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

That is so cool!

[tswinzig]

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

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...

[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.

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.