[filmscanners] Re: Grain aliasing: Thoughts, solutions?

["George Hartzell" <hartzell@kestrel.alerce.com>]

Tony Sleep writes:
 > [...]
 > With all aliasing the easy cure is to degrade the frequency of image
 > information so that it falls well within the Nyquist limit.
 > Defocussing, or
 > antialiasing filters, do the job. I presume software that attempts to
 > deal
 > with it relies on some sort of blur function, which is how you can
 > attempt
 > to deal with it in PS. It could be clever and only act on areas where
 > aliasing occurs, but there is no way to deal with aliasing and retain
 > the
 > HF info that causes it. Aliasing is just an inescapable property of
 > pixels.
 > [...]

I think that it can make a big difference between whether you degrade
the frequency of the image before/while it's scanned (e.g. defocusing
the scanner) or whether you try to blur in photoshop.

When you do it as part of the scan, you just have to throw away enough
information to get within the Nyquist limit.

Once you've collected aliased data though, the problems are usually
much larger blobs and you have to blur the daylights out of them to
get them to go away.  You end up throwing away much larger details (is
a large detail like a jumbo shrimp?).

g.

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