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filmscanners: Re: Unsharp mask

> "Frank Nichols" <frank@theNichols.net> wrote:
" The scariest part so far has been trying to figure out the USM to use.
These are Provia 100F slides scanned at 2700 DPI on my Scanwit and they look
a bit "soft". However, where I normally start getting nervous if I use over
150% at 1.2 radius with threshold of 4 on negatives (Kodak Super 100) here I
am up into 250% or more before I see the effect I want - and I seem to have
to be more careful to avoid pixelization at those levels."

>"Rob Geraghty" <harper@wordweb.com> replied:
"Gad, unsharp mask over 100%?  I've been using a radius of 2.0 and only 60%.
Is there something I'm seriously missing about USM?"

Preston adds:

I think unsharp masking is the most important (and probably most
mis-understood) aspect of producing outstanding scans.  Back in the good old
days, skilled operators on high-end scanners could produce beautiful scans
with appropriate levels of USM.  The images appeared crisp and sharp, with
no noticeable halos, yet the edge sharpening was there.

USM in Photoshop can do an OK job, but it is not very intuitive and most of
us don't understand how to use it properly.  Stephen Marsh has links to
several good USM articles on his site at

For screen-display images, I use a small Radius (.5) a small Threshold (3),
and I vary the Amount to whatever looks right on the screen.  I do all USM
at 100% so that Photoshop anti-aliasing doesn't mask the effects.

Print images can be over-sharpened slightly since the halftoning process
will reduce the sharpening effects.

USM is a complicated subject and I don't pretend to know a great deal about
it, but I do know a properly sharpened image can mask a lot of other

Preston Earle

I've known lots of trouble in my life, most of which never happened.---Mark


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