Posted on 11/17/2005 11:50:52 AM PST by LibWhacker
BLURRY snaps could be a thing of the past with the development of a digital camera that refocuses photos after they have been taken.
The camera could be useful for action shots taken by sports photographers or for CCTV surveillance cameras, which often produce fuzzy shots due to poor lighting.
In an ordinary digital camera, a sensor behind the lens records the light level that hits each pixel on its surface. If the light rays reaching the sensor are not in focus, the image will appear blurry.
Now, Pat Hanrahan and his team at Stanford University have figured out how to adjust the light rays after they have reached the camera. They inserted a sheet of 90,000 lenses, each just 125 micrometres across, between the camera's main lens and the image sensor. The angle of the light rays that strike each microlens is recorded, as well as the amount of light arriving along each ray.
Software can then be used to adjust these values for each microlens to reconstruct what the image would have looked like if it had been properly focused. That also means any part of the image can be refocused - not just the main subject.
Tracing the rays like this removes the conventional trade-off between the aperture size, which controls the amount of light that the camera takes in, and the depth of field. If light is low, a larger aperture will let enough light into the camera to form a clear image, but the laws of optics mean that a narrower slice of the world in front of the camera will appear in focus.
Hanrahan's system would be particularly useful for surveillance cameras, which must work at night but also need to have objects in focus at different distances from the camera.
If you know the exact specifications of an optical system, you can recover out of focus information. You can also sharpen things that are in focus. The correction to Hubble was quite useful, but the "before" pictures were sharpened with software.
By the way, you recover a signal that is "below the noise" either by averaging, which builds signal more rapidly (t) than noise (Sqrt(t)), or, if you known what your signal looks like, by using some sort of matched filter that reduces the noise bandwidth (until the signal does emerge out of the noise). Neither approach can be used to sharpen one-off astronomical photos of unknown objects.
Thanks for the info. I am continually amazed by the collective breadth of knowledge within FReeper nation.
I do not deny that you can sharpen blurry photos of high-signal-to-noise scenes, e.g. deconvolution with a known point spread function.
The situation is different in the case of dim objects, which is frequently the case in interesting astronomical photos. If there are three noise photoelectrons in each pixel with a Poisson distribution, and a dim object would contribute only six additional photoelectrons, it makes a lot of difference whether those few additional signal photons are spread among a dozen pixels or only one - are those 6 signal electrons spread among ~36 noise electrons, or ~3? You don't know which ones are noise, or even how many are noise, except on average. And when there's only one picture, there's nothing to average.
I'll stick with my current camera -- unless they provide depth of field adjustment too.
GIGO
I'm not denying the Hubble correction was necessary.
Boy, where was this technology last weekend at the football game I shot. Some absolutely STUNNING actions shots were out of focus.
Actually, I'm not sure the idea is all that brilliant. If nothing else, its like processing the picture at every conceivable lens focusing length. If they can do that electronically, then this should be a piece of cake. It would be like manually taking a shot with the focus ring all the way to the right, then taking a shot at each interval while moving the focus ring a small distance after the shot and reshooting. Almost anyone can do this in 30 seconds on most cameras. We just need the camera to do it in at least 1/500th of a second; more if the apeture is open wider.
Let me know if they invent one of these things for a 500 series Hasselblad. The Zeiss glass on there is great, but a pain for low light focusing.
Gee, could this technology be used to help 'focus' the Democrats on the TRUTH once in a while?
JPL has used computers to fix blurry images for decades.
Yeah, how could they fail to test the curvature of the mirror on the ground? Boggles the imagination...
Exactly! If they didn't test it properly on the ground, how could they possibly have tested it after it was already launched? There's something not right about that whole episode.
I'm sure Karl Rove had something to do with it.
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