Slashdot Mirror
Seeing Around Corners With Dual Photography
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!"
The exploding server one has already rendered me speechless. Why in the name of god do they do it!
..it would be much easier.
Mirrordot link to the video file.
I find it highly unlikely that many will manage that :0
Brocklesby Park Cricket Club
Suppose you shine a projector upwards from the ground.... and take a photo of a girl... what will the technique generate?
Online backup with Mozy, sounds like Ozzie, but more!
Quick, shine a light into your monitor and take a picture. Then use their software to capture an image of their exploding server!
Where does seeing around corners come in?
isn't this just the same in principle as ray tracing? or am I missing something
Anyone please mirror the movie?
J.
You're only jealous cos the little penguins are talking to me.
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).
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.
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?
DARN, /. just hiked Stanford's tuition rates again.
Bacardi + slashdot = negative karma.
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.
Other than using electrons instead of light, that's how a scanning electron microscope works. An object is scanned (raster scan) and one or more sensors near the target pick up the reflections to generate an image. In the SEM the image appears as viewed from the scanning electron beam source.
In the optical one mentioned in the article, the light source is a raster scanning projector which lights a target. The image is produced from photodiodes picking up reflected light.
These two systems are very much alike. One uses photons and the other electrons. The end image is generated the same way.
The truth shall set you free!
Note: I haven't read the paper yet, but it is downloading.
It seems like this might have some military applications as a result. Imagine sticking a photo-resistor array under a door or through a window and then getting "viewpoints" from any of the lights in the room. Could aid in target aquisition and elimination.
Not sure how well it works for something like that, but this is a rather impressive (at least to me) research project.
There are only 10 kinds of people in this world... those who understand binary and those who don't
They make the point that if you illuminate an object with a projector, you can get the image with a photocell. That's because the projector scans the image with a light beam. If you know when you see the reflection, you know where the light beam was when it reflected because you have prior knowledge of the scanning pattern. That technique has been used forever. It's like the flying spot scanners that predate camera tubes.
The 3D part is obtained when you offset the detector and the projector. If I look at a particular point on an object and scan the object with a beam of light, I can get the distance between me and the object as a function of the scanning angle.
All these people are doing, are using the first barcode technique to, take a picture of the scene. Instead of using a laser, an animation of a moving white dot is sent to the projector. The Camera, is then treated like a light sensor, for each point in the animation, the camera is queried for the brightness of the perhaps, brightest dot in it's field of view. Gradually the picture is built up, pixel by pixel, untill, finally a picture is formed in memory. This picture would be from the perspective of the projector.
Maybe we could use that mirror to get a different viewpoint of the article?
Well, I've begun the download for this video, and seeing as how mirrordot is being slashdotted, I have only downloaded about 20 megs out of the 60 meg file, with an ETA of about 25 minutes. At any rate, I've put the mirror up linking to the file that's being created -- and in 25 minutes that file will be complete, until then it'll be some percentage of the total.
Enjoy.
I totally lack any scientific degrees, but this technique looks an awful lot like raytracing in reverse(or even real world application of algebra)... the projector is necessary to help map the way certain areas of the subject react to light based on the surface quality, and using pixel level illumination from the projector recreates the camera... FUCKING BRILLIANT.
this technique works because of the lcd/dlp array in a projector, but i wonder if it can be reproduced if the light source is already a pinpoint(chrismas light, or very small bulb). what happens when the light source is very broad, like that of a computer monitor/ TV? i wonder if this technique could also be used to extrapolate what someone is watching/reading/viewing on screen? taking another stab from a raytracing perspective, i wonder if an environment could be revealed thru image analysis, aka reverse-HDRI?
hats off to the dually photo boys of stanford and cornell... keep up the cool work.
three can keep a secret, if two are dead - benjamin franklin
Only the first part for now :
a rt1.mp4.torrent
http://dload.digitalriviera.com/DualPhotography-p
Second part in 30 minutes !
First torrent I host, I hope it's ok.
Was I the only one that saw that as:
Seeing Around Corners With Dual Pornography.
I need more coffee.
Well, there's spam egg sausage and spam, that's not got much spam in it.
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.
I'll throw my poor server into the flames
http://www.whaleweb.net/mirror.html
2x 1.1Mbit DSL lines + PacketShaper
*ducks behind table*
1. Reverse transformation for any interesting case (note that no places are actually revealed on their example!) will always be close to singular, that means in practice that your noises (due to raster, finite precision, and just measurement error) will eat any signal in result.
2. You should know not only amplitude, but *phase* of the source signal, that means for light that you have to use coherent light source and utilize interference on the receiver.
1 + 2 = holography, so what is new?
(Read the article, but still downloading the movie)
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...
> extrapolate what someone is watching/reading/viewing on screen?
h tml
Something like this?
http://www.cl.cam.ac.uk/~mgk25/emsec/optical-faq.
Voltara
It is already possible and demonstrated to view what is on a CRT by analyzing the brightness changes of the surrounding room through a telescope.
http://graphics.stanford.edu.nyud.net:8090/papers/ dual_photography/
Come on kids, coralcache is the way to go. no more direct linking to servers that go down quicker than, well, you know.
BitTorrent file here. http://bisqwit.iki.fi/torrents/DualPhotography.mp4 .torrent
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
Although several other movies and TV shows have had this "error", Blade Runner is not one of them. The picture was always intended to be a futuristic 3d hologram sort of thing; you can actually see a visual effect in some of the shots, but it's not very good, and so a lot of people just thought it was a regular photgraph.
Bruce
Several projects at SIGGRAPH last year addressed the question of what you could do with a planar array of cameras. You could consider this the natural extrension of stereoscopy (two cameras) or a cost-effective approximation of real-time holography. Some of this research is motivated by that commodity digital cameras and real time digital image processing computers can be bought at low prices, and assembled like RAID disk arrays or cluster computers.
Applications of these arrays included several kinds of real-time 3D TV (without silly glasses). The Stanford group pushed "conformal imaging", that is a cube of image planes at various depths and all viewpoints. This has the effect of looking around corners and through keyholes: if there a path for light to get through, you can probably extract a complete image. This does involve some mathematical massaging of multiple-camera images. Cheap Graphical Processing Units (GPU) from game machines can be reprogrammed to process images in real-time.
I will, in the mean time, here's another mirror
Gosh, how fascinating. Now compare this to a *really cool* imaging technique, like using an x-ray beam and an array of photodiodes to detect the scatter patterns as the beam passes through a human body, then calculate an image of the actual bones and organs inside. It's called Computed Axial Tomography or a CAT scan. And if you want something *realy really* cool, check out the technique that uses a magnetic field gradient to delay the re-emission of photons from an RF pulse, and then calculates the position of molecules in a body from their RF scinillations. Its called Magnetic Resonance Imaging or MRI. Somwhow I think the images they produce are slightly more profound that scanning the back of a playing card. Consider yourselves offcially Harumphed.
"Sic Semper Path of Least Resistance"
http://ftp.acc.umu.se/mirror/media/DualPhotography /DualPhotography.mp4
Forget that. This would be a perfect application for Dijjer.
Rather than dual photography I would be more inclined to describe the method as real-world ray tracing. A focused pixel of light is captured for each pixel of the light source, then the scene is transformed so that the camera image is in the plane of the light source and the lighting function discovered earlier is inverted.
The article claims that there is no need to describe the geometry of the scene, and I understand why that is true for the structure of the subject, but it seems as though the geometry of the light and camera would still have to be known. Anything that isn't in view of the camera in the first image is unlit in the second image, and vice versa, but I don't understand how you would determine what transformation would result in that exchange without any information on the camera-light geometry in relation to the scene.
LibBT: BitTorrent for C - small - fast - clean (Now Versio
Or imagine sticking a miniaturised camera under a door or through a window and then getting a clear viewpoint of the room!
To analyze the projector's image quickly, they need to control the projector, sampling its pixels' images to factor out redundant pixels. Trojan-horse programs which control the projector probably won't trigger current antivirus SW. Any screen can now spy on you, if a camera can only get a glimpse of its reflected light. Combined with laser microphones, you're on candid camera! Beware untrusted screensavers!
--
make install -not war
So, could you do something useful with a structured light source and a structured receiver? Or would you just get redundant information?
You get redundancy or rather parallelism which is used to speed up the process.
A witty
I was imagining upskirt cam technology rapidly advancing up until i read your post..