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[filmscanners] Re: Grain from negs with Multi Pro



> You mention unsharp mask.  I really don't know how this feature should be
> used (I don't have docs with PS).  I commonly use about 50 in usharp mask.


There are 3 variables:

Radius:

      the distance in pixels that the algorithm inspects to decide whether
it should sharpen. Note the radius need not be an integer - I usually use
about 0.9 with my digicam but 1.4-1.8 with the scanner. If I have up-sampled
an image from the optical resolution then I increase the radius and
conversely if I have down-sampled an image I decrease the radius.


Threshold:
      is the required difference in values of pixels within the radius that
is required to trigger the sharpening.

Amount:
      is how much sharpening effect should be applied to the pixels selected
by the combination of radius & threshold


Increasing radius or decreasing threshold will reduce the value for amount
that a picture can tolerate.

Decreasing radius or increasing threshold will increase the value for amount
that a picture can tolerate.

To avoid sharpening grain and/or noise you need to set threshold higher the
variance in values caused by grain.

To sharpen everything a bit you should use a smaller radius a larger radius
will only effect more significant boundaries (more edge sharpen than overall
sharpen).

For images that I am printing I usually view the image at a size around
1.5x-2x actual target print size

It's sometimes advantageous to sharpen an image twice - once to gently
overall sharpen and once to add slight extra sharpening to the edges.

Steve

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