Double USM doubles your sharpening control: you can set a Radius, an Amount and a Threshold for Dark Halos, and different ones for Light Halos. As Color-Correction expert Dan Margulis has demonstrated, Light Halos tend to be visually more offending and need to be toned down - both in their intensity (Amount) and in their thickness (Radius).
Standard Sharpening Home Page - http://cc-extensions.com/products/doubleusm/
A heavy handed pre-press default USM is 500-1 (Amount-Radius), that you can always tone down with Layer's opacity. Double USM gives a more natural effect with (400-1.5) for Dark Halos and (250-0.7) for Light Halos - about half intensity and half thickness.
HiRaLoAm Sharpening
Also known as High-Radius, Low Amount: used to give shape and sort of a 3D look. A starting point could be (50-50) for Dark Halos and (30-30) for Light Halos. As you see, the Radii are unusually high, while Amounts are below the values you would expect.
Creative Sharpening
With Double USM nothing prevents you from experimenting: a creative sharpening might imply a Standard USM for Dark Halos (say, 400-1.5) and HiRaLoAm for Light Halos (say, 30-50) in order to get the best of both worlds!
Presets
Create and apply your own Sharpening Presets! Mind you, when it comes to Sharpening there are no perfect receipts nor absolute values: it always depends on the image's resolution, subject, and eventually on your own taste!
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