So, in case you didn't like the Better Invisibility Suit.
To recap, the problem is to adapt the old idea of "cameras on one side linked to a screen on the opposite side" so that it works when viewed from all angles.
As before, we'll assume we want an invisible cube, for now.
There are two problems to solve:
1) how to have a camera on each face, but keep the camera itself invisible
2) how to have the image viewable from all angles, without parallax.
Here's how. We'll start with a clunky version which is easy to understand. We'll also imagine (for now) that we only want to be able to walk around this cube, and not climb above or dive below it.
On the front of the cube, we have a series of cameras. The cameras are strange, because each one is very tall (as tall as the cube) and narrow (maybe 1mm wide). It "sees" only a vertical stripe of its surroundings, looking straight out from the face of the cube. The face is covered with maybe a hundred of these tall skinny cameras, spaced 2mm apart.
In between these cameras are the display elements. Each element is a single column of LEDs, 1mm wide. Each display strip is linked to a single camera on the opposite face.
Everything is now fine: each face will display what is shown on the opposite face, in the form of vertical strips 1mm wide, with gaps of 1mm.
However, the gappiness is a problem. There's also a second, more serious problem - the illusion will only work if you're standing square-on to the front or back faces. If you look from an angle, you'll get a parallax error and the illusion will fail.
Now the cunning bit.
We take a clear plastic sheet with vertical ridges on it. The ridges are vertical lenses. If you put this sheet in front of the face of the cube, the lenses will direct the light from the LED stripes straight forward. Likewise, the cameras in the interleaved strips will see only the image from straight-forward.
Now move the sheet just a tiny fraction to one side. Now, the lenses in the sheet direct the LED output off at an angle, so that they can be seen only by someone who is off at that angle (the viewer standing square-on will not see anything - the lenses are bending the light from the LEDs away from him). Likewise, the camera strips will see an image from the same angle. (Remember, the camera strips on the front face are connected to the LEDs on the rear face, and vice versa).
Thus, as we move the lens-covered plastic sheet s l o w l y from left to right (on both the front and back faces of the cube, at the same time), the invisibility illusion will work first for someone standing off to the right of the cube, then for someone standing face-on, then for someone standing off to the left. When the illusion isn't "working" for someone (ie, when the sheet sweeps away from them), they just see darkness.
Now, persistence of vision is a wonderful thing. If we oscillate the sheet back and forth at sufficient speed, *all the viewers* will see the illusion working perfectly. Or, equally, a single viewer can walk past the face of the cube, and will see a perfect, parallax-error-free image at all times!
OK, now, we need to make it all a bit better. First, we may have difficulties keeping these oscillating lens- sheets "in sync" between the front and back faces of the cube. No problem: electronics can delay the image (as it passes from the cameras on one side to the displays on the other side) by a millisecond or two as necessary, to restore the sync.
Next, we want the illusion to work not just as someone walks around the cube, but also as they climb above it or crouch below it. Again, no problem: we use two sheets, at right angles, oscillating at right angles, so allow both vertical and horizontal compensation.
Finally, we might not want mechanical sheets (they will be hard to oscillate quickly, if they're big). Again, no problem: there are electrorefractive materials whose refractive index can be changed by a voltage, and these can be fashioned into lens systems which will "sweep" back and forth (and up and down) in the same way.
Gadulka!-- MaxwellBuchanan, May 28 2011 Apart from the rustling sound of a plastic cape being flogged about one's person by a frantic oscillating apparatus, what's to notice?-- infidel, May 28 2011 *ahem* I'm over here.-- MaxwellBuchanan, May 29 2011 Yeah, I know... and your fly is undone.-- infidel, May 29 2011 A kimono has no fly.-- MaxwellBuchanan, May 29 2011 What is that power cord, which apparently goes nowhere, doing in here?-- Boomershine, May 29 2011 Since you are after very precise directional projection, lasers might be better than LEDs. (Of course, with a sufficiently powerful laser, it's relatively trivial to ensure that any bystanders are unable to see the cube).
//A kimono has no fly.// (Consults list) Yep, that checks out.-- spidermother, May 29 2011 Make the suit spherical-ish, swap out the camera/led's for braded fiber optic cables and you could climb above or below it all you'd like and not see the suit. No power supply either.-- 2 fries shy of a happy meal, May 29 2011 //swap out the camera/led's for braded fiber optic cables//
I think the problem there is that the brightness will only be a small fraction of what it "should" be, since each fibre-path will collect and relay only a small fraction of the ambient light; you need some sort of amplification.
On the other hand, you could use fibres but have a "light amplifier" for each fibre in the middle of the sphere (ie, incoming light is detected, and a proportionately stronger light of the same colour is then emitted into the outgoing fibre). It then becomes, in effect, a camera/LED system again, but with the electronics remote from the lenses.-- MaxwellBuchanan, May 29 2011 I think the lag could be made quite small, given some very good electronics - a millisecond or two should be attainable, perhaps less.
In the first instance, I think a demonstration could be done (rather clumsily) using existing displays and cameras, albeit at low-res and slow speed. Once you put together a proof-of-concept (maybe make a simple cube invisible from front and back, with a viewed pixel-count of maybe 10 pixels per inch), you'd get serious interest in developing a dedicated system.
The spinning lens system is nice - I wondered about it, but wasn't sure how you'd avoid some sort of radial effect due to different sweep-speeds (plus you're then limited to a circular area). However, I suspect that clever lens design could get around that.
Also, clever lenses could mask the alternating stripes of the cameras (thin though these would be), by displacing some of the light sideways, as well as angling it for the viewers.-- MaxwellBuchanan, May 29 2011 random, halfbakery