graphics.stanford.edu — Check out the video of how these guys use a technique called "dual photography" to generate a picture of the FRONT of a playing card (from the perspective of their light source) even though the camera is placed BEHIND the card.
May 10, 2005 View in Crawl 4
Closed AccountMay 10, 2005Submitter
Yeah -- my original description tried to explain a little, but then the 350 character limit killed it. The basic idea is they use a projector to illuminate an object from one angle, and photograph the scene with a camera at a different angle. (I'm sure this is a horribly inaccurate way of describing it, but...) they run a function that "reverses" the rays of light that hit the camera and it generates a picture from the perspective of the projector, essentially making the projector a virtual "camera." In the video on that page (torrent link at the bottom), they place a projector in front of a playing card and photograph the card from an angle where all you can see is the card's back. But by tracing the rays back to the projector, they're able to generate an image of what the projector would "see" even though the projector doesn't have any image-capture ability itself.
Closed AccountMay 10, 2005Submitter
Yeah, that still might not have made any sense. Let me try this: in theory, using this type of technique, you could point a television at a wall, and even if you were only able to photograph the light bouncing off that wall, you might be able to regenerate the picture that was being displayed on the TV. (If I'm way off and completely misunderstanding the situation, somebody please correct me.)
jmccormMay 10, 2005
Or put another way, you can turn a digital projector into a scanner. And because of this, in combination with a camera, you could do some simple correlation in order to make it as though the camera was a light source, and the projector was a camera.You can also just turn a projector into a camera by using a light sensor to read the intensity the reflection of every pixel the projector puts off. When the scene is put back together, because of that reciprocity thing, it will be as though the light sensor (photosensor) was a light source, and the projector was a camera. This is very cool.
wormdrinkMay 11, 2005
Good lord, I wish I had the time and equipment to play with this. Very, very, very nice find.
amwmediaMay 11, 2005
WOW! SOOOOO COOOL