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Noise reduction by image averaging
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PostPosted: Fri Mar 25, 2011 5:47 pm    Post subject: Noise reduction by image averaging Reply with quote
This sounds interesting.
Does anybody have experiences with that method?


PostPosted: Fri Mar 25, 2011 6:13 pm    Post subject: Reply with quote
It's of limited use, whenever you have something moving in the image (trees clouds hair), it makes it useless. Basically it only serves in the studio with still life subjects.


PostPosted: Fri Mar 25, 2011 6:16 pm    Post subject: Reply with quote
Maybe something like twilight mode on Nex - not bad but nothing special.


PostPosted: Fri Mar 25, 2011 8:39 pm    Post subject: Reply with quote
Orio wrote:
It's of limited use, whenever you have something moving in the image (trees clouds hair), it makes it useless. Basically it only serves in the studio with still life subjects.


Not quite. Wink

Image stacking/averaging is incredibly popular for astrophotography. So much so that dedicated software packages are available to help with the workflow. Many packages include alignment features to help in cases where a fixed tripod is used (instead of a tracking mount which counters the earth's rotation), or alternately you can additively stack the images to show long-exposure star trails behind stationary earth objects/scenery.


In terms of moving objects, the technique is not necessarily harmed - in some cases it is even *more* useful. With multiple source images with moving subjects, you can use masking to selectively use portions from different images in the final result. A usage example would be a popular monument or building which always has people around it. By taking a number of shots while people are moving around, you can use bits and pieces from each to selectively remove groups of people, birds, etc, and end up with a photo as if nobody was around at all. Cool


Image stacking/averaging can also help in cases where motion is unavoidable. For example, long-exposure telephoto shots which are handheld or with an unsteady tripod. By taking a few dozen short shots instead of one long exposure shot, you can selectively discard those which have too much motion blur, then align and average the rest to get a well-exposed noise-free shot that otherwise would have not been possible. You can also use this to obtain greater depth-of-field, for cases where the shot *could* have been taken as-is in available light, but only by using a wider aperture than you would have preferred.


PostPosted: Fri Mar 25, 2011 8:57 pm    Post subject: Reply with quote
Other mean of use : reduce the noise to very low levels (as if you were at ISO 10 or less) and then boost contrast, when using long telephoto lenses and having low contrast due to the lens + weather conditions Wink
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