Slashdot Mirror

← Back to Stories (view on slashdot.org)

Seeing Around Corners With Dual Photography

Posted by timothy on from the expand-e6-expand-expand dept.

An anonymous reader writes "This project (which is part of this year's SIGGRAPH) has absolutely blown my mind. Basically they photograph an object with the photosensor at one point, and the light projector at another, and use the Helmholtz reciprocity algorithm to virtually switch the locations of the camera and projector, showing exactly what the light source "sees"! If that doesn't make sense to you, check out the research page and make sure to watch the 60MB video at the bottom. The playing card trick will leave you speechless!"

13 of 381 comments (clear)

  1. Why don't they just move the camera? by nmg196 · · Score: 5, Funny

    ..it would be much easier.

    1. Re:Why don't they just move the camera? by famebait · · Score: 5, Interesting

      Which gets me wondering: say you can see in someone's window, but the view is not very interesting: you only see a section of wall; everything else in the room is out of view. But: there is a CRT TV on in that room, and you can see its reflected light on the wall.

      How much information can you gather from that reflected light?

      You could of course recinstruct the image on the CRT, but that's not very interesting.
      The TV does not scan a focused image on its surroundings like the projector does, so you couldn't get a TVs-eye view of the room witht eh same technique.

      OTOH, it is clear that from sampling even just a single point on the wall, you could get a silhouette of anything occlusion over the screen seen from that point. At least provided you had a pure white image on the CRT, OR knew what image was on and could calibrate for it.

      How far could you get with all the information escaping the window in your direction?

      --
      sudo ergo sum
    2. Re:Why don't they just move the camera? by merlin_jim · · Score: 5, Informative

      How far could you get with all the information escaping the window in your direction?

      It's called optical tempest. With a high enough sampling rate you can reconstruct what is being shown on the monitor/TV. Each pixel as it illuminates causes a brief spike in the ambient brightness; by measuring this spike one can reconstruct the pixels being shown. After that, it's pretty simple to find the horizontal and vertical retraces.

      more info

      --
      I am disrespectful to dirt! Can you see that I am serious?!
  2. ARTICLE CONTENTS by Anonymous Coward · · Score: 5, Informative

    Dual Photography

    Abstract

    We present a novel photographic technique called dual photography, which exploits Helmholtz reciprocity to interchange the lights and cameras in a scene. With a video projector providing structured illumination, reciprocity permits us to generate pictures from the viewpoint of the projector, even though no camera was present at that location. The technique is completely image-based, requiring no knowledge of scene geometry or surface properties, and by its nature automatically includes all transport paths, including shadows, interreflections and caustics. In its simplest form, the technique can be used to take photographs without a camera; we demonstrate this by capturing a photograph using a projector and a photo-resistor. If the photo-resistor is replaced by a camera, we can produce a 4D dataset that allows for relighting with 2D incident illumination. Using an array of cameras we can produce a 6D slice of the 8D reflectance field that allows for relighting with arbitrary light fields. Since an array of cameras can operate in parallel without interference, whereas an array of light sources cannot, dual photography is fundamentally a more efficient way to capture such a 6D dataset than a system based on multiple projectors and one camera. As an example, we show how dual photography can be used to capture and relight scenes.

    (a) Conventional photograph of a scene, illuminated by a projector with all its pixels turned on. (b) After measuring the light transport between the projector and the camera using structured illumination, our technique is able to synthesize a photorealistic image from the point of view of the projector. This image has the resolution of the projector and is illuminated by a light source at the position of the camera. The technique can capture subtle illumination effects such as caustics and self-shadowing. Note, for example, how the glass bottle in the primal image (a) appears as the caustic in the dual image (b) and vice-versa. Because we have determined the complete light transport between the projector and camera, it is easy to relight the dual image using a synthetic light source (c) or a light modified by a matte captured later by the same camera (d).

  3. A totally uninformed post! by Sir_Real · · Score: 5, Funny

    Seeing that R-ing the F-ing A is an impossibility for me right now, due to an inexcuseable lack of .torrent or google cache link, I'll just post some outright fabrications about it's content.

    This technology proves that there was a third gunman on the grassy knoll. This technique is like what they did in the Matrix, except "backwards." With this technology, any man can find the g-spot. When you look at the videos upside down, you can see into the past.

    1. Re:A totally uninformed post! by goneutt · · Score: 5, Funny

      That post is more relevant than the majority

      --
      Bacardi + slashdot = negative karma.
  4. A Mirror? by Bob(TM) · · Score: 5, Funny

    Doesn't it seem a little funny that we need a mirror to get a look at this movie?

    --

    The little guy just ain't getting it, is he?
  5. Re:around corners? by Anonymous Coward · · Score: 5, Informative

    Seeing around corners is really stretching it. You switch positions with the light source, so you can technically look at the scene from a point which is "around a corner". What they so casually mention as "structured lighting" is really the key to the whole algorithm and means that the light source shines a pattern on the scene which then allows the camera to retrace where every bit of light it sees is coming from. This means that the light source needs to be part of the scheme. You won't be able to switch yourself into the position of arbitrary lights on the street.

  6. Torrent by spadadot · · Score: 5, Informative

    Only the first part for now :

    http://dload.digitalriviera.com/DualPhotography-pa rt1.mp4.torrent

    Second part in 30 minutes !

    First torrent I host, I hope it's ok.

    1. Re:Torrent by pairo · · Score: 5, Informative

      http://bragi.wolfheart.ro/DualPhotography.mp4.torr ent

  7. Blame The Slashdot Editors by dohboy · · Score: 5, Insightful

    Don't blame their webserver/fileserver for not being able to see the movie they raved about.

    It is the laziness and irresponsibility of the slashdot editors to not provide a bittorrent link.
    I am disgusted that slashdot raves about a site/file/mpeg then DDOSs
    it so that nobody sees it. This is particularly bad when a hobbyist site is crushed.

    Mod me into oblivion, I don't care.

  8. Another mirror... by Malcolm+Scott · · Score: 5, Informative

    Another mirror here. No guarantees as to how long it will stay up; if it pushes me close to my monthly bandwidth limit I'll kill it...

  9. Re:Homebrew solution possible? I own a LCD project by famebait · · Score: 5, Funny

    Could I image my hot neighbour's bedroom and see her make out in her bed from the perspective of her bedroom's ceiling light ? That would be killer ;)

    No, that would be stalker. Still pretty bad, but not quite up to murder.

    --
    sudo ergo sum