1845

“ Okay, I wrote earlier that there isn’t a magic starting place that applies to all images. While that’s true for Amount, both the Radius and Threshold probably should be started at specific points: Amount:
Radius: start with .5 and try to avoid going much higher, if possible. I believe it’s better to apply Unsharp Mask twice with .5 and .3 than using an initial radius of .8. Why? Because any value larger than .5 starts to affect more than one pixel beyond the transition point, which starts to produce more visible halos, especially if you need to use aggressive amount values. If you’re printing with an inkjet printer, the dot gain you get from the ink spreading on the paper often masks these halos, so go ahead and try higher values if you’d like, but only if you analyze the results from the final output (not the screen).
Threshold: start with 0 and leave it there if your image is relatively noise-free. Using any other value for Threshold applies the filter to only parts of the image, and I believe there are better ways of handling partial sharpening than using Threshold (see Edge Sharpening, below). Sometimes you can get away with using modest threshold changes. But I’m starting to notice that I can detect images that have been sharpened with the threshold set to something other than 0. Sharpening tends to apply a film-like grain to the overall image, especially if you’re working with a digital camera or scanner that has channel noise in it (look at the individual RGB channels for a sky area under high magnification; are all channels smooth gradations, or is there a random pattern of darker and lighter pixels in one or more channels?). Personally, I sometimes like that effect, but using Threshold other than 0 tends to make for unevenness to this “grain.”
Sharpening Rules Before continuing, let’s set some specific rules down for dealing with standard sharpening: Perform all other changes (color correction, saturation changes, distortion corrections, etc.) before sharpening.
Save a copy of the corrected, but unsharpened version. (And you’ve already saved a copy of the original, right?)
Use the Unsharp Mask for basic sharpening, as it provides more control than the other related filters.
If submitting to a professional designer, send the unsharpened version, as you don’t know how dot gain may change the amount of sharpening necessary.
If printing on an inkjet printer, error on the side of slight oversharpening.
Try to use a Threshold of 0 and Radius of .5, if possible.