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



On Thu, 10 Oct 2002 00:14:35 -0500  Laurie Solomon (laurie@advancenet.net)
wrote:

> (1) can one actually get grain alaising
> with these films such that the methods for dealing with that problem will
> work with those films and (2) does it act and respond to grain reduction
> functions in scanning software in the same way as true grain.

Chromagenic is no different from any colour film, the dye clouds are quite
capable of appearing grainy in an ordinary enlarger print. The grain
aliasing issue arises because some spatial frequencies of grain
distribution (micro-tonal variations) in the image are close to the spatial
frequency of the pixel matrix which comprises the scan. No different from
digital Moire, essentially, except grain pattern is random, not geometric.

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.

Regards

Tony Sleep - http://www.halftone.co.uk
Online portfolio & exhibit + film scanner info & comparisons
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