Optical Camouflage

Mike Siekkinen writes "This optical camouflage project is pretty interesting. It contains three videos demonstrating it in action. Basically they overlay a video projection of what the background behind the object to be camouflaged looks like. So if you were standing in front of a book shelf an image of the portion of the bookshelf you are blocking would be projected on to you. The results are probably better than you would expect."

Comments

Still can't figure out how it works...

[alphaseven]

Saw this on fark and boingboing a few days ago.

A number of posters on those site feel it's no big deal, a guy holding things in front of a projector... That's what I thought at first. But what I can't figure out is why doesn't the image show on the guys hands and face. You'd think at least some light would be reflected off of his hands.

Re:Still can't figure out how it works...

[uradu]

> why doesn't the image show on the guys hands and face.

What guy?

Re:Still can't figure out how it works...

[Orne]

When you watch football, and you see the yellow line drawn on the screen, do you wonder why it looks like it goes under their feet and not through their bodies? Think of it the same way the local weatherman stands in front of the map... real-time color analysis/replacement.

1. Take a picture of the background.
2. Put an object in front of the camera, painted with an obviously different color than the objects in the background.
3. Profit... no wait, I mean... using a computer, replace all the pixels of that special color with the pixels of the background image, and you have modern television overlays.
4. But this only works through a video feed; to move into real-space, you need a video projector. Take the image with the special color, and use it as a mask... the image will only shine where the special color exists, and not shine where it doesn't. That's how they get the projector to not shine on the hands.
5. Note that their special color is silver; like a white screen, a sufficiently light color such that color projected on it will appear. Viola!

Re:Still can't figure out how it works...

[Jonny 290]

Note that their special color is silver; like a white screen, a sufficiently light color such that color projected on it will appear. Viola!


If you use a different color, could you get, say, a cello, or perhaps a double bass?

Re:Still can't figure out how it works...

[alphaseven]

Answering my own question here (guess I'm the first person to read the pdf).

We used a pinhole as the projector's iris in order to obtain a perfectly focused image. Furthermore, the projected image through the small aperture on the normal surface is too dim to be perceived by human eyes.

However the light coming out from the projector is reflected on the half mirror then on the screen and goes straight back in the eye to form the image, which is about ten or hundred times brighter than the image on the normal surface. Therefore the image only appears on the retroreflective material so that the viewer can observe as if the images projected on the retroreflective material are occluded by the object which exists in front of the screen.

So the image projected is too dim to be seen, but the objects are covered in a special highly reflective material (not just colored lightly like a projector screen).

I guess it might be sort of like a dim flashlight hitting a bicycle reflector at night, you only see the reflector lit up.

That is so cool!

[tswinzig]

Now we just need to get the enemy to aim these giant projectors at us!

Re:holy sh*t

[lommer]

Ya, and it also requires that you have a half-mirror (one of those ones the cops use to watch interrogation rooms) in between you and the viewer. That is fine when you are dealing with a camera, but it isn't practically applicable to most areas that this would be useful in.

Re:Theator applications

[lommer]

I dunno, the half-way mirror thing kind of limits this application. Not to mention the parralax problems you'll get with an audience that is spread out.

Slashdot requires you to wait 2 minutes between each successful posting of a comment to allow everyone a fair chance at posting a comment.

"The results are probably better than you would.."

[Superfreaker]

I expect it to work as well as it did in James Bond.

Instead of using projectors though, Q explained that the car was made up of a material that acted like a screen. I guess like a plasma screen, or even that new electronic paper, it may not be that far off.

It would be much better than a projector...hmmm...

I love the references they made

[mselmeci]

* M. Shiro, Ghost in the Shell, Kodansya, 1991

I love it how they credited manga for the idea.

ohhhhh-kaaaay

[Twirlip of the Mists]

Two giant problems jump right out at me.

One: depth perception. Because we're watching movies of the demonstration instead of seeing it in person, it looks fairly good. But if you saw this technique in person, with binocular vision, you would be able to tell without any difficulty what you were seeing. If the background is sufficiently cluttered-- like a jungle backdrop-- and if the camouflaged thing is stationary, it might be good enough to fool a passing glance. But then again, so is your average ghilie suit.

Two: parallax. (This has been mentioned upthread already.) The demonstrations are all shot with a stationary camera. If the camera were to move, the illusion would be ruined. I'd imagine from looking at the illustrations that the geometry of the projector, reflector, mirror, and observer are all pretty critical. If the observer takes a step in any direction, the illusion will be broken.

All in all, I can't see how this could ever be practical. The most important flaw is that it's not even remotely adaptive. You have to have a perfect still photograph of your background to project against the mirror. If a bird flies behind the camouflaged object or person, the game is up.

Neat trick, but not very impressive.

Why not a simpler method?

[Simon Field]

Since this scheme is only good for hiding from one watcher at a time, and only from a one-eyed watcher when close, it seems that a simpler method will work.

Hold a rear-projection screen in front of you as a shield. It will have a pole coming toward you, that is long enough so the end of it is behind you when you hold the shield. On this end is a camera looking at the scene behind you.

Now it works without half-silvered mirrors, it is portable (you carry it around), and it works even if the background is moving.