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That’s kind of like how you can reduce noise in low light images by taking a series of photos and averaging them together.

by valine 8y ago

ssfrr 8y ago
That assumes the noise is uncorrelated though (which the noise on a camera sensor generally would be). If the noise is correlated then averaging doesn't help.
- zaarn 8y ago
  There is lots of noise you don't get removed by averaging, ie the base noise of the sensors. For those you usually (for amateur astrophotography) take four sets of pictures (usually about 20); with the lens removed and cap on the mount, lens mounted with lens cap, lens mounted into telescope but telescope cap on and lastly telescope aimed at target but a thick cloth over the opening. All those compensate for the various ways light may enter the camera (lens mount, lens frontmount, telescope housing, telescope lenses and mirrors) and let you subtract those out after averaging your result.
kqr 8y ago
I really don't think that's the same thing. Taking multiple shots of the same subject is just taking a shot with a really long shutter time, except in slices, a little bit at a time. What OP was talking about was something akin to using the noise in a photo of one subject to reduce noise in another photo of a completely different subject but with the same camera. That works, to a point, but not great.
- dylan604 8y ago
  In astro-photography, this is quite common. You take a series of normal images. You then cover the the lens, and take the exact same exposure. After a series of processing, the noise pattern from the dark frames is subtracted from the normal images. It works quite well.
- jlarocco 8y ago
  FWIW, some cameras can use that technique to help de-noise long exposure shots. The control image is a long exposure with the shutter closed, and that image (which should be completely black) is subtracted from the long exposure shots.
- mrob 8y ago
  It's only the same as a really long shutter time if the subject is stationary, and in the case of Earth-based astrophotography it never is, because atmospheric turbulence is always moving the image. If you take multiple separate shots you can combine only the good ones: https://en.wikipedia.org/wiki/Lucky_imaging https://en.wikipedia.org/wiki/Lucky_imaging

That’s kind of like how you can reduce noise in low light images by taking a series of photos and averaging them together.

by valine 8y ago

That’s kind of like how you can reduce noise in low light images by taking a series of photos and averaging them together.

ssfrr 8y ago

That assumes the noise is uncorrelated though (which the noise on a camera sensor generally would be). If the noise is correlated then averaging doesn't help.

zaarn 8y ago
There is lots of noise you don't get removed by averaging, ie the base noise of the sensors. For those you usually (for amateur astrophotography) take four sets of pictures (usually about 20); with the lens removed and cap on the mount, lens mounted with lens cap, lens mounted into telescope but telescope cap on and lastly telescope aimed at target but a thick cloth over the opening. All those compensate for the various ways light may enter the camera (lens mount, lens frontmount, telescope housing, telescope lenses and mirrors) and let you subtract those out after averaging your result.

kqr 8y ago

I really don't think that's the same thing. Taking multiple shots of the same subject is just taking a shot with a really long shutter time, except in slices, a little bit at a time. What OP was talking about was something akin to using the noise in a photo of one subject to reduce noise in another photo of a completely different subject but with the same camera. That works, to a point, but not great.

dylan604 8y ago
In astro-photography, this is quite common. You take a series of normal images. You then cover the the lens, and take the exact same exposure. After a series of processing, the noise pattern from the dark frames is subtracted from the normal images. It works quite well.
jlarocco 8y ago
FWIW, some cameras can use that technique to help de-noise long exposure shots. The control image is a long exposure with the shutter closed, and that image (which should be completely black) is subtracted from the long exposure shots.
mrob 8y ago
It's only the same as a really long shutter time if the subject is stationary, and in the case of Earth-based astrophotography it never is, because atmospheric turbulence is always moving the image. If you take multiple separate shots you can combine only the good ones: https://en.wikipedia.org/wiki/Lucky_imaging https://en.wikipedia.org/wiki/Lucky_imaging