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High-Speed Video Using a Dense Camera Array
karvind writes "Researchers at Stanford have demonstrated multi-thousand frame-per-second (fps) video using a dense array of cheap 30fps CMOS image sensors. A benefit of using a camera array to capture high speed video is that we can scale to higher speeds by simply adding more cameras. Even at extremely high frame rates, our array architecture supports continuous streaming to disk from all of the cameras. Now we know where to use 100TB tape drives and what to expect in the next sci-fi movie."
time pulse code. (SMTPE? or something like that)
Same way they sync audio and video in sound studios.
Video track (or a seperate track) carry a pulse carrier. Audio track syncs to that.
The truth about Led Zep should never be told on
But you could cheaply get intermediate quality video. The multiple CMOS give a rolling image (look at the guys' shoulders and you'll notice the rotation from the multiple POV) and gives slow-mo without (as another poster points out) having a quick enough shutter time for high-speed analysis. But these 30fps things that make up webcams are usually pretty low quality.
With these you can get more detail than the shitty webcams without shelling out on high end equipment. This has remarkably few uses, but with this theory working in practice opens up other avenues - like using higher quality CMOS sensors, which are improving all the time (think digital cameras), so that rather than 50 CMOS giving a crappy picture you either use 20 higher fps/quality ones for the same/better output with less roll, or 50 for more fps/higher quality.
Still, there are only a few applications, but the software to run it should be pretty easy to manage - then all you need to do is plug in X number of cameras depending on your needs.
I think.
This idea was invented by Shampoo.
I believe the point in producing this is to show that instead of purchasing expensive high-framerate cameras that has some sky-high pricetag, one can use an alternate and cheaper solution by using CMOS sensors. So let's try placing a couple of things into perspective.
Say you require a camera that can record say 90fps. To a manufacturer of electronic parts, this can be achieved with a little bit of engineering. Basically, take 3 of those 30fps CMOS sensors, pack them together, set a uniform color correction setting, and an interface to send the captured information to. All this would probably costs lots less than a specialized camera that can capture 100fps or so.
If you were to walk around in a computer shop or your local Best Buy, CompUSA, Microcenter, Circuit City, or Fry's, you might have noticed that there are quite a few webcams around, all of which uses the same 30fps CMOS described at the link. The CMOS themselves are likely cheap enough that, in theory, you can assemble a few together and have a 90fps camera. I would assume that the spatial distortion would be next to nil since 3 sensors are closely together.
Please correct me on any points. I believe the concept is interesting and would have some useful uses out there (ie. spectator sports, research, film).
~ Old Warriors Society
From the pdf text,
All of the CCDs run at 30 FPS. So, yes, they can scale this almost endlessly (until the parallax variation from non-colocated image captures becomes extreme, basically, or until the trigger timing required becomes too hard to achieve and jitter begins to be large enough to significantly alter your frame timing/sequencing).
The trick is that A runs on 0.000, 1.000, 2.000, etc. while B runs on 0.001, 1.001, 2.001, etc., C is on 0.002, 1.002, 2.002, etc. (units are frames relative to a starting time), and then the frames are sequenced appropriately (ABCABCABC etc.). This gives a very high frame rate while using relatively low-cost sensors - effectively, they're exploiting parallelism as a way to increase the array's effective sampling rate.
Basically, if you have N sensors capable of sampling X times per second each, and are capable of accurately triggering each sensor to a high degree of time accuracy, your effective sampling rate can be NX. Neat trick.
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I would be interested to see how this could present itself in a regular consumer atmosphere...
It is funny that you used the word "atmosphere" but that might be one of the applications: combustion research.
A friend of mine works at General Motors doing combustion chamber research. Basically, with a high-speed camera, he films the combustion in what basically amounts to an engine with a glass block and cylinder head. They currently film at 900fps with an industrial film based camera. This is quite expensive so it takes a lot of paperwork to run the thing.
This new digital unit would be ideal. Ultimately, it will probably allow reduced emmissions from automobiles. Diesel is the next big thing but we've got to reduce emmissive levels on those before they become widely accepted.
So yes, this will present itself to the consumer atmosphere. Just indirectly. Oh, and when you watch that balloon popping, just imagine Keanu saying, "whoa!" and you get another application.
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The frame rate and exposure time aren't necessarily related. Ideally, exposure time should be 0 (otherwise you'll get motion blur), but for obvious physical reasons it needs to be non-zero. Having overlapping exposures probably isn't that big of a deal as long as you can compensate for motion blur by correlating successive frames.
.205msec down to a minimum of .205msec. Timing accuracy is good to 200nsec, and the start of the exposure can be shifted arbitrarily to within 200nsec.
In anycase, the paper on the site has the following details about their hardware:
Camera exposure times can be set in multiples of
52 cameras total at 30Hz each for a synthetic 1560Hz
The bulk of the paper deals with these topics:
Hardware construction/documentation
Geometric alignment
Colometric alignment
Compensating for "rolling shutter"
- The camera shutter actually does things on a row-by-row basis, the last row of the image has its shutter-open time delayed by 1/30 of a second relative to the first row.
Notes on future stuff - mainly the compensating for overlapping exposures "temporal superresolution" they call it.
Not a bad project.
General notes:
image sensor "bandwidth" typically relates to the pixel rate (and correspondingly framerate) that can be used with a given sensor. Given the right stimulus, image sensors should be able to correctly capture alternating full-on and full-off images. Mind you there will be some residuals, especially if the detector gets "overloaded/saturated", but considering that all the pixels pass through the same analog interface, it would be very odd to have a sensor that "ghosts" its images. In this case, 640x480x30Hz cameras have a pixel rate of 9.2Mpixels/sec (with some multiplier in there to handle the color conversion), so changes are the analog bandwidth is a good sight larger than 10Mhz.
The limitation on CCD/CMOS sensors is typically brightness. If there is an extremely bright image, then the shutter time can be reduced down to stupidly small intervals - in the single digit microsecond range with the proper detectors. "Brighter" images are gotten by
1) lots of light (easy up to a point)
2) big optics (expensive and a pain)
3) big pixels (just plain expensive)
BTW, its spelled "frequency"
California Governor Leland Stanford employed Eadweard Muybridge to settle a bet whether a horse gallopss with all four feet off the ground. Muybridge took the first motion picture by chaining 16 cameras together. The horse farm of this experiment is tucked away in a corner of the Stanford college campus which was founded ten years later.