Image sharpening - why use different software - what is it for - what works best

Sharpening images for print, web and fixing lens problems. How Keith uses different software packages for different types of image sharpening. Three different software packages from old to new still have their place.
There is much more info and examples of using the software packages in Keith's reviews:
Focus Magic:
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Nik Sharpener Pro 3 - shows different ways of sharpening and what the settings do:
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DxO Nik Collection - current versions of the Nik collection:
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Topaz Sharpen AI - each of these reviews has different examples showing where I'd use the software:
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Sharpening and enlargement - looking at upsizing and sharpening:
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