High-Pass-Sharpening

 
Sharp Noise
Every photographer as well as artisans of all sorts know how important it is to have an extra specialty tool available for when things don't quite work out the way you expect them to. Photoshop'sHigh Pass Filteris one of those tools. Let's see how to use it.
Unsharp Maskingis the way that everyone who works with digital image processing knows to sharpen their files. Of course the use of this ill-named tool has nothing to do either with masking, or unsharpness. It's just a carryover from the days when an unsharp negative was sandwiched with a sharp one to enhance edge contrast. And that is in fact what the Unsharp Mask tool in Photoshop does, it increases edge contrast. (For a look at the best methods for doing Unsharp Masking have a look at my tutorialInstant Photoshop.)
But, as useful as it is, the USM tool has problems, and one of these is that it also increases any noise present in the file. Particularly noisy photographs therefore can suffer when USM is applied....