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I always have been intrigued by high speed/fps video. And I have looked online how much it would cost to buy one myself. However they are often very expensive, I do not know what the average price range was, but to much for me to buy for "fun".

I recently saw this video which made me realize that instead of reducing the exposure time, you can also influence the lighting within the exposure. However in the video this was used to make high speed photos, which made me think if this could not be used for a video camera. My initial idea was to place multiple cameras around a fast rotating mirror. However this might be dangerous when not correctly balanced.

My other idea was also partially based on an article I saw a few years ago. I want to keep it simple, so instead of using some sort of "filter" to only illuminate certain pixels of the sensor at certain times, I would like to take advantage of the fact that it would be a color camera. This involves a red, green and blue light source, such that each frame would be exposed by each light source for a short moment at different times. After shooting I would need to separate each color layer out of frame and possibly convert it into grey-scale images. This would mean that I would only be able to reach three times as high frame rates, the object, which is being filmed, has roughly the same emission/absorption for all three colors and is not highly fluorescent with "large" stokes shift.

This was a bit of a long introduction, but here are my related questions:

  • Would colored LED's suffice for the different light sources? Such as their spectrum, assuming a Bayer filter sensor is used.
  • Are there any theoretical/technical limitations to this idea? Such as the exposure time, since if this is to small compared to the time between each frame then there would still be a substantial gap between every 3 frames.
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2 Answers

You could use multiple cheap cameras recording at low fps, but slightly out of phase. Bennett Wilburn talks about this in his 2004 Stanford Doctoral thesis, "High Performance Imaging Using Arrays of Inexpensive Cameras".

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That's an interesting concept, though I challenge their assertion that they produced a high speed camera. Each image capture appears to still be taking a longer period of time, they simply offset the starts of the exposure. Thus, it will not actually stop motion, but display an approximation of the 1/30th second time frame over a much faster interval. It's still an interesting accomplishment, but isn't going to produce the same thing as a high speed camera. Some amount of recovery may be possible through interpolation, but it's still a much slower shutter speed. –  AJ Henderson Jan 14 at 14:16
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There's video on his website. graphics.stanford.edu/papers/highspeedarray –  Jason Conrad Jan 14 at 17:19
    
That video appears to confirm what I expected, the detail in each shot is still limited to the shutter speed of the camera capturing that time slice, which is going to be a limiting factor on the overall speed you can really achieve with the method. If each camera can only take a 1/1000th second exposure, then you are meaningfully limited to 1000 fps with such an array. You can produce more than 1000 frames per second, but each sequential frame will actually capture more time than it is on the screen for, thus you lose clarity of what was happening due to what I'll call a temporal blur. –  AJ Henderson Jan 14 at 17:44
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This will not work because of the difference in absorption of light. The scene will look completely different lit by different colors of light and thus each of the frames will not fit together in a sequence. There is no shortcut for capturing high speed video, you need a high speed camera. You can get cameras up to about 240fps at consumer price points (look at Lumix (Panasonic) in particular), but much beyond that you need a true high speed camera which is more comparable to the cost of a house than the cost of a consumer camera.

You could use an array of sensors and try to account for the differences in position, but you are still limited to the shutter speed of each of the cameras you use and would require elaborate timing equipment to make sure they all fire in sequence and behave similarly optically.

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I stated in my question that this technique would only be appropriate for scenes with: "roughly the same emission/absorption for all three colors and is not highly fluorescent with "large" stokes shift.". If this is the case then it should work right? –  fibonatic Jan 16 at 19:13
    
@fibonatic - if everything is precisely neutral grey, then yes, you would be ok. Very, very few things have "roughly the same emission/absorption for all three colors". Even so, you are going to have to manage to coordinate and time the lights and will only triple the frame rate, which for most cameras gets you up to only 180fps on a very limited set of subject matter. One of the 240fps cameras that Lumix makes would probably be a better deal (though I suppose you could try to do it for getting 720fps with the 240fps camera, but your still talking some pretty advanced custom lighting. –  AJ Henderson Jan 16 at 19:59
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