made a person or object appear over the real scene.

Back to Wikipedia to define how Pepper’s Ghost works – “The essential device employed to stage the illusion is an optical beam splitter operated in reverse to combine two images towards the audience's point of view. The image of one scene is reflected from the glass surface towards the viewers, and the image of a second scene is transmitted through the glass. The stage lighting is controlled to selectively illuminate the scenes, but not the glass itself, which is invisible to observers. The combined image is genuine and not an illusion; the illusion consists of the audience not detecting the glass.”

The majority of contemporary “holograms” are actually variations on Pepper’s Ghost. Many will have experienced this illusion in one of its many guises.

A high profile variation on this has been used in live music performances to bring performers such as Tupac Shakur back to life, to have animated characters play “live” gigs or to have performers in more than one location at the same time. It is equally used in visitor attractions and theme parks to give the illusion of celebrities being onstage in front of you or holographic characters introducing you to the ride or experience. In these instances, it is somewhat different to the traditional Pepper’s Ghost as it’s typically an ultrabright, high resolution projection onto a semi reflective “scrim” – when done well the illusion feels very real, and when adding a level of creativity in set design and programmed objects such that the “hologram” appear to do something a projection couldn’t do, such as knocking over a physical container on a desk, it can be really impressive.

For a range of promotional purposes, point of sale displays, visitor attractions and museums the technique has been widely used to create smaller scale cubic or pyramid shaped displays that present “holographic” animated/video content. Disney’s “It’s a Small World” ride had a marvellous magical display featuring small windows viewers could look into and view “holographic” animated characters appearing in physical miniature rooms.

Home users aren’t excluded from creating a fun Pepper’s Ghost illusion as it’s so simple – a sheet of Perspex and a monitor or projector with suitable content is really all you need. We used this technique regularly for Halloween parties over the years much to the delight of our neighbours. If you want to give it a shot without too much rigmarole you could try out grabbing some content from AtmosFX and follow their simple tutorials to get yourself up and running.

No matter how you spin it though, Pepper's Ghost based displays are an illusion, not a hologram.

Holograms in a Spin

Talking of spin, one of the more unusual “hologram” displays I’ve come across is a type of rotating LED array – a sort of fan that displays an animation when rotating. Quite bizarrely this does provide an interesting illusion and can grab attention due to it’s unique appearance. Videos of this in action don’t really do it justice – but equally it should be noted this does have a particular circular motion trail effect that somewhat gives away where the image is coming from. In saying that for a low cost item it does generate some visual intrigue.

But it's not a hologram.

Magic Misty Holograms

Another interesting display solution that has had the "h" word bandied about is mist screen projection. In this case an almost invisible screen is generated using water vapour which is sprayed out in a thin stream such that an image can be projected onto it. It creates an interesting illusion of a floating mid air "hologram" especially as you can walk through image that is projected onto the screen.

This is used commonly in theme parks and is a relatively straight forward display technology, in fact it's really generating the mist screen that is unique, otherwise it just a straightforward projection. Definitely not a hologram.

Augmented Reality Holograms

One of my first experiments with Augmented Reality was to create “hologram” business cards for myself and some of my Multiply colleagues at the time. Of course, this is yet another illusion whereby we’d shoot videos on greenscreen and use visual effects to make the video look like a Hollywood imagined “hologram”. These videos were then presented at 90 degrees to our business cards when viewed through our App – and voilà we appeared to float as holograms attached to our business cards.

These were good fun and a nice demonstration of simple AR in action – but they most definitely weren’t holograms.

Holographic Glasses Free 3D Screens

3D screens which can deliver 3d imagery without the need for users to wear glasses is used in digital signage to create some tremendous “holographic” style illusions, most often having products appear to float above the screen. These have been used in out-of-home (OOH) marketing and advertising, for theme parks, retail and trade shows with each successive generation of display improving on viewing angles and 3d fidelity.

These displays generally use lenticular lenses to deliver a stereoscopic image to the viewer and the fidelity improves as the number of possible view increases. With the viability of 8K displays hitting the market this now allows the technology to deliver higher possible numbers of views and with that better 3d fidelity.

These can present quite impressive 3d “holographic” illusions with 3d objects visibly extending beyond the screen when viewed in ideal conditions, but yet again they aren’t holograms.

Holographic Lightfield Displays

The most impressive of all the modern 3d glasses free screens I’ve experienced has been the Lightfield Displays from Looking Glass Factory.

These displays look somewhat like a block of Perspex and present what looks like solid objects within the screen. It’s quite difficult to describe this – words don’t really do the displays justice. In general these displays are excellent at displaying 3D modelled content whether static, interactive or even pre-animated viewers get a near perfect 3d view of the objects/scene and generally have the ability to move this around within the screen.

These screens aren’t really made for filmed content, although there are techniques in development to generate the multiple views required to deliver some type of 3d stills and video playback.

The development of volumetric video however, whereby video and 3d information is captured simultaneously to generate a 3d modelled version of whatever is recorded does start to present ways for live footage to be fully used on this type of display. Time will tell how well this approach works for longer form content.

Is this a hologram? I’m still really not sure!

Princess Leia, you are our only hope.

So as you can see although there are a great number of often unique displays purporting to be “holographic” but these still aren’t really holograms – based on the laws of physics it seems unlikely that the type of hologram imagined by Hollywood will be possible, never say never of course but it’s going to be quite some time before our AI assistants project a floating hologram onto your desk letting you know your coffee is ready!

Andrew Murchie is a creative technology consultant based in Edinburgh, Scotland specialising in stereoscopic 3d virtual reality films. He has produced Virtual Reality experiences for clients including Kimberly-Clark, Kraft-Heinz, Loch Lomond Distillers, Highland Spring and Tennent Caledonian Breweries.

Unsplash Photo Credits

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