> 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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